Thermal degradation of an aromatic polypyromellitimide in air and vacuum I — Rates and activation energies

Abstract

The thermal degradation of a polypyromellitimide (condensation product of pyromellitic anhydride and an aromatic diamine, designated as ‘H-film’ by E. I. du Pont de Nemours and Company, Inc.) was studied in air and vacuum in the range of 400° to 700°C by thermogravimetry using a recording electrobalance. Although this organic polymer is remarkably stable in air up to approximately 420°C, at temperatures in excess of this it begins to volatilize. At 485°C practically total volatilization takes place within approximately five hours. In a vacuum (∼10 −3mm of mercury) the polymer shows even greater heat stability with no appreciable weight loss even after prolonged exposure to temperatures up to approximately 500°C. Above this temperature it begins to volatilize leaving a brittle, carbonized residue which appears to reach a limiting weight corresponding to approximately 45 per cent of the original sample and showing no infra-red absorption bands. From the thermal degradation profiles the rates of volatilization were calculated, from which the Arrhenius relationship gave an activation energy of 33 kcal/mole and 74 kcal/mole for the degradation in air and vacuum, respectively. The general shapes of the rate curves of this polymer as the result of thermal degradation in vacuum resemble those of polytrivinylbenzene as investigated by other workers.