“…They are more or less intimate mixtures of two or more distinct, cross-linked polymer networks held together by permanent entanglements with only accidental covalent bonds between the polymers, for example, they are polymeric "catenanes" (212,213). They are produced either by swelling a cross-linked polymer with monomer and cross-linking agent of another polymer and curing the swollen polymer in situ (209)(210)(211)214) or by blending the linear polymers, prepolymers, or monomers in some liquid forms (latex (207, (217,218), or bulk (219, 220)), together with cross-linking agents, evaporating the vehicle (if any), and curing simultaneously the component polymers.…”