Kinetic tests on pyrolysis of polystyrene (PS) and polypropylene (PP) were carried out with a thermogravimetric analysis (TGA) technique at the heating rate of 0.5, 1.0, and 2.0degreesC min(-1) in a stirred batch reactor. The polystyrene was mainly decomposed between 370 and 410degreesC at the heating rates, whereas the polypropylene between 400 and 460degreesC. The apparent energy of activation and the apparent order of reaction were determined at conversions from 1 to 100%. The ranges of apparent energies of activation of polystyrene were from 164 to 249 kJ mol(-1) at conversions in the range of 1-100% and the apparent order of reaction was 0.32. The apparent energies of activation of polypropylene increased slowly from 208 to 288 kJ mol(-1) and the apparent order of reaction was 0.01. The effects of heating rate on the product distribution have been studied. The selectivity of hydrocarbons corresponding to the styrene monomer and dimer was very high for the pyrolysis of polystyrene. The selectivity of specific hydrocarbons, however, was not observed for the case of polypropylene. (C) 2003 Elsevier B.V. All rights reserved.