Acid-Labile Temperature-Responsive Homopolymers and a Diblock Copolymer Bearing the Pendent Acetal Group

A novel acid-labile temperature-responsive homopolymer of poly(2-(2-(2-(2-((tetrahydrofuran-2-yl)oxy)ethoxy)ethoxy)ethoxy) ethyl methacrylate) (PTFEO4MA) combining the oligo ethylene glycol (OEG) moiety and acetal group was prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization. PTFEO4MA exhibited a lower critical solution temperature (LCST) of 32 °C in aqueous solution and a tunable upper critical solution temperature (UCST) in different alcohol solvents. Its LCST was firmly correlative with the length of the OEG moiety and the carbon number in the acetal group; the parameters affecting thermoresponsive phase transition of PTFEO4MA including the polymerization degree, polymer concentration, different sodium salts, urea, and solvents were also studied. The phase transition mechanism of PTFEO4MA was explained by the temperature-variable 1H NMR analysis. Furthermore, PTFEO4MA is neutral but sensitive to acids; by adjusting the pH of the solution, it was found that its LCST disappeared under acidic conditions, while it remained unchanged under alkaline conditions. Finally, a diblock copolymer of poly(methoxy tetraethylene glycol methacrylate-block-2-(2-(2-(2-((tetrahydrofuran-2-yl)oxy)ethoxy)ethoxy)ethoxy) ethyl methacrylate) (PMEO4MA-b-PTFEO4MA) was prepared, and its temperature-/acid-induced phase transition and micellization behavior were investigated. The synthesized acid-labile temperature-responsive homopolymers and copolymer not only provide new ideas for the design of multistimuli-responsive polymers but also have potential applications in biomedicine and self-assembly due to their unique properties.