A Versatile Reversible, Degenerative Chain Transfer Mechanism for the Catalytic Living Ring‐Opening Metathesis Polymerization

Most metathesis polymers based on norbornene derivatives carry a vinyl end group. Here we show that these vinyl end groups readily undergo a degenerative exchange of the terminal methylene unit in the presence of sub‐stoichiometric amounts of a propagating metathesis polymer carrying a Grubbs ruthenium complex. We show that this degenerative exchange can be exploited in synthesizing ROMP polymers in a catalytic living fashion. Chain transfer agents based on styrene, or monosubstituted conjugated 1,3 diene derivatives are used as initiating sites for the catalytic living polymerization. Suitable derivatives of these chain transfer agents not only allow the linear living growth of polymers but also the synthesis of block copolymers from macro‐initiators or star polymers from multi‐functional chain transfer agents. This reversible exchange mechanism offers a cheaper, greener, and more sustainable alternative for the synthesis of living ROMP polymers compared to the classical synthetic route.