Study On Epoxy Resin Modified With Mesogen-jacketed Liquid Crystalline Copolymers P(DBVT-co-GM)

Epoxy resins have been widely used in adhesives, coating materials, electronics andaerospace industries owing to their high strength and modulus, good chemical resistance,dimensional stability and adhesive properties. However, their poor fracture resistance,inherit brittleness, and poor thermal resistance limit their applications. Therefore, thisdrives research on modified epoxy resins. In this work, we have synthesized a new kind ofthermotropic liquid copolymer P(DBVT-co-GM) using the method of free radicalpolymerization and modified epoxy resin by chemical reaction methods. The curingkinetics of P(DBVT-co-GM)/DGEBA systems were investigated by non-isothermal DSC.In addition, the influence of P(DBVT-co-GM) contents on the mechanical property, thermalbehavior and dynamic mechanical property of P(DBVT-co-GM)/DGEBA composites werestudied. The main works as follows:The P(DBVT-co-GM) copolymers with different contents of epoxy were synthesized.The chemical structures of P(DBVT-co-GM) copolymers were confirmed by GPC, FTIR,NMR and epoxy titration method. The results indicated that molecular weights of P1-P5were about100,000and PDI were about1.8; the copolymers had the functional groups ofthe monomers and all the monomers had copolymerized; the epoxy groups of P1-P5were0.00321mol/100g,0.00532mol/100g,0.00878mol/100g,0.01087mol/100g,0.01315mol/100g respectively. Besides, the thermal property and liquid crystalline property ofP1-P5copolymers were also studied. The TGA showed that the temperature of5%weightloss of all copolymers was above320℃and the corresponding temperature of maximumdecomposition rate was above400℃, indicating that the P1-P5copolymers had goodthermal stability. The POM found that P1and P2had the birefringence phenomenon whenthe temperature was about100℃and95℃respectively, while the the P3, P4and P5had nothe birefringence phenomenon all the time. The1D WAXD indicated that P1and P2hadliquid crystalline when the temperature reached about90℃and the liquid crystallineexisted when continue heating or cooling, while P3, P4and P5always had no liquidcrystalline. So we chose P2, which had the liquid crystalline and had more content of epoxygroup, as the modifier of epoxy resin.The curing kinetics of P(DBVT-co-GM)/DGEBA systems were investigated bynon-isothermal DSC. The results indicated that the apparent activation energy decreasedwith the addition of P(DBVT-co-GM), indicating that the chemical reaction method ofepoxy resin could decrease the apparent activation energy, maintained the A and the reaction order values were close to1, which meant that the reaction was close to first-orderreaction. In addition, based on the data of DSC, the the optimized curing process ofP(DBVT-co-GM)/DGEBA systems was80℃/2h→100℃/2h→120℃/1.5h, which wasconfirmed by variable temperature FTIR.P(DBVT-co-GM)[P2]/DGEBA systems were cured at80℃/2h→100℃/2h→120℃/1.5h and called P(DBVT-co-GM)[P2]/DGEBA composites. The mechanical property, SEMmicrographs of the impact and tensile fracture surfaces, liquid crystalline, thermal propertyand dynamic thermal mechanical property of P(DBVT-co-GM)[P2]/DGEBA compositeswere investigated. The results suggested that①the impact strength, tensile strength andelongation at break of1phr-5phr P(DBVT-co-GM)[P2]/DGEBA composites initiallyincreased and then decreased with the increasing of P(DBVT-co-GM)[P2] content, buthigher than that of neat epoxy all the time. When the P(DBVT-co-GM)[P2] content was3phr, the impact strength reached the maximum25.11kJ/m2, which was two times than thatof epoxy resin. Meanwhile, the tensile strength and elongation at break from the tensile testreached the maximum, increased by67%and176%than that of neat epoxy respectively.②compared with the neat epoxy resin, the SEM micrographs of the impact fracturesurfaces have more crack branching and the tensile fracture surfaces were rather rough,showing obvious ductile fracture morphology.③P(DBVT-co-GM)[P2]/DGEBA compositesalways have liquid crystalline phase investigated by1D WAXD.④the temperature ofinitial decomposition and maximum decomposition rate were higher than that of neat epoxystudied by TGA.⑤the glass temperature of P(DBVT-co-GM)[P2]/DGEBA compositeswas slightly higher than that of neat epoxy investigated by DMA.