Facile prepared bis(carbazyl thiocarbonyl) disulfide as chain transfer agent for RAFT polymerization of methyl methacrylate

摘要

The bis(thiocarbonyl) disulfide compounds are key intermediates for the preparation of the high-performance reversible addition-fragmentation chain transfer (RAFT) agents with 2-cyanoprop-2-yl or its homologous group as R group. In this article, a synthetic method in water was developed to prepare high-purity bis(carbazyl thiocarbonyl) disulfide (BCTD) based on a straightforward oxidation reaction using K _3[Fe(CN) _6] as the oxidant. This method was proved to be a convenient, economical, and eco-friendly route to synthesize bis(thiocarbonyl) disulfides with high purity and high yield. Subsequently, the RAFT polymerizations of methyl methacrylate (MMA) have been studied by using BCTD and azobis(isobutyronitrile) (AIBN) to in situ generate RAFT agent 2-cyanoprop-2-yl N-carbazylcarbodithioate (CYCBD). After a very short initial nonliving phase, the polymerization exhibited typical living polymerization characteristics, including that the molecular weights of PMMA linearly increase with monomer conversions and PDI can remain in a relatively low range. The results further indicated that the ratio of BCTD to AIBN and the reaction temperature had a significant impact on the MMA polymerization, and the living features were most prominent when the ratio of BCTD to AIBN is in the range of 1-2 and polymerization temperature at 60°C. In addition, ~1H-NMR analysis and fluorescence spectroscopy of the resultant polymethyl methacrylate (PMMA) confirm the formation of carbazole end-labeled PMMA chains due to CYCBD generated in situ by the reaction of BCTD with AIBN. This can offer an alternative and complementary route to obtain well-defined polymers, especially for preparation of polymers with high molecular weight and a relatively low polydispersity.