Abstract: In a process for the peroxide-free grafting of ethylenically unsaturated carboxylic acids, carboxylic anhydrides and/or their derivatives to a homopolymer or copolymer of ethylene having a density equal to or greater than 0.930 g/cm.sup.3, the monomers to be grafted are used in a concentration of from 0.01 to 0.5% by weight and the grafting reaction is carried out at from 210.degree. to 300.degree. C. in a conventional extruder or mixer in the absence of a free radical initiator. The graft copolymers are used for the preparation of ionomers and adhesion promoters.