Graft copolymers containing poly(ethylene oxide) side chains attached to a polyethylene backbone were prepared by coupling of poly(ethylene-co-acrylic acid) (PEAA) and poly(ethylene oxide) monomethyl ethers (MPEO) by esterification in o-xylene at 140 degrees C. The MPEO side chains had molecular weights of 750 to 5000. The chemical composition of the graft copolymers was analyzed by NMR and FT-IR spectroscopy. The weight fraction of the MPEO grafts in the graft copolymers was found to be around 0.4. The graft copolymers exhibited a phase-separated morphology with the backbones and the MPEO grafts forming separate crystalline phases. The MPEO phase had a melting temperature 8-25 degrees C lower than the corresponding MPEO homopolymers, as determined by DSC. The melting point of the crystalline phase formed by the PEAA main chains was close to that of the pure PEAA. Crystallinity was also confirmed by x-ray diffraction.