OPTICAL ANISOTROPY OF FLEXIBLE POLYIMIDE THIN-FILMS

Optical anisotropy of thin films of an organo-soluble flexible polyimi de based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and 2,2-dimethyl-4,4'-methylene dianiline (DMMDA) was detected by a pr ism-coupler technique. A mechanism is proposed, based on the model of gel film collapse. The degrees of optical anisotropy of the thin films were evaluated via the level of negative birefringence. The residual solvent in the films lessens the levels of negative birefringence so t hat the residual solvent must be evacuated. The levels of negative bir efringence are independent on the solid content of the initial solutio n, but dependent on the thickness of the films. For a film of 16 mu m thick, zero birefringence was achieved, postulated from the dependence of negative birefringence on the thickness of thin films. The relatio nship between the optical anisotropy and solution properties shows tha t the degrees of optical anisotropy of thin films on the same scale of thickness depend on macromolecular sizes in their dilute solutions.