Some Starting Points for Conducting an ATRP
Some Starting Points for Conducting an ATRP
When you read the section on Determination of the Redox Potential of Copper Complexes in the Catalyst Development page you will see that catalysts have been developed for an ATRP whose relative activity cover a range of six orders of magnitude. Obviously one cannot select any ligand to form a catalyst complex that is suitable for any monomer under any set of conditions. Some selection has to occur, e.g. conditions developed for a methacrylate monomer with a copper bromide complex with a pyridineimine ligand as catalyst will not work if the ligand is changed to Me6TREN and reaction conditions and/or catalyst concentration are not changed.
Here is a list of starting points that have worked in our laboratories covering preparation of a range of polymers using ATRP.
These are only suggested starting points. If the run does not go as expected you can/should make adjustments; e.g. add some Cu(II), change the temperature, purge the reaction mix better, add some reducing agent, etc?etc?
Conducting an ATRP
Homogeneous or Heterogeneous
Targeted rate of polymerization
Structure/topology of molecule
Order of addition of monomers
Get control over the process
Reaction too fast
Reaction too slow
Reaction does not start
Control over MW, PDI, Functionality
Formation of byproducts
How do you select initiator, catalyst, solvent and reaction conditions for a specific reaction?
Selecting catalysts for different monomers
PMDETA or X6TREN are not the best ligands for everything!
Selecting solvents for different monomers
Use of water or another polar solvent
Correct order of polymerization of monomers
Is halogen exchange required?
Is there an alternative to halogen exchange for low copper ATRP?
Appropriate selection of halogen or other transferable atom or group
Select appropriate ratio of activator to deactivator.
Determine the role of solvent
Concentration of monomers/solubility/viscosity
In many of the examples reported in the literature by the Matyjaszewski group and other academic laboratories, the monomers and other components of the reaction medium, have been subjected to rigorous purification. This is conducted because we are often interested in following the kinetics of the reaction not necessarily because rigorous purification is required indeed some of the examples describe conducting the reaction in the presence of limited amounts of air which is normally not advised for a radical polymerization.
In some of the starting points listed below, detailed conditions are provided. When such a set of conditions are provided later examples using the same components, with different ratios of reagents, generally use the same conditions.
Styrene MW 1100, 2000, 4500, 6400, 18,000
Di-functional Polystyrene Macroinitiator
Styrene Polymerization in Aqueous Dispersed Media
Miniemulsion: initiated by a) Reverse ATRP, b) SR&NI, c) AGET ATRP
Homogeneous Aqueous Media: Sodium Styrene Sulfonate
n-Butyl Acrylate Target DP ~300, ~120
Difunctional Poly(n-Butyl Acrylate) MW ~20,000; ~50,000; ~68,000
AGET n-Butyl Acrylate
Two Step ab initio Emulsion Polymerization
ARGET n-Butyl Acrylate 150 ppm Cu; 50 ppm Cu
n-Butyl Acrylate from a Multifunctional Macroinitiator
ARGET ATRP of Butyl Acrylate from the Surface of a Silicon Wafer
n-Butyl Acrylate Polymerization in Aqueous Dispersed Media
n-Butyl Acrylate from Initiator-coated Silica Colloids in Miniemulsion
n-Butyl Acrylate molecular brushes via AGET ATRP in miniemulsion
AGET ATRP of t-Butyl Acrylate in Miniemulsion
2-Hydroxyethyl Acrylate (HEA)
Bulk Polymerization of HEA
Polymerization of HEA with Water as a Solvent
Bulk AGET ATRP of MMA
Silica Functionalized ATRP Mini-Emulsion of N-BMA
Protected Methacrylic acids
Octadecyl Methacrylate AGET ATRP
2-Hydroxyethyl Methacrylate, (HEMA)
AGET ATRP of HEMA
Estimation of Absolute MW of P(HEMA)
HEMA-TMS and Conversion to P(BiBEM)
Olig(ethylene oxide) methoxy-capped methacrylate (OEOMA)
High MW PAN via ARGET ATRP
CopolymÈrisation of Styrene and Acrylonitrile
In Protic Media
In Non-Protic Media
Forced Gradient Copolymerization by AGET ATRP in Miniemulsion
Examples of Block Copolymers
P(ODMA-b-MMA) by AGET ATRP
P(nBA-b-St) by ARGET ATRP
Poly(n-BA-b-(polyMMA-co-St) by ARGET ATRP
Poly(n-BA-b-(polyMMA-co-St) by ICAR ATRP
Green ARGET ATRP (Use of Ascorbic Acid as Reducing Agent)
Some abbreviations used in the following examples
Initiators BPN: 2-bromopropanitrile
EBiB: ethyl 2-bromoisobutyrate
EBrP: ethyl 2-bromopropionate
MBrP: methyl 2-bromopropionate
1-PhEtBr: 1-phenyl ethylbromide
DMDBHD dimethyl 2,6-dibromoheptanedioate
TsCl: tosyl chloride
Ligands bpy: 2,2'-bipyridine
dNbpy: 4,4'-Di-5-nonyl-2,2'-bipyridine (It is not commercially available. The group presently uses 4,4-dinonyl-2,2'-dipyridyl from Aldrich. )
HMTETA : 1,1,4,7,10,10-Hexamethyltriethylenetetramine
ATRP of Styrene
Preparation of a low MW, 1100 and 2000, monofunctional polystyrene macroinitiator
0.3146 g CuBr (2.2?10-3 mole) was added to a round bottom flask. The flask was sealed with a rubber septum, degassed and back-filled with N2 3 times, then left under N2. 50 ml of deoxygenated styrene (4.4?10-2 mole) was added via syringe, followed by 1 ml deoxygenated anisole as an internal standard. 0.46 ml of deoxygenated PMDETA (2.2?10-3 mole) was added via syringe. The solution turned light green as the CuBr/PMDETA complex formed. The reaction medium remained heterogeneous. After the majority of the metal complex had formed, 3 ml of 1-phenylethyl bromide (2.2?10-3 mole) was added. A sample was removed to measure the initial monomer to internal standard ratio and compare that against the final ratio to determine total monomer conversion. The flask was placed in an oil bath thermostated at the desired temperature and the polymerization was allowed to proceed for a given amount of time. After the flask was removed from the oil bath, a sample was dissolved in tetrahydrofuran, monomer conversion was determined and molecular weight analysis was performed.
Macroinitiator purification: The contents of the flask were dissolved in acetone, slurried with DOWEX MSC macroporous ion-exchange resin for up to one hour, then filtered through alumina. Both the resin and alumina served to remove the copper catalyst from the polymer. The acetone was removed by evaporation and the residual polymer was redissolved in diethyl ether, and then precipitated by addition into MeOH. The dissolution/precipitation procedure was repeated 1 or 2 more times, or until the polymer precipitated as a powder instead of a sticky liquid (this is a function of the amount of monomer, solvent, or internal standard remaining). It was then dried under vacuum and analyzed by 1H NMR to determine degree of polymerization (for lower molecular weights).
Summary of reaction conditions:
Ratio of reagents, reaction temperature, time, MW and PDI of polymer.
1) [St]:[1-PhEtBr]:[CuBr]:[PMDETA] = 10:1:0.1:0.1; bulk, 100?C, 260 min
Mn th = 1070; Mn ex = 1,300; Mw/Mn = 1.23.
2) [St]:[1-PhEtBr]:[CuBr]:[PMDETA] = 20:1:0.1:0.1, bulk, 100?C, 240 min
Mn th = 1100; Mn ex = 1,100; Mw/Mn = 1.15.
3) [St]:[1-PhEtBr]:[CuBr]:[PMDETA] = 20:1:0.2:0.2; bulk, 100?C, 480 min
Mn th = 2030; Mn ex = 2,800; Mw/Mn = 1.15.
Low MW Polystyrene MW 4500
(Run DHC-1-2; i.e. second run by a new group member)
Conditions similar to those detailed above.
[St]:[MBP]:[CuBr]:[PMDETA] = 78:1:1:1 (mol ratio) in anisole at 90 &Mac186;C
Conv. 55.5% Mn th = 4,500; Mn ex = 4,420; Mw/Mn = 1.10
Low MW Polystyrene MW 6400
CuBr was degassed in a Schlenk flask by three vacuum/nitrogen-inletting cycles. Then the pre-deoxygenated monomer (Styrene) and ligand (PMDETA) were injected into the flask. After stirring for 20 minutes at room temperature to form the catalyst complex, the flask was put in an oil bath set at a temperature of 80&Mac176;C. The initiator, methyl 2-bromopropionate was injected to start the reaction. Samples were removed from the flask by degassed syringes, at timed intervals, to analyze conversion. When the conversion reached around 50%, the reaction was stopped by cooling the reaction down to room temperature and opening the flask to air. The mixture was passed through a neutral aluminum oxide column to remove the oxidized catalyst. The polymer was purified by precipitation into methanol. After drying under vacuum, the macroinitiator was obtained as a white powder.
[St]:[MBrP]:[CuBr]:[PMDETA] = 100:1:1:1 and T = 80&Mac176;C.
Mn 6,390; Mw/Mn = 1.18
Preparation of a Di-functional Polystyrene Macroinitiator
Styrene was purified by passing through a basic alumina column and then bubbled with N2 for 30 minutes. CuBr was charged in a flask and after 30 min under nitrogen atmosphere, styrene, PMDETA and 0,5 mL of anisole were added. The solution turned light green as the catalyst complex formation occurred. A sample was removed to measure the initial monomer/internal standard ratio used to determine the conversion as the reaction progressed. Dimethyl 2,6-dibromoheptanedioate (DMDBHD) was then added and the flask was then placed in an oil bath thermostated at 100&Mac176;C for 11 hours 10 minutes. The flask was removed from the oil bath, the solution was diluted in tetrahydrofuran and purified by passing through a neutral alumina column. The solvent and monomer were then removed under vacuum at 45&Mac176;C.
Ratio [St]:[ DMDBHD]:[CuBr]:[PMDETA]= 300:1:0.5:0.5
Mn = 18,145 g/mol; Mw = 19,675 g/mol; Mw/Mn = 1.08; conversion = 58.2%
AGET ATRP of Styrene
Styrene (5.0 ml, 44 mmol) , CuCl2 (29.3 mg, 21.8?10-2 mmol) and dNbpy (178 mg, 43.6?10-2 mmol) were placed in a 25 mL Schlenk flask and bubbled with nitrogen for 15 min. Sn(EH)2 (32 ?l, 9.8?10-2 mmol), and a purged solution of EBiB (29.7 ?l, 20.3?10-2 mmol) in toluene were added, and the sealed flask was placed in thermostated oil bath at 110 &Mac176;C. The polymerization was stopped after 7 hours by opening the flask and exposing the catalyst to air.
[St]:[EBiB]:[CuCl2]:[dNbpy]:[ Sn(EH)2] = 216:1:1:0.45 (i.e. less than one equivalent of reducing agent in order to leave some Cu(II) present at all times.)
Mn, GPC = 14,000; Mw/Mn= 1.37. Conversion = 83%)
General procedure for ARGET ATRP of styrene (DPn) of 200 with 50 ppm of Cu) (1)
Degassed styrene (5.0 ml, 44 mmol) and anisole (1.5 ml) were transferred via degassed syringes to a dry, thoroughly purged by flushing with nitrogen, Schlenk flask. Next, a solution of CuCl2 (0.29 mg, 0.22?10-2 mmol)/Me6TREN (0.57 ?l, 0.22?10-2 mmol) complex in degassed anisole (0.5 ml) was added via a syringe. The mixture was stirred for 10 minutes and then a purged solution of Sn(EH)2 (7.0 ?l, 2.2?10-2 mmol) and Me6TREN (5.7 ?l, 2.2?10-2 mmol) in anisole (0.5 ml) was added. Finally the initiator EtBrIB (32.1 ?l, 21.9?10-2 mmol) was added. An initial sample was taken and the sealed flask was placed in thermostated oil bath at 110 &Mac176;C. Samples were taken at timed intervals and analyzed by gas chromatography and gel permeation chromatography to follow the kinetic of the polymerization which was stopped after 7.6 hr by opening the flask and exposing the catalyst to air.
[St]:[EBiB]:[CuCl2]:[Me6TREN]:[Sn(EH)2]:[Me6TREN] = 216:1:0.001:.01:.01 in anisole
Mn, GPC = 12,700; Mw/Mn = 1.11. Conversion = 59%
When the polymerization was run with lower amounts of ligand the polymerization was stopped after 20 hr by opening the flask and exposing the catalyst to air, conversion was higher.
[St]:[EBiB]:[CuCl2]:[Me6TREN]:[Sn(EH)2]:[Me6TREN] = 216:1:0.001:0.01:0.03 in anisole. Mn, GPC = 15,900; Mw/Mn = 1.28. Conversion = 76%
Styrene Polymerization in Aqueous Dispersed Media
Early work in the Matyjaszewski group established that ATRP emulsion/miniemulsion systems using non-ionic surfactants (i.e. Brij 98) and bipyridine ligands with long alkyl substituents (i.e. dNbpy) were feasible. (2, 3) However, a large amount of surfactant (13.5 wt% based on monomer) was required to obtain stable latexes with relatively low solids content (~ 13 %). Several improvements had to be made to make this procedure environmentally acceptable. These included: starting with a stable catalyst complex, reducing the concentration of catalyst, removing/recycling the catalyst, bringing the ratio of surfactant to monomer closer to industrially acceptable ratios, increasing % solids, and finally developing a ?true? emulsion polymerization procedure. The following examples describe the critical steps.
Typical recipes for miniemulsion polymerizations employing different procedures for catalyst activation are listed below.
a) Reverse ATRP in Miniemulsion
Monomer Surfactant Solid content Conversion Mn,sec Mn,theo Mw/Mn
Styrene Brij 98 20% 78.4% 31,200 32,600 1.49
[M]0 : [tNtpy] : [CuBr2] : [VA-044] = 400 : 1 : 1 : 1;
[Surfactant] = 5 mM (0.58 wt% based on water); * [Brij 98] = 7.5 mM;
[Hexadecane] = 3.6 wt% based on monomer;
20 % solid content; reaction temperature = 70 oC.
b) Typical Recipe for SN&RI ATRP in a Miniemulsion Systema
Monomer BA 5.0 g 200 equiv.
Alkyl halide MBP 0.0326 g 1 equiv.
Ligand tNtpy 0.0239 g 0.2 equiv.
Catalyst CuBr2 0.0087 g 0.2 equiv.
Costabilizer Hexadecane 0.18 g
Surfactant Brij 98 0.115 g
Deionized water H2O 19.88 g
Initiator AIBN 0.004 g 0.125 equiv.
a [Brij 98] : [hexadecane] = 2.3 : 3.6 wt% based on monomer; solid content = 20 % (based on 100% conversion); 80 oC.
Detailed Procedure: The radical deactivator (CuBr2 and ligand), monomer, and costablizer (hexadecane) were charged to a round-bottom flask, and heated with magnetic stirring at 60 0C for 10 to 20 minutes to form a homogeneous solution. The surfactant solution was added after cooling the solution down to room temperature, and the mixture was ultrasonicatfied (Heat Systems Ultrasonics W-385 sonicator; output control set at 8 and duty cycle at 70% for 1 minutes) in an ice bath to prevent a significant temperature rise resulting from sonification. The resulting miniemulsion exhibited good shelf life stability at room temperature, as evidence by a lack of visible creaming or phase separation over 3 days of aging. After homogenization, the miniemulsion was then transferred to a 25 ml Schlenk flask, where pure argon was bubbled through the miniemulsion for 30 minutes before it was immersed in an oil bath thermostated at 80 0C. The magnetic stirring speed was set at 700 rpm. When a water-soluble azo initiator, (e.g. VA-044), was used the polymerization was initiated by the injection of a pre-deoxygenated aqueous solution of the initiator into the miniemulsion. When a water-insoluble azo initiator (e.g. AIBN) was employed it was pre-dissolved in the oil phase at room temperature before sonification. Time zero for the polymerization was marked when the Schlenk flask was immersed in the oil bath. Samples were withdrawn periodically via a pre-degassed syringe to monitor the monomer conversion and molecular weight.
