Polymer composition comprising more than 50 % by weight, with respect to the total weight of the composition, of a nonfunctionalized polyolefin (PO1), and more than 0.5 % by weight, with respect to the total weight of the composition, of at least one polyolefin comprising carboxyl grafts [polyolefin (POg)] which is functionalized by grafting using at least one grafting agent chosen from ethylenically unsaturated carboxylic acids, their anhydrides and their metal salts, at least a portion of the carboxyl grafts of which is neutralized by a metal, optionally by the neutralization, concomitant with and/or subsequent to the grafting, of the carboxyl grafts by at least one metal base, and which has been synthesized from a nonfunctionalized polyolefin (PO2), at least 0.5 % by weight and at most 50 % by weight of the repeat units of which are derived from at least one ethylenically unsaturated monomer which has a different chemical nature from that of the repeat units of the nonfunctionalized polyolefin (PO). Article comprising the composition described above.