Preparation And Properties Of High Toughness Benzoxazine Resin Based On Aldehyde Functionalization

As a new thermosetting material,benzoxazine resin(BOZ)has many advantages,such as flexible molecular design,zero shrinkage on curing,etc.It has been widely used in many fields,such as aerospace,electronics and appliances,train and automobile,medicine and chemical industry and so on.Although benzoxazine resin has many advantages,its brittleness and high curing temperature limit its further application in the field of aerospace.Therefore,the toughening modification of benzoxazine resin has important theoretical significance and practical value.In this thesis,benzoxazine was toughened by copolymerization of amine compounds and blending of polyhexahydrotriazine.Using aldehyde functionalized benzoxazine(PHB-a)as raw material,5-aminoindole was copolymerized with PHB-a to prepare high toughness benzoxazine cured product by using the special reaction between indole and aldehyde group.Based on the difference of curing temperature between polyhexahydrotriazine and benzoxazine,Benzoxazine/polyhexahydrotriazine interpenetrating network polymer was prepared by controllable sequential curing to realize the toughening of benzoxazine.Its curing behavior,thermal stability,mechanical properties and toughening mechanism were studied by structure and performance characterization.The main contents and conclusions of this thesis are as follows:1.Aldehyde functionalized benzoxazine monomer(PHB-a)was synthesized by one pot method with formaldehyde,aniline and p-hydroxybenzaldehyde as raw materials.Different proportions of benzoxazine/5-aminoindole prepolymer(PHB-a-indole)were synthesized by reacting PHB-a with 5-aminoindole at the molar ratio of 1:1,1:2 and 2:1,respectively.It is found that the toughening mechanism of phb-a-indole is the copolymerization of benzoxazine and 5-aminoindole,and a special reaction will occur between aldehyde and indole groups to form a special rose indole structure.Pure benzoxazine resin poly(PHB-a)is brittle and difficult to form film.However,toughness of the cured product after copolymerization with5-aminoindole has been significantly improved.Its tensile modulus is 3.05 GPa,elongation at break is about 2.54%,and breaking strength is 72.35 MPa.The thermal stability of modified benzoxazine(PHB-a-indole)decreased,and the residual carbon rate at 800?was 63.6%,indicating that it still maintained good thermal stability.During the curing process,the modified resin can form a self-supporting film at 120?,while the benzoxazine resin is still viscous liquid Different from poly(PHB-a)with smooth section,the scanning electron microscope of the modified cured product showed a ridge shape.2.Using formaldehyde,PHB-a and 1,3-bis(4'aminophenoxy)benzene as raw materials,aldehyde based functional polybenzoxazine(PHB-a)and polyhexahydrotriazine(PHT)interpenetrating polymer networks with different molar ratios were designed and prepared,and their structure,mechanics,thermal properties and degradability were studied.Infrared spectroscopy and ¹³C NMR show that there is an intermolecular hydrogen bond between poly(PHB-a)and PHT,forming PHB-a/PHT interpenetrating polymer network,which enhances the compatibility of the two polymers.When the molar ratio of PHB-a to PHT is 2.4,the modified polymer shows better mechanical properties,with elongation at break of 9.36%,tensile modulus of 118.56 MPa and breaking strength of 114.49 MPa.The results of dynamic thermomechanical analysis(DMA)showed that the glass transition temperature(Tg)reached211?,and there is no phase separation in the modified IPN system.At the same time,poly(PHB-a/PHT)IPNs has excellent degradation performance.It is expected to be used as composite matrix resin to solve the problem of difficult recovery of high-performance thermosetting materials in the future.