Syntheses of novel benzoxazines having vinyl groups and thermal properties of the thermosets

Novel benzoxazines having vinyl groups were synthesized from phenol or bisphenol A, 3- or 4-vinylaniline and paraformaldehyde. The chemical structures of the monomers were confirmed by Fourier transform infrared and ¹H-NMR analyses. The polymerization behavior of the monomers was monitored by differential scanning calorimetry. Exothermic peak of the monomers appeared in the range of 219–252 °C, due to the chain polymerization of the vinyl group and the ring-opening polymerization of benzoxazine occurring at the same temperature range. The thermal cure of the monomers afforded polybenzoxazines that have higher thermal properties than those from typical benzoxazines without vinyl groups. For example, glass transition temperature (T_g) increased for 40 to 100 °C by the introduction of vinyl groups, the highest T_g being observed at 290 °C. The 5% weight loss temperature determined by thermogravimetric analysis also increased by the introduction of vinyl groups.