Synthesis and Characterization of Two Classes of Hyperstar Polymers Bearing Hyperbranched Cores Grafted with Linear Arms Frank D€ abritz, 1,2 Albena Lederer, 1 Hartmut Komber, 1 Brigitte Voit 1,2 1 Leibniz-Institute of Polymer Research Dresden e.V., Hohe Strasse 6, Dresden D-01069, Germany 2 Organic Chemistry of Polymers, Technische Universit€ at Dresden. 01062 Dresden, Germany Correspondence to: B. Voit (E-mail: voit@ipfdd.de); Phone: 49-351-4658590 Received 21 December 2011; accepted 31 January 2012; published online 5 March 2012 DOI: 10.1002/pola.25972 ABSTRACT: 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 polyconden- sation reaction. For the core-first approach, the hb cores have been modified to hb macroinitiators initiating either the cati- onic 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 non- functionalized 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. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 1979–1990, 2012 KEYWORDS: cationic polymerization; hyperbranched polymers; hyperstar polymers; SCVP; star polymers INTRODUCTION Hyperbranched (hb) polymers have attracted much interest during the last decades. 1–4 They exhibit several advantages over their linear counterparts. Because of the high number of branches, entanglements are reduced improving both solubility and viscosity characteristics. Consequently, their structure gives them excellent flow and processing prop- erties. Their thermal and material properties usually depend on the repeating units’ structure, the degree of branching (DB), and significantly on the nature of the numerous end groups which altogether allows for fine-tuning the hb struc- ture for specific applications by controlling those parameters. Because of their low viscosity compared with linear analogues hb polymers were used, for example, as rheology modifiers in blends and resins. Further uses are for sensor layers, in func- tional nanocomposites, in optical and electronic devices, in adhesives and as nanocontainers for drug delivery. 1 The highly branched structure gives further access to a large number of reactive end groups and thus, hb polymers have been successfully used as multifunctional cross linkers in vari- ous coating and resin applications including epoxy systems to improve their properties like reduced shrinkage, and increase in gel content, thermal stability, modulus, toughness, and reworkability, which is a matter of industrial interest. 5–10 By use of the aliphatic hb polymer, Boltorn H30, reduced shrink- age and improved flexibilization was achieved. 11 E-modulus and impact strength of epoxy thermosets were improved by addition of hb polymer Hybrane TM . 12 In addition, their special properties make hb polymers also extremely interesting for UV-curable coatings. 13–16 In this article, special highly branched polymers where con- structed named hyperstar polymers (HSP), which consist of a hyperbranched core grafted with linear arms. In general, hyperstars can be prepared via different methods: mainly, a core first strategy is used starting with a hb core molecule and grafting from or grafting onto of linear polymers involv- ing the numerous reactive end groups of the hb core; 17–23 but also an arm first approach combined with core crosslink- ing, for example, mixing Br-terminated polymers with a difunctional crosslinker, as divinylbenzene 24–26 leads to poly- mers qualifying as ‘‘hyperstars.’’ Because of the combination of a hyperbranched core with linear arms (hybrid structure) HSPs possess some advan- tages over simple hyperbranched polymers. Hyperstars ex- hibit much higher molar masses and due to their larger size and branched nature they have a more particle-like charac- ter. The inner branched structure provides them with a lower viscosity in comparison to linear molecules; hence, they can be used as rheology modifiers with excellent proc- essing properties. Furthermore, numerous interesting Additional Supporting Information may be found in the online version of this article. V C 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1979–1990 1979 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE