Thermal decomposition of dithioesters and its effect on RAFT polymerization

Thermal decomposition of dithioesters, e.g., cumyl dithiobenzoate (CDB), poly( methyl methacrylate) ( PMMA) end-capped with dithioester, and 2-(ethoxycarbonyl) prop-2-yl dithiobenzoate (EPDB), and the consequent effect on reversible addition-fragmentation chain transfer polymerization were investigated. The former two dithioesters underwent thermal decomposition at 120 degrees C. The thermal decomposition yielded unsaturated compound and dithiobenzoic acid, leading to some loss of living character of the polymerization, such as retarded reaction rate and broadened molecular weight distribution. Nevertheless, thermal decomposition of EPDB, a model compound for PMMA dithioester, does not yield unsaturated product despite the resemblance of the chemical structures. Thermogravimetric analysis shows that PMMA dithioesters are more thermally unstable than the other two.