High char yield polybenzoxazines are obtained from acetylene-functional benzoxazine monomers. Polymerization of acetylene functional group, in addition to oxazine ring opening polymerization, contributes greatly to the exceptional thermal stability. A significant change in char yield is found for these polybenzoxazines by different polymerization environments. The polymerization behaviour of these compounds under air and nitrogen atmosphere has been studied by Fourier transform infra-red spectroscopy, ultra-violet-visible spectroscopy, differ ential scanning calorimetry and proton nuclear magnetic resonance spectroscopy.