Synthesis and characterization of new thermally stable polynorbornenes functionalized with pendent flexible side-chains are reported. The flexible side-chains with terminal hydroxy groups were synthesized via SNAr reactions of cyclopentadienyliron-complexed chlorobenzenes with aliphatic diols. Condensation of these side-chains with exo,endo-5-norbornene-2-carboxylic acid led to the formation of substituted monomers which were characterized using one- and two-dimensional NMR techniques. Ring-opening metathesis polymerization of these monomers yielded polynorbornenes with pendent side-chains.