Phase Equilibrium in Polymer-Solvent Systems

An ideal inhibited plastic material combines considerable phase and diffusion mobility of Cl with mechanical strength and high barrier characteristics. These contradictory requirements are met when a polymer-solvent system is used as the inhibited plastic base (with high polymer content). The required physical-mechanical parameters in the described systems are promoted by the polymer, while the solvent is either a liquid Cl or its solution (dispersion) in PI. 

Polymer solutions differ from those of low-molecular-weight matter by specific properties of macromolecules characterized by large size, broad molecular-mass distribution, flexibility range, numerous conformations and capability of conformal recombinations in response to temperature fluctuations and solvent type [29]. 

True polymer solutions in low-molecular-weight liquids are probable only within a certain temperature range. Mutual solubility of components beyond 

Phase equilibrium in polymer-solvent systems is subdivided into the following five types [41,65,68]  

Crystalline equilibrium, which is characteristic for polymer solutes separating into phases when transferring into the temperature and concentration zone of confined compatibility of components (i) crystalline polymer and (ii) non-saturated (low-concentration) polymer solution in a solvent. 

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S.P. Papkov. Phase Equilibrium in Polymer-Solvent System. Moscow, Khimiya, 1981. 

Pappa, G.D., Voutsas, E.C., and Tassios, D.P., 2001. Liquid-liquid phase equilibrium in polymer-solvent systems Correlation and prediction of the polymer molecular weight and the pressure effect. Ind. Eng. Chem. Res., 40(21) 4654. 

Papkov, S. P. (1981). Phase equilibrium in polymer-solvent system. Khimiya, Moscow, [in Russian]. 

Studies of various kinds of equilibria provide a wealth of information about polymer systems. Classical thermodynamics, which is concerned with the macroscopic properties of a system and the relations that hold between them at equilibrium, form a sufficient basis for description of these equilibria in polymer systems. We shall consider in a major part of this chapter methods of study of polymer solutions that deal with equilibria and can be fully described by thermodynamic relations. These include vapor pressure, osmotic pressure, and phase separation in polymer-solvent systems. 

Tong, Z. Einaga, Y. Fujita, H., "Phase Equilibrium in Polymer + Polymer + Solvent Ternary Systems. III. Polystyrene + Polyisoprene + Cyclohexane System Revisited," Polym. J., 19, 965 (1987). 

T01 Tong, Z., Einaga, Y., Miyashita, H., and Fujita, H., Phase equilibrium in polymer + polymer + solvent ternary systems. 2. Phase diagram of polystyrene + polyisoprene + cyclohexane, Macroffro/ecw/ex, 20, 1888, 1987. 

The present survey examines the current state of ignorance wherever polymers form part of a phase equilibrium in non-electrolyte systems, whether in or with solids, liquids, gases or surfaces (by adsorption). Overall we note the absence of a reliable means to estimate the effect of molecular-weight distribution on the shape of phase equilibria. An exception may be fractional precipitation by solvent/non-solvent combinations. 

In the intermediate state (line b) the free energy curve also delivers the points that satisfy the thermodynamic conditions for equilibrium [51-54]. Thus the chemical potentials of each component (polymer or solvent) must be the same in both phases I and II). For a polymer-solvent system, this is mathematically... 

The phase behaviour of many polymer-solvent systems is similar to type IV and type HI phase behaviour in the classification of van Konynenburg and Scott [5]. In the first case, the most important feature is the presence of an Upper Critical Solution Temperature (UCST) and a Lower Critical Solution Temperature (LCST). The UCST is the temperature at which two liquid phases become identical (critical) if the temperature is isobarically increased. The LCST is the temperature at which two liquid phases critically merge if the system temperature is isobarically reduced. At temperatures between the UCST and the LCST a single-phase region is found, while at temperatures lower than the UCST and higher than the LCST a liquid-liquid equilibrium occurs. Both the UCST and the LCST loci end in a critical endpoint, the point of intersection of the critical curve and the liquid liquid vapour (hhg) equilibrium line. In the two intersection points the two liquid phases become critical in the presence of a... 

For ternary polymer-polymer-solvent systems, the compositions of the equilibrium phases may be determined using a variety of microanalytical methods depending upon the chemical nature of the polymers (Dobry and Boyer-Kawenoki, 1947). Each of the phases is sampled, weighed, and dried to determine the solvent concentration. If the two polymers are sufficiently different chemically, microanalytical determination of carbon and hydrogen may be used. In systems containing polystyrene, the proportion of polystyrene may be determined by precipitating it with acetic acid and weighing the precipitate. Other microanalytical methods have also been used to determine phase compositions. 

Phase Equilibrium in a Rigid-Chain Polymer-Solvent System.81... 

Phase equilibrium in a rigid-chain polymer-solvent system may be considerably affected by various factors. In particular, this applies to... 

The phase behavior for the polymer-solvent systems can be described using two classes of binary P-T diagrams, which originate from P—T diagrams for small molecule systems. Figure 3.24A shows the schematic P-T diagram for a type-III system where the vapor-liquid equilibrium curves for two pure components end in their respective critical points, Ci and C2. The steep dashed line in figure 3.24A at the lower temperatures is the P-T trace of the UCST... 

Since then. Dr. Woldfarth s main researeh has been related to polymer systems. Currently, his research topics are molecular thermodynamics, continuous thermodynamics, phase equilibria in polymer mixtures and solutions, polymers in supercritical fluids, PVT behavior and equations of state, and sorption properties of polymers, about which he has published approximately 100 original papers. He has written the following books Vapor-Liquid Equilibria of Binary Polymer Solutions, CRC Handbook of Thermodynamic Data of Copolymer Solutions, CRC Handbook of Thermodynamic Data of Aqueous Polymer Solutions, CRC Handbook of Thermodynamic Data of Polymer Solutions at Elevated Pressures, CRC Handbook of Enthalpy Data of Polymer-Solvent Systems, and CRC Handbook of Liquid-Liquid Equilibrium Data of Polymer Solutions. 

Certain principles mnst be obeyed for experiments where liquid-liquid equilibrium is observed in polymer-solvent (or snpercritical flnid) systems. To understand the results of LLE experiments in polymer solutions, one has to take into acconnt the strong influence of polymer distribution functions on LLE, because fractionation occnrs dnring demixing. Fractionation takes place with respect to molar mass distribution as well as to chemical distribution if copolymers are involved. Fractionation during dentixing leads to some effects by which the LLE phase behavior differs from that of an ordinary, strictly binary mixture, because a common polymer solution is a mnlticomponent system. Clond-point cnrves are measnred instead of binodals and per each individnal feed concentration of the mixtnre, two parts of a coexistence cnrve occnr below (for upper critical solution temperatnre, UCST, behavior) or above the clond-point cnrve (for lower critical solution temperature, LCST, behavior), i.e., produce an infinite nnmber of coexistence data. 

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