THERMAL-DEGRADATION OF POLYETHERIMIDES AS INFLUENCED BY THE SYNTHETICAND TESTING CONDITIONS

The effect of various factors on thermal stability of thermoplastic po lyetherimides on the basis of 2,2'-bis[4-(3,4-dicarboxyphenoxy)phenyl] propane dianhydride was studied using TGA at high temperatures and in steady-state conditions at 320-degrees-C (the temperature at which the se polymers are processed in the molten state). It was established tha t low thermal stability is characteristic of polyetherimide synthesize d by nucleophilic polynitro substitution, and which contains unsubstit uted terminal nitro groups. It was also shown that admixtures of solve nts and atmospheric oxygen produce a significant effect on thermal sta bility of polyetherimides. Substitution of unreactive terminal groups for reactive ones improves thermal stability of the studied polymers a nd precludes an increase in their viscosity in melts. Cross-linking of polyetherimides in melts at 320-degrees-C in the presence of said fac tors was studied in detail. The strong effect of solvent admixtures an d oxygen on the extent of cross-linking was demonstrated.