Solid state coagulation of rigid-rod polymer thin films

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) 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. (C) 1997 Elsevier Science Ltd.