Interfacial Failure in Graft Block Copolymer-Reinforced Polymer Blends

Graft block copolymers have the potential to serve as universal compatibilizers for immiscible polymer blends, but their engineering is impeded by the lack of a theoretical framework explaining how the enhanced interfacial adhesion of the compatibilized system is impacted by molecular architecture. We address this problem via coarse-grained molecular dynamics simulations of the uniaxial elongation of a ternary system of AB graft copolymers adsorbed at an immiscible, glassy, A/B homopolymer interface. The resulting toughness data are explained by a model for the removal of interfacial crossings that reflects the more facile reptation of grafts relative to the trapped entanglements that constrain the backbone. The model predicts that the toughness should be approximately linear with respect to the geometric mean of total backbone and graft entanglements prior to elongation, consistent with the molecular dynamics simulations and thus providing a direct connection between the macroscopically observable toughness and the microscopic entanglement network.