Reactive composition includes a reactive component able to form an adhesive bond between two substrates, at least one of which comprises a plastic material. The substrate may include an initiator on or near the surface thereof. The initiator may be present in the plastic material inherently, by blending in an additive package, through injection molding, or other process. The reactive component may comprise a methylene malonate, a reactive multifunctional methylene, a methylene beta ketoester, a methylene beta diketone. A carrier component for the reactive component may be selected to interact with the plastic substrate to soften and/or penetrate the surface to be bonded. The surface of the plastic may be abraded or otherwise treated to expose the initiator. The reactive component, upon contact with a suitable initiator, is able to polymerize to form an interpenetrating polymer weld.