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.