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). On one hand, the chemical ageing mechanisms have been analysed and elucidated by FTIR spectrophotometry and by differential 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, thus causing the disappearance of their characteristic IR absorption band at 2970 cm⁻¹ and the growth of a new IR absorption band at 3350 cm⁻¹, attributed to alcohols. In addition, oxidation leads successively to a relative predominance of chain scissions and crosslinking, resulting in a non-monotonic change of T_g. On the other hand, the consequences of oxidation on the elastic properties have been analysed and elucidated by micro-indentation on polished cross-sections of PEI plates of 3 mm thickness. The diffusion control of oxidation leads to the development of profiles of Young's modulus within the sample thickness, which correlate perfectly with the changes in chemical structure determined by FTIR spectrophotometry. However, the increase in Young's modulus in the superficial oxidized layer is not the direct consequence of oxidation but of a physical ageing.

已经在很宽的温度范围（180至250℃）和氧气分压（0.21至50巴）之间研究了PEI的热降解。一方面，已经通过FTIR分光光度法和差示热量法（DSC）对足够薄的PEI膜（厚度在10到60μm之间）完全消除了氧扩散的影响进行了分析和阐明了化学老化机理。如所期望的，并且类似于具有类似化学结构的其他芳族聚合物，氧化优先发生在双酚A部分的异亚丙基单元的甲基上，从而导致其在2970cm ^-1处的特征IR吸收带消失并且生长。 3350 cm ^-1处新的红外吸收带，归因于酒精。另外，氧化相继导致链断裂和交联的相对优势，导致T _g的非单调变化。另一方面，已经通过在3 mm厚的PEI板的抛光截面上的微压痕分析并阐明了氧化对弹性性能的影响。氧化的扩散控制导致样品厚度内杨氏模量分布的发展，这与通过FTIR分光光度法测定的化学结构变化完全相关。然而，表面氧化层中杨氏模量的增加不是氧化的直接结果，而是物理老化的结果。