SYNTHESIS AND CHARACTERIZATION OF PH-SENSITIVE POLY(ORGANOPHOSPHAZENE) HYDROGELS

A new class of pH-sensitive hydrogens has been designed and synthesize d. These are novel polyphosphazenes that bear various ratios of sodium oxybenzoate and methoxyethoxyethoxy side groups. These water-soluble macromolecules were cross-linked by Co-60 gamma irradiation and the pr oducts were allowed to absorb water to form hydrogels. The hydrogels h ad higher equilibrium degrees of swelling in basic than in acidic buff er solutions, and polymers with a higher loading of the ionic side gro up showed higher swellability than those with a lower loading of this side group. The effects of ionic strength, cation charge and radiation dose on the degree of swelling were also studied. A study of the diff usion of the dye Biebrich Scarlet from the hydrogels showed complete r elease of the dye in 4-12 h in pH 7.4 buffer solution but significantl y lower release at pH 2 even after 48 h. The release rate also varied as the side-group ratios were changed. The prehydrogel polymers were s ynthesized via the macromolecular substitution reactions of poly(dichl orophosphazene) with sodium methoxyethoxyethoxide and the sodium salt of propyl 4-hydroxybenzoate, followed by ester hydrolysis to yield the sodium carboxy late. The hydrogels are of interest for possible use a s pH-sensitive membranes and for a number of potential biomedical appl ications. (C) 1996 Elsevier Science Limited.