Effects of Substituent Groups on Curing Reaction and Thermal Stability of Nitrile Functional Benzoxazine Resins
Three nitrile functional benzoxazine monomers(PH-bn,mPH-bn,aPH-bn)were synthesized based on phenols containing different substituents and m-aminobenzonitrile,and their cured products(poly(PH-bn)、poly(mPH-bn)、poly(aPH-bn))were obtained.The structures and compositions of benzoxazine monomers were characterized by Fourier Transform Infrared spectroscopy(FT-IR),Nuclear Magnetic Resonance spectroscopy(1H-NMR)and Gel Permeation Chromatography(GPC).The effect of the substituents on curing behaviors was compared by differential scanning calorimetry(DSC),and the curing reaction mechanism was further discussed.In addition,thermogravimetric analysis(TGA)and TGA-FTIR were used to compare the thermal stability and pyrolysis mechanism of the three cured products.The results showed that the crosslinking reactions of the oxazine rings and a part of nitrile groups occurred simultaneously during the curing process.Due to the presence of the electric-donating methyl group,the peak temperature of the curing reaction increased and the thermal stability decreased.However,the electric-absorbing aldehyde group made the curing peak temperature decrease.Moreover,the thermal stability significantly increased because of the crosslinking reaction of the aldehyde groups.The 5% mass loss temperature of poly(aPH-bn)was 380℃,and its char yield was as high as 67.3% in N2 atmosphere at 800℃.
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