Synthesis And Application Of 5-hydroxymethyl Resorcinol Diglycidyl Ether

The epoxy resin is an important thermosetting resin,which is widely used in many fields,for example,as adhesives for aerospace,as electronic packaging materials,as coatings and so on.However,due to the high crosslinking density after curing,it has low impact strength,poor crack propagation resistance and high brittleness,which limits its application in some special fields.Therefore,in the past few decades,the toughening modification of epoxy resin has been a focus of researchers.At present,there are many toughening modification methods for epoxy resin,including thermoplastic resin toughening,liquid rubber toughening and nanoparticles toughening.In this study,firstly,the 5-aldehyde resorcinol diglycidyl ether is synthesized.Then,the aldehyde group in its structure is reduced and the 5-hydroxymethyl resorcinol diglycidyl ether is synthesized.Finally,the epoxy-terminated polyurethane is synthesized by capping isocyanate-terminated polyurethane prepolymer with 5-hydroxymethyl resorcinol diglycidyl ether.By blending epoxy-terminated polyurethane with soft segment and the common bisphenol A epoxy resin（DGEBA）to improve the toughness of epoxy resin curing system.The bonding properties,mechanical properties and thermal properties of a series of blending systems are analyzed and discussed.Firstly,the 5-aldehyde resorcinol diglycidyl ether（ARDGE）is synthesized by ring-opening etherification and alkali-adding ring-closing two-step method.The optimum synthesis conditions are determined as follows:the benzyltriethylammonium chloride is selected as phase transfer catalyst in the etherification stage,the amount of catalyst is 2%of 3,5-dihydroxybenzaldehyde molar number,etherification temperature is 95℃,etherification time is 6 h,the dosage ratio of 3,5-dihydroxybenzaldehyde to epichlorohydrin is 1:8,NaOH solid particles are selected to be added in the closed-loop stage,the dosage of NaOH is 2.4 times the molar number of DHBA.It is added in batches at 33°C.After the addition,the mixture is stirred at 33°C for 2 h,then heated to75℃and continued to react for 2 h.The epoxy value of the final product is 0.79 and the yield is 95%.Then,the ARDGE is reduced to synthesize the target product5-hydroxymethyl resorcinol diglycidyl ether（HMRDGE）.The reduction process of ARDGE is tracked by thin layer chromatography（TLC）to optimize the dosage of NaBH₄.The results show that the optimal dosage of NaBH₄ is 4 times the molar number of ARDGE.The structures of ARDGE and HMRDGE are determined by Fourier transform infrared spectroscopy（FT-IR）,nuclear magnetic resonance hydrogen spectrum（¹H NMR）and nuclear magnetic resonance carbon spectrum(¹³C NMR).The molecular weight and purity of HMRDGE and ARDGE are investigated by gel permeation chromatography（GPC）and high performance liquid chromatography（HPLC）.The epoxy-terminated polyurethanes（ETPU1000 and ETPU2000）with different molecular weights are prepared by reacting HMRDGE with two kinds of polyurethane prepolymers（they have different chain lengths）.The synthesis reaction time is determined by FT-IR.The curing kinetics of 4,4-diaminodiphenylmethane（DDM）curing DGEBA/ETPU1000 blends with the ETPU1000 addition amount of 50 wt%（50wt%ETPU1000+DGEBA/DDM）and DGEBA/ETPU2000 blends with the ETPU2000addition amount of 50 wt%（50 wt%ETPU2000+DGEBA/DDM）are studied by non-isothermal DSC method,the curing temperature,apparent activation energy,reaction order,reaction rate constant and curing kinetic equation of the curing system are determined.The adhesion properties of ETPU1000 and ETPU2000 modified epoxy resin systems are studied.The results show that when the addition amount of ETPU1000 and ETPU2000 is 50 wt%of their mixtures,the shear strength of the two mixtures at room temperature reaches the maximum value which is 42.76 MPa and 37.74 MPa respectively,which is 49.15%and 31.64%higher than that of pure epoxy resin curing system.When the addition amount of ETPU1000 and ETPU2000 is 25 wt%of their mixtures,comparing with the pure epoxy resin curing system,the shear strength at 70℃has increased by 39.03%and 23.37%respectively,the shear strength at 100℃has increased by 2.62%and 1.56%respectively,and the shear strength at 120°C has increased by 13.57%and 7.65%respectively.The 90°peel strength at room temperature of both mixed systems increases with the increase of the content of epoxy-terminated polyurethane.The mechanical properties of the modified system are investigated.It is found that the impact strength and elongation at break of epoxy resin are improved to different degrees by the addition of ETPU1000 and ETPU2000.The toughening effect of ETPU2000 on epoxy resin is more obvious.When the addition amount of epoxy-terminated polyurethane in the two modified epoxy resin systems is 25 wt%,the tensile strength of the each blend reaches the maximum value.The thermal properties of the two kinds of mixed systems are studied by means of DSC,DMA and TGA.The study shows that the glass transition temperature（T_g）,crosslinking density and thermal stability of the system decrease to different degrees by mixing epoxy-terminated polyurethane into DGEBA.The fracture surface morphology of DGEBA/ETPU2000 blending system is studied by scanning electron microscopy（SEM）.It is found that with the addition of epoxy-terminated polyurethane,the fracture surface transforms brittle fracture into ductile fracture.The greater the amount of ETPU2000 added,the more pronounced the ductile fracture characteristics of the fracture surface is.