The development of novel cyclotriphosphazene and oligoethyleneoxy-functionalized poly-(7-oxanorbornenes) for possible use as solid polymer electrolytes in the electrolyte layer of rechargeable lithium batteries is described. The length of the oligoethyleneoxy group on the cyclotriphosphazene has been varied, and the effects on ion transport were studied. The synthesis of 5-[2-(2-methoxyethoxy)ethoxymethyl]-7-oxanorbornene and 5-[2-(2-methoxyethoxy)ethoxymethyl]norbornene, their polymerization through ring-opening metathesis polymerization, and the characterization of the polymers are also discussed to illustrate the effect of oxygen atoms in the polymer backbone and in the cyclotriphosphazene side groups on the thermal and ion transport properties of these materials.