The polymerizations were quenched with a large excess of vinylene carbonate (VC), the volatiles removed in vacuo, and the polymers isolated by repeated precipitation from benzene into MeCN. Polymers 2 and 2-Z showed good thermal stability as established by thermogravimetric analysis (TGA), revealing an onset of decomposition of ca. 200 °C (Figure ). DSC analysis of 2 did not reveal a clear glass transition (Tg) within the range of -20 to +180 °C (Figure ), most likely because the relatively rigid structure of the polymer results in a Tg above the accessible temperature range. The molecular weight distributions were analyzed by gel permeation chromatography (GPC) in tetrahydrofuran (THF) with a refractive index detector (GPC-RI) relative to narrow polystyrene (PS) standards. GPC-RI analysis for the polymer obtained with G2 (1 mol%) at 0.1 M monomer concentration (entry 3) gave a monomodal molecular weight (MW) distribution with a number average molecular weight of Mn = 8100 Da and a dispersity (Đ) of 1.76 (Figure ). Similar results were obtained for HG2 (entry 4) and HGM2001 (entry 7) (Figure ). The theoretically predicted molecular weights are significantly higher (31100 at 100% conversion), but the GPC-RI data are likely an underestimation because of the use of structurally different narrow PS standards. Indeed, molecular weights derived from GPC-LS detection were significantly higher (Figure ). Attempts to further verify the chain lengths and distributions by MALDI-TOF MS with various matrices and ionizing agents proved unsuccessful. To further study the controlled nature of the ROMP of 1 with G2 and HG2 as catalysts we carried out kinetic experiments at 0.3 M monomer concentration (Table , entries 5, 6 and Figure ). At room temperature in benzene the monomer conversion reached 80% within 4.5 hours for G2 and 93% within 1 hour for HG2. The conversion of Dewar isomer 1 with G2 followed first-order kinetics as illustrated by a linear plot of ln([M0]/[M]) vs time that gave a calculated kobsd,G2 = 0.38 M -1 s -1 . Meanwhile, HG2 showed firstorder kinetics but very fast conversion over the first 5 minutes, followed by faster first-order kinetics than for G2 with kobsd,HG2 = 1.54 M -1 s -1 (Figure ). This suggests that HG2 is more effective in promoting the polymerization than G2. However, G2 showed better first-order kinetic behavior, thus we chose G2 as catalyst in the subsequent studies.