Adsorption of cationic dyes on poly(acrylic acid-co-sodium acrylate-co-acrylamide) superabsorbents

Inverse suspension polymerization was carried out to synthesize poly(acrylic acid-co-sodium acrylate-co-acrylamide) superabsorbent polymers (SAPs) crosslinked with ethylene glycol dimethacrylate (EGDMA). The equilibrium swelling capacities of the SAPs, determined by swelling them in DI water, were found to vary with the acrylamide (AM) content. The SAPs were used to adsorb four cationic dyes (Acriflavine, Auramine-O, Azure-I and Pyronin-Y). The effect of AM content in the SAPs on the adsorption of the cationic dyes was investigated. Different initial concentrations of Azure-I were used with the same amount of the SAP to explore the effect of initial dye concentration on the adsorption. The effect of the adsorbent amount was investigated by taking different amounts of SAP with a fixed initial concentration of Acriflavine. The kinetics of the dye adsorption was modeled by a first order model and the equilibrium amount of the dye adsorbed, adsorption rate coefficients, removal efficiency and partition coefficients were determined. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Photo and Thermal Degradation of a Cationic Superabsorbent Polymer

A cationic superabsorbent polymer (SAP) was synthesized by carrying out the polymerization of 2-(methacryloyloxy)ethyl] trimethyl ammonium chloride) with N,N'-methylenebisacrylamide as the cross-linking agent. The SAP was subjected to degradation in dry and the equilibrium swollen state by thermo gravimetric analysis and exposure to ultraviolet radiation, respectively. The photodegradation was monitored by measuring changes in the swelling capacity and the dry weight of the SAP. The thermal degradation of the SAP occurred in three stages after the initial removal of moisture and the activation energies of the decomposition were determined.

Synthesis of some copper(II)-chelating (dialkylamino)pyridine amphiphiles and evaluation of their esterolytic capacities in cationic micellar media

Three new (dialkylamino)pyridine (DAAP)-based ligand amphiphiles 3-5 have been synthesized. All of the compounds possess a metal ion binding subunit in the form of a 2,6-disubstituted DAAP moiety. In addition, at least one ortho-CH2OH substituent is present in all the ligands. Complex formation by these ligands with various metal ions were examined under micellar conditions, but only complexes with Cu(II) ions showed kinetically potent esterolytic capacities under micellar conditions. Complexes with Cu(II) were prepared in host comicellar cetyltrimethylammonium bromide (CTABr) media at pH 7.6. Individual complexes were characterized by UV-visible absorption spectroscopy and electron paramagnetic resonance spectroscopy. These metallomicelles speed the cleavage of the substrates p-nitrophenyl hexanoate or p-nitrophenyl diphenyl phosphate. To ascertain the nature of the active esterolytic species, the stoichiometries of the respective Cu(II) complexes were determined from the kinetic version of Job's plot. In all the instances, 2:1 complex ligand/Cu(II) ion are the most kinetically competent species. The apparent pK(a) values of the Cu(II)-coordinated hydroxyl groups of the ligands 3, 4, and 5, in the comicellar aggregate, are 7.8, 8.0, and 8.0, respectively, as estimated from the rate constant vs pH: profiles of the ester cleavage reactions. The nucleophilic metallomicellar reagents and the second-order "catalytic" rate constants toward esterolysis of the substrate p-nitrophenyl hexanoate (at 25 degrees C, pH 7.6) are 37.5 for 3, 11.4 for 4, and 13.8 for 5. All catalytic systems comprising the coaggregates of 3, 4, or 5 and CTABr demonstrate turnover behavior in the presence of excess substrate.

The effects of cholesterol inclusion on the vesicular membranes of cationic lipids

Small unilamellar vesicles formed from four cationic lipids in the absence and the presence of varying amounts of cholesterol were studied using fluorescence polarization and H-1-NMR techniques. The fluorescence polarization data clearly indicate that the packing order in the cationic lipid bilayers are affected by inclusion of cholesterol. importantly, this effect exists also with a cationic lipid that is devoid of any formal linkage region where the interaction of the lipid with cholesterol through hydrogen bonding is not feasible. The interactions of cholesterol with different types of cationic lipids in excess water have also been examined in multilamellar dispersions using proton magnetic resonance spectroscopy. In all the cases, the methylene proton linewidths in the NMR spectra respond to the addition of cholesterol to vesicles. Hydrophobic association of the lipid and cholesterol imposes restriction on the chain (CH2)(n) motions, leaving the terminal CH3 groups relatively mobile. On the basis of energy-minimized structural models, a rationale of the cholesterol-cationic lipid assembly has also been presented.

The first observation of a Na2TiS2 related structure in a 2-D anionic manganese trimesate intercalated by cationic imidazole

A hydrothermal reaction of Mn(OAc)2·4H2O, trimesic acid, imidazole, KOH and water at 75 °C for 24 h gave rise to a 2-D compound, [HImd][Mn(BTC)(H2O)] (Imd = imidazole; BTC = trimesate), with protonated imidazole molecules occupying the inter-lamellar space, and the structure resembles the classic inorganic compound, the sodium intercalated TiS2 (Na2TiS2).

