New hyperstar polymers (HSP) consisting of two different hyperbranched (hb) aromatic/aliphatic cores grafted with linear polymer arms were successfully synthesized. The hb cores were based on either hb poly(vinylbenzylchloride) synthesized by SCVP-ATRP or hb polyester from a polycondensation reaction. For the core-first approach, the hb cores have been modified to hb macroinitiators initiating either the cationic ring-opening polymerization of oxazolines (Oxa) or the atom transfer radical polymerization of alkylmethacrylates. For potential use as reactive binders in epoxy coatings the HSPs were equipped with a defined amount of OH-groups during arm growth via controlled block-copolymerization with nonfunctionalized and OH-functionalized monomers, either an oxazoline (OH)Oxa (2-[1-(hydroxymethyl)ethyl]-oxazoline) or a methacrylate HEMA (2-hydroxyethyl methacrylate). The amount of OH-groups could be well adjusted in this way. The hyperstars were comprehensively characterized with respect to chemical structure and molecule dimension. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000000, 2012