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 (Ph2I+PF6 (-)) photoinitiating system in a CH2Cl2/n-hexane mixture at -30 degrees 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 center dot 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); D < 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(beta-pinene) with M-n = 5000 g mol(-1) and D similar to 2.0 was successfully synthesized using the same photoinitiating system.