An Investigation of the Pathways for Oxygen/Sulfur Scramblings during the Copolymerization of Carbon Disulfide and Oxetane

Abstract

The catalytic coupling of oxetane, the symmetric isomer of propylene oxide, with carbon disulfide has been investigated utilizing (salen)­CrCl in the presence of various onium salts. Oxygen and sulfur atom exchange was observed in both the polymeric and cyclic carbonate products. The coupling of oxetane and CS₂ was selective for copolymer formation over a wide range of reaction conditions. Five different polymer linkages and two cyclic products were determined by ¹H and ¹³C NMR spectroscopy, and these results were consistent with <i>in situ</i> infrared spectroscopic monitoring of the process. The major cyclic product produced in the coupling process was trimethylene trithiocarbonate, which was isolated and characterized by single crystal X-ray crystallography. Upon increasing the CS₂/oxetane feed ratio, a decrease in the O/S scrambling occurred. The reaction temperature had the most significant effect on the O/S exchange process, increasing exchange with increasing temperature. The presence of the onium salt initiator both accelerated the coupling process and promoted O/S scrambling. COS (observed), and CO₂ intermediates are proposed in the reactions leading to various polymeric linkages