GRAFT COPOLYMER

The invention relates to a graft copolymer comprising the reaction product of maleic anhydride and a backbone polymer wherein said graft copolymer comprises between 0.50 and 5.0 weight percent of maleic anhydride, wherein said backbone polymer is selected from the group consisting of poly-olefins and copolymers of ethylene and α-olefins with 3 to 8 carbon atoms, the graft copolymer has a MFI of more than 50 dg/min (@190° C., 2.16 kg), and more than 25% of the graft copolymer chains have a chain-end unsaturation. These graft copolymers are suitable as processing aids in e.g. extrusion of high molecular weight polymers. The invention relater also to a method for grafting maleic anhydride to polymers, comprising the steps of: melting an ethylene polymer by heating and down-shearing the polymer in a co- rotating, twin-screw extruder while injecting maleic anhydride and a free radical initiator into a polymer filled, pressurized section of the extruder; and mixing the polymer and the maleic anhydride in the extruder for sufficient time to graft the maleic anhydride wherein the free radical initiator is an organic peroxide that has a half-life (t1/2) of more than 1 second if measured in mono-chlorobenzene at 240° C.