A new hyperbranched polymer (HBPpeg) has been obtained via pegylation of an aromatic hyperbranched polyester. This polymer has been used as modifier of a commercially available cycloaliphatic epoxy resin in its cationic UV photocuring, using arylsulfonium salts as photoinitiator. The addition of the HBP slows down the curing as well as reduces the overall conversion achieved at room temperature, due to its interaction with the photoinitiator, but fully cured materials were achieved for formulations containing up to 10 phr of the HBP. The amphiphilic structure of the HBPpeg allows it to phase-separate in the epoxy matrix, which was confirmed by means of FESEM. The thermomechanical characteristics and the thermal stability have been also studied. (C) 2011 Elsevier Ltd. All rights reserved.