Cross-shaped mesogens in main chain polymers

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Abstract
The synthesis of semiflexible main chain polyesters with cross-shaped mesogens and their phase behaviour, investigated by polarizing microscopy, DSC and X-ray diffraction, is presented. Polyesters of this type show mesophases with dominating nematic character and relatively high clearing temperatures. Systematic variation of the spacer and the terminal groups of the mesogens shows that longitudinally fixed rod-like parts of the mesogens have a strong influence on the clearing temperature and, therefore, on the mesophase behaviour. The corresponding rod-like but laterally fixed parts of the cross-shaped mesogens influence the melting temperatures significantly. This is critical in determining crystallization. However, laterally fixed rod-like parts contribute also to the formation of mesophases, but clearly to a far less extent.