Random copolymers based on <i>N</i>-isopropylacrylamide (NIPAAm) containing 2-aminoethyl methacrylamide
hydrochloride (AEMA) and 5-methacrylamido-1,2-benzoboroxole (MAAmBo)
were synthesized and subsequently evaluated for their performance
in solid–liquid separation at various pH and temperatures.
The strong interactions between benzoboroxole residues and kaolin
hydroxyl groups were evaluated for the first time in the flocculation
of fine particle suspensions. The lower critical solution temperatures
(LCSTs) of PAMN decreases because of the hydrophobic nature of the
benzoboroxole moieties, resulting in strong hydrophobic interaction
at temperatures higher than the LCSTs. Temperature and pH responsive
polymer, P(AEMA<sub>51</sub>-<i>st</i>-MAAmBo<sub>76</sub>-<i>st</i>-NIPAM<sub>381</sub>) (denoted as PAMN) shows
the ability to induce fastest settling at a low dosage of 25 ppm and
under the condition of pH 9 and 50 °C. The accelerated settling
rate is considered to be due to the strong adhesion of benzoboroxole
residues to the kaolin hydroxyl groups, the electrical double layer
force, and the hydrophobic force. During condensation phase, increasing
the pH of sediment to pH 11 could attain the most compact structure.
Random copolymers containing benzoboroxole groups act as dispersants
(due to pH-responsive character) rather than flocculants at pH 11,
providing repulsive force that enables particles to rearrange their
position and consolidate well. Through a two-step solid–liquid
separation including settling phase and consolidation phase, rapid
settling and compact sediment are feasible simultaneously