Synthesis and characterization of 4-vinylimidazole ABA triblock copolymers utilizing a difunctional RAFT chain transfer agent

Abstract

Reversible addition–fragmentation chain transfer (RAFT) polymerization strategies enabled the unprecedented synthesis of 4-vinylimidazole (4VIM)-containing ABA triblock copolymers in glacial acetic acid. The synthesis of a novel, difunctional trithiocarbonate RAFT chain transfer agent (CTA) controlled the divergent RAFT polymerization of methacrylic and 4VIM monomers with controlled molecular weights and narrow polydispersity indices (PDIs). The triblock copolymers consisted of a low-Tg di(ethylene glycol) methyl ether methacrylate (DEGMEMA) center block (Mn = 26 000 g mol−1) and an amphoteric 4VIM external, mechanically reinforcing block (Mn = 6500–16 500 g mol−1). Varying the 4VIM content probed the influence of the triblock copolymer composition on the macromolecular thermomechanical and morphological properties. Dynamic mechanical analysis (DMA) of the triblock copolymers exhibited a rubbery plateau region over a wide temperature range (∼200 °C), which confirmed the establishment of microphase-separated morphologies with flow temperatures above 200 °C. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS) collectively probed the solid state morphologies of the triblock copolymers; all techniques revealed phase separation at nanoscale dimensions. The triblock copolymers with 40 wt% 4VIM formed lamellar morphologies. Well-defined, amphoteric, 4VIM ABA triblock copolymers (PDIs < 1.10) with microphase-separated morphologies now permit imidazole-containing macromolecules of controlled architectures for emerging applications.