Cumyl phenyldithioacetate and 1-phenylethyl phenyldithioacetate: Versatile ambient-temperature RAFT agents

Abstract

Agents for the reversible addition fragmentation chain transfer (RAFT) polymerization were invented by CSIRO a few years ago [ 1 , 2 ] and have since been proven to be very well suited for controlling both the molecular-weight outcomes and the polydispersity of free-radical polymerization processes. The RAFT process is governed by the RAFT equilibrium depicted below in Scheme 1. Some reported RAFT agents, however, are not suitable for polymerizations of styrene and methyl acrylate (MA) at low reaction temperatures (e.g. 25°C) due to high retardation of the polymerization process. This retardation is most likely associated with significant stabilization of the intermediate RAFT radical (species (1)). If the stabilization of the macroRAFT radical is reduced by substitution of the Z-group with a less stabilizing moiety, the RAFT agents become suitable for ambient-temperature polymerizations. Cumyl phenyldithioacetate (CPDA) and 1-phenylethyl phenyldithioacetate (1-PEPDA) have recently been added to the existing library of available RAFT agents [ 3 , 4 ] and are, due to the relatively poor radical stabilizing ability of the CH 2 Ph group, well suited for controlling styrene (CPDA and 1-PEPDA) and MA (1-PEPDA) polymerizations at ambient temperature. The synthesis of both compounds proceeds by a Grignard reaction of benzyl chloride with carbon disulfide and subsequent reaction of the resulting phenyldithioacetic acid with styrene (to give 1-PEPDA) [ 3 ] or α-methylstyrene (to give CPDA). [ 4 ] formula phys. Z-group Z-group.