Thermoresponsive Properties of Sugar Sensitive Copolymer of N‐Isopropylacrylamide and 3‐(Acrylamido)phenylboronic Acid

Summary: The copolymer of N ‐isopropylacrylamide and 3‐(acrylamido)phenylboronic acid (82:18, M ₙ = 47 000 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 32 °C by increasing the pH from 6.5 to 9.7, because of ionization of the phenylboronate units. The p K 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 μ M , Δ T P = 1–1.5 °C), because of complex formation with a high binding constant. At a higher concentration of polyols (560 μ M , pH > 8) the increase of T P was maximal for the copolymer complexes with fructose (7–10 °C) and decreased in the order: fructose > glucose ≈ mannitol > 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 (27 °C, pH 8.5) was possible in the presence of fructose or mannitol but required higher concentrations (1.4–3.6 × 10 3 μ M ) as compared to those which enabled the shift of T P in the soluble copolymer. The dissolution rate increased with fructose concentrations. Effect of pH on T P of poly(NIPAAM‐ co ‐AAPBA) in the presence of various monosaccharides. image Effect of pH on T P of poly(NIPAAM‐ co ‐AAPBA) in the presence of various monosaccharides.