| The side chain siloxane liquid crystalline polymers has the characteristics of low glass transition temperature(Tg),strong flexibility of the main chain,low viscosity,good heat resistance and high mechanical strength,ect,so it is widely used in such as adhesives,protective coatings and bio-phases capacitive materials fields.Epoxy resin has the characteristics of good processing properties,high adhesion,small shrinkage,good stability,excellent electrical insulation properties,high strength,etc,and thus it has been widely used in the fields of machinery,electronics,aerospace,paint,bonding,etc.But the cured product of ordinary epoxy resin is relatively brittle,which limits its application development.Side chain siloxane liquid crystalline epoxy resin combines the flexibility and compatibility of siloxane,the order of liquid crystalline and the crosslinked network of epoxy resin,it shows better dimensional stability,better heat resistance and better impact resistance compared with ordinary epoxy resin,and it also has special properties in mechanical,thermal,electrical,optical,etc.It can be said that it is a new functional material with great potential.Four liquid crystal monomers were designed and synthesized in this thesis:4ethoxybenzoic acid-4’-undecenoic acid biphenyl phenolate(11YL),4-(((4-(11-carbon-10-)Dienoyloxy)phenyl)imino)methyl)phenyl 4-ethoxybenzoate(11XF),4-allyloxybenzoic acid cholesteryl(M1)and 4’-((4-(Ally loxy)benzoyl)oxy)-[1,1’-biphenyl]-4-yl(4-cyanophenyl)adipate(XLJCN).The monomer 11LY and AMO were graft copolymerized onto PMHS in different proportions to obtain P series liquid crystalline epoxy polymer;the monomer 11XF and AMO were graft copolymerized onto PMHS in different proportions to obtain P’ series liquid crystalline epoxy polymer;the monomer M1,XLJCN and AMO were graft copolymerized onto PMHS in different proportions to obtain L series liquid crystalline epoxy polymer.In this paper,the molecular structure was characterized by Fourier transform infrared(FTIR)and nuclear magnetic resonance(1H-NMR)spectrometer.The phase behaviors and thermal properties of the monomers and the liquid crystalline epoxy polymers were tested by differential scanning calorimetry(DSC)and polarizing microscope with heating table(POM).And the thermal stability of the liquid crystalline epoxy polymers were investigated by thermal stability tester(TGA),and the liquid crystalline phase was verified by X-ray analysis(WAXD).The experimental results showed that the four liquid crystalline monomers have a wide liquid crystalline phase interval,in which the liquid crystalline monomer M1 is cholesteric liquid crystalline,the liquid crystalline phase range was from 113.7 ℃ to 245.8 ℃,and the liquid crystalline monomers 11LY,11XF and XLJCN are all nematic.The phase liquid crystalline monomers had a liquid crystalline phase range of 92.8℃-212.1℃,88.1℃-242.9℃ and 132.5℃-261.1℃ respectively;P series and P’ series liquid crystalline epoxy polymers exhibited nematic phase,L series liquid crystalline epoxy polymer was cholesteric phase,and the glass transition temperature(Tg),liquid crystalline clearing point temperature(Ti),and liquid crystalline phase interval temperature(△T)of the three series of liquid crystalline epoxy polymers were all showed a decreasing trend,and it was related to the content of AMO’s(epoxy group)increasing in content.The TGA test showed that all three series of polymers have good thermal stability.Finally,the thermal curing behavior and cured properties of P series and L series liquid crystalline epoxy polymers were studied.DDM was used as the curing agent.According to the dynamic curing results,the exothermic peak temperature(Tp)of the curing system shifted to the low temperature as the epoxy group content increased;As the curing temperature increases,the Tp of the curing system moves toward the high temperature.The isothermal curing indicates that the content of the epoxy group was the main influence factor of the curing reaction rate.The curing process was observed by POM,it can be seen that whether the P series liquid crystalline epoxy polymer/DDM system or the L series liquid crystalline epoxy polymer/DDM system produced a color liquid crystalline phase during the curing process,the liquid crystalline phase of the L series polymer cured system was fixed in the crosslinked network by a crosslinking reaction,while the P series did not.The liquid crystalline phase analysis of the cured product R series and R’ series epoxy resin was carried out by using WAXD,and it was found that both the R series and the R’ series epoxy resin retained the original liquid crystalline phase.The DSC test of R’ series epoxy resin showed that the T,of the corresponding epoxy resin showed an increasing trend with the increase of the epoxy group content in the curing system.In addition,thermogravimetric analysis(TGA)was used to conduct thermal weight loss analysis of R series and R’ series epoxy resins.and it was found that the higher the degree of crosslinking,the better the thermal stability. |
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