Abstract: The invention enables solution modification of a polyolefin with an unsaturated anhydride, unsaturated acid, or unsaturated ester, with high efficiency without the formation of undesirable impurities resulting from the competing reaction of the solvent with the unsaturated anhydride, unsaturated acid, or unsaturated ester. The process entails combining a polyolefin; a solvent; an unsaturated anhydride, unsaturated acid or unsaturated ester and a free-radical initiator to form a reaction mixture. The solvent is selected from the group consisting of substituted aromatic solvents which do not contain benzylic hydrogens and mixtures thereof. This reaction mixture is reacted under suitable conditions to produce a modified polyolefin.