Provided herein are phthalonitrile adhesive formulations and methods of making and using the adhesive formulations. An illustrative adhesive formulation comprises a phthalonitrile additive selected from a group consisting of 1,2-dicyanobenzene; a derivative of 1,2-dicyanobenzene; and combinations thereof; a bisphthalonitrile compound; and a curing agent; wherein the phthalonitrile additive does not comprise an ether functional group and does not comprise a thioether functional group.