Branched Poly(p-phenylene benzobisthiazole) Crystallized from Dilute Solution

Poly(p-phenylenebenzobisthiazole) P (PBZT) chains with average molecular length of 61 nm have been reacted with trimesic acid to link each other. The product, a mixture of Y-, V-shaped and linear P (PBZT)'s, was dissolved into conc.SCU at a concentration of 0.1 wt%, and isothermally crystallized. The precipitate was composed essentially of curved rod-like crystals. Four or five crystals having different length coagulated each other with many branches at an angle of ca 60°. This morphological feature was in contrast to that of pure linear P (PBZT) precipitate in which several tens straight rod-like crystals of the same length were oriented parallel to each other to make a group. This difference in morphology between linear P (PBZT) and the mixture of Y, and V-shaped and linear P (PBZT)'s was well explained by the crystallization mechanism of P (PBZT). 100 lattice fringe was observed throughout the central area of the rod-like crystal. This means that the center was composed of linear part of Y-, V-shaped and linear polymers, which were accomodated normal to the rod. In some area, the 001 lattice fringe crossed 100 lattice fringe at an angle of ca 75°, suggesting that P (PBZT) unit cell might not be Fratini's monoclinic type. On both sides of the 100 lattice fringe, there were dark belts. These belts corresponded to thick parts which were composed of the other counterparts in the Y- and V-shaped poly mers.