Handbook of Solvents - George Wypych - ChemTech - Ventech!

4.4 Measurement of solvent activity 215
approaches are used. Pure polymer parameters strongly influence the calculation of gas solubilities,
Henry’s constants, and limiting solvent activities at infinite dilution of the solvent
in the liquid/molten polymer. Additionally, the polymer parameters mainly determine the
occurrence of a demixing region in such model calculations. Generally, the quantitative representation
of liquid-liquid equilibria is a much more stringent test for any model, what was
not discussed here. To calculate such equilibria it is often necessary to use some mixture
properties to obtain pure-component polymer parameters. This is necessary because, at
present, no single theory is able to describe correctly the properties of a polymer in both the
pure molten state and in the highly dilute solution state. Therefore, characteristic polymer
parameters from PVT-data of the melt are not always meaningful for the dilute polymer solution.
Additionally, characteristic polymer parameters from PVT-data also may lead to
wrong results for concentrated polymer solutions because phase equilibrium calculations
are much more sensitive to variations in pure component parameters than polymer densities.
All models need some binary interaction parameters that have to be adjusted to some
thermodynamic equilibrium properties since these parameters are a priori not known (we
will not discuss results from Monte Carlo simulations here). Binary parameters obtained
from data of dilute polymer solutions as second virial coefficients are often different from
those obtained from concentrated solutions. Distinguishing between intramolecular and
intermolecular segment-segment interactions is not as important in concentrated solutions
as it is in dilute solutions. Attempts to introduce local-composition and non-random-mixing
approaches have been made for all the theories given above with more or less success. At
least, they introduce additional parameters. More parameters may cause a higher flexibility
of the model equations but leads often to physically senseless parameters that cause troubles
when extrapolations may be necessary. Group-contribution concepts for binary interaction
parameters in equation of state models can help to correlate parameter sets and also data of
solutions within homologous series.
4.4.5 REFERENCES
1 Wen Hao, H. S. Elbro, P. Alessi, Polymer Solution Data Collection, Pt.1: Vapor-Liquid Equilibrium,
Pt.2: Solvent Activity Coefficients at Infinite Dilution, Pt. 3: Liquid-Liquid Equilibrium, DECHEMA
Chemistry Data Series, Vol. XIV, Pts. 1, 2+3, DECHEMA, Frankfurt/M., 1992.
2 R. P. Danner, M. S. High, Handbook of Polymer Solution Thermodynamics, DIPPR, AIChE, New York,
1993.
3 Ch. Wohlfarth, Vapour-liquid equilibrium data of binary polymer solutions, Physical Science Data 44,
Elsevier, Amsterdam, 1994.
4 J. Brandrup, E. H. Immergut, E. A. Grulke (eds.), Polymer Handbook, 4th ed., J. Wiley & Sons.,
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J. Wiley & Sons., Inc., New York, 1999, pp. VII/247-264.
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Sons., Inc., New York, 1999, pp. VII/649-670.
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Woodbury, New York, 1996, pp. 177-198.
8 R. A. Orwoll, Rubber Chem. Technol., 50, 451 (1977).
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E. A. Grulke (eds.), 4th ed., J. Wiley & Sons., Inc., New York, 1999, pp. VII/85-213.
10 D. C. Bonner, J. Macromol. Sci. - Revs. Macromol. Chem., C, 13, 263 (1975).
11 A. F. M. Barton, CRC Handbook of Polymer-Liquid Interaction Parameters and Solubility
Parameters, CRC Press, Boca Raton, 1990.