Dynamic-Mechanical Behavior of Hybrid Thermotropic Liquid Crystalline Block Copolymers

The preparation and the dynamic-mechanical behavior of a novel class of liquid crystalline block copolymers is described. In a first step, hydroxyl terminated oligoesters were obtained by polycondensation reaction of methylhydroquinone and 4,4'-dicarboxy-1,10-dibenzoyloxydecane in pyridine solution in the presence of tosyl chloride and dimethylformamide. Hydroxyl terminated oligoesters were then further polymerized with 4,4'-azo-bis(4-cyanopentanoyl chloride) and, in a third step, the macroinitiators obtained were employed in the free-radical polymerization of styrene. The DMA analysis showed that the two different blocks were only partly compatible in the glassy and melt phases and underwent distinct phase transitions. The nematic-isotropic transition temperature of the polyester block was constant throughout the whole composition range and the phase transition enthalpy was directly proportional to the percent of the polyester block.