Polybenzoxazines containing an ortho-amide group in the backbone with a significant degree of aromaticity have been synthesized and characterized in this study. This class of materials makes use of smart chemistry to be able to readily process the monomer and later transform from polybenzoxazine into polybenzoxazole. All the benzoxazine monomers studied contain amide groups that form 5-membered intramolecular hydrogen bonds with the oxazine rings. Systematic manipulation of the diamine structure has allowed the structure property relationship of polybenzoxazines to be examined. Polymerization behavior of monomers is studied by differential scanning calorimetry (DSC) and in situ Fourier transform infrared spectroscopy (FT-IR). Thermal stability and flammability are characterized by thermogravimetric analysis (TGA) and microscale combustion calorimetry (MCC), respectively. The experimental results are fitted to the major thermal decomposition processes contributing to the specific heat release rate histories Q'(T). This family of materials show one of the lowest heat release capacity values of all polymers indicating the excellent flame retardancy.