Investigation of pH sensitivity of poly(acrylic acid-co-acrylamide) hydrogel

It was found that the upper critical solution temperature (UCST) of poly(acrylic acid-co-acrylamide) hydrogel decreases with increase in pH. The UCST of samples equilibrated in a buffer at pH 2.5 was 33.7 degreesC, whereas it shifted to below 0 degreesC when swollen in buffers above pH 10. FT-IR showed that COOH group of acrylic acid ionized gradually in alkaline media. The morphology change of the hydrogel swollen in different buffers was studied by environmental scanning electron microscopy (ESEM). ESEM images showed that the pore size of the sample increased with increase in pH, and in strongly basic media the three-dimensional network was replaced by a `sausage-like' or `desert-like' structure. A study of the pH-dependent release of cefazolin sodium was also carried out. (C) 2003 Society of Chemical Industry.