Preparation and characterisation of liquid crystalline epoxy/epoxy resin composites

A novel liquid crystalline epoxy resin, PHQEP, containing aromatic ester mesogen was synthesised from di(p-hydroxyl benzoic acid) hydroquinone (PHQ) and epichlorohydrin by phase transfer catalysis. The molecular structure of PHQEP was characterised by means of Fourier transformed infrared spectroscopy, hydrogen nuclear magnetic resonance spectroscopy, while its liquid crystalline phase behaviour was observed by a polarised optical microscope. The curing behaviour of PHQEP/diglycidylether of bisphenol A (E-51)/4,4'-diaminodiphenyl sulphone (DDS) system was studied by non-isothermal differential scanning calorimetry. Mechanical performance, thermal stability and dynamic mechanical property of PHQEP/E-51 composites were also investigated. The results revealed that PHQEP is a typical nematic liquid crystalline polymer. Impact strength of 5 wt-% PHQEP/E-51 was 2.6 times higher than that of E-51/DDS, and the initial decomposition temperature was 10 degrees C higher than the value of E-51/DDS. The detailed reasons for the improvement of strength and thermal stability lie in the fact that origination of the mesogenic units of PHQEP was kept in the epoxy networks during the curing process.