Miniemulsion Polymerization of Styrene with a Macroinitiator PBA-(b-PS)3 (4)
This example used a trifunctional PBA-Br3 macroinitiator, prepared via bulk ATRP, in a miniemulsion system where the initiation or activation of the catalyst complex was conducted by means of SR&NI.
[St]/[PBA-Br3]/[CuIIBr2-tNtpy]/[VA-044] = 300/1/0.6/0.375 (the ratio would be 100/1/0.2/0.125 for each arm); at 80 oC.
Miniemulsion system: [Brij 98]/[Hexadecane] = 2.3/3.6 wt% based on monomer; 20 % solid based on 100% conversion. Conversion was 93% therefore solids = 18%, Mw/Mn =1.37.
The final polymer had ~12% homopolymer present in the product.
c) AGET Miniemulsion Polymerization of Styrene with a Macroinitiator PBA-(b-PS)3
Polymerization conditions for the preparation of a pure star block copolymer: [Styrene]0: [(PMA-Br)3]0: [CuBr2/BPMODA]0: [Ascorbic Acid]0 = 400: 1: 0.6: 0.24; 80 oC.
Miniemulsion conditions: [Brij 98] = 0.58 wt% with respect to water (2.3 wt% with respect to the oil phase); [Hexadecane] = 3.6 wt% with respect to monomer.
The copolymerization was faster in miniemulsion than in bulk, which indicated a gradual diffusion of Cu(II) complex out of the monomer droplets to water. Therefore at high conversion star-star coupling reactions were difficult to avoid, especially for styrene polymerization. The contribution of coupling reaction increases with conversion but could be reduced by stopping the polymerization at a limited conversion ~50%.
An introduction to the polymerization of substituted styrene?s can be found in a paper authored by Jain Qiu, and Kris (5). A series of substituted styrenic monomers were studied: 4-CN, 4-CF3, 3-CF3, 4-Br, 4-Cl, 4-F, 4-H, 3-Me, 4-Me, 4-CMe3, and 4-OMe. The ATRP of the substituted styrenes were conducted in diphenyl ether at 110 &Mac176;C. [M]0 = 4.37 M and [M] 0:[1-PEBr] 0: [CuBr] 0:[bipy] 0 = 100:1:1:3. Monomers with electron-withdrawing (EW) substituents resulted in better polymerization control and polymerize faster than those with electron-donating (ED) substituents. The apparent polymerization rate constants follow the Hammett equation with ? = 1.5. The difference of polymerization rates for different monomers can be attributed to both propagation constant, kp?, and the equilibrium constant, Keq, for atom transfer. Monomers with EW substituents have larger kp? and Keq values than those with ED substituents; therefore, EW substituents increase the monomer reactivity and decrease the stability of dormant species, while ED substituents have the opposite effect.
The general procedure for the polymerizations was similar to that described above for the polymerization of styrene. CuBr and ligand (bpy or dNbpy were employed, the examples were conducted early in development of ATRP) were added to a round bottom flask followed by the degassed solvent and monomer then the addition of the initiator. The flask was then immersed in an oil bath thermostated at 110 &Mac176;C. At timed intervals, the same amount of sample was withdrawn from the flask and dissolved in THF for further analysis. The polydispersity for polymers with EW substituents had PDI?s below 1.2 while ED substituents resulted in broader PDI?s, but still >1.5 except for 4-OMe styrene which did not yield high MW polymer.
Sodium Styrene Sulfonate (NaSS)
The initial example of polymerization of NaSS was conducted with H2O as solvent and using a CuI-based catalyst and conducting the reaction at 30oC after 15 min conversion was 30% and Mn g/mol was 6,620 with Mw/Mn = 1.81 and after 150 min conversion was 32% and Mn g/mol was 6,800 with Mw/Mn = 2.06.
In the case of NaSS, catalyst disproportionation presumably took place as well (the solutions turned blue in several minutes), although precipitation of Cu0 could hardly be observed. Conversions reached 20-30 % in less than 20 minutes and after this point the reactions did not proceed further.
However once the role of a pseudo ligand was understood addition of pyridine to the reaction improved control. Conducting the reaction in H2O-PyH (1:1), CuI-based catalyst, at 30oC after 15 min conversion was 38% and Mn g/mol was 8,100 with Mw/Mn = 1.20 and after 150 min conversion was 70% and Mn g/mol was 10,800 with Mw/Mn = 1.26.
Polymerization Conditions: The monomer (5 mmol) was dissolved in 3 ml of solvent (D2O or mixtures of D2O and Pyridine) and the solution was degassed by five freeze-pump-thaw cycles. The reaction flask was filled with nitrogen and the catalyst (mixture of copper (I) and (II) bromides (0.05 mmol of total copper) and 0.0156 g (0.1 mmol) of 2,2?-bipyridine (bpy)) was added to the still frozen solution. The flask was closed and evacuated and back-filled with nitrogen three times. Homogeneous brown solution was obtained after the flask was immersed in a water bath thermostatted at 25oC or 30oC the initiator, 2-bromopropionate for the ATRP of NaSS), was added at the end.
ATRP of ACRYLATES
The solubility of different poly(acrylates) should be taken into consideration when selecting a solvent for the reaction. In the following series of examples different solvents are indicated.
Materials: n-Butyl acrylate (BA, Aldrich), 2-ethylhexyl acrylate (EHA, Aldrich) and lauryl acrylate (LA, Aldrich) were purified by passing it through an inhibitor removal column filled with basic aluminum oxide (Aldrich), respectively. The monomers were stored at ?5 oC for later use. 4,4?-Di(5-nonyl)-2,2?-bipyridine (dNbpy), tris(2-bis(3-butoxy-3-oxopropyl)aminoethyl)amine (BA6TREN), and tris(2-bis(3-(2-ethylhexoxy)-3-oxopropyl)aminoethyl)amine (EHA6TREN) were synthesized according to previous published procedures, (6-7). Tris(2-bis(3-dodecoxy-3-oxopropyl)aminoethyl)amine (LA6TREN) was prepared, via a slightly modified procedure in a reported work, by further extending the reaction at 50 oC for another 24 hours. CuBr2 (Aldrich), tris(2-aminoethyl)amine (TREN, Aldrich), Brij 98 (Aldrich), NOIGEN RN20 (Montello), Hexadecane (Aldrich), 2,2?-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044, Wako Chem. Inc.) were used as received.
ATRP of Methyl Acrylate
The experimental procedures used for the following polymerizations are fundamentally the same as those detailed above for styrene.
MA : EbiB : CuBr : PMDETA = 200 : 1 : 0.5 (anisole as solvent) at 60 oC for 220 min;
Mn GPC = 10,200; Mw/Mn = 1.07.
N,N,N?,N?-tetra[(2-pyridal)methyl]ethylenediamine (TPEDA) as Ligand: The ATRP of MA using ethyl 2-bromoisobutyrate (EtBIB) as initiator, 10 mol % of CuBr/TPEDA relative to EtBIB, in bulk at 80 oC, was very fast (98% conv. in 1.5 h) and yielded PMA with low PDI of 1.13.
M:I:Cu:L = 116:1:0.1:0.1, Mn GPC = 9,700; Mw/Mn = 1.13.
Bulk Polymerization of Methyl Acrylate/Methyl 2-Bromopropionate/PMDETA
As a representative example, a 10 mL Schlenk flask was charged with Cu0 (2 mg; 0.032 mmol), Cu(OTf)2 (12 mg; 0.033 mmol), N,N,N?,N??,N??- pentamethyldiethylenetriamine (14 ?L; 0.067 mmol), methyl 2-bromopropionate (37 ?L; 0.33 mmol), and methyl acrylate (6 mL; 66.6 mmol) followed by 0.6 mL of chlorobenzene as an internal reference. The reaction flask was charged with a stir bar and then fitted with a rubber septum. The reaction solution was then put through freeze-vacuum-thaw cycles three times to remove dissolved gases and then put under an argon atmosphere. The flask was then immersed in an oil bath and held by a thermostat at 80 &Mac176;C with rigorous stirring. A homogeneous blue solution was observed. At various times, samples were taken via syringe and diluted with THF. The volume lost by sample removal was replaced with argon. The samples were used to monitor percent monomer conversion relative to the internal reference (GC) and molecular weight (SEC). After 60 min, 75% monomer conversion was observed.
Mn = 12,900; Mw/Mn = 1.16)
ATRP of n-Butyl Acrylate (For actual DP ~= 300)
MBP - 64 ?l (0.536 mmol) : CuBr - 0.0780 g (0.536 mmol) : PMDETA - 112 ?l (0.536 mmol) : BA - 30 ml (0.26 mole) plus anisole 5 ml. T = 700C
All liquid reagents were put in a Schlenk flask, the solution was degassed by three F-P-T cycles, the flask with the frozen liquids was filled with nitrogen, CuBr was added, and several times the flask was evacuated followed by filling with nitrogen (the mixture was still frozen). Then the flask was put in an oil bath at 70oC. After 21 hours (conversion 81.7% based on GC), the polymer was isolated and purified by passing its solution in THF through a column filled with alumina. The molecular weight of the macroinitiator, after removing the unreacted BA by drying in vacuum at 70oC to a constant weight was determined by GPC to be 32,290; Mw/Mn = 1.17 (THF as the eluent, polystyrene calibration) or 44,220; Mw/Mn = 1.13 (DMF as the eluent, polystyrene standards).
For DP ~= 120: The targeted MW here was lower than in the previous experiment, but a ratio of the catalyst to the initiator 1:2.5 was used instead of the previous one of 1:1 in order to slow down the reaction.
MBP - 40 ?l (0.335 mmol) : CuBr - 0.0193 g (0.134 mmol) : PMDETA - 28 ?l (0.134 mmol) ? BA - 10 ml and anisole 4 ml. T = 700C
The same procedure as the above was used. The reaction was stopped after 13 hours (conversion 70.7% based on GC). Te obtained polymer was isolated and purified as in the previous case. The molecular weight of the macroinitiator was determined by GPC was 14,650 and Mw/Mn = 1.20 (THF as the eluent, polystyrene calibration) or MW 18,850 and Mw/Mn = 1.11 (DMF as the eluent, polystyrene standards).
Preparation of a poly(butyl acrylate) difunctional macroinitiator (150:1:0.5:0.5)
Degassed butyl acrylate (20 mL) was added to a reaction flask, followed by degassed anisiole (2 mL). The solution was then degassed for several minutes. The initiator (dibromo dimethyl heptanedioate, 101 microliters) was then added, followed by PMDETA (48.5 microliters) and CuBr (33.4 mg). The solution was degassed for several minutes after each addition was made. The reaction mixture was then lowered into a 70&Mac176;C oil bath. The reaction was monitored by GC (with anisole as the internal standard). The conversion was fairly linear with time, and the reaction was stopped after 215 minutes (final conversion 50%).
According to THF GPC results, the Mn was 19,800 g/mol, with a Mw/Mn of 1.14.
Synthesis of difunctional P(n-butyl acrylate) macroinitiator for a thermoplastic elastomer (BS-02-67, MW~50,000)
CuBr (0.233 g, 1.62 mmol) was added to a 500-mL Schlenk flask. The flask was purged by repetitions of vacuum and nitrogen filling (x3). Nitrogen-purged BA (125 g, 975 mmol) and anisole (14 mL) were added via syringe under a nitrogen atmosphere. The resulting solution was purged for an additional 15 minutes by bubbling with nitrogen. N,N,N?,N?,N?-Pentamethyldiethylene-triamine (PMDETA) (0.34 mL, 1.63 mmol) was added by syringe followed by purging with nitrogen for 35 min. Dimethyl 2,6-dibromoheptanedioate (0.36 mL, 1.63 mmol) was via syringe and the sealed flask was placed in a preheated oil bath at 70 oC. Samples were taken periodically and after 8 h, when conversion determined by GC was 77% the flask was removed from the heat and opened to air overnight to ensure complete oxidation of the catalyst. The polymerization solution was diluted with THF and passed through an alumina (activated neutral) column to remove the catalyst. The excess solvent was removed by rotary evaporation, and the remaining material was dried under high vacuum for 48 h. MW determined by GPC with PS calibration was 49,000 vs. 59,000 theoretical with a Mw/Mn = 1.23.
Synthesis of PBA-based difunctional macroinitiator (8)
3.13 x 10-2 g (1.8 x 10-4 mol) PMDETA was dissolved in 20 ml (17.88 g, 0.14
mol) BA and 1 ml of anisole (internal standard for GC) in a Schlenk flask. The mixture
was then degassed by four freeze-pump-thaw cycles, the flask was filled with nitrogen,
and 2.55 x 10-2 g (1.8 x 10-4 mol) of CuBr was added while the mixture was still frozen.
Then the flask was sealed and air was removed by evacuating the flask and back-filling
with nitrogen several times. After thawing the mixture, the reaction flask was immersed
in oil-bath heated to 700C, and the initiator DM-2,6-DBHD (3.8 x 10-2 ml, 6.04 x 10-2 g,
1.8 x 10-4 mol) was added through the side arm. After 16 h, the product was
dissolved in 200 ml of THF, and the solution was passed through a column filled with
alumina to remove the catalyst. Then the solvent was removed and the PBA was dried
under vacuum at 600C to constant weight. The molecular weight based on PBA standards
was Mn = 67,600; Mw/Mn = 1.16.
AGET ATRP of Acrylates
CuBr2 and BPMODA were charged to a round bottom flask together with the selected monomer, such as nBA or tBA. The reagents were heated to 60oC in an oil bath in order to form the Cu(II) complex. The flask was cooled to 0oC before the addition of an ATRP initiator, the surfactant solution and the co-surfactant. The mixture was sonicated for 1 minute and then transferred to a Schlenk flask for argon purging. After 30 minutes purging, the Schlenk flask was immersed in an oil bath thermostated at 80oC. The polymerization was started by injection of a solution of ascorbic acid.
[ascorbic acid]:[CuII] = 0.4. [BA]:[EBiB]:[CuBr2/BPMODA] = 200:1:0.4, Temp. 80oC; [Brij 98]:[hexadecane] = 2.3/3.6% based on monomer; based on solid content = 2%
Reation was conducted over 275 minutes and the MW remained close to theoretical up to 90% conversion and Mw/Mn = 1.2.
ARGET ATRP of n-butyl acrylate with 150 ppm Cu
The ratio of BA/EtBrIB/Cu(II)/tri(2-pyridylmethyl)amine (TPMA)/Sn(EH)2 was 156/1/0.01(50 ppm)/0.03/0.05. The reaction was carried out in anisole 0.2 vol. eq. vs. monomer at 60 oC. The GPC traces were monomodal with molecular weight close to theoretical values and low Mw/Mn =1.15.
