Free Radical Precipitation Polymerization Research Articles

Synthesis and characterization of poly(N-isopropylmethacrylamide-acrylic acid) smart polymer microgels for adsorptive extraction of copper(II) and cobalt(II) from aqueous medium: kinetic and thermodynamic aspects.

Extraction of toxic heavy metal ions from aqueous medium using poly(N-isopropylmethacrylamide-acrylic acid) (P(NiPmA-Ac)) microgels as adsorbent has been investigated in present study. P(NiPmA-Ac) microgel particles were prepared by free radical precipitation polymerization in aqueous medium. Morphology and size of the prepared microgel particles was investigated by transmission electron microscopy (TEM). The Fourier transform infrared (FT-IR) analysis of pure and metal ion-loaded microgel particles was performed to confirm the presence of various functionalities of microgel particles and their interaction with metal ions extracted from aqueous medium. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to investigate the thermal stability and thermal behavior of pure and metal ion-loaded microgel particles. Contents of metal ions loaded into microgel particles were determined by TGA analysis. It was observed that P(NiPmA-Ac) particles have a potential to extract Cu2+ and Co2+ ions from aqueous medium. The Freundlich adsorption isotherm model best interprets the adsorption process as compared with the Langmuir model. Value of R2 according to the Freundlich adsorption isotherm was found to be 0.994 and 0.993 for Cu2+ and Co2+ ions, respectively. Adsorption process was followed by pseudo second order kinetics for Cu2+ and Co2+ ions with R2 values of 0.999 for both metal ions. Thermodynamic study showed that adsorption process was spontaneous, feasible, and endothermic in nature. Entropy was decreased at adsorbate-adsorbent interface during adsorption process. Adsorbent was recycled and reused for removal of Cu2+ ions, and adsorption efficiency was found to be maintained up to three cycles. Microgel particles also have ability to extract Cu2+ ions efficiently from electroplating wastewater. Graphical abstract.

Effect of Divalent Cation on Swelling Behavior of Anionic Microgels: Quantification and Dynamics of Ion Uptake and Release

Poly(N-vinylcaprolactam-co-itaconate) (P(VCL-co-IADME) microgels were synthesized varying the molar ratio between VCL and IADME via free radical precipitation polymerization in the presence of quaternary ammonium surfactant. In order to determine the effect of the divalent metal ions on the structure and the swelling behavior of the microgel systems, both neutral and charged forms of the hydrogels after hydrolysis were investigated. The triggered gel collapse caused by the divalent metal ion together with the quantification of the metal ion uptake was studied in detail by titration and ion chromatography methods and revealed the minimum concentration around 0.1 mM to trigger gel collapse on the treated gels. Uptake and release dynamics of the gels were followed by turbidity measurements and were in the time-range of 2 and 17 s, depending on the composition and the concentrations.

Synthesis and thickening properties of copolymers of acrylic acid and alkoxy(С12-С14)oligoethylene glycol methacrylates

Samples of hydrophobically modifi ed polyacrylic acid containing 1% of alkoxy(С12-С14)oligoethylene glycol methacrylate units have been synthesized by free radical precipitation polymerization. The infl uence of the length of ethoxylated spacer of macromonomers and neutralization degree of carboxylic groups on thickening properties of obtained polymers in water and waterpropylene glycol mixtures at diff erent temperatures has been determined.

Towards the realistic computer model of precipitation polymerization microgels

In this paper we propose a new method of coarse-grained computer simulations of the microgel formation in course of free radical precipitation polymerization. For the first time, we simulate the precipitation polymerization process from a dilute solution of initial components to a final microgel particle with coarse grained molecular dynamics, and compare it to the experimental data. We expect that our simulation studies of PNIPA-like microgels will be able to elucidate the subject of nucleation and growth kinetics and to describe in detail the network topology and structure. Performed computer simulations help to determine the characteristic phases of the growth process and show the necessity of prolongated synthesis for the formation of stable microgel particles. We demonstrate the important role of dangling ends in microgels, which occupy as much as 50% of its molecular mass and have previously unattended influence on the swelling behavior. The verification of the model is made by the comparison of collapse curves and structure factors between simulated and experimental systems, and high quality matching is achieved. This work could help to open new horizons in studies that require the knowledge of detailed and realistic structures of the microgel networks.

