| The imidization characteristics of a common polyimide precursor, pyromellitic dianhydride oxydianiline ethyl ester (PMDA/ODA ethyl ester) have been examined in the solid and molten states using model compounds. The model compounds synthesized for this work are meta (MDOP) and para (PDOP) isomers of diethyl-p,p-oxydiphenylene pyromellitamide, an amide based on phthalic anhydride and 1-aminopyrene, and an amide based on phthalic anhydride and 4-phenoxyaniline. The imidization reaction has been studied using thermal analytical techniques, mass spectrometry, optical microscopy and X-ray diffraction.;Differences in the imidization characteristics of meta and para isomers were studied using both DOP model isomers, and a 50/50 mixture of the two (50/50DOP). In all cases, imidization was found to occur only after the material had melted. The order of occurrence of the melt endotherm as well as the onset of imidization was determined to be 50/50DOP < MDOP < PDOP. This is not the same as the order of imidization of polymer isomers. Also, studies of the same model compounds show that the imidization onset temperature is the same when tested in solution. Measurements of the glass transition temperatures of the model compounds show them to occur in the following order; PDOP < 50/50DOP < MDOP, which is the same order as the imidization onset temperatures of the PMDA/ODA ethyl ester polymer. There may be a relationship between the glass transition temperature and the imidization onset temperature of the PMDA/ODA ethyl ester polymers that is similar to the relationship of the melt temperature and imidization temperature of the model compounds that we establish here.;Modifications of the crystal lattice of all of the model compounds by precipitation, addition of impurities, and formation of glasses has shown that the imidization characteristics are very dependent on the morphology of the model compounds. It has been found that perturbations that lower the melt temperature also lower the imidization onset temperature.;The morphology of the pyrene based imide model compound has been investigated and found to be similar to polymeric systems. It easily forms a glass and relaxes to a crystalline material in the time scale of several days. |
