Processive ring-opening metathesis polymerization of low ring strain cycloalkenes via molecularly confined catalyst

Controlling the reactivity of the propagating chain end in polymerization reactions is crucial for achieving well-defined polymers in both synthetic polymer chemistry and biology. Processive enzymes in nature have evolved substrate-enclosing structures, safeguarding the catalytic center against reentry by the nascent polymer. Here, we present a strategy for processive catalytic polymerization by encapsulating catalysts for ring-opening metathesis polymerization (ROMP) into the sub-surface cages of a metal-organic framework. The sub-surface encapsulation of the catalysts within the framework allowed the nascent polymer to grow out of the framework with minimal impedance and achieve continuous chain growth, while protecting the propagating polymer chain end from the secondary metathesis reaction with the alkenes in the backbone of the nascent polymer. As a result, ultra-high-molecular-weight polymers with low dispersity were generated from the ROMP of low ring strain cycloalkenes such as cis-cyclooctene and cyclopentene. We demonstrate that ultra-high-molecular-weight polymers with degradable backbones and enhanced mechanical and adhesive properties could be readily generated from this approach. Controlling the reactivity of the propagating chain end in polymerization reactions is crucial for achieving well-defined polymers. Here, the authors present a strategy for processive catalytic polymerization by encapsulating catalysts for ring-opening metathesis polymerization into the sub-surface cages of a metal-organic framework.