Preparation Of Imidazole Derivatives As Latent Curing Agents For Epoxy And Their Application In Electronic Encapsulation Adhesives

2-ethy-4-methylimidazole(EMI)are often used for epoxy crosslinking due to its high curing reactivity and curing efficiency.However,the shelf life of one-pot composition of epoxy with EMI is too short,and its corresponding curing products are too fragile and not heat-resistant enough.The polyurethane pre-polymer was introduced to EMI through substation reaction,and the rigid group was introduced followed by complexation reaction.Finally,the two kinds of functional latent curing agents have been got,and they were applied in electric encapsulation adhesives by compositing with epoxy resin,diluent,and fillers.Three kinds of –NCO terminated polyurethane pre-polymer were prepared,and then three kinds of 1-substituted imidazole derivatives M-EMI were achived through the reaction between polyurethane pre-polymer and the N-H on the ring of imidazole.And their structure were comfirmed by FT-IR.The curing behavior and storage stability of E-51/M-EMI were researched by viscosity test,DSC and FT-IR.And the adhesive properties,mechanical strength,thermal stability and other performance of E-51/M-EMI curing products were also analyzed.The results indicated that the active H has been replaced by polyurethane pre-polymer and that the shelf life,the curing activation energy,and the tensile shear strength of E-51/M1-EMI were 75 days,78.15 kJ/mol,and 20 MPa,respectively.In addition,the impact strength and the Tg of E-51/M3-EMI curing products were 27.1 MPa and 94.5 ?,and the fracture form was ductile fracture.Five kinds of imidazole organic acid salt MEMI-A were prepared though reaction between 1-substituted imidazole and organic acid,and their structure were characterized by FT-IR.The curing behavior and storage stability of E-51/MEMI-A were researched by viscosity test and DSC.And the adhesive properties,mechanical strength,thermal stability and other performance of E-51/ MEMI-A curing products were also analyzed.Our research turned out that the curing reactivity has been weakened by substituted reaction on 1 N and complex reaction on 3 N.And the time of losting liquidity,the curing activation energy,the tensile shear strength on steel plates of E-51/MEMI-A3 were 160 days,89.76 kJ/mol,and 20 MPa,respectively.Moreover,the HDT of E-51/MEMI-A increased by 1.2-12.6 ? compared with E-51/EMI.And the water absorption rate of those curing products were all less than 0.7%.The one-component epoxy electric encapsulation adhesive has been prepared through compositing that two kinds of functional latent curing agents with E-51 epoxy resin,active diluent,filler,pigment,anti-settling agent,and defoaming agent.The tensile shear strength of the electric encapsulation adhesives on copper plate were greater than 15 MPa,and the tensile strength retention rate were over than 90% after water absorption for 7 days.Futhermore,the volume resistivity values were all 1013 magnitude and the heat deformation temperature were all above 120? while the water absorption rate at room temperature were less than 0.1%.