Influence of Cross-linking Processes on the Orientation in Thermotropic Copolyesters Studied by FT-IR Spectrometry

Abstract

Dynamic (rheo-optical) FT-IR measurements during deformation of a cross-linkable thermotropic main chain copolyester are presented. Maximum orientation functions of 0.6 for the flexible spacers and 0.8 for the stiff mesogenic units were calculated From the dichroic ratios of specific IR bands. The characterization of thermal and photochemical cross-linking processes in the 400% stretched copolyester foils to achieve a fixation of aligned domain-structure in the liquid crystalline state was the focus of interest. A complete cross-linking is reached only by UV irradiation at 135 degrees C for 120 min, and is connected with a decrease of the orientation of the mesogens and spacers by about 50 and 35% respectively. The IR results were confirmed by solubility experiments and size-exclusion chromatography.