Synthesis And Curing Behaviour Of Liquid Crystalline Epoxy Resin

Epoxy resins are widely applied as engineering thermosets for their many desirable properties. Liquid-crystalline epoxy resins (LCERs) that contain rigid-rod mesogenic units in their backbone have been extensively studied for decades.Two novel LCERs, diglycidyl ether of 4,4'-bisphenylol (DGEBP) and diglycidyl ether of 4,4'-bis(4-hydroxybenzoyloxy)-3,3',5,5'-tetramethyl biphenyl (DGE-BHBTMBP), were synthesized based on the recent literatures. Their spectroscopic structure, thermal properties, and phase structrure were investigated by FT IR, NMR, GC-MS, element analysis (EA), differential scanning calorimetry (DSC) and polarized light microscopy (PLM), respectively. Two enanti-isomers of DGEBP were found by GC-MS with the ratio of 2.81: 97.19. The monotropic and polymesomorphous structure of DGE-BHBTMBP was observed by DSC and PLM.Cure behaviors and thermal properties of DGEBP/diaminodiphenylsulfone (DDS) and DGEBP/biphenyl diamine (BPDA) systems were studied and compared each other by means of DSC and PLM. For both systems, the mesogenic phase appeared during the curing processes. It can be also learned that thermal stability of DGEBP/DDS network obtained is higher than that of DGEBP/BPDA.Similarly, Cure behaviors and thermal properties of DGE-BHBTMBP/DDS and DGE-BHBTMBP/diaminephenoxyldiphenylsulfone (BAPS) systems were studied and compared each other by means of DSC and PLM during isothermal and dynamic processes. Only one exothermal peak was observed in both isothermal DSC curves. Nematic phase was observed in the isothermal cure process of DGE-BHBTMBP/DDS system under PLM. Ferroelectric liquid-crystalline (LC) phase was appeared during the isothermal cure of DGE-BHBTMBP/BAPS.In order to investigate thoroughly, the cure kinetics of LCERs with different aromatic diamines was studied using an advanced isoconversional method (AICM). The variations ofthe effective activation energy,E_α, with the extent of conversion, α, of different cure systems was obtained and compared. The reaction process of LCER cure can be deduced by the relationship of E_α vs α, and it can be divided as three different reaction stages. ForDGE-BHBTMBP/DDS system, the maximal effective activation energy E_α,max is 132 kJ/mol and the average effective activation energy E_α,average is 82.08 kJ/mol. While, for DGE-BHBTMBP/BAPS system, the maximal effective activation energy E_α,max is 100 kJ/mol and the average effective activation energy E_α,average is 58.08 kJ/mol. So, it can beconcluded that BAPS is a more reactive curing agent of DGE-BHBTMBP than DDS.What's more, a novel nanocomposite of was prepared by liquid crystalline epoxy (LCE)/ DDS/ organic montmorillonite (MMT). DGE-BHBTMBP was choosed as the matrix material. The curing processes and thermal properties of the novel LCETs obtained were investigated by nonisothermal DSC. The peak temperature increased with an increase in the heating rate for the different amount of organic MMT. The exothermal peaks of the samples containing organic MMT shift toward a lower temperature comparing with the samples without organic MMT in the same curing condition. The glass transition temperature (T_g) of cured composites is increased with the decreasing the heat rates.