Process of controlled radical grafting of a polyolefin

A controlled radical grafting process of a polyolefin, derived from monomeric units comprising α-olefins, comprising the reaction of the polyolefin and at least one radical reaction initiator with a grafting system which comprises at least one grafting compound having an electron donator heterocyclic aromatic ring conjugated to at least one —HC═CR1R2 group in which at least one of R1 and R2 is an electron acceptor functional group, wherein said grafting system further includes at least one unsaturated compound which has at least one group which is able to react with an aminic and/or carboxylic and/or hydroxylic functionality and is chosen from acrylic and methacrylic compounds, maleic anhydride, derivatives ester of maleic anhydride, and their mixtures.