Synthesis,characterization, and platinum-catalyzed cross-linking of 1,4-bis(1-methyl-1-silacyclobutyl) benzene,co-oligo(1-silacyclobut-1-ylidene-1,4-phenylene), and co-oligo(1-silacyclobut-1-ylidene-4,4′-diphenylene)

1,4-bis(1-Methyl-1-silacyclobutyl)benzene (I) has been prepared by the reaction of 1-chloro-1-methyl-1-silacyclobutane with the di-Grignard reagent prepared fromp-dibromobenzene. In a similar manner, co-oligo(1-silacyclobut-1-ylidene-1,4-phenylene) (II) and co-oligo(1-silacyclobut-1-ylidene-4,4′-biphenylene) (III) have been prepared by condensation oligomerization between 1,1-dichloro-1-silacyclobutane and the di-Grignard reagents prepared fromp-dibromobenzene and 4,4′-dibromobiphenyl, respectively. These have been characterized by¹H,¹³C, and²⁹Si NMR as well as FT-IR and UV spectroscopy. The molecular weight distributions of these co-oligomers have been determined by GPC. Their thermal stabilities have been evaluated by TGA. Thermal degradation of these co-oligomers in nitrogen gives high (60%) char yields. The stability of these chars in air has been determined. TheT _g's of these co-oligomers have been measured by DSC. Platinum-catalyzed ring opening of the silacyclobutane rings ofI,II, andIII cross-links these to thermoset materials. The bending moduli (logE′), tan δ, andT _g's of these materials have been determined by DMTA. The dielectric constant and dissipation factor of cross-linkedII are reported.     

Synthesis and Properties of Soluble and Light-Colored Poly(amide-imide-imide)s Based on Tetraimide-Dicarboxylic Acid Condensed from 4,4'-Oxydiphthalic Anhydride, 2,2-Bis[4-(4-aminophenoxy)phenyl]sulfone, and m-Aminobenzoic Acid, and Various Aromatic Diamines

A new-type of tetraimide-dicarboxylic acid (I) was synthesized starting from the ring-opening addition of m-aminobenzoic acid (m-ABA), 4,4'-oxydiphthalic anhydride (ODPA), and 2,2-bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS) at a 2:2:1 molar ratio in N-methyl-2-pyrrolidone (NMP), followed by cyclodehydration to the diacid I. A series of soluble and light-colored poly(amide-imide-imide)s (III _a-j) was prepared by triphenyl phosphite-activated polycondensation from the tetraimide-diacid I with various aromatic diamines (II _a-j). All films cast from DMAc had cutoff wavelengths shorter than 390 nm (379–390 nm) and had b ^* values between 24.17–35.50; these polymers were much lighter in color than those of the alternating trimellitimide series. All of the polymers were readily soluble in a variety of organic solvents such as NMP, N,N-dimethyl acetamide, N,N-dimethylformamide, dimethyl sulfoxide, and even in less polar m-cresol and pyridine. Polymers III _a-j afforded tough, transparent, and flexible films, which had a strength at break ranging from 93 to 118 MPa, elongation at break from 8 to 11%, and initial modulus from 2.2 to 2.8 GPa, and some films showed yield points in the range of 95–111 MPa at stress–strain curves. The glass transition temperature of the polymers was recorded at 240–268°C. They had 10% weight loss at a temperature above 540°C and left more than 55% residue even at 800°C in nitrogen.     

Preparation and Characterization of Pillared Zirconium Phosphite-Diphosphonates with Tuneable Inter-Crystal Mesoporosity

A series of -pillared zirconium phosphite-diphosphonates of general formula Zr(O₃PH)_x(O₃P-C₆ H₄-PO₃)_y was prepared in water, dimethylsulfoxide-water andn -propanol-water, by changing the ratios and the concentrations of the reagents. Pure mesoporous solids with a large surface area (230 to 400 m² g^-2) and a great pore volume (0.3 to 0.7 cm³ g^-2) were obtained. These materials showed a narrow distribution of pores that was tuneable over the range 4–14 nm diameter by simply varying the conditions of preparation, especially the concentration of the reagents. The formation of interparticle mesoporosity has been attributed to edge-edge interactions between rigid packets of a few pillared -layers giving rise to stable aggregates with a house of cards structure.     

