Epoxy networks modified with functionalized liquid polyisoprene rubbers with enhanced toughness and stiffness

Toughening epoxy thermosets with good mechanical strength and thermal properties has been a challenge for many material researchers. In this work, new epoxy systems with improved impact resistance, flexural strength and glass transition temperature were developed for the first time by mixing functionalized liquid polyisoprene (LIR) rubbers with diglycidyl ether of Bisphenol A -type epoxy resin followed by curing with methyl-tetrahydrophthalic anhydride/benzyl-dimethyl amine system. Anhydride- and carboxyl-functionalized LIR rubbers with two different amounts of functional groups and viscosities were employed. The addition of 10 phr of the less viscous rubber component accelerated the curing process of the epoxy, evaluated by chemorheological measurements. LIR bearing anhydride groups promoted an increase in the impact resistance and flexural properties of the epoxy networks. All modified epoxy thermosets presented higher glass transition temperature than the neat epoxy network, evaluated by dynamic-mechanical analysis and contributed for an improvement of thermal stability, confirmed by thermogravimetric analysis. The presence of carboxyl-functionalized LIR promoted an increase in the adhesion properties of the epoxy adhesive. These results are unusual and open new possibilities for the development of epoxy adhesives and coatings with simultaneous outstanding of toughness, stiffness and thermal properties.