Well-defined multiarm star copolymers, hyperbranched poly(glycidol)-b-poly(epsilon-caprolactone), with an average of 100-110 arms per molecule and a molecular weight of arms of 3000 g/mol (PGOH-b-PCL(30)) and 1000 g/mol (PGOH-b-PCL(10)) were synthesized by cationic ring-opening polymerization of epsilon-caprolactone from a poly(glycidol) core and used to modify diglycidylether of bisphenol A formulations. The curing process, studied by dynamic scanning calorimetry, was only slightly retarded when PGOH-b-PCL(x) were added to the formulation. By rheometry, the effect of this new topology and the arm length on the complex viscosity (eta*) and gelation of the reactive mixture was analyzed in detail. The addition of these new reactive modifiers decreases the global shrinkage and increases the conversion at gelation. In addition, the modified thermosets have an improved reworkability. The homogeneity of pure DGEBA and modified thermosets was proved by dynamic thermomechanical analysis and electronic microscopy (FESEM). Addition of star-like structures led to a more toughened fracture of the thermoset in comparison to pure DGEBA. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2395-2406, 2011