Temperature dependence of the properties of vapor-deposited polyimide

Abstract

The Young’s modulus and helium gas permeability of vapor-deposited poly(4,4′-oxydiphenylenepyromellitimide) were measured at cryogenic and elevated temperatures (10–573 K). The Young’s modulus decreased with increasing temperature from 5.5 GPa at 10 K to 1.8 GPa at 573 K. The temperature dependency of the permeability followed the Arrhenius’ relationship, with different activation energy for permeation for samples imidized under different conditions. The effect of the imidization conditions on the permeation properties could be explained in terms of morphology/crystallinity as determined by x-ray diffraction techniques. Imidizing in air instead of nitrogen increased the permeability while lowering the activation energy for permeation and crystallinity. Imidizing at higher heating rates (in nitrogen) resulted in higher permeability, lower activation energy for permeation, and larger and fewer crystallites with better-aligned lattice planes.