Progress in Organic Coatings 73 (2012) 62–69 Contents lists available at SciVerse ScienceDirect Progress in Organic Coatings j ourna l ho me p ag e: www.elsevier.com/locate/porgcoat Multiarm star poly(glycidol)-block-poly(styrene) as modifier of anionically cured diglycidylether of bisphenol A thermosetting coatings Mireia Morell a , Xavier Fernández-Francos a , Jordi Gombau a , Francesc Ferrando b , Albena Lederer c , Xavier Ramis d , Brigitte Voit c , Àngels Serra a,∗ a Department of Analytical and Organic Chemistry, Universitat Rovira i Virgili, C/Marcel·lí Domingo s/n, 43007, Tarragona, Spain b Department of Mechanical Engineering, Universitat Rovira i Virgili, C/Països Catalans, 26, 43007, Tarragona, Spain c Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Strasse 6, 01069, Dresden, Germany d Thermodynamics Laboratory, ETSEIB Universitat Politècnica de Catalunya, Av. Diagonal 647, 08028, Barcelona, Spain a r t i c l e i n f o Article history: Received 4 July 2011 Received in revised form 2 September 2011 Accepted 3 September 2011 Keywords: Star polymers Hyperbranched Epoxy resin Anionic polymerization Thermosets a b s t r a c t Well-defined multiarm star copolymer poly(glycidol)-b-poly(styrene) (PGOH-b-PS) with an average number of PS arms per molecule of 85 has been prepared. The core first approach has been selected as the methodology using atom transfer radical polymerization (ATRP) of styrene to grow the arms from an activated hyperbranched poly(glycidol) as core. This activated hyperbranched macroinitiator was prepared by esterification of hyperbranched poly(glycidol) (PGOH) with 2-bromoisobutyryl bromide. PGOH-b-PS was used to modify diglycidylether of bisphenol A coatings cured by anionic ring-opening mechanism using 1-methyl imidazole as the initiator. The kinetics of the curing process, studied by dynamic scanning calorimetry (DSC), was not much affected when PGOH-b-PS was added to the formu- lation. By rheometry the effect of this new polymer topology on the complex viscosity ( * ) of the reactive mixture was analyzed. The phase-separation of the modified coatings was proved by dynamic thermo- mechanical analysis (DMTA) and electronic microscopy (SEM and TEM) showing nano- or microphase separation as a function of the modifier content. The addition of this star polymer led to increase in the rigidity in terms of Young’s modulus and in the microhardness in comparison to neat DGEBA. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Epoxy resins are known to be commonly used as thermosetting coating materials due to their excellent thermal and mechanical properties [1–3]. It has been observed that the formation of micro- or nanostructures in epoxy thermosets improves the overall prop- erties without reducing the crosslinking degree of the epoxy matrix [4,5]. One of the possibilities employed to generate self-assembled structures is to start using a block copolymer completely misci- ble in the reactive mixture. In this case, phase separation of one of the blocks is achieved during the crosslinking polymerization while the other one remains miscible at high degree of conver- sion. This methodology has been commonly applied employing diblock, triblock or tetrablock linear copolymers [6]. Another alter- native to the formation of nanostructures in thermosets consists in the pre-selfassembly of block copolymers where the precursors of thermosets act as the selective solvents. The subsequent cur- ing process preserves the formed nanophases in the matrix [7]. It ∗ Corresponding author. Tel.: +34 977559558. E-mail address: angels.serra@urv.cat (À. Serra). has been reported that the size of these phases can be adjusted tuning the concentration of the modifier in the pre-cured mixture [8]. Additionally to linear block copolymers, multiarm stars can also be considered as a new class of modifiers for epoxy resins capa- ble of generating self-assembled matrices [9]. Using this strategy, Meng et al. obtained nanostructured diglycidylether of bisphenol A (DGEBA) thermosets using core-crosslinked stars (CCS) based on poly(styrene) core with poly(ethylene oxide) or poly(styrene)- b-poly(ethylene oxide) arms both synthesized by the “arm first” approach. The non-reactive end groups of the arms hinder the chemical incorporation of the star copolymers into the epoxy matrix [10,11]. We reported in a recent study the use of a hydroxyl-terminated multiarm star copolymer poly(styrene)-b- poly(-caprolactone), obtained by the “core first” approach strategy to modify DGEBA coatings. In that case, no evidence of clear nanophase separation of the star copolymer was obtained but a nanograined morphology was observed [12]. Therefore, different morphologies can be fixed depending on several factors: (i) the initial miscibility of the star copolymer in the epoxy resin, (ii) the reactivity of the multiarm star with the epoxy resin and (iii) the homogeneity of the pure thermosetting matrix mainly caused by the type of curing initiator employed. 0300-9440/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2011.09.001