Synthesis and Self-Assembly Behavior of Temperature Responsive 2-Hydroxy-3-Isopropoxypropyl Hydroxyethyl Cellulose

Responsive polymers have attracted great interests in many application fields. Thermoresponsive polymers are especially appealing, and have been applied in biomedical and biotechnological fields. A thermoresponsive polymer, 2-hydroxy-3-isopropoxypropyl hydroxyethyl cellulose (HIPEC), was prepared by etherification reaction, which grafted isopropyl glycidyl ether (IPGE) onto hydroxyethyl cellulose (HEC). The HIPEC was characterized by H-1 NMR, C-13 NMR, and 2D HSQC NMR, and the molar substitution (MS) of HIPEC was determined by 1H NMR. The lower critical solution temperature (LCST) of HIPEC can be tuned from 17.0 similar to 43.0 degrees C by changing MS of hydrophobic groups from 1.21 similar to 2.88. The salt concentration has a significant influence on LCST, the experiment results indicated that the LCST of HIPEC decreased with increasing NaCl concentration. Amphiphilic, thermoresponsive polymers can form micelles in aqueous solution and encapsulate guest molecules. Fluorescence spectroscopy and dynamic light scattering (DLS) showed that HIPEC can assemble into micelles, and micelles diameter significantly increase with increasing temperature. It is indicated that the morphologies of the HIPEC micelles can be varied by changing temperature. The critical micelle concentrations (CMC) of HIPEC which were measured by fluorescence spectroscopy decreased with increasing of the MS of hydrophobic groups. Additionally, using Nile Red as a probe, fluorescence spectroscopy and confocal laser scan microscope (CLSM) were applied to the HIPEC aqueous solution to examine the encapsulation of Nile Red aqueous solutions of the HIPEC. The research results show that Nile Red can be encapsulated and stabilized in the hydrophobic core of HIPEC micelles. The fluorescence intensity of Nile Red increased with increasing of HIPEC concentration, and there is a sharp increase in the number of HIPEC micelles above CMC. Because the morphologies of HIPEC micelles were disrupted when the temperature reached the LCST, the Nile Red which was capsulated in HIPEC micelles can be slowly released from HIPEC micelles over a much longer period of time, and the release process can be controlled by changing temperature.