Several compositions for use as structural adhesives are disclosed. The compositions include a monomer component and a catalyst component. In one aspect, the monomer component includes a first elastomeric material of a block copolymer of styrene and isoprene, a second elastomeric material of a block copolymer of styrene and butadiene, and a cross-linked rubber of a copolymer of acrylonitrile and butadiene. In a second aspect, the monomer component includes a first elastomeric material of a block copolymer of styrene and butadiene, and a cross-linked rubber of a copolymer of acrylonitrile and butadiene. In another aspect, isophthalic acid is utilized as a polymerizable acid monomer in combination with a phosphate ester. In another aspect, the monomer component includes a cohesive failure mode promoter of rosin esters or of talc.