Competitive interactions in hydrogel-interpolyelectrolyte complex systems

Abstract-Substitution reactions between weakly crosslinked anionic hydrogels (network sodium polyacrylate or network sodium poly(2 acrylamido-2-methyl-1-propanesulfonate)) and nonstoichiometric inter-polyelectrolyte complexes formed by a blocking linear sodium polyacrylate and lyophilizing poly(N,N’-diallyl-N,N’-dimethylammonium chloride) in aqueous media have been revealed and studied. It has been found that both sulfonate and carboxylate networks take up a linear polycation via the formation of a stoichiometric interpolyelectrolyte complex, a phenomenon that results in the collapse of the network. In this case, the blocking polyacrylate anions are quantitatively expelled from the particles of the nonstoichiometric watersoluble complex into the environment and occupy lyophilizing polycations uniformly, a circumstance that results in their precipitation and, consequently, the termination of the substitution reaction. This outcome suggests the presence of feedback in the studied processes. The result for carboxylate networks is completely new and nontrivial; it is indicative of the important role of macromolecular architecture in selecting the direction of a process.