Homopolymer interfaces reinforced with random copolymers

The strengthening of the interface between polystyrene (PS) and poly(methyl methacrylate) (PMMA) using a random copolymer P(Sf-r-MMA1-f), where f is the fraction of styrene in the copolymer, was investigated. The maximal fracture toughness, measured by crack propagation, was found when f = 0.68. Neutron reflectivity measurements showed that this value of f corresponded to the point where the interfacial broadening on the PS and PMMA sides of the interface was symmetric. The symmetry of broadening and the optimization of the toughness at f = 0.68 are attributable to a composition-dependent segmental interaction parameter.