Abstract: Polymer composition, comprising as main components: a polyolefin polymer grafted with an ethylenically unsaturated functionalised compound with at least a first functional group; a reactive thermoplastic polymer with a second functional group which can react with the first; and a base polymer, comprising at least 55 wt % of a single site catalyst polymerised polyolefin, wherein the proportion of the base polymer amounts to more than 50 wt %, preferably to at least 55 wt % and the proportion of the reactive thermoplastic polymer to at least 10 wt % of the total of the main components, the proportion of the reactive thermoplastic polymer amounts to more than 50 wt % of the total of the reactive thermoplastic polymer and the polyolefin polymer grafted with an ethylenically unsaturated functionalised compound and the quantity of the ethylenically unsaturated functionalised compound in the grafted polyolefin polymer is between 0.05 and 1.0 mgeq/g, and a method for the preparation of such a composition.