The preparation of soluble and processable polybenzoxazine precursors capable of forming high performance networks is an important field of research with a broad spectrum of application. This study demonstrates an approach that utilizes aromatic sulfonediamine, bisphenol-A, and formaldehyde in Mannich-type polycondesation to prepare polybenzoxazine precursor. The structure of the oligomeric precursor (M-n = 2600) was confirmed by FTIR and H-1 NMR spectral analysis. The precursor contained both sulfone and benzoxazine ring structures in the backbone. It was shown that small amount of ring-opened phenolic groups were also present. Thermally activated self-curing behavior of precursor in the absence of catalyst was studied by differential scanning calorimetry. Thermal properties of the cured polymers were also investigated by thermo gravimetric analysis. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2445-2450, 2011