Study On The Preparation And Properties Of2-Hydroxy-3-isopropoxypropyl Starches And Its Thermoresponsive Hydrogels

New thermoresponsive2-hydroxy-3-isopropoxypropyl starches (HIPS) was synthesized by changing the hydrophobic-hydrophilic balance of starch using using Hylon V starch as raw material, isopropyl glycidyl ether as hydrophobic reagent.1H-NMR was used for characterization of HIPS and calculation of its molar degree of substitution (MS). The effect of MS on the LCST behavior of HIPS was studied, which was found that the LCST decreased from69℃to28℃with an increase of the MS from0.86to2.77; The phase transition behavior became sharper by increasing the solution concentration and the rate of the phase transition was the fastest when the concentration increased to10g/L. The transmittance values of the solution in the heating cycle (or cooling cycle) were almost equal to each other and only slight or no hysteresis took place. Because the LCST behavior originated from varying inter-and intra-molecular interactions upon heating, the effect of addition of small molecules to the polymer solutions on tuning the LCST behaviors was studied. The result indicated that the effect of NaCl concentration on lowering the LCST of the polymer solutions followed Hofmeister series and the LCST was lowered by7.2℃when the NaCl concentration increased to25g/L. The addition of the acetone to HIPS solution initially decreased the LCST, and a further addition increased the LCST. The addition of the ethanol to HIPS solution initially decreased LCST then no LCST was observed. The addition of the butanol to HIPS solution decreased LCST when the concentration was below4%. The surface tensions of aqueous solution of HIPS have been investigated. The critical micelle concentrations (cmc) of HIPS were in range of0.36g/L to0.021g/L depended on MS.To further expand the application of thermo-responsive polymer based on starch, in this paper, we synthesized HIPS macroporous gels by precipitation polymerization above its LCST (50℃) for3h, using2-hydroxy-3-isopropoxypropyl starches (HIPS-3, MS=1.55) as raw materials, ethylene glycol diglycidyl ether (EDGE) and poly(ethylene glycol diglycidyl ether)(PEDGE) as cross-linkers respectively. In addition, we choose divinyl sulfone (DVS) with higher cross-linking ability as cross-linker and synthesized HIPS gels by polymerization for3h at the room temperature, then polymerization for1h above its LCST. The macroporous structure has been observed by SEM. Then the swelling ratio (SR), the deswelling kinetics and the reswelling kinetics of the three hydrogels were studied. It indicated that the three hrdrogels show quite fast deswelling ratio, but the reswelling ratio was different. HIPSE gel (EDGE as crosslinker) and HIPSD gel (DVS as crosslinker) only need3min for reswelling to equilibrium state. However, the HIPSP gel (PEDGE as crosslinker) needed2h. HIPSE gel presented good reversibility in the heating and cooling cycle. And the swelling ratio keeped almost unchanged after four heating and cooling cycles in the16minutes. The effect of the MS of HIPS on the swelling ratio of HIPSE gel was studied. The SRs decreased with the increasing of MS but there is no obvious effect on the deswelling kinetics and the reswelling kinetics. The NaCl concentration has no effect on the swelling behavior of HIPSE gel. The swelling ratio of the hydrogels was different in the different solvents followed the order: H2O>ethanol>butanol>isopropanol>acetone.