C6-ROMP Enabled by Structure-Guided Monomer Design for Chemically Recyclable Polymers.

Cyclohexene, a minimally strained cyclic olefin, presents a long-standing challenge for ring-opening metathesis polymerization (ROMP) due to its inherently low ring strain energy. In this study, we present a rational monomer design framework for cyclohexene-derived monomers that leverages adaptive ring strain modulation via fused five-membered heterocycles-including carbonate, carbamate, acetal, silyl ether, and boronic ester motifs-to enhance polymerizability while enabling closed-loop recycling. Density functional theory (DFT) calculations and experimental thermodynamic analyses reveal how monomer conformation, ethenolysis ring strain energy (ERSE), and substituent effects govern ROMP thermodynamics and ring-closing metathesis depolymerization (RCMD) efficiency. An ERSE threshold of approximately 4.3 kcal/mol is identified as necessary for effective polymerization under mild conditions. Additionally, entropy differences driven by substituent flexibility significantly impact depolymerization temperature and efficiency. The resulting polymers exhibit tunable thermal properties, with glass transition temperatures ranging from -42 to 120°C and efficient depolymerization performance. This study provides practical design principles for the development of sustainable functional polymers with predictable reactivity and recyclability.