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Silver nanoparticles with average diameter of 10 ± 3 nm were synthesized within the sieves of poly(N-isopropylacrylamide-2-hydroxyethylmethacrylate-acrylic acid) (p(NIPAAm-HEMA-AAc))polymer microgels.Free radial emulsion polymerization was employed for synthesis of p (NIPAAm-HEMA-AAc) polymer microgels.Silver nanoparticles were introduced within the microgels sphere by in situ reduction method.Microgels and hybrid microgels were characterized by Fourier transform infrared spectroscopy,ultra violet-visible spectroscopy,transmission electron microscopy and dynamic light scattering measurements.Catalytic activity of Ag-p(NIPA-HEMA-AAc) hybrid microgels was studied using catalytic reduction of 4-nitrophenol (4-NP) as a model reaction in aqueous media.The influence of sodium borohydride (NaBH4) concentration,catalyst dose and 4-NP concentration on catalytic reduction of 4-NP was investigated.A linear relationship was found between catalyst dose and apparent rate constant (kapp).The mechanism of catalysis by hybrid microgels was explored for further development in this area.The deep analysis of catalytic process reveals that the unique combination of NIPAAm,HEMA and AAc does not only stabilize silver nanoparticles in polymer network but it also enhances the mass transport of hydrophilic substrate like 4-NP from outside to inside the polymer network.