Spatio-kinetic variation of methane oxidizing bacteria in paddy soil at mid-tillering: effect of N-fertilizers

Laboratory experiments were conducted to evaluate the variation ofpopulation size of methanotrophs (MOB) and CH₄ oxidation pattern inflooded rice soils sampled at three spatial points (rhizosphere, bulk and baresoils). Rhizosphere soil had higher MOB population size (301.1 ×10⁵ cells g^–1 dry soil) than bulk(37.2× 10⁵ cells g^–1 dry soil) andbare soil (19.1 × 10⁵ cells g^–1dry soil). The population size of MOB followed a decreasing trend with respectto fertilizer (urea NH₄NO₃ NH₄Cl control). The result indicated that rhizosphere soil presented thestrongestCH₄ oxidation activities, as shown by the highest values of the twokinetic parameters (K _m(app) andV _max). K _m andV _max increased significantly from bare to bulkto rhizosphere soil in control and fertilized soil and ranged from 6.2 to 133.2g g^–1 dry soil and from 0.03 to 0.41g h^–1 g^–1 dry soil,respectively. The differences in K _m andV _max among the three soils (rhizosphere, bulkand bare) in this study could be due to differential species composition ofmethanotrophic community and/or to conditioning of MOB under different soilmicroenvironments. The present study has demonstrated a competitive inhibition effectof NH₄ ⁺-N on CH₄ oxidation.     

Plasticizing and Reinforcing Features of Siloxane Domains in Amine‐Cured Epoxy/Silica Hybrids

Organic/inorganic hybrid materials comprising an amine‐epoxide network and siloxane domains are produced by the sol/gel method. The presence of both plasticizing flexible linear siloxane sequences and reinforcing nanosized silica particles and branched silsesquioxanes (SSQO) structures is confirmed by ²⁹Si NMR and SAXS analysis. The hybrids display simultaneously a monotonical reduction in T_g and an increase in rubbery plateau modulus with increasing siloxane content. At the same time, nanoindentation tests reveal an improved resistance to plastic deformation. The effect of siloxane content on the values of the rubbery plateau modulus is evaluated through the EBM model for blends and composites exhibiting the characteristic co‐continuity of the two constituent phases.

     

Solution-Combustion Synthesis of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> as a Cathode Material for Lithium-Ion Batteries

A cathode material for lithium-ion batteries–LiNi_1/3Co_1/3Mn_1/3O₂–was prepared by solution combustion synthesis and characterized by XRD, SEM, and galvanostatic charge/discharge cycling. The sample calcined at 950°C for 10 h showed best charge/discharge performance. An initial discharge capacity (C) of 150.5 mA h g^–1 retained 95.7% of its value after 75 charge/discharge cycles at I_c = 14 mA g^–1 (0.2C rate), I_d = 70 mA g^–1 (0.5C rate).     

Synthesis and characterization of soluble (porphyrinato)iron(II) polymers

The use of (tetrakis(4-hexylphenyl)porphyrinato)Fe(II) in polymerization reactions with bidentate ligands such as 9,10-diisocyanoanthracene and 1,4-diisocyanobenzene led to well-defined stacked polymers1 and2 which are still soluble in common organic solvents such as chloroform, dichloromethane, and tetrahydrofurane. They have been completely characterized by¹H-NMR and UV/vis spectropscopy in solution, even allowing end-group analysis for determination of the average degree of polymerization, yieldingn=10 andn=5 for1 and2, respectively. Mößbauer and IR spectroscopy further established the strong Fe-CN bonding reflected by very small isomer shifts and quadrupole splittings (E _Q0.2 mm s^–1) and a large decrease in the IR stretching frequency (v _CN60 cm^–1). The axially stacked polymers exhibit semiconducting properties only upon doping.Presented at the 5th International Symposium on Macromolecule-Metal Complexes (MMV), Summer 1993 in Bremen, Germany.     

Vanadia layers supported on TiO2/SiO2 mixed oxides — An ESR and Raman investigation

ESR and Raman spectroscopy have been used to characterize monolayers of vanadia, which had been immobilized on titania and on a 20% TiO₂/80% SiO₂ mixed oxide support from a vanadyl alkoxide precursor. Characteristic vibrations observed in the Raman spectrum, as well as UV-visible reflection data, indicate that the most abundant vanadia species on the surface consists of disordered polymeric arrays: the central vanadium ion is surrounded by the tightly bound vanadyl oxygen, four oxygen ions in the basal plane, and a distant sixth oxygen ligand in bridging position to the support. From the ESR spectra the principal values ofg andA tensors are obtained, and their dependence on the support material and on the vanadia loading is investigated. Comparison with TPR measurements indicates that for structurally and chemically similar catalysts, the ESR-derived deviationg = g – g _e from the free electrong value provides a useful measure of the V=O bond strength.     

