Preparation and characterization of poly(propylene carbonate)/montmorillonite nanocomposites by solution intercalation

Poly(propylene carbonate) (PPC) is a new biodegradable aliphatic polycarbonate. However, the poor thermal stability and low glass transition temperatures (T_g) have limited its applications. To improve the thermal properties of PPC, organophilic montmorillonite (OMMT) was mixed with PPC by a solution intercalation method to produce nanocomposites. An intercalated-and-flocculated structure of PPC/OMMT nanocomposites was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal and mechanical properties of PPC/OMMT nanocomposites were investigated by thermal gravimetric analysis (TGA), differential scanning calorimetric (DSC), and electronic tensile tester. Due to the nanometer-sized dispersion of layered silicate in polymer matrix, PPC/OMMT nanocomposites exhibit improved thermal and mechanical properties than pure PPC. When the OMMT content is 4 wt%, the PPC/OMMT nanocomposite shows the best thermal and mechanical properties. These results indicate that nanocomposition is an efficient and convenient method to improve the properties of PPC.     

Modification of poly(propylene carbonate) with chain extender ADR-4368 to improve its thermal,barrier, and mechanical properties

Melt blending with the application of epoxy compound ADR-4368 as a chain extender was used to chemically modify polypropylene carbonate (PPC). ¹H nuclear magnetic resonance spectroscopy (¹H NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tests using a universal material testing machine, a gas permeability tester, a water vapor permeability tester and other instruments were used to assess changes in the chemical structure, thermal and mechanical properties, and barrier efficacy of PPC before and after modification.The epoxy group in ADR-4368 reacted with the terminal hydroxyl group in PPC, considerably enhancing its mechanical properties, thermal stability and barrier efficacy to O₂ and CO₂. With the addition of 1% ADR-4368, the glass transition temperature of PPC was increased from 17 °C to 26.9 °C, while the thermal decomposition temperature (T_−5%) of PPC was increased from 177.3 °C to 240.6 °C. Moreover, the tensile strength of the modified PPC was improved from 3.3 MPa to 20.7 MPa.     

Physico‐Chemical Studies on Cu(II) Complexes of Acrylate Chelating Polymers

Abstract

Metal chelating polymers containing amide and carboxylic groups were prepared by gamma‐radiation polymerization of acrylic acid (AA) monomers in the presence of polyacrylamide (PAM). The resins obtained were loaded by copper ions and characterized by FT‐IR spectroscopy, electron spin resonance (ESR), thermogravimetric analysis (TGA), and differential scanning calorimetery (DSC). The IR spectra indicated a lower frequencies shift in the carbonyl bands due to copper ion chelation with carbonyl groups in the polymer resins. Also, the IR spectra reveal a splitting in the band at 3600–3200?cm^?1 that due to the coordination of the NH and OH groups with copper ions. The ESR spectrum was anisotropic with hyperfine structure having the following values 2.3808 and 2.07218 for g _∥ and g _⊥, respectively. These spectra for copper ions have square planar coordination with two nitrogen and two oxygen atoms. TGA and DSC studies show that radiation crosslinking and complexation with copper ion increase the thermal stability of PAM–AA resins. Meanwhile, resin complexes with copper ion showed a higher thermal stability than pure resin. The increase in thermal stability may be correlated with the metal ions coordination with NH and OH groups; this coordination prevents the splitting of ammonia and water molecules. Also, the metal ions providing a coordination crosslink between polymer chains could increase thermal stability.     

UO<Subscript>2</Subscript>(VI), Sn(IV), Th(IV) and Li(I) complexes of 4-azomalononitrile antipyrine

UO₂(VI), Sn(IV), Th(IV) and Li(I) complexes of 4-azomalononitrile antipyrine (L) have been isolated and characterized based on IR spectra, ¹H NMR, elemental analyses, molar conductance and thermal analysis (DTA/TG). The study revealed that the ligand behaves as a neutral bidentate one and coordination takes place via the carbonyl atom of pyrazolone ring >C=O and the azomethine nitrogen >C=N. The thermal stability of the metal complexes were investigated by thermogravimetry (TG), differential thermal analysis (DTA) techniques and infrared spectra, and correlated to their structure. The thermal study revealed that Th(IV) complexes show lower thermal stability than both UO₂(VI) and Sn(IV) complexes.     

