Degradable Thermoresponsive Polymers Prepared by Photo-Induced Radical Copolymerization of Isopropyl Lipoamide and N , N -Dimethylacrylamide under Blue Light

Abstract

Integrating both degradability and responsiveness remains challenging for developing functional polymer platforms. α-Lipoic acid (LA) has emerged as a versatile monomer for introducing cleavable disulfide linkages into polymer backbones. Here, we report a lipoic acid-derived monomer, N-isopropyl lipoamide (IpLp), for the synthesis of degradable and thermoresponsive vinyl copolymers via blue-light photoiniferter RAFT (PI-RAFT) polymerization under mild, initiator-free conditions. The incorporation of IpLp introduces disulfide linkages that enable composition-dependent degradation behavior in response to reductive, thermal, and photochemical stimuli. Notably, LCST-type thermoresponsive behavior emerges when IpLP is copolymerized with N,N-dimethylacrylamide at a relatively low IpLp incorporation level (i.e., ∼10 mol%), with transition temperatures that can be tuned by both copolymer composition and concentration. In contrast, a composition-matched N-isopropylacrylamide-based control does not exhibit thermoresponsive behavior under identical conditions, highlighting the distinct role of the lipoamide motif in imparting thermoresponsiveness. Copolymerization of IpLp with other hydrophilic monomers affords well-defined polymers with controlled molecular weight. This work demonstrates a monomer design strategy for integrating degradability and thermoresponsiveness into vinyl polymers.