Process for preparing polyimides from diamines and dianhydrides in the presence of abasic catalyst

Claim 1

A PROCESS FOR PREPARING POLYIMIDES WHEREIN MATERIALS SELECTED FROM THE CLASS CONSISTING OF AN AROMATIC DIAMINE TOGETHER WITH AN AROMATIC DIESTER DIACID, IN WHICH ALL AMINO, ESTER AND ACID GROUPS ARE DIRECTLY ATTACHED TO AROMATIC RINGS AND IN WHICH ONE ACID AND ONE ESTER GROUP FORM A PAIR ATTACHED TO ADJACENT CARBON ATOMS, ARE REACTED AT FROM 100 TO 200*C. IN SOLUTION AND IN THE PRESENCE OF FROM 1 TO 30 MOLE PERCENT, AS CALCULATED ON THE ACID GROUPS, OF A BASE SELECTED FROM THE CLAS CONSISTING OF ALKOXIDES CONTAINING FROM 1 TO 6 CARBON ATOMS; SALTS OF LOWER FATTY ACIDS CONTAINING FROM 1 TO 6 CARBON ATOMS; CARBONATES; AND HYDROXIDES; OF THE ALKALINE EARTH METALS AND ALKALI METALS, TO FORM AN ANHYDRIDE WHICH IN TURN REACTS WITH THE AMINE PRESENT TO FORM A POLYAMIDE ACID WHICH CYCLIZES AT FROM 100 TO 200*C. TO FORM A PRECIPITATE OF POLYIMIDE IN THE FORM OF A POWDER HAVING A SURFACE AREA OF AT LEAST 1 SQUARE METER PER GRAM.