Effect of pentaerythritol and organic tin with calcium/zinc stearates on the stabilization of poly(vinyl chloride)

The stabilization effect of calcium and zinc stearates (CaSt₂/ZnSt₂) combined with pentaerythritol (PeE) and organic tin on poly(vinyl chloride) was investigated. The results show that the addition of calcium/zinc stearates combined with PeE and organic tin can improve thermal and colour stability of poly(vinyl chloride) in both static and dynamic tests. Mechanisms for improving stability of PVC are also discussed. The increase of stabilizing effectiveness of calcium/zinc stearates is ascribed to the synergistic effect between CaSt₂/ZnSt₂ and PeE and the interaction between organic tin and double bonds formed during the degradation of PVC. There is no synergistic action between organic tin and PeE or organic tin and calcium/zinc stearates.     

Thermal Analysis of Fe(III) Complexes with Salicylaldehyde Semi-, Thiosemi- and S-methylisothiosemi-carbazones

The paper describes the results of differential thermal analysis of the octahedral Fe(III) complexes of the general formula [Fe(HLⁿ)₂]Cl and Fe(HL³)L³, as well as of the corresponding ligands H₂Lⁿ (H₂Lⁿ — tridentate salicylaldehyde semi thiosemi- and S-methylisothiosemi-carabazones with n=1, 2 and 3 respectively). The decomposition of the complexes involving sulphur-containing ligands (H₂L² and H₂L³) starts with sulphur elimination. In case of the complexes [Fe(HL²)]Cl and [Fe(HL³)]Cl sulphur evolves independently, whereas with Fe(HL³)L³ it is eliminated within the SCH₃ group. In the former case, sulphur elimination takes place at the same temperature for both complexes. The change in the coordination mode, being a consequence of the replacement of O by S, has no essential effect on thermal stability of the coordination polyhedron. The complexes involving ONN coordination, realized with the H₂L³ ligand, exhibit a comparatively highest thermal stability of the coordination polyhedron.This revised version was published online in November 2005 with corrections to the Cover Date.     

Polyaniline/SiO2 Nanocomposite Catalyzed Efficient Synthesis of Quinoxaline Derivatives at Room Temperature

Polyaniline/SiO₂ nanocomposite material has been synthesized by using chemical oxidative method. Prepared catalytic material was characterized by means of transmission electron microscopy (TEM), thermal analysis (TG‐DTA), X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT‐IR). Solvent stability for the catalyst has been screened using UV‐Visible spectroscopy. Polyaniline/SiO₂ catalyzed route has found to be an efficient and rapid protocol for the synthesis of quinoxaline derivatives by cyclocondensation of 1,2‐diketones and o‐phenylenediamines at room temperature. This protocol has several advantages such as high yield, good thermal stability, simple work up procedure, non‐toxic, clean, and easy recovery and reusability of the catalytic system.     

Zum Komplexbildungsverhalten der 5,6-Dihydroxy-7-oxa-bicyclo[2.2.1]heptan-2,3-dicarbonsäure gegenüber 3 d-Übergangsmetallen

Complex Formation of 5,6-Dihydroxy-7-oxa-bicyclo[2.2.1]heptane-2,3-dicarboxylic Acid with 3 d-Transition Elements Binary carboxylate complexes of bivalent 3 d-transition metal ions with 5-exo,6-cis-dihydroxy-7-oxabicyclo[2.2.1]heptane-2-exo,3-cis-dicarboxylic acid ( 2 ) have been synthesized in aqueous solution and characterized by elementary analysis, infrared and electronic spectra and magnetic susceptibility measurements. The coordination compounds have been found to undergo thermal decomposition with loss of water molecules, followed by the organic ligand to give metal oxides. The stability constants of the complexes have been determined by potentiometric measurements. It could be shown by X-ray analysis, that the dicarboxylate anion of 2 has different coordination behaviour in complexes [NiL²(H₂O)₃] · H₂O ( 2 c ) and [CuL²(H₂O)₂] · 2 H₂O ( 2 d ), respectively. In 2 c it acts as a tridentate chelating ligand forming together with three water molecules an only slightly distorted octahedral coordination sphere and its hydroxyl groups are coordinatively inactive. In 2 d , however, the oxygen atom of one hydroxyl group is included in coordination and by its interaction with a Cu atom of a neighboring molecule a polymeric chain structure is built up in the crystal. Two corners of the tetragonally extended coordination octahedron are occupied by water molecules. In both complexes the molecular packing is stabilized by a network of hydrogen bonds in which also the crystal water molecules are included.     

