Polymers, phenylated aromatic decomposition

A number of studies were done to assess thermal stability of aromatic polyesters. Some of these studies describe flash pyrolysis [27-32]. Some studies are dedicated to slow thermal degradation in an inert atmosphere, and others describe the decomposition in specific conditions such as in the presence of humidity or in the presence of catalysts [33]. For example, thermal decomposition of poly(butylene terephthalate) was significantly influenced by the presence of water vapor, and the amount of the residues decrease with increasing the partial pressure of water in the atmosphere [34]. In another study, thermal stability of some small molecule phthalate esters was studied [35]. The results can be used for inferring information on the thermal stability of related polymers. The influence of substitution on the p-carbon atom was evaluated on compounds such as bis(2-aminobutyl) phthalate, bis(2-nitrobutyl) phthalate, bis(2,4-diphenylbutyl) phthalate, and dineopentyl phthalate. Only the phenyl groups were found to improve the heat resistance by the obstruction of the planar configuration necessary for the c/s-elimination and the hindrance of the formation of a six-membered cyclic transition state. 

Goyal and co-workers [10] in their Fourier-transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) investigation of the thermal stability of N-phenyl substituted aromatic-aliphatic and of aromatic amides derived from 4,4-dianilodiphenyl showed that the aromatic-aliphatic polyamides had glass transition temperatures in the range 76-116 °C, whilst the aromatic polyamides had transition temperatures of 207-255 °C. The polymers were thermally stable, and had decomposition temperatures in excess of 400 °C in air. 

All investigations on the mechanism of the thermo-oxidative degradation of PETP presuppose [3] that this process has a radical-chain character that proceeds by the formation and decomposition of peroxides and hydroperoxides. Simultaneously with the oxidation of aliphatic links, resulting in the formation of H O, CO, CO, and aldehydes, and in the appearance of new carboxyl and phenyl groups, there are also changes in the aromatic links of the chain associated with the formation of biphenyl structures and crosslinking of the polymer. 

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