Oxygen-Tolerant, Red Light-Driven Controlled Synthesis of Easily Degradable and High Molecular Weight α-Lipoic Acid-Vinyl Copolymers.

α-Lipoic acid (LA) has recently emerged as an attractive, inexpensive monomer for synthesizing degradable polymers via ring-opening of its 1,2-dithiolane, introducing easily cleavable disulfide linkages into polymer backbones. Reversible addition-fragmentation chain transfer (RAFT) copolymerization with vinyl monomers enables access to degradable poly(disulfide)s with controlled molecular weights. However, conventional thermal RAFT methods suffer from oxygen sensitivity, limited LA incorporation (<40 mol%), and modest degrees of polymerization (DP < 300). Here, we report an oxygen-tolerant, red-light-driven RAFT approach using methylene blue (MB⁺) as a photosensitizer, and triethanolamine (TEOA) as a sacrificial electron donor. This photoRAFT strategy affords well-defined LA-vinyl copolymers with DPs exceeding 6000, relatively low dispersities (Đ = 1.1-1.6), and LA incorporations up to 68 mol%. The method is compatible with a broad range of functional comonomers, including hydrophilic, charged, and zwitterionic acrylates and acrylamides, yielding water-soluble degradable polymers. The resulting copolymers are readily degradable by disulfide-reducing agents, UV light, and ambient sunlight. Overall, this mild and efficient platform overcomes the limitations of thermal RAFT, providing improved access to functional, high-molecular-weight degradable LA copolymers, suggesting potential applications as biocompatible plastics and biomedical materials.