Polymerization dithiocarbamate synthesis

Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization using xanthanes and dithiocarbamates is described [266]. Narrow polydispersities and good control of molecular weight for polymers of M < 30 000 are achieved for these polymers. The living nature of RAFT polymerization allows the synthesis of block copolymers, star polymers and gradient copolymers [266]. 

Thiuram disulfides, described above as photoiniferters, can also act as thermal iniferters. The mechanism of the polymerization is the same and polymer chains are invariably end-capped at both ends with iniferter segments. The use of thiurams as thermal or photoiniferters for the preparation of block copolymers greatly depends on the quantum yield of dissociation. The synthesis of dithiocarbamate functional polymers by direct photolysis of the iniferters is limited due to the low quantum yield of dissociation, especially in the case of the thiuram disulfide (e.g., the quantum yield of dissociation (rf) of TD is 0.0025 in cyclohexane [81]). This very low value makes the photochemical dissociation much less attractive than the thermal one. It was suggested that better dithiocarbamate functionalization can be achieved by either thermal initiation with TD at 95°C or polymerization in the presence of AIBN as a thermal initiator and TD as a chain transfer agent. In the latter case, monofunctional or bifunctional TD-PSt were formed, depending on the mole ratio AIBN/TD. Interestingly, the quantum yield of BDC was found to be 0.06, which is 24 times higher than that of TD. Thus, BDC can be used both as a thermal initiator and as a photoiniferter [81]. 

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