This article is devoted to the elaboration of a nonempirical kinetic model for the thermal oxidation of molten unstabilized polypropylene (PP), which occurs typically at 170-250 degrees C, a current temperature range for PP processing. The validity of the kinetic model has been successfully checked with the kinetic curves of mass changes and ketone group buildup of quasihomogeneously oxidized PP films (approximate to 40 mu m thick) at 190, 200, and 230 degrees C in atmospheric air. The orders of magnitude of the model parameters, determined with the kinetic model as an inverse method, are physically reasonable. Large differences obtained between some rate constant values determined in this study for PP and published elsewhere for polyethylene are tentatively explained. (C) 2008 Wiley Periodicals, Inc.