No abstract

Toughened epoxy systems cured with anhydride-based hardener were successfully prepared by incorporating nonpolar liquid polybutadiene (PB) previously functionalized with isocyanate groups (PBNCO). The NCO groups in PBNCO react with the hydroxyl and/or epoxy groups of the matrix forming a ER-PB-ER triblock copolymer. The block copolymer is evidenced by transmission electron microscopy (TEM). In fact the modified epoxy resin (ER) networks presented domains with cocontinuous-like morphology, composed by PB and ER phases in nanomeric dimensions. The effect of PBNCO on the curing process of ER was studied by rheometry. Also the resulting networks were characterized by mechanical and dynamic mechanical properties, differential scanning calorimetry, and TEM. By adding an amount of rubber as high as 20 phr, a great improvement of toughness (around 140%) and impact resistance as well as a good transparency were achieved without significantly affecting the modulus and stiffness. Also the glass transition temperature (Tg) increased around 10 C with the presence of 5 phr of PBNCO. Even with the addition of 20 phr of rubber, the Tg of the system was superior than that found for the neat epoxy network. The outstanding physic-mechanical performance is attributed to the peculiar morphology.