Preparation And Properties Of Temperature Sensitive Phosphotungstic Acid Composite Hydrogel

Heteropolyacids, which have not only structural features of coordination compounds and metal oxides, but also redox and acidic properties, are widely used in the catalytic reaction of organic and inorganic chemistry. The classical Keggin type of heteropolyacid attracts many attentions in application of acid-catalyzed oxidation reactions for being cheap and easily available. In this paper, We combined advantages of the Keggin type of phosphotungstic acid and thermo-sensitive hydrogels to synthesize composite hydrogel.The temperature-sensitive monomers and phosphotungstic acid(HPW) were used to synthesis hydrogels with catalytic properties by chemical and physical crosslinking. Characterization of the hydrogels were investigated.Meanwhile the catalytic properties of the hydrogels and their influencing factors were studied by catalyzing the oxidation of N,N-diethyl-p-phenylenediamine sulfate(DPD) using H2O2 as oxidizer. And main research works include:1. P(NIPAM-co-AM)/PEG/HPW hydrogels were synthesized by aqueous copolymerization of temperature-sensitive non-ionic monomer N-isopropylacrylamide(NIPAM) and acrylamide monomer(AM) in the presence of HPW and co-solvent PEG. HPW was physical cross-linked into the hydrogel through hydrogen bonding and coordination with monomers. The hydrogel was characterized by FT-IR, TG-DSC, SEM and EDX. The hydrogel exhibited a higher critical solution temperature(UCST) which could be readily tuned by the addition of PEG. The temperature-sensitive and photochromic behaviors had good reversibility. P(NIPAM-co-AM)/PEG/HPW hydrogels had better catalytic properties that the absorbance of catalysate could reach to 0.014 with low concentration of 9.8×10-4 mol/L of H2O2.So the hydrogel could be used to quickly quantitatively detect H2O2. The increasing of the concentration of H2O2, the amount of catalyst and the temperature were conducive to catalytic reaction.2. P(DMAEMA-co-AM)/HPW hydrogels were synthesized by aqueous copolymerization of temperature-sensitive cationic monomer N,N-dimethylaminoethyl methacrylate(DMAEMA) and AM in the presence of HPW. The hdyrogels were both chemically and physically crosslinked. HPW interacted with polymer chains through hydrogen bonding, electrostatic interaction and coordination. The hydrogels were characterized by FT-IR, TG, TEM. The hydrogel were sensitive to temperature and pH. The swelling rate of the hydrogels would increases as the temperature increasing or the pH decreasing. The load of HPW also affected the properties of hydrogels. The temperature and pH sensitivity of hydrogels became worse when the load increasing. Hydrogel showed better catalytic properties that the absorbance of catalysate could reach to 0.118 with low concentration of 9.8×10-4 mol/L of H2O2. The increasing of the concentration of H2O2, the amount of catalyst and the temperature were conducive to catalytic reaction. There was improved catalytic performance at pH=3.3. P(DEA-co-DMAEMA)/HPW were synthesized by aqueous copolymerization of two kinds of temperature-sensitive monomers DMAEMA and N,N-dimethylacrylamide(DEA) in the presence of HPW. The hydrogels were sensitive to temperature and pH. The swelling of the hydrogels would increase as the temperature increasing, and high swelling was obtained at pH=3. The temperature and p H sensitivity of hydrogel was dependent of molar ratio of DEA to DMAEMA, which was more obvious at molar ratio of 3:1. Hydrogel had better catalytic properties that the absorbance of catalysate could reach to 0.051 with low concentration of 9.8×10-4 mol/L of H2O2. The increasing of the concentration of H2O2 and the amount of catalyst were beneficial to catalytic reaction. Catalytic effects of hydrogel under alkaline conditions were better than under acidic conditions, and they would be greatly enhanced when tempareture and p H simultaneously acted on the hydrogel.