1710 Research Article Received: 26 October 2011 Revised: 2 January 2012 Accepted: 5 January 2012 Published online in Wiley Online Library: 16 May 2012 (wileyonlinelibrary.com) DOI 10.1002/pi.4259 Modification of epoxy – anhydride thermosets using a hyperbranched poly(ester-amide): I. Kinetic study Xavier Fern ´ andez-Francos, a* Andrzej Rybak, b Robert Sekula, b Xavier Ramis c and Angels Serra a Abstract An epoxy-anhydride formulation used for the coating of electrical devices was modified with a commercially available hyperbranched poly(ester-amide), Hybrane S2200, in order to improve the thermal degradability of the resulting thermoset and thus facilitate the recovery of substrate materials after use of the component. The curing kinetics of the unmodified and modified formulations were studied in detail with differential scanning calorimetry, Fourier transform infrared spectroscopy and rheology. The results suggest that S2200 gets incorporated into the network structure and the curing kinetics are accelerated by the presence of hydroxyl groups from S2200. c  2012 Society of Chemical Industry Keywords: epoxy; hyperbranched; FTIR; DSC; kinetics INTRODUCTION Epoxy resins are widely used in a variety of applications because of their good thermomechanical, adhesive and electrical properties, thermal and chemical stability and ease of processing. However, their high thermal stability, caused by the densely crosslinked network achieved in the curing process, can be a drawback in what is called reworkability. In certain applications, once the lifetime of a component has expired, it may be desirable to recover the substrate materials and reuse them for a different purpose. For instance, in microelectronics it is better to replace a faulty chip rather than the whole electronic assembly. Reworkability can be achieved by the introduction of thermally cleavable linkages in the network structure. A controlled thermal degradation can lead to a partial breakdown of the network structure of the material, which degrades its mechanical properties and facilitates its removal by mechanical means. Chen and co-workers 1,2 reported the use of a newly synthesized epoxy monomer with cleavable tertiary ester groups, which could be used in epoxy formulations. We have reported the modification of epoxy formulations with a variety of lactones 3–5 or cyclic carbonates, 6 which resulted in the incorporation of ester or carbonate groups into the network structure, thus enhancing the thermal degradability of the resulting materials. Hyperbranched polymers (HBPs) are types of dendronized polymers that can be used as modifiers of thermosetting materials because of (1) their high degree of branching, which makes them less viscous than their linear counterparts with the same equivalent molecular weight and (2) the high concentration of surface groups which can be modified in order to fine-tune their physical compatibility with a matrix or make possible their covalent linkage to a matrix. The properties of the final material can thus be tailored as a function of the core structure, the degree of branching and the type of functional end-groups. 7 One of the most relevant applications of thermosets is their use as toughening agents that phase-separate during curing 8–14 or else get incorporated into the network structure. 15 Recently, we studied the use of hyperbranched poly(ester-amide)s as modifiers for epoxy – anhydride formulations. 16 The presence of terminal OH groups in the HBPs facilitated their incorporation into the network structure. It was reported that there was a significant lowering of the thermal stability of the resulting materials, because of the presence of internal ester groups in the HBP structure, without compromising their thermomechanical behaviour. Indeed, the impact strength of the resulting materials could even be improved. In the work reported in the present paper we aimed to profit from this enhanced degradability with a view to obtain thermosets for electrical applications with comparable thermal, mechanical and electrical properties with respect to the unmodified material, but which may facilitate the recovery of the substrate by controlled thermal degradation. Reactive HBPs with internal ester groups in their structure appear to be good candidates for this purpose, because (1) the covalent bonding of the multi- functional HBP into the network structure can help to prevent a significant loss in the crosslinking density, ensuring that the thermomechanical behaviour of the material is not compromised ∗ Correspondence to: Xavier Fern´ andez-Francos, Department of Analytical and Organic Chemistry, Universitat Rovira i Virgili, C/ Marcel·l´ ı Domingo s/n, 43007 Tarragona, Spain. E-mail: xavier.fernandez@urv.cat a Department of Analytical and Organic Chemistry, Universitat Rovira i Virgili, C/Marcel·l´ ı Domingo s/n, 43007 Tarragona, Spain b ABB Corporate Research Center, Starowislna 13A, 31-038 Krakow, Poland c Thermodynamics Laboratory, ETSEIB, Universitat Polit` ecnica de Catalunya, Av. Diagonal 647, 08028 Barcelona, Spain Polym Int 2012; 61: 1710–1725 www.soci.org c  2012 Society of Chemical Industry