The free radical suspension polymerization of vinyl chloride is modelled at the elementary reaction level, systematically taking into account diffusion limitations. The resulting kinetic model enables the quantitative description of conversion, molecular mass distribution and the formation of structural defects as a function of polymerization time for a wide range of industrially relevant conditions. By deriving population balance equations for structurally distinct radical species the formation of structural defects could be determined. From model calculations it follows that structural defects are predominantly formed at conversions higher than 75% as the rates of the monomolecular reactions responsible for the formation of structural defects are not limited by diffusion and thus become favoured at higher conversion. This threshold value for the monomer conversion is in good agreement with experimental observations. (c) 2006 Elsevier Ltd. All rights reserved.