The Preparation And Charactaristic Of Inorganic/Organic Nanocomposite Stimulus-Responsive Hydrogels

Smart hydrogels have became a hot topic of science research, which have been applied in many fields, like drug release, tissue engineering, special material recognition, chemical catalysis, substance separation, microchannel components, shape memory materials, and stimuli-responsive devices. However, due to the shortcomings of traditional chemical cross-linked hydrogels, such as slow responsive rate, weak mechanical properties etc, most of researches have focused on improving the mechanical properties, response rate and extending the function.In this thesis, the nanosized inorganic clay and POSS were used as additive, through choosing the monomers and designing the structure, a series of nanocomposite hydrogels with excellent properties, fast response rate and multi-responsiveness were prepared. Their synthesis, structure and properties have been systematically investigated. The results and conclusions are as follows:Firstly, the work focused on the further improvement of the response rate and mechanical properties based on PNIPA/clay nanocomposite hydrogels (NC gels).(1) The PNIPA NC gels were prepared by freezing polymerization for improving the response rate. Through the control of the freezing time, the gels with various properties were gotten. Freezing the pre-polymerization solution before the formation of clay-polymer brush makes the gels own absolute interconnect porous structure, and thereby resulting in an ultrarapid deswelling rate, such as losing90wt%of water within10s, while the mechanical strength decreases significantly due to the decrease of the effective crosslinked polymer chains between the clay. With the delay of freezing time, the response rate decreases while the mechanical properties enhances.(2) Based on the results above, the tetramethoxysilane (TMOS) solution were added into the freezing polymerized PNIPA NC gels to form the second-Si-O-network by polycondensation, which was confirmed by SEM, polarizing microscope and TGA analysis. This kind of IPN hydrogels exhibits excellent mechanical properties with very fast response rate. Meantime, comparing the normal NC gels, this IPN gels own better dimensional stability in deswelling process.(3) The cellulose nano-whisker prepared by acid decomposing cotton cellulose was added into the freezing polymerized PNIPA NC gels for reinforcement, the effect of cellulose whisker on the properties of hydrogels with various swelling ratio was investigated detailedly. The results showed that the cellulose interacts in gels, which causes the obvious enhancement and faster response rate, the effect of reinforcement is determined by the swelling ratio of gels and the amount of cellulose directly, the smaller swelling ratio makes the cellulose whisker be closer so as to interact strongly, which results in the significant enhancement of the strength of gels.Secondly, preparing the multi-responsiveness clay cross-linked nanocomposite hydro gels for extending the application of NC gels.(1) The monomer dimethylaminoethyl methacrylate (DMAEMA) was cross-linked by clay L-G and L-S respectively in situ free radical polymerization to prepare nanocomposite gels (named as G-NC gels and S-NC gels). From the analysis of yield, FTIR, X-Ray and SEM, it was proved that the clay L-S is an appropriate crosslinker for preparing PDMAEMA NC gels with better homogeneous and higher yield due to the uniform dispersion of clay in gels. The resulting S-NC gels show obvious temperature and pH double-sensitiveness. Comparing to traditional chemically crosslinked gels, S-NC gels own better mechanical properties and swelling properties, lower LCST than40℃, faster response rate and better repetitive swelling properties.(2) Linear carboxymethyl chistosan (CMCS) was introduced into the PDMAEMA NC gels as semi-IPN gels (C-NC gels) for adding the bonding point of drug. The amount and substitution degree of CMCS makes a significant impact on the pH responsiveness of gels, especially, the swelling ratio decreases considerabley around the isoelectric point of system. In the drug load and release test in simulated human intestinal and stomachic condition by using theophylline as target, the C-NC gels exhibits an excellent load ability and controlled-release in stomachic condition.(3) Water soluble azo monomers [4-(4’-carboxyphenylazo) phenoxy] acrylate (CPA), exhibiting fast UV responsiveness and the recoverability under visible light, was synthesized and used to prepare temperature/UV responsive P(NIPA-co-CPA) NC gels. The gels with high content of CPA exhibit obvious volume shrink under the UV-light, while the temperature responsiveness still is kept well. Meantime, the mechanical properties of gels decrease significantly with the increase of CPA.Thirdly, the POSS hybrid hydrogels were prepared for developing new organic-inorganic hydrogels systems with excellent properties.(1) POSS hybrid P(NIPA-co-DMAEMA) hydrogels with organic-inorganic co-crosslinked networks were synthesized by using both organic cross-linker BIS (N,N’-methylenebis(acrylamide)) and inorganic cross-linker OvPOSS (octavinyl polyhedral oligomeric silsesquioxane). The resulting gels display obvious temperature and pH double responsiveness, OvPOSS particles dispersed in polymer make a dominant effect on the properties of gels. With the increase of OvPOSS, the aggregation of particles on nano or micro-scale happens, which is proved by SEM and X-ray analysis. The increase of OvPOSS leads to the change of gels’properties, such as the lower LCST and better compression strength. Specially, the interconnected microporous structure of gels ascribed to the micro-phase separation results in faster deswelling rate, which makes the gel become attractive. Meanwhile, the swelling ratio and tensile behavior of gels is still need to be improved.(2) OvPOSS particles were incorporated into PNIPA NC gels via a two-step technique. The second PNIPA network crosslinked by OvPOSS was polymerized in the presence of the first clay-PNIPA network. The OvPOSS makes a similar effect on the properties of gels, which is described in (1). In brief, with the increased OvPOSS, the gels show lower swelling ratio, faster deswelling rate and better compression strength, the LCST of gels rise first and then decline slightly. Most importantly, the gels keep the good toughness of NC gels with a higher tensile strength, despite that the elongation at break decreases.(3) For improving the properties of PDMAEMA NC gels, the water-soluble octaammonium-POSS was added into the gels by in situ polymerization. The aggregation of POSS is directly dependent on its content in gels. Comparing to the POSS-free gels, the tensile strength and resilience of gels is improved obviously. Meantime, the gels show lower LCST being closer to the temperature of human body, and higher deswelling rate. Most interestingly, the gels exhibit discriminative reswelling behavior after deswelling and thoroughly drying, which may be attributed to the rearrangement of structure of gels.