A new interpretation of the kinetic model for the imidization reaction of PMDA-ODA and BPDA-PDA poly(amic acid)s - Polyimides and Other High Temperature Polymers - page 39

Figure 2. FTIR spectrum of PMDA-ODA poly(amic acid) cured at 165°C for different times (a) 20
sec, (b) 4 min, (c) 110 min, and (d) 400°C for two hours.
In order to quantify the degree of imidization reaction, the peak at 1380 cm -1
was used to represent the conversion from poly(amic acid)s to polyimides. Figure
3 shows the FTIR absorption peak at 1380 cm -1 for PMDA-ODA poly(amic acid)
at 165°C at different curing times and for the fully imidized PMDA-ODA. It can
be observed that the intensity of the peak increases with curing time, suggesting
the progress of the imidization reaction. The imidization of the poly(amic acids)
was studied at different curing temperatures and times.
Figures 4 and 5 show the degrees of imidization of PMDA-ODA and BPDA-
PDA poly(amic acid)s, respectively, at different curing temperatures ranging from
120 to 225°C with the curing time. The degree of imidization was obtained from
eq. (2) by comparing the peak areas at 1380 cm -1 . It can be observed from these
two figures that the degree of imidization increases rapidly at a short curing time
and then reaches a steady value. The higher the curing temperature, the shorter the
curing time for reaching the steady value. The solid lines in Figures 4 and 5 repre-
sent the fitting curves for the experimental results based on Seo model (eq. (4)).
Figure 6 shows the rate constant (k) of imidization of the PMDA-ODA poly(amic
acid) at different curing temperatures. As can be observed from this figure, the
rate constant k drops rapidly with increasing curing time and temperature. The pa-
rameters a and b were obtained from eq. (4) and Figures 4-6. Figure 7 shows the
variation of ln(a) and ln(b) with 1/T for the imidization of PMDA-ODA and
BPDA-PDA poly(amic acid)s. From the Arrhenius plots, the activation energies