Single-End-Functionalized Polycyclopentene via Ring-Opening Metathesis Polymerization with Concurrent Chain Transfer

Macromonomers bearing a functional group exclusively at one end are often synthesized by terminating a living polymerization with a suitable agent, at the cost of one initiator molecule per chain. An attractive alternative is to use chain transfer to install the functional endgroup. Herein, polycyclopentene (PCP) bearing a single styryl endgroup is synthesized by ring-opening metathesis polymerization with a well-defined Mo-based (Schrock) initiator, by employing divinylbenzene as a chain-transfer agent. High regioselectivity of the chain-transfer step, with minimal secondary metathesis of double bonds in the PCP backbone, is confirmed by mass spectral endgroup analysis. A styryl-functional PCP macromonomer copolymerizes effectively with styrene in a free-radical process (styrene reactivity ratio r_S ≈ 1.7), producing a comb copolymer with a polystyrene backbone and PCP "teeth".