Synthesis And Application Of A Liquid Crystalline Epoxy With Biphenol And Aromatic Ester Group

With low shrinkage upon curing, low dielectric constant, great thermal andorientational stability etc, considerable interests have been focused on the synthesis,curing behavior, and mechanical and optical properties of liquid crystalline epoxyresin (LCERs).This article demonstrates two methods to synthesize a series of liquid crystallineepoxy oligomers containing biphenol and aromatic ester group. In the one-stepmethod,3,3’,5,5’-tetramethylbiphenyl-4,4’-diylbis (4-hydroxybenzoate) wassynthesized at first. And then by adjusting the ratio of3,3’,5,5’-tetramethylbiphenyl-4,4’-diylbis (4-hydroxybenzoate) and epichlorohydrin,the liquid crystalline epoxy oligomers were prepared. While in the two-step method,3,3’,5,5’-tetramethylbiphenyl-4,4’-diylbis (4-(oxiran-2-ylmethoxy) benzoate)(DGE-TMBPBHB) was firstly synthesized, then liquid crystalline epoxy oligomerswere prepared by direct reaction between DGE-TMBPBHB and3,3’,5,5’-tetramethylbiphenyl-4,4’-diylbis (4-hydroxybenzoate). The chemicalstructure and number average molecular weight of liquid crystalline epoxy oligomerswere characterized by FT-IR,1H-NMR, epoxy value and gel permeationchromatography (GPC).Chemorheological property of liquid crystalline epoxy thermosets(DGE-TMBPBHB/DGEBA/DDM) was studied by differential scanning calorimetry(DSC) and parallel plate Rheometer (Physica MCR301). It can be concluded fromdynamic DSC experiment that the effective activation energy of the thermosets whichwas detected by using the isoconversional method decreased significantly at the earlystages of curing by addition of DGE-TMBPBHB. The alignment of the oligomerslimits the total number of possible reaction situations to a few situations which occuralong the path of oligomers toward alignment, so that the curing reaction is controlledby diffusion effect at the very beginning stages of curing. An isothermal curing reaction kinetic model was established according to the isothermal DSC data,indicating that the autocatalytic kinetic model can precisely describe the cure kineticsof the curing system. The TTT (phase-time-temperature-transformation) diagram wasplotted based on parallel plate rheological experimental data, and it can be served as atool for process optimization in manufacture. The phenomenon that izod notchedimpact strength reach maximum value by addition of2%(EW) DGE-TMBPBHB wasexplained from the perspective of rheology.Glass fiber-reinforced nylon66was modified with DGE-TMBPBHB. Theinfluence of the concentration of DGE-TMBPBHB on the thermal and mechanicalproperties was studied. The modified system possessed a higher initial decompositiontemperature and lower melting point with respect to glass fiber-reinforced nylon66.The initial decomposition temperature of modified system increased by about10℃byadding7%wt DGE-TMBPBHB. The melting point decreased approximately20℃,showing the improvement of the processing property. Nevertheless, the curveperformance of the modified system decreased due to the poor compatibility betweenDGE-TMBPBHB and glass fiber-reinfroced nylon66.