Poly(organophosphazenes) with poly(alkyl ether) side groups: a study of their water solubility and the swelling characteristics of their hydrogels

Five different poly((alkyl ether)phosphazenes) were synthesized for studies of their water solubility as well as the swellabilities of their corresponding hydrogels in aqueous media. They are poly(bis(methoxyethoxy) phosphazene), poly(bis((aminoethoxy)ethoxy) phosphazene), poly(bis((methoxyethoxy)-ethoxy)phosphazene), poly(bis((ethoxyethoxy)ethoxy) phosphazene), and poly(bis((butoxyethoxy) ethoxy)phosphazene). Lower critical solution temperatures (LCST) were detected for four of the polymers. This phenomenon was independent of polymer concentration. However, poly(bis((aminoethoxy)ethoxy) phosphazene) possessed no LCST in aqueous media and remained fully soluble at all polymer concentrations. Hydrogels of these polymers were prepared by subjecting them to gamma radiation (1, 5, and 10 Mrad). The cross-linked polyphosphazenes behaved in a manner similar to that of their soluble counterparts. As the temperature of the aqueous media was increased, the hydrogels became opaque and released water. During these experiments, the percentage of water lost by the hydrogels was independent of both the pH of the aqueous media and the radiation dose received by the gels. No detectable decomposition of the soluble polymers was found nor was any loss of integrity of the hydrogels detected through several heating and cooling cycles. This solubility phenomenon was characteristic only of the interaction with water and was not detected in organic solvents. The potential biomedical applications of these materials are discussed.