ARGET ATRP of n-butyl acrylate with 50 ppm Cu (9)
The general procedure for ARGET ATRP of nBA, (targeting number average degree of polymerization (DPn) of 160), with 50 ppm of Cu. Degassed nBA (5.0 ml, 35 mmol) and anisole (0.5 ml) were transferred via degassed syringes to a dry, thoroughly purged by flushing with nitrogen, Schlenk flask. Next, CuCl2 complex (0.24 mg, 0.18?10-2 mmol)/Me6TREN (0.51 ?l, 0.18?10-2 mmol)) in degassed anisole (0.5 ml) was added. The resulting mixture was stirred for 10 minutes and then a purged solution of Sn(EH)2 (7.29 ?l, 2.2?10-2 mmol) and Me6TREN (5.8 ?l, 2.2?10-2 mmol) in anisole (0.5 ml) was added. Then EtBrIB (32.4 ?l, 22.1?10-2 mmol) initiator was added to initiate the polymerization. An initial sample was taken and the sealed flask was placed in thermostated oil bath at 60 oC. Samples were taken at timed intervals and analyzed by gas chromatography (GC) and gel permeation chromatography (GPC) to follow the progress of the reaction. The polymerization was stopped after 6.2 h (Mn GPC=19,400 and Mw/Mn =1.26, conversion=91%) by opening the flask and exposing the catalyst to air.
ARGET ATRP of nBA was also carried out in the presence of glucose as an exemplary organic reducing agent with the initial ratio of reagents: nBA/EtBrIB/Cu(II)/TPMA/glucose = 160/1/0.0078/0.03/0.1 (50 ppm Cu vs. nBA)
after 44 h at 80 oC in 20 % vol/vol anisole, PnBA with Mn = 10,500 and Mw/Mn=1.47 was formed in 48% yield (Mn th=9,600).
ATRP of n-Butyl Acrylate from a Polyethylene Multifunctional Macroinitiator (10)
Use of a less active TREN based ligand to polymerize nBA in a grafting from a PE-macroinitiator. [nBA]0 : [PE-MI]0 : [CuCl]0 : [CuCl2]0 : [[BA6TREN]0 = 100 : 1 : 1 : 0.05 : 1.05. Solvent: Chlorobenzene = 80 vol%. Temperature: 100 0C.
A polyethylene multifunctional macroinitiator (PE-macroinitiator), Mn = 36,000, Mw/Mn = 3.04 with 0.90 mol% of ?-bromoisobutyrate functionality, was synthesized as reported
in reference 11. ATRP was performed using standard Schlenk techniques. Solvents and monomers were degassed through bubbling with nitrogen for 30 min prior to use. A stock solution of the catalyst was prepared by dissolving CuCl (31.2 mg, 3.15 x 10-4 mol), CuCl2 (2.1 mg, 1.56 x 10-5 mol), and BA6TREN (301.8 mg, 3.30 x 10-4 mol) in chlorobenzene (5 mL). Separately, the PE-macroinitiator (119.1 mg, 3.49 x 10-5 mol-Br) was placed in a 25 ml Schlenk flask and then BA (0.5 mL, 3.49 x 10-3 mol), chlorobenzene (1.8 mL), anisole (0.1mL), and catalyst stock solution, (0.59 ml, 3.51x10-5 mol-CuCl/BA6TREN, 1.74 x 10-6 mol-CuCl2/BA6TREN) were added sequentially to the flask. The resulting mixture was warmed up to 100 oC to start the polymerization, the PE-macroinitiator dissolved in the solvent/monomer mixture within a few minutes. Polymerization was stopped after 0.5, 1.0 or 3.75 h, and the resulting graft copolymers were precipitated by addition to excess methanol. The graft copolymers were filtrated, washed with methanol and dried under vacuum at 60 oC.
Side Chain Cleavage and Analysis The graft copolymer (30 mg) was dissolved in
chlorobenzene (1 mL) at 100 oC. n-Butanol (4 mL) and H2SO4 (3 drops) were added to the solution and the resulting mixture was stirred at 100 oC for 3 days. After cooling, OH type anionic ion exchange resin was added to neutralize the acid catalyst, and then the solution was decanted from the ion-exchange resin. After evaporation of the solvent, the residual polymer was extracted with THF, and GPC of the cleaved side chain PBA was taken using THF GPC.
ARGET ATRP of Butyl Acrylate from the Surface of a Silicon Wafer in the Presence of a Limited Amount of Air (12)
A 22 mL glass vial containing initiator-modified silicon wafer and a small stir bar was charged with butyl acrylate (15.0 mL, 105 mmol) and ethyl 2-bromoisobutyrate (32.8 ?L, 0.224 mmol). Then a solution of CuCl2 (0.71 mg, 0.0053 mmol) and TPMA ligand (6.5 mg, 0.013 mmol) in anisole (2 mL) was added. After sealing the vial with a rubber septum, the solution of tin(II) 2-ethylhexanoate (109 ?L, 0.337 mmol) in anisole (1 mL) was injected. The initial sample was taken and the sealed vial was placed in an oil bath thermostated at 70 oC. Samples were taken at timed intervals and analyzed by GC and SEC. The polymerization was stopped after 5 h (Mn, SEC = 13,900, Mw / Mn = 1.22, conversion = 18.4%) by opening the flask and exposing the catalyst to air.
The silicon wafer was taken out for analysis of thickness, and the solution was capped and stored in dark. In order to remove the free polymer physically adsorbed onto the surface, the resulting silicon wafer was washed with methylene chloride in Soxhlet extractor for 24 hours. The thickness of the dry poly(n-butyl acrylate) brushes, measured by ellipsometry in air, was 12.3 nm. The error of the measurement was less than 0.5 nm. The grafting density (?) was calculated using the following equation: ? = NAh?/Mw, where Mw is the weight average molecular weight, NA is Avogadro?s number, and ? = 1.0 g/cm3 is the bulk poly(n-butyl acrylate) density.
Bulk ATRP of n-Buthyl Acrylate from 2-Bromoisobutyrate Functional Colloids
Silica colloidal initiators (500.0 mg, 0.13 mmol), Cu-(I)Br (12.0 mg, 0.130 mmol), Cu(II)Br2 (2.0 mg, 0.010 mmol), and dNbpy (121.0 mg, 0.29 mmol) were added to a 25 mL Schlenk flask containing a magnetic stir bar. The flask was fitted with a rubber septum, and the flask was evacuated (1-5 mmHg) for a period of 5 h. The flask was then backfilled with nitrogen, and the flask was evacuated again for 5 min, followed by additional backfilling with nitrogen. This evacuation/backfilling cycle was repeated, and then n-BA (8.6 g, 67 mmol) (bubbled for 1 h with nitrogen before use) was added to the flask via syringe. The rubber septum fitted on the Schlenk flask was replaced with a greased glass stopper under high nitrogen purge, and the reaction mixture was homogenized by agitation on a vortex mixer for 5-10 min. The reaction flasks were then placed in a 90 &Mac176;C oil bath. Samples were taken periodically via syringe for kinetic analysis of the polymerization. After 52.6 h, a monomer conversion reached 10%, as determined from gravimetric analysis. Samples were diluted with tetrahydrofuran, filtered through neutral alumina, concentrated in vacuo to a volume of approximately 10 mL, then precipitated into solution of methanol (400 mL) and deionized water (50 mL), yielding a clear viscous oil (Mn SEC cleaved pBA ) 6800; Mw/M n ) 1.26).
ATRP of n-Butyl Acrylate from Initiator-coated Silica Colloids in Miniemulsion Using Simultaneous Reverse and Normal Initiation (SR&NI)
0.0085g CuBr2, (3.8 X 10-5 mol), 0.017g BPMODA and 4.86g (5.44mL/0.0379mol) of n-butyl acrylate were added to a round bottom flask and allowed to stir at 60?C for ~20 min to dissolve the solid reagents. The solution was then cooled by immersing the flask in ice. While on ice, 20g of 5mm solution of Brij 98 in deionized water, 0.0039g purified AIBN, 0.125 mL (0.18g) hexadecane, and 0.61g of the silica particles functionalized with bromoisobutyrate were added to the flask. The mixture was sonicated for 3-4 minutes while remaining under contact with ice and then transferred to a Schlenk flask and bubbled with argon gas for 30 minutes. The flask was transferred to an oil bath heated to 80?C and allowed to react for 6 hours. The polymerization was stopped by quickly adding the miniemulsion to methanol to precipitate the solids which were filtered for collection. Etching of silica for SEC measurements was done as reported previously.
[n-BA]:[SiO2-Br]:[AIBN]:[CuBr2]:[BPMODA] = 200:1:0.125:0.2:0.2;
In a reaction targeting higher DP, the ratio of reagents were:
[nBA]:[ SiO2-Br]:[hexadecane]:[AIBN]:[CuBr2]:[BPMODA] = 200:0.2:3.6, wt%:0.025:0.2:0.2.
Actual Mn after etching the silica cores, of the final material is in very nice agreement with theoretical at 15,900 g/mol. Mw/Mn = 1.34
Synthesis of n-Butyl Acrylate molecular brushes via AGET ATRP in miniemulsion
In a typical run, the macroinitiator pBPEM (0.026 g), CuBr2 (0.0087 g) and BPMODA (0.0176 g) were dissolved in BA (5.0 g) in a round-bottom flask at 60 oC. After the formation of the Cu(II) complex, hexadecane (0.18 g) and an aqueous solution of Brij 98 (20 mL, 5 mmol/L) were added to the cooled solution before the mixture was subjected to sonication. The resulting homogenized suspension was transferred to a 25 mL Schlenk flask and purged with argon for 30 minutes. The flask was then immersed in an oil bath thermostated at 80 oC. An aqueous solution (0.5 mL) of ascorbic acid (0.0034 g) was injected into the flask to initiate the polymerization. Aliquots were taken at regular intervals to measure the conversion gravimetrically.
Miniemulsion conditions: [Brij 98]: [hexadecane] = 2.3/3.6% based on monomer; solid content = 20% (based on 100% conversion). When the ratio of ascorbic acid to Cu(II) was maintained at 0.35 and the polymerization was stopped at ~56% monomer conversion, majority of the polymers present are still single entities.
ATRP of BA in microemulsion and ab-initio emulsion ATRP of BA ? two steps: (14)
Step 1: Before conducting a microemulsion polymerization, the Cu(II) complex was prepared by dissolving CuBr2 (7.8 mg, 0.035 mmol) and BPMODA (23.7 mg, 0.053 mmol) in BA (1 mL, 7 mmol) at 60 oC. The initiator, ethyl 2-bromoisobutyrate (EBiB, 10.2 ?L, 0.07 mmol), was then dissolved in this complex. The resulting solution was slowly added to an aqueous solution of polyoxyethylene oleyl ether (Brij 98) (30 mL, 0.06 mol?L-1) under stirring to form an optically clear microemulsion. After purging the microemulsion with nitrogen for 30 minutes, the flask was immersed in an oil bath thermostatted at 80 oC. A pre-deoxygenated aqueous solution (0.5 mL) of ascorbic acid (2.4 mg) was injected to the microemulsion to initiate polymerization. Aliquots were withdrawn at regular intervals to measure the monomer conversion gravimetrically.
Step 2: This microemulsion polymerization was then employed as the first step (nucleation step) in the designed ?two-step? procedure to create an ab-initio emulsion ATRP. When monomer conversion reached a certain level in the microemulsion polymerization, additional monomer was added to the reaction. The polyBA-Br generated in the initial microemulsion ATRP functioned as a macroinitiator for further emulsion polymerization of additionally added monomer. Because there was no initiator or catalyst in the added monomer, monomer diffused from the droplets to the polymerizing particles.
Step 3: AGET ATRP of block copolymer in ab-initio emulsion: An ab-initio emulsion ATRP was initiated using the same procedure as above. The second monomer, styrene, was added to the reaction when the first monomer reached ~50% conversion.
An ab-initio emulsion ATRP was thereby successfully developed.
Schematic illustration on the procedure for an ATRP in an ab-initio emulsion.
A Typical Mono-functional t-Butyl Acrylate Polymerization
t-BA (Aldrich, 98%) was extracted 3 times with 5% aq. NaOH, and then washed with distilled water. After drying over CaCl2 and filtering off the drying agent, the monomer was distilled under vacuum (60 ?C /60 mmHg). CuBr (39.1 mg, 2.73 x 10-4mol) and CuBr2 (3.0 mg, 1.4 x 10-5 mol) were added to a dry round-bottom flask. The flask was sealed with a rubber septum, degassed and back-filled with nitrogen three times, and left under nitrogen. Deoxygenated acetone (1 mL) was added, after which t-BA (4.0 mL, 2.7 x 10-2 mol) was added, both via syringes that had been purged with nitrogen. PMDETA (60 ?L, 2.9 x 10-4 mol) was added, and the solution was stirred until the Cu complex had formed. This is easily visualized through a change of the solution from cloudy and colorless to clear and light green. After complex formation, methyl 2-bromopropionate (61 ?L, 5.5 x 10-4 mol) was added to the flask, an initial sample was removed, and the flask was placed in an oil bath thermostated at 60 &Mac176;C. After 320 min, a sample was dissolved in toluene, and GC analysis showed a monomer conversion of 93%.
Starting with [t-BA]:[MBrP]:[CuI][CuII]:[PMDETA] = 100:1:1:.05:1.05
The polymer had a Mn = 6,000 and a Mw/Mn = 1.11.
(Note: for reactions performed at temperatures higher than 60 ?C, approximately 2 % p-dimethoxybenzene or anisole, relative to the volume of monomer, was additionally added. This was to ensure conversion measurements were not affected by loss of solvent or monomer at elevated temperatures.)
Difunctional poly(t-butyl acrylate)
?Classic? Conditions are: t-Butyl acrylate is purified by passing through a basic alumina column and then bubbled with N2 for 30 minutes. CuBr was charged in to the flask and after 30 min under nitrogen atmosphere, t-butyl acrylate, PMDETA and anisole are added. The solution should be light green in colour as complex formation occurs. A sample was removed to measure the initial monomer/internal standard ratio used afterward to determine the conversion. Dimethyl 2,6-dibromoheptanedioate (DMDBHD) was then added and the flask was placed in an oil bath thermostated at 60&Mac176;C. After the desired conversion was attained the flask was then removed from the oil bath, the solution was diluted in tetrahydrofuran and purified by passing through a neutral alumina column. The solvent and monomer were then removed under vacuum at 45&Mac176;C.
Mole Ratio: [tBA]:[DMDBHD]:[CuBr]:[PMDETA] = 100:1:0.25:0.25; 25% acetone;
heated at 60? C for 370 minutes. Conversion 53% Mn = 6,800 Mw/Mn = 1.16
Mole Ratio: [tBA]:[DMDBHD]:[CuBr]:[PMDETA] = 300:1:0.33:0.33
Mn =15,000 g/mol; Mw = 18,835 g/mol; Mw/Mn = 1.25; conversion = 37.2%
CuBr (12 mg, 8.5x10-5 mol) and DMDBHD (55 mg, 1.7x10-4 mol) were added to a 10 ml round bottom flask. The flask was degassed and back-filled with nitrogen three times before introducing deoxygenated tBA (5.0 ml, 3.4x10-2 mol) and anisole (100 ?l, as an internal standard) via purged syringes. PMDETA (18 ?l, 8.5x10-5 mol) was added and the copper complex formed. The solution was heterogeneous. An initial sample was removed and the flask was placed in an oil bath thermostated at 60 &Mac186;C. After 6.5 hours, a sample was removed, dissolved in toluene and GC analysis was performed.
Monomer conversion was 79%, with a Mn = 25,100; Mw/Mn = 1.24.
