Liquid-crystalline polymorphism in a class of low molar mass analogues of mesogenic polyesters

Low molar mass analogues of liquid-crystalline polyesters were prepared in which two alpha-methylstilbene groups are joined through an alkyl spacer. Their mesogenic behaviour was investigated using differential scanning calorimetry, X-ray diffraction and optical microscopy. The experimental results show that the formation of smectic phases is favoured by increasing the length of the terminal chains and by decreasing the length of the flexible spacer. For a given flexible spacer, the melting point and the nematic-isotropic transition temperature are enhanced by decreasing the length of the terminal chains. The terminal chains seem to have no substantial effect on the large odd-even effect exhibited by the thermodynamic properties associated with the nematic-isotropic transition.