Programming Copolymer Microstructure and Selective Degradability via Red-Light Photoinduced Electron/Energy Transfer Reversible Addition–Fragmentation Chain Transfer (PET-RAFT) Polymerization

Abstract

Photocontrolled radical ring-opening polymerization (rROP) offers opportunities for the synthesis of degradable vinyl polymers with controlled architectures. However, thionolactone-based systems have remained incompatible with light-mediated methods due to the intrinsic photoreactivity of the thiocarbonyl group under blue and green light. Here, we demonstrate that red-light-mediated photoinduced electron/energy transfer reversible addition–fragmentation chain transfer (PET-RAFT) polymerization overcomes this long-standing limitation. Our approach enables the first controlled copolymerization of the thionolactone dibenzo[c,e]oxepine-5(7H)-thione (DOT) with acrylamide monomers under ambient conditions. By exploiting the minimal spectral overlap between the DOT chromophore and 635 nm light, we suppress unwanted side reactions while maintaining efficient photopolymerization. The resulting copolymerizations proceed with predictable molar-mass evolution, narrow dispersities (<1.3), and high incorporation of degradable thioester units. Kinetic analyses reveal a distinct reactivity between acrylamide and DOT comonomers, leading to preferential incorporation of DOT and the formation of gradient-like microstructures that dictate subsequent polymer degradation. Importantly, we leverage the spatiotemporal control property of PET-RAFT polymerization to dynamically regulate DOT incorporation through synchronized ON/OFF irradiation cycles and sequential monomer additions. This temporal control allows us to redistribute cleavable units along the polymer backbone, significantly enhancing degradation efficiency. Beyond thionolactone incorporation, this platform is extended to lipoate-based monomers, enabling the construction of more sophisticated degradable architectures and selective degradation pathways in which lipoate-derived units can be degraded without affecting thioester functionalities. Broadly, this work establishes wavelength-selective PET-RAFT as a powerful, general strategy to program polymer degradability through the precise control of copolymer microstructure.