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.
The monomer, 2,2,2-trifluoroethyl 3-(N-(2-(diethylamino)ethyl)acrylamido)propanoate (TF-DEAE-AM), which contains both O2 and CO2-responsive functionalities, was first synthesized from commercially available N,N-diethylethylenediamine, 2,2,2-trifluoroethyl acrylate, and acryloyl chloride. Subsequently, a series of dual-gas responsive polymers, poly(2,2,2-trifluoroethyl 3-(N-(2-(diethylamino)ethyl)acrylamido)propanoate) (poly(TF-DEAE-AM)) and poly(ethylene glycol)-b-poly(2,2,2-trifluoroethyl 3-(N-(2-(diethylamino)ethyl)acrylamido)propanoate) (PEG-b-poly(TF-DEAE-AM)), were synthesized by employing reversible addition–fragmentation chain transfer (RAFT) polymerization. Due to the protonation between CO2 and DEAE groups, and the specific van der Waals interactions between O2 and C–F bonds, micelles consisting of poly(TF-DEAE-AM) or PEG-b-poly(TF-DEAE-AM) display distinct CO2 and O2 responsiveness in aqueous media. Pyrene, which is a model hydrophobic drug, is able to be effectively encapsulated in the micelles based on PEG-b-poly(TF-DEAE-AM). It is found that the release of pyrene sharply increases after bubbling CO2 or O2 compared to N2, and the release rate of the solution bubbling with CO2 is the fastest. Since both CO2 and O2 are key gases for the human body, the CO2- and O2-induced release property of poly(TF-DEAE-AM) may open opportunities for the preparation of functional materials with special CO2 and O2 responsiveness for potential applications in biomedicine.
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