Synthesis and properties of liquid crystalline polyurethanes

Abstract

1,4-Bis(p-hydroxybenzoate)phenylene was prepared using 1,4-bis(trimethylsiloxy)benzene andp-hydroxybenzoyl chloride as starting materials. A series of novel 1,4-bis(p-hydroxyalkoxybenzoate)phenylene were synthesized by reaction of 1,4-bis (p-hydroxybenzoate) phenylene with 3-bromopropanol and 4-bromobutanol, respectively. The liquid crystal polyurethanes were prepared by 1,4-bis(p-hydroxyalkoxybenzoate)phenylene with MDI (p-methylene diphenylenediisocyanate) and 2,4-TDI(2,4-toluenediisocyanate), respectively. The thermotropic properties, the melting point (T_m) and the isotropization temperature (T_i) of the synthesized polyurethanes were characterized by DSC, IR and POM. It showed that all of the polyurethane polymers exhibited thermotropic liquid crystalline properties between 144ºC and 260ºC. The transition temperature (T_m and T_i) decreased with an increase in the length of the methylene spacer.