Reversible Addition Fragmentation Chain Transfer Polymerization of Methyl Methacrylate in the Presence of Lewis Acids: An Approach to Stereocontrolled Living Radical Polymerization

Abstract

Reversible addition fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) can be carried out in the presence of cyanoisopropyl methyl trithiocarbonate [CH3SC(S)SC(CH3)2CN] and scandium triflate [Sc(OTf)3] to provide simultaneous RAFT-controlled (reversible addition-fragmentation chain transfer controlled) molecular weight and molecular weight distribution (Mw/Mn 95% conversion), Lewis acid-controlled tacticity (mm:mr:rr = 12:44:44 for a mole ratio Sc(OTf)3/MMA = 1:8.5 at 60 °C) and an enhanced rate of polymerization. The tacticities observed for poly(methyl methacrylate) (PMMA) are similar to those observed with scandium triflate in the absence of the RAFT agent. The stability of dithiobenzoate RAFT agents [ZC(S)SR] in the presence of scandium triflate is strongly dependent on both the Z and R substituent. 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate [PhC(S)SC(CH3)2CO2CH3] and the polymeric RAFT agent [PhC(S)S−(CH3)(CO2CH3)CH2−PMMA] appear relatively stable. However, cu...