Birefringence and dichroism of rubbery copolymers

The Kuhn‐Grün theory for the birefringence and dichroism of rubbery polymers is extended to the case of copolymers consisting of two or more statistical segments of differing lengths. It is shown that the previous equations are applicable provided that the anisotropy of polarizabilities and absorptions are replaced with suitable averages in which the segment anisotropies are weighted by the squares of their segment lengths. This indicates that the stress‐optical coefficient will not generally vary linearly with composition. The orientation measured from the dichroism of bands arising from different segments will be different.