Synthesis and characterization of polystyrene/poly(4-vinylpyridine) triblock copolymers by reversible addition-fragmentation chain transfer polymerization and their self-assembled aggregates in water

Reversible addition-fragmentation chain transfer polymerization (RAFT) was developed for the controlled preparation of polystyrene (PS)/poly(4-vinylpyridine) (P4VP) triblock copolymers. First, PS and P4VP homopolymers were prepared using dibenzyl trithiocarbonate as the chain transfer agent (CTA). Then, PS-b-P4VP-b-PS and P4VP-b-PS-b-P4VP triblock copolymers were synthesized using as macro-CTA the obtained homopolymers PS and P4VP, respectively. The synthesized polymers had relatively narrower molecular weight distributions (M-w/M-n < 1.25), and the polymerization was controlled/living. Furthermore, the polymerization rate appeared to be lower when styrene was polymerized using P4VP as the macro-CTA, compared with polymerizing 4-vinylpyridine using PS as the macro-CTA. This was attributed to the different transfer constants of the P4VP and PS macro-CTAs to the styrene and the 4-vinylpyridine, respectively. The aggregates of the triblock copolymers with different compositions and chain architectures in water also were investigated, and the results are presented. Reducing the P4VP block length and keeping the PS block constant favored the formation of rod aggregates. Moreover, the chain architecture in which the P4VP block was in the middle of the copolymer chain was rather favorable to the rod assembly because of the entropic penalty associated with the looping of the middle-block P4VP to form the aggregate corona and tailing of the end-block PS into the core of the aggregates. (C) 2003 Wiley Periodicals, Inc.