Callimatic and T-shaped liquid crystalline compounds with fluorinated terminal groups

A series of liquid crystalline polyesters with a rigid T-shaped or a stick-like mesogenic fragment and fluorinated terminal groups of various structures was synthesized and studied by means of polarization optical microscopy, differential scanning calorimetry, and IR and 1H NMR spectroscopy. It was shown that the effect of the fluorinated group on the thermostability of the mesophase depends on the shape of the mesogenic fragment. The thermostability of the mesophase in callimatic liquid crystalline compounds with perfluorinated terminal groups is higher and in those with difluoromethyl terminal groups containing one hydrogen atom is lower compared with their alkyl analogs. This is connected with the possibility of weak hydrogen bonding that destroys the liquid crystalline order. The thermostability of the mesophase in compounds with a T-shaped mesogenic fragment and any fluorinated terminal groups is always higher compared with their alkyl analogs.