Group molar attraction constants

TABLE 14.13 Representative Group Molar Attraction Constants... 

Table I. Group Molar Attraction Constant, Fj, and Molar Volume Group Contributions V, of Rubbery Amorphous...

Solubility parameters may also be calculated by a molar-additivity approach if the chemical composition is known. Tables of group molar attraction constants, G, obtained from molar heats of vaporization (Sperling, 2001) may be used. The solubility parameter, S, is then given by summing these for all species Q G) in the monomer repeat unit of molar mass M and density p ... 

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. 

Table 4 Representative Group Molar Attraction Constants G [(cal/cm ) mol ] at 25°C...

Values of the solubility parameter may be calculated from a knowledge of the chemical structure of any compound, polymer or otherwise. Use is made of the group molar attraction constants, G, for each group. 

Group molar attraction constants have been calculated by Small (11) and Hoy (12). Table 3.3 (11) presents a wide range of values of G for chemical groups. 

Table 3.3 Group molar attraction constants at 25°C (according to Small derived from measurement of heat of evaporation) ...

Taking into account the molar volume group contributions for glassy polymers 18) and the group molar attraction constants at 25°C, the calculated values of 5ptba... 

He also proposed new group contributions and assigned F values for specific structural features that must be added to the group contributions Solubility parameter values can be empirically calculated either from the F group molar attraction constants or from the cohesive energy group contribution constants that have been developed for polymers [26-29] ... 

The sets of group constants of Small (112), Hoy (61) van Krevelen ( 12 1) and van Krevelen and Hoftyzer (122) seem to be most comprehensive. Table 2 gives the group molar attraction constants at 25°C. Small s values were derived from measurements of the heat of vaporization. Hoy s values were derived from vapor pressure measurements. The group contribution values of van Krevelen and Hoftyzer are based on cohesive energy data of polymers. 

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