The present disclosure provides a resin blend containing a blend of a phthalonitrile resin and a thiadiazole substituted phthalonitrile compound. The present disclosure also provides an article including a polymerization product of such a resin blend. Further, a thiadiazole substituted phthalonitrile compound and an article including a polymerization product of the compound are provided. The present disclosure additionally provides a method of making a thiadiazole substituted phthalonitrile compound. Certain thiadiazole substituted phthalonitrile compounds can act as curatives for the phthalonitrile resin.