Cure Kinetics of Epoxy/Rubber Polymer Blends

During the past decades, the toughening of epoxy resins has received increasing attention because many different applications demand epoxy materials with improved mechanical properties. Different approaches have been employed to toughen the epoxy system: agents as liquid rubbers, block copolymers, core–shell particles, glass beads, epoxidized thermoplastics, hyperbranched organic, and hybrid compounds and combinations of them have been considered as toughening agents for epoxy systems. The morphology of epoxy resins and, consequently, their mechanical properties strongly depend on the cure kinetics, and in the case of soluble liquid rubbers, phase separation takes place as the polymerization proceeds. Subsequently, the evolution of size and distribution of the rubber particles in the epoxy during the curing reaction represents a critical point for the success of the effect of rubber systems in terms of mechanical improvement of neat resin system. Therefore, different methods have been studied and developed to control the cure kinetic parameters of epoxy resins, in order to develop models and control their final morphology and properties. Among them, some of the most used are those based on chemical changes such as differential scanning calorimetry (DSC) and infrared (IR) spectroscopy methods, as well as those centered on bulk property changes such as rheological and pressure–volume–temperature (PVT) methods. In this chapter, these methods are discussed and the results obtained on toughening various types of epoxy systems are compared. Moreover, the studies are extended to nanostructured systems, where the presence of the nanofiller plays a crucial role in the evolution of the reaction kinetics.