“Exhaust gas” converted into polymers with high added value

2018-06-29 Global Communications

With the advent of the Industrial Revolution, mankind has stepped into an era featured by heavy reliance on fossil fuels, concomitant with which has been the emission of massive exhaust gas. Carbonyl sulfide (COS), a key intermediate of the atmospheric sulfur cycle and the most abundant sulfur-containing gas in the troposphere, causes haze, acid rain, and ozonosphere damage, and is also a one-carbon (C1) heterocumulene and structural analog of carbon dioxide (CO2).

The research team led by ZHANG Xinghong, a professor with the Department of Polymer Science and Engineering, synthesized sulfur-containing polymers via cooperative dual organocatalysts with high activity.

Metal-free and controlled synthesis of sulfur-containing polymer poses a tough challenge in polymer chemistry. ZHANG Xinghong et al report the metal-free, living copolymerization of COS with epoxides via the cooperative catalysis of organic Lewis pairs including bases (e.g. phosphazene, amidine, and guanidine) and thioureas as hydrogen-bond donors, afford well-defined poly(monothiocarbonate)s with 100% alternating degree, >99% tail-to-head content, controlled molecular weights (up to 98.4 kg/mol), and narrow molecular weight distributions (1.13–1.23). They investigate the effect of the types of Lewis pairs on the copolymerization of COS with several epoxides. The turnover frequencies (TOFs) of these Lewis pairs are as high as 112 h−1 at 25°C. Kinetic and mechanistic results suggest that the supramolecular specific recognition of thiourea to epoxide and base to COS promote the copolymerization cooperatively. This strategy provides commercially available Lewis pairs for metal-free synthesis of sulfur-containing polymers with a precise structure.

These findings are published in the May 30 issue of Nature Communications. The lead author and the corresponding author are ZHANG Chengjian, a postgraduate student in the Department of Polymer Science and Engineering, and Prof. ZHANG Xinghong.

Image Credit: LU Shaoqing