Regulating intracellular ROS signal by a dual pH/reducing-responsive nanogels system promotes tumor cell apoptosis.

Purpose: The levels of reactive oxygen species (ROS) in tumor cells are much higher than that in normal cells, and rise rapidly under the influence of exogenous or endogenous inducing factors, eventually leading to the apoptosis of tumor cells. Therefore, this study prepared a dual pH/reducing-responsive poly (N-isopropylacrylamide-co-Cinnamaldehyde-co-D-α-tocopheryl polyethylene glycol 1000 succinate, PssNCT) nanogels, which employed two exogenous ROS inducers, cinnamaldehyde (CA) and D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS), to selectively induce apoptosis by regulating ROS levels in tumor cells.Methods: The PssNCT nanogels were prepared by the free radical precipitation polymerization under the crosslink between pH-sensitive hydrazone and reducing-sensitive disulfide bonds, followed by the physicochemical and morphological characteristics investigations. Plasma stability, dual pH/reducing responsive degradation and in vitro release were also assessed. In cell experiments, cytotoxicity in different cells were first detected. The intracellular ROS levels and mitochondrial functions of tumor cells were then evaluated. Moreover, the apoptosis and western-blot assays were employed to verify the association between ROS levels elevation and apoptosis in tumor cells.Results: The nanogels exhibited a round-like hollow structure with the diameter smaller than 200nm. The nanogels were stable in plasma, while showed rapid degradation in acidic and reducing environments, thus achieving significant release of CA and TPGS in these media. Furthermore, the sufficient amplification of ROS signals was induced by the synergistically function of CA and TPGS on mitochondria, which resulted in the opening of the mitochondrial apoptotic pathway and enhanced cytotoxicity on MCF-7 cells. However, nanogels barely affected L929 cells owing to their lower intracellular ROS basal levels.Conclusion: The specific ROS regulation method achieved by these nanogels could be explored to selectively kill tumor cells according to the difference of ROS signals in different kinds of cells.

Reduction of nitroarenes catalyzed by microgel-stabilized silver nanoparticles.

Poly(N-isopropylacrylamide-co-acrylamide) (PNA-BIS-2) microgels were synthesized by free radical precipitation polymerization in aqueous medium. Spherical Ag nanoparticles with diameter of 10-20 nm were fabricated inside the PNA-BIS-2 microgels by in-situ reduction of silver nitrate using sodium borohydride as reducing agent. The Ag nanoparticles- loaded hybrid microgels were characterized by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy dispersive X-ray (EDX), Scanning transmission electron microscopy (STEM), Ultraviolet visible spectroscopy (UV Visible), Thermogravimetric analysis (TGA) and X-ray diffraction (XRD). Ag contents in the hybrid system were determined by inductively coupled plasma - optical emission spectrometry (ICP-OES). Various nitroarenes were successfully converted into their respective aromatic amines with good to excellent yields (ranging from 75% to 97%) under mild reaction conditions. The catalyst has ability to successfully convert substituted nitroarenes into desired products keeping many functionalities intact. The catalyst can be stored for long time without any sign of aggregation and can be used multiple times without any significant loss in its catalytic activity.

Stimuli-Responsive Microgel-Based Surface Plasmon Resonance Transducer for Glucose Detection Using a Competitive Assay with Concanavalin A

Glucose responsive microgels composed of poly(N-isopropylacrylamide-co-glycosyloxyethyl methacrylate) (p(NIPAm-co-GEMA)) were synthesized by free radical precipitation polymerization. The resultant microgels were shown to collapse upon addition of Concanavalin A (ConA) owing to its ability to bind up to four GEMA molecules. We showed that the microgel could reswell upon addition of free glucose due to the competitive binding of GEMA and glucose with ConA, effectively breaking the cross-links responsible for the collapse. Thus, by monitoring the contraction/expansion process of the p(NIPAm-co-GEMA) microgels bound to a Au surface via surface plasmon resonance (SPR), the concentration of glucose in solution can be quantified. We go on to show that there is a ninefold SPR signal enhancement compared to exposure of bare Au to glucose and a similar enhancement compared to microgels without GEMA. Finally, we showed that the p(NIPAm-co-GEMA) microgel-based SPR sensor surfaces were not responsive to other interfering species. Taken together, the results show that the competitive binding concept can be useful for detecting small biologically relevant molecules that are usually difficult to detect via SPR. Therefore, this concept can be expanded upon to detect other small molecules of interest in the future.

