Polymer, Vol.38, No.5, 1029-1034, 1997
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 around 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 modulus and the complex strain-optical ratio were separated into two component functions (denoted by G and R) for which the ordinary stress-optical rule held well individually. A comparison of the component functions was made with a conventional amorphous polyarylate (UP) and bisphenol 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-chain structure. This high flexibility was in accord with a zigzag structure of 2,2’-dicarboxy biphenyl unit of the main chain. The stress-optical coefficient for the R component of PAr1 was 9.0 x 10(-10) Pa-1, and 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 main chain with flexible junctions and also optical anisotropy are effective in decreasing CR The stress-optical coefficient for the G component of PAr1 was 3.1 x 10(-11) Pa-1. This value agreed well with that for the polymers containing phenyl rings in their repeating unit.