Convenient synthesis of phthalonitrile-containing mono-benzoxazines with exceptional thermal stability and improved curing activity

Abstract

Simple synthesis and high performance are eternal pursuit for polymers. To lower the curing temperature, lower the melt viscosity and improve the processability of high performance phthalonitrile resins, a solvent-free method was applied to synthesize three from different phenols. Their chemical structure was confirmed by FTIR and NMR spectra, the curing behavior was investigated by DSC and rheology. It was found that the polymerization of phthalonitrile groups could be effectively promoted by benzoxazine moieties and the curing temperature of phthalonitrile groups dropped to around 240°C. Consequently, owing to the high curing reactivity, polymers obtained at relatively low curing temperature possessed high crosslinking density and extremely high thermal stability. P-apn-200, which was cured at 200°C, showed 5 wt% weightloss temperature (T_d5) of 472°C and char yield (Y_c) of 75.77% at 800°C. Moreover, the polymers obtained after curing at 280°C showed superior dimensional stability, CN-apn-280 showed extremely low linear expansion coefficient (CTE) of 10.7 ppm/°C. And mP-apn-280 showed HR capacity of 3.99 J/g‧K, peak HRR of 4.0 W/K and total HR of 0.8 kJ/g.