Study Of The Synthesis And Properties Of Smart Hydrogels With Porous Structure

In this study,A novel technique to synthesize macroporous hydrogels with ultra rapid environmental sensitive properties was proposed.Moreover,the porous structures of hydrogels were controlled by several methods.A novel freezing polymerization method of synthesizing macroporous poly(N-isopropylacrylamide)(PNIPA) hydrogels was proposed.Polymerization process was taken place in the presence of dodecyl dimethyl benzyl ammonium bromide(DDBAB).A hydrophobic initiator dodecyl dimethyl benzyl ammonium persulfate(DDBAPS) was proved to be produced in situ by the reaction of DDBAB and the water-soluble initiator ammonium persulfate(APS),and a heterogeneous initiation mechanism was proposed.The resulted poly(N-isopropylacrylamide) (PNIPA) hydrogels were macroporous with large swelling ratios and ultra rapid thermo responce rates.Mixed solvents which were composed of pure water and 1,4-dioxand at various concentrations were used instead of pure water during the novel freezing polymerization process.The aggregate size of the hydrophobic initiator DDBAPS became smaller when the concentration oF 1,4-dioxane increased.The effects of the mixed solvent on morphology,swelling ratio,and thermo response kinetics of the resulted hydrogels were investigated.Moreover,the resulted hydrogels were used for emulsified paraffin concentration.The different separation performance attributed to the different structure of gel matrix.Poly(vinyl alcohol)(PVA) was involved to control the pore size of the hydrogels. Morphology of the resulted hydrogels was studied by both optical microscope and scanning electron microscope(SEM).Moreover,the pore size and its distribution were examined by mercury intrusion porosimetry(MIP) examination.The results indicated that size of the pores decreased with the increase of the amount of added PVA.The mechanism was explained after dynamic light scattering(DLS) measurement of the size of hydrophobic initiator DDBAPS aggregates which were formed in situ in PVA aqueous solutions of various concentrations as the product of the reaction between DDBAB and APS.Thermosensitive hydrogel made up of chitosan/PNIPA semi-interpenetrating network(semi-IPN) was synthesized.Horseradish peroxidase(HRP) was then immobilized on this hydrogel that acted as an enzyme-carrier by glutaraldehyde bridge.Polymerization of acrylamide was initiated by a redox system and was catalyzed by the immobilized enzyme at room temperature.The attention was focused on the properties of the carrier-enzyme systems.The properties of the immobilized enzyme such as enzyme activity,storage stability,and thermo stability were also studied.The immobilized enzyme could be used repeatedly.The macroporous hydrogel would be a suitable enzyme carrier for practical applications in future. Moreover,a novel enzymatic-mediated process using PNIPA hydrogels was proposed.Porous polyacrylamide(PAAm) hydrogels were hydrolyzed under alkaline condition to form anionic PAAm hydrogels with super rapid pH sensitive properties as well as very high swelling ratios.