The free-volume theory of polymer solutions initiated by Prigogine and developed by Flory and Patterson is reduced to practice. This theory, which represents a substantial improvement over the older theory of Flory and Huggins, facilitates calculation of solvent activities in polymer solutions from a minimum of experimental binary data. However, it is necessary to characterize each pure component with three molecular parameters which can be obtained from PVT data; such data, unfortunately, are often unavailable. Nevertheless, using reasonable approximations based on Bondi's correlations as needed, molecular parameters are given for 22 solvents and for 16 polymers. SCOPEPolymer processing often occurs in the dissolved state, and it is therefore of practical importance in polymerprocess design to know the vapor pressure of the solvent as a function of its concentration in the polymer-solvent solution. Such vapor pressures can be calculated from a theory of polymer solutions with only limited experimental data.The well-known theory of Flory and Huggins, now 30 years old, has serious deficiencies and often gives poor results. An improved theory, first suggested by Prigogine, has been developed by several polymer chemists, notably Flory and Patterson. This paper discusses the new theory and shows how it may be used in practical design work. Toward that end, molecular parameters required for numerical results are given for a series of solvents, polymers, and binary systems. CONCLUSIONS AND SIGNIFICANCEThe statistical-mechanical theory of Prigogine is useful for calculating solvent vapor pressures in polymer solutions containing nonpolar (or slightly polar) components. Compared to the older lattice theory, this free-volume theory gives a better estimate of the effect of solvent concentration on solvent activity. It is simple to use provided all necessary parameters are available: three molecular parameters are needed for each pure component but only one binary parameter is required. The three purecomponent parameters are determined from PVT data (density as a function of temperature and pressure). These are often not at hand but reasonable estimates can sometimes be made using Bondi's correlations. In this work pure-component parameters are given for 22 common solvents and for 16 polymers. Binary parameters are presented for 20 systems. The simplified form of the Prigogine-Flory theory, as given here, is useful for calculating solvent vapor pressures as needed in polymer-process design.Industrial polymers comprise a large fraction of the economic value of all manufactured chemicals. Polymers are often processed in solution; therefore, rational design of polymer processes often requires calculation of phase equilibria in polymer solutions.We discuss here a theoretical treatment of polymer solution thermodynamics which can be used to calculate solvent partial pressures in binary, polymer/solvent solutions using only limited data. The partial pressure of a solvent is of practical interest in design of solvent-removal proc...
Following synthesis in a high-pressure reactor, low-density polyethylene Is partially separated from ethylene by decompression. The statistical mechanical theory developed by Prigogine and Flory for solutions of chain molecules is used to calculate phase equilibria in the system polyethylene-ethylene at 260°and at 200, 500, and 900 atm. Attention Is given to the effect of molecular-weight distribution and to the algorithm for calculating the results.
Solubilities of several solvents were measured in four molten polymers by using an isobaric vapor‐pressure apparatus. Solvent concentration ranged from 0.5 to 15 wt‐%. The systems polyisoprene–benzene and polyisobutylene–benzene were studied at 80.0°C; polyisobutylene–cyclohexane was studied at 100.0°C; ethylene–vinyl acetate copolymer (EVA)–cyclohexane, EVA–isooctane, and poly(vinyl acetate)–isooctane were studied at 110.0°C. Of six polymer–solvent systems studied, all except poly(vinyl acetate)–isooctane appear to exhibit hysteresis in a single sorption–desorption cycle starting with dry polymer. The desorption curves of solvent activity plotted versus solvent weight fraction show an inflection point, suggesting localized adsorption of solvent molecules. Experimental data were analyzed with a theory which takes into account adsorption of solvent by polymer in addition to differences in free volumes and intermolecular forces. The theory gives a semiquantitative representation of the experimental data.
Activity coefficients of benzene, toluene, cyclohexane, carbon tetrachloride, chloroform, and dichloromethane in binary solutions with polystyrene at 23.5°C have been determined using a piezo‐electric sorption apparatus. The investigated solvent concentration ranges were 15 to 39 wt % for benzene, 14 to 29 wt % for toluene, 15 to 28 wt % for cyclohexane, 26 to 38 wt % for carbon tetrachloride, 24 to 46 wt % for chloroform, and 21 to 41 wt % for dichloromethane. The polystyrene (weight‐averaged) molecular weights were 1.1 × 105 and 6.0 × 105 g/gmole. The weight‐fraction activity coefficients (Ω1 = a1/w1) of cyclohexane, toluene, and carbon tetrachloride in polystyrene solutions determined in this work agree within experimental error with previously published values determined by measurement of vapor pressure lowering and vapor absorption by thin films. We find disagreement, at low solvent concentrations, between our results for benzene and chloroform and previously published results. We have analyzed our results using Flory's version of corresponding‐states polymer solution theory. The theory can account, qualitatively, for the cyclohexane and carbon tetrachloride results. It cannot account for the toluene, benzene, dichloromethane, or chloroform results.
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