Cyclobutene ROMP is relatively underexplored in comparison to other strained olefins, such as norbornene, likely due to the paucity of strategies to synthesize cyclobutenes on scale. However, endotricyclo[4.2.2.0 ]deca-3,9-dienes (TDDs) are a class of thermally stable cyclobutenes that are easily synthesized via the one-pot 6-π electrocyclization/[4+2]-cycloaddition between 1,3,5,7-cyclooctatetraene and various dienophiles (Figure ). This simple reaction provides ready access to TDD monomers suitable for ROMP. As described herein, we have found that hydrazine-catalyzed ROMP of TDD monomers proceeds with high efficiency, resulting in polymers with excellent control over molecular weight, low dispersity values, and high chain-end fidelity (Figure ). Importantly, these materials are inherently metal-free, and so require no special purification to remove such impurities. For our initial explorations, we selected TDD 1 17 derived from N-2-ethylhexyl succinimide (Table ), due to the increased solubility and decreased melting point typically seen in monomers containing a 2-ethylhexyl substituent. Our initial attempt entailed the reaction of hydrazonium 3 with TDD 1 (100 equiv) neat at 140 °C. While the resulting polymer 2 exhibited a low dispersity value (Đ) as well as excellent matching of its number-average molecular weight (Mn exp ) with the theoretical value (Mn theo ), these conditions led to only modest conversion of monomer to polymer (entry 1). Discoloration of the reaction mixture along with 1 H NMR analysis led us to conclude that the poor performance was due to oxidation of the hydrazine to the corresponding diazene with adventitious oxygen. Because such oxidations are known to be facile with free-base hydrazines, we examined the addition of exogenous acid to help ensure protonation of the hydrazine. Indeed, the addition of one equivalent of TFA resulted in 96% conversion of monomer, producing a polymer with excellent agreement between Mn exp and Mn theo and a low Đ (entry 2). We also found that the ROMP of 1 proceeds well by mixing hydrazine salt 4 and one equivalent of an aldehyde (e.g. 5, entry 3). Again, one equivalent of TFA was necessary for high conversion, but increasing TFA loading beyond one equivalent had no additional benefit (entry 4). We were able to target a range of molecular weights by altering the cyclobutene to aldehyde ratio (entries 4-6), as long as we kept the amount of TFA at one equiv per 100 equiv of monomer. In each case, the molecular weight distribution exhibited a low Đ , and the Mn exp matched well with Mn theo , suggesting that one aldehyde molecule leads to one polymer chain. Importantly, no reaction occurred in the absence of hydrazine 4 or aldehyde 5, demonstrating that this is not a Brønsted acid-mediated process (entries 7 and 8).