POLYIMIDES FROM COMPLEXES OF BENZOPHENONE-TETRACARBOXYLIC ACID DIESTERS WITH DIAMINES .5. MECHANISM OF THERMAL CYCLIZATION OF H-COMPLEXES

The results of a study, by thermal mass spectrometric analysis and NMR spectroscopy, of the polycondensation of H-complexes are presented fr om which it is possible to propose a mechanism for the reaction. It is shown that conversion of the H-complexes into polyimides takes place through the formation of intermediate zwitterions with an amino acid b ond after initial separation of methanol, following which elimination of water commences in one stage to form an imide ring. The role of the ortho position of the functional groups in the acid ester during the formation of the hydrogen bond is discussed.