Study On The Effect Of Meta-Substituents On The Polymerization Activity And Properties Of Benzoxazine Resin

Benzoxazine resin,as a new thermosetting resin,has the characteristics of high strength and modulus,high heat resistance and flame retardant,low dielectric constant and water absorption,and its melt viscosity is low,low heat release during curing,no small molecules are released during curing,the volume is close to zero shrinkage before and after curing,prepreg storage performance is good,very suitable for high performance resin matrix composite matrix resin.Although benzoxazine resin has excellent comprehensive properties,high polymerization temperature limits its wide application.Therefore,how to reduce the polymerization temperature is one of the important research directions of benzoxazine resin.The polymerization activity of benzoxazine resin is closely related to its molecular structure.It is of great value and significance to study the relationship between molecular structure and properties of benzoxazine resin.The law of influence of oxazine performance.In this paper,a series of monofunctional benzoxazine monomers and their polymers containing different electron effect substituents were synthesized,and their polymerization activity and polymer properties were systematically studied.In this paper,a series of mono-functional benzoxazine monomers and polymers containing different electronic effect substituents were designed and synthesized,and their polymerization activities and polymer properties were systematically studied.1.In the monomer synthesis stage,9 monomers of benzooxazine were synthesized by solvent method using a unified primary amine route.Phenol/aniline type benzoxazine monomer（BOZ（H-H））was synthesized from phenol and aniline.Benzoxazine monomers synthesized from meso-substituted phenol and aniline include m-cresol/aniline benzoxazine（BOZ（CH₃-H））,3-chlorophenol/aniline benzoxazine（BOZ（Cl-H））,3-methoxyphenol/aniline benzoxazine（BOZ（OCH₃-H））,methyl 3-hydroxybenzoate/aniline benzoxazine（BOZ（OCH₃-H））,COOCH₃-H)).Benzoxazine monomers synthesized from phenol and m-substituted aniline include phenol/m-methylaniline benzoxazine（BOZ（H-CH₃））,phenol/m-chloraniline benzoxazine（BOZ（H-Cl））,phenol/m-methoxyaniline benzoxazine（BOZ（H-OCH₃））,phenol/m-nitroaniline benzoxazine（BOZ（H-NO₂））.The monomers were characterized by nuclear magnetic resonance spectroscopy（NMR）and Fourier transform infrared spectroscopy（FT-IR）.The results showed that nine monomers were synthesized successfully.2.The curing behavior and curing kinetics of 9 monomers were studied by non-isothermal DSC and isothermal DSC,and molecular simulation was performed by Material Studios software.The results showed that the ring-opening polymerization temperature of benzoxazine decreased when the electron-absorbing group substituted at the phenol source intersite,the conversion rate increased at the same temperature,the average activation energy decreased,the length of C-O bond in the oxazine ring increased,and the results were opposite when the electron-donating group substituted at the phenol source intersite.The polymerization temperature of 3-methoxyphenol/aniline benzoxazine（BOZ（OCH₃-H））was the lowest at 227℃.The ring-opening polymerization temperature of benzoxazine had no obvious rule when the electron-absorbing groups substituted in the intersite of amine source.The polymerization temperature of phenol/m-methoxyaniline benzoxazine（BOZ（H-OCH₃））was the lowest at 234℃.3.Nine kinds of polybenzoxazines were prepared by curing monomer of monomfunctional benzoxazines.The structure of polybenzoxazines was characterized by FT-IR and DSC.The results showed that the nine kinds of polybenzoxazines were cured completely.The thermal resistance of nine polybenzoxazines was studied by non-isothermal DSC.The results showed that there was no significant correlation between the electronic effects of substituents and the Tg of polybenzoxazines.The Tg of methyl3-hydroxybenzoate/aniline benzoxazine polymer was the highest at 210℃.The thermal stability of 9 kinds of polybenzoxazines was studied by TGA.The results showed that the thermal stability of the corresponding polybenzoxazines was improved when the electron-absorbing groups were substituted in the phenol source.The thermal stability of polybenzoxazine was improved when substituents were substituted at aniline intersite.The thermostability of polybenzoxazine at high temperature was decreased by the introduction of meso-substituents.