Isomer-driven polymerization, depolymerization, and reconstruction†

We report that differences in ring strain enthalpy between cis and trans isomers of sila-cycloheptene provide a driving force for both polymerization and depolymerization via olefin metathesis. A need for new methods to reintroduce the low-strain isomer into the plastic economy inspired the development of a polymerization based on ring-opening/cross-metathesis step polymerization, which afforded perfect sequence control for an alternating copolymer. The chemical principles are a platform for achieving both efficient polymerization and depolymerization with high mass recovery in functional polymers.