Site Transformation of Polyisobutylene Chain Ends into Functional RAFT Agents for Block Copolymer Synthesis

Block copolymers consisting of polyisobutylene (PLB) and either poly(methyl methacrylate) (PMMA) or polystyrene (PS) block segments were synthesized by a site transformation approach combining living cationic and reversible addition-fragmentation transfer (RAFT) polymerizations. The initial PIB block was synthesized via quasi-living cationic polymerization using the TMPCl/TiCl4 initiation system and Subsequently converted into a hydroxyl-terminated PIB. Site transformation of the hydroxyl-terminated PIB into a macro-chain-transfer agent (PIB-CTA) was accomplished by N,N'-dicyclohexylcarbodiimide/dimethylaminopyridine-catalyzed esterification with 4-cyano-4-(dodecylsulfanylthiocarbonylsulfanyl) pentanoic acid. Structure of the PIB-CTA was confirmed by both H-1 and C-13 NMR spectroscopy. The PIB-CTA was then employed in a RAFT polymerization of either methyl methacrylate or styrene, resulting in PIB block copolymers with narrow polydispersity index and predetermined molecular weights confirmed by both H-1 NMR and GPC.