Abstract
Activity coefficients and Gibbs free energies of mixing were calculated for aromatic polyimides in various polar aprotic solvents. Group additivity approaches were used to derive approximate solubility parameters for the polymers. Free energies of mixing were found to be negative, and limiting activity coefficients were indicative of very strong solvating forces. Contrary to experiment, these results would predict complete miscibility. Two explanations are proposed for these findings: (i) a single cohesive energy density parameter may not properly characterize specific interactions; and (ii) even nominally amorphous samples may contain various degrees of crystalline-like order which provide additional free energy differences.
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