Thermal decomposition processes in polyhydrazides and poly-oxamides investigated by mass spectrometry

The thermal decomposition processes of some totally aromatic or totally aliphatic polyhydrazides and polyoxamides were studied by direct pyrolysis mass spectrometry, using both chemical ionization and electron impact modes. The results indicate that the primary thermal decomposition processes of these polymers (containing COCO and NRNR linkages) are strongly influenced by structural factors. The polyhydrazide I, derived from isophthalic acid and hydrazine, experiences primary loss of water, producing a polymer with oxadiazole units. The latter thermally decomposes with formation of compounds with nitrile, phenyl, amino and/or acid end groups. The thermal decomposition of the polyhydrazide II, derived from isophthalic acid and N,N′-dimethylhydrazine, proceeds via an α CH hydrogen transfer process from methyl groups, with formation of pyrolysis products containing secondary amide and/or imine end groups. Hydrolysis of the latter groups leads to the formation of primary amide end groups and subsequent formation of nitrile end groups. The primary thermal decomposition process of the polyhydrazide III, derived from adipic acid and hydrazine, proceeds via a CH hydrogen transfer to the nitrogen atom, with formation of compounds with amine and/or cyclopentanone end groups. In the pyrolysis of this polyhydrazide, secondary thermal fragments are also formed: cyclopentanone, carbon dioxide and compounds with azomethine and isocyanate groups. The polyoxamide IV, derived from oxalic acid and m-phenylenediamine, decomposes via a NH hydrogen transfer process with formation of compounds with amine and/or isocyanate end groups. Finally, the thermal degradation of the polyoxamide V, derived from oxalic acid and ethylenediamine, proceeds via a β CH hydrogen transfer process, with formation of compounds with olefin and amide end groups.