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Poly(N‐isopropylacrylamide‐co‐acrylic acid) [p(NiPA‐co‐AAc)] microgel particles were synthesized by free radical precipitation polymerization in aqueous medium. Silver nanoparticles (Ag NPs) were fabricated inside the microgels by in situ reduction method. UV–visible, Fourier transform infrared (FTIR), and dynamic light scattering techniques were used for characterization of pure microgels. The Ag‐p(NiPA‐co‐AAc) hybrid microgels were characterized by UV–visible, FTIR, X‐ray diffraction, and transmission electron microscopy. The hybrid microgel system was used as a catalyst for reduction of 4‐nitroaniline (4‐NA) in aqueous medium. The kinetics of the catalytic reduction of 4‐NA under various conditions of concentration of hybrid microgels, sodium borohydride (NaBH4), and 4‐NA was monitored by UV–visible spectrophotometry. It was found that the value of apparent rate constant (kapp) increases with increase of concentration of NaBH4 and catalyst dosage while it remains constant at various concentrations of 4‐NA. The kinetic data were used to elaborate the conversion of 4‐NA into p‐phenylenediamine on the basis of electron relaying effect of Ag NPs present inside the microgels. POLYM. COMPOS., 39:645–653, 2018. © 2016 Society of Plastics Engineers

Abstract Three different poly(N-isopropylacrylamide-co-acrylic acid) [p(NIPAM-AA)] microgel samples were prepared using a precipitation polymerization method by varying the concentration of NIPAM and AA in aqueous medium. The microgels were used as microreactors to fabricate Ag nanoparticles (NPs) by in situ a reduction method. Fourier transform infrared (FTIR) and UV-visible spectroscopy were used to characterize the pure and hybrid microgels. The hybrid microgels with different AA content were used as catalysts for reduction of nitrobenzene (NB) into aniline. The progress of the reaction was monitored by a UV-visible spectrophotometer. The results show that the value of the apparent rate constant for catalytic reduction of NB decreases from 0.431 min-1 to 0.227 min-1 by increasing AA content from 3 mol% to 7 mol%, respectively. Decrease in apparent rate constant with increase of AA content can be attributed to an increase in hydrophilicity with increase of AA contents of the microgels. The increase in induction period with increase of AA contents indicates that diffusion of NB towards the catalytic surface becomes difficult due to an increase of hydrophilicity.

Abstract:We synthesized poly(N-isopropylacrylamide-co-acrylic acid) microgels with 1, 3, 5, and 7 mol percentage of acrylic acid. Silver nanoparticles were fabricated inside these microgels at room temperature. Pure microgels were characterized by Fourier transform infrared (FTIR) spectroscopy and dynamic light scattering (DLS). Hybrid microgels were characterized by UV-Visible spectroscopy. The size of the silver nanoparticles increased with an increase in the content of acrylic acid. Catalytic activity of these hybrid microgels was investigated using UV-Visible spectrophotometry.Induction time decreased from 8.8 to 2.6 min and the value of apparent rate constant decreased from 0.226 to 0.109 min −1 , when the content of acrylic acid was increased from 1 to 7 mol %. This decrease in induction time was due to decrease in the surface area of nanoparticles present within the microgels with an increase in the feed contents of acrylic acid. The decrease in the value of apparent rate constant was due to an increase in the size of nanoparticles fabricated within the microgels with an increase in mol percentage of acrylic acid. The linear relation between apparent rate constant and feed contents of acrylic acid can be used for quantitative analysis of contents of acrylic acid present in polymer microgels.

AbstractIn this article, the classification, synthesis, properties, and applications of responsive microgels fabricated with gold (Au) nanostructures have been systematically reviewed. Microspheres, core-shell, core-shell-shell, hollow rings, and yolk-shell are different types of hybrid microgels containing Au nanostructures that have been reported in the literature. Hybrid microgels have tunable properties of both Au nanomaterial and smart polymeric material. Due to this unique combination, hybrid microgels containing Au nanomaterial are potential candidates for applications in drug delivery, photothermal therapy, glucose sensing, insulin delivery, catalysis, photonics, and ultrasensitive analyte analysis. Recent research progress in the design, characterization, and applications of Au nanomaterial containing smart polymer microgels has been described here. Many gaps in the literature and future perspectives of Au nanomaterial-based hybrid microgels have been highlighted in this review, which will be helpful for the people working in this area to plan their future work.