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Swelling pressures (ir) in H+, Li+, Na+, and K+ forms of Dowex 50W resins of 2, 4, 8, and 12% DVB content in methanol and water have been determined from their solvent sorption isotherms, treating 1 % DVB resins as reference "uncross-linked" exchangers. These swelling pressures have been discussed in terms of ionic solvation and ion pair formation in the resins. The linear relationships between tt and the measured equivalent volumes of the various ionic forms have been discussed in terms of properties of solvents particularly dielectric constant and ion-solvent interactions. The total electrostriction of the solvent at zero swelling pressure [AVes(b)] and at maximum swelling [ Ves] was found to be the same within experimental precision. The electrostriction per mole of solvent is much higher in MeOH than in water indicating stronger binding of methanol to cations in the resin phase. The integral free energies of swelling (AGSJ of these resins are negative. The -AGav/ values follow the sequence H+ > Li+ > Na+ > K+ and 1% > 2% > 4% > 8% > 12% DVB. The contribution of the resin cross linking (swelling pressure) to the free energy of swelling of cross-linked resins has been computed with reference to 1 % DVB resins. This contribution was found to be small and positive. It has been concluded that generation of swelling pressures is at the expense of secondary solvation of ions and osmotic effects.

2-43 between the vis-cosity expansion coefficient in eq 32 and the geometrical expansion coefficient in eq 33. In the present treatment the two coefficients were taken equal. It should also be mentioned that numerous attempts have been made to improve the original polymer theory, notably In the refinement of the mathematical treatment of the models which lead to eq 26 and 32. In this text the theory Is used In its original form, refinements appearing of trivial significance at the present staged experimental work.