4-Halogeno-3,5-dimethyl-1H-pyrazole-1-carbodithioates: versatile reversible addition fragmentation chain transfer agents with broad applicability

Pyrazole-based dithiocarbamates are versatile reversible addition fragmentation chain transfer (RAFT) agents that provide molar mass and dispersity (Đ) control over the radical polymerization of both more and less activated monomers (MAMs and LAMs). In this paper we report on theoretical and experimental findings demonstrating that their activity as RAFT agents can be significantly enhanced by introducing electron-withdrawing substituents to the pyrazole ring. This enhancement is most noticeable in methyl methacrylate polymerization where product molar masses are more accurately predicted by the RAFT agent concentration, and significantly lower Đ values, with respect to those seen with the parent RAFT agent under similar conditions, are observed. Thus, use of 4-chloro-3,5-dimethyl-1H-pyrazole-1-carbodithioate provides a poly(methyl methacrylate) with the anticipated molar mass and Đ as low as 1.3 at high monomer conversion. Good control is retained for monosubstituted MAMs, styrene, methyl acrylate and N,N-dimethylacrylamide. Low dispersities and less molar mass control are also achieved for homo- and copolymerizations with the LAM vinyl acetate, albeit with some retardation.