Structure and Rheology of Cationic Molecular Hydrogels of Quinuclidine Grafted Bile Salts. Influence of the Ionic Strength and Counter-Ion type

Quinuclidine grafted cationic bile salts are forming salted hydrogels. An extensive investigation of the effect of the electrolyte and counterions on the gelation has been envisaged. The special interest of the quinuclidine grafted bile salt is due to its broader experimental range of gelation to study the effect of electrolyte. Rheological features of the hydrogels are typical of enthalpic networks exhibiting a scaling law of the elastic shear modulus with the concentration (scaling exponent 2.2) modeling cellular solids in which the bending modulus is the dominant parameter. The addition of monovalent salt (NaCl) favors the formation of gels in a first range (0.00117 g cm-3 (0.02 M) < TNaCl < 0.04675 g cm-3 (0.8 M)). At larger salt concentrations, the gels become more heterogeneous with nodal zones in the micron scale. Small-angle neutron scattering experiments have been used to characterize the rigid fibers ( ≈ 68 Å) and the nodal zones. Stress sweep and creeprecovery measurements are used to relate the lack of linear viscoelastic domain to a mechanism of disentanglement of the fibers from their associations into fagots. The electrostatic interactions can be screened by addition of salt to induce a progressive evolution toward flocculation. SEM, UV absorbance, and SAXS study of the Bragg peak at large Q-values complete the investigation.

Metal chelates in vinyl polymerization: Bulk polymerization of acrylonitrile initiated by Cu(II)-imine complexes

This article deals with the kinetics and mechanism of acrylonitrile (AN) polymerization initiated by Cu(II)-4-anilino 3-pentene 2-one[Cu(II)ANIPO], Cu(II)-4-p-toluedeno 3-pentene 2-one [Cu(II)TPO], and Cu(II)-4-p-nitroanilino 3-pentene 2-one [Cu(II)NAPO] in bulk at 60°C. The polymerization is free radical in nature. The exponent of initiator(I) is 0.5. The initiation step is a complex formation between the chelate and monomer and subsequent decomposition of the intermediate complex giving rise to free radical and Cu(I). This is substantiated by ultraviolet (UV) and electron spin resonance (ESR) studies. The activation energies and kinetic and chain transfer constants have also been evaluated.

Initiation Reactions in Thermal Polymerization of Vinyl Monomers in the Molten State

Evidence of the initiation process during uncatalyzed thermal polymerization of vinyl monomers is presented. DSC studies reveal a prominent endothermic effect just before the polymerization exotherm, which is substantiated by the identification of the free radicals produced in the initiation by a quick quenching technique and subsequent detection by ESR at low temperatures.

Reactivity of Cationic Terminal Borylene Complexes: Novel Mechanisms for Insertion and Metathesis Chemistry Involving Strongly Lewis Acidic Ligand Systems

The reactions of terminal borylene complexes of the type [CpFe(CO)(2)(BNR2)](+) (R = `Pr, Cy) with heteroallenes have been investigated by quantum-chemical methods, in an attempt to explain the experimentally observed product distributions. Reaction with dicyclohexylcarbodiimide (CyNCNCy) gives a bis-insertion product, in which 1 equiv of carbodiimide is assimilated into each of the Fe=B and B=N double bonds to form a spirocyclic boronium system. In contrast, isocyanates (R'NCO, R' = Ph, 2,6-wXy1, CY; XYl = C6H3Me2) react to give isonitrile complexes of the type [CpFe(CO)(2)(CNR')]+, via a net oxygen abstraction (or formal metathesis) process. Both carbodiimide and socyanate substrates are shown to prefer initial attack at the Fe=B bond rather than the B=N bond of the borylene complex. Further mechanistic studies reveal that the carbodiimide reaction ultimately leads to the bis-insertion compounds [CpFe(CO)(2)C(NCy)(2)B(NCY)(2)CNR2](+), rather than to the isonitrile system [CpFe(CO)(2)(CNCy)](+), on the basis of both thermodynamic (product stability) and kinetic considerations (barrier heights). The mechanism of the initial carbodiimide insertion process is unusual in that it involves coordination of the substrate at the (borylene) ligand followed by migration of the metal fragment, rather than a more conventional process: i.e., coordination of the unsaturated substrate at the metal followed by ligand migration. In the case of isocyanate substrates, metathesis products are competitive with those from the insertion pathway. Direct, single-step metathesis reactivity to give products containing a coordinated isonitrile ligand (i.e. [CpFe(CO)(2)(CNR')](+)) is facile if initial coordination of the isocyanate at boron occurs via the oxygen donor (which is kinetically favored); insertion chemistry is feasible when the isocyanate attacks initially via the nitrogen atom. However, even in the latter case, further reaction of the monoinsertion product so formed with excess isocyanate offers a number of facile (low energetic barrier) routes which also generate ['CpFe(CO)(2)(CNR')](+), rather than the bis-insertion product [CpFe(CO)(2)C(NR')(O)B(NR')(O)CNR2](+) (i.e., the direct analogue of the observed products in the carbodiimide reaction).