Metal complexes of porphyrin–anthraquinone hybrids: DNA binding and photocleavage specificities

A cationic porphyrin–anthraquinone hybrid and its Zn(II), Cu(II), Co(III), and Mn(III) complexes were synthesized and their interactions with duplex DNA were studied using a combination of absorption, fluorescence titration, circular dichroism spectroscopy, thermal DNA denaturation, viscosity measurements, gel electrophoresis, and gas chromatography. Metal coordination induces intermolecular steric hindrance and thus the metal hybrids have smaller DNA binding affinities than the free base hybrid; the steric hindrance could relax the intermolecular aggregation and increase ¹O₂ generation of the metal hybrids. The DNA photocleavage abilities of these hybrids were investigated.     

A modern technique for preparation of zinc(II) and nickel(II) nanometric oxides using Schiff base compounds: synthesis,characterization, and antibacterial properties

The purpose of the work reported in this paper was the preparation and characterization of Zn(II) and Ni(II) nanometric oxides by using a simple Schiff compound as precursor for complexation then thermal degradation at 600 °C. Metal complexes [Ni(L)₂(Cl)₂] and [Zn(L)₂](NO₃)₂, where L is the Schiff base formed by condensation of 2-thiophenecarboxaldehyde with phenylhydrazine, were prepared and characterized by elemental analysis and by magnetic and spectroscopic measurements (infrared, Raman, X-ray powder diffraction, and scanning electron microscopy). Elemental analysis of the chelates suggests the stoichiometry is 1:2 (metal–ligand). Infrared spectra of the complexes are indicative of coordination of the nitrogen of the phenylhydrazine (–Ph–NH–) group and the sulfur atom of the thiophene ring with the central metal atom. Magnetic susceptibility data and electronic and ESR spectra suggest a distorted octahedral structure for the Ni(II) complex and tetrahedral geometry for the Zn(II) complex. The Schiff base and its metal chelates were screened for in-vitro activity against four bacteria, two Gram-positive (Bacillus subtilis and Staphylococcus aureus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa), and two strains of fungus (Aspergillus flavus and Candida albicans). The metal chelates were shown to have greater antibacterial activity than the free Schiff-base chelate.     

Synthesis,spectral and thermal studies on pyrazolatebridged palladium(II) coordination polymers

Synthesis, spectroscopic characterization and thermal behavior of pyrazolate-bridged palladium complexes [Pd(μ-Pz)₂]_n (1), [Pd(μ-mPz)₂]_n (2), [Pd(μ-dmPz)₂]_n (3), [Pd(μ-IPz)₂]_n (4) {pyrazolate (Pz^–), 4-methylpyrazolate (mPz^–), 3,5-dimethylpyrazolate (dmPz^–), 4-iodopyrazolate (IPz^–)} have been described in this work. The exobidentate coordination mode of pyrazolato ligands in 1–4 was inferred on basis of IR spectroscopic evidences. TG investigations indicated that the introduction of substituents at the 4 position in the pyrazolyl moiety into coordination polymers do not affect significantly their thermal stability, whereas at the 3 and 5 position reduced the stability of the main chain. Metal palladium was the final product of the thermal decompositions, which was identified by X-ray powder diffraction.     

Effect of stearate preheating on the thermal stability of plasticized PVC compounds

Effect of preheating of stearates on the processing and post-processing thermal stability of poly(vinyl chloride) compounds, plasticized with di(2-ethylhexyl) phthalate (DEHP) and epoxidized soybean oil (ESO), using several ratios of calcium/zinc stearates and DEHP/ESO is reported. The compounds were prepared as follows: (1) dry-blending the compound components, (2) pelletizing the dry-blend and (3) extruding the pellets to obtain a ribbon geometry. Processing stability was determined by: (a) mechanical characterization and (b) visual color comparison of extruded samples. Post-processing thermal stability was followed by: (a) measurement of HCl release from heated pellets and (b) color changes in heated ribbon samples. From a practical point of view, the preheating has a negligible effect on the initial color of formulations; except for the case of formulations without both ESO and CaSt₂. However, the effect of the preheating on the post-processing thermal stability is strongly determined by the composition formulation.     

