Synthesis of an oligomeric thickener for supercritical carbon dioxide and its properties

摘要

The applications of supercritical CO2 as a solvent are limited by its very low viscosity. A four-armed oligomeric CO2 thickener containing fluorine 1,6-bis(1,3-perfluorooctanoic add biester-2-Urea)Hexane (BPFAUH) was synthesized with 2-amino-1,3-propanediol, (Boc) 2 D, pentadecafluorooctanoic acid, thionyl chloride, hexamethylene-1,6-diisocyanate (HMDI) as crude materials by using amino protection, esterification, deprotection, and nucleophilic addition reaction. and characterized using FTIR, C-13 NMR and elemental analysis. TG analysis showed that the oligomeric thickener was thermally stable below 473.15 K. Its solubility in CO2 correlated well with the pressure. The viscosity of the system increased with increasing thickener concentration, but the viscosity of the thickener decreased with increasing temperature and shear rate.The system viscosity reached 192 mPa.s, a 480-fold increase compared to the initial viscosity, when 2.0 wt% thickener was added; this increase greatly exceeds that of other reported thickeners. The CO2-philic fluorocarbon groups promoted the solubility of the thickener; while intra-molecular thickener crosslinking occurred via O center dot center dot center dot H bonds. Thus, the molecule with four fluorocarbon groups and two urea groups formed a network structure to achieve superstrong CO2-thickening ability. (C) 2020 Published by Elsevier B.V.