Viscoelastic properties and birefringence of amorphous polymers around the glass transition region

The strain-induced birefringence of most polymers around the glass transition region can be related to the stress through a modified stress-optical rule, MSOR. The rule says that both the birefringence and stress can be separated into two component functions, denoted by R and G. In addition, a similar relation to the ordinary stress-optical rule separately holds well for each component function The molecular interpretation of MSOR is described: The R component is related to the chain orientation and the G component is related to the rotational orientation of the structure units around the main chain axis. In order to examine the molecular interpretation of MSOR, model calculations of the orientation mechanism of the two components are presented and the results are compared with the experiments. Studies focusing on the relation to the molecular structure are described. These studies show that characteristic features of the component functions can be related to the flexibility of the chain. The MSOR is compared with other versions of stress-optical relation and comments on 2D-IR method are also given.