High-Speed AFM Reveals the Detailed Mechanism of Dynamic Protein Adsorption Onto Individual Hydrogel Microspheres

Hydrogel microspheres, i.e., microgels have both colloidal and hydrogel properties, which are composed of cross-linked hydrophilic polymer network. Due to the colloidal size property and biocompatibility, microgels are promising for advanced bio-nanomaterials such as protein drug delivery vehicles [1]. In order to establish the design concept of such protein carrier, understanding the dynamic interaction between the protein and microgels is essential. Up to now, the dynamic interaction between protein and microgels is well characterize by means of scattering, spectroscopy, and sensor [2]. However, to the best of our knowledge, there are no study that direct visualization during protein adsorption to individual microgels at nanoscale in real-time. Against this background, we visualized individual microgels during protein adsorption onto the microgels at nanoscale in real-time for the first time [3]. This approach, which enabled us to monitor the moment of protein adsorption to individual microgels, was realized by high-speed atomic force microscopy (HS-AFM) [4]. This method allows the direct visualization of the dynamics of biological molecules in action, without significantly disturbing the physiological function of the molecules [5]. We have already monitored the dynamic adsorption behavior of microgels onto solid/liquid interface [6]. The microgels were synthesized through aqueous free-radical precipitation polymerization of N-isopropyl acrylamide, the cross-linker N,N'-methylenebis (acrylamide), and acrylic acid with different content. In this presentation, the effect of protein interaction on the microgels’ dynamics will be discussed. Partially reproduced with permission from [6] Copyright (2017) John Wiley and Sons.

Real-Time Volume Changes in Individual Hydrogel Microspheres Observed By High-Speed AFM

Many thermo-responsive polymers show a lower critical solution temperature (LCST), and thus they display a coil-globule transition across the LCST by changing temperature. Hydrogel microspheres (microgels) composed of thermo-responsive polymer are taken over the property from the polymer, as a result, they show a volume phase transition temperature around the LCST. Owing to their rapid temperature-responsiveness, microgels are expected the various application such as sensors and separation technology [1]. Thermo-responsive properties of the microgels have been mainly evaluating by light scattering so far because typical size range of the microgels are tens nanometer to sub-micron order, which can not be clearly observed by optical microscopy. Against this background, the real-time volume transition of individual microgels during heating was visualized for the first time using high-speed atomic force microscopy (HS-AFM) [2]. This method allows the direct visualization of the structural dynamics of biological molecules in action, without significantly disturbing the physiological function of the molecules [3-4], and allows the monitoring dynamic adsorption behavior of microgels onto solid substrate in aqueous solution [5]. The microgels were synthesized from N-isopropyl acrylamide and cross-linker N,N'-methylenebis(acrylamide) with different content by aqueous free-radical precipitation polymerization. In the present study, we will discuss the real-time changes in morphology of the microgels. Partially reproduced with permission from [5] Copyright (2017) John Wiley and Sons.

Poly(N-isopropylmethacrylamide-acrylic acid) microgels as adsorbent for removal of toxic dyes from aqueous medium

Poly(N-isopropylmethacrylamide-acrylic acid) [pniM-Ac] microgel particles were synthesized by surfactant free radical precipitation polymerization method. Microgel particles were used as adsorbent for the removal of toxic dyes such as Congo red (CR) (anionic), methylene blue (MB) (cationic) and Rhodamine B (Rh-B) (cationic) from aqueous medium at ambient temperature. Due to presence of carboxylate groups inside the polymer chains of microgel particles, uptake of cationic dyes such as MB and Rh-B was high as compared to anionic dye CR at low temperature and high pH of the medium. But at high temperature, microgel particles were shrunken and their hydrophobicity was increased. Under such conditions, uptake of anionic dye CR was high due to increased hydrophobic interaction between polymer chains of microgel particles and dye molecules. Effect of dye concentration, adsorbent dose, pH of the medium and agitation time on the percentage removal of dyes was also investigated and their optimum values were determined. Langmuir isotherm model best explained the adsorption of CR, MB and Rh-B on microgel particles. Pseudo second order has well explained the kinetics of adsorption of all dyes on microgel system as compared to other kinetic models as reflected by the values of regression coefficients (R2). Mechanism of adsorption of all dyes on microgel particles was explained by intra-particle diffusion model. Microgel particles also showed high capacity to extract toxic dyes simultaneously from aqueous medium as compared to their individual adsorption. Pure and dye loaded microgel particles were analyzed by UV–visible (UV–vis) spectroscopy and Fourier transform infrared (FTIR) spectrometry. Size and morphology of microgel particles were investigated by transmission electron microscopy (TEM).

