A polymeric material from the styrene family, consisting of macromolecular chains grafted by nitrogen-containing heterocyclic groups; wherein the macromolecular chains consist of a polymeric backbone to which a grafted agent is attached by at least one covalent bond, the grafting agent comprises, in a single molecule, one or more associative groups capable of being bound by hydrogen bonds, and one or more reactive groups capable of forming covalent bonds with the polymeric backbone, at least one of the associative groups of the modifier is an imidazolidone heterocyclic ring. The polymeric material of the invention can also be blended with other materials such as other polymers, and can thus be modified by elastomeric phases that enhance the impact strength thereof.