Para-, meta-, and mixed isomeric poly( amic ethyl ester) precursors of the polyimide based on pyromellitic dianhydride( PMDA) and 3,4＇-oxydianiline( 3,4＇-ODA) were synthesized. The intrinsic viscosity of each of the isomers was measured in an NMP solution and found to be less than corresponding isomers derived from PMDA and 4,4＇-oxydianiline (4,4＇-ODA) precursors with comparable molecular weight. The imidization and solvent retention were measured as a function of imidization temperatures, T-i using forward recoil spectrometry (FRES). For samples cast from a single solvent, either N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO), no difference was observed in the temperature-dependent imidization behavior between the isomers. In all cases the imide fraction f increased as T-i increased, and reached a value of unity, i.e., full conversion at 400 degrees C. At the same T-i, samples cast from DMSO showed a slightly higher f than samples cast from NMP. FRES and time of flight FRES (TOF-FRES) were used to measure the interdiffusion distance, to, of deuterium-labeled tracers into nondeuterated base layers of the polyimide of PMDA/3,4＇-ODA treated at various T-i. The primary determinant of to for all isomers was T-i, and the particular isomer used as either the base or the tracer molecule did not seem to affect w.