Dynamics of polyimide curing and degradation: An i n s i t u x-ray photoemission study

Abstract

Dynamic time- and temperature-dependent x-ray photoemission studies of polyimide (PI) show the evolving valence bands and core level spectra, starting from partially polymerized PI and continuing through PI degradation at 500 °C. For temperatures below∼200 °C, we see little change, but curing above 300 °C is accompanied by changes in core level and valence-band positions relative to the Fermi level. These changes are associated with the removal of defect induced states in the band gap of the polymer. Comparison of the valence-band spectrum of the fully cured PI to recent electronic structure calculations shows good agreement. PI degradation occurs at temperatures between 450 and 500 °C, where there is a decrease in carbonyl and pyromellitic dianhydride benzene ring carbon 1s emission due to loss of CO or CO2, and an increase in carbon atom density. Nitrogen 1s spectra exhibit the growth of new low binding energy components which indicate that the feature previously assigned to an isoimide structure is a metastable reaction intermediate of the degradation process. The oxygen 1s features are primarily affected in the carbonyl oxygen peak, indicating ether oxygen bonds are more stable with respect to high temperatures.