Analytical study of the thermal degradation of poly(ether imide)

Abstract

The thermal degradation of PEI has been studied in wide ranges of temperature (between 180 and 250 °C) and oxygen partial pressure (between 0.21 and 50 bars). First of all, the thermal ageing mechanisms have been analysed and elucidated by FTIR spectroscopy and by differential scanning calorimetry (DSC) on sufficiently thin PEI films (between 10 and 60 μm thickness) to be totally free of the effects of oxygen diffusion. As expected, and by analogy with other aromatic polymers of similar chemical structure, oxidation occurs preferentially on the methyl groups of the isopropylidene unit of the bisphenol A part, leading to the disappearance of their characteristic IR absorption band at 2970 cm -1 and the growth of a new IR absorption band centered at 3350 cm -1 and attributed to alcohol groups. In addition, oxidation leads successively to a relative predominance of chain scissions (decrease in T g ) and crosslinking (increase in T g ). Finally, the consequences of oxidation on the elastic properties have been analysed and elucidated by micro-indentation on preliminarily polished cross-sections of PEI plates of 3 mm thickness. However, the increase in Young's modulus in the superficial oxidized layer is mainly due to a physical ageing.