The synthesis of ABA triblock copolymers is described, in which the A blocks are poly(benzyl ether) dendrons and the B block is polycyclooctene or polyethylene. Bis-dendritic cis-olefins were synthesized and used as chain transfer agents in ring-opening metathesis polymerization of cyclooctene in a process that inserts the dendrons at the polymer chain-ends. Evaluation of the polymer products by spectroscopic, chromatographic, and titration methods supports their triblock structure. Hydrogenation of the unsaturated polycyclooctene B-block of these ABA triblock copolymers provides the first reported synthesis of bisdendritic polyethylene. (c) 2005 Wiley Periodicals, Inc.