Phase Separation and Fractionation

As an example, the maintenance of near constant viscosity in motor oils over wide operating temperatures will be considered. In the old days, people changed their oil for summer and winter use otherwise, at low temperatures the summer oil would become too thick, the reverse being tme for using winter oil in summer. Of course, thickness in this case refers to viscosity. The viscosity of today s motor oils bears designations such as SAE 5W-30. According to crankcase oil viscosity specification SAE J300a, the first number refers to the viscosity at -18°C, and the second number at 99°C. The closer the two numbers are, the less the temperature variation of the viscosity. 

Introduction to Physical Polymer Science, by L.H. Sperling ISBN 0-471-70606-X Copyright 2006 by John Wiley Sons, Inc. 

Sodium carboxymethyl cellulose Soapy water Selective precipitation onto clothing fibers Prevents oils from redepositing on clothing during detergent washing antiredeposition agent 

Diblock copolymers Motor oil Colloidal suspensions dissolve at high temperatures, raising viscosity Mnltiviscosity (constant viscosity) motor oil. Example lOW-40 

Poly(ethylene oxide) M = 10 g/mol Water Reduces turbulent flow Heat exchange systems, reduces pumping costs 

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Using Flory-Huggins theory it is possible to account for the equilibrium thermodynamic properties of polymer solutions, particularly the fact that polymer solutions show major deviations from ideal solution behavior, as for example, the vapor pressure of solvent above a polymer solution invariably is very much lower than predicted from Raoult s law. The theory also accounts for the phase separation and fractionation behavior of polymer solutions, melting point depressions in crystalline polymers, and swelling of polymer networks. However, the theory is only able to predict general trends and fails to achieve precise agreement with experimental data. 

If solubility or miscibility are the properties used to separate components in a multicomponent polymer, one cannot expect the separations to be very effective. The relative differences between the neighboring chain lengths are extremely small, and so are the differences in the property used. Nevertheless, procedures have been developed that still permit the isolation of reasonably sharp fraction distributions, and are in use, particularly to prepare large-size polyolefin fractions. We discuss these procedures briefly they are fractionation by liquid liquid phase separation, and fractionation by crystallization from solution. 

The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice. 

SYNTHESIS A solution of 0.67 g 5-hydroxyindole (indol-5-ol) in 10 ml dry MeOH was treated with a solution of 0.30 g NaOMe in MeOH, followed by 0.70 g benzyl chloride. The mixture was heated on the steam bath for 0.5 h, and the solvent removed under vacuum. The residue was suspended between H20 and CH2CI2, the organic phase separated and the aqueous phase extracted once with CH2CI2. The combined organics were stripped of solvent under vacuum, and the residue distilled. A colorless fraction came over at 170-190 °C and spontaneously crystallized in the receiver. There was obtained 0.90 g (80%) 5-benzyloxyindole with a mp 81-86 °C which increased, on recrystallization from toluene / hexane, to 94-96 °C. A sample prepared from the decarboxylation of 5-benzyloxyindole-2-carboxylic acid has been reported to have a mp of 102 °C from benzene. 

To a 500-ml reaction flask were added, l,l-diphenyl-2-propyn-l-ol (0.1 mol, 20.8 g, Farchan Laboratories), 2-naphthol (0.11 mol, 15 g) and 200 ml of toluene. The mixture was warmed to 55°C with stirring while dodecylbenzenesulfonic acid was added dropwise until a permanent dark red-black color was obtained. The temperature was maintained at 55°C until thin-layer chromatography (TLC) indicated the reaction was complete (approximately 1 h). Then the mixture was poured into an equal volume of 10% aqueous sodium hydroxide, shaken, and the organic fraction separated. The toluene solution was washed with water, phase separated, and the solvent removed on a rotary evaporator. The resulting light tan crystals were slurried with hexane, suction filtered, and dried to yield 18.4 g of product with a melting point range of 156-158°C. 

Chankvetadze et al. have demonstrated the potential of flow-counterbalanced capillary electrophoresis (FCCE) in chiral and achiral micropreparative separations [27], Unlimited increase of separation selectivity can be achieved for binary mixtures, such as (+ )-chlorpheniramine with carboxymethyl-(3-cyclodextrin chiral selector, or a- and (3-isomers of a asparatame dipeptide. The carrier of the chiral selector or pseudo-stationary phase, electroosmotic flow (EOF), pressure-driven flow, or hydrodynamic flow can be used as a counterbalancing flow to the electrophoretic mobility of the analyte or vice versa, resulting in dramatic changes of the effective mobilities of the sample mixture components [28], This approach can be used for micropreparative CE, stepwise separations, and fraction collection of multicomponent mixtures [27],... 

Table 2 shows combinations of solvent and non-solvent suitable to fractionate CA using SSF 39 - 42). For the fractionation of CTA, acetic acid and chlorinated hydrocarbons, which have a low dielectric constant e, have been used extensively. Unfortunately, the fractionation efficiency achieved with these solvents was poor, and numerous attempts made so far have met with very limited success 43). Judging from the easiness of two-liquid phase separation and of solvent recovery, Kamide et al. 39) chose l-chloro-2,3-epoxy-propane (epichlorohydrine) as a solvent and heptane as a precipitant. 

This method starts off by fixing the temperature and pressure and iterating around the vapor fraction to calculate the equilibrium phase separation and compositions. The first step is an isothermal Hash calculation. If T and P are in fact the independent variables, the solution obtained in the first step is the desired solution. If either Tori and one more variable are specified, then another, outer iterative loop is required. The outer loop iterates around P or T (whichever is not fixed) until the other specified variable is satisfied. 

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