Thermally activated ring opening polymerization of benzoxazines plays an important role in the fabrication of high performance phenolic thermosets with enhanced thermal and mechanical properties. In the present work, a novel synthetic strategy based on 1,3-benzoxazine-thiol ring opening reaction for the functionalization of polymers is reported. For this purpose, thiol reactive main chain benzoxazine polymer (PBZ) was synthesized by the reaction of bisphenol-A, 1,6-diaminohexane and paraformaldehyde in toluene:methanol mixture (2:1, v:v) following the monomer synthesis procedure. The obtained polybenzoxazine precursor was then reacted at room temperature with various thiol compounds, namely thiophenol, 2-ethanethiol and 1-butanthiol in CH3OH/CHCl3 for 24 h. Successful incorporation of the thiol compounds to PBZ was confirmed by spectral and molecular weight characterizations. The thermally activated curing of the remaining benzoxazine rings occurs at lower temperatures than that reported for the conventional benzoxazines. The described strategy represents a unique approach not only for the polymer modifications but also for the preparation of high performance thermosets. (C) 2015 Elsevier Ltd. All rights reserved.