AGET ATRP of t-Butyl Acrylate in a Miniemulsion
CuBr2 and BPMODA were charged to a round bottom flask together with the selected monomer, such as nBA or tBA. The reagents were heated to 60oC in an oil bath in order to form the Cu(II) complex. The flask was cooled to 0oC before the addition of an ATRP initiator, the surfactant solution and the co-surfactant. The mixture was sonicated for 1 minute and then transferred to a Schlenk flask for argon purging. After 30 minutes purging, the Schlenk flask was immersed in an oil bath thermostated at 80oC. The polymerization was started by injection of a solution of ascorbic acid. The ascorbic acid was added slowly over a 10 minute period. This resulted in the reaction attaining more linear kinetics than that obtained when all of the ascorbic acid was added at the very beginning of the reaction. In order to leave some excess of Cu(II) species to regulate ATRP, the sub-stoichiometric amount of the reducing agent was used, a ratio of Cu/ascorbic acid = 1/0.4 worked quite well.
Lauryl Acrylate (15)
Use of a ligand that increases the solubility of the catalyst complex in the monomer is suggested, e.g. an alkyl substituted bipyridine ligands instead of PMDETA yields a homogeneous catalyst solution without requiring a co-solvent. A low rate of termination in Lauryl Acrylate (LA) polymerization leads to high molecular weight polymer at low conversions if additional deactivating species (Cu(II) 4 mole%) is not present in the solution when the reaction is initiated.
[LA] = 3.5 M in toluene, [MPB] = 17.3 mM, [CuBr(dNbpy)2] = 17.3 mM, [CuBr2] = 0.7 mM, T = 90&Mac176;C. Conversion 89% after 500 min. Mw/Mn = 1.2.
ATRP of Lauryl Acrylate
LA (2.5 mL; 9.2 mmol) and dNbpy (0.0755g; 0.18 mmol) were dissolved in 2.5 mL toluene and nitrogen gas was bubbled through the solution while stirring for 45 minutes. CuBr (0.0129 g; 0.09 mmol) was added and an initial kinetic sample was taken by syringe. The solution was bubbled with nitrogen for an additional 10 minutes until homogeneous and the flask was placed in a 90&Mac176;C oil bath. Methyl 2-bromopropionate (MBP; 10 mL) was added and samples were removed at timed intervals. After 6.75 hours, the conversion was 59 % (1H NMR).
Mn th = 14,200; Mn GPC = 12,400; Mw/Mn = 1.26.
2-Hydroxyethyl Acrylate (HEA) (16)
2-Hydroxyethyl acrylate (HEA) (Aldrich) was purified by first dissolving the monomer in water (25% by volume). Hydroquinone (0.1%) was then added to the solution to inhibit thermal polymerzation. The solution was extracted with hexane (10 times) to remove diacrylate, and the aqueous solution was salted (250 g/L NaCl). The monomer was then separated from the aqueous phase by ether extraction (4 times) to remove acrylic acid. Hydroquinone was added to the ether solution. CaSO4 drying agent was used to remove traces of water before evaporation of the ether phase. The purified monomer was subsequently kept over molecular sieves and distilled under pressure immediately prior to use. Methyl 2-bromopropionate (MBP) (Aldrich), di-ethyl 2-methyl-2-bromomalonate (DEMBM) (Aldrich), CuBr (98%, Aldrich), and 2-2*-bipyridine ??CuX/2L?? complex. Halogenated initiators and (bpy) (Aldrich) were used as received.
Bulk Polymerizations: These polymerizations were conducted in sealed glass tubes. Typical ratios of the reactants were M : I : Cu : L = 100 : 1 : 1 : 2. The initiators used were either MBP or diethyl 2-methyl-2-bromomalonate (DEMBM). All reagents were added to the glass tube, and the mixture was degassed three times before sealing tubes under vacuum. Reactions were conducted in an oil bath regulated at 900C. Tubes were removed at regular intervals for kinetic experiments, the resulting polymer was dissolved in DMF, and samples were injected directly into the SEC. The solution was additionally passed over alumina to remove the catalyst and dried in a vacuum oven overnight to remove monomer and DMF to isolate the polymer for NMR (d6-DMSO) and MS analysis.
For example: 0.0337 g (0.2 mmol) of bpy, 0.0154 g (0.1 mmol) of CuBr, 12 mL (0.1 mmol) of MBP and 0.5 mL (4.3 mmol) of HEA were combined in a reaction tube and degassed via three freeze?pump?thaw cycles. The tube was then sealed under vacuum and placed in an oil bath 900C for 2 h. The tube was then immediately frozen in liquid nitrogen and broken open. Part of the contents was dissolved in d6-DMSO, and the rest, in DMF. The deuterated sample was used to determine conversion by 1H-NMR. About 0.5 mL of the DMF solution was filtered through a 0.2 mm filter with one drop of diphenyl ether as standard and injected directly into the GPC. The remaining DMF solution was passed over alumina and dried in a vacuum oven at 600C overnight. Part of the remaining sample was dissolved in d6-DMSO to determine molecular weight from NMR by end group analysis and the residual concentration of DMF, and the rest was used for preparation of MALDI samples. Mn = 3,800 (NMR), Mw/Mn 1.15; conversion 91%.
Polymerizations Using Water as Solvent: These polymerizations were conducted in a 1:1 (v/v) ratio of HEA/H2O. The ratio of reactants was M : I : Cu : L = 100 : 1 : 1 : 3.
The reaction mixture was degassed twice to remove traces of oxygen before tubes were sealed. Polymerization was carried out at 900C, and the reaction was terminated after 12 h. The tube contents were dried over MgSO4 and dissolved in DMF. The Cu/bpy complex was homogeneous in both the bulk and aqueous polymerizations forming a brown solution that is characteristic of Cu(I) complexes.
HEA-TMS (2-(trimethylsilyloxy)ethyl acrylate) (17)
2-Trimethylsilyloxyethyl acrylate was synthesized by silylation of 2-hydroxyethyl acrylate (50 mL, 435.3 mmol) with trimethylsilyl chloride (61 mL, 479 mmol) in CH2-Cl2/NEt3 (500 mL/73 mL) at 0 &Mac176;C under Ar and then allowed to come to room temperature. The solution was filtered to remove NEt3.HCl, and the CH2Cl2 was removed by distillation. The product was filtered again, dissolved in EtOAc (300 mL), which was washed 3 times with water, the EtOAc solution was dried and EtOAc evaporated off, and the product was distilled in vacuo (103 &Mac176;C/38 mmHg). The difunctional initiator bis(2-bromopropionyloxy)ethane (F ) 1.66 g/cm3) was prepared by esterification of ethylene glycol with 2-bromopropionyl bromide and NEt3.
The polymerizations were conducted in predried round-bottom flasks. CuBr was added and the flask tightly closed with a rubber septum. After the air was removed by evacuation and purging with Ar (2 cycles), the monomer(s), solvent(s), internal standard(s) (for the conversion measurements by GC), and/or the ligand were added via syringe. The mixture was stirred and purged with Ar for 10 min and then, via syringe, the initiator was added and the flask placed in a preheated oil bath. After specified time intervals, samples (ca. 10 mg) were taken to determine conversions via 1H NMR. After the specified conversion was reached, the flask was removed from the oil bath and the reaction mixture diluted (1:1 to 1:4) with THF or DMF. The solution was filtered through a column with neutral alumina (Fisher-Scientific, 80-200 mesh) to remove the catalyst and a sample taken for SEC analysis. The rest of the solution was concentrated by rotary evaporation, and the polymer was dried in vacuo at 60-80 &Mac176;C (p < 0.1 mmHg).
Homopolymerization of HEA-TMS: [M]:[I]:[Cu] = 50:1:0.5
A 38.0 mg (0.266 mmol) sample of CuIBr was weighed into a 10 mL round-bottom flask,
which was tightly closed with a rubber septum, and the air was removed by evacuation and purging with Ar (2 cycles). Then 5.26 mL (5.0 g, 26.6 mmol) of the monomer TMS-HEA was added via syringe, followed by 55.4 ?L (46 mg, 0.265 mmol) of the ligand PMDETA. The mixture was stirred and purged again with Ar for 10 min, and then, via syringe, 59 ?L (88.5 mg, 0.53 mmol) of the initiator MBP was added and the flask placed in the preheated oil bath at 80 &Mac176;C. After 20 min the conversion (determined by 1H NMR) reached >95% and the flask was removed from the oil bath. The reaction mixture was diluted 1:2 with THF and the solution filtered through an Al2O3 column. A sample was taken for SEC analysis, while the rest of the solution was concentrated in the rotary evaporator and the polymer finally dried in vacuo at 60 &Mac176;C overnight (p < 0.1 mmHg). Yield: 3.40 g (68%). SEC: Mn = 9,390; Mn calc = 9,415; Mw/Mn = 1.20. DSC: Tg -43 &Mac176;C.
Hydrolysis of Poly(HEA-TMS)
The homopolymers of HEA-TMS were hydrolyzed using a catalytic amount of HCl in THF/H2O. The degree of hydrolysis was >99% as determined by 1H NMR. The byproduct, hexamethyldisiloxane, accumulated at the top of the reaction mixture and was easily separated. The polymers were water soluble and contained a small amount of NaCl (<5%) due to neutralization of HCl with NaOH.
Homopolymerization of HEA-TMS at 80 &Mac176;C in Bulk, (I:Cu:L = 1:0.5:0.5)
Sample [M]:[I] time (h) Mn(calc) Mn(1H NMR) Mn(SEC) Mw/Mn
AM2-A 25:1 0.3 4700 4700 4810 1.24
AM2-B 50:1 0.3 9400 9600 9390 1.20
AM2-C 100:1 0.7 18900 >12000 17030 1.26
AM2-A 200:1 2.75 37700 >12000 33000 1.24
High Molecular Weight P(HEA-TMS)
Run BS-02-60 had stoichiometry of HEMA-TMS : EBiB : CuCl : CuCl2 : dNbpy = 1400 : 1 : 2 : 0.2 : 4.4, 10 vol% anisole, T = 90 &Mac176;C. There was only a slight coupling shoulder observed while high molecular weights were obtained.
Mn = 141,000; (DPn = 697); Mw/Mn = 1.11
Glycidyl Acrylate (18)
Glycidyl acrylate was purified by vacuum distillation over iBu3Al. The purified monomer was stored over mole sieves.
dNbpy was used the ligand (see below for synthesis) and the initiator was MBrP.
Typical ratio of reagents were M : I : Cu : L = 100 : 1 : 0.03 : 0.06.
Bulk polymerizations were conducted in sealed glass tubes. The reagents were added to the tubes and the mixture was degassed three times before the tubes were sealed under vacuum. The reactions were conducted at 90 &Mac176;C. Tubes were removed periodically to follow kinetics and it was possible to prepare high MW polymer with low PDI.
[M] Conv. Mn th. Mn exp gpc Mw / Mn
25 95% 3,440 4,320 1.23
150 98% 25,000 27,500 1.21
300 98% 50,000 52,800 1.20
ATRP of Methacrylates
Methyl Methacrylate (19)
4,4?-Bis(5-nonyl)-2,2?-bipyridine was synthesized as follows:
250 mL of 4-(1-butyl-pentyl)pyridine and 10 g of Pd/C were placed in a 500 mL flask, and heated to 210 &Mac176;C in an oil bath under argon with reflux and rapid stirring. After 1 week, the reaction mixture was cooled, filtered first through filter paper (Pd/C was rinsed with Et2O), then filtered over celite. The ether was removed by rotoevaporation, and the
remaining yellow/beige liquid was vacuum distilled to remove the unreacted pyridine. The residue was then distilled under high vacuum; 41 g of 99% pure dinonylbipyridine
were collected at 180 &Mac176;C under 10-7 Torr, which slowly started to crystallize upon cooling.
The polymerizations were carried out in Schlenk flasks (Mn < 30 000) under dry argon or in sealed tubes under vacuum for higher molecular weights. Methyl methacrylate was filtered through an alumina column and then dried over molecular sieves, degassed by argon bubbling, and stored under argon. Diphenyl ether was dried over molecular sieves, degassed and stored in the same way. Copper bromide was purified with glacial acetic acid and washed with pure ethanol, then stored under argon. p-Toluenesulfonyl chloride was used as received. When using a Schlenk flask, all reagents were added except initiator, and the mixture was degassed three times by freeze-pump-thaw cycles. The mixture was heated at reaction temperature (90 &Mac176;C) until homogeneous (about 2 min) and then initiator was added. When using sealed tubes, a single solution (5 mL of MMA + 5 mL of DPE + catalyst and ligand) was prepared for all the tubes. Then 2 mL of the reaction mixture was distributed to each tube, initiator was added, and the reaction mixture was degassed three times before sealing under vacuum. The resulting polymer solutions were cooled down after sampling, dissolved in THF and analyzed by gas chromatography (residual concentration of monomer is determined with dodecane as an internal standard). Prior to injection on to the SEC, samples were passed through a neutral alumina column in order to remove catalyst. SEC calibration curves were calculated with poly(methyl methacrylate) standards from Polymer Laboratories.
The Mn,SEC are very close to the theoretical values, Mn th, defined by eq 1,24 which assumes that one molecule of initiator generates one growing polymer chain:
Together with the straight kinetic plot ln([M]o/[M]) vs time, this confirms that the polymerization process is controlled/?living? with a negligible amount of transfer and termination. Polydispersities decreased from 1.18 to 1.09 and remained very low, indicating a fast exchange between active and dormant species.
Results of Methyl Methacrylate Solution Polymerization in Diphenyl Ether (50% vol) at 90 0C
Conv 103[p-TSCl] Ln([M]o/ time
(%) (mol/L) [M]) (h) Mn, th Mn, sec Mw/Mn
52a 21.25 0.73 2 11,400 10,600 1.15
95a 21.25 2.99 20 20,900 19,800 1.09
98a 9.35 3.91 15 49,000 43,300 1.16
92b 4.675 3.52 20 92,100 83,000 1.18
82b 2.05 1.71 24 186,900 169,000 1.4
85b 2.05 1.89 49 194,000 183,000 1.5
a Schlenk flask. 5 mL. of MMA + 5 mL. DPE. Conversion = 52% after 2 h and
conversion ? 95% after 20 h (80% conversion reached after 6 h)
b Sealed tube, 2 mL. solution.
[MMA]:[EBiB]:[CuBr]:[CuBr2]:[PMDETA] = 100:1:0.35:0.15:0.5 toluene as solvent at 55 &Mac176;C. Result: Mn = 5,200; Mw/Mn = 1.29
[MMA]:[EBriB]:[CuBr]:[Cu Br2]:[PMDETA] = 600:1:0.35:0.15:1 in acetone (50 vol %), 50 &Mac176;C. Mn = 40,000; Mw/Mn = 1.25.
[MMA]:[1-PEBr]:[Fe Br2][dNbpy] = 1000:1:4:4 in 50 vol% o-xylene at 80 &Mac176;C for 19 hr gave 74.9% conversion and Mn,th = 75,100; with Mn,GPC = 75,100 and Mw/Mn = 1.24.
Bulk AGET ATRP of Methyl Methacrylate.
MMA (4.0 ml, 37 mmol) and CuCl2 (25.2 mg, 18.7?10-2 mmol) were added to a 25 mL Schlenk flask and the mixture was bubbled with nitrogen for 15 min. A purged solution of PMDETA (39.1 ?l, 18.7?10-2 mmol) in anisole was added, and the mixture was stirred. Sn(EH)2 (27 ?l, 8.4?10-2 mmol) and a purged solution of EtBrIB (27.4 ?l, 18.7?10-2 mmol) in anisole were added, and the sealed flask was heated in thermostated oil bath at 90 &Mac176;C. The polymerization was stopped after 2.5 hours by opening the flask and exposing the catalyst to air.
