A phenylethyl substituted dimer of ethylene and maleic anhydride, named 7-phenyloctane-(1,2),(5,6)-dianhydride, is chemically synthesized by(a) alkylating alkyl 2,4-dihalobutyrate with alkyl 2-cyano-3-phenylbutyrate,(b) alkylating the resulting halide condensation product with a carboxylate selected from the group consisting of trialkyl ethane-1,1,2-tricarboxylate and dimethyl cyanoethane-1,2-dicarboxylate,(c) acid hydrolyzing the resulting tetra or pentaester accompanied by decarboxylating, and(d) dehydrating the resulting tetra-acid to yield the desired phenylethyl substituted dimer of ethylene and maleic anhydride,wherein the alkyls in the butyrate and carboxylate ester groups each contain from one to about four carbon atoms and halo is selected from the group consisting of bromo, chloro and iodo.