Selective Cascade Metathesis Polymerization of Dicycloalkenes and Their Chemical Recycling.

Cascade metathesis polymerization (CMP) offers a powerful route to complex yet precise polymer microstructures. However, achieving both high cascade selectivity and polymerization efficiency remains a significant challenge. Herein, we report our efforts to enhance cascade efficiency (CE) in CMP of various dicycloalkenes and explore their closed-loop chemical recycling. A comprehensive investigation revealed that second-generation Grubbs catalysts (G2 and DIPP-G2) exhibited superior cascade selectivity (CE up to >99%) and polymerization efficiency (turnover numbers up to 3550) compared to first-generation Grubbs catalyst (G1). This is attributed to a preferred intramolecular cascade pathway that suppresses competing ring-opening metathesis polymerization (ROMP). Polymers with high CE showed markedly improved glass transition temperatures (Tg), by up to 47 °C. Remarkably, in-depth studies on sulfonamide-based dicycloalkenes uncovered an unexpected intramolecular cascade transformation, forming new bicyclic monomers, which underwent ROMP and yielded highmolecular-weight polymers (Mn up to 141 kDa). Importantly, these well-defined polymers underwent selective and complete depolymerization into small molecules via reverse CMP or ROMP, which then were repolymerized thereby achieving closed-loop recycling. Computational studies explained how these small molecules were preferentially formed. Overall, this work underscores the potential of our insights (understanding the detailed mechanistic pathways of CMP transformation depending on catalysts and monomer structures) toward sustainable chemical recycling.