Metal-Free Alternating Copolymerization of CS<sub>2</sub> and Oxetane
Guofei Feng, Ximin Feng, Xiong Liu, Wenqi Guo, Chengjian Zhang, Xinghong Zhang
Abstract
The conversion of CS 2, which is discarded on a large scale as a pollutant, into valuable sulfur-containing polymers is of significance for both environmental and polymer science. However, the copolymerization of CS 2 and cyclic ether suffers from complex polymer structures and massive byproducts. Here, we use a cooperative organocatalyst system composed of alkyl borane and onium salts for CS 2 and oxetane copolymerization. Of interest, the copolymerization is highly efficient with a turnover frequency up to 1103 h –1, avoids small-molecule byproducts, and yields previously inaccessible polythiocarbonates bearing highly regular sequences. The in-chain sulfur atoms make polythiocarbonate demonstrate desirable thermal and mechanical properties, with a melting temperature of 83 °C, an ultimate tensile strength of 20.7 ± 3.1 MPa, and an elongation at break of 480 ± 20%. For the mechanism, the Lewis acid of borane activates oxetane as well as forms the borate complex with the growing anion, as revealed by density functional theory studies.