Study On The Synthesis And Performance Of A New Type Of Epoxy Resin

The epoxy resin are widely used in adhesives,coatings,electronic packaging,composite materials and other fields for its excellent bonding properties,thermal stability and chemical resistance,high mechanical strength,easy processing and forming.However,due to the high crosslink density,the cured epoxy resins are intrinsically brittle with poor toughness,fatigue durability and impact resistance.The rigid skeleton structure of epoxy resin can be changed to a more flexible one by chemical modification,and the crosslinking density of the cured epoxy resin can be reduced,thereby the toughness of the epoxy resin will improve.In this paper,a new type of flexible epoxy resin was synthesized by introducing ether bond or polyurethane flexible chain in the main chain and blended with bisphenol A type epoxy resin(DGEBA)respectively.The mechanical properties,thermal stability and bonding properties of the blends were studied.Firstly,the 4,4'-dihydroxydiphenyl ether epoxy resin with ether bond structure was synthesized by the two-step method.The effects of synthesis conditions on epoxy value and viscosity were investigated.The optimum synthesis conditions were determined as follows: The ratio of 4,4'-dihydroxydiphenyl ether to epichlorohydrin was 1:12,the etherification temperature and time were 105? and5 h,the closed-loop temperature was 75?,the dropping rate of Na OH solution was 4.5 g / 10 min.The dropping rate of Na OH solution was 4.5 g/10 min,and finally a creamy solid epoxy resin was obtained.The epoxy value was 0.602 and the viscosity at 85 ? was 22.8 cp.The DHPOP structure was characterized by the Fourier transform infrared spectroscopy(FT-IR)and1H-NMR.The purity was analyzed by the gel chromatography(GPC)and differential scanning calorimetry(DSC).Then,p-hydroxymethylphenylglycidyl ether(MPEP)was synthesized by one-step reaction,and the reaction was carried out with four kinds ofpolyurethane prepolymers to prepare different types of terminal epoxy polyurethanes,including two polytetrahydrofuran epoxy-terminated polyurethanes(M1EPU,M2EPU)and two polypropylene glycol type epoxy-terminated polyurethanes(210EPU,220EPU).The synthesis conditions of polyurethane prepolymer and terminal epoxy polyurethane were determined by FT-IR method.The curing kinetics of DDM cured DHPOP and DGEBA was studied by non-isothermal DSC method.The curing characteristics temperature of the curing system was determined.The Kissinger,Crane and Arrhenius equations were used to calculate the apparent activation energy,reaction order,curing rate constant of the curing reaction and to confirm the kinetics equation of curing reaction.The rheological analysis found that the DHPOP/DDM's processing window are wider than DGEBA/DDM's.The result of mechanical properties was found that the tensile strength of DGEBA/DHPOP blended resin was almost constant,and the bending strength and bending modulus decreased,however the impact strength greatly improved.The pure DHPOP system was 22.5k J/m2,which was increased by 1.5 times compared with the pure DGEBA system.The glass transition temperature and heat resistance of the system remained basically unchanged.The scanning electron microscopy(SEM)showed that with the addition of DHPOP the fracture form of DGEBA/DHPOP blended resin changed from the brittle fracture to ductile fracture.The introduction of epoxy-terminated polyurethanes made a greater improvement in the toughness of the blends.The bonding strength of M2 EPU and DGEBA blends increased firstly and then decreased with the increasing content of M2 EPU.The shear strength at room temperature and the 90o peel strength were increased by 22.1% and348.9% to 37.89 MPa and 10.37 k N/m,respectively.The elongation at break increased with the increasing content of M2 EPU,and reached 153.8% at the time of 80 phr.The elongation at break increased with the,and reached the maximum which was 153.79%increased by 35.1 times.The comprehensive performance of polytetrahydrofuran typeepoxy-terminated polyurethanes was better than that of polypropylene glycol type epoxy-terminated polyurethanes.When the quantity of epoxy-terminated polyurethanes were fixed,once the molecular weight of the polyurethane prepolymer increased,the90o peel strength,elongation at break and thermal stability would improve,but the shear strength would decline.