Photoinduced cationic polymerization of β‐pinene: understanding the origin of chain transfer reaction

Abstract The visible‐light‐induced cationic polymerization of β‐pinene with the Mn 2 (CO) 10 /Ph 2 I + X − (X ≡ PF 6 − , B(C 6 F 5 ) 4 − , BF 4 − , I − , OTf − ) initiating system is reported for the first time. In particular, poly(β‐pinene)s with relatively high molecular weight ( M n ~ 8000 g mol –1 , Đ < 1.8), glass transition temperature ( T g ~ 88 °C) and content of 1,4 units (42–43 mol%) were synthesized using the Mn 2 (CO) 10 /Ph 2 I + PF 6 − and Mn 2 (CO) 10 /Ph 2 I + BF 4 − initiating systems. Varying the composition of diphenyliodonium salt, it was demonstrated that not only the basicity but also the size (ionic radius) of counterion strongly affects the polymer M n . Additionally, the polymer microstructure and the nature of end groups were thoroughly investigated. According to 1 H and heteronuclear single quantum coherence NMR analysis, the cationic polymerization of β‐pinene is accompanied by intensive chain transfer to monomer leading to the formation of four types of terminal groups (conjugated cyclohexadiene, isolated cyclohexadiene, endo ‐olefin and exo ‐olefin groups). The proposed mechanism of chain transfer to the monomer is supported by corresponding density functional theory calculations. Understanding the origin of the chain transfer reaction would facilitate the development of new initiating systems for the preparation of high molecular weight poly(β‐pinene). © 2026 Society of Chemical Industry.