Preparation And Properties Of Temperature And Ph-sensitive Xanthan Gum / Pnipaam Gel

In recent years, considerable research attention has been focused on the environment-sensitive hydrogels because of they possess great potential applications in many aspects, including drug delivery system, enzyme immobilization and biomaterials separation purification, etc. From the point of view of molecule design, a series of novel type of temperature and pH responsive hydrogels was prepared based on the poly(N-isopropylacrylamide) (PNIPAAm) and a natural material xanthan (Xan) with a good biocompatibility in this dissertation. Two different types of dual temperature and pH sensitive hydrogels were synthesized, and the structures of the product were characterized by infrared spectroscopy (IR), differential scanning calorimetry (DSC). The effect of the feeds composition on the swelling and deswelling properties of these hydrogels has been systematically studied, and the swelling, deswelling behavior and response mechanism was discussed. The main results obtained are as follows:a) N, N-dimethylformamide (DMF) as the solvent, a dual-functional group of maleic anhydride is programmed imported to the natural polymer xanthan elements, from FTIR results show that maleic anhydride successful grafted to xanthan C6 position.b) A kind of semi-IPN hydrogels based on xanthan and cross-linked poly(N-isopropylacrylamide) was prepared with semi-interpenetrating network (semi-IPN) technique. The swelling behaviors of the Xanthan/PNIPAAm semi-IPN hydrogel which sensitive to both temperature and pH, were investigated in detail. Results show swelling of the hydrogel in deionized water as well as in the buffer solution (pH = 2.2 and pH = 7.4) gradual increase with Xanthan compositon increase, Xanthan / PNIPAAm semi-IPN hydrogels have shown a typical "thermal-negative" thermo-sensitive properties. At the same time, Xanthan/PNIPAAm semi-IPN hydrogel show clear pH sensitivity. Swelling and deswelling property of Xanthan/PNIPAAm semi-IPN hydrogel related to the content of Xanthan which attribute to a spiral of rigid structure of xanthan providing a "Channel" led water in and out. But the addition of Xanthan has little impact on the critical solution temperature (LCST).c) Through radical solution polymerization, a kind of grafting xanthan gum and NIPAAm copolymer hydrogel (Xan-MA/PNIPAAm) were synthesized, it was found that environmental responsive, swelling, and deswelling property of Xan-MA/PNIPAAm is similar with semi-IPN hydrogel, but the feed composition of Xan-MA/PNIPAAm in the precursor have a greater impact on the LCST, we can adjust proportion of m_Xan-MA:m_PNIPAAm to regulate the LCST of copolymer hydrogel.