Studies On The Phase Transition Of PNIPAM Induced By Small Molecule Weak Acids And Preparation And Properties Of IPN Nanogel

Hydrogel is a kind of polymer which has three-dimensional network structure. It is a multivariate system composed of hydrogel with water. Hydrogels are widely used in biomedical devices, super-absorbents and personal care product due to their high water content, biodegradability and excellent biocompatibility. Intelligent hydrogel is also known as environmental responsive hydrogel. And it can swell or collapse reversibly in response to external stimuli. The researchers are mostly interested in thermo-, pH-and pH/thermo-hydrogels which have potential applications in many fields, such as drug release, biomass separation, biological sensor, etc. As a typical kind of temperature-sensitive material, the application of poly (N-isopropylacrylamide)(PNIPAM) intelligent hydrogel got much attention in recent years. How to adjust the volume phase transition temperature (VPTT) is a focal point of research. We have analyzed and summarize predecessor’s research results. The paper firstly presents that there is a phase transition of PNIPAM induced by small molecule weak acids and mechanisms of this were discussed as well. The preparation and characterization of an adjustable color hydrogel were briefly introduced. In addition, interpenetrating (IPN) PNIPAM/PMAA and PDEA/PMAA nanogels were synthesized and investigated. These novel nanogels promise to find a varity of applications in the fields of construction decoration, cosmectics and biomedicine. The main contributions in this thesis are as follows:(1) This chapter discussed the effect of the small molecule weak acids on the phase transition of PNIPAM nanogel. These small molecule weak acids included:acry acid (AA), methacrylic acid (MAA), lactic acid (MAA), citric acid (CA) and acetic acid (AC). And the VPTT of PNIPAM in the small molecule weak acid system of different concentration and pH values was characterized by dynamic light scattering, separately. The results showed that, all of the five weak acids can reduce the VPTT of PNIPAM nanogel. The higher the acid concentration, the lower the VPTT of PNIPAM nanogel. Also, we reckoned that as the acid effect of AA and MAA, so the higher the pH values, the higher the VPTT of PNIPAM nanogel. And increasing pH value in the nanogels reduced the VPTT of PNIPAM due to the salt effect of ionized LA, CA and AC.(2) Emulsion precipitation polymerization was utilized to synthesize NIPAM/HEAc copolymer nanogels in aqueous media. The corresponding structure color was displayed when the copolymer nanogel concentration increased to a certain value. Nanogels were cross-linked by using crosslinker divinylsulfone (DVS) under alkaline condition. The color of cross-linked nanogels can be controlled by adjusting concentration and particle size of the nanogels. The corresponding structure color of the copolymer nanogels has blue-shifted with increasing the nanogels concentrations or the particle diameter of the nanogels. And also, its color can reversible change in response to temperature. This work may lead to technological applications, ranging from sensors and displays to home decoration.(3) The nanogels with IPN structure (PNIPAM/PMAA IPN nanogels) based on PNIPAM and PMAA were synthesized by seed-emulsion polymerization using redox initiator at21℃. The experimental results indicated that both the components were existed in an IPN structure. Under neutral conditions, the VPTT of IPN nanogels were consistent with that of the PNIPAM nanogel, but compared to PNIPAM nanogel, the heat shink extent of IPN nanogels were significantly reduced, and as the amount of PMAA was increased, this heat shink extent become increasingly weak.(4) The nanogels with IPN structure (PDEA/PMAA IPN nanogels) based on PDEA and PMAA were synthesized by seed-emulsion polymerization using redox initiator at21℃. The experimental results indicated that both the components were existed in an IPN structure. Under neutral conditions, the VPTT of IPN nanogels were consistent with that of the PDEA nanogel, but compared to PDEA nanogel, the heat shink extent of IPN nanogels were significantly reduced, and as the amount of PMAA was increased, this heat shrinkable degree became increasingly weak.