SYNTHESES AND CHARACTERIZATION OF MODEL IMIDE COMPOUNDS AND CHEMICAL IMIDIZATION STUDY

In order to characterize various depolymerization and imidization reactions involved during thermal and chemical imidazation of poly(amic acid) by UV-visible and fluorescence spectroscopies, several model compounds have been synthesized and characterized from 1,5-diaminonaphthalene (DAN) and phthalic anhydride. The model compounds synthesized are the derivatives of DAN such as amic acid-amine, diamic acid, amine-imide, amic acid-imide, diimide, and diisoimide. Only DAN is found to be strongly fluorescent while amic acid-amine, amine-imide, and diisoimide are very weakly fluorescent. The others have negligible fluorescence. During imidization, therefore, the fluorescence intensity can be used to quantify the amount of depolymerized DAN. Due to strong substituent effects on the UV-visible spectra, the model compounds exhibit characteristic absorption maxima and extinction coefficients. Proton NMR, IR, and differential scanning calorimetry have been used also to confirm the chemical structures and the purity of the model compounds. Chemical imidization using acetic anhydride and pyridine for polyamic acid made from DAN and a partially fluorinated dianhydride has been investigated. Deconvolution of UV-visible spectra on the basis of the model compounds provided the composition of the involved species such as diamic acid, diimide, and diisoimide. The rate constants for chemical imidization occurring in 1 % solution in N-methyl-2-pyrrolidinone indicate a fast first step in which simultaneous conversion of diamic acid to diimide and diisoimide takes place, followed by slower conversion of diisoimide to diimide in a second step.