Preparation And Properties Of Maleimide Functional Benzoxazine Resins

As a new type of phenolic resin,benzoxazine resin retains the advantages of traditional phenolic resins in terms of thermodynamic properties and flame retardancy.Besides,benzoxazine resin overcomes some shortcomings,such as very flexible designability of benzoxazine molecules,nearing to zero shrinkage during the curing process,and no need to add catalysts for its polymerization.Therefore,benzoxazine resin is favored by many scientific researchers,and it also has great potential to replace traditional thermosetting resin materials,such as phenolic resin and epoxy resin in many application fields.With the fast development of high-end technology fields,such as aerospace,electronics,5G communications,many particular perfomances of materials have been highly disired durning applications,such as high heat resistance,excellent flame retardancy and low dielectric constants.Commercialized benzoxazine resins are difficult to meet the material performance requirements of high-end fields at the current stage.In this paper,by designing new molecular structures,the maleimide group,furan ring and alkynyl group with crosslinkable functions have been introduced into the benzoxazine molecules to synthesize a series of new maleimide functionalized benzoxazines with excellent properties.In addition,structural characterization and performance testing of newly synthesized benzoxazine monomers and their corresponding polybenzoxazines were performed using various characterization methods.Moreover the curing mechanism of benzoxazine was also studied.The main contents of this article are as follows:?1?Using maleic anhydride and 4-aminophenol to synthesize p-maleimide phenol,and then react it with paraformaldehyde and 2-furanmethylamine to synthesize a new type AB benzoxazine monomer?HPMI-fa?.Polybenzoxazine was obtained by heating through ring-opening polymerization.The structure of benzoxazine was characterized by ¹H NMR,¹³C NMR,2D nuclear magnetic resonance?HMQC and NOSEY?,and Fourier transform infrared spectroscopy?FT-IR?.Differential scanning calorimetry?DSC?and in-situ FT-IR,thermal weight loss analysis?TGA?,and micro-burn calorimetry?MCC?were used to study the thermal curing process of benzoxazine monomers and the thermosets after curing.The dynamic mechanical analysis?DMA?was used to study its glass transition behaviors.The above analysis explored its various aggregation mechanisms.The T_g of polybenzoxazine obtained by direct thermal activation polymerization was 296°C,and Td₅ and Td₁₀ were 350°C and 403°C,respectively.Additionally,it also showed self-extinguishing and non-flammability,with HRC of33.4Jg^-1K^-1 and THR of 7.0KJg^-1.?2?HPMI was synthesized by using maleic anhydride and 2-aminophenol.HPMI is reacted with paraformaldehyde and aniline to synthesize ortho-maleimide benzoxazine monomer?oHPMI-a?.Polybenzoxazine was obtained by heating through ring-opening polymerization.The structure of benzoxazine was characterized by nuclear magnetic hydrogen spectroscopy?¹H NMR?,nuclear magnetic carbon spectroscopy(¹³C NMR)and Fourier transform infrared spectroscopy?FT-IR?,and the solidification temperature was characterized by in-situ DSC.According to the calculation,the activation energy value of oHPMI-a is obtained.The activation energy value calculated by Kissinger method is78.78KJ/mol,and the activation energy value calculated by Ozawa method is 82.62KJ/mol.The activation energy value calculated using the Starink method is 72.43 KJ/mol.In addition,by studying the kinetics of oHPMI-a,it was concluded that the polymerization mechanism of oHPMI-a follows the autocatalytic reaction mechanism,and it was verified.?3?Using maleic anhydride and 2-aminophenol to synthesize HPMI,and then synthesize it with paraformaldehyde,4-chloroaniline,4-methylaniline and 3-ethynylaniline to synthesize three novel ortho-benzoxazines monomers?oHPMI-t,oHPMI-ac and oHPMI-ch?.Polybenzoxazines was obtained by heating through ring-opening polymerization.Structural characterization of benzoxazine using nuclear magnetic hydrogen spectroscopy?¹H NMR?,nuclear magnetic carbon spectroscopy(¹³C NMR)and Fourier transform infrared spectroscopy?FT-IR?,using differential scanning calorimeter?DSC?and in-situ FT-IR,Thermal Weight Loss Analysis?TGA?,and Micro Combustion Calorimetry?MCC?respectively studied the thermal curing process of benzoxazine monomer and the thermal stability and flame retardant properties of thermosetting resin materials after curing.In addition,the glass transition temperature and elastic modulus of poly?oHPMI-ac?were studied using static mechanical analysis?TMA?and dynamic mechanical analysis?DMA?,and the dielectric constant and dielectric loss of the material were tested using a dielectric constant tester.The performance of poly?oHPMI-ac?is extremely excellent.The Td₅ value?weight loss temperature is 5%?is 420 ^oC,the residual carbon rate is as high as 65%,and the flame retardancy reaches the V-0 level in the UL-94 standard.In the frequency range of 10 MHz,the dielectric constant is 2.62-2.30,which proves that the material has great application potential in the field of electronic packaging.