Cyclic methacrylic acid oligomer as a novel pH‐sensitive carrier material

Abstract

AbstractThe pH effect of inclusion of methylene blue (MB) in cyclic methacrylic acid oligomer (CMAA) with degree of polymerization 14, which was a novel cationic host material with pKa 4.83, was investigated in methanol. The self‐diffusion coefficients of MB in methanol at pH 7.0 and 4.0 with and without CMAA were measured by 1H‐NMR spectrometry with pulsed‐field‐gradient stimulated‐echo pulse (PGSE) analysis. At both pH values, the addition of CMAA to MB solution resulted in the complex formation between CMAA and MB. MB was included in CMAA in methanol at a wide range of pH. The molar fraction of the slow diffusion component corresponding to the complex increased by varying the pH from 7.0 to 4.0. Then, SiO–CMAA was synthesized by immobilization of CMAA on silica gel beads. The time dependence of adsorption of MB to SiO–CMAA was investigated by UV–Vis spectrometry. At pH 7.0, the absorbance of MB–methanol solution gradually decreased by the addition of SiO–CMAA. The absorbance drastically decreased on varying the pH from 7.0 to 4.0, and the absorbance quickly increased on varying the pH from 4.0 to 7.0. The inclusion of MB in CMAA was fast and reversible on changing the pH of the solution. CMAA was the novel pH sensitive host material. Inclusion of MB in CMAA enhanced at pH 4.0 rather than at pH 7.0. Copyright © 2008 John Wiley & Sons, Ltd.