Ultrasound assisted continuous‐mixing for the preparation of PP/SEBS/OMMT ternary nanocomposites

Polypropylene (PP)/polystyrene‐block‐poly(ethylene‐co‐butylenes)‐block‐polystyrene (SEBS)/organo‐montmorillonite (OMMT) nanocomposites of varying concentrations of maleic anhydride‐grafted polypropylene (PP‐g‐MA) were prepared by continuous mixing assisted by ultrasonic oscillation. The structure and morphology of nanocomposites were investigated by X‐ray diffraction (XRD), transmission electron microscopy, and scanning electron microscopy. It was found that both PP‐g‐MA and ultrasonic oscillation could enhance the intercalation and exfoliation of OMMT in PP matrix. Meanwhile, the formation of PP could be induced by ultrasonic irradiation at a power of more than 540 W. Rheological properties including complex viscosity, storage, and loss modulus of nanocomposites were increased after adding PP‐g‐MA or ultrasonic treatment. The results of mechanical properties showed that PP‐g‐MA could improve the tensile strength and tensile modulus of nanocomposites, but with the sacrifice of impact strength. This problem could be improved by ultrasound due to the reduced particle size of SEBS. However, the mechanical properties would be reduced by ultrasonic treatment with higher intensity due to the polymer degradation. Therefore, the synergistic effect of both compatibilizer and ultrasound should account for the balance between toughness and stiffness of PP/SEBS/OMMT ternary nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41202.     

Electrochemical study and complete factorial design of Toluidine Blue immobilized on SiO2/Sb2O3 binary oxide

SiO₂/Sb₂O₃ of specific surface area S _BET = 788 m² g^–1 and 4.7 wt % of Sb was prepared by the sol–gel method. Toluidine Blue (TB⁺) was immobilized on SiO₂/Sb₂O₃ by ion exchange reactions and the amount of dye bonded to the substrate surface was 13.72 mol g^–1 for SiO₂/Sb₂O₃. This material was used to modify carbon paste electrodes and the electrochemical properties of Toluidine Blue (TB⁺) immobilized on a silica surface modified with antimonium trioxide were investigated by cyclic voltammetry. The electron mediator property of toluidine blue was optimized using a factorial design, consisting of four factors each at two levels. Factorial analysis was carried out by searching for better reversibility of the redox process, that is, the lowest separation between anodic and cathodic peak potentials and a current ratio near unity. The aqueous phase pH does not appear to influence the peak separation, E, and the |I _pa//I _pc| current ratio response. The other factors studied, the scan rate, type of electrolyte and electrolyte concentration are important for this chemically modified electrode system demonstrating significant influences on the reversibility of electron transfer. The experimental observations and data analyses on this system indicate that the smallest peak separation occurs using 20 mV s^–1 and 1.0 mol L^–1 KCl while values of |I _pa//I _pc| close to unity are found for 20 mV s^–1 with 1.0 mol L^–1 concentrations of either KCl or CH₃COONa. The electrodes presented reproducible responses and were chemically stable for various oxidation-reduction cycles.     

Silphenylene and silphenylene-siloxane oligomers: Structure-property relationships

Some representative oligomers were prepared by polycondensation reactions of dimethyldichlorosilane with 1,4-di-Grignard reagent prepared from 1,4-dibromobenzene in diethyl ether. The structural characterization of the oligomers was carried out by FTIR and¹H,¹³C, and²⁹Si NMR spectroscopy. TheM _n values were determined by vapor pressure osmometry. TheT _g values were measured by DSC and the thermodegradation process was analyzed by TGA. In all cases the oligomers prepared in the absence of the blocking end group showed siloxane units in the main chain, which were quantified by¹H and²⁹Si NMR.²⁹Si NMR was also used to determine the oligomer sequence. It was possible to correlate the and structure withT _g and with temperature at 3% weight loss. The results agree with these obtained for structurally similar polymers.     

