Hybrid POSS-Hyperbranched polymer additives for simultaneous reinforcement and toughness improvements in epoxy networks

Tremendous effort is focused on improving epoxy toughness, but common approaches diminish processability and mechanical properties. This work presents hybrid additives which simultaneously enhance toughness, modulus, and other mechanical properties without reducing the network's processability. The hybrid herein was molecularly designed to contain hard nanoparticles and soft organic segments which both covalently bond and interact to form strong interfaces with epoxy networks. It is shown that a hyperbranched epoxy (HBE) reacted with a molecular silica, polyhedral oligomeric silsesquioxane (POSS), can provide the desired simultaneous reinforcement and toughness enhancements while maintaining processability. Epoxy network incorporation of the hybrid toughener led to a 220% increase in fracture toughness while also bringing about an increase in Young's modulus of over 20%. These significant improvements are described by the cured network's multi-scale morphologies and toughener dispersion states, and are related to strong interactions which occur between POSS's pendants and the HBE. Published by Elsevier Ltd.