Enhancement of the impact strength of cationically cured cycloaliphatic diepoxide by adding hyperbranched poly(glycidol) partially modiﬁed with 10-undecenoyl chains Marjorie Flores a , Mireia Morell a , Xavier Fernández-Francos a,⇑ , Francesc Ferrando b , Xavier Ramis 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 Thermodynamics Laboratory, ETSEIB Universitat Politècnica de Catalunya, Av. Diagonal 647, 08028 Barcelona, Spain article info Article history: Received 5 November 2012 Received in revised form 14 February 2013 Accepted 17 February 2013 Available online 6 March 2013 Keywords: Cycloaliphatic epoxy Thermoset Hyperbranched polymer Impact strength abstract A hyperbranched poly(glycidol) has been synthesized and modiﬁed by acylation with 10- undecenoyl chloride to obtain hyperbranched polymers (HBPs) with different degree of modiﬁcation. These HBPs have been used as reactive modiﬁers in a proportion of 3%, 5%, and 10% with respect to a biscicloaliphatic diepoxide cured using ytterbium triﬂate as ther- mal cationic initiator. The materials obtained have been characterized and their mechani- cal properties evaluated. Phase separated materials have been obtained, with a 2-fold increase in impact resistance without sacriﬁcing thermomechanical properties, thermal stability or processability. This good combination of properties can be explained by the achievement of a regular microphase separation with a good interfacial interaction between the microparticles and the epoxy matrix. The compatibility between the HBP and the matrix can be tuned by changing the degree of modiﬁcation, which leads to a var- iable amount of available hydroxyl groups of the HBP that can react with the epoxy groups. This chemical bonding occurs through the activated monomer mechanism (AM) which is typical of the cationic homopolymerization of epoxides. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Epoxy resins are commonly used as thermosetting materials due to their excellent thermomechanical proper- ties and chemical and environmental stability. They pres- ent also good processability before curing. These materials are one of the most important classes of thermo- setting polymers, used world-wide since their industrial introduction in 1946 in the ﬁeld of coatings, adhesives, molding compounds and polymer composites [1]. Their broad range of applications can be explained due to the fact that they are probably one of the most versatile ther- mosets because not only the type of resin and the chemis- try of the curing can be varied, but also a huge number of organic and inorganic modiﬁers and ﬁllers can be added to improve their properties [2]. Although rigidity and strength are desired properties in engineering applications, toughness is one of the restrictions in the use of epoxy res- ins. The low toughness, coming from the high crosslinking density, affects the durability of coatings and places strong constraints on design parameters [3]. The ﬁrst attempts to improve toughness were based on the addition of liquid rubbers or thermoplastics, but usu- ally these additives compromise the modulus and thermo- mechanical characteristics of the thermosets and the processability of the formulation [4]. Toughness implies energy absorption and it is achieved through various defor- mation mechanisms before failure occurs. One of the most effective methods of preventing the crack to freely develop 0014-3057/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.eurpolymj.2013.02.011 ⇑ Corresponding author. Tel.: +34 977558288; fax: +34 977558446. E-mail address: xavier.fernandez@urv.cat (X. Fernández-Francos). European Polymer Journal 49 (2013) 1610–1620 Contents lists available at SciVerse ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj