Kinetic Study of the Imidization of a Poly(ester amic acid) by FT-Raman Spectroscopy

Abstract

The kinetics of thermal imidization of a poly(ester amic acid) in solid state was investigated in the temperature range 120−180 °C. FT-Raman spectroscopy was used for the measurement of imidization. Data on changes in intensity were collected on compressed thin specimens that had been isothermally cured. FT-Raman spectral changes as a function of imidization time are adequately modeled by assuming two first-order imidization reactions. Activation energies for the first and second ring closure processes were almost the same, 20.5 and 19.9 kcal/mol, respectively. However, the activation energy increased slightly (24.6 kcal/mol) when the second-order reaction model was adopted for the first reaction. Increase in activation energy was screened by the increase of the pre-exponential factor, implying the absence of significant changes in the reaction rate ratio. A new time dependent model is proposed which is easy to apply and shows good agreement with the experimental data, both quantitatively and qualitatively. The activation energy calculated by the new model was 24.3 kcal/mol. It takes into consideration the evolution of different amic acid stages. The proposed model also correlates the two-step imidization reaction very well.

Influence of azobenzene units on imidization kinetic of novel poly(ester amic acid)s and polymers properties before and after cyclodehydration

“…Therefore, the reaction rate is strongly dependent on the basicity of the amine, the electrophilicity if the anhydride carbonyl, and the basicity of the solvent. The thermal imidization of poly(amic acid)s involves cyclization through a nucleophilic attack on the acid carbonyl carbon by the free electron pair of the amide nitrogen 34. Although two groups, CONH and COOH, are involved in imidization, this reaction should be treated as first‐order, since these groups belong to the same fragment of poly(amic acid), and interaction of the groups with different macromolecules is practically impossible, especially in the solid state 34.…”

Kinetic study of low‐temperature imidization of poly(amic acid)s and preparation of colorless, transparent polyimide films

“…It has been reported that E a for thermal imidization of a poly(ester amic acid) is about 20 kJ/mol. 32 In another report, E a for chemical imidization of a poly(amic acid) of 4,4 0 -(hexafluoroisopropylidene)diphthalic anhydride and 1,5-diaminonaphthalene was presented to be 12.3 kJ/mol when an approximately 13:1 molar ratio of amine catalyst to PAA repeating unit was used. 28 …”

15N NMR spectroscopy as a method for comparing the rates of imidization of several diamines

“…A number of other researchers have noted and studied the reaction kinetics of imide formation [8][9][10][11][12]. There seems to be some agreement that the imidization reaction from the amide-acid proceeds through an initial fast step and a later slower step, although there are differing views on the cause of this difference.…”