About 43% clay containing humic acid (HA) was used as a phenol source for the production of polybenzoxazine composites. The use of humic acid as a phenol source from coal is the first attempt for the production of these materials. For poly(benzoxazine) precursor synthesis, solvent-less conventional and more economical and time-saving microwave heat treatments were applied. Molecular structures of the poly(benzoxazine) precursors were investigated by spectral analysis. Differential scanning calorimetry and thermal gravimetric analysis were used for the thermal characterizations. Nearly 300 and 250 degrees C decomposition temperatures and 40 and 30% char yields were obtained at 900 degrees C for HA-based polybenzoxazines and bisphenol-based polybenzoxazines, respectively. The morphology of the polybenzoxazines was examined by scanning electron microscopy (SEM) and X-ray analyses. The obtained results show the possibility of manufacturing the new polybenzoxazine composite materials by the method of solvent-less microwave process. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013