Phases liquid polymer systems

The purpose of this chapter is to explain theoretically the formation of liquid crystal phases in polymer systems and to provide the basic concepts for designing and synthesizing liquid crystalline polymers. Liquid crystalline polymers combine features of both polymers and liquid crystals, thus we discuss the materials from two sides liquid crystallinity and polymer properties. Theoretical descriptions have encountered many difficulties in the past. One is that the present theoretical understanding of neither polymers or liquid crystals is complete. 

Liquid-crystalline equilibrium is typical of solutions decomposing into two phases with increasing polymer content, i.e. isotropic (low-concentration) and anisotropic (highly concentrated) polymer solutions converting further into a single-phase liquid-crystalline system. 

The addition of a second liquid to a binary liquid-polymer system to produce a ternary system is used widely for a variety of purposes. If the seeond liquid is a poor solvent, or a pre-eipitant for the polymer, the dissolving potential of the liquid medium can be reduced and eventually phase separation may even occur. This does not neeessarily take place in every case and sometimes mixtures of two relatively poor solvents can even produce an enhancement of the solvent power. The mixed solvent is then said to exhibit a synergistic ef feet. ... 

Liquid-liquid extraction, either aqueous-organic or aqueous-aqueous, is another isolation technique suitable for vaccine purification. In a two-phase aqueous polymer system, the separation is based on the selective partitioning of the product from an aqueous Hquid phase containing, for example, polyethylene glycol (PEG), into a second, immiscible aqueous Hquid phase that contains another polymer, for example, dextran, or containing a salt [KeUey and Hatton, 1992]. 

FIG. 22-85 Phase diagram for a PEG/Dextran, hiphasic, aqueous-polymer system used in liquid-liquid extraction operations for protein separations. Alheiisson, Partition of Cell Particles and Macromolecules, 3d ed., Copyright 1986. Reprintedhy petTTUssion of John Wiley Sons, Inc.)... 

Ic. Ternary Systems Consisting of a Single Polymer Component in a Binary SolventMixture.—Three conditions must be satisfied for equilibrium between two liquid phases in a system of three components. In place of the conditions (1) we have... 

An answer to that important challenge can now be provided, thanks to the use of a two-phases liquid system. In that system, the two different polymers are dissolved each in a good solvent of theirs, the two solvents used being immiscible. The critical point is to provide one of the two partners with a reactive end-group (i.e. x on PA in solvent A ) having a preferential compatibility with the solvent (i.e. B ) of the other partner (i.e. PB-y), and vice-versa. 

The average molecular mass of synthesized polymers can be measured by SEC. This system has been called gel-permeation liquid chromatography, using porous polystyrene gel as the stationary phase material. Polymers are usually dissolved in THF or chloroform for separation by SEC. The molecular density... 

The formation of two aqueous phases can be exploited in the recovery of proteins using liquid-liquid extraction techniques. Many factors contribute to the distribution of a protein between the two phases. Smaller solutes, such as amino acids, partition almost equally between the two phases, whereas larger proteins are more unevenly distributed. This effect becomes more pronounced as protein size increases. Increasing the polymer molecular weight in one phase decreases partitioning of the protein to that phase. The variation in surface properties between different proteins can be exploited to improve selectivity and yield. The use of more hydrophobic polymer systems, such as fatty acid esters of PEG added to the PEG phase, favors the distribution of more hydrophobic proteins to this phase. In Fig. 10.13, partition coefficients for several proteins in a dextran-PEG system are given [27]. 

In their test system, the researchers used the ionic liquid l-butyl-3-methylimidazol-ium hexafluorophosphate (bmim)(PF6), which is stable in the presence of oxygen and water, with naphthalene as a low-volatility model solute. Spectroscopic analysis revealed quantitative recovery of the solute in the supercritical CO2 extract with no contamination from the ionic liquid. They found that CO2 is highly soluble in (bmim)(PF6) reaching a mole fraction of 0.6 at 8 MPa, yet the two phases are not completely miscible. The phase behavior of the ionic liquid-C02 system resembles that of a cross-linked polymer-solvent system (Moerkerke et al., 1998), even though... 

Macroheterogeneous photoconversion systems can thus be constructed by utilizing solid phase of polymers. These results on the solid phase and solid-liquid interface electron relay are surely of use when designing macroheterogeneous conversion systems. The findings obtained in these studies were used to develop a new photodiode composed of polymer pendant Ru(bpy)i film as described in Section 4 of Chapter 5. 

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