Dihydrooxadiazinones are provided which can be used as blowing agents in various thermoplastic polymeric materials to produce high performance thermoplastic foams. A ketone having at least one .alpha.-hydrogen atom is halogenated and hydroxylated to produce an .alpha.-hydroxyketone. Condensation of the .alpha.-hydroxyketone with an organocarbazate produces the corresponding carboorganooxyhydrazone which is cyclized to a dihydrooxadiazinone.