A bifunctional benzoxazine monomer, 6,6'-bis(3-methyl-3,4-dihydro-2H-benzo[e] [1,3]oxazinyl) sulfone (BS-m), was synthesized from bisphenol-S, methylamine, and formaldehyde via a solution method. The chemical structure of BS-m was characterized with H-1 and C-13-nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and elemental analysis. The ring-opening polymerization reaction of BS-m monomer was studied by FTIR, C-13 solid-state NMR, and differential scanning calorimetry. With the polymerization reaction proceeding, the intensities of the FTIR absorption peaks of CH2, C-O-C, and C-N-C of the oxazine ring decreased gradually, and some of these absorption peaks disappeared. The shapes and intensities of the absorption peaks associated with benzene ring, sulfone group, and aromatic C-S bond changed in various ways. The changes in the solid-state C-13-NMR pattern, including chemical shifts, intensity of resonances, and line-width, were observed from the spectra of BS-m and the corresponding polybenzoxazine. The melting process of BS-m overlapped with the beginning of the ring-opening polymerization reaction. The polymerization kinetic parameters were evaluated for nonisothermal and isothermal polymerization of BS-m. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012