A Versatile Platform to Degradable Polymers via Cascade Metathesis Polymerization of Macrocyclic Enyne Monomers

The development of synthetic methods capable of flexible introduction of diverse degradability into the polymer backbone in a controlled manner could simplify monomer design but remained challenging. Herein, we report a platform approach to access degradable polymers with tunable degradability and a defined backbone architecture using controlled cascade enyne metathesis polymerization of macrocyclic monomers. A small library of 12 enyne monomers with built-in sequences that simultaneously contain a size-tunable sulfonamide polymerization trigger and a degradation site was designed and synthesized in routes that permit divergent incorporation of diverse labile groups (o-nitrobenzyl, coumarin, disulfide, and phosphate) and variations of monomer ring size and sequence. Enhanced control over polymerization could be achieved through modulation of the sulfonamide size and olefin geometry, and this enabled the production of high-molecular-weight polymers with narrow molar mass distributions. The living character of the polymerization was confirmed by the observation of first-order kinetics of a representative monomer as well as block copolymerization with norbornene derivatives to access block-selective degradable copolymers. The resulting polymers underwent backbone degradation upon exposure to appropriate stimuli such as photoirradiation, acid, and reduction. Further statistical copolymerizations with all-carbon bonded monomers enabled facile generation of fully degradable copolymers as well as the ability to tune thermal properties.