A Borinic Acid Polymer with Fluoride Ion- and Thermo-responsive Properties that are Tunable over a Wide Temperature Range

A new type of smart borinic acid polymer with luminescence and multiple stimuli‐responsive properties is reported. In DMSO with small amounts of water, the homopolymer PBA shows a tunable upper critical solution temperature (UCST). As the amount of water increases from 0 to 2.5 % (v/v), the UCST rises linearly from 20 °C to 100 °C (boiling point of water). Thus, the thermal responsive behavior can be tuned over a wide temperature range. Furthermore, polymer solutions in DMSO show a reversible response to fluoride ions, which can be correlated to the presence of the Lewis acidic borinic acid groups. Upon addition of fluoride, the polymer becomes soluble because the functional R2BOH groups are converted into ionic [R2BF2]− groups, but turns insoluble again upon addition of H2O, which reverses this process. Reversibly multi‐responsive: A new type of smart polymer with borinic acid moieties has been developed. Polymer PBA has an upper critical solution temperature (UCST) that is tunable from 20 to 100 °C; it also responds to the binding of fluoride to the Lewis acidic boron centers, enabling potential applications in trace water detection and anion recognition.