Stabilized polypropylene resin compositions containing a dinitrodiamine compound

A method for improviding mechanical properties and thermal processing stability of a modified polypropylene resin which comprises incorporating into the modified polypropylene resin an effective amount of a dinitrodiamine compound represented by the following formula:

• ##STR9## wherein X is a divalent aliphatic, alicyclic or aromatic group which may contain halogen or oxygen in the group, R.sup.1 is hydrogen or an aliphatic, alicyclic or aromatic group, provided that two nitrogen atoms linking through X may further link through R.sup.1 when both X and R.sup.1 are the aliphatic groups, and R.sup.2 and R.sup.3 independently of one another are each hydrogen or an alkyl of 1 to 12 carbon atoms, provided that R.sup.2 and R.sup.3 may conjointly form a ring, said modified polypropylene resin being selected from the group consisting of crystalline polypropylene, crystalline propylene/ethylene random copolymer and crystalline propylene/ethylene block copolymer, each of which is modified with an unsaturated compound, thereby improviding the thermal processing stability of said modified polypropylene resin as well as improviding mechanical properties of said modified polypropylene resin.