[MMA]:[EBriB]:[CuCl2]:[PMDETA]:[ Sn(EH)2] = 200:1:1:1:0.5
Mn, GPC=23,000; Mw/Mn=1.45, conversion=79%
n-Butyl Methacrylate (BMA)
PMDETA is actually not considered to be a good ligand for the controlled polymerization of BMA because BMA is quite an active monomer. But this polymerization can be controlled with a ratio of [M]:[I]:[Cu-complex] = 200: 1: 0.5 with 10% added Cu(II) and a lower amount of catalyst at a lower temperature (60 &Mac176;C) providing a polymer of MW ~10,000 and Mw/Mn 1.34 after 35 min.
Typical Recipe for a Reverse ATRP of BMA in Miniemulsion System a
Monomer BMA 5.0 g 400 equiv.
Ligand EHA6TREN 0.11 g 1 equiv.
Catalyst CuBr2 0.0197 g 1 equiv.
Costabilizer Hexadecane b 0.18 g
Surfactant Brij 98 c 0.115 g
Deionized water H2O 19.88 g
Water-soluble initiator VA-044 0.0284 g 1 equiv.
a Solid content = 20 % (based on 100% conversion);
b 3.6 wt% based on monomer;
c 2.3 wt% based on monomer; 0.58 wt% based on water.
The radical deactivator (CuBr2 and ligand), monomer, and the costablizer (hexadecane) were mixed and heated with magnetic stirring at 60 oC for 10 minutes to form a homogenous solution. After cooling down to the room temperature, the surfactant solution was added and the mixture was ultrasonified (Heat Systems Ultrasonics W-385 sonicator; output control at 8 and duty cycle at 70% for 2 minutes) in an ice bath to prevent a significant temperature rise resulting from sonification. The resulting miniemulsion exhibited good shelf-life stability at room temperature, as evidenced by a lack of creaming or phase separation over 3 days of aging.
After homogenization, the miniemulsion was immediately transferred to a 25 ml Schlenk flask, where pure argon was bubbled through the miniemulsion for 30 minutes before it was immersed in an oil bath thermostated at 70 oC. The magnetic stirring speed was set at 700 rpm. Then, the polymerization was initiated by the injection of pre-deoxygenated aqueous solution of the initiator. Samples were withdrawn periodically via pre-degassed syringe to monitor the kinetics. Further chain extension reactions were performed as follows: a first-step miniemulsion polymerization via reverse ATRP process was carried out as described above; after the polymerization reached high conversion (> 90%, monitored by GC), pre-mixed and deoxygenated monomer and surfactant solution were continuously fed into reaction media via syringe pump at a controlled rate for a period of time. The reaction was continued to complete the polymerization.
Mini-emulsion ATRP of n-BMA from functionalized silica
0.0042g (1.85 X 10-5 mol) CuBr2, 0.0085 g (1.85 X 10-5 mol) BPMODA and 6.727 g (7.52 mL/0.47375 mol) of n-BMA were added to a round bottom flask and allowed to stir and dissolve the solids at 60?C for ~20 min. It was then cooled on ice. While on ice, Brij 98 (used a 20mm solution-> took 5 g diluted to 20 g with DI water), 0.0015 g (9.4 X 10-6 mol) purified AIBN, 0.125 mL (0.18 g) hexadecane, and 0.3 g (9.4 X 10-5 mol of 0.31 mmol Br/1 g) Si-bromoisobutyrate was added to the flask. The mixture was sonicated for 3-4 minutes while on ice and then transferred to a Schlenk flask and bubbled with argon gas for 30 minutes.
Ratios were [BMA]:[Si-Et2BrIB]:[ Surfactant/Brij98]:[Co-stabilizer/hexadecane]:[AIBN]:[CuIIBr2/BPMODA] = 500:1:X:3.6%:0.125:0.2/0.2. Reaction was run at 80?C for 6 hours.
GPC of polymer isolated after silica etching was 70,000; with Mw/Mn =1.32 (pMMA standards). The polymer was precipitated by addition to methanol.
Glycidyl Methacrylate Copolymers:
Two copolymers of GMA and MMA were prepared at 10 g scale. The copolymerization was first carried out using a bpy-based catalyst but it was too slow and the polymers were then synthesized using HMTETA-based catalysts.
A typical procedure follows:
MMA ? 9.6 mL (0.09 mol) (exp. nvt-12-43) or 7.54 mL (0.07 mol) (exp. nvt-12-44)
GMA ? 1.3 mL (0.01 mol) (exp. nvt-12-43) or 3.97 mL (0.03 mol) (exp. nvt-12-44)
acetone ? 10 mL
Ph2O ? 0.5 mL (internal standard for GC measurements)
CuBr ? 0.0287 g (0.2 mmol), CuBr2 ? 0.0113 g (0.05 mmol), HMTETA ? 68 ?L (0.0576 g, 0.25 mmol)
EBiB ? 73 ?L (0.5 mmol; targeted DP = 200)
Temperature: 50 oC
MMA, acetone and diphenyl ether were mixed in a Schlenk flask and the solution was degassed by 6 freeze-pump-thaw cycles. The copper salts were added to the frozen mixture and the flask was closed, evacuated and back-filled with nitrogen several times. Then, deoxygenated HMTETA was injected through the side arm of the flask, and the mixture was heated to 50 oC. After formation of the complex, GMA was added (to avoid reaction with the free amine, HMTETA), followed by the initiator. The reaction was carried out for 280 min (nvt-12-44 with 30 mol % GMA; conversion of MMA = 73 % and of GMA = 89 %; Mn = 20,400 g/mol, Mw/Mn = 1.44) or 290 min (nvt-12-43 with 10 mol % of GMA; conversion of MMA = 72 % and of GMA = 82 %; Mn = 20,200 g/mol, Mw/Mn = 1.24). The polymers were purified by reprecipitation in ether from THF.
3-Azidopropyl Methacrylate (20)
The typical procedure for the ATRP of 3-azidopropyl methacrylate follows. A mixture of 3-azidopropyl methacrylate (2.0 mL, 13 mmol), acetone (2 mL), and diphenyl ether (0.15 mL) in a 10 mL Schlenk tube was degassed by 5 freeze-pump-thaw cycles, and CuBr (9.3 mg, 0.065 mmol) and 2,2?-bipyridine (bpy, 20.2 mg, 0.129 mmol) were added to the frozen mixture under nitrogen flow. The tube was closed, evacuated, and back-filled with nitrogen several times, and the reaction mixture was heated to 50 &Mac176;C. After dissolving the complex, deoxygenated EBriB (9.5 ?L, 0.065 mmol) was injected. Samples were withdrawn periodically to monitor molecular weight evolution and conversion. After 8 h, the flask was removed from heat and opened to expose the catalyst to air. The resulting solution was diluted with chloroform, passed through a neutral alumina column to remove the catalyst, and precipitated into methanol to give poly(3-azidopropyl methacrylate) Mn = 12,300; Mw/Mn = 1.44.
In another experiment, in which the targeted degree of polymerization at complete conversion was lower (100), the amounts of catalyst and initiator were decreased twofold.
Protected Methacrylic Acids (21)
The ATRP of tert-Bu or benzyl methacrylate under appropriate conditions afforded well-defined polymers. Benzyl methacrylate was polymerized via ATRP as a precursor to methacrylic acid. The monomer was used due to its readily availability and unique mode of deprotection of benzyl group. Typically, benzyl group can be deprotected by stirring under H2 with Pd/C at room temperature. The polymer might be useful as a precursor to poly(methacrylic acid) especially in a block copolymer since the deprotection is selective and the work up is simple (filtrate of Pd/C).
The monomer was purified by passing through a column packed with 1/1 mixture of basic and neutral alumina. The polymerization was carried out at 90 ?C in 50% anisole using different ligands. TMEDA, HMTETA and dNbpy were used since previous kinetic studies indicate that use of these ligands led to no significant termination in ATRP of MMA. All polymerization media were more or less homogenous during most of polymerization but slowly turned cloudy towards the end.
In a typical polymerization reaction a dry, degassed Schlenk flask was charged with CuCl (5.1 mg, 0.052 mmole), HMTETA (14.1 ml, 0.052 mmole) and a magnetic stirring bar. Degassed benzyl methacrylate (BnMA, 2 ml, 11.8 mmole) and anisole were added via a degassed syringe and the flask was immersed in an oil bath thermostated to 90 0C then ethyl 2-bromoisobutyrate (EBiB, 7.6 ml, 0.052 mmole) was added to initiate the reaction. Samples were taken periodically to follow reaction kinetics.
CuBr/Ligand/EBiB/BnMA = 0.5/0.5/1/113, 90 ?C in 50% anisole.
Ligand Time (h) Conv. (%) Mn,th Mn PD
dNbpy (2 eq.) 1.4 70.1 14,020 15,740 1.25
TMEDA 3.75 89.7 17,940 14,190 1.33
HMTETA 1.4 79.9 15,980 18,230 1.26
Kinetic studies using HMTETA as the ligand indicated that the polymerization results in significant degree of termination at 90 ?C. Initially the polymerization was quite fast with the conversion of monomer reaching 45.6% conversion within 0.5 h. However, the conversion leveled off at around 65% conversion without significant further monomer conversion or increase in polymer molecular weight.
Higher MW: CuBr/Ligand/EBiB/BnMA = 0.5/0.5/1/227, 90 ?C in 50% anisole.
Results after 1.5 h conversion was 62.7% and Mn,th = 25,000 with Mn,sec = 26,700 and Mw/Mn = 1.18.
Benzyl Methacrylate (BnMA)
In a typical polymerization reaction, a dry degassed round-bottom flask was charged with CuCl (5.1 mg, 0.052 mmol), hexamethyltriethylenetetramine (HMTETA, 14.1 ml, 0.052 mmol), and a magnetic stir bar. Degassed benzyl methacrylate (BnMA, 2 ml, 11.8 mmol) and anisole (2 ml) were added via syringe. The flask was immersed in an oil bath thermostated at 90 ?C, and ethyl 2-bromoisobutyrate (EBiB, 7.6 ml, 0.052 mmol) was added dropwise. At timed intervals, aliquots of the reaction solution were withdrawn via syringes fitted with stainless steel needles, and were dissolved in THF to measure conversion (GC) and molecular weight (SEC). Detailed kinetic studies using HMTETA as the ligand indicate that the polymerization resulted in significant termination at 90 ?C. Initially the polymerization was quite fast with the conversion of monomer reaching 45.6% conversion within 0.5 h. However, the conversion leveled off at around 65% conversion without increase in monomer conversion or polymer molecular weight. The polymerization carried out at 60 ?C showed biphasic kinetic with a very fast initially polymerization stage and a slower linear kinetic second stage. At both temperatures, the molecular weight increased linearly with the conversion and were close to the theoretical values. Polydispersities remained narrow throughout the reaction. Subsequent hydrolysis with H2 on Pd/C afforded well-defined poly(methacrylic acid).
Octadecyl Methacrylate (ODMA)
ODMA was purified as followed: the original ODMA was dissolved in hexane, washed five times with 5%NaOH solution. After drying over magnesium sulfate, all the solvent was removed by evaporation. The pure ODMA monomer was stored at ?5&Mac176;C.
P(ODMA) DPn = 40: ODMA (1.80 g, 5.32 mmol) was placed in a 25 mL Schlenk flask and bubbled with nitrogen for 15 minutes. dNbpy (108 mg, 0.27 mmol) CuCl (13 mg, 0.13 mmol) and CuCl2 (1 mg, 6.6 x 10-3 mmol) were added to a 10 ml round bottom flask and dissolved in degassed diphenylether (2 mL). The resulting solution was transfered via a degassed syringe to the Schlenk flask. Next, ethyl 2-bromoisobutyrate (25.9 mg, 0.13 mmol) was added and the flask was placed in a thermostated oil bath at 70 ?C and stirred. The polymerization was stopped after 2 hours by exposing the catalyst to air, diluted with THF, filtered through a neutral Al2O3 column and precipitated into cold methanol. The polymer was filtered and dried under high vacuum.
[ODMA]:[EBriB]:[CuBr]:[CuBr2]:[dNbpy] = 41:1:1:0.5:2.
Mn, GPC = 11,100; Mw/Mn = 1.14 ; conversion = 88%
ODMA AGET ATRP: The AGET ATRP of ODMA was attempted in bulk using Sn(II) as reducing agent. This polymerization worked perfectly, although it was still a fast reaction. After 5 minutes the molecular weight was over 20K but the molecular weight distribution remained narrow. To confirm this result, regular ATRP of ODMA in xylene was also performed. Almost the same behavior was observed.
[ODMA]:[EBiB]:[CuBr2]:[tNtpy]:[Sn(II)] = 200:1:1:1:0.5, solvent xylene at 60 &Mac176;C; 200min. Mn = 64,400; Mw/Mn = 1.15
Dimethylaminoethyl Methacrylate (DMAEMA)
Poly(DMAEMA) DPn = 25: DMAEMA (0.3 g, 1.91 mmol) was placed in a 25 mL Schlenk flask and bubbled with nitrogen for 15 minutes. dNbpy (60.5 mg, 0.15 mmol) and CuCl (7.3 mg, 7.3 x 10-5 mol) were dissolved in degassed anisole (2 mL) in a separate 10 ml round bottom flask, and transferred via a degassed syringe to the Schlenk flask. Next, ethyl 2-bromoisobutyrate (14.9 mg, 0.08 mmol) was added and the flask was placed in a thermostated oil bath at 90 ?C and stirred. The polymerization was stopped after 18 hours by exposing the reaction to air, diluted with THF, filtered through a neutral Al2O3 column and precipitated into hexane. Polymer was dried under high vacuum.
[DMAEMA]:[ EBriB]:[CuCl]:[dNbpy] = 24:1:1:2
Mn, GPC = 2,800; Mw/Mn = 1.15, conversion = 63%.
Synthesis of poly(DMAEMA) linear MI
[DMAEMA]:[2-bromopropanitrile]:[CuBr]:[HMTETA] = 150:1:1:1 in acetone at 50 &Mac176;C,
DMF line GPC condition: RI detector, linear polyMMA as standard.
Results Mn, GPC = 10,000; Mw/Mn = 1.29
[DMAEMA]:[EBiB]:[CuBr]:[CuBr2]:[HMTETA] = 150 : 1 : 0.7 : 0.3 : 1
Solvent was 50% (v) acetone, at 50&Mac176; C, with diphenylether as GC standard. After 4 hour conversion was 50% providing Mn 7,700 and Mw/Mn = 1.24.
[CuBr]0 = [HMTETA] 0 = [EBiB] 0 = 0.0233 M; [DMAEMA] 0 = 2.96 M in sealed tubes.
In a typical sealed tube experiment, a dry long glass-tube was charged with CuBr (6.7 mg, 0.047 mmol), ligand (0.047 or 0.093 mmol), ethyl 2-bromoisobutyrate (6.8 ?L, 0.047 mmol), 2-(dimethylamino)ethyl methacrylate (1 mL, 5.9 mmol), solvent (dichloro benzene 1 mL), and a magnetic stir bar. The glass tube was degassed by three freeze-pump-thaw cycles and sealed by flame. The glass tube was immersed in an oil bath thermostated at 22.5, 50, 70, or 90 &Mac176;C. After a certain time, the glass tube was taken out and broken. The sample was dissolved in DMF to measure conversion (GC) and molecular weight (GPC).
