Controlled Radical Polymerization of 4-Vinylimidazole

We report the unprecedented controlled radical polymerization of 4-vinylimidazole (4VIM). Reversible addition–fragmentation chain transfer (RAFT) of 4VIM in glacial acetic acid afforded homopolymers with well-defined molecular weights and narrow polydispersity indices (PDIs). The polymerizations in acetic acid mediated with 4-cyano-4-(ethylsulfanylthiocarbonylsulfanyl)pentanoic acid (CEP) displayed linear pseudo-first-order kinetics and linear molecular weight growth with monomer conversion. Systematic variation of numerous polymerization parameters included solvent composition, initiator concentration, monomer concentration, and the calculated degree of polymerization. Aqueous size exclusion chromatography (SEC) confirmed linear molecular weight growth to number-average molecular weights (Mn) of 65 000 g/mol with low PDIs (<1.20). Subsequent monomer addition confirmed the presence of the trithiocarbonate functionality at the chain ends, which provided further evidence of controlled polymerization conditions. Polymerizations in traditional aqueous RAFT solvents (acidic buffers) failed to achieve controlled molecular weight growth. Effectively controlling 4VIM homopolymerizations enables the design of amphoteric block copolymers for emerging applications including nucleic acid delivery and electroactive membranes.