Formation of Macrozwitterions in the polymerization of β‐propiolactone initiated by betaine. 4th Communication on Macrozwitterions

The anionic polymerization of β‐propiolactone at 25°C in ethanol initiated by the betain {article}{empty}{document}(CH₃ )₃ N^ ⊕ - CH₂ COO^ ⊖{document} was investigated. Macrozwitterions of the structure were produced, n being intentionally as low as ca. 11. The structure of the product was proven by the nitrogen content of the reprecipiated polymer, by IR and NMR spectroscopy and by titration of the carboxylate endgroups. Some carboxylic acid endgroups were formed by chain transfer with the solvent ethanol. The positive charge at the polymer chain was proven by electrophoresis of polymer after esterification of the carboxylate chain end. Furthermore the dielectric constant of dilute solutions of the polymer in CHCl3 was determined and is discussed. The kinetics of the polymerization process were investigated by IR‐spectroscopy. The initiation reaction between monomer and betain is about 5 times slower than the consecutive propagation by addition of monomer to the anionic chain end.