Methacrylate-endcapped poly(d,l-lactide-co-trimethylene carbonate) oligomers. Network formation by thermal free-radical curing

A series of 3-arm, methacrylate-endcapped poly(

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-lactide-co-trimethylene carbonate) prepolymers was synthesized using

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-lactide:trimethylene carbonate (DLL:TMC) molar feed ratios of 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100. Number average molecular weights were in the range (2.3–2.6) × 10³ g mol⁻¹. The prepolymers were free-radically crosslinked in the absence of reactive diluents to give amorphous, bioabsorbable networks with a broad range of thermal, mechanical, and degradative properties. Extraction studies indicated that sol-contents ranged from 2.89%–6.17%. Tensile modulus, ultimate strength, and T_g increased with increasing

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-lactide content. Networks containing higher contents of

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-lactide, 100:0, 80:20, and 60:40 (DLL:TMC), were strong and fairly rigid, but failed catastrophically at the yield point; networks containing lower contents of

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-lactide, 20:80 and 0:100, showed a higher elongation to break, failing catastrophically at the yield point. A 40:60 DLL:TMC network fit perfectly within the series of compositions with regard to modulus and tensile strengh; however, it showed a yield point, followed by a regime of plastic flow prior to break. Hydrolytic degradation experiments revealed that the network based on poly(

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-lactide) homopolymer degraded fastest owing to its hydrophilicity. Hydrolytic degradation in the copolymer networks was controlled by two opposing effects which occurred as the trimethylene carbonate was increased: T_g depression, which increased water uptake, and increased hydrophobicity, which decreased water uptake. Increasing trimethylene carbonate in the 80:20 and 60:40 DLL:TMC copolymer networks caused a decrease in the water uptake and the degradation rate since these network are both glassy at the degradation temperature of 37°C. The observed increase in degradation rate in the 40:60 copolymer network was due to increased water uptake caused by depression of the T_g to a value below the test temperature of 37°C. The 20:80 and 0:100 DLL:TMC networks were the slowest to degrade owing to their hydrophobicity. © 1997 Elsevier Science Ltd.     

Organometallic and coordination chemistry on phosphazenes. III. Synthesis, characterization, and electrochemical behavior of transition metal-cinnamonitrile cyclophosphazene derivatives

Hexakist 4-formylphenoxy cyclophosphazene (1) reacts with six equivalents of cyanomethylenetriphenylphosphorane to give hexakist 4-cinnamonitrile cyclotriphosphazene bearing 12 functional groups tsix nitriles and six olefins' able to coordinate up to 12 metals. In this way a series of polynuclear phosphazene metal derivatives (8–12) was prepared with different transition metals and in different oxidation states. Pt(0), Pt(II) and Rh(I). The analogous cinnamonitrile derivatives (3–7) were prepared and used as models for the characterization of corresponding phosphazene compounds. The redox properties of the complexes3–5 and8–10 as well as of the free cinnamonitrile2 and the free substituted cyclophosphazene1 have been investigated by cyclic voltammetry (CV) and controlled potential electrolysis (CPE) in aprotic media (THF, CH₂Cl₂, or NCMe 0.2M [NBu₄][BF₄]), at Pt electrodes. Cathodic processes have been detected only when the unsaturated C=C bond of the cinnamonitrile group is uncoordinated: hence, for compounds1. 4. and9. they are irreversible occur at potentialsE _p ^red ca. –1.3 to ca. –1.9V vs SCE which are less cathodic than that exhibited by the free cinnamonitrile (2:E _p ^red ca. –2.0 V vs SCE), and are believed to be centered at the electron-acceptor empty ^* (C=C) orbital of each of the cinnamonitrile groups present in the molecule. Anodic processes are displayed only by complexes3. 5. 8. and10 with at least one Pt(0) site: they are irreversible, conceivably centered at such a metal center, and occur at potentials (E _p ^bv ca. 0.7 1.2 V vs SCE) which are dependent on the electronic effects of the ligands, in particular the strong electron-withdrawing ability of the cyclophosphazene group. Complex10 undergoes dissociation in NCMe to form9 and possibly solvated [Pt(PPh₃)₂] species which adsorb at the electrode surface. No evidence for any redox process centered at the phosphazene ring has been found.Presented at the 1st Italian Workshop on Cyclo- and Poly(phosphazene) Materials, February 15–16, 1996, at the CNR Research Area in Padova, Italy.     

