Methacrylates - Matyjaszewski Polymer Group - Carnegie Mellon University

ATRP of Methacrylates

Methyl Methacrylate

n-Butyl Methacrylate

Glycidyl Methacrylate Copolymers

3-Azidopropyl Methacrylate

Benzyl Methacrylate

Octadecyl Methacrylate

Dimethylaminoethyl Methacrylate

2-Hydroxyethyl Methacrylate

Methoxy-capped Oligo(ethylene oxide) Methacrylate


Methyl Methacrylate

(Grimaud, T.; Matyjaszewski, K. Macromolecules 1997, 30, 2216-2218.)

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 the initiator, and the mixture was degassed three times by freeze-pump-thaw cycles. The mixture was heated at reaction temperature (90 °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 TFH 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,ex 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 a controlled/"living" procedure 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 oC

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 °C.  Result: Mn = 5,200; Mw/Mn = 1.29

[MMA]:[EBiB]:[CuBr]:[Cu Br2]:[PMDETA] = 600:1:0.35:0.15:1 in acetone (50 vol %), 50 °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 °C for 19 hr gave 74.9% conversion and Mn,th = 75,100; with Mn,ex = 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 ml, 18.7´10-2 mmol) in anisole was added, and the mixture was stirred. Sn(EH)2 (27 ml, 8.4´10-2 mmol) and a purged solution of EBriB (27.4 ml, 18.7´10-2 mmol) in anisole were added, and the sealed flask was heated in thermostated oil bath at 90 °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

Conversion = 79%, Mn = 23,000; Mw/Mn = 1.45.

ARGET ATRP of MMA in the Presence of Excess Nitrogen-based Ligand as Reducing Agent

Cu(II)Br2 (111.5 mg, 0.49 mmol) was added to a dried Schlenk flask equipped with a stir bar. After sealing with a rubber septum, the flask was degassed and backfilled with N2 five times and then left under N2. Subsequently, anisole (10.68 mL), MMA (10.00 g, 99.9 mmol), HMTETA (230.0 mg, 0.999 mmol), and EBriB (195.0 mg, 0.999 mmol) were added to a glass vial and degassed by three freeze-pump-thaw cycles. The solution was then transferred to the Schlenk flask, which was placed in a thermostated oil bath at 90 oC. The polymerization was stopped after 25 min reaction by opening the flask and exposing the catalyst to air. The mixture was then passed through a neutral alumina column to remove copper complex. The polymer was precipitated by addition to a large amount of hexane. Dissolution and precipitation was repeated until a white powder was obtained. The precipitated polymer was dried in a vacuum oven at 40 oC until a constant weight was reached and analyzed by GPC (Mn = 3850, Mw/Mn = 1.16).

Chain Extension of PMMA-Br Macroinitiator with MMA

The PMMA macroinitiator (300 mg, 0.078 mmol), HMTETA (71.8 mg, 0.31 mmol), anisole (3.3 mL), and MMA (3.12 g, 31.0 mmol) were mixed in a 10-mL round bottom flask and subjected to three freeze-pump-thaw cycles. This solution was transferred to a Schlenk flask containing degassed Cu(II)Br2 (33.8 mg, 0.155 mmol). The flask was then placed in a thermostated oil bath at 90 oC. The polymerization was stopped after 70 min by opening the flask and exposing the catalyst to air. The polymer was analyzed by GPC (Mn = 27500, Mw/Mn =1.12).

ATRP of Methyl Methacrylate Initiated by Alkyl Dithiocarbamate

(Kwak, Y.; Matyjaszewski, K. Macromolecules 2008, 41, 6627-6635.)

Conditions are similar to those detailed for styrene polymerization.

