Revisiting the Problem of Adsorption/Desorption Isotherms on Hypercrosslinked Polymers

This contribution is focused on the examination of adsorption/desorptiom isotherms for nitrogen at 77 K and benzene vapors at 293 K on various hypercrosslinked polystyrene (HP) resins. All isotherms for N₂ are identical in their shapes and are characterized by a steep rise of the adsorption branch at low p/p₀ followed by a less steep hoisting of the branch with increasing relative pressure. Adsorption isotherm for benzene demonstrates an ill-defined convex initial part followed by a significant rise in network loading with further increase in relative pressure. In the both cases we assume the rise in adsorption to reflect the relaxation of inner stresses with the simultaneous increase in the volume of networks. The distinction between the two types of isotherms is conditioned upon the fact that in the networks cooled down to 77 K stresses are stronger and the initial volume of the sample is more compressed. The amounts of nitrogen and benzene absorbed at relative pressure of 0.95 are the same order of magnitude, indicating similar swelling of HP in the both adsorbates. The adsorption behaviors of hypercrosslinked PIM-type polymers are governed by the same effects.