A new interpretation of the kinetic model for the imidization reaction of PMDA-ODA and BPDA-PDA poly(amic acid)s

摘要

In this study, a new interpretation is given for the imidization of poly(amic acid)s based on the Seo model: k(t) = b x sech(-at). The parameters a and b in the original Seo model are the rate constant of the imidization reaction and the invariant constant, respectively. However, according to the equation k(t) = b x seeh(-at), k(t) approaches b at the initial time, t→0. The assumption that the parameter b is independent of temperature conflicts obviously with the fact that the rate constant of first-order reaction k(t) is a function of temperature. In this study, the activation energies of a and b were proposed as the energy barriers for the transition state and the rate constant of the imidization reaction, respectively. The new interpretation was tested by imidizing two commercially available poly(amic acid)s: PMDA-ODA and BPDA-PDA from 120 to 225°C. The extent of imidization was determined by a comparison of the intensity of the 1380 cm~(-1) peak in the FTIR spectra. The experimental results suggested that the activation energy from the new interpretation was similar to the literature reports. However, the activation energy from the original Seo model was significantly different from the literature values reported.