Boronic Acid Terminated Thermo-Responsive and Fluorogenic Polymer: Controlling Polymer Architecture for Chemical Sensing and Affinity Separation

Thermo-responsive poly( N -isopropylacrylamide) (polyNIPAm) containing terminal boronic acid was synthesized using atom transfer radical polymerization (ATRP) in combination with Cu(I)-catalyzed alkyne–azide 1,3-dipolar cycloaddition (CuAAC) reaction. Alkyne-terminated polyNIPAm was first synthesized by ATRP using an alkyne-containing initiator. A fluorogenic boronic acid, 3-(2-azido-acetylamino)phenylboronic acid (APBA) was then linked to the polyNIPAm through CuAAC. The synthesized polymers were characterized by 1 H NMR, FT-IR, UV–vis, matrix-assisted laser desorption/ionization time-of-flight (MALDI–TOF) mass spectrometry, and turbidity measurements. The intensity of fluorescence emission of the boronic acid-terminated polyNIPAm (BA-polyNIPAm) was found to increase when increasing amount of a cis-diol compound (i.e., fructose) was added. At physiological pH value, the BA-polyNIPAm effectively bound fructose and could be easily separated from aqueous solution by raising the temperature above its lower critical solution temperature (LCST).