One-pot synthesis of structure-controlled temperature-responsive polymer gels

Abstract

The simultaneous use of metal Lewis acids and photo-radical generators for dithioesters, which are the common dormant species for cationic and radical polymerization, made it possible to convert a cationic species into a radical upon photoirradiation. In this study, we attempted one-pot synthesis of temperature-responsive polymer gels with controlled network structure by using temperature-responsive telechelic polymers prepared by cationic polymerization in the dark followed by the mechanistic transformation into radical cross-linking reaction under photoirradiation. Specifically, the polymerization of 2-(2-ethoxy)ethoxyethyl vinyl ether (EO2) in the presence of a crosslinking agent (divinyl adipate) was performed at 4 °C in toluene using a vinyl ether-type bifunctional RAFT reagent as initiator, a Lewis acid (Et₃Al₂Cl₃) and a photo radical generator (TPO). The conditions for gelation by radical polymerization with photoirradiation were investigated in detail by considering the molecular weight control and overlapping concentration of the telechelic polymers obtained by cationic polymerization. As a result, small-angle X-ray scattering revealed that polymer gels with a relatively uniform network structure can be obtained compared to the cross-linked network of polymer gels obtained by conventional free-radical polymerization.