The effect of solvent to the kinetics of imidization of poly(amic acid)

Kinetics of the imidization reaction of poly (amic acid) (PAA) film based on pyromellitic anhydride (PMDA) and 4,4′-diaminodiphenyl ether (ODA) was studied by infrared spectroscopy. Attention is paid to the effect of solvent content inside the sample to the reaction kinetics. The results show that the presence of solvent favors the imidization reaction, rendering a much higher reaction kinetics than the case of without solvent. The data indicates that there is almost one NMP solvent molecule lost per imidization reaction. The kinetics of isothermal imidization reaction exhibits huge heterogeneity and is well-fitted by the Kohlraush-Williams-Watts (KWW) equation, from which the characteristic reaction time and the stretching exponent are determined. Both of them decrease with the increasing of the imidization reaction temperature, demonstrating the reaction is retarded with the proceeding of the reaction together with the creation of bigger dynamical heterogeneity.