Study On Integrated Structure And Function Of Modified Cyanate Ester Resin With High Temperature Resistance And Its Adhesive Film

As a structure-function component of aircraft and missiles,radome protects radar antenna against harsh environmental conditions.It must have wave transmitting function and bearing a certain structural strength.Therefore,both resin and adhesive are required to have good adhesion properties,dielectric properties,process performance and heat resistance to meet the manufacturing and using requirements of heat-resistant radomes.Cyanate ester(CE)is a new type of high-performance functional resin matrix.It has very low polarity and excellent dielectric properties,and maintains low and stable dielectric constant and dielectric loss tangent in a wide temperature range and frequency range(50Hz～10GHz),which outshines polyimide(PI),bismaleimide(BMI)and epoxy resin(EP).By virtue of its excellent dielectric properties,heat resistance and bonding properties,CE has become the optimal material for the production of stealth structure and radome,with very broad application prospects in aerospace,electronic packaging,insulation materials and other fields.It has become a resin matrix with huge social and economic benefits in the 21st century,and is called "the most competitive high-performance structural and functional resin of the 21st century".However,just like other thermosetting resins,CE resin has shortcomings such as fragile cured substance,which have limited its application.In view of this,the following aspects of the modification and adhesives of CE resin were studied.(1)By using diamine to introduce a flexible group,we used aromatic:dianhydride to synthesize wholly aromatic ethynyl polyimide(Si)with a isomeric structure.By controlling molecular weight and molecular weight distribution and introducing flexible ether bond and isomeric structure,we rendered the prepolymer good solubility,dispersity in CE resin system,and good heat resistance and high-temperature mechanical strength after curing.S1 resin had a glass transition temperature(Tg)of 374.2℃.Its 5%thermal decomposition temperature Td5 was 508℃,10%thermal decomposition temperature Td10 was 553℃,and carbon residue rate at 800℃ was 68%.This proved that S1 resin we synthesized had high temperature resistance and thermal stability,as well as good solubility.By adopting synthesized polyimide(S1)-modified BPA CE and through infrared and variable temperature dynamic mechanical analysis(DMA),we studied the curing mechanism and kinetics of S1/BCE resin system,explored its interpenetrating network formation mechanism,analyzed the dynamic mechanical behaviors(including loss tangent and storage modulus)of the cured samples,and studied the relationship between the structure of the synthesized ethynyl polyimide and BPA CE and their mechanical properties,heat resistance and other properties.In order to study the impact of the curing sequence of ethynyl polyimide and BPA CE on the properties of the resin system,we added copper naphthenate catalyst to the ethynyl polyimide/CE system(CS103)with a mass ratio of 10:3,and then studied the heat resistance and processability of the CE system catalyzed by polyimide-modified catalyst.(2)Modified CE resin was prepared by using polymethyl methacrylate(PMMA)@polybutadiene(PB)core-shell structure particles toughened BPA CE(BCE)resin.The mechanical properties,heat resistance,microstructure,rheological properties and dielectric properties of the modified CE resin were tested by using tensile machine,DMA and TG-DTA,SEM and TEM,DHR and dielectric tester.When the amount of core-sherll rubber was 6%,good toughening eeffect could be achieved.Core-shell rubber had good dispersity in BCE resin matrix,and its addition didn’t reduce the heat resistance of the resin and basically didn’t affect the rheological properties and dielectric properties of BCE resin.PMMA@PB/BCE resin system has excellent performance,can be used as prepreg matrix resin,and is suitable for the production of aerospace low-dielectric composite materials.(3)MWCNTs were treated with a mixture of concentrated sulfuric acid and concentrated-nitric acid,and the acidized MWCNTs were used to modify CE resin system.The results showed the oxygen-containing functional groups on the surface of the treated MWCNTs are mainly-COOH,C-OH,-CO,-C-OP,etc.The increase of polarity made MWCNTs well dispersed in resin matrix.The mechanical properties data showed that when the addition amount of the treated MWCNTs was 0.6 wt%,the system’s KIC and GIC values were 1.39 Pa-m0.5 and 364 J/m2 respectively,and its fracture toughness increased by 45.7%and 76.0%respectively.After the treated MWCNTs were added,the Tg of the cured resin was lower than that of the original system,but the decrease was not significant.The addition of MWCNTs increased the dielectric constant and dielectric loss of CE resin.When the addition amount was 0.6 wt%,the dielectric constant and dielectric loss underwent abrupt changes;when the addition amount was 0.8 wt%,the dielectric constant and dielectric loss at 1 GHz were 5.1 and 0.032 respectively.Such CE resin with high dielectric constant and dielectric loss is no longer suitable for the production of stealth wave-transrmitting materials such as radome,but has wide application prospects in the fields such as printed-circuit board,electrical engineering,micro-electromechanics and bioengineering.(4)Phenolic aldehyde cyanate ester(NCE)resin has the best heat resistance among CE resins.In order to farther break through the technical bottleneck of heat resistance of NCE resin,bisphthalonitrile(BPh)resin with better heat resistance was introduced as a heat resistance modifier which further enhanced the heat resistance of NCE and positively affected the mechanics of the modified resin system.As pure bisphthalonitrile resin is difficult to be cured,allyl BPA/bismaleimide resin prepolymer was adopted for catalyzing.The DSC peak temperature of the modified BPh resin was 250.6℃,and such a curing temperature could be coordinated with the curing temperature range of CE resins.As for the NCE resin modified with BPh resin,the 90%carbon residue rate increased significantly from 420℃ to 480℃ and finally to 550℃.The tensile properties and bending properties changed little,while the impact strength and fracture toughness increased slightly.(5)Modified high temperature-resistant CE adhesive film was prepared by using the compound of NCE resin and BPA CE resin as main resins,BPh resin as the heat-resistant reinforcing agent,and thermoplastic resin or core-shell rubber as the toughening agent.The adhesive film could be cured below 260℃.It owned good toughness(roller peel strength:over 20N-mm/mm),heat resistance(glass transition temperature:360℃,5%thermal weight loss temperature:500℃),and bonding properties(shear strength at room temperature:16.10MPa,shear strength at 350℃:10.36 MPa).The adhesive film had satisfactory compatibility with composites,so could be used for their bonding.