Temperature Time (h) Convn (%) Mn,th Mn,sec Mw/Mn
90.0 1.25 77.6 15,520 15,770 1.43
70.0 1.25 63.7 12,740 13,100 1.37
50.0 1.80 68.9 13,780 14,140 1.37
22.8 4.67 67.2 13,440 18,910 1.25
Higher molecular weight P(DMAEMA)
[DMAEMA]:[EBriB]:[CuBr]:[CuBr2]:[ HMTETA] = 2000:1:4:0.2:4.2.
Run at 35?C in acetone.
GPC: 75,000; Mw/Mn = 1.2 in ~24 hours
2-Hydroxyethyl Methacrylate (HEMA) (23)
Purification of Monomer: The first procedure involved washing an aqueous solution (25 vol % HEMA) of monomer with hexanes (4 x 200 mL), salting the monomer out of the aqueous phase by addition of NaCl, drying over MgSO4, and distilling under reduced pressure. The second procedure included passing monomer through a neutral silica column, eluted with 30/70 benzene/ethyl acetate, and distilling under reduced pressure. Both methods yielded monomer that polymerized readily and without cross-linking as shown by SEC.
ATRP of HEMA: The following are typical reaction conditions. In a 10 mL round-bottom flask 0.0123 g (0.12 mmol) of CuCl and 0.0386 g (0.241 mmol) were degassed by vacuum followed by argon backfill three times. Solvent (70/30 v/v MEK/1-propanol; 3.0 mL) and HEMA (3.0 mL; 25 mmol) which had been degassed with bubbling argon for at least 45 min were added by syringe and placed in a thermostated oil bath. An initial sample was taken by syringe, and BriB =36 ?L; 0.12 mmol) was added. At timed intervals, kinetic samples were taken by syringe. Conversion was measured by GC.
The theoretical line for Mn, th = 26,000 fits the experimental data targeting Mn = 13,000, and the same is true of Mn th = 52,000 and the data for Mn = 26,000. This suggests that either the efficiency of initiation is only 50% or the molecular weights obtained by SEC could be close to twice the actual value. (see below) Mn = 21,000; Mw/Mn 1.29
AGET ATRP of HEMA was carried out in a mixture of methyl ethyl ketone and methanol (MEK/MeOH = 3/2 v/v). Sn(EH)2 was used as a reducing agent to react with an oxidatively stable precursor Cu(II)/ligand complex and generate the active Cu(I)/ligand complex in this AGET ATRP. A ratio of Cu(II)/Sn(EH)2 = 1/0.45 was used. It should be noted that Sn(EH)2 is not soluble in most protic solvents including MeOH, but is soluble in the mixture of MeOH/MEK. EBiB was used as the ATRP initiator. The standard experimental condition was the initial molar ratio of [HEMA]0/[EBiB]0/[CuCl2]0/[bpy]0 = 100/1.6/1/2. The reaction can be conducted at either 50, 60 or 70 0C with the rate increasing with temperature. All polymerizations at studied temperatures appeared to be well controlled. Molecular weights based on linear PMMA standards increased linearly with conversion, but were higher than theoretically predicted values. This is due to the difference of hydrodynamic volumes of PHEMA and PMMA in DMF. [See below] Polydispersity remained as low as 1.15 ? 1.25.
Estimation of the Absolute MW of PHEMA: In the AGET ATRP of HEMA described above, the values of Mn determined by the GPC with linear PMMA standards were around 2 times higher than the theoretically expected values. The discrepancy could be attributed to the difference of hydrodynamic volumes of PMMA standards and PHEMA in DMF. In order to validate this idea end-group analysis using 1H-NMR spectroscopy was performed. A pyrene-PHEMA was synthesized by a normal ATRP in the presence of an ATRP initiator containing a pyrene substituent in a mixture of MEK/MeOH (3/2/v/v) at 50 &Mac186;C. Molecular weight at 72% conversion was Mn = 23,500 with Mw/Mn = 1.19 as determined by GPC with PMMA standards.
The reason why a pyrene aromatic ring was chosen as an initiating moiety was that its nine protons could provide a strong enough NMR signal whose integral could be compared to the long PHEMA chain. The absolute Mn of PHEMA was determined based on the integration of the NMR signals for protons in the initiating species and monomer units of the polymers. The results were compared with those obtained from the GPC measurement. Based on integration, the mole ratio of HEMA/py = 98/1, corresponding to a target DP = 98, which is nearly half that (Mn = 23,500, i.e. DP = 180) determined by GPC measurement with PMMA standards.
Poly(HEMA-TMS) (High MW) and Conversion to P(BiBEM)
Run BS-02-60 targeted a high MW polymer and used halogen exchange to improve initiation efficiency. The initial stoichiometry of reagents was [HEMA-TMS] : [EBiB] : [CuCl] : [CuCl2] : [dNbpy] = 1400 : 1 : 2 : 0.2 : 4.4, with 10 vol% anisole, T = 90 &Mac176;C. Only a slight coupling shoulder was observed while a high molecular weight polymer was obtained; Mn = 141,000; DPn = 697, Mw/Mn = 1.11.
This sample was used to prepare P(BiBEM) with reaction conditions that involved a higher excess of reagents than what is typically used during the synthesis of P(BPEM). The reaction conditions were [P(HEMA-TMS)] : [KF] : [TBAF] : [2BriBuBr] = 1:3:0.03:3 (BS-02-62). The result was a backbone with over 97% functionalization to BiBEM. Thus, the conditions employed in the polymerization of HEMA-TMS (BS-02-60) and the subsequent reaction to prepare PBiBEM can be considered the best derived so far for preparing high molecular weight backbones suitable for brush synthesis by ATRP.
AGET ATRP of Olig(ethylene oxide) methoxy-capped methacrylate (OEOMA)
This experiment was began with the synthesis of water-soluble ATRP macroinitiator (PEO5000-Br) by the reaction of poly(ethylene glycol) monomethyl ether with M = 5,000 g/mol (PEO5000-OH) with 2-bromo-2-methylpropionic acid in methylene chloride in a good yield (95%). The functionality of bromine chain end remained over 95%.
Polymerization of PEOMA1000
A mole ratio of PEMA1100/PEO5000-Br/CuBr2-TPMA = 70/1/0.5 was employed in the first experiment. The volume ratio of PEOMA1000/water = 1/1 and amount of ascorbic acid used as the reducing agent was 35 mole% of Cu(II) complex. All ingredients including PEOMA1100, PEO5000-Br, CuBr2, and TPMA were completely dissolved in water. A slightly green transparent homogeneous solution formed and was purged by argon for 30 min to remove oxygen, and then an aqueous ascorbic acid solution was added over 1 min. It was found that the solution became viscose in a few minutes, and then the reaction was stopped due to high viscosity. A magnetic bar did not stir at the time. GPC traces of the reaction mixture consisting of poly(PEOMA1100), PEOMA macromonomer, and PEO5000-Br during polymerization showed that the peak corresponding to P(PEOMA1100) was shifted to higher molecular weight from Mn = 55,400 to Mn = 66,800, and the macromonomer peak got smaller, indicating that polymerization occurred. From the ratio of the area of P(PEOMA1100) to total area, one can calculate conversion which reached to 95% in 10 min. However, there was some unreacted macroinitiators left in the reaction medium. It is probably unfunctionalized PEO5000-OH. Polymerization was surprisingly well controlled with narrow PDI (Mw/Mn = 1.21) up to 95% conversion.
In another set of experiments, the targeted DP was increased. The initial reaction conditions has the mole ratio PEMA1100/PEO5000-Br/CuBr2-TPMA = 300/1/0.5 with PEOMA1000/water = 1/3.8 v/v. The amount of ascorbic acid was 35% of Cu(II) complex.
The results are presented below:
Time (min) Conv. Mn, theo Mn, GPC Mw/Mn
25 84% 281,000 126,700 1.26
35 89% 299,000 151,900 1.25
65 96% 320,000 159,900 1.31
Polymerization of PEOMA300
The mole ratio of reagents were PEOMA300/PEO5000-Br/CuBr2/TMPA = 300/1/0.5/0.5 with 15 mole% ascorbic acid compared to mole fraction of CuII. Conversion reached 57% in 15 minutes and the polymer had a Mn, th of 61,000; Mn, gpc = 61,500 and Mw/Mn =1.21
ATRP of Acrylonitrile (24, 25)
Synthesis of PAN: 2.28 x10-2 g (1.60 x10-4 mol) of CuBr, 7.49 x10-2 g (4.80 x10-4 mol) of bpy, and 25 g of ethylene carbonate were added into a 50 mL Schlenk flask. The flask was tightly sealed with a rubber septum, degassed under vacuum, and charged with argon after melting ethylene carbonate (mp ) 37 &Mac176;C). Acrylonitrile (10.0 mL, 1.52 x10-2 mol) and 1.42 x10-1 mL (1.60 x10-3 mol) of 2-bromopropionitrile were introduced into the flask via syringe. The reaction mixture was immersed in an oil bath heated at 44 &Mac176;C. After 23 hours conversion was 38% and the final polymer Mn, th 2,060 had a Mw/Mn 1.04.
(Run DHC-3) Polyarylonitrile was prepared from a mixture of 10.0 mL (151.9 mmol) arylonitrile, 0.38 mL (3.80 mmol) 2-bromopropionitrile, 0.178 g (1.14 mmol) bpy, and 54.4 mg (0.38 mmol) CuBr in 10 mL DMF at 44 &Mac186;C by the similar procedures described above for the preparation of PBA. Samples were periodically withdrawn with a nitrogen-purged syringe, and were diluted with either THF (GC analysis) or DMF (GPC analysis). Monomer conversion was determined by GC analysis and molecular weights by GPC using PMMA calibration. The molecular weight of the final polymer is also estimated by 1H NMR analysis. The results are shown below.
Because of the difference of polarity between PAN and PMMA in DMF, GPC greatly overestimates the molecular weight of PAN. Normally, the GPC result is six times higher than the real molecular weight. However the final molecular weight estimated by 1H NMR is very close to the theoretical value, indicating that the polymerization is well controlled.
ATRP of Acrylonitrile (AN/BPN/CuBr/bpy = 40:1:0.1:0.3 in DMF at 44&Mac186;C)
Sample Time (min) % Conv. (GC) Mn * Mw/Mn *
1 30 9.0 5,360 1.05
2 60 16.1 6,260 1.06
3 90 19.6 6,320 1.06
4 120 25.5 6,770 1.06
5 150 28.3 8,010 1.07
* Using PMMA calibration in DMF
For DP = 200: [AN]:[MBrP]:[CuBr]:[CuBr2]:[bpy] = 200:1:0.40:0.10:1 in either ethylene carbonate or DMF (30-50 vol %), 70 &Mac176;C. Conversion 41%, Mn 34,700 Mw /Mn = 1.29.
Well-Defined High-Molecular-Weight Polyacrylonitrile via Activators Regenerated by Electron Transfer ATRP (26)
In a typical procedure for the synthesis of PAN by ARGET ATRP acrylonitrile (3.0 mL, 0.0456 mol) and ethylene carbonate or DMSO (7.20 mL) were added to a dry Schlenk flask followed by the initiator, BPN (1.97 ?L, 0.0228 mmol). A solution of CuIICl2 complex (0.153 mg, 1.14 ?mol)/TPMA (0.331 mg, 1.14 ?mol) in DMF (0.15 mL) was added into the flask. The resulting mixture was degassed by four freeze-pump-thaw cycles. After melting the mixture, a solution of the reducing agent: Sn(EH)2 (3.69 ?L, 0.0114 mmol) or glucose and TPMA (3.31 mg, 0.0114 mmol) in DMF (0.15 mL) was slowly added to the reaction medium. An initial sample was taken and the sealed flask was placed in an oil bath thermostated at 65 oC. Samples were taken at timed intervals and analyzed by 1H NMR and gel permeation chromatography (GPC) to follow the progress of the reaction. The polymerization was stopped by opening the flask and exposing the catalyst complex in the solution to air. When the initial ratio of reagents were AN/ BPN/ CuIICl2/ TPMA/ glucose = 4000: 1: 0.20: 2.20: 2.0; the rate of reaction was slow but reached 69% after 288 h. giving a polymer with Mn gpc/2.5 = 132,100 and Mw/Mn = 1.18.
The very small amount of copper catalyst (typically 25 to 75 ppm) used in the system effectively suppressed the occurrence of side reactions, such as OSET reduction of an active growing radical to a carbanion by CuIX. Well controlled polymerizations were carried out with both Sn(II) and glucose as an organic reducing agent, yielding PAN with high molecular weight (> 100 000) and low polydispersity (< 1.30).
Copolymerization of Styrene and Acrylonitrile by ARGET ATRP (27)
Styrene (4.0 mL, 0.0349 mmol), acrylonitrile (1.52 mL, 0.0231 mmol) and anisole (4.22 mL) were added to a dry Schlenk flask. Then, an initiator EBiB (8.12 ?L, 0.0533 mmol) and a solution of CuCl2 complex (0.223 mg, 1.66 ?mol)/Me6TREN (0.38 ?L, 1.66 ?mol) in anisole (0.8 mL) were added. The resulting mixture was degassed by four freeze-pump-thaw cycles. After melting the mixture, a solution of Sn(EH)2 (8.95 ?L, 0.0278 mmol) and Me6TREN (6.36 ?L, 0.0278 mmol) in anisole (0.5 mL) was added. An initial sample was taken and the sealed flask was placed in thermostated oil bath at 80 oC. Samples were taken at timed intervals and analyzed by gas chromatography (GC) and gel permeation chromatography (GPC), based on polystyrene standard, to follow the progress of the reaction. The polymerization was stopped by opening the flask and exposing the catalyst to air. One of the runs that show the scope of this procedure started with the following molar ratio of reagents: St:AN:EBiB:CuCl2: Me6TREN/Sn(EH) 2 = 2000:1300:1:0.03:0.5:0.5 provided 60% conversion after 92 hours and a copolymer with Mn = 166,200 and a Mw/Mn = 1.26.
Controlled polymerization of (meth)acrylamides was achieved by ATRP using the initiating system methyl 2-chloropropionate/CuCl/tris(2-dimethylaminoethyl) amine. Linear increase of molecular weights with conversion and low polydispersity (Mw /Mn = 1.2) were obtained in toluene, at room temperature, when N,N-dimethylacrylamide
was used as the monomer. However, the polymerization reached limited conversion, which could be enhanced by increasing the catalyst/initiator ratio. The limited conversion is not due to the loss of the active chain end, but rather to the loss of activity of the catalytic system.
[DMAA]0 = 2.4 M; [MCP] 0 = 23.7 mM; [CuCl] 0 = [Me6TREN] 0 = 47.4 mM; solvent = toluene; T = 20 0C. Conversion 79%, Mn 9,600; Mw /Mn = 1.2.
Poly(N-isopropylacrylamide) by ATRP in Solution
Coordination between the polymer/monomer and catalyst affects the level of control attained in the polymerization. Still under discussion whether it is chain end death or catalyst deactivation that stops the polymerization
% Mn theor
100/1/3/0.6/3.6 1.5 26.8 3 000 16 600 1.03
500/1/5/0.25/5.25 2.5 49.2 27 800 68 800 1.14
51.2 55 400
57 900 127 000
138 100 1.14
NIPAM/EBiB/CuCl/Me6TREN = 1000/1/10/10 in DMF 4 hr at 35 ?C.
