Combined type liquid crystalline polymers composed of poly(p-phenylene terephthalate) main chain and azobenzene mesogenic side groups attached through polymethylene spacers

A series of combined main chain-side group thermotropic polyesters having varying lengths of oxypolymethyleneoxy spacers between the aromatic polyester main chain and the side azobenzene mesogenic unit have been synthesized and their liquid crystalline properties have been investigated. The thermal and liquid crystalline (LC) properties of the polymers were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), optical microscopy, and X-ray diffractometry. The main chain is the poly(p-phenylene terephthalate) structure, and side mesogenic groups are attached through spacers onto terephthaloyl units. The spacer length was varied from oxytrimethyleneoxy (PAZO-3) to oxyhexamethyleneoxy (PAZO-6). A polymer with a longer spacer oxydecamethyleneoxy (PAZO-10), also was included in this investigation. The polymers with spacers up to the oxyhexamethyleneoxy spacer form nematic LC phases. In contrast, the polymer (PAZO-10) with the oxydecamethyleneoxy spacer was found to form a layered morphology in the mesophase. Moreover, a fiber spun from PAZO-10 revealed a biaxial molecular orientation where the side mesogenic groups including the spacer were oriented slightly tilted to the main chain. Other compositions produced only the fibers of the oriented nematic phases.