DYNAMIC BIREFRINGENCE OF VINYL-POLYMERS

The complex strain-optical ratio, O(omega), and the complex Young's m odulus, E(omega), of four vinyl polymers, atactic polypropylene, 1,2- polybutadiene, poly(ethylethylene), and poly(4-vinylbiphenyl), were me asured from the rubbery plateau to the glassy zone to investigate the origin of the birefringence and the chain orientation in the glassy zo ne. The data, including those for polystyrene and poly(vinyl naphthale ne), were analyzed through a modified stress-optical rule: The rule st ates that O(omega) and E*(omega) are described as a sum of two compon ent functions (denoted by R and G) and that a proportional rule simila r to the ordinary stress-optical rule holds well for each of the R and G components with different stress-optical coefficients. The R and G components have been interpreted to be respectively related to the ori entation of the main chain axis toward the stretch direction and tilti ng of the structural units by a rotational orientation about the main chain axis. According to this interpretation, the stress-optical coeff icients for the R and G components are predicted to decrease and incre ase, respectively, with increasing size of the side chain. The present study shows the validity of this prediction. In addition, it is sugge sted that the degree of the rotational orientation responsible for the G component becomes larger with increasing size of the side chain.