A series of AB diblock copolymers have been synthesized by transformation of living anionic polymerization into ring opening metathesis polymerization (ROMP). Ethylene oxide was polymerized anionically using diphenylmethylpotassium as the initiator and was terminated with vinylbenzyl chloride to produce a series of poly(ethylene oxide) (PEO) macromonomers with a terminal vinyl group. An alkylidene exchange reaction was then realized with ruthenium propylidene complex RuCl2(=CHC2H5)(PCy3)(2), transforming PEO macromonomers into ruthenium ROMP macroinitiators. A variety of norbornene derivatives were then subjected to ROMP using PEO macroinitiators to synthesize well-defined block copolymers of varying molecular weights and compositions.