Solid-state Thermal Polymerization of Sodium Acrylate

Initiation and propagation processes in thermally initiated solid-state polymerization of sodiumvacrylate have been studied. The kinetics of initiation, followed with the electron spin resonancev technique, leads to an activation energy E of 28.8 kcal/mol, which is attributed to the formation of dimeric radicals. The activation energy of 16 f 1 kcaVmol obtained for the solid-state polymerization of sodium acrylate by chemical analysis and differential scanning calorimetry has been attributed to the propagation process.

Thermal polymerization of acrylamide in the solid state

The role of imperfections in thermal polymerization of acrylamide in the solid state was studied. The polymer yield and the degree of polymerization are highly dependent on the particle size and on the pressure to which the monomer is subjected prior to polymerization reaction. There is an enhancement in the rate of polymerization in air unlike in the case of radiation-induced polymerization. Thermal polymerization of acrylamide in pelletized form results in the formation of water-soluble linear polymer and water-insoluble cross-linked product with the evolution of ammonia. The activation energy (E) values obtained in the present investigation reveal that basically there are two processes taking place, one with E = 34–36 kcal/mole, corresponding to the initiation process, and the other with E = 19 ± 3 kcal/more for the propagation process.

Metal Chelates in Vinyl Polymerization: Kinetics and Mechanism of Acrylonitrile Polymerization Initiated by Cu(I1) Imine Complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(I1) 4-anilino 3-pentene 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(I1) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCld), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were 22 at two different temperatures and in different solvents. The square-root dependence of R, on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formatign was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.

New initiators for the ring-opening thermal polymerization of hexachlorocyclotriphosphazene: synthesis of linear poly(dichlorophosphazene) in high yields

Ring-opening thermal polymerization of hexachlorocyclotriphosphazene (N3P3C&h)a s been investigated at 250 "C and at 1.333-Pa pressure using chlorocyclotriphosphazenes N3P3C15(N=PPh3) and N3P3Cl,.,(NMe2), (n = 2-4), salt hydrates, triphenylphosphine, and benzoic acid as initiators. The linear poly (dich1orophosphazene) products are phenoxylated, and the phenoxy polymers are characterized by gel permeation chromatography and dilute solution viscometry. Among the various initiators investigated, CaS04.2H20b rings about a high conversion (>60%) of N3P3C&to the linear [NPC12], polymer which possesses a high molecular weight (>5 X lo6). The rationale for the choice of the initiators and possible mechanism(s) of polymerization is discussed. Several mixed substituent polymers, [NP(OPh),(OC6H4Me-p)2,1, and [NP(OPh),(OCHzCF3)2,]nh, ave been prepared and their thermal properties evaluated.

A Theoretical Investigation of the Ni(II)-Catalyzed Hydrovinylation of Styrene

We report a detailed and full computational investigation on the hydrovinylation reaction of styrene with the Ni(II)-phospholane catalytic system, which was originally presumed to proceed through a cationic mechanism involving a nickel hydride intermediate. The following general features emerge from this study on a specific catalyst complex that was found to give quantitative yield and moderate selectivity: (a) the activation barrier for the initiation (18.8 kcal/mol) is higher than that for the reaction due to a low-lying square-planar pentenyl chelate intermediate originating from a Ni(II)-allyl catalyst precursor. Consequently there is an induction period for the catalysis; (b) the exit of product from the catalyst is via a β-H-transfer step instead of the usual β-H elimination pathway, which has a very high activation energy due to a trans effect of the phospholane ligand; (c) the turnover-limiting and enantio- determining transition state is also the β-H-transfer; (d) because of the absence of a hydride intermediate, the unwanted isomerization of the product is prevented; (e) since the enantio-discrimination is decided at the H-transfer stage itself, the configuration of the product in a catalytic cycle influences the enantioselectivity in the subsequent cycle; (f) the trans effect of the sole strong ligand in the d8 square-planar Ni(II), the stability of the η3-benzyl intermediate, and the availability of three coordination sites enable regioselective hydrovinylation over the possible oligomerization/polymerization of the olefin substrates and linear hydrovinylation. This work has also confirmed the previously recognized role of the hemilabile group at various stages in the mechanism.

Metal chelates in vinyl polymerization: Kinetics and mechanism of acrylonitrile polymerization initiated by Cu(II) imine complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(II) 4-anilino 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(II) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCl4), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were 2 at two different temperatures and in different solvents. The square-root dependence of Rp on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formation was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.