| abstract |
A class of soluble polymers having a rigid rod backbone, which when used to cast films, undergo a self-orientation process whereby the polymer backbone becomes more or less aligned parallel to the film surface. This in-plane orientation results in a film that displays negative birefringence. The degree of in-plane orientation and thus, the magnitude of the negative birefringence is controlled by varying the backbone linearity and rigidity of the class of polymers which includes polyesters, polyamides, poly(amide-imides) and poly(ester-imides) through selection of substituents in the polymer backbone chain. By increasing the polymer backbone linearity and rigidity, the degree of in-plane orientation and associated negative birefringence can be increased, and that conversely, by decreasing the polymer backbone linearity and rigidity, the negative birefringence can be decreased. |