BIREFRINGENCE OF AMORPHOUS POLYARYLATES .2. DYNAMIC MEASUREMENT ON A POLYARYLATE WITH LOW OPTICAL ANISOTROPY

The complex strain-optical ratio and the complex Young's modulus of a polyarylate with a low molecular anisotropy, PAr1, were measured aroun d the glass-to-rubber transition zone. The polyarylate was synthesized from 2,2'-dicarboxy biphenyl and 4,4'-dioxydiphenyl-2,2'-propane. The data were analysed with a modified stress-optical rule: The Young's m odulus and the complex strain-optical ratio were separated into two co mponent functions (denoted by G and R) for which the ordinary stress-o ptical rule held well individually. A comparison of the component func tions was made with a conventional amorphous polyarylate (UP) and bisp henol A polycarbonate (PC). The limiting modulus of the R component at high frequencies for PAr1 was about two times higher than that for UP and PC. This result suggested that PAr1 had a highly flexible main-ch ain structure. This high flexibility was in accord with a zigzag struc ture of 2,2'-dicarboxy biphenyl unit of the main chain. The stress-opt ical coefficient for the R component of PAr1 was 9.0 x 10(-10) Pa-1, a nd approximately five times smaller than that for UP. Conversely, the intrinsic birefringence for PAr1 was estimated to be 2.5 times smaller than that for PC. This result indicates that reducing stiffness of ma in chain with flexible junctions and also optical anisotropy are effec tive in decreasing CR The stress-optical coefficient for the G compone nt of PAr1 was 3.1 x 10(-11) Pa-1. This value agreed well with that fo r the polymers containing phenyl rings in their repeating unit. (C) 19 97 Elsevier Science Ltd.