Synthesis,spectral and thermal studies of zinc(II) and mercury(II) complexes with bidentate Schiff-base ligand (234-MeO-Ba)<Subscript>2</Subscript>En: the crystal structure of Zn(234-MeO-Ba)<Subscript>2</Subscript>En)I<Subscript>2</Subscript>

New Symmetric bidentate Schiff-base ligands N,N′-bis(2,3,4-trimethoxybenzylidene)-1,2-di-aminoethane, (234-MeO-Ba)₂En, and its corresponding zinc(II) and mercury(II) complexes, Zn((234-MeO-Ba)₂En)I₂ (I), Hg((234-MeO-Ba)₂En)Cl₂ (II) have been synthesized and characterized by elemental analyses (CHN), FT-IR and 1H NMR spectroscopy. The thermal behaviors of complexes were study using thermogravimetry in order to evaluate their thermal stability and thermal decomposition pathways. The crystal structure of I was determined from single-crystal X-ray diffraction. The coordination polyhedron about the zinc(II) center in complex I is best described as a distorted tetrahedron.     

Thermal stability of amine-functionalized MCM-41 in different atmospheres

In the present work, we report on the thermal stability of NH₂-MCM-41 hybrid material under different atmospheres (nitrogen and air). The thermal stability of this hybrid material is very important because of its common use in catalysis, adsorption, biomedical and biotechnological applications, based on mesoporous and aminopropyl functionalities. Samples were prepared by one pot co-condensation method with different loadings of 3-aminopropyltriethoxysilane (APTES). The thermal stability of hybrid samples (NH₂-MCM-41) heat treated in nitrogen and air at 30–800 °C has been investigated. Samples were synthesized under basic media in the presence of cetyltrimethylammonium bromide (CTABr) as structure-directing agent, tetraethyl orthosilicate as silica source, and APTES as functionalizing agent with molar composition of 0.055 CTABr:045 SiO₂:0.054 APTES:5.32 NH₄OH:14.99 H₂O at 50 °C for 24 h at pH 12.4. The obtained hybrid materials have been characterized by thermogravimetric analysis (TG), derivative thermogravimetric analysis, differential scanning calorimetry, X-ray powder diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, and surface area determination by the BET method. Based on TG measurements of the treated samples, it was found out that the thermal stability varied greatly in different atmospheres.     

Synthesis and characterization of Li1.05Co1/3Ni1/3Mn1/3O1.95X0.05 (X = Cl,Br) cathode materials for lithium-ion battery

In order to improve the thermal stability and dynamic performance of LiCo_1/3Ni_1/3Mn_1/3O₂ materials, Cl-doped and Br-doped materials were synthesized via the co-precipitation method. The morphology, structure, electrochemical performance and thermal stability were characterized by environment scanning electron microscopy (ESEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), charge–discharge cycling and differential scanning calorimetry (DSC). Results show that all materials had a stable layered structure with α-NaFeO₂ and that Cl-doping slightly increased the size of grains. Both Cl-doping and Br-doping improved the high rate of discharge capacity, cycle-life performance and thermal stability, but Cl-doping was better than Br-doping in improving the material structure stability, dynamic performance and thermal stability.     

Thermoanalytical study of selected transition bivalent metal complexes with 5-carbaldehyde-4-methylimidazole

To compare thermal stability of Co(II), Zn(II), and Cd(II) complexes with 4-CHO-5-MeIm, the two compounds of formula [MnL₂(NO₃)₂] and [NiL₃](NO₃)₂ have been prepared and structurally characterized. Elemental analysis and spectroscopic studies have confirmed a bidentate fashion of coordination of the ligand to Mn(II) and Ni(II) ions. IR and Raman spectra indicate that there are different coordination modes of the NO₃ ^? in compounds: non-coordinated and coordinated. The decomposition process of the studied complexes in nitrogen and argon (Ni(II) complex) atmosphere proceeds in three main stages, except Zn(II) complex, in temperature range 353?C1163?K. The final products of decomposition are CoO, MnO, Cd, ZnN₄, NiN₃. In addition, we have to admit that the different coordination mode of the NO₃ ^? ions in complexes: non-coordinated (in the (1), (4), and (5)) and coordinated (in the (2) and (3)) correlate with its thermal behavior. Thus, temperature ranges of its decompositions are observed: below 533?K and above 533?K, respectively. In Co(II), Mn(II), and Cd(II) complexes the fragments of N-donor atom-containing ligands decompose in the last stages, contrary to Zn(II) and Ni(II) compounds, in which metal ion surrounded by N atoms remains until the end. The course of pyrolysis and molecular structure of the complexes lead to the same conclusion about the strength of metal?Cligand bonds. On the basis of obtained results, it is concluded that the thermal stability of the studied compounds follows the order: (1)?<?(5)?<?(2)?<?(3)?<?(4).     

