ATRP of Acrylonitrile
(Matyjaszewski, K.; Jo, S. M.; Paik, H.-j.; Gaynor, S. G. Macromolecules 1997, 30, 6398-6400.
Matyjaszewski, K.; Jo, S. M.; Paik, H.-j.; Shipp, D. A. Macromolecules 1999, 32, 6431-6438.)
Synthesis of Polyacrylonitrile (PAN):
a) 2.28 x 10-2 g (1.60x10-4 mol) of CuBr, 7.49 x 10-2 g (4.80 x 10-4 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 °C. Acrylonitrile (10.0 mL, 1.52 x 10-2 mol) and 1.42 x 10-1 mL (1.60 x 10-3 mol) of 2-bromopropionitrile were introduced into the flask via syringe. The reaction mixture was immersed in an oil bath heated at 44 °C. After 23 hours conversion was 38% and the final polymer Mn,th 2,060 had a Mw/Mn 1.04.
b) Polyacrylonitrile was prepared from a mixture of 10.0 mL (151.9 mmol) acrylonitrile, 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 ºC by the procedures described 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 Samples were periodically withdrawn with a nitrogen-purged syringe, and were diluted with either THF (GC analysis) or DMF (GPC analysis).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 44ºC)
% Conv. (GC)
* 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 °C.
Conversion 41%, Mn 34,700 Mw /Mn = 1.29.
Well-Defined High-Molecular-Weight Polyacrylonitrile via ARGET ATRP:
(Dong, H.; Tang, W.; Matyjaszewski, K. Macromolecules 2007, 40, 2974-2977.)
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 μL, 0.0228 mmol). A solution of CuIICl2 complex (0.153 mg, 1.14 μmol)/TPMA (0.331 mg, 1.14 μmol) in DMF (0.15 mL) was added to the flask. The resulting mixture was degassed by four freeze-pump-thaw cycles. After melting the mixture, a solution of the reducing agent: either Sn(EH)2 (3.69 μL, 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
(Pietrasik, J.; Dong, H.; Matyjaszewski, K. Macromolecules 2006, 39, 6384-6390.)
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 EBriB (8.12 μL, 0.0533 mmol) and a solution of CuCl2 complex (0.223 mg, 1.66 μmol)/Me6TREN (0.38 μL, 1.66 μmol) 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 μL, 0.0278 mmol) and Me6TREN (6.36 μL, 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:EBriB:CuCl2: Me6TREN/Sn(EH) 2 = 2000:1300:1:0.03:0.5:0.5
Conversion 60% after 92 hours providing a copolymer with Mn = 166,200 and a Mw/Mn = 1.26.