The cationic polymerization of DGEBA with two hyperbranched polymers (HBPs) with epoxy or vinyl end groups, using ytterbium Vitiate as initiator, has been studied. These HBPs have been obtained from commercial Bottom H30 of which terminal hydroxyl groups have been replaced with long aliphatic ester chains having vinyl or epoxy end groups. Differences between the HBPs added as modifiers are observed with respect to the curing kinetics, network development, properties and morphology of the cured materials. While terminal epoxy groups ease the solubility of the HBP in DGEBA and allows its covalent incorporation into the network structure, the HBP with vinyl terminal groups is only miscible at high temperature and phase-separates during curing. As a consequence, morphology and thermal-mechanical properties are strongly dependent on the HOP employed. (C) 2010 Elsevier Ltd. All rights reserved.