Thermoresponse and self-assembly of an ABC star quarterpolymer with O2 and redox dual-responsive Y junctions

Abstract

Multicomponent miktoarm stars with multifunctional Y junctions may provide us with new insights into their physicochemical properties and prospective applications. Considering the unique role of a gas stimulus in smart materials and the promising gradient-type properties induced by combined stimuli, this study aims at the synthesis, thermoresponsive and self-assembly behaviors of an O₂-, redox-, thermo-, and pH-responsive 3-miktoarm star quarterpolymer. A robust method involving controlled polymerization, amine–thiol–ene conjugation and hydrolysis was developed to achieve a poly(N-isopropylacrylamide-co-4-(2-(2,2,2-trifluoroethylcarbamoyl)ethylthio)-2-(acrylamido)-N-(2-hydroxyethyl)butanamide)-arm-poly(ε-caprolactone)-arm-poly(acrylic acid) star. Owing to the changes in amphiphilicity, chemical composition and mutual interactions, a single stimulus or various stimuli combinations could lead to switchable LCSTs and morphological transformations. Upon increasing pH, O₂ treatment and oxidation, the copolymer solution was liable to exhibit enhanced LCST due to the improved hydrophilicity. The star quarterpolymer could self-assemble into multicompartment vesicles (pH 3.0), vesicles (pH 5.9) and small micelle/vesicle mixtures (pH 10) at ambient temperature. Upon thermo, redox and O₂ stimuli, the assemblies formed at different pHs could be further converted into some other morphologies such as compound micelles and nanocapsules with hollow caves. Our research affords a general route to synthesize MMSs with tailored Y junctions, and the combination of the O₂ stimulus with other stimuli may potentially expand the scope of multi-triggered properties and applications of star copolymers.