Harnessing the β-Silicon Effect for Radical Cyclopolymerization: Direct Access to Si-Containing Cyclic Olefin Polymers.

Cyclic olefin polymers (COPs) are important functional materials with extensively studied properties and syntheses. By contrast, silicon-containing cyclic olefin polymers (Si-COPs)-promising alternatives to conventional COPs-remain largely unexplored. Herein, we report a radical cyclopolymerization strategy enabled by the β‑silicon effect for the efficient synthesis of Si-COPs. Harnessing the β-silicon effect to stabilize radical intermediates suppresses the inherent chain transfer tendency of non-conjugated diene monomers in radical cyclopolymerization and enables the control of the cyclization selectivity. Density functional theory (DFT) calculations provide mechanistic insight into the polymerization pathway. The resulting Si-COPs serve as versatile platforms for post-polymerization modification and undergo controlled degradation under mild conditions. Furthermore, cross-linked Si-COPs fabricated via thiol-ene chemistry exhibit optical properties comparable to those of commercial COPs, together with outstanding adhesion performance.