Thermoresponsive oligo(ethylene glycol) methyl ether methacrylate homopolymers via RAFT polymerization in 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids

Abstract

Responsive polymer-based materials vary their physicochemical properties upon external stimuli. In the past decades, these materials have been utilized in diverse applications such as drug delivery, tissue engineering, biosensors, and surface coatings. In these applications, stimuli-responsive polymers with narrow dispersity are ideal to ensure good sensitivity. RAFT polymerization remains one of the living polymerization techniques that affords great control over polymer size and dispersity. Herein, we investigated how the solvent size, RAFT agent choice, and monomer size affect the RAFT polymerization of thermoresponsive OEGMEMA in hexafluorophosphate-based RTILs. Gel permeation chromatography (GPC) results showed that increased RTIL chain length resulted in an increased polymerization rate, polymer size and dispersity. The RAFT agent CPDB provided better control over the polymerization kinetics. Moreover, GPC data revealed an inverse relationship between the monomer size and the dispersity of its polymer. Monomer size also restricted polymer growth with decreasing rate through time. Among the homopolymers, P(DEGMEMA) synthesized in [HMIM]PF6 and CPBD exhibited the highest percent conversion, fastest reaction rate, and relatively high size uniformity. Our findings demonstrate that a thermoresponsive P(DEGMEMA) can be rapidly obtained in high molecular weights and conversion in RTILs.