Handbook of Solvents - George Wypych - ChemTech - Ventech!

5.4 Mixed solvents - polymer solubility 267
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5.4 MIXED SOLVENTS, A WAY TO CHANGE THE POLYMER
SOLUBILITY
Ligia Gargallo and Deodato Radic
Facultad de Quimica
Pontificia Universidad Cat�lica de Chile, Santiago, Chile
5.4.1 INTRODUCTION
In general, a mixture is often found to be unexpectedly potent for a particular purpose. Examples
are known in several branches of Science and Technology. In the field of solubility,
the synergistic effect is, sometimes, spectacular. Innumerable cases of synergism in solvent
extraction are known. 1-9
Eucaliptus oil has been found to act as a cosolvent, special type of synergistic solvent
in case of water-ethanol-gasoline. 10
It has been frequently observed that certain polymers can be readily dissolved in mixtures
of two or more solvents, whereas they are not soluble in the individual constituents of
this mixture. This phenomenon, known as cosolvency is of great practical importance.
The scientific and technological importance of polymers has led to extensive study of
their solution properties. Most techniques rely on dilute solution methods such as
viscometry, light scattering, osmometry, gel swelling or dipole moments. However, these
need solvents which completely dissolve the polymer, and many important polymers either
are not very soluble, or completely insoluble. In general, polymer solubility normally increases
with rising temperature, but negative temperature coefficients are also observed. Increase
in polymer molecular weight reduces solubility. Certain combinations of two
solvents may become nonsolvents. However, mixtures of non-solvents may sometimes become
solvents. In this article, we will review major information for the evaluation of solubility
behavior of polymers in binary solvents. Experimental results are compiled and
discussed. The emphasis here is on solubility-cosolvency phenomenon, the
thermodynamical description of ternary systems and the influence of the polymer structure
on preferential adsorption. Finally, interrelationships between polymer structure and thermodynamic
properties of the mixture will be discussed relative to the properties and conformation
of the dissolved polymer.