Thermal curing of an epoxy-anhydride system modified with hyperbranched poly(ethylene imine)s with different terminal groups
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Epoxy resins are widely used in applications such as adhesives, coatings, electric laminates, encapsulation of semiconductor devices, matrix material for composites, structural components and cryogenic engineering because of their mechanical properties, adhesion and chemical resistance. However, epoxy resins are inherently brittle due to their high cross-link density. To increase their toughness different modifiers such as rubber, thermoplastic and glass particles can be added, but they always limit the processability of the formulation. Hyperbranched polymers (HBP) are a new kind of polymers used as modifiers of epoxy resins to increase their toughness, but they maintain the processability of the formulation due to their highly branched dendritic structure, which is a key point in coatings applications [1-2]. In this paper, the influence of three hyperbranched poly(ethylene imine) polymers with different terminal groups (two of them with t-butyl terminal groups and the other one with phenyl groups) on the thermal curing of an epoxy-anhydride system has been studied. The synthetic procedure to prepare the polymeric modifiers is quite easy and it consists in reacting commercial poly(ethylene imine) with the corresponding isocyanate in chloroform solution at room temperature. The epoxy resin and the anhydride we selected are Epikote 828 and 4-methyl hexahydrophtalic anhydride, respectively. As initiator we have used N,N-dimethylbenzylamine . The techniques employed in this study have been DSC (differential scanning calorimetry) and DMTA (dynamic mechanical thermal analysis). The kinetics of the thermal curing has been analyzed using isoconversional methods. The addition of the hyperbranched polymers with t-butyl terminal groups hardly changes the thermal curing process of the epoxy-anhydride system, but if the poly(ethylene imine) with phenyl end-groups is added, the thermal curing of the system is decelerated. In the systems studied, all the HBPs used decrease the glass transition temperature of the epoxy-anhydride system, acting therefore as plasticizers.  B. Voit, J. Polym. Sci. A: Polym. Chem., 38 (2000) 2505  L. Boogh, B. Pettersson, J.-A.E. Manson, Polymer, 49 (2001) 2249  M. Flores, X. Fernández-Francos, F. Ferrando, X. Ramis, A. Serra, Polymer, 53 (2012) 5232
CitacióMorancho, J., Fernandez-Francos, X., Acebo, C., Ramis, X., Salla, J., Serra, À. Thermal curing of an epoxy-anhydride system modified with hyperbranched poly(ethylene imine)s with different terminal groups. A: Central and Eastern European Conference on Thermal Analysis and Calorimetry. "Book of abstracts: 3rd Central and Eastern European Conference on Thermal Analysis and Calorimetry: CEEC-TAC3: 25-28 August 2015, Ljubljana, Slovenia". Ljubljana: 2015, p. 324.