Synthesis,spectroscopy, thermal behavior,and X-ray crystal structure of two lead(II) complexes with 4′-(4-tolyl)-2,2′;6′,2″-terpyridine (ttpy)

Two new lead(II) complexes with 4′-(4-tolyl)-2,2′;6′,2″-terpyridine (ttpy), [Pb(ttpy)(µ-AcO)]₂(PF₆)₂ (1) and [Pb(ttpy)(µ-AcO)I]₂ (2), have been synthesized and characterized by CHN elemental analysis, ¹H NMR, ¹³C NMR, IR spectroscopy, and structurally analyzed by X-ray single-crystal diffraction. The thermal stability of these compounds has been studied by thermal gravimetric analysis and differential thermal analysis. Single crystal X-ray analysis shows that 1 and 2 are dimeric units with Pb–(µ-AcO)₂–Pb-type bridging, and the coordination number in 1 is six and in 2 is seven. The arrangement of donors suggests a gap in the coordination geometry around lead, possibly occupied by stereo-active lone pair of electrons on lead(II), so the coordination sphere is hemidirected. Furthermore, dimeric units are connected by a network of hydrogen bonds and π–π stacking as well. Electrochemical properties of free ligand and complexes have been investigated in the presence of tetrabutyl ammonium perchlorate as supporting electrolyte and by using a glassy carbon electrode. Both lead complexes show irreversible Pb(II) oxidation. Cyclic voltammetry indicates that these processes are diffusion-controlled. The data from electrochemical studies show that the total limiting current of each of the studied complexes corresponds to two-electron transfer.     

Sonochemical synthesis and structural characterization of a nano-structure Pb(II) benzentricarboxylate coordination polymer: new precursor to pure phase nanoparticles of Pb(II) oxide

Microcrystals of a new Pb(II) coordination polymer, [Pb₂(1,3,5-HBTC)₂(H₂O)₄] · H₂O (1) (1,3,5-H₃BTC = 1,3,5-benzentricarboxylic acid), was synthesized by a sonochemical method. The structure was characterized by scanning electron microscopy, X-ray powder diffraction, elemental analyses, and IR spectroscopy. Thermal stability was studied by thermal gravimetric and differential thermal analyses. After the calcination of nanosized 1 at 400°C, pure phase nanosized Pb(II) oxide has been produced.     

Crystallization of polypropylenewith a minute amount of β-nucleator

Triammonium-N-dithiocarboxyiminodiacetate, (NH₄)₃L, a new dithiocarbamato derivative of iminodiacetate, has been synthesized. The coordination properties of the ligand were tested in reactions with copper(II), nickel(II) and palladium(II) salts in acidic solutions. Complexes with a general formula M(H₂L)₂ were obtained, with the coordination taking place through the sulfur atoms of the dithiocarbamate moiety. The new compounds were characterized by elemental analysis, UV/VIS and IR spectroscopy, thermal analysis and magnetic measurements. In addition, the ligand was characterized by ¹H- and ¹³C-NMR spectroscopy and molar conductivity measurements. The copper(II) complex is paramagnetic, while the nickel(II) and palladium(II) compounds are diamagnetic. The thermal decomposition of all compounds is continuous and the thermal stability of the complexes is higher than that of the ligand, as expected.     

Synthesis,characterization and biological applications of new copper(II) complexes of aryl hydrazones

On treatment of copper(II) acetate with aryl hydrazone ligands, four new solid derivatives of copper(II) were produced in appreciable yields. Various characterization techniques including infrared, UV–visible, NMR, electron paramagnetic resonance and mass spectroscopies, elemental analysis, scanning electron microscopy, powder X‐ray diffraction and thermogravimetric analysis revealed a tetra‐coordination in all the mononuclear crystalline complexes with high thermal stability. Further, significant interaction of these novel complexes with calf thymus DNA via intercalative mode of binding was revealed by electronic absorption spectroscopy. The chemical nuclease activity of the complexes on pBR322 DNA was investigated in the presence and absence of oxidizing agent (H₂O₂). A potent nuclease activity was observed only in the presence of H₂O₂. Further, antibacterial and antifungal studies of the new ligands and complexes revealed that the latter possessed comparatively better activity.