Mn 73,000; Mw/Mn 1.19
Polymerization of 4-Vinyl Pyridine (4-VP) in Protic Media (29)
Earlier work showed that CuCl/HMTETA served as an efficient catalyst for the aqueous ATRP of 4-VP. However, although the polymerization carried out in the presence of CuCl2 yielded a polymer of narrow MWD, the polymerization was relatively slow, taking 30 h to reach ca. 80% monomer conversion. Thus, a more active catalyst, namely CuCl/TPMA should be used. (The following example details a preparation made as part of a kinetic study and more ?normal? conditions employing non-deuterated reagents can also be used.)
A mixture of CD3OD (1.5 mL), D2O (1.5 mL), and 4VP (3 mL) was degassed by 6 freeze-pump-thaw cycles, the mixture was frozen in liquid nitrogen, the flask was filled with nitrogen, and a mixture of CuCl (0.0192 g, 0.194 mmol), CuCl2 (0.0133 g, 0.098 mmol, 30 % of the total Cu), and TPMA (0.0848 g, 0.29 mmol) was added quickly. The flask was then closed, evacuated and back-filled with nitrogen several times, and placed in a water bath thermostated at 30 oC. The nitrogen-purged MeOPEOBiB macroinitiator (MW = 699 g/mol, 0.162 mL) was then added. Samples were periodically withdrawn with a nitrogen-purged syringe, and were diluted with either CD3OD (NMR analysis) or 50 mM solution of LiBr in DMF (SEC analysis). Monomer conversion was determined by 1H NMR analysis and molecular weights by SEC using polySt standards for calibration. The results are presented in the following table. Polymers with monomodal MWD were obtained and the PDI values were even lower than with the best system studied so far (CuCl + CuCl2 / HMTETA).
ATRP of 4VP using CuCl + CuCl2/HMTETA as the catalyst
Sample Time, h % Conv. (NMR) Mn g/mol Mw/Mn
1 0.5 24.1 10,460 1.10
2 1 30.9 12,460 1.11
3 2.5 45.0 16,890 1.12
4 4.5 57.5 20,000 1.15
5 7 64.8 23,200 1.17
4-VP in Non-protic Media (DMF)
A mixture of DMF (3 mL) and 4-VP (3 mL, 28 mmol) was degassed by 10 freeze-pump-thaw cycles, the mixture was frozen in liquid nitrogen, and the flask was filled with nitrogen. The flask was opened and a mixture of TPMA (0.0848 g, 0.292 mmol), CuCl (0.0192 g, 0.194 mmol), and CuCl2 (0.0133 g, 0.098 mmol) was added. The flask was quickly closed with a rubber septum, evacuated and back-filled with nitrogen several times. The mixture was then allowed to thaw in a thermostated oil bath, and the nitrogen-purged initiator, MePEOBiB (MW = 699 g/mol (0.16 mL)) was injected. Conversions were determined by GC. The results are presented in the following table.
ATRP of 4VP in DMF using CuCl + CuCl2/TPMA as the catalyst at 40 oC.
Sample* Time, h % Conv. (GC) Mn, kg/mol* Mw/Mn *
1 2.75 13.8 6.74 1.07
2 6 28.9 8.89 1.07
3 20.5 48.1 14.40 1.11
4 32.75 55.6 16.45 1.12
* PolySty standards were used.
Dimethyl(1-ethoxycarbonyl)vinyl Phosphate) (DECVP)
Polymers with controlled molecular weight and relatively low polydispersity (PDI < 1.5) were obtained through ATRP initiated with ethyl 2-bromoisobutyrate (EBriBu) in the presence of Cu(I)Cl/2,2?-bipyridine (bpy). A faster rate of polymerization and higher monomer conversion were obtained in the polymerization using Cu(I)Cl/ N,N,N?,N??,N??-pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) as the catalyst system.
Homopolymerization of DECVP (30) A typical ATRP was carried out as follows: in a 10 mL dried Schlenk flask, DEVCP (1 g, 4.5 mmol), EBriBu (6.7 µL, 0.045 mmol) and 2-butanone (1 mL) were added. After three freeze-pump-thaw cycles, bpy (14.1 mg, 0.09 mmol) and Cu(I)Cl (4.4 mg, 0.045 mmol) were added under N2. After stirring for 10 minutes at room temperature (rt), the flask was placed in a thermostated oil bath at 70 ?C. Samples were taken to analyze the monomer conversion by 1H NMR and molecular weight by GPC in different time intervals during the polymerization. The polymerization was stopped by cooling to rt and opening the flask to air. The mixture was then dissolved in 10 mL acetone and passed through neutral alumina column. The final pure product was obtained after precipitating in hexanes.
M/I/Cu/L = 100/1/1/2. Temp. 70 ?C. Time 8 hr. % Conversion = 26%, Mn = 7,000; Mth = 5,800; Mw/Mn = 1.50.
Preparation of Poly(2-acrylamido-2-methyl-N-propanesulfonic acid) (P(AMPSA)):
2-Acrylamido-2-methyl-N-propanesulfonic acid (AMPSA) (5 g, 24.2 mmol) was added to a 25 mL Schlenk flask and degassed for 30 minutes. Degassed tributylamine (5.8 mL, 24.3 mmol) was added to turn the AMPSA into a salt, followed by degassed DMF (8 mL). The mixture was stirred until the AMPSA dissolved, then degassed for 20 minutes. The copper/ligand complex was prepared in a separate Schlenk flask. CuCl (34.2 mg, 0.35 mmol) and bpy (114 mg, 0.73 mmol) were placed in a 10 mL Schlenk flask. The flask was subjected to vacuum for 30 seconds, then flushed with nitrogen. This process was repeated 4 times, in order to remove all the oxygen from the flask. Degassed DMF (3 mL) was then added, and the mixture was stirred for 10 minutes, under nitrogen, in order to make the copper/ligand complex. EBiB (18 ?l) was added to the polymerization flask, and the mixture was degassed. A 1 mL portion of the copper/ligand complex (11.4 mg CuCl, 38 mg bpy) was removed and added to the main reaction flask. The mixture was degassed for 4 minutes, then lowered into a 60?C oil bath and heated for 41 hours. The polymer was diluted with 20 ml water. The polymer was dialyzed against water to remove the un-reacted monomer the solvent and the catalyst. The solution was then passed through Diowex ion exchange resin column. poly(AMPSA) containing polymers of low polydispersity index (1.1-1.4) were obtained. However, in all cases studied, the monomer conversion was limited to 10-15%. (DP ~30)
The best conditions were monomer:initiator:copper:ligand/300:1::1:0.7 with a 5% excess of TBA, with EBiB as initiator, CuCl as the metal, and bpy as the ligand.
The polydispersity from these materials was relatively low ~1.2, much lower than those for the polyAMPSA produced by RAFT (~1.5-1.6).
ATRP of MAA in aqueous media (water-methanol = 1:1) using Cu(I)/Na2EDTDAA as the catalyst (EDTDAA is ethylenedithiodiacetic acid)
Flask 1: 0.2395 g (0.94 mmol) of Na2EDTDAA in 2 ml of D2O. The solution was degassed by 5 f-p-t cycles and 0.0672 g (0.472 mmol) CuBr was added over the frozen solution. The flask was closed, evacuated and back-filled with nitrogen several times. After warming up the flask, a clear solution was formed.
Flask 2: 4 ml of MAA (4.06 g, 0.047 mol) was dissolved in 2 ml of MeOH-d4. The solution was degassed by 5 f-p-t cycles.
The solution in flask 2 was added to the first one, and as in the previous reaction, a heterogeneous solution was formed. The flask was immersed in a thermostated oil bath at 75oC and 250 ?l of MePEGBiB was added. The results are summarized below.
Sample Time, h Conversion Mn, g/mol* Mw/Mn *
Maa11-1 1.5 0.221 - -
Maa11-2 4 0.383 10920 1.28
Maa11-3 9 0.583 15440 1.33
Maa11-4 21 0.826 17600 1.41
* 0.2 M NaNO3 in water as the eluent, PEO standards
One-pot Forced Gradient Copolymerization by AGET ATRP in Miniemulsion: (31)
Copolymerization of nBA and tBA was carried out by AGET ATRP in miniemulsion. The monomers (nBA (1.8 g, 14 mmol), tBA (1.8 g, 14 mmol)), catalysts (CuBr2 (0.0125 g, 0.056 mmol) and BPMODA (0.0254 g, 0.056 mmol)), mono-functional initiator EBiB (21µL, 0.14 mmol) and co-stabilizer hexadecane (0.17 mL) were mixed in a round bottom flask at 60 &Mac186;C. After the formation of the Cu(II) complex, an aqueous Brij 98 solution (16 mL, 5 mol/L) was added to the system. The resulting mixture was subject to sonication (Heat Systems Ultrasonics W-385 sonicator; output control set at 8 and duty cycle at 70%) for 1 min in an ice bath (to prevent a possible temperature rise resulting from sonication) to form a stable miniemulsion. The stable miniemulsion was transferred to a Schlenk flask and bubbled with nitrogen for 30 min. The flask was immersed into an oil bath preheated at 80 &Mac186;C. The polymerization was initiated by the injection of a pre-deoxygenated aqueous solution (0.5 mL) of ascorbic acid (0.0044 g) to activate the copper complex. Aliquots were withdrawn from the reaction at the different time intervals to determine conversion by Gas Chromatography (GC). The samples were dried under vacuum and dissolved in THF before they were subjected to gel permeation chromatography (GPC) for molecular weight analysis. The polymerizations were stopped by exposing the catalyst to air.
Forced gradient copolymerization by AGET ATRP in miniemulsion: Several monomer pairs were subject to the preparation of forced gradient copolymers by AGET ATRP in miniemulsion. In a typical run, CuBr2 (0.0125 g, 0.056 mmol), BPMODA (0.0254 g, 0.056 mmol), nBA (1.8 g, 14 mmol), EBiB (21 µL, 0.14 mmol) and hexadecane (0.17 mL) were mixed in a 25 mL round bottom flask at 60 oC. After the formation of the Cu(II) complex, an aqueous solution of Brij 98 (16mL, 5 mmol/L) was added to the system and the mixture was subject to sonication for 1 min in an ice bath to form a stable miniemulsion. The stable miniemulsion was transferred to a Schlenk flask and bubbled with nitrogen for 30 min. The flask was immersed in an oil bath preheated at 80 oC. The polymerization was initiated by injection of a pre-deoxygenated aqueous solution (0.5 mL) of ascorbic acid (0.0044 g). Simultaneously the pre-deoxygenated tBA monomer (1.8 g, 14 mmol) was continuously added to the miniemulsion at a predetermined rate with the aid of a syringe pump (KdScientific KDS 210 infusion/withdrawal syringe pump). Aliquots were periodically withdrawn via a pre-degassed syringe to monitor monomer conversion by gravimetry and 1H NMR. The samples were dried under vacuum and dissolved in THF before they were subjected to GPC for molecular weight analysis. The polymerizations were stopped by exposing catalysts to air. In the present study, the following monomer pairs: nBA/tBA, BMA/MMA and nBA/St, were selected for preparation of forced gradient copolymers in miniemulsion. The polymerization conditions are summarized in the following table.
Preparation of Forced Gradient Copolymers by AGET ATRP in Miniemulsion a
M 1 M2 Temp Feed rate and period Conversion (total)
Run 1b nBA/tBA 80 55 %
Run 2b nBA tBA 80 0.01 mL/min for 200 min 50 %
Run 3b nBA tBA 80 0.015 mL/min for 60 minutes, 0.01 mL/min for the following 60 minutes, and 0.005 mL/min for the following 120 minutes. 47 %
Run 4c BMA MMA 75 0.01 mL/min for 180 min 85 %
Run 5c MMA BMA 75 0.01 mL/min for 120 min 77 %
Run 6b nBA St 80 0.01 mL/min for 190 min 100 %
a Miniemulsion conditions for all runs in the table: [Brij 98]/ [Hexadecane] = 2.3/3.6 wt% with respect to monomer; solids content = 20 % (based on 100% conversion). The total monomer conversion was measured by gravimetry.
b [M1]: [M2]: [EBiB]: [CuBr2/BPMODA]: [Ascorbic acid] = 100: 100: 1: 0.4: 0.16.
c [M1]: [M2] : [EBiB]: [CuBr2/BPMODA]: [Ascorbic acid] = 200: 100: 1: 0.4: 0.16.
Cumulative compositions (A) and instantaneous compositions (B) of nBA and tBA in the forced copolymer resulting from AGET ATRP in miniemulsion with tBA as a fed monomer and the feeding rate of 0.01 mL/min for 200 minutes.
Polymerization conditions: Run 2 in above table.
Block copolymers (32-34)
The best order of chain extension from (macro)initiators: AN > MMA > MA > Sty.
Going from MA to MMA or AN requires halogen exchange (CuCl-based catalyst)
In chain extension of Sty with MMA or AN, halogen exchange improves control but not sufficiently.
Synthesis of diblock copolymer Poly(styrene-b-t-butyl acrylate)(34) There are a series of chain extensions described in references 32-34 one of which is excerpted below. All polymerization reactions were catalyzed by CuBr/PMDETA. The GPC traces showed relatively clean blocking in most cases, with movement of the entire polymer distribution to higher molecular weights. This confirmed that the end functionality was maintained throughout the reactions. CuBr2 was added to the reactions where lower molecular weight p(tBA) blocks were targeted. On the basis of other results from this laboratory the addition of Cu(II) can slow down the rate of the reaction. In addition, the use of a more polar solvent, such as acetone, can also result in a more controlled reaction through better solvation of both the activator and deactivator. Both of these modifications help to produce polymers with lower polydispersities than those prepared without either the added Cu(II) or the polar solvent. For higher molecular weight p(tBA) blocks, no additional Cu(II) was necessary because decreasing the initiator and catalyst concentrations by dilution functioned in the same manner.
Typical run: The macroinitiator and CuBr were added to the flask initially. The flask was sealed with a rubber septum, degassed, backfilled three times with N2, and then left under N2. The monomer and internal standard/solvent were added, and only after dissolution of the macroinitiator was the PMDETA ligand added. Again, an initial sample was removed to measure the initial ratio of monomer and internal standard for comparison against the final ratio. Reactions were run in a thermostated oil bath for the desired amount of time, after which the flask was removed, the final monomer conversion was measured, and the molecular weight analyses were performed. The most important aspect of these polymerizations was the optimization of the catalyst system to obtain the desired molecular weights, while at the same time maintaining reasonable rates of polymerization, resulting in polymers with narrow molecular weight distributions.
[tBA]:[MI]:[Cu(I)]:[Cu(II)]:[ PMDETA] = 50:1:0.5:0.025:0.525 plus 25% acetone at 60&Mac176;C for 180 minutes provided 43% conversion and a Mn, th of 3,800 compared to Mn, exp of 3,725.
A dry glass tube with a stir bar was charged with CuCl (2.6 mg), the PMMA-Cl macroinitiator (Mn, SEC = 7700, Mw/Mn = 1.06, 100 mg), DMF (0.5 mL), Me6TREN (7.1 ?L), and 4VP (1.0 mL). Three freeze-pump-thaw cycles were performed, and the tube was sealed under vacuum and placed in an oil bath held at 50 &Mac176;C. After 3.0 h, the tube was opened, and the contents were dissolved in DMF. Monomer conversion and SEC measurements were performed on the reaction mixture. For the 1H NMR analysis, the block copolymer was recovered by removing the solvent under reduced pressure, redissolving the polymer in chloroform, passing the polymer solution through an alumina column to remove the metal containing residues, and precipitation in cold hexane. The polymer was dried at 80 &Mac176;C under vacuum for 48 h. 1H NMR indicated that the block copolymer had 87 wt % of P4VP and a molecular weight of Mn,NMR = 62,500 which was in good agreement with the calculated value (Mn,Cal = 63,800 at 84% monomer conversion) assuming quantitative cross-propagation and the absence of any chain-breaking reactions. However, the molecular weight determined by SEC with PMMA standards was much higher (Mn,SEC = 89,500).
