We note that Grubbs' 2 nd generation catalyst 11, while able to effect ROMP with cyclopropene, did not result in a substantially larger polymer or a better yield compared to the hydrazonium initiator (entry 3). Additionally, the larger dispersity (Đ = 1.6) was likely the result of a slower initiation rate of the Ru-benzylidene species at room temperature (prior literature reported 54% consumption after 1 h and 95% consumption after 15 h). The issue of slow initiation was known and had been addressed by increasing the reaction temperature to 50 °C, leading to complete consumption of the initiator within 46 minutes. Nevertheless, most reported Ru-benzylidene initiated polymerization trials to produce large polymers have been conducted at room temperature, under the conjecture that higher temperatures could cause decomposition of the monomer and/or result in large Đ values. It is noteworthy that while it had been reported that alkylidene 11-initiated ROMP had low dispersity (Đ ≤ 1.4) , at various M/I loadings the targeted and experimental Mn values for those reactions disagreed by at least 3.2 kDa (up to 82 kDa) , with the exception of two entries. This discrepancy, as observed with both hydrazonium 6-and ruthenium alkylidene 11-initiated polymerizations, speaks to the inherent instability of the highly strained cyclopropene 3 under the reaction conditions.