| The liquid crystal polyurethane has been paid more and more attention to as a new kind of functional materials in the new material's research area. A new kind of aromatic azo liquid crystal unit(LCU) was synthesized by coupling reaction, then a series of polyurethane was blocked by the LCU and a series of aromatic azo liquid crystal polyurethane was synthesized. The structures of LCU and LCPU were characterized by FTIR, NMR and UV; the TGA method indicated that the thermostability of LCU was bad compared with LCPU; the DSC method showed that the melting point of LCU was 148.44℃, and there was no phase transition in LCPU from room temperature to 233.45℃; The XRD curve analysis indicated that the crystallinity of LCU was very high, the serious of LCPU was nematic liquid crystal, and the space between molecular chains was d≈0.42 nm. The liquid crystal behavior of LCU and LCPU showed from POM method proved that the LCU and LCPU were both lyotopic liquid crystal and thermotropic liquid crystal. The critical concentration of LCU Cp*=2%, and that of LCPU was Cp*=3%-6%; The LCPU synthesized by prepolymer, in which the mole ratio of TDI and PEG-400 was 4:3, presented a stable typical nematic liquid crystal structure when elevating temperature. The influences of PP composite material preparied by LCPU on mechanical properties were studied. The bending strength of PP composite material mixed LCPU (4:3) was tesed. The results showed that the influence of the content of LCPU (4:3) on bending strength of PP materials was irregular along with the increase of LCPU amount. When the content of LCPU was 3%, the bending strength enhanced 17.52%, while it was 6%, the bending strength reduced 9.99%. The impact strength of all the sample added with LCPU(4:3) were higher than that of pure PP, and when the content of LCPU was 6%, the impact strength was the highest, and enhanced to 196.70%.
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