Catalytic Alternating Copolymerization to Access Mechanoresponsive Cyclic Olefin Copolymers with On-Demand...

Precise sequence control remains a fundamentally important yet synthetically challenging strategy for tailoring the properties of polymeric materials. Although it offers great potential for accessing functional polyolefins with novel properties, progress toward this goal has been limited. Here we report a catalytic alternating copolymerization protocol between ethylene and bicyclic cyclobutenes, affording cyclic olefin copolymers densely functionalized with bicyclic cyclobutane mechanophores. The spatial distribution of these bicyclic mechanophores along the polymer backbone plays a critical role in determining the copolymer's properties, including strength, toughness, and crystallinity. Notably, transitioning from a random to an alternating copolymer structure leads to marked changes in both stress and strain responses. Meanwhile, near-alternating ethylene/bicyclic cyclobutene copolymers exhibit both high optical performance and desirable toughness. Furthermore, the alternating copolymer can be transformed into an unsaturated polymer via force-induced mechanophore cycloreversion upon bulk ball-milling, enabling upcycling into chemically recyclable polymers.