Microwave-assisted RAFT polymerization of N-(2-hydroxypropyl) methacrylamide and its relevant copolymers

摘要

A rapid and eco-friendly reversible addition-fragmentation chain transfer (RAFT) polymerization reaction of the N-(2-hydroxypropyl) methacrylamide (HPMA) monomer under microwave irradiation (MWI) was demonstrated. A systematic investigation to determine the optimal conditions for the polymerization, such as the reaction time, solvents, monomer stoichiometry and RAFT agents, was implemented. The polymerization kinetics were obtained using two different chain transfer agents (CTAs), namely, commercial 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid and synthesized 4-cyano-4-(((ethylthio)carbonothioyl)thio)pentanoic acid, in the presence of 4,4?-azobis(4-cyanovaleric acid) as the initiator in various solvents. The controlled living character of the RAFT polymerization under MWI conditions was demonstrated by the linear increase in the number-average molecular weight (Mn) with monomer conversion. Moreover, good agreement between the theoretical and experimental Mn values was verified with pseudo-first-order kinetic plots, with low dispersities (? ? 1.04) if a favorable solvent and/or CTA was chosen. In addition, the ability of MWI to facilitate copolymer formation was demonstrated by the preparation of relevant copolymers, such as poly(HPMA-b-bocAPMA), poly(HPMA-bMABH) and poly(HPMA-b-PDPA). Altogether, these facile synthetic approaches can find applications for the synthesis of PHPMA-based homo- and copolymers that have already been clinically tested and serve as hydrophilic high-potential alternatives to polyethylene oxide.