Designed synthesis of silver nanoparticles in responsive polymeric system for their thermally tailored catalytic activity towards hydrogenation reaction

Poly(N-isopropylacrylamide-acrylamide-methacrylic acid) [p(NIPa-AAm-Ma)] polymer microgels were prepared by free radical precipitation polymerization method. AgNPs were fabricated in the sieves of polymer network by chemical reduction using AgNO3 salt as a precursor of silver ions. Various techniques like dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared microscopy (FTIR), and UV-Visible spectroscopy were used for characterization of pure and composite microgels. The diameter of AgNPs fabricated in polymeric network was found to be in the range of 10-15 nm. Stimuli responsive behavior of hybrid microgels was same as that of pure microgels. Catalytic efficiency of the hybrid microgels was investigated by reducing 4-Nitroaniline (4-NA) into 4-Aminoaniline (4-AA) using NaBH4 as reducing agent under different conditions of temperature of the medium, concentration of reducing agent, 4-Nitroaniline and hybrid microgels to explore the catalysis process. Kinetic and thermodynamic aspects of reduction of 4-Nitroaniline in the presence of catalyst were also discussed on the basis of values of Arrhenius and Eyring parameters like pre-exponential factor, activation energy, enthalpy of activation and entropy of activation. Catalytic activity of the hybrid microgels was found to be thermally tunable in the temperature range of 25-70 oC. The value of rate constant (k app ) for reduction of 4-NA was minimum at 55 °C, which can be attributed to volume phase transition of the hybrid microgels.

Facile synthesis of silver nanoparticles in a crosslinked polymeric system by in situ reduction method for catalytic reduction of 4-nitroaniline

ABSTRACTIn this study, poly(N-isopropylmethacrylamide-co-methacrylic acid) microgels prepared by free radical precipitation polymerization were used as micro-reactors for the synthesis and stabilization of silver nanoparticles. UV-Visible spectroscopy, Transmission Electron Microscopy and Fourier-transform infrared spectroscopy were used to characterize both pure and hybrid microgels. The catalytic reduction of 4-nitroaniline was carried out in the presence of hybrid microgels to test their catalytic activity, and the catalysis mechanism was explored by varying the concentrations of reacting species like 4-nitroaniline and NaBH4, as well as the dose of the catalyst. The kinetic data indicates that this reaction follows pseudo-first order. The variation in apparent rate constant (kapp) with respect to NaBH4 concentration also discloses it to be the following Langmuir–Hinshelwood mechanism. The relationship between catalyst concentration and apparent rate constant was found to be increasing in a linear manner. The data obtained also confirmed that silver nanoparticles loaded microgels have the potential to be used as an excellent micro-reactor for selective reduction of 4-nitroaniline to p-phenylenediamine.

Facile Synthesis of Peptide Cross-Linked Nanogels for Tumor Metastasis Inhibition

Cancer metastasis is one of the major factors contributing to high mortality, and here we designed and synthesized a peptide cross-linked nanogel for hydrophilic functional molecule encapsulation and tumor metastasis inhibition. In this investigation, matrix metalloproteinase-2 (MMP2)-responsive peptide cross-linker is prepared by coupling acrylate-functional groups at both peptide terminals. The peptide cross-linked nanogel is then synthesized by free radical precipitation polymerization using N-isopropylacrylamide as the scaffold. Meanwhile, the hydrophilic tumor metastasis inhibition peptide P-5m is encapsulated into the nanogel in the one-pot synthesis step without complex cooperation. Importantly, the size-uniformed and narrow-distributed nanogel exhibits high P-5m loading capacity (43.4%). Interestingly, the nanogel is stable in vitro and in vivo, showing excellent and specific MMP2-triggered payload release property. As expected, the nanogel suppresses cancer cell migration and invasion in high performance, ultimately achieving remarkable tumor metastasis inhibition in vivo.

