Toughening of cycloaliphatic epoxy resin improved by reactive copolymers with flexible alkyl side chains

Reactive copolymers with flexible alkyl side chains were used as modifiers to improve the toughness of a cycloaliphatic epoxy resin. In this study, we used three types of copolymers with different alkyl chain length (C4H9, C6H13, and C10H21). As a result, the system with an added copolymer having the longest alkyl chain length (C10H21) formed a phase separation structure. The addition of this copolymer (C10H21) led to a 50% increase in the fracture toughness (KIC) of the cured resin at the slight expense of its glass transition temperature. Scanning electron microscope observations in the vicinity of a crack tip after a compact tension test showed that cavitation of the dispersed phase occurred. The crack growth was inhibited and thus the toughness was improved due to the plastic deformation of the epoxy matrix followed by cavitation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011