Thermal decomposition processes in aromatic polythiocarbonates

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Abstract
The thermal degradation of some polythiocarbonates obtained from bisphenol A bischloroformate and dithiols have been investigated by thermogravimetry and by direct pyrolysis in the mass spectrometer operating both in electron and chemical ionization. Poly(bisphenol A‐co‐tri‐methylenedithiocarbonate) decomposes by an intramolecular exchange process (back‐biting) producing trimethylene‐1,3‐dithiocarbonate and bisphenol A polycarbonate. The latter undergoes further thermal degradation at higher temperature yielding cyclic oligomers. Polymers containing tetramethylene‐1,4‐dithiocarbonate and hexamethylene‐1,6‐dithiocarbonate units decompose by the same mechanism, but the elimination of the dithiocarbonate units is not as fast and selective as the previous case. Some bisphenol A units are eliminated in the first thermal degradation stage and a rearrangement reaction producing ether linkage also occurs. Poly(phenylene‐1,3‐dithiocarbonate) decomposes by CO and COS loss with formation of sulfide and disulfide bridges along the polymer chains, which undergo further thermal degradation by a back‐biting process yielding a series of cyclic compounds. The thermal degradation of Poly(bisphenol A‐co‐phenylenedithiocarbonate) takes place through an interchange reaction producing phenylene‐1,3‐dithiocarbonate sequences which further decompose as the corresponding polymer. The remaining bisphenol A polycarbonate decomposes at higher temperature producing cyclic carbonates.