Effect of Additives on the Cloud Point Temperature of 2‑Hydroxy-3-isopropoxypropyl Starch Solutions

Temperature-responsive polymers with a lower critical solution temperature (LCST) have attracted much attention in biomedical and biotechnological fields. It is important to tune their cloud point temperature (<i>T</i>_<i>c</i>) in a broad temperature range as desired by the applications. In this study, new thermo-responsive 2-hydroxy-3-isopropoxypropyl starches (HIPS) was synthesized using Hylon V starch as raw material and isopropyl glycidyl ether as hydrophobic reagent. The phase transition behavior of HIPS and their <i>T</i>_<i>c</i> were determined by spectrophotometry. The effects of several conditions on the <i>T</i>_<i>c</i> of the HIPS were also investigated, which indicated that varying the molar substitution (MS) of HIPS can adjust <i>T</i>_<i>c</i> in a broad temperature range from 69 to 28 °C by changing the hydrophobic–hydrophilic balance of starch. The phase transition became fast and the <i>T</i>_<i>c</i> decreased with increasing polymer concentration. The effect of a series of sodium salts on the <i>T</i>_<i>c</i> of aqueous HIPS solutions was reported and the effectiveness of ions follows a trend, known as Hofmeister series. Several organic solvents were selected and the organic additives with small molecular weight can also regulate the <i>T</i>_<i>c</i> of HIPS in a certain range by changing the polymer–water interactions