Polyacrylamide hydrogels with trapped polyelectrolyte rods

A new type of intermacromolecular system consisting of a flexible polymer gel with embedded synthetic rigid-rod linear polyelectrolyte has been investigated for polyacrylamide hydrogel and linear poly(4,4 "-(disodium 2,5-dimethyl-1,1':4',1 "-terphenyl-3',2 "-disulfonate)). It has been shown that the incorporation of stiff-chain polyelectrolyte inside the uncharged network improves both the ability to absorb water and the mechanical strength of the gel. This makes such systems potentially promising as superabsorbent materials. Study of the kinetics of the release of polyelectrolyte rods has shown that the rods are effectively retained by the gel although they are not covalently attached to the network chains. This is apparently due to the formation of aggregates of rods including some of the network chains. The release can be completely suppressed by the addition of low-molecular-weight salt, which favors the self-aggregation of similarly charged rods. An interpenetrating network consisting of a physical network of anionic rods cross-linked by bivalent cations and of chemically cross-linked polyacrylamide has been synthesized. It has been shown that the binding of the polyelectrolyte by bivalent, cations in a physical network prevents very effectively its release to the solution. The quantitative theory of the kinetics of gel swelling coupled with the release of rods from the gel has been developed. The main results of the theory are in good agreement with the experimental data.