The resulting chain-end provides an opportunity for functionalization and chain extension after polymerization. Subjecting the isolated polymer 2 (Mn exp = 15 kg/mol) to the standard conditions and 150 equivalents of additional monomer generated a 41 kg/mol polymer with a Đ = 1.11 (Figure 3, 10). Importantly, the polymer underwent a unimodal shift to higher molecular weights with excellent matching between Mn exp and Mn theo and a low Đ, indicating efficient chain extension and high chain-end fidelity. Previous studies from our group have shown that the ring-opening carbonyl-olefin metathesis of TDDs 14g or other cyclic olefins 14a,d is highly stereoselective, resulting in only trans olefins. This outcome is a result of the preference for cycloaddition of the (E)-hydrazonium isomer via an exotransition state, leading to cycloadduct 12 and thence (E)olefins via stereospecific cycloreversion to hydrazonium 13 (Figure ). In addition, despite the necessarily syn configuration of the fused-ring cyclobutene stereocenters of the TDD monomer, the relative orientation of these sites upon ring-opening is exclusively anti, resulting from epimerization of the intermediate hydrazonium ion (or the free aldehyde) to the more stable configuration 14. Consistent with our previous study, 14g NMR analysis of polymer 2 reveals that the relative orientation of the allylic protons is indeed anti. 18 In summary, we have developed an efficient hydrazinecatalyzed ROMP of TDD monomers. The reaction occurs via a chain-growth mechanism with living characteristics. The resulting polymers show good agreement between Mn exp and Mn theo , low Đs, and high chain-end fidelity. Most importantly, the polymers are obtained inherently free of metal contaminants, obviating the need for the purification procedures that are typically needed to remove these impurities. As such, this chemistry should facilitate the use of ROMP in applications that require metal-free materials. Furthermore, while this reaction does not currently allow for the polymerization of common monomers such as norbornenes, we expect that the design of more reactive hydrazine catalysts should enable a broader application of this process.