a Conditions: aldehyde (1.0 equiv), monomer (100.0 equiv) and catalyst 4 (1.0 equiv) were added to a sealed vial and heated for 4 h under an N2 atmosphere. Conversion determined via 1 H NMR analysis. Mn exp and Đ determined on purified products via SEC-MALS. b Reaction performed using 1.0 equiv of a preformed initiator via condensation of catalyst 4 with aldehyde 8. Reaction performed using 1.0 equiv of a preformed initiator via condensation of catalyst 4 with aldehyde 9. d Reaction run in 1,2-dichlorobenzene (1.0 M) for 12 h. The low Đs observed for these polymerizations suggest that initiation is faster than propagation. Furthermore, because the hydrazine/aldehyde condensation step is reversible, we hypothesized that chain transfer by hydrolysis of the growing chain-end followed by recondensation of the hydrazine with another polymer should enable the use of catalytic loadings of hydrazine 4. To test this hypothesis, we combined aldehyde 5, cyclobutene monomer 1, TFA, and 25 mol% of hydrazine catalyst 4 (Table , entry 1). Under these conditions, we observed efficient polymerization to 86% conversion in 6 h, generating a polymer with a narrow Đ of 1.09 and good agreement between Mn exp and Mn theo . Importantly, the addition of 20 equivalents of water resulted in better agreement between Mn exp and Mn theo (entry 2), further supporting our hypothesis that chain transfer is likely occurring by a hydrolysis/recondensation mechanism. The addition of water did not impact the kinetics of the polymerization. Table . Demonstration of catalytic hydrazine.