The mean-square dipole moment per repeating unit, [mu(2)]/x, of the semialiphatic poly(imide-ester) prepared by condensation of N-(4-carboxyphenyl)trimellitimide acid and diethylene glycol (PIEDEG) was measured at several temperatures in a dioxane solution. The value of [mu(2)]/(x) was 12.70 D-2 at 30 degrees C, and the temperature coefficient expressed in terms of d(ln [mu(2)])/dT was lower than 1 x 10(-4) K-1. For comparative purposes, the mean-square dipole moment of N-[4-[(decyloxy)carbonyl]phenyl]-4-[(decyloxy)carbonyl]phthalimide (NDDPT), a model compound of the acid residue, was also measured in dioxane solutions and found to be 11.63 D-2 at 30 degrees C. MD simulations, employing the Amber force field, were used to study the conformational characteristics of NDDPT. These results, in combination with the conformational energies of the flexible residue, permitted a preliminary characterization of the statistics of the chains. Owing to the asymmetry of the acid residue, PIEDEG is a random copolymer of A and B units. The influence of both the distribution of these units and the number of repeating units on the polarity of the poly(ester-imide) is discussed. In general, reasonable agreement between theory and experiment is found. The lack of a strong correlation between the a angles formed by successive rods in the melt may be responsible for the fact that the poly(imide-ester) used in this study does not develop mesomorphic order.