Re(V)-Mediated Living Radical Polymerization of Styrene: ReO₂I(PPh₃)₂/R−I Initiating Systems

Abstract

Rhenium(V) iododioxobis(triphenylphosphine) [ReO 2 I(PPh 3 ) 2 ] proved an effective metal catalyst for living radical polymerization of styrene in conjunction with alkyl iodide as an initiator [R−I: CH 3 CH(Ph)I, (CH 3 ) 2 C(CO 2 Et)I, and CH 3 CH(CO 2 Et)I] in the presence of Al(O i -Pr) 3 . Compared to RuCl 2 (PPh 3 ) 3, the group 7 complex was highly effective for styrene, so as to induce the living polymerization even at 30 °C to yield well-controlled polystyrene, with M̄ n up to ∼4 × 10 4 and very narrow molecular weight distributions (MWDs) ( M̄ w / M̄ n = 1.19). The polystyrene thus obtained possessed one initiator moiety (R) at the α-end and one iodine atom at the ω-end, both from the initiator R−I, which indicates that the polymerization proceeds via activation of the C−I terminal, derived from R−I, by the Re(V) complex. Addition of methanol or water did not inhibit these polymerizations, while a stable nitroxide radical (TEMPO) immediately and completely quenched them. The quenching experiments thereby supported intervention of radical species in the Re(V)-mediated living polymerization.