Synthesis of Poly(vinyl acetate)-b-polystyrene and Poly(vinyl alcohol)-b-polystyrene Copolymers by a Combination of Cobalt-Mediated Radical Polymerization and RAFT Polymerization

摘要

Well-defined poly(vinyl acetate)-block-polystyrene (PVAc-b-PSt) block copolymers were successfully synthesized by a combination of cobalt-mediated radical polymerization (CMRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. PVAc and PVAc-b-PSt (with ail average PSt repeating unit of 2 or 6) were first synthesized via CM RP with cobalt(II) acetylacetonate as a regulating agent. ne cobalt complexes attached to their to chain ends were modified into a phenyl dithioester group by reacting with bis(thiobenzoyl) disulfide, producing PVAc and PVAc-b-PSt macro-chain-transfer agents (PVAc-CTA and PVAc-PSt-CTA), respectively. The RAFT polymerization of styrene with PVAc-CTA or PVAc-PSt-CTA was conducted in N,N-dimethylformamide at 80 degrees C. PVAc-b-PSt block copolymers synthesized with PVAc-PSt6-CTA (with an average PSt repeating unit of 6) exhibited narrowest molecular weight distributions (M-w/M-n = 1.28-1.30) even at high conversions. The PVAc-b-PSt block copolymer (M-n(GPC) = 21000 g/mol, M-w/M-n = 1.28) was hydrolyzed to amphiphilic poly(vinyl alcohol)-block-PSt (PVA-b-PSt) block copolymer under basic conditions. The PVA-b-PSt micelles were spherical in shape with in average diameter of 44 +/- 18 nm.