Commercial5‑Vinyl-2-Norbornene as a ReversibleDeactivation Chain-Transfer Monomer in Ring-Opening Metathesis Polymerizationto Produce Branched Copolymers

The use of reversible deactivation chain-transfer monomers (RDCTMs) in homopolymerization and copolymerization is a key strategy for creating branched polymers with well-controlled chain structures. We herein report the use of cost-effective 5-vinyl-2-norbornene (VNB) as an effective RDCTM in ring-opening metathesis polymerization (ROMP). Detailed analysis revealed that the terminal alkene of VNB predominantly undergoes α-addition throughout the cross-metathesis process, thus enabling facile quasiliving polymerization to produce branched block copolymers. More importantly, by tuning the reactivity ratios during copolymerization and incorporating fluorescent comonomers, the change in branch distribution was clearly observed by stimulated emission depletion microscopy from a molecular level.