A family of precisely defined amphiphilic polyethylene-g-poly(ethylene glycol) copolymers has been synthesized using ADMET polycondensation chemistry. Altering the graft distribution and graft end group controls the morphology of the material: the polymers can be either semicrystalline or rendered completely amorphous. The precise monomer structures have been confirmed by H-1 and C-13 NMR, high-resolution mass spectrometry, and elemental analysis; the corresponding polymer structures have been confirmed by H-1 and C-13 NMR and FTIR. Melting temperatures can be controlled over a 60 degrees C range and glass transition temperature over 40 degrees C. Melting temperatures are incident with n-paraffin molecules having lengths similar to the static methylene sequence length between PEG branches. The observed thermal data are attributed to the crystallization of the polyethylene backbone, resulting in the exclusion of the PEG branches from the crystal, a result confirmed by X-ray diffraction.