Destructive effects of sodium allyl sulfonate monomer on the rheological properties of poly (acrylamide) microgels achieved via precipitation polymerization

In the present study, hydro-soluble copolymers of acrylamide with sulfonic groups have been synthesized using thermally initiated free-radical precipitation polymerization in Ethanol. The considered monomer in this study is Sodium Allyl Sulfonate (SAS), which is the sodium salt of allyl sulfonic acid and belongs to the polyelectrolytes group. SAS is an ionic monomer, which can easily be dissociated in polar media to produce mobile ions. Mobile ions create an osmotic pressure difference between the polymer and the solvent phase resulting in the swelling enhancement. This behavior is known as polyelectrolyte effect. Acrylamide (AM) is another monomer used in this study. A new innovation of our study is the preparation and investigation of rheological properties of poly (AM-SAS) in the precipitation polymerization. 1-6 Hexandiol diacrylate (HDDA) and 2, 2′-azobis isobutyronitrile were considered as cross-linker and initiator, respectively. The effects of (HDDA) concentration and mol fraction of sodium allyl sulfonate comonomer (SAS) on the properties of microgels (i.e., spectral characteristics, glass transition temperature, equilibrium swelling, gel content and rheological properties) were also investigated. The rubber elasticity theory was applied to discuss the network structure of microgel. Apparent and rotational viscosities were used to determine the optimal cross-linker concentration and mole fraction of SAS. Despite of our prediction, SAS monomer not only enhance the rheological properties of microgels but also cause to reduce considerably gel content, swelling, viscosity and rheological properties of PAM microgels.

Synthesis and characterization of PAA microgels using multifunctional epoxy cross-linkers with a new cross-linking mechanism via a precipitation polymerization method

Polyacrylic acid (PAA) microgels were prepared by a free radical precipitation polymerization method. Initially, epoxy type cross-linkers were used to prepare PAA microgels by the precipitation polymerization method. Different types of multifunctional cross-linkers such as ethylene glycol diglycidyl ether (EGDGE), Triphenylol methane triglycidyl ether (TMTGE) and 4,4′- Methylenebis(N,N-diglycidyl aniline) (MBDGA) were used as bi-, tri- and tetra-functional cross-linkers, respectively. Epoxy type cross-linkers are able to cross-link PAA by reaction between the –COOH groups of PAA and the epoxide groups of the cross-linkers. Some of the epoxy rings do not react with acid groups of PAA chains during the polymerization stage; unreacted epoxy rings can be reacted during the sample drying time, a stage we designated as the ‟post-curing stage”. The effect of cross-linker concentration and its functionality on the behaviors of samples (i.e., swelling capacity, gel content, glass transition temperature and rheological properties) were investigated. A new relationship between average molecular weight of two successive cross-links ( Mc) and epoxy concentration ([epoxy]) was defined. The microgel properties, such as rotational viscosity and rheological properties, were compared with those of microgels prepared by divinyl type cross-linkers. Our results show that microgels synthesized by this novel mechanism have higher rheological properties (at low shear rate, strain and frequency) than those synthesized by conventional methods. These behaviors can be due to the increase in polymer side chains of the polymer network generated by this new cross-linking method.

Controlled release profile of 5-fluorouracil loaded P(AAM-co-NVP-co-DEAEMA) microgel prepared via free radical precipitation polymerization

A new microgel was prepared by free radical precipitation polymerization of acrylamide (AAM), 1-vinyl-2-pyrrolidone (NVP) and 2-(diethylamino)ethyl methacrylate (DEAEMA) to be used for the controlled drug release. The zeta-potential and particle size of P(AAM-co-NVP-co-DEAEMA) microgel were measured by dynamic light scattering (DLS) measurements and found to be around − 36.4 ± 6.29 mV and 592 nm, respectively. P(AAM-co-NVP-co-DEAEMA) microgel was loaded with 5-Fluorouracil (5-Fu) as a model drug. In vitro drug release profiles demonstrated that 5-Fu release from P(AAM-co-NVP-co-DEAEMA) microgel at pH 7.4 was much faster than at pH 5.5 and pH 2.1. In addition, release kinetic studies showed that P(AAM-co-NVP-co-DEAEMA) microgel fit into Higuchi model release. The cytotoxicity study indicated that P(AAM-co-NVP-co-DEAEMA) microgel did not exhibit apparent cytotoxicity against L929 cell line. When all of the results were evaluated, it can be seen that P(AAM-co-NVP-co-DEAEMA) microgel can be effectively used as a polymeric drug carrier for the potential drug delivery systems in medical applications.

