This article demonstrates that a fractionation technique, based on molecular segregation during the crystallization from the melt and dissolution of the crystals, allows a complete characterization of the molecular heterogeneity in the comonomer distribution of linear low density polyethylene. An ethylene-l-hexene copolymer with a bimodal short chain branching distribution has been fractionated by multiple step crystallizations followed by selective dissolutions in tetrachloroethylene. The relative amount of each component of the distribution in each fraction was determined from the melting curves of isothermally crystallized fractions. (C) 2000 Elsevier Science Ltd. All rights reserved.