THE ROLE OF THE PYRIMIDINE RING IN THE MAIN-CHAIN OF POLYAMIC ACIDS AND POLYIMIDES .4. INFLUENCE OF PYRIMIDINE RING BASICITY ON THERMOIMIDIZATION OF POLYAMIDOACIDS

Thermoimidization kinetics of polypyromellitamic acids prepared from 2 ,5-bis(p-amino-phenyl)pyrimidine and 4,4''-diaminoterphenyl have been investigated by IR spectroscopy. It has been shown that the activation energy for the pyrimidine-containing polymer is nearly twice as low a s that for the aromatic analog. This is explained by base catalysis of cyclization of the amidoacid fragments by pyrimidine rings in polymer chains. Base catalysis facilitates the process of imidization and fav ors the formation of polyimidic macromolecules with a lower incidence of defects. Also, the pyrimidine rings obviously catalyze the resynthe sis of amidoacid fragments from the anhydride rings and amino groups f ormed on the destruction of the polymer chain during thermoimidization , and ensure almost complete recovery of the macromolecules with the p revious bonds.