at least 28 carbon atoms is used as the feed olefin the resulting composition usually has a melting point of from 55 u00b0 to 95 u00b0 c and a viscosity of from 30 to 150 cp at 100 u00b0 c further the unreacted maleic anhydride remaining in the reaction product is usually less than 3 relative to the charged amount while according to the conventional process the unreacted maleic anhydride remaining in the product caused a trouble during the purification operation or an attempt to reduce the amount of the remaining unreacted maleic anhydride by a reaction at a high temperature for a long period of time led to the deterioration of the product according to the process of the present invention no substantial amount of unreacted maleic anhydride remains whereby no trouble during the purification operation is brought about further the hue and quality of the product have been improved whereby the product can be used advantageously as e g a resin modifier a dispersing agent or a rust preventing agent now the present invention will be described in further detail with reference to examples however it should be understood that the present invention is by no means restricted by these specific examples into a flask 650.