Formation of the intermediate cyclic six-membered oxonium ion in the cationic polymerization of β-propiolactone initiated with CH3CO⊕SbF

Analysis of the ¹H NMR spectra of documentclass{article}pagestyle{empty}begin{document}$ {rm CH}_{rm 3} mathop {rm C}limits^ oplus {rm OSbF}_{rm 6}^ ominus $end{document} /β-propiolactone and of the model systems documentclass{article}pagestyle{empty}begin{document}$ {rm CH}_{rm 3} mathop {rm C}limits^ oplus {rm OSbF}_{rm 6}^ ominus $end{document}/(CH₃)₂O and documentclass{article}pagestyle{empty}begin{document}$ {rm CH}_{rm 3} mathop {rm C}limits^ oplus {rm OSbF}_{rm 6}^ ominus $end{document}/CH₃COOCH₃ in liquid SO₂ in the temperature region ?70 to ?20°C revealed that the reaction of the acetylium cation with β-propiolactone leads to the cyclic six-membered oxonium ion 4 , participating as an intermediate in the initial stage of polymerization.