Visible-Light-Induced Cationic Polymerization of Isobutylene: A Route toward the Synthesis of End-Functional Polyisobutylene.

The visible-light-induced cationic polymerization of isobutylene with a dimanganese decacarbonyl (Mn 2 (CO) 10 )/diphenyl iodonium hexafluorophosphate (Ph 2 I + PF 6 - ) photoinitiating system in a CH 2 Cl 2 / n -hexane mixture at -30 °C was reported. It was shown that polymerization is initiated by chloromethylisobutyl carbocations generated by the oxidation of chloromethylisobutyl radicals by Ph 2 I + PF 6 - . The latter are formed via chlorine abstraction from solvent (CH 2 Cl 2 ) by MnCO 5 · radicals, which are generated by the photoinduced decomposition of Mn 2 (CO) 10 , followed by single isobutylene addition. This initiating system allowed us to synthesize valuable low molecular weight polyisobutylene with a relatively low polydispersity ( M n = 2000-3000 g mol -1 ; Đ < 1.7) and high content of exo -olefin end groups (up to 90%). The molecular weight of polyisobutylenes could be easily controlled in the range from 2000 to 12000 g mol -1 by changing the diphenyl iodonium salt concentration. Poly(β-pinene) with M n = 5000 g mol -1 and Đ ∼ 2.0 was successfully synthesized using the same photoinitiating system.