Thermo-mechanical properties of hyperbranched polymer modified epoxies
The thermo-mechanical properties of hyperbranched polymer-epoxy blends and their dependence on hyperbranched polymer shell chemistry were investigated. Hyperbranched polymers were shown to be able to increase resin toughness by inducing both a heterogeneous and homogeneous morphology. While the former was better performing in terms of toughness, the latter showed satisfactory toughness together with complete transparency. In order to understand fracture toughness enhancement, toughening mechanisms as well as the properties of both matrix and particles were studied. Particle composition was derived by combining dynamic mechanical analysis and the Fox equation. This resulted in an evaluation not only of particle composition but also of glass transition temperature and stiffness, whose value was cross-checked by a micro-mechanical model. The complete picture concerning particle and matrix properties, as well as toughening mechanisms and their dependence on hyperbranched polymer shell chemistry, finally enabled defining the optimum molecular design of the hyperbranched polymers in order to achieve the desired fracture toughness.