High yield preparation of uniform polyurea microspheres through precipitation polymerization and their application as laccase immobilization support

Uniform polyurea (PU) microspheres were prepared through precipitation polymerization using isophorone diisocyanate (IPDI) as the only monomer in mixed solvent of water-acetonitrile. The highest IPDI loading allowed to have uniform PU microspheres went up to 23wt%, with a high yield of about 95% for the microspheres. The productivity of microspheres thus obtained was about 22 times higher than that by free radical precipitation polymerization, and practically doubled that previously reported on the same polymerization in the mixed solvent of water-acetone. In addition, the polymerization was done under quiescent process with the reactor standing still without any stirring or shaking. TGA and FTIR tests indicated that the microspheres were of high thermal stability with abundant amine group on the surface. As a model enzyme, laccase was immobilized on the surface of the PU microspheres via glutaraldehyde coupling. Compared with the free laccase, the immobilized one exhibited higher activity in alkaline environment and higher thermal stability. The immobilized laccase was used as biocatalyst for degradation of Remazol Brilliant Blue R and showed good decolorization capacity with good reusability. About 65% of its initial catalytic activity was retained after 7 cycles of reuse. This work provides a practically operational protocol for large scale production of uniform PU microspheres, and also demonstrates that these microspheres have promising applications as enzyme immobilization carrier and as biocatalyst in organic dyes degradation.

Biomass trans-anethole-based heat-resistant copolymer microspheres: Preparation and thermostability

Preparing biobased heat-resistant vinyl polymers remains as a big challenge. We successfully used trans-anethole (ANE), a typical natural and sustainable vinyl compound with abundant sources yet scarcely taken for preparing polymers, for preparing polymer microspheres through copolymerizing it with N-phenylmaleimide (N-PMI). The copolymer microspheres were efficiently obtained with high yield (>87%), clean surface, good spherical morphology, and narrow size distribution (CV=6.22%) by free radical precipitation polymerization. The content of ANE units in the copolymer was found to be approximately 50mol%. Growth of the microspheres was investigated in detail. Glass transition temperature (Tg) and decomposition temperature of the present copolymers were up to respectively 170 and 380°C, which cannot be achieved in normal polymeric microspheres. The present biobased microspheres are expected to find practical applications as novel thermal stable polymer materials and heat-resistant additives.

Fluorescent Polyamide-Based Rhodamine Hydrazide Moieties with Oxethyl as Spacer for Detection of Cr(3+), Fe(3+), and Hg(2+) Ions in Water.

An acrylic monomer bearing xanthene group, N-oxethyl acrylate-N'-rhodamine B hydrazide (ARBHE) was synthesized from N-hydroxyl ethyl-N'-rhodamine hydrazide (RBHE) and acryloyl chloride (Ac) in the presence of triethylamine in dry dichloromethane (CH2Cl2) at room temperature. The synthesized ARBHE was identified by FTIR, (1)H NMR spectra and elementary analysis. Copolymer poly(AM-ARBHE) of ARBHE and AM was synthesized with thermal initiator by free radical precipitation polymerization and it was characterized by the method of FTIR and (1)H NMR. Its molecular weights (Mη) was 7.03×10(3)gmol(-1) and the content of rhodamine units in the polymer chains was 1.44% in mole fraction. The ability of the poly(AM-ARBHE) to detect different metal cations (Ag(+), Ba(2+), Cd(2+) Co(2+), Cr(3+), Cu(2+), Co(2+) K(+), La(3+), Mg(2+), Na(+), Ni(2+), Pb(2+), Fe(2+), Fe(3+), Hg(2+) and Zn(2+)) in water was investigated. Upon addition of Cr(3+), Fe(3+) or Hg(2+) ions to the aqueous solution, visual color change and fluorescence enhancement were observed. Moreover, other metal ions did not induce obvious changes to the fluorescence spectra except to Fe(2+). The detection limit of poly(AM-ARBHE) was less than 1×10(-11)M. The results suggest that this copolymer may offer potential as a polymeric sensor for Cr(3+), Fe(3+) and Hg(2+) ions in water.

Synthesis and characterization of inorganic–organic polymer microgels for catalytic reduction of 4‐nitroaniline in aqueous medium

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