Poly(oxy-2,6-dimethyl-1,4-phenylene) samples with bicyclic olefin end groups were obtained by esterification of the hydroxyl end group of the poly(phenylene oxide) with bicyclo[2.2.1]hept-5-ene-2-carbonyl chloride. Mixtures of these macromonomers with bicyclo[2.2.1]hept-5-ene-2-carboxylic acid 2-(2-(2-methoxyethoxy)ethoxy)ethyl ester were copolymerized by ring-opening olefin metathesis polymerization (ROMP) to produce graft copolymers with poly(phenylene oxide) side chains. The catalyst used for the metathesis polymerization was RuCl3(hydrate). Molecular weights of the graft copolymers were in the range of 130 000 to 250 000. Macromonomers containing exclusively exo-linked bicyclic end groups were found to be more reactive than macromonomers with 55% exo- and 45% endo-substituted end groups.