Solid state coagulation of rigid-rod polymer thin films

Abstract

A novel coagulation processing scheme has been developed to fabricate optical quality polymer thin films for non-linear optical applications. In this process, termed solid state coagulation, an optically isotropic polymer solution is rapidly frozen into a solid mixture to preserve the molecular dispersion of the polymer in the solvent. It is then coagulated at a cryogenic temperature in a proper coagulant to extract the frozen solvent without disrupting the molecular distribution of the polymer. Thin films of rigid-rod poly( p-phenylene benzobisthiazole) (PBZT) prepared by this technique showed an optical attenuation coefficient of about 300 cm −1 (or 1300 db cm −1), significantly lower than the 990 cm −1 (or 4300 db cm −1) obtained from the thin films prepared by the conventional solution-state coagulation process. Wide angle X-ray scattering confirmed that the domain structures in the solid-state coagulated PBZT thin films are smaller and less ordered than those in the solution-state coagulated thin films. This solid state coagulation processing scheme is particularly valuable for polymer systems, such as rigid-rod polymers, ladder polymers, crystalline polymers and polymer blends of incompatible systems, which cannot be processed with significant optical clarity by melt processing or solution casting.