MALDI-TOF characterisation of thermally generated gel from Nylon 66

Progress in understanding the thermal decomposition processes occurring in Nylon 66 (Ny66) was obtained by using matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry techniques. Ny66 samples were subjected to thermal degradation under inert atmosphere heating them at 290 and 315 deg C. The formation of a gel fraction was observed after about 15 min of heating and the addition of a condensing agent such as triphenyl phosphite (TPP) made the gelation complete in a few minutes. The MALDI-TOF mass spectra of the soluble fraction showed that secondary amino groups and cyclopentanone chain ends were generated in the heating process. The gel fraction was partially hydrolyzed to destroy the network structure and the soluble material was analyzed by MALDI-TOF. The spectra revealed the presence of N,N-substituted amide as side chains generated by the condensation of carboxyl end groups with secondary amino groups and azomethine structures originating from the reaction of cyclopentanone moieties with the terminal amino groups. These structures were most likely responsible for the gel formation on heating Ny66 samples. Comparison with similar experiments conducted on Ny6, showed that only secondary amino groups were formed in Ny6, leading to branched structures but not to crosslinking.