The pH changes of diluted dispersions of poly(N-isopropylacrylamide) below and over the LCST in the presence of chlorhexidine.

ABSTRACT

The pH of diluted aqueous dispersions of modified poly(N-isopropylacrylamide) with chlorhexidine was evaluated, at normalized skin surface temperature, as well below and over the lower critical solution temperature value. Three different poly-N-isopropylacrylamides were synthesized by surfactant free emulsion polymerization. They were evaluated in the terms of pH in the aqueous dispersions in the presence of chlorhexidine. The tendency was similar in all investigated systems at increasing temperature between 25 degrees C and 45 degrees C. The pH value decreased from the range between 9.87-9.94 down to the range 9.38-9.46. The course of pH decrease between the temperature of 32 degrees C and 45 degrees C was more radical, comparing to 25 degrees C and 32 degrees C, however in general the decrease was monotonic. The systems with chlorhexidine tend to change the pH with temperature increase more radically, in the comparison to the chlorhexidine alone. The formulations applied on the skin surface or in the oral cavity should be evaluated in proper temperature spectrum.