Processive Catalytic Polymerization 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 chemistry1,2 and biology3. Processive enzymes in nature have evolved substrate-enclosing structures to protect the catalytic center from reaccess by the nascent polymer4. However, substrate enclosure has not been adopted in polymer chemistry for improving catalytic processivity. 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 protects the propagating polymer chain end from the secondary metathesis reaction with the alkenes in the backbone of the nascent polymer, while allowing the nascent polymer to grow out of the framework with little impedance and achieve continuous chain growth. As a result, ultra-high-molecular-weight polymers with low dispersity were generated from the ROMP of low-strain cyclic olefins 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.