Thermochemistry of Carbonization of Polypyromellitimide

Abstract

The mechanisms of thermal degradation processes in polypromellitimide films were investigated by mass-spectrometric thermal analysis and high-resolution NMR spectroscopy in the solid state. Both the structures of the solid residues of pyrolysis products of the PM polyimide and the process of carbonization proper up to 1200 ~ were studied. It was established that the breaking of the Ca,---O----Ca, bond in the diamine moiety is not the primary act of degradation of the molecular structure of the polymer, as might be expected on the basis of the value of the bond energy. The process of intermolecular crosslinking following polymer degradation under hightemperature conditions is completed by the formation of a complex nitrogen-containing heterocyclic structure.The search for promising methods of increasing the thermal stability of polyimides is related to the investigation of thermochemical processes occurring when polymers are heated at temperatures higher than that of the beginning, of degradation [1]. The directed process of the carbonization and graphitization of polyimides to prepare artificial carbon from them [2] is also impossible without investigation of the main relationships of the high-temperature transformations of the polymers.A num 9er of papers have been published on the processes of thermal degradation of polyimides under vacuum and in an inert medium [3][4][5][6][7]. The problem of a detailed mechanism for the degradation of polyheteroarylenes, and polyimides in particular, remains unsolved, although many hypotheses and mechanisms have been suggested to explain the qualitative and quantitative compositions of the thermal degradation products [4,5,8,9]. In most papers, the mechanism of John Wiley & Sons, Limited, Chichester AkadOmiai Kiadr, Budapest

The role of nitrogen atoms in forming the carbon structure in the carbonization of polymer composites

“…This gives practical recommendations on intensifying the dehydrogenation of the carbonizate at 670°C and the onset of graphitization around 1000°C instead of 1300°C [19]. That has led one to continue research on using polyimides as precursors in making carbonized and graphitized materials.…”

“…The charge on the nitrogen atom is redistributed because of delocalization in the phenyl substituent of the diphenyl oxide fragment. Then the unpaired electron on the nitrogen atom is conjugated with the π electrons in the phenyl substituent, which stabilizes the biradical in accordance with There may be various subsequent thermochemical PPI transformations, and the possible paths have been discussed in the literature [15][16][17][18][19], but we need to emphasize the decisive role of the nitrogen in forming the primary thermal destruction products, which under certain conditions produce the framework of the carbonizate with a flexible bond system, which weakens the intramolecular stresses by comparison with the carbonization of carbon-chain structures.…”