BLENDS OF SOME NON-FLEXIBLE AND FLEXIBLE POLYMERS - ROUTES TO MOLECULAR COMPOSITES

The definition of a molecular composite is a blend of a rigid rod poly mer and a flexible coil polymer that is miscible at the molecular leve l. This concept has been tested using systems in which the chain flexi bilities differ as widely as possible as judged by the difference in g lass transition temperatures (Delta Tg). The biggest variation (Delta T similar to 360 degrees C) was obtained by mixing poly benzimidazole with copolymers of poly(vinyl acetate-ran-vinyl alcohol). It was obser ved that the blends were distinctly two phase when the hydroxyl conten t was less than 50 mol %. Above this value clear blends were obtained with finely dispersed phases although it is doubtful if mixing at the molecular level takes place. Miscible blends could be obtained from co mbinations of the sodium salt of poly(phenylene terephthalamide) with poly(4-vinylpyridine) and mixtures of poly(phenyl imino-1,4-phenyleneo xyterephthalate) with poly(styrene-stat-hydroxylstyrene) where coulomb ic interactions and hydrogen bonding respectively promoted the miscibi lity.