Novel triaromatic ester mesogenic liquid crystalline epoxy resin containing both methyl substituent and ethoxy flexible spacer: Synthesis and curing

A novel triaromatic ester liquid crystalline epoxy resin (LCER) that contains both a methyl substituent and an ethoxy flexible spacer, p-methylphenylene di{4-[(2,3-epoxypropoxy)ethoxy]-benzoate} (MPEPEB), has been synthesized. The mesotropic property has been investigated by differential scanning calorimetry (DSC) and polarized light optical microscopy (POM). MPEPEB shows a lower melting temperature at 78.7 degrees C and a broad nematic mesophase temperature range of about 55 degrees C. Meanwhile MPEPEB shows a mesophase to -50 degrees C upon cooling. The curing behavior of MPEPEB with 2,6-diamino-3,5-diethyltoluene (DAE) has been investigated by means of DSC and POM during isothermal and dynamic processes. Although there is little difference between the activation energies obtained from the kinetic data, a marked difference is found between the isothermal and dynamic investigation. The curing reaction in the isothermal investigation roughly obeys n-th order kinetics, while two exothermal peaks appear in the dynamic DSC curves of MPEPEB/DAE. A comparison of the isothermal and dynamic data shows that the curing rate is not a unique function of temperature and curing degree. The cured networks have lower glass temperatures and show a mesophase at room temperature which disappears at about 86-88 degrees C.