New Family of Multistimuli-Responsive Acrylamide-Based Homopolymers: Synthesis, Responsive Behavior, and Application in Controlled Release

Abstract

A new family of multistimuli-responsive acrylamide-based homopolymers with different end pendant substituents were prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization. They include three types of multistimuli-response: temperature/pH/CO₂-response, temperature/pH/redox-response, and temperature/pH/light-response. When the terminal substituent was ethyl and tetrahydropyran, P(Et-N-AM) and P(THP-N-AM) exhibited lower critical solution temperature (LCST) behavior in water, which can be adjusted by degree of polymerization (DP) and concentration of polymer, additives, pH, and the injection of CO₂/N₂ to the solution. When the terminal substituents were phenyl, ferrocene, and azobenzene, P(Ph-N-AM), P(Fc-N-AM), and P(Azo-N-AM) were insoluble in water due to the increase of hydrophobicity, but the upper critical solution temperature (UCST) was exhibited in the mixed solution of ⁿBuOH/water and can be adjusted by the addition of acid or base. P(Fc-N-AM) was also redox-responsive, and its UV/vis absorption peaks changed with the addition of FeCl₃/VC. P(Azo-N-AM) was also light-responsive, and under UV/blue light radiation, the characteristic peaks of its UV/vis absorption spectrum changed reversibly. In addition, the three homopolymers were amphiphilic, which can self-assemble in solution, and the obtained micelles were also responsive. Finally, nile red (NR) was used as a hydrophobic drug model, and the controlled release behavior of NR-loaded micelles of P(Fc-N-AM) and P(Azo-N-AM) under different stimuli was investigated. This work has greatly enriched the family of multistimuli-responsive poly(N-substituted acrylamide)s, and the synthetic steps of homopolymers were simple; the responsive behavior was sensitive, and the species were rich. It provides a reference for the design of novel stimuli-responsive polymers and has a good application prospect in self-assembly, drug release, and other fields.