Swelling behavior of an aromatic polyimide

Abstract The swelling behavior of poly( N, N '‐bisphenoxyphenylpyromellitimide) (PMDA‐ODA) using dimethylsulfoxide DMSO and N ‐methylpyrollidinone NMP was investigated by gravimetric means. For PMDA‐ODA samples imidized on a substrate, the weight uptake was found to depend linearly on time over a temperature range from 25 to 150°C. For a given temperature of imidization, the equilibrium swelling concentration was found to be independent of the temperature at which the swelling studies were performed. However, the rate of solvent uptake depended strongly on the swelling temperature, yielding an activation energy of about 50 kJ/mol. In general, increasing the initial imidization temperature caused a decrease in the rate of swelling but did not alter the equilibrium swelling concentration. This swelling behavior resembles Case II diffusion typically seen in glassy polymers with some noteworthy exceptions. In cases, where PMDA‐ODA was imidized in a free‐standing state, no swelling was observed. However, deformation of these isotropic specimens was found to induce substantial swelling.