Solubility and the Cohesive Energy Density

Values of the solubility parameter for simple liquids can be readily calculated from the enthalpy of vaporization. The same method cannot be used for a polymer, and one must resort to comparative techniques. Usually, 8 for a polymer is established by finding the solvent that will produce maximum swelling of a network or the largest value of the limiting viscosity number, as both indicate maximum compatibility. The polymer is then assigned a similar value of 8 (see Table 8.2). Alternatively, Small and Hoy have tabulated a series of group molar attraction constants from which a good estimate of 8 for most polymers can be made. 

Average Solubility Parameters for Some Common Polymers 

The suggested group contributions are shown in Table 8.3, and the solubility parameter for a polymer can be estimated from the sum of the various molar attraction constants F for the groups that make up the repeat unit i.e.. 

V is the molar volume of the repeat unit whose molar mass is Mg, and p is the polymer density. 

for poly(methyl methacrylate) with Mg = 100.1 and p = 1.19 g cm, we have, using the Hoy values. 

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