The potential of Cu(I)Cl/2,2 '-bipyridine catalysis in a triblock copolymer preparation by atom transfer radical polymerization

The ability of atom transfer radical polymerization (ATRP) in the sequentia l synthesis of triblock copolymers was examined using Cu(I)Cl/2,2 ' -bipyri dine catalysis at 110 degreesC in toluene, starting from PMMA macroinitiato rs terminated with the C-Br group. The PMMAs were prepared by living anioni c or group transfer polymerization (GTP), followed by bromination of the re spective active site with Br, or N-bromosuccinimide (NBS). The yield of the terminal bromination in the products of both living polymerizations was 60 -64% at best, compared with the yield of the bromination of 1-methoxy-(1-tr imethylsilyloxy)prop-1-ene (a model of the GTP active site) with NBS, as fo und by H-1-NMR. The PMMA macroinitiators prepared were utilized to start th e sequential ATRP, finally affording PMMA-b-PBuA-b-PSt (M-n 69,100), PMMA-6 -PStb-PBuA (M-n 21,300) and PMMA-b-PSt-b-PMMA (M-n 35,200), which have not yet been synthesized by ATRP. After the second block has been formed, the B r-unterminated part of PMMA macroinitiator was removed by extraction or rep eated precipitation. In the third (last) sequence polymerization, induction periods were observed. The first two triblock copolymers were free of prec ursors and have M-w/M-n values 1.5-1.6 (SEC). In the course of the last ste p of PMMA-b-PSt-b-PMMA synthesis, the content of the PMMA-b-PSt precursor s lowly decreased with increasing MMA conversion. Still, at approximate to 90 % MMA conversion, about 10-15% of the precursor remained in the product. (C ) 2001 John Wiley & Sons, Inc.