Direct Controlled Polymerization of a Cationic Methacrylamido Monomer in Aqueous Media Via the RAFT Process

Controlled radical polymerization (CRP) combines the benefits of the robust nature of conventional radical polymerization with the ability to prepare advanced macromolecular architectures common to living polymerization techniques. Of the major CRP techniques, the reversible addition-fragmentation chain transfer (RAFT) technique appears to be the most tolerant of aqueous reaction conditions and a variety of monomer functionalities. To date, however, there have been no reports of the RAFT polymerization of a cationic (meth)acrylamido monomer directly in aqueous media. Herein we report the polymerization of N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) directly in aqueous media utilizing 4-cyanopentanoic acid dithiobenzoate (CTP) as the chain transfer agent (CTA). Polymerization in water at neutral pH allowed a moderate level of control over the polymerization up to 50% conversion. Polymerization in an aqueous buffer (pH = 5), on the other hand, afforded excellent control up to 98% conversion (M-n = 38 000, M-w/M-n = 1.12). Purification of the poly(DMAPMA) macro-CTA under conditions that minimize the exposure of the macro-CTA to an unbuffered aqueous environment was necessary for the retention of functional chain ends. Block copolymers of DMAPMA and N,N-dimethylacrylamide (DMA) or (ar-vinylbenzyl)trimethylammonium chloride (VBTAC) were successfully prepared from a macro-chain-transfer agent (macro-CTA) of poly(DMAPMA)