NMR and FTIR investigation of the solution imidization kinetics of model compounds of PMDA/ODA polyamic ethyl ester

Meta- and para-diethyl-p,p-oxydiphenylene pyromellitamide (DOP), the model compounds of the meta and para PMDA/ODA polyamic ethyl ester, were synthesized and characterized by NMR and FTIR spectroscopy. Investigation of the imidization in d₆-DMSO solution using NMR and FTIR techniques has shown that both the half imide and imide were formed. Quantitative analysis of the curing rates and degrees of conversion of the isomers in dilute d₆-DMSO solution as a function of time under isothermal conditions or as function of temperature at fixed time (1 h) indicated that the kinetics of the ring closure reaction of the meta and para isomers were the same within 10%. This suggests that intrinsic reactivity differences between the isomers do not have much effect on the imidization process and do not account for the differences in rate that have been observed for the meta and para polymers in the solid state. No interconversion between the two isomeric forms occurred below 180°C, as has been observed for polyamic acids and their model compounds. The degree of conversion strongly depended on the reaction temperature and increased quickly after 170°C. The rate constant of the second ring closure reaction was found to be approximately three to four times the rate constant of the first ring closure reaction. © 1996 John Wiley & Sons, Inc.