MECHANISMS AND KINETICS OF THE POLYMERIZATION OF THERMOPLASTIC POLYIMIDES .1. STUDY OF THE PYROMELLITIC ANHYDRIDE AROMATIC AMINE SYSTEM

We have synthesized model compounds representing the repeating units of a polyamic acid prepared from pyromellitic anhydride and an aromatic amine. They were characterized with HPLC, H-1 and C-13 liquid and solid NMR and FTIR. The kinetic study of the ring dehydration reaction of model compounds showed that the reaction paths were very different, depending on the experimental conditions (isotherms, liquid, or solid states). They could lead to a deterioration of the polyamic acid by the formation of side reactions. These reactions could predominate as a result of the existence of an equilibrium between the amic acid group and starting monomers.