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

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.