Poly(p‐phenylene sulfide), a poly(arylene sulfone), and a poly(arylene sulfonate) were subjected to thermal degradation in vacuo, at temperatures between 250 and 620°C. The volatile and solid degradation products were analyzed by mass spectroscopy, infrared spectroscopy, and elemental analysis. The major decomposition product of poly‐(phenylene sulfide) is a condensate, which consists of di‐ and trimeric chain fragments, dibenzothiophene, and possibly thianthrene. The residual polymer loses two thirds of its sulfur as hydrogen sulfide, however, one third is retained even at 620°C. The most characteristic decomposition reaction of the polysulfone and of the polysulfonate is the almost complete removal of the sulfur as sulfur dioxide. The elimination of sulfur dioxide is practically complete at 450°C for the polysulfone and at 350°C for the polysulfonate.

The breakdown mechanism of an aromatic polyamide and four polyimides has been studied under vacuum in the temperature range of 375–620°C, by using techniques described earlier, involving collection and analysis of volatile products as well as analyses of residues at different temperatures. The decomposition of the polyamide up to 375°C yielded predominantly carbon dioxide, while between 375 and 450°C about equal amounts of carbon dioxide and carbon monoxide formed. Hydrogen is the major product between 450 and 550°C, along with hydrogen cyanide, methane, and carbon monoxide. The major reaction at the lower temperatures seems to be the cleavage of the linkage between the carbonyl group and the ring, with subsequent formation of a carbodiimide linkage via isocyanate intermediates, and liberation of carbon dioxide. Alternatively, cleavage between the carboxyl and the NH‐group leads to the formation of carbon monoxide. Carbon dioxide and carbon monoxide are also the major volatile decomposition products of the polyimides at the lower temperatures. The primary cleavage reaction is believed to be the rupture of the imide ring between a carbonyl and nitrogen, with subsequent formation of isocyanate groups. The latter react with each other to form carbodiimide linkages and carbon dioxide, while the remaining benzoyl radical is the source for carbon monoxide.

The thermal degradation of polyphenylenes and poly(phenylene oxides) was studied under vacuum at temperatures between 350 and 620°C. The volatile and solid degradation products were analyzed by mass spectroscopy, infrared spectroscopy, and elemental analysis. Overall mechanisms for the thermal breakdown have been proposed. Polyphenylene decomposes to form polymer carbon, while hydrogen is the major volatile product. Some ring breakdown occurs with evolution of methane. Poly(phenylene oxide) forms mainly low molecular weight chain fragments, partially with hydroxyl endgroups. Some of the ether linkages decompose with ring breakdown, yielding carbon monoxide, water, and some carbon dioxide. Pendent groups on polyphenylenes and poly(phenylene oxides) are removed at the lower temperatures. The hydroxyl group yields essentially carbon monoxide and dioxide (the carbon being supplied by the rings), the methyl group methane, and the methoxy group methane and some methanol.

Polybenzoxazoles, when heated up to 660°C in vacuum, lose most of their oxygen as carbon monoxide and carbon dioxide and possibly form Schiff base‐type structures. The carbon required for the formation of carbon monoxide is predominantly supplied by the benzene rings. About one out of every six CN linkages is eliminated as hydrogen cyanide, and some free nitrogen from this group is reduced to ammonia. The elimination of about 1 hydrogen atom per polymer unit (in the form of free hydrogen, hydrogen cyanide, ammonia, and methane) results in free radical formation and crosslinking. Carbon monoxide and carbon dioxide are also some of the major decomposition products of the benzoxazole in poly‐2,2′‐(1,8‐perfluorooctane)‐6,6′‐bibenzoxazole. In addition, fluorine from the perfluoroalkyl chain combines with ring hydrogen to form hydrogen fluoride, which in turn attacks the quartz of the crucible and reaction vessel to form silicon tetrafluoride. A polybenzothiazole, on heating to 625°C, crosslinks with elimination of some hydrogen. One out of every ten sulfur atoms is removed, essentially as hydrogen sulfide, leaving a Schiff‐base linkage; very few of the CN‐groups are eliminated as hydrogen cyanide. Two less stable polybenzothiazole systems, heated to 660 and 670°C, lose about 50% of their sulfur, mainly as hydrogen sulfide, and 20% of their nitrogen as hydrogen cyanide. Flash pyrolysis of model benzoxazoles and benzothiazoles was tried as a means to provide supporting data.

The thermal decomposition of three aromatic polyesters was studied in vacuo. The degradation products were analyzed by mass spectroscopy, infrared spectroscopy, and elemental analysis. Breakdown mechanisms are proposed. Primary cleavage of the ester linkages appears to take place either between the carbonyl and the oxygen or between the oxygen and the ring, yielding carbon monoxide and carbon dioxide in varying ratios. Another major decomposition product is a sublimate which seems to consist mainly of the phenolic component of the polyester. A polyester with a 2,2‐propylene linkage showed, as expected, early loss of methane. A pendent pentyloxy chain in one of the polymers is removed almost completely below 350°C with formation of alkanes and alkenes. Lack of oxygen in the fragments indicates that the main cleavage must occur between the ether oxygen and the aliphatic chain or with in the aliphatic chain.