Quantum chemical PM-3 study of the thermal stability of heterocyclic fragments of heteropolymers, 2. Six-membered heterocycles

✍ Scribed by Vladimir A. Zubkov; Alexander V. Yakimansky; Svetlana E. Bogdanova; Vladislav V. Kudryavtsev

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 488 KB
• Volume: 3
• Category: Article
• ISSN: 1022-1344
• DOI: 10.1002/mats.1994.040030218

✦ Synopsis

Abstract

Dissociation energies (E~D~) of various heterocyclic fragments of repeating units of thermally stable heteropolymers have been calculated by the semiempirical PM‐3 method. Fragments with heterocycles containing carbonyl and/or amine groups and/or oxygen (or sulfur) atoms (benzazoles, phthalimides, benzoxazinones, etc.) have fairly close E~D~ values. The correlation between E~D~ values of fragments and the initial degradation temperature (T~D~) of heteropolymers comprising these fragments reveals that the T~D~ values depend both on E~D~ of corresponding heterocycles and on the manner of heterocycle decomposition: whether it leads to an immediate weight loss (polyimides, polybenzoxazinone, etc.) or just to a chain scission (polybenzazoles). Quinoline and quinoxaline are characterized by higher E~D~ values, but it seems that decomposition of these compounds during the initial degradation of polyquinoline and polyquinoxaline proceeds via mechanisms different from the straightforward homolytic decomposition characteristic of other considered heterocycle decompositions.