  1. [MMA]/[MANDC]/[CuBr]/[bpy] = 200/1/1/2, bulk, 100 oC, 10 min: Conv. = 21.5%, Mn =6710; Mw/Mn=1.33.
  2. [MMA]/[MANDC]/[CuBr]/[bpy] = 200/1/1/2, bulk, 100 oC, 20 min:Conv. = 43.3%, Mn =11390; Mw/Mn=1.25.
  3. [MMA]/[MANDC]/[CuBr]/[bpy] = 200/1/1/2, bulk, 100 oC, 40 min: Conv. = 74.9%, Mn =18170; Mw/Mn=1.16.
  4.  [MMA]/[MANDC]/[CuBr]/[bpy] = 1000/1/1/2, bulk, 100 oC, 15 min:Conv. = 22.7%, Mn =25,770; Mw/Mn=1.21.
  5. [MMA]/[MANDC]/[CuBr]/[bpy] = 1000/1/1/2, bulk, 100 oC, 60 min:Conv. = 59.2%, Mn =59,910; Mw/Mn=1.19.


n-Butyl Methacrylate (BMA)

PMDETA is actually not considered to be a good ligand for the controlled polymerization of BMA because BMA is quite a reactive 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 °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.  The 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.  The polymers were then synthesized using HMTETA-based catalysts.

A typical procedure follows:

MMA - 9.6 mL (0.09 mol) or 7.54 mL (0.07 mol)

GMA - 1.3 mL (0.01 mol) or 3.97 mL (0.03 mol)

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 mL (0.0576 g, 0.25 mmol)

EBriB - 73 mL (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.  In order to avoid reaction with the free amine, HMTETA, GMA was added after formation of the catalyst complex followed immediately by the initiator.

The reaction was carried out for 280 min for the reaction with 30 mol % GMA and conversion of MMA = 73 % and of GMA = 89 %; Mn = 20,400 g/mol, Mw/Mn = 1.44) or 290 min with 10 mol % of GMA providing conversion of MMA = 72 % and GMA = 82 %; Mn = 20,200 g/mol, Mw/Mn = 1.24).

The polymers were purified by reprecipitation in ether from THF.

3-Azidopropyl Methacrylate 

(Sumerlin, B. S.;  Tsarevsky, N. V.;  Louche, G.;  Lee, R. Y.; Matyjaszewski, K. Macromolecules 2005, 38, 7540-7545.)

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 then the reaction mixture was heated to 50 °C to dissolve the complex and deoxygenated EBriB (9.5 mL, 0.065 mmol) was injected to start the polymerization.  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 and kill the catalyst complex.  The resulting solution was diluted with chloroform, passed through a neutral alumina column to remove the catalyst, and precipitated by addition to methanol to give poly(3-azidopropyl methacrylate)

Mn = 12,300; Mw/Mn = 1.44. 

In another experiment targeting a lower degree of polymerization at complete conversion (100), the amounts of catalyst and initiator were decreased twofold.

Protected Methacrylic Acids

(Zhang, X.;  Xia, J.; Matyjaszewski, K. Polym. Prepr. 1999, 40, 440-441.)

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 availability and unique mode of deprotection of benzyl group.  Typically, a benzyl group can be deprotected by stirring under H2 with Pd/C at room temperature.  Therefore 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, filter off the Pd/C. 

Benzyl Methacrylate (BzMA)

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 as exemplary ligands since previous kinetic studies indicate that use of these ligands to form the catalyst complex 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 (EBriB, 7.6 ml, 0.052 mmole) was added to initiate the reaction. Samples were taken periodically to follow reaction kinetics.

CuBr/Ligand/EBriB/BnMA = 0.5/0.5/1/113, 90 °C in 50% anisole.

Ligand

Time (h)

Conv. (%)

Mn,th

Mn

PDI

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 resulted in a 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/EBriB/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,ex = 26,700 and Mw/Mn = 1.18.

Othe Examples with BzMA:

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 (EBriB, 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°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 transferred 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. 

Conv. = 88%, Mn = 11,100; Mw/Mn = 1.14.

AGET ATRP ODMA

The AGET ATRP of ODMA was initially 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]:[EBriB]:[CuBr2]:[tNtpy]:[Sn(II)] = 200:1:1:1:0.5

(solvent) xylene at 60 °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 ´ 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

Conversion = 63%, Mn, GPC = 2,800; Mw/Mn = 1.15.

