The fast precipitation of mixtures of low-density polyethylene (LDPE) with ethylene-propylene-diene terpolymer (EPDM) and ethylene-vinyl acetate (EVA) copolymer, from xylene solutions by cooling, leads to fractionation of the mixtures; LDPE/EPDM mixtures are also fractionated by cooling followed by nonsolvent addition. Studies by density-gradient centrifugation, IR spectroscopy, optical microscopy and wide-angle X-ray diffraction showed that the composition and morphology of LDPE/EPDM fractions depend on the precipitation procedures. LDPE crystalline structure in each fraction is different, changes with the time and depends on EPDM content. EVA fractions that co-precipitate are richer in -CH2-CH2-units. LDPE/EPDM and LDPE/EVA precipitates showed chemical composition distribution and morphological characteristics different among themselves. Larger aggregates were observed in the LDPE/EPDM precipitates. These differences were attributed to differences in the phase diagrams and in the phase separation mechanisms. (C) 1997 Elsevier Science Ltd.33813871393