Iniper azo-initiators are symmetrical azonitrile compounds decomposing thermally by cleavage of the two carbon–nitrogen bonds to form two alkyl radicals and a nitrogen molecule. The resulting tert-alkyl radicals are generally more stable than most of the radicals generated from peroxide initiators. In addition, these radicals do not abstract hydrogens from the polymer backbones, which results in formation of linear polymers since the branched grafting is suppressed.
Azonitrile decomposition rates show minor solvent effects and are not affected by transition metals, acids, bases and many other components of the environment. These result in two advantages of azo-initiators; their decomposition rates are predictable and they can be used for curing resins that contain a variety of extraneous materials. A drawback of azonitriles over peroxides, however, is the formation of toxic tetrasubstituted succinonitrile derivatives due to recombination of the alkyl radicals.