ABSTRACT
This chapter outlines the water-soluble polyphosphazene polyelectrolytes relative to their synthesis, physicochemical behavior in solution, gelation mechanism, and applications in microencapsulation and protein delivery. Polyorganophosphazenes are attracting attention as biomedical polymers, membranes, hydrogels, bioactive and biodegradable polymers. Phosphazene polymers have a long-chain backbone of alternating nitrogen and phosphorus atoms with two side groups attached to each phosphorus. The synthetic route for polyphosphazenes containing reactive functionalities, including ionic groups, was designed to avoid the reaction of poly(dichlorophosphazene) with difunctional reagents, which cause an inevitable cross-linking of the polymer. The same “side group transformation” approach was later simplified by All-cock for the synthesis of water-soluble carboxylic acid-bearing polyphosphazene. The physicochemical behavior of phosphazene polyelectrolytes in aqueous solutions has been the focus of very few studies. Phosphazene polyelectrolytes form highly swollen ionotropic gels in the presence of calcium and other multivalent ions in aqueous media.
