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Effects of functional groups on the solubilities of polyhedral oligomeric silsesquioxanes (POSS) in supercritical carbon dioxide

The phase behavior of the binary systems containing CO2 and various hybrid polyhedral oligomeric silsesquioxanes (PUSS) with different functional groups were investigated. A high-pressure view cell was used to measure the dew-points or cloud-points at temperatures between 308 and 323 K, up to 30 MPa. Among the studied PUSS structures, methacryl, isooctyl and octaisobutyl PUSS were observed to form homogenous solutions with CO2, while octamethyl PUSS was found to be insoluble in the supercritical fluid. The solubilities of both methacryl and isooctyl PUSS in scCO(2) decrease with increasing temperature, while isooctyl PUSS exhibits nearly an order of magnitude higher solubility than methacryl PUSS at both temperatures. The octaisobutyl PUSS-CO2 binary system exhibits a crossover pressure, below which the solubility of the component decreases with increasing temperature. Above this pressure, as the temperature is increased, the solubility of PUSS in scCO(2) increases. These results show that the functional groups of PUSS affect its solubility in scCO(2) and the phase behavior of the PUSS-CO2 binary system significantly. The scCO(2)-soluble PUSS can be implemented in environmentally benign material processing applications using the supercritical fluid. (C) 2015 Elsevier B.V. All rights reserved.