Oxidation-responsive polymer vesicles with order–disorder–order multiple-phase transitions

Abstract

Reaction-induced phase transition (RIPT) is an emerging strategy that allows the self-assembly of polymers and the regulation of nanoparticle morphology by in situ chemical reactions. Despite the great potential, the driving force for RIPT is to a great extent limited to the change in amphiphilicity. In this manuscript, we report the order–disorder–order multiple-phase transitions that are driven by the change in amphiphilicity and sulfone bonding. Oxidation-responsive vesicles were first prepared via RAFT-mediated dispersion polymerization-induced self-assembly (PISA) of poly(ethylene glycol)-b-poly(4-vinylbenzyl methyl sulfide) (PEG-b-PVBMS) in ethanol/water (85/15, wt/wt). The oxidation-induced order–disorder–order phase transitions of the vesicles were carefully investigated in terms of the oxidation-induced changes in the polymer structure, amphiphilicity, chain mobility, and morphology of the assemblies. During the oxidation, the PEG-b-PVBMS copolymer undergoes a thioether-to-sulfoxide-to-sulfone conversion in structure. Consequently, the amphiphilic PEG-b-PVBMS gradually converts to hydrophilic poly(ethylene glycol)-b-poly(4-vinylbenzyl methyl sulfoxide) (PEG-b-PVBMSx), which eventually leads to the order–disorder phase transition when the thioether groups completely convert into sulfoxides. Although the further oxidation of the sulfoxide to sulfone does not change the hydrophilic nature of the copolymer, the strong sulfone bonding in the poly(4-vinylbenzyl methyl sulfone) (PVBMSf) block drives the re-assembly of the copolymers. Our results indicate that sulfone bonding could be used as the driving force for RIPT, and provide a new paradigm for endowing polymer vesicles with oxidation-responsive multiple-phase transitions.