Thermoresponsive properties of sugar sensitive copolymer of N-isopropylacrylamide and 3-(acrylamido)phenylboronic acid

The copolymer of N-isopropylacrylamide and 3-(acrylamido)phenylboronic acid (82:18, (M) over bar (n)=47000 g. mol(-1)) was prepared by free radical polymerization. The copolymer showed typical thermal precipitation behavior in aqueous solutions, its precipitation temperature (T-P) being increased from 23 to 32degreesC by increasing the pH from 6.5 to 9.7, because of ionization of the phenylboronate units. The pK(a) was evaluated as 8.9+/-0.1 from the effect of pH on T-P. At pH>9, i.e., in the anionic form of the copolymer, T-P was affected by a very low concentration of glucose (5.6 muM, DeltaT(P)=1-1.5degreesC), because of complex formation with a high binding constant. At a higher concentration of polyols (560 muM, pH>8) the increase of T-P was maximal for the copolymer complexes with fructose (7-10degreesC) and decreased in the order: fructose>glucoseapproximate tomannitol>pentaerythritol>galactose>Tris>glycerol. Di- and oligosaccharides (lactose, sucrose, and dextran) caused a slight increase of T-P at pH 7.5-8.7 while no effect was observed at pH>9. Isothermal dissolution of the copolymer suspension in water (27degreesC, pH 8.5) was possible in the. presence of fructose or mannitol but required higher concentrations (1.4-3.6 x 10(3) muM) as compared to those which enabled the shift of T-P in the soluble copolymer. The dissolution rate increased with fructose concentrations.