Synthesis and application of liquid crystalline polyurethanes/epoxy resin composites

Liquid crystal polyurethans (HBLCP) containing imide units were synthesized by polyaddition reaction of N, N'-bis(2-hydroxyhexyl)-dicarboxyimide (BHDI) with 2, 4-toluenediisocyanate (2, 4-TDI) and hydroquinone dibenzoate ester (HQB) through changing the molar ratio of BHDI and HQB, and blending HBLCP with epoxy resin (E-51), to prepare HBLCP/E-51 composites. The structure and liquid crystalline phase behavior of HBLCP were characteristied by using FTIR, DSC, polarized light microscopy (POM), X-ray diffraction (WAXD), and the fracture structure of the HBLCP/E-51 composites was investigated by SEM, and the toughening mechanism was also explored. Experimental results reveale that the impact strength of the epoxy resin modified with 3 wt% HBLCP is 2.3 times higher than that of unmodified epoxy resin, and the tensile strength as well as the bending strength is also improved, present the typical ductile fracture. The thermal decomposition temperature of HBLCP/E-51 composites is also 12~20 ℃ higher than that of the pure epoxy resin, and the temperature for the maximum decomposition rate of composites is 12~15 ℃ higher than that of the pure epoxy resin.