It is known that polypropylene can be modifi ed by a free radical catalyzed grafting reaction with maleic anhydride (maleation) in the melt phase under extruder processing conditions. The reaction involves hydrogen abstraction from polypropylene backbone followed by chain scission. The polypropylene chain fragments with secondary radical or unsaturated chain ends undergo an addition reaction with maleic anhydride forming a modifi ed polypropylene with anhydride functionality bound to the polymer chains. The process involves some chain degradation that must be controlled by amount of peroxide used and the temperature and mixing conditions used. Typically, about 0.5% maleic anhydride can be grafted to PP. Similarly, other unsaturated anhydrides can be used to modify PP.