Thermochimica Acta 544 (2012) 17–26 Contents lists available at SciVerse ScienceDirect Thermochimica Acta jo ur n al homepage: www.elsevier.com/locate/tca Novel epoxy-anhydride thermosets modified with a hyperbranched polyester as toughness enhancer. I. Kinetics study Marjorie Flores a , Xavier Fernández-Francos a,∗ , Xavier Ramis b , Angels Serra a a Department of Analytical and Organic Chemistry, Universitat Rovira i Virgili, C/Marcel·lí Domingo s/n, 43007 Tarragona, Spain b 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 12 April 2012 Received in revised form 4 June 2012 Accepted 4 June 2012 Available online 12 June 2012 Keywords: Epoxy Anhydride Hyperbranched FTIR DSC Kinetics a b s t r a c t A hyperbranched polyester (Boltorn TM H30) has been modified in order to partially replace the terminal hydroxyl groups with aliphatic vinyl chains. This novel hyperbranched polymer (HBP) has been used as a modifier of epoxy-anhydride thermosets with the purpose of enhancing the fracture toughness. The curing kinetics of the neat and the modified formulations have been studied in detail with DSC and FTIR. Model-free and model-fitting kinetic methods have been applied to DSC data to determine the kinetic parameters. The curing mechanism has been elucidated with FTIR. Incorporation of the HBP into the thermoset matrix is assured by the reaction of remaining hydroxyl groups. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Epoxy resins are one of the most important classes of thermoset- ting polymers, widely used world-wide in coatings, adhesives, moulding compounds and polymer composites, because of their good thermomechanical properties and ease of processability. However, the use of epoxy resins is often restricted by their fragility, which places strong constraints on design parameters. Fragility and toughness are issues of great importance in terms of impact resistance, fatigue behaviour and damage tolerance [1,2], which are properties which greatly influence the durability of the compo- nents that use epoxy resins as one of their relevant constituents. Many efforts have been made until now in order to improve the toughness of epoxy thermosets. Toughness implies energy absorp- tion and it is achieved through various deformation mechanisms before failure occurs [3,4]. One of the most effective mechanisms to increase toughness is the addition of a second phase that induces the formation of particles [5–9]. The effect produced depends on the particles characteristics, e.g. size, interparticle distance, par- ticle/matrix interaction, among others. The use of hyperbranched polymers (HBPs) has been proposed [1,10–13] in order to overcome the limitations of traditional modifiers such as linear thermoplas- tics or rubber particles. Hyperbranched polymers (HBPs) are a ∗ Corresponding author. Tel.: +34 977558288; fax: +34 977558446. E-mail address: xavier.fernandez@urv.cat (X. Fernández-Francos). type of dendronised polymers that can be used as modifiers of thermosetting materials because of (1) their high degree of branch- ing, which makes them less viscous than their linear counterparts with the same equivalent molecular weight and (2) the high con- centration of surface groups which can be modified in order to fine-tune their physical compatibility with the matrix or make pos- sible their covalent linkage to the matrix. The properties of the final material can thus be tailored as a function of the core struc- ture, the degree of branching and the type of functional end-groups [14]. In order to obtain an effective toughening, good compatibil- ity between the matrix and the modifier is required. For instance, Mezzenga and Manson [10] successfully modified an epoxy-amine formulation with different reactive epoxy-terminated HBPs and found that the best toughness enhancement was achieved using partially modified HBPs which were rather compatible but could phase-separate. Boogh et al. [1] hypothesized that there was a concentration gradient within the separated particles as a con- sequence of the good compatibility with the matrix, and which ensured a good transmission of stress between the matrix and the particle. A certain degree of physical compatibility rather than chemical grafting could also help to increase the toughness of HBP- modified epoxy-amine thermosets, as reported by Ratna and Simon [11]. A significant in situ reinforcement could also be achieved in homogeneous HBP-modified epoxy-anhydride formulations [15] or photocured epoxy formulations [16]. The effect of HBPs on the curing kinetics of epoxy thermosets depends largely on the structure and molecular weight of the HBPs, 0040-6031/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.tca.2012.06.008