Synthesis ofortho-methyltetrahydrophthalimide functional benzoxazine containing phthalonitrile group: Thermally activated polymerization behaviors and properties of its polymer

Two novel benzoxazine monomers,oHMTI-a andoHMTI-pn, have been obtained via the modified Mannich condensation fromortho-4-methyltetrahydrophalimide functional phenol, paraformaldehyde, and aniline/4-aminophthalonitrile, respectively. The chemical structures of both benzoxazine monomers have been studied by Fourier transform infrared (FT-IR) and(1)H and(13)C nuclear magnetic resonance (NMR) spectra. Their polymerization processes are investigated usingin-situFT-IR and different scanning calorimetry (DSC). Specifically, the phthalonitrile group inoHMTI-pn can react at a relatively lower temperature without adding any catalysts, which suggests the presence of the thermal synergistic polymerization effect in this benzoxazine monomer. In addition, the thermal and fire related properties of the resulting polybenzoxazines are evaluated by thermogravimetric analysis (TGA) and micro-scale combustion calorimetry (MCC). The polybenzoxazine derived fromoHMTI-pn shows both high thermal stability and outstanding flame retardancy, with aT(g)of 350 degrees C, aT(d10)value of 417 degrees C, a high char yield value of 65%, and a very low heat release capacity value of 35.2 J/(g center dot K).

Automated summary

Two novel benzoxazine monomers, oHMTI-a and oHMTI-pn, were obtained via modified Mannich condensation, with oHMTI-pn showing unique polymerization characteristics at lower temperatures. The resulting polybenzoxazines derived from oHMTI-pn exhibited high thermal stability and excellent flame retardancy, highlighting the potential for practical applications in the future.