Chain folding in liquid-crystalline main-chain polymers with a smectic phase

Thermotropic main-chain liquid-crystalline polymers (LCPs) composed of azobenzene or azoxybenzene mesogens and flexible spacers with and without a phenyl side group have been characterized by gel permeation chromatography, differential scanning calorimetry, and X-ray diffraction. The polymers exhibit smectic phases in the well-accessible temperature range from room temperature up to 160 degrees C. The morphology of thin films on a solid substrate was studied by X-ray reflectometry and scanning force microscopy (SFM). The smectic layers are mainly oriented parallel to the film surface. On the basis of X-ray reflectometry and SFM. investigations, it is concluded that, at least in thin films, the polymer main chains are not extended like in the common model for main-chain LCPs, but almost regularly folded.