AbstractButadiene–acrylonitrile copolymers were prepared with such variations in molecular structure as molecular weight, degree of long branching, and gel. The acrylonitrile content was varied from 28% to 44%. Viscoelastic behavior of gum elastomers, uncured compounds, and vulcanizates were characterized. Thus, the effects of molecular architecture on the properties were followed through the processing steps of compounding and vulcanization. Also, the effects of molecular parameters on the large deformation of vulcanizates were examined by the tensile stress–strain behaviour. The fracture toughness was examined with the tensile failure characteristics and De Mattia Flex