**8. Application of IPNs**

As described in the preceding sections, polyurethane/epoxy IPNs are of interest because they own enhanced glass transition temperature, impact strength, tensile strength, and damping properties relative to the neat/individual polymers [7, 8, 37, 46–49]. These properties are definitely superior to the polymer blends, which are usually obtained by blending the polymers together. If two homopolymers are blended, in most of the cases two distinct glass transition temperatures are observed. A major advantage is that the IPN may display a broad glass transition temperature. In this regard, Zhang and Hourston et al. [37] prepared a series of rigid interpenetrating polymer networks of rosin‐based polyure‐ thane and epoxy resin by a simultaneous polymerization technique. The chemical structure, dynamic mechanical properties, and morphology of the materials were investigated using relevant techniques. The PU/epoxy IPN showed a single broad glass transition over a wide range of composition, with the tan *δ* peaks of the IPN shifting to a lower temperature. This implies that the PU/epoxy IPN foam system was miscible over a wide range of composi‐ tion. In other words, the single broad glass transition temperature indicated good compat‐ ibility of the two polymers contributing to IPNs. As the epoxy graft content was increased, tan *δ* peaks move toward the peak of neat epoxy. This broad glass transition temperature is highly advantageous for energy absorption and vibration damping [53, 54]. In drug delivery, IPNs have been used to maximize the therapeutic benefits of the drug. Moreover, biologically active materials have been prepared when controlled release is desirable. The physiochemical properties such as drug diffusivity, erosion rate, and controlled dissolution can be tailored *in vivo* through selection of the materials, composition and crosslink density. Another important application of IPNs is in dental applications. IPNs have been used as a synthetic teeth and cavity filler. Moreover, the IPN offers a number of advantages such as less temperature sensitivity and stronger bonding to the tooth. In engineering applications, the IPN has advantage over homopolymers or homopolymer composites. Using IPNs, the material properties can be tailored to a higher degree at different stages of polymerization. However, IPN complexity may arise from processing conditions affecting the material prop‐ erties, kinetics, and thermodynamic instabilities driving phase separation. The use of these IPNs has also been exploited in hydrodynamic machines such as water turbine pumps. PU/epoxy IPNs have the ability to prevent the damage of cavitation corrosion. These IPNs are used to form cavitation corrosion resistant coating due to good adhesion to metals, abra‐ sive resistance, water resistance, elasticity, toughness, and damping property. PU/epoxy IPNs have also been used in several applications such as thermally conductive adhesives in electronic components. The thermal conductivity of composites can be improved by using polyurethane/epoxy fully formed IPNs [55, 56]. To explore and implement more technical applications of PU/epoxy IPNs, fabrication processes, processing conditions, and develop‐ ing trends must be focused in future.
