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

Abstract

The visible-light-induced cationic polymerization of isobutylene with a dimanganese decacarbonyl (Mn₂(CO)₁₀)/diphenyl iodonium hexafluorophosphate (Ph₂I⁺PF₆^-) photoinitiating system in a CH₂Cl₂/<i>n</i>-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 Ph₂I⁺PF₆^-. The latter are formed via chlorine abstraction from solvent (CH₂Cl₂) by MnCO₅· radicals, which are generated by the photoinduced decomposition of Mn₂(CO)₁₀, followed by single isobutylene addition. This initiating system allowed us to synthesize valuable low molecular weight polyisobutylene with a relatively low polydispersity (<i>M</i>_n = 2000-3000 g mol^-1; <i>Đ</i> < 1.7) and high content of <i>exo</i>-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 <i>M</i>_n = 5000 g mol^-1 and <i>Đ</i> ∼ 2.0 was successfully synthesized using the same photoinitiating system.