Ring-Opening Metathesis Polymerization of a Macrobicyclic Olefin Bearing a Sacrificial Silyloxide Bridge.

Ring-opening metathesis polymerization (ROMP) has been regarded as a powerful tool for sequence-controlled polymerization. However, the traditional entropy-driven ROMP of macrocyclic olefins suffers from the lack of ring strain and poor regioselectivity, whereas the relay-ring-closing metathesis polymerization inevitably brings some unnecessary auxiliary structure into each monomeric unit. We developed a macrobicyclic olefin system bearing a sacrificial silyloxide bridge on the α,β'-positions of the double bond as a new class of sequence-defined monomer for regioselective ROMP. The monomeric sequence information is implanted in the macro-ring, while the small ring, a 3-substituted cyclooctene structure with substantial ring tension, can provide not only narrow polydispersity, but also high regio-/stereospecificity. Besides, the silyloxide bridge can be sacrificially cleaved by desilylation and deoxygenation reactions to provide clean-structured, non-auxiliaried polymers.