Thermally stable polybenzoxazines via tetrahydrophthalimide-functional monobenzoxazines: Synthesis, characterization and thermally activated polymerization kinetics

Abstract

Two benzoxazine monomers with attached tetrahydrophthalimide at para and ortho position have been synthesized via Mannich condensation. The chemical structures of obtained monomers have been confirmed by 1H and 13C nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FT-IR). The ring-opening polymerization has been examined by differential scanning calorimetry (DSC) analysis, which reveals that the ortho-tetrahydrophthalimide benzoxazine monomer exhibits lower polymerization temperature compared with its para-counterpart. Besides, the kinetic parameters have been determined by non-isothermal DSC at various heating rates. The apparent activation energy values of para- and ortho-tetrahydrophthalimide functional benzoxazine monomers are determined to be 107.12 and 91.00 kJ/mol, respectively, according to the Starink method. In addition, the polymerization processes of both monomers can be well described by autocatalytic kinetic models. The predicted curves based on the developed models from this study fit well with the experimental DSC thermograms. Moreover, the thermal properties of polybenzoxazines have also been evaluated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA).