Process for making graft propylene polymers

A process for making a graft propylene copolymer comprising contacting a propylene polymer, said propylene polymer selected from the group consisting of propylene homopolymers and propylene copolymers, with at least one polymerizable, ethylenically unsaturated carboxylic acid or acid derivative in the presence of a coagent, said coagent, present in a concentration of between about 0.01% and about 30% by weight, based on the weight of the propylene polymer, selected from the group consisting of a first compound having the structural formula ##STR7## where R is a hydrocarbyl or a radical containing at least one atom of oxygen, sulfur, nitrogen, phosphorus or silicon;

• R.sup.1 is hydrogen or C.sub.1 -C.sub.12 alkyl or aryl;
• and x is an integer of 1 to 4, and a second compound having the structural formula ##STR8## where R' is a hydrocarbyl or a radical containing at least one atom of oxygen, sulfur, nitrogen, phosphorus or silicon;
• R.sup.2 is hydrogen or C.sub.1 -C.sub.12 alkyl or aryl;
• and y is an integer of 2 to 4, and a free radical generating compound, said process conducted at a temperature above both the melting point of said propylene polymer and the decomposition temperature of said free radical generating compound.