A novel amorphous and a novel crystalline modification of 1,1',1"-nitrilo{tri-2-propyl-tris-¢2,2'-ethylidene-bis(4,6-di-tert-butylphenyl)!phosphite}is discosed. The amorphous modification is obtained by cooling rapidly said compound from the melt to ambient temperature. The crystalline modification is obtained by crystallizing said compound from the melt at elevated temperatures. The amorphous and crystalline modifications are effective processing stabilizers for polyolefins, particularly polypropylene.
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