Especially,
they showed superior ability to store water in external pressure
tests . These polymers convert to gels when they
absorb water. Only a few cross-links reduce greatly the solubility of
a polymer and tend to produce what is called a gel-polymer, which,
although insoluble, usually will absorb (be swelled by) solvents in
which the uncross-linked polymer is soluble. The tendency to
absorb solvents decreases as the degree of cross-linking is
increased because the chains cannot move enough to allow the
solvent molecules to penetrate between the chains