Reactive Core-Shell Bottlebrush Copolymer as Highly Effective Additive for Epoxy Toughening

Herein, we designed a core-shell structured bottlebrush copolymer (BBP), which is composed of rubbery poly(butyl acrylate) (PBA) core and an epoxy miscible/reactive poly(glycidyl methacrylate) (PGMA) shell, as an epoxy toughening agent. The PGMA shell allows BBP to be uniformly dispersed within the epoxy matrix and to react with the epoxy groups, while the rubbery PBA block simultaneously induced nanocavitation effect, leading to improvement of mechanical properties of the epoxy resin. The mechanical properties were measured by the adhesion performance test, and the tensile and fracture test using universal testing machine. When BBP additives were added to the epoxy resin, a significant improvement in the adhesion strength (2-fold increase) and fracture toughness (2-fold increase in K_Ic and 5-fold increase in G_Ic) compared to the neat epoxy was observed. In contrast, linear additives exhibited a decrease in adhesion strength and no improvement of fracture toughness over the neat epoxy. Such a difference in mechanical performance was investigated by comparing the morphologies and fracture surfaces of the epoxy resins containing linear and BBP additives, confirming that the nanocavitation effect and void formation play a key role in strengthening the BBP-modified epoxy resins.