Effect of N‐methyl substitution on the thermal decomposition processes in aliphatic–aromatic polyamides

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Abstract
The thermal decomposition processes of two polyamides, derived from succinic acid and two aromatic diamines, were studied by direct pyrolysis mass spectrometry.Fast atom bombardment (FAB) mass spectrometry has been also used in order to provide additional information for the elucidation of the thermal degradation mechanism of the polymers investigated. FAB mass spectra, obtained by introducing in the FAB ion source the solid residues from polymer pyrolysis performed in thermogravimetric experiments, allowed the detection of diagnostic compounds up to about 1600 amu.Our results indicate that the thermal stability of the N‐methyl‐substituted polyamide is higher than that of the unsubstituted polyamide. The difference in the thermal degradation mechanism accounts for the difference in the thermal stability of the two polyamides. In fact, the unsubstituted polyamide decomposes via an intramolecular exchange and a concomitant NH hydrogen transfer process with formation of compounds with amine and/or succinimide end groups. Instead, the N‐methyl‐substituted polyamide decomposes via an α CH hydrogen transfer process from the methyl group to the nitrogen atom with formation of compounds with amine and/or 2,5‐piperidinedione end groups.

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