The present disclosure provides a resin blend. The resin blend includes at least one diluent containing a single phthalonitrile functional group and at least one diphthalonitrile resin. Also provided are prepregs including the resin blend impregnated into continuous reinforcing fibers or a cloth. Similarly, the present disclosure provides a molding compound including chopped reinforcing fibers distributed in the resin blend. An article is also provided, which includes polymerization product of the resin blend. An alternative article includes a substrate and a layer of the resin blend disposed on the substrate. The diluent typically improves processability of the resin blend and lowers the softening temperature of the polymerization product of the resin blend.