SUPERCRITICAL ANTISOLVENT FRACTIONATION - MEASUREMENTS IN THE SYSTEMSMONODISPERSE AND BIDISPERSE POLYSTYRENE CYCLOHEXANE CARBON-DIOXIDE

As a model system for new polymer-separation processes utilizing compr essed gases the system polystyrene-cyclohexane-carbon dioxide with mon odisperse polymers (M-w/M-n=1.09) was investigated experimentally at t emperatures up to 250 degrees C and pressures up to 160 bar. Small amo unts of carbon dioxide shift the lower critical solution temperature ( LCST) to dramatically lower temperatures. When looking at the pressure -concentration representation there is a striking similarity between t he effect of temperature and the effect of gas content on the shape of the two-phase region. Pressure has a pronounced effect on the chain p artitioning of polystyrenes of different molecular weights in the two liquid phases as determined by gel permeation chromatography. The resu lts are discussed in the context of industrial application. (C) 1997 E lsevier Science B.V.