Degradable Alternating Copolymers With Strained Cyclobutane Backbones via Photocontrolled RAFT Polymerization

In this study, we report a reversible addition‐fragmentation chain transfer (RAFT) alternating copolymerization of 1,3‐disubstituted bicyclo[1.1.0]butanes (BCBs) with maleimides, maleic anhydride, or bio‐based fumarate derivatives, affording a class of well‐defined copolymers with strained cyclobutane backbones. Under visible‐light irradiation, a chain transfer agent (CTA)‐mediated photoiniferter process delivers BCB‐derived copolymers with a high degree of alternation, tunable molecular weights, and excellent end‐group fidelity. Our design leverages electronically and sterically tuned BCB monomers bearing an aryl substituent at one bridgehead and an electron‐withdrawing group at the other, facilitating precise control over radical reactivity and selective cross‐propagation. The resulting polymers exhibit high thermal stability with decomposition temperature up to 429°C, yet undergo highly efficient degradation under mechanical stimulation.