This invention relates to the compositions and processes for preparing thermoset and thermoplastic polyimides derived from novel asymmetrical dianhydrides: specifically 2,3,3′,4′ benzophenone dianhydride (a-BTDA), and 3,4′-(hexafluoroisopropylidene)diphthalic anhydride (a-6FDA). The a-BTDA anhydride is prepared by Suzuki coupling with catalysts from a mixed anhydride of 3,4-dimethylbenzoic acid or 2,3-dimethylbenzoic acid with 2,3-dimethylphenylboronic acid or 3,4-dimethylphenylboronic acid respectively, to form 2,3,3′,4′-tetramethylbenzophenone which is oxidized to form 2,3,3′,4′-benzophenonetetracarboxylic acid followed by cyclodehydration to obtain a-BTDA. The a-6FDA is prepared by nucleophilic triflouoromethylation of 2,3,3′,4′-tetramethylbenzophenone with trifluoromethyltrimethylsilane to form 3,4′-(trifluoromethylmethanol)-bis(o-xylene) which is converted to 3,4′-(hexafluoroisopropylidene-bis(o-xylene). The 3,4′-(hexafluoroisopropylidene)-bis(o-xylene) is oxidized to the corresponding tetraacid followed by cyclodehydration to yield a-6FDA.