Interpenetrating Polymer Networks (IPN

Interpenetrating polymer network (IPN) refers to a type of elastomer in which two chemically distinct networks coexist, ideally having a structure that is homogeneous down to the segmental level [1]. The two components are present as co-continuous, interlocking networks (catenanes). This co-continuity can be achieved by kinetic retention of an initially miscible mixture of the monomers used to form the network chains, with phase segregation inhibited by the network structure, or be the result of thermodynamically compatibility of the constituent polymers. A specific type of IPN relies on solvent to promote miscibility of the two polymers. Hydrogel IPNs, which use water as the solvent, are not included in this review (see related entry ▶Double Network Hydrogels: Soft and Tough IPN).