Polysulfones with benzoxazine end groups (PSU-B-a) were obtained using monomer synthesis method from the phenol terminated polysulfone (PSU-OH), aniline and paraformaldehyde as starting materials. For this purpose, the precursor PSU-OHs with different molecular weights were prepared by condensation of bisphenol-A and bis(p-chlorophenyl) sulfone in presence of potassium carbonate. The structure of the polymers before and after functionalization was confirmed by proton nuclear magnetic resonance spectroscopy (H-1 NMR) and Fourier transform infrared spectroscopy (FT-IR). Thermally activated crosslinking behavior of these polymers was investigated by differential scanning calorimetry (DSC). Thermal and tensile properties of the crosslinked polymers obtained from PSU-B-a alone or with low molar mass benzoxazine (P-a) were studied by thermal gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). (C) 2011 Elsevier Ltd. All rights reserved.