Grafting dicarboxylic anhydrides onto polyolefins has great practical importance. The process of grafting maleic anhydride onto high-density polyethylene in the presence of various comonomers in an intermeshing corotating twin-screw extruders was studied. Three types of comonomers were investigated : (i) vinyl monomers, including styrene and methacrylic acid; (ii) eaters of dicarboxylic acids forming succinic groups after grafting, such as fumaric acid; and (iii) esters of fumaric and maleic acid and ethylenically unsaturated cyclic dicarboxylic anhydrides, such as Diels-Alder adducts of maleic anhydride; and (iv) dienes and dodecenyl succinic anhydride.