Photo-Induced Radical Coupling Reaction of Polychloroprene: Mechanistic Insight into Termination Reaction and Synthetic Applications

Abstract The termination mechanism in the radical polymerization of chloroprene (Cp), a representative conjugated diene monomer, was investigated using structurally well-defined polychloroprene (PCp) end radicals generated by photoactivation of organotellurium dormant species. Product analyses revealed that PCp end radicals terminate almost exclusively by combination (Comb), with >98% selectivity even under highly viscous conditions, in sharp contrast to styrene-derived radicals but similar to isoprene-derived radicals. The results indicate that viscosity-independent Comb termination is a characteristic feature of diene-derived radicals. This mechanistic insight was further exploited for polymer synthesis. The Cp-mediated radical coupling reactions of macro-chain transfer agents prepared via organotellurium-mediated radical polymerization proceeded with high coupling efficiency, affording well-defined coupled polymers bearing approximately two Cp units at the junction. In addition, AB diblock copolymers containing a PCp segment were efficiently converted into symmetric ABA triblock copolymers by photoinduced coupling. These findings provide valuable insights into the molecular design of advanced polymer materials by exploiting Cp as both a polymerizable monomer and an efficient radical coupling agent.