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

Abstract

Pyrazole-based dithiocarbamates are versatile reversible addition fragmentation chain transfer (RAFT) agents that provide molar mass and dispersity (Ð) 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 Ð 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 Ð 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 homoand copolymerizations with the LAM vinyl acetate, albeit with some retardation.

Aromatic Xanthates and Dithiocarbamates for the Polymerization of Ethylene through Reversible Addition–Fragmentation Chain Transfer (RAFT)

“…Forschungsartikel methylpyrazolyl shows by far the lowest tendency to undergo fragmentation of all the CTAs used in the present work. [26,35] As ar esult, systems with 9 produced PE only for rather low CTAa nd high AIBN concentrations ([CTA]/[AIBN] = 0.5:1 and 100 mg of AIBN compared to the normal conditions of [CTA]/[AIBN] = 3:1a nd 50 mg of AIBN). Molar mass and NMR data indicated no participation of 9 in an RDRP process under these conditions and it will therefore not be further discussed.…”

Manganese phosphinocarbodithioate for RAFT polymerisation with sunlight-induced chain end post-treatment

“…Recently, the CSIRO group designed dithiocarbamate RAFT agents comprising 3,5-dimethylpyrazole Z groups which allowed the synthesis of low Ð PDMA-b-PVAc copolymers without a need to switch the CTA reactivity, 13 but led to poor control for MMA. The introduction of a chlorine or a bromine atom at the 4-position on the pyrazole ring 14 slightly improved the control of MMA polymerisation, but significantly retarded the polymerisation of vinyl acetate (VAc) with limited conversions. More conventional RAFT agents of intermediate reactivity, e.g.…”

Tailoring Polymer Dispersity by Controlled Radical Polymerization: A Versatile Approach

“…2a and Supplementary Table 2, Entry 1). When the even lower transfer activity 2-cyanobutan-2-yl 4-chloro-3,5-dimethyl-1H-pyrazole-1-carbodithioate (CTA 3) was used, 49 PMMA with monomodal MWDs and a Ɖ of 1.65 could be obtained (Supplementary 5 and Supplementary Table 4), respectively, following a trend as shown in Supplementary Fig. 6.…”