HIGH-TEMPERATURE PROPERTIES OF PBZT FIBERS

Molecular dynamics simulations were performed in an attempt to elucida te the molecular mechanism of a relaxation measured experimentally in poly(p-phenylene benzobisthiazole) (PBZT) fibres. Results for the coef ficient of thermal expansion and tensile modulus parallel to the molec ular axis agreed favourably with published experimental values. The X- ray peak intensity ratio of (200)/(010) versus temperature obtained fr om the simulations showed a variation qualitatively similar to that fr om experiments. The torsion angle between the benzobisthiazole and phe nyl moieties increased with temperature. A distortion of the phenyl an d benzobisthiazole moieties also occurred and the molecules were obser ved to undergo increased oscillatory ribbon-like motions perpendicular to the (010) plane as the temperature increased. Finally, translation al oscillations of the molecules parallel to the c-axis occurred. Thes e molecular motions are coupled to the tensile stress and could play a role in the relaxation.