Comparison of the Anionic Ring-Opening Polymerizations of N-(Alkylsulfonyl)azetidines

N-sulfonylazetidines undergo anionic ring-opening polymerization (AROP) to form poly(N-sulfonylazetidine)s, which are potential precursors to valuable polyimines: In this work, the impacts of alkyl sulfonyl substitution on the AROP of (N-(ethanesulfonyl)azetidine (EsAzet), N-(2-propanesulfonyl)azetidine (iPsAzet), and N-(tert-butylsulfonyl)azetidine (tBsAzet) are studied and compared to those of the previously reported polymerization of N-(methanesulfonyl)azetidine (MsAzet). The polymerization kinetics of EsAzet and iPsAzet is of the first order with respect to their monomers and produces p(EsAzet) and p(iPsAzet), which are both soluble in DMF and DMSO. In contrast, the polymerization of tBsAzet proceeds only to low conversion due to precipitation of p(tBsAzet) under identical conditions. At lower temperatures (120 degrees C), iPsAzet polymerizes with the fastest rate, while at higher temperatures (180 degrees C), the rate of MsAzet is the fastest. The reordering of the relative polymerization rates of MsAzet, EsAzet, and iPsAzet occurs due to the interplay of the Arrhenius frequency factors and the Arrhenius activation energies of each system. The difference in the solubility of p(EsAzet) and p(iPsAzet) compared to p(tBsAzet) occurs because the polymer chains of p(EsAzet) and p(PsAzet) have branched structures, whereas those of p(tBsAzet) are linear. The branched structures of p(EsAzet) and p(iPsAzet) arise due to chain transfer by deprotonation of the alpha-sulfonyl protons and nucleophilic addition of the resulting methanide anion to subsequent monomers during the polymerization.