Synthesis of Poly(DMAEMA) Linear MI

[DMAEMA]:[2-bromopropanitrile]:[CuBr]:[HMTETA] = 150:1:1:1 in acetone at 50 °C,

DMF line GPC condition: RI detector, linear polyMMA as standard. Results Mn = 10,000; Mw/Mn = 1.29

[DMAEMA]:[EBriB]:[CuBr]:[CuBr2]:[HMTETA] = 150 : 1 : 0.7 : 0.3 : 1

Solvent was 50% (v) acetone, at 50° C, with diphenylether as GC standard. After 4 hour conversion was 50% providing Mn 7,700 and Mw/Mn = 1.24.

DMAEMA: Affect of Temperature on Reaction

(Zhang, X.;  Xia, J.; Matyjaszewski, K. Macromolecules 1998, 31, 5167-5169. )

[CuBr]0 = [HMTETA] 0 = [EBriB] 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 μL, 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 °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

ARGET ATRP of DMAEMA with Monomer as Internal Reducing Agent, Reaction Conducted Under Nitrogen  

(Dong, H.; Matyjaszewski, K. Macromolecules 2008, 41, 6868-6870.)

A dry 10 mL Schlenk flask was charged with DMAEMA (3.0 mL, 17.8 mmol), anisole (1.0 mL) and ethyl 2-bromoisobutyrate (5.2 μL, 0.036 mmol). The resulting mixture was degassed by four freeze-pump-thaw cycles. After melting the mixture, a bubbled solution of CuCl2 (0.24 mg, 0.0018 mmol) and TPMA ligand (2.6 mg, 0.009 mmol) in anisole (0.5 mL) was slowly added to the reaction medium. The sealed flask was placed in an oil bath thermostated at 30 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 after 63.3 h by opening the flask and exposing the catalyst to air. Conversion was 44.3% with Mn theo = 34,820 and Mn GPC = 29,340 with PDI = 1.20.

ARGET ATRP of DMAEMA with Monomer as Internal Reducing Agent in the Presence of Air

(Dong, H.; Matyjaszewski, K. Macromolecules 2008, 41, 6868-6870.)

A 22 mL glass vial containing a stir bar was charged with DMAEMA (12.0 mL, 71.2 mmol), anisole (5.6 mL), and ethyl 2-bromoisobutyrate (20.9 μL, 0.142 mmol). Then a solution of CuCl2 (0.95 mg, 0.0071 mmol) and TPMA ligand (10.3 mg, 0.036 mmol) in anisole (0.4 mL) was added. After sealing the vial with a rubber septum, the vial was placed in an oil bath thermostated at 30 oC. Samples were taken at timed intervals and analyzed by 1H-NMR and GPC to follow the progress of the reaction. The polymerization was stopped after 64.7 h by opening the flask and exposing the catalyst to air. Conversion was 76.9% with Mn theo = 60,450 and Mn GPC = 42,650 with PDI = 1.32


2-Hydroxyethyl Methacrylate (HEMA)

(Beers, K. L.;  Boo, S.;  Gaynor, S. G.; Matyjaszewski, K. Macromolecules 1999, 32, 5772-5776.)

Purification of Monomer:  The first procedure involved washing an aqueous solution (25 vol % HEMA) of monomer with hexanes (4 ´ 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 μL; 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: 

The solvent selected for this polymerization was 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. EBriB was used as the ATRP initiator. The standard experimental condition was the initial molar ratio of [HEMA]0/[EBriB]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 thretically 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 ºC. 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 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).

Optimum Conditions for Preparation of the Backbone for a Linear Brush Copolymer

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] : [EBriB] : [CuCl] : [CuCl2] : [dNbpy] = 1400 : 1 : 2 : 0.2 : 4.4, with 10 vol% anisole, T = 90 °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) under a set of 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 (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 Methoxy-capped Oligo(ethylene oxide) Methacrylate (OEOMA)

This experiment began with the synthesis of a 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 was 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 mol % 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 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 had occurred. From the ratio of the area of P(PEOMA1100) to total area, one can calculate that conversion reached 95% in 10 min. However, there was some unreacted macroinitiators, probably PEO5000-OH, left in the reaction medium. 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,th                Mn,ex            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,ex = 61,500 and Mw/Mn = 1.21.