Solvent cast thermoplastic and thermoset rigid-rod molecular composites

Acid-base interaction-mediated compatibilization between rigid-rod and matr ix polymer components facilitated the formation and processing of solvent c ast aromatic heterocyclic rigid-rod thermoplastic as well as thermoset mole cular composites above the critical concentration (C-cr) of the rigid-rod p olymer in solution, without phase separation. The blends were solvent cast by the mechanism of ionic interchange between a sulfonic acid-pendent poly( p-phenylenebenzobisimidazole) (SPBI), solubilized in alcohol as its triethy lammonium salt and basic thermoplastics such as poly(vinylpyridine)s or sec ondary or tertiary amines with thermosettable phenylethynyl, nadimide and b isbenzoxazine functionalities. Morphological characterization, utilizing SE M, WAXS and SAXS of as cast as well as annealed/thermally cured optically c lear film composites of a broad range of compositions revealed homogeneous microstructures with no observable phase-separated domains, indicating high miscibility, ascribable to the favorable negative enthalpy of the ionic as sociation between the rod-matrix components. A preliminary dynamic mechanic al study of compression molded rigid-rod thermoplastic blends with relative ly low rod contents showed significant enhancement in thermomechanical prop erties vis-a-vis the pristine matrix. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.