close to theoretical values for all p(TCN) samples (Figure ). as was also reported for Mo-initiated ROMP of this monomer (Figure ). Distillation of TCND-(CO2Me)2 (discarding the first and last ~10-15% of the distillate) and/or quenching the ROMP reaction after 2 min substantially decreased the size of this shoulder peak. Notably, conversion was unaffected by decreasing the reaction time to 2 min, as evidenced by the similar SEC traces, suggesting that this monomer is highly reactive. Moreover, these results suggest that the cyclobutene component of TCND-(CO2Me)2 remains intact under these ROMP conditions, providing an opportunity for further modification post-polymerization (vide infra). While the synthesis of p(TCND-CO2Me) appeared to be no different than for the other samples prepared here, the polymer product did not re-dissolve after the first precipitation. We hypothesized that polymer-associated residual Ru led to cross-linking reactions upon precipitation; the addition of excess pyridine (~2000 equiv relative to G3) to the quenched ROMP reaction suppressed this cross-linking (Supporting Information Section 3), enabling NMR and SEC analysis of p(TCND-CO2Me). However, SEC analysis showed a significant high molecular weight shoulder (Figure ). Notably, while cyclobutene 1-carboxylic esters, like the cyclobutene fragment of TCND-CO2Me, cannot homopolymerize via G3-initiated ROMP, they are known to slowly form eneoic carbenes that are kinetically stabilized by intramolecular chelation. Thus, we propose that ROMP of TCND-CO2Me occurs first through rapid polymerization of its NB-like alkene followed by slow cross-linking of its cyclobutene pendants, which are more sterically accessible than for TCND-(CO2Me)2 above.