Synthesis of diblock copolymer PODMA-b-PMMA by AGET ATRP
In a 25 mL Schlenk flask, PODMA macroinitiator (Mw=13800, Mw/Mn =1.10) (3.0g, 0.2 mmol) and CuCl2 (31 mg, 7.3 x 10-5 mol) were dissolved in monomer (MMA, 9.4 g, 0.1 mol) and bubbled with nitrogen for 15 minutes. A purged solution of PMDETA (48 µl, 0.23 mmol) in toluene (5ml) was added, and the mixture was stirred. Sn(EH)2 (34 ?l, 0.1 mmol) in toluene (4ml) was added next, and an initial sample was taken. Flask was placed in a thermostated oil bath at 90 ?C and stirred. The polymerization was stopped after 17 hours by opening the flask and exposing the catalyst to air.
[MMA]:[MI]:[ CuCl2]:[ Sn(EH)2]:[PMDETA] = 500:1:0.073:0.5:2.3
Mn, GPC 38100; Mw/Mn 1.09, conversion = 58%
Synthesis of diblock copolymer PnBA-b-PS by ARGET ATRP
A PnBA macroinitiator (Mw=19400, Mw/Mn =1.26) (2.35 g, 0.12 mmol) was dissolved in styrene monomer (St, 2.75 ml, 24.0 mol) in a 25 mL Schlenk flask and bubbled with nitrogen for 15 minutes. Next, a solution of CuCl2 (4.84?10-2 mg, 0.36?10-3 mmol)/Me6TREN (0.10 ?l, 0.36?10-3 mmol) complex in degassed anisole (0.7 ml) was added. The resulting mixture was stirred for 10 minutes and then 3.9 ?l (1.2?10-2 mmol) of a purged solution of Sn(EH)2 and Me6TREN (3.2 ?l, 1.2?10-2 mmol) in anisole (0.7 ml) was added. An initial sample was taken and the sealed flask was placed in thermostated oil bath at 110 oC. Samples were taken at timed intervals and analyzed by GC and GPC. The polymerization was stopped after 30.8 h (Mn, GPC = 34,900 and Mw/Mn = 1.18, conversion=88%) by opening the flask and exposing the catalyst to air.
Synthesis of PolyBA-b-Poly(MMA-co-St) and PolySt-b-Poly(MMA-co-St) using an ARGET or ICAR ATRP. (35)
As noted in the synthesis section chain extension from a secondary macroinitiator to controlled polymerization of a tertiary monomer is not efficient and ?halogen exchange? was developed. Halogen exchange can not work when low concentrations of catalyst are employed and so another means of control had to be developed. This was conducting a copolymerization in the second block.
PolyBA-b-Poly(MMA-co-St): PolyBA-Br (1 g, 0.0556 mmol) and anisole (1 mL) were added to a Schlenk flask, and purged with nitrogen. Next, MMA (1.1 mL, 10.0 mmol) and St (0.13 mL, 1.11 mmol) purged with nitrogen were added to the flask, followed by CuCl2 (0.075 mg, 0.556 ?mol) and TPMA (0.97 mg, 3.33 ?mol) in purged anisole (0.5 mL). Sn(EH)2 (1.8 ?L, 5.56 ?mol) in purged anisole (0.5 mL) was added to begin polymerization. An initial sample was taken via purged syringe, and the sealed flask was placed in an oil bath at 90 &Mac176;C. Samples were taken at timed intervals and analyzed by gas chromatography (GC) and gel-permeation chromatography (GPC) to follow the progress of the reaction. The polymerization was stopped by opening the flask and exposing the catalyst to air, and polyBA-b-poly(MMA-co-St) was obtained. When a PolyBA-Br macroinitiator of Mn = 18,000 and Mw/Mn = 1.12 was chain extended with MMA/St/PBA-Br/CuCl2/Sn(EH)2 = 180/20/1.0/0/01/0.06/0.1 a block copolymer with Mn = 30,100 and Mw/Mn 1.23 was obtained at 83% monomer conversion.
PolySt-b-Poly(MMA-co-St): A similar procedure was used to synthesize polySt-b-poly(MMA-co-St). A polystyrene macroinitiator of Mn = 19,500 and Mw/Mn = 1.09 was chain extended to brovide a block copolymer with Mn = 38,100 and Mw/Mn = 1.30 at 86% monomer conversion.
Synthesis of PolyBA-b-Poly(MMA-co-St) by Initiators for Continuous Activator Regeneration (ICAR) ATRP In this case 5.56 ?mol of AIBN was added in place of Sn(EH)2, 0.556 ?mol of TPMA was used, and the oil bath was thermostated at 60 &Mac176;C.
I.e. when a PolyBA-Br macroinitiator of Mn = 18,000 and Mw/Mn = 1.12 was chain extended with MMA/St/PBA-Br/CuCl2/AIBN = 180/20/1.0/0/01/0.01/0.1 a block copolymer with Mn =36,000 and Mw/Mn 1.38 was obtained.
Synthesis of Polymers via ARGET ATRP by Using Ascorbic Acid as Reducing Agent: (36) The limited solubility of ascorbic acid in organic solvents, such as anisole, provides a slow reduction of Cu(II) species which facilitates well-controlled atom transfer radical polymerization (ATRP) of various monomers using the recently developed activators regenerated by electron transfer (ARGET) technique.
In polymerizations with 25 ppm, or less than 25 ppm of Cu, a stock solution of Cu(II)/Me6TREN was made by dissolving CuBr2 (0.0223 g, 0.1 mmol), Me6TREN (264 ?L, 1 mmol) in 5 mL of DMF. In a typical run, EBiB (14.7 ?L, 0.1 mmol), MA (3.6 mL, 40 mmol), 50 ?L of the Cu(II) stock solution and anisole (2.4 mL) were added to a 10 mL Schlenk flask. The flask was sealed and then deoxygenated by several cycles of freeze-pump-thaw. Then ascorbic acid (0.0088 g, 0.05 mmol) was added to the flask and the flask was immersed in an oil bath, thermostated at 60 oC, to initiate polymerization. Aliquots were taken at intervals to measure conversion and to examine the evolution of molecular weight.
Synthesis of poly(methyl acrylate) (PMA) by ARGET ATRP using ascorbic acid as reducing agent. Polymerization temperature: 60 oC. Polymerizations were carried out in 60% v/v solutions. Initiator: ethyl 2-bromoisobutyrate (EBiB). Ligand: Me6TREN. The amount of ligand has been fixed at 10 times the amount of Cu(II) initially added to the reaction in order to assure coordination of the ligand with Cu(II) in the presence of a large excess of monomer.
When the concentration of Cu: molar ratio of Cu to monomer 25 ppm and [MA]: [I]: [Cu(II)]= 400: 1: 0.01; conversion reached 87% after 5.3 hours and Mn (theo) =30,000 Mn (GPC) = 27,700 and Mw/Mn 1.19. Continuing the reaction to 98% conversion provided a polymer with Mn (theo) =33,750 Mn (GPC) = 34,400 and Mw/Mn 1.18.
When the concentration of copper was reduced to 10 ppm and [MA]: [I]: [Cu(II)]= 400: 1: 0.004 the reaction reached 91% conversion provided a polymer with Mn (theo) =31,340 Mn (GPC) = 29,700 and Mw/Mn 1.40.
All polymerizations carried out with 25 ppm or lower concentration of Cu resulted in the preparation of essentially colorless polymers; therefore, catalyst removal may not be necessary for some applications.
Synthesis of poly(butyl acrylate), poly(methyl methacrylate) and polystyrene by ARGET ATRP with ascorbic acid as reducing agent*
Entry M Ascorbic acid (to Cu) Cu (ppm)a Solvent Time (h) Conv. Mn(theo) Mn(GPC) Mw/Mn
7 b BA 10 25 Anisole 21.5 89% 45500 43000 1.28
8 b MMA 10 25 Anisole 18 59% 23260 30700 1.27
9 c St 10 25 Anisole 64.7 68% 27580 25200 1.18
10 d St 10 25 Anisole 52 55% 53540 60900 1.27
* Polymerizations were carried out in 60 % v/v solutions.
Initiator: EBiB for BA and St, ethyl ?-bromophenylacetate for MMA. Ligand: Me6TREN.
The amount of ligand has been fixed at 10 times the amount of Cu(II) initially added to the reaction.
a Concentration of Cu: molar ratio of Cu to monomer.
b [M]: [I]: [Cu(II)]= 400: 1: 0.01. Reaction temperature: 60 oC; c [M]: [I]: [Cu(II)]= 400: 1: 0.01.
Reaction temperature: 90 oC; d [St]: [PMA-Br]: [Cu(II)]= 400: 1: 0.01. Reaction temperature: 90 oC.
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10. ?Graft Copolymers from Linear Polyethylene via Atom Transfer Radical Polymerization?; Inoue, Y., Matsugi T., Kashiwa, N. and Matyjaszewski, K. Macromolecules 2004, 37, 3651.
11. ?Functionalization of polyethylene based on metallocene catalysis and its application to syntheses of new graft copolymers possessing polar polymer segments?; Kishiwa N.; et.al. J. Polym. Sci., Part A:Polym. Chem. 2003, 41, 3657-3666.
12. ?Grafting from Surfaces for \"Everyone\": ARGET ATRP in the Presence of Air,? Matyjaszewski, K.; Dong, H.; Jakubowski, W.; Pietrasik, J.; Kusumo, A. Langmuir 2007, 23, 4528-4531.
13. ?Activators regenerated by electron transfer for atom-transfer radical polymerization of (meth)acrylates and related block copolymers,? Jakubowski, W.; Matyjaszewski, K. Angewandte Chemie, International Edition 2006, 45, 4482-4486.
14. ?Development of an ab Initio Emulsion Atom Transfer Radical Polymerization: From Microemulsion to Emulsion,? Min, K.; Gao, H.; Matyjaszewski, K. J. Am. Chem. Soc. 2006, 128, 10521-10526.
15. ?The atom transfer radical polymerization of lauryl acrylate?; Beers, K. L.; Matyjaszewski, K. J. Macromol. Sci., Pure Appl. Chem. 2001, A38, 731-739.
16. ?Polymerization of acrylates by atom transfer radical polymerization. Homopolymerization of 2-hydroxyethyl acrylate?; Coca, S.; Jasieczek, C. B.; Beers, K. L.; Matyjaszewski, K. J. Polym. Sci., Part A: Polym. Chem. 1998, 36, 1417-1424.
17. Synthesis of Amphiphilic Block Copolymers by Atom Transfer Radical Polymerization (ATRP) Muehlebach, A.; Gaynor, S. G.; Matyjaszewski, K. Macromolecules 1998, 31, 6046-6052.
18. Polymerization of acrylates by atom transfer radical polymerization. Homopolymerization of glycidyl acrylate Matyjaszewski, K.; Coca, S.; Jasieczek, C. B. Macromol. Chem. Phys. 1997, 198, 4011-4017.
19. ?Controlled/\"Living\" Radical Polymerization of Methyl Methacrylate by Atom Transfer Radical Polymerization?; Grimaud, T.; Matyjaszewski, K. Macromolecules 1997, 30, 2216-2218.
20. ?Highly Efficient \"Click\" Functionalization of Poly(3-azidopropyl methacrylate) Prepared by ATRP,? Sumerlin, B. S.; Tsarevsky, N. V.; Louche, G.; Lee, R. Y.; Matyjaszewski, K. Macromolecules 2005, 38, 7540-7545.
21. ?Atom transfer radical polymerization of protected methacrylic acids?; Zhang, X.; Xia, J.; Matyjaszewski, K.; Polym. Prepr. 1999, 40(2), 440-441.
22. "Controlled/\"Living\" Radical Polymerization of 2-(Dimethylamino)ethyl Methacrylate." Zhang, X.; Xia, J.; Matyjaszewski, K. Macromolecules 1998, 31, 5167.
23. "Atom Transfer Radical Polymerization of 2-Hydroxyethyl Methacrylate." Beers, K. L.; Boo, S.; Gaynor, S. G.; Matyjaszewski, K. Macromolecules 1999, 32, 5772.
24. "Synthesis of Well-Defined Polyacrylonitrile by Atom Transfer Radical Polymerization." Matyjaszewski, K.; Jo, S. M.; Paik, H.-j.; Gaynor, S. G. Macromolecules 1997, 30, 6398.
25. "An Investigation into the CuX/2,2'-Bipyridine (X = Br or Cl) Mediated Atom Transfer Radical Polymerization of Acrylonitrile." Matyjaszewski, K.; Jo, S. M.; Paik, H.-j.; Shipp, D. A. Macromolecules 1999, 32, 6431.
26. ?Well-Defined High-Molecular-Weight Polyacrylonitrile via Activators Regenerated by Electron Transfer ATRP,? Dong, H.; Tang, W.; Matyjaszewski, K. Macromolecules 2007, 40, 2974-2977.
27. ?Synthesis of High Molecular Weight Poly(styrene-co-acrylonitrile) Copolymers with Controlled Architecture,? Pietrasik, J.; Dong, H.; Matyjaszewski, K. Macromolecules 2006, 39, 6384-6390.
28. "Controlled polymerization of (meth)acrylamides by atom transfer radical polymerization." Teodorescu, M.; Matyjaszewski, K. Macromol. Rapid Commun. 2000, 21, 190.
29. "Atom Transfer Radical Polymerization of 4-Vinylpyridine." Xia, J.; Zhang, X.; Matyjaszewski, K. Macromolecules 1999, 32, 3531.
30. ?ATRP of Dimethyl(1-ethoxycarbonyl)vinyl Phosphate and Corresponding Block Copolymers?; Huang, J.; Matyjaszewski, K. Macromolecules 2005, 38, 3577-3583.
31. ?Preparation of gradient copolymers via ATRP in miniemulsion. II. Forced gradient,? Min, K.; Oh, J. K.; Matyjaszewski, K. Journal of Polymer Science, Part A: Polymer Chemistry 2007, 45, 1413-1423.
32. Controlled/living radical polymerization in the undergraduate laboratories. 1. Using ATRP to prepare block and statistical copolymers of n-butyl acrylate and styrene. Beers, K. L.; Woodworth, B.; Matyjaszewski, K. J. Chem. Educ. 2001, 78, 544-547.
33. Controlled/living radical polymerization in the undergraduate laboratories. 2. Using ATRP in limited amounts of air to prepare block and statistical copolymers of n-butyl acrylate and styrene. Matyjaszewski, K.; Beers, K. L.; Woodworth, B.; Metzner, Z. J. Chem. Educ. 2001, 78, 547-550.
34. ?Preparation of block copolymers of polystyrene and poly(t-butyl acrylate) of various molecular weights and architectures by atom transfer radical polymerization.? Davis, K. A., Charleux, B., Matyjaszewski, K.: J. Polym. Sci., Part A: Polym. Chem., 2000, 38: 2274-2283.
35. ?Successful Chain Extension of Polyacrylate and Polystyrene Macroinitiators with Methacrylates in an ARGET and ICAR ATRP,? Mueller, L.; Jakubowski, W.; Tang, W.; Matyjaszewski, K. Macromolecules, Web Release Date: 02-Aug-2007.
36. ?Use of Ascorbic Acid as Reducing Agent for Synthesis of Well-Defined Polymers by ARGET ATRP,? Min, K.; Gao, H.; Matyjaszewski, K. Macromolecules 2007, 40, 1789-1791.