The Synthesis, Cure And Performances Of The Liquid Crystalline Compound Based On Bisphenol-S And Bisphenol-F Mesogen

Liquid crystalline thermosets (LCTs) can form high-orderly and deep-crosslinked polymeric materials. Compared to ordinary epoxy resins, liquid crystalline epoxy resins (LCER) have capabilities of heat-resistant, a relatively low coefficient of thermal expansion and higher dimensional stability, higher dielectric strengh and lower dielectric dissipation. Therefore, it can be applied in many industrial scopes as adhesive, matrix for advanced composites, electronic packaging material, et al. In this article, some novel LC epoxy resins based on bisphenol-S and bisphenol-F mesogen were synthesized and their curing behaviors, kinetics and reaction mechanism were investigated.A series of novel LC compounds which have different length and different flexible groups aromatic unsaturated or epoxy end group based on bisphenol-S and bisphenol-F mesogen were synthesized from bisphenol-F, bisphenol-S,3-bromopropene,6-brome-1-hexene, allyl 2-hydroxyethyl ether. Their molecular structures and liquid crystalline behaviors and textures were characterized by FTIR, DSC,1H NMR, POM and XRD. The melting point and cleaning point were mensurated.Curing behaviors and curing morphology of these novel LCERs with different curing agents (such as DDM, DDS, DDE, and MeTHPA) and catalyzed activation of hydroxyl group for curing reaction were characterized by DSC, FTIR, TBA, POM, XRD and 1HNMR. Curing process and cure kinetics were investigated by isothermal and non-isothermal DSC. The relationships of the apparent activation energy Ea with the conversionαin the curing process were determined by the isoconversional method (Ozawa's equation, Kissinger equation, Friedman equation) and the overall curing reactions can be described by autocatalytic kinetic model. Some parameters (the even reaction orders m, n, the pre-exponential factor A, the rate constant k) and the activation entropy AS were evaluated. The results show that the hydroxyl group has catalyzed activation and can decrease the Ea for curing system in DSC experiment. The curing reaction molecular mechanism was proposed further.The curing reactions were evaluated used an non-isothermal autocatalytic kinetic model of Sestak-Berggren equation, which there are some deviations for those theoretically calculated with experimental data at higher heating rates and last stages of curing reaction. The diffusion effect in the non-isothermal curing reaction was discussed and a diffusion factor f'(α) was proposed and introduced into Sestak-Berggren equation, which is possible to describe and predict the non-isothermal curing reaction of epoxy resin. The theoretical values agree very well with the experimental data according modified Sestak-Berggren equation.The ordinary epoxy resin were modified with the novel synthetical LCER, The thermal properties, mechanics properties, morphology and curing kinetics of the mixed systems were studied. The effect of the different liquid crystalline contents on curing reaction and the heating rate and curing conversion rate were discussed. The curing process, thermal behavior and morphological structure of these systems were investigated by DSC and torsional braid analysis (TBA) and scanning electron microscope (SEM). The results show that the glass transfer temperature Tg and the mechanical properties increases with adding of LCER and has a best content.So these studied results will impel the development of LCTs fields and provide instruction to practical production.