Toughening Modification Of Bisphenol A Cyanate Ester And Development Of Styrofoam Film

The rapid development of the aerospace industry has put forward higher requirements for the materials.Some special parts(such as radomes)require materials with excellent mechanical strength and high-temperature resistance,as well as excellent wave transmission property.The dielectric property is one of the important parameters for evaluating the properties of wave-transmitting materials.In the manufacture of aircraft,foam adhesive is an important connecting material,which is widely used in the connection between honeycombs,between honeycomb and beams,skins,etc.Therefore,the development of foam adhesive with excellent dielectric properties is of great significance.Cyanate esters exhibit excellent adhesion,heat resistance,and processability.The cured product has good mechanical properties,low shrinkage and low water absorption.In addition,the highly symmetrical triazine ring structure and extremely low molecular polarity make it an ideal matrix material for the preparation of foam adhesive with excellent dielectric properties.However,its cured product is very brittle and needs to be toughened during use.In this work,the bisphenol A cyanate(BADCy)is first toughened,and a foam film adhesive is developed based on the toughened BADCy.The main research contents are as follows:1.First,BADCy was toughened with polysulfone to prepare a semi-solid cyanate prepolymer at room temperature,and the curing behavior of the prepolymer and the properties of the cured prepolymer were studied.The results show that the conversion rate of cyanate monomer in the cyanate ester prepolymer is 39.70%,and the curing temperature is positively related to the curing degree.When the curing temperature is 140℃,the curing degree is less than 50%.The curing degree can reach more than 90% when the curing temperature exceeds 170℃.Polysulfone can significantly improve the toughness of the cured prepolymer,but the polysulfone toughened system of this project can not form a tough fracture mode.The curing temperature has a certain effect on the toughening effect.The curing temperature has little effect on the properties of tensile,bending and impact when the curing degree exceeds 90%.In addition,the cured prepolymer shows good heat resistance and heat aging resistance.Although the addition of polysulfone reduced the dielectric properties of the modified cyanate ester system,the modified system still exhibits excellent dielectric properties.The dynamic DSC method was used to study the curing reaction of cyanate ester prepolymer.The amount of catalyst,heating rate and glass transition of polysulfone could affect the reaction characteristics of the prepolymer.The addition of the catalyst reduced the apparent activation energy and increased the pre-exponential factor.And the curing reaction occurred easier,more violently and faster.The apparent activation energy of the prepolymer-catalyst system ranges from 70.43 to 79.42 kJ/mol and the catalytic curing reaction of the prepolymer is generally close to the first-order reaction,indicating that the catalyst will not change the reaction mechanism.The curing process of the prepolymer-catalyst system with 1% and 7% catalyst addition was 195℃/3 h and 123℃/3 h,respectively.2.The core-shell rubber particles and catalyst were added to the prepolymer,and the toughening effect of core-shell rubber particles was studied.The results show that the addition of core-shell rubber particles can further improve the toughness of the prepolymer.Combined with the test results of peel strength and shear strength,it was determined that the optimal dosage of catalyst and rubber particles were 3% and 15-17.5%,respectively,and the optimal curing temperature was 180℃.3.The foam film adhesive was prepared by adding the blowing agent,filler and other components to the cyanate prepolymer containing core-shell rubber particles and catalyst,and the performance of the adhesive was studied.The results show that the initial density,pipe shear strength,expansion rate,flowability,volatile content,compressive strength,honeycomb tensile strength,dielectric properties,and resistance to media,salt spray,boiling,and humid heat of the foam adhesive are all meet the technical requirements of the project.