Miscible polybenzimidazole blends with a benzophenone‐based polyimide

Miscible blends of the aromatic polybenzimidazole, poly(2,2( m ‐phenylene)‐5,5′‐benzimidazole) (PBI), and the aromatic polyimide formed from 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride and 3,3′‐diaminobenzophenone (LaRC TPI) have been prepared. Blends with PBI were prepared in N,N ‐dimethylacetamide solution starting with either the polyamic acid or a 95% imidized form of LaRC TPI; the blend was then precipitated into water or cast as films. The mixture was then imidized thermally to obtain PBI/LaRC TPI blends. Evidence for miscibility was obtained in the form of single composition dependent T g 's intermediate between those of the component polymers and single tan δ dynamic mechanical relaxation peaks. The IR spectra displayed shifts in the NH stretching band, thereby providing evidence for specific interactions related to the miscibility of these two polymers.