Snake-in-the-cage ion-exchange (retardion)
membranes can be synthesized by saturation of a
suitable ion-exchange resin (the cage) with an organic
counter ion that can be polymerized to form
a linear chain of oppositely charged polymer (the
snake). The polymer chain cannot be removed
from the host resin due to strong electrostatic
interaction and the restricted mobility of the linear
polymer chains. The ionic sights of the resin cage
are neutralized in the presence of oppositely charged
polymer chains. This provides mechanical stability
leading to decreased swelling and shrinking
properties.