ESR Observation of W5+ and Zr3+ States in Pt/WOx/ZrO2 Catalysts

Electron spin resonance (ESR) studies of Pt/WO _x /ZrO₂ catalysts over the temperature range of 5–330 K are reported. Two sets of ESR signals, one with g =1.98 and g =1.96 and the other with g _x =1.39, g _y =1.70 and g _z =1.54 are identified as intrinsic signals from the W⁵⁺ and Zr³⁺ states, respectively, formed in the sample. These signals are absent in samples without Pt. Studies on samples annealed at 773 K showed possible electron transfer between the W⁵⁺ and Zr³⁺ states in which the concentration of one state increases at the expense of the other.     

Rheological behavior of waterborne polyurethane/starch aqueous dispersions during cure

Isothermal rheological behaviors of waterborne polyurethane (WPU)/starch aqueous dispersions during cure were investigated with a small-amplitude oscillatory shear flow experiment to evaluate their crosslinked structure and to predict their mechanical properties, for the first time. An abrupt increase in the elastic storage modulus (G′), the viscous loss modulus (G″), the complex dynamic viscosity (η^*) and the loss tangent (tan δ) was observed during the curing process of the dispersions, as a result of the formation of a fractal polymer gel. The gel point (t_gel) was determined from the intersection in tan δ vs curing time for different constant shear frequencies, where tan δ was frequency independent and all curves crossed over, indicating the validity of the Winter–Chambon criterion for the complex system. The values of the power law exponent (n) and the gel strength (S_g) at the gel point indicated that with an increase of starch content the crosslinked WPU/starch gels underwent a transition from weak fractal to strong elastic ones. Moreover, the WPU/starch composite sheets, obtained from the aqueous dispersions with relatively high S_g values, also exhibited the increased tensile strength (σ_b) and Young's modulus (E). Their structure–mechanical properties relationship and the phase transitions of dispersed starch–dual-phase continuity–starch matrix were revealed. This work confirmed that the rheological characters could be used to predict the mechanical properties of the WPU materials blended with natural polymer.     

Multiwalled carbon nanotubes/polypyrrole/graphene/nonwoven fabric composites used as electrodes of electrochemical capacitor

The reduced graphene oxide/nonwoven fabric (rGO/NWF) composites have been fabricated through heating the NWF coated with the mixture of GO and HONH₂·HCl at 130°C, during which the GO is chemically reduced to rGO. Then the composites of polypyrrole (PPy)/rGO/NWF have been prepared through chemically polymerizing pyrrole vapor by using the FeCl₃·6H₂O adsorbed on rGO/NWF substrate as oxidant. Finally, multiwalled carbon nanotubes (MWCNTs) are used as conductive enhancer to modify PPy/rGO/NWF through dip‐dry process to obtain MWCNTs/PPy/rGO/NWF. The prepared composites have been characterized and their capacitive properties have been evaluated in 1.0M KCl electrolyte by using two‐electrode symmetric capacitor test. The results reveal that MWCNTs/PPy/rGO/NWF possesses a maximum specific capacitance (C_sc) of about 319 F g^?1 while PPy/rGO/NWF has a C_sc of about 277.8 F g^?1 at the scan rate of 1 mV s^?1 and that optimum MWCNTs/PPy/rGO/NWF retains 94.5% of initial C_sc after 1000 cycles at scan rate of 80 mV s^?1 which is higher than PPy/rGO/NWF (83.4%). Further analysis reveals that the addition of MWCNTs can increase the charger accumulation at the outer and inner of the composites, which is favorable to improve the stability and the rapid charge‐discharge capacity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41023.     

Molecular dynamics simulation study on the structure and properties of polyimide/silica hybrid materials

A type of polyimide/silica (PI/SiO₂) copolymer model was established through the dehydration of tetraethyl orthosilicate molecules (TEOS) and bonding to a silane coupling agent. The content of SiO₂ was controlled by adjusting the number of molecules which bound to the TEOS. Finally, the silica was formed into a hybrid model (hybrid PI/SiO₂) with a small molecule embedded in the PI. The model was optimized by geometric and molecular dynamics and the changes in the model structure, Young's modulus, shear modulus, and glass-transition temperature (T _g) were analyzed. The results showed that the density and cohesive energy density of the composites could be improved by doping SiO₂ in PI. Young's modulus and shear modulus of PI/SiO₂ hybrid materials were higher than undoped PI. The tensile strength reached 568.15 MPa when the doping content was 9%. Therefore, the structure design and content control of SiO₂ was an effective way to improve the performance of a PI/SiO₂ composite. The variation of T _g and tensile strength of PI/SiO₂ hybrid composites is consistent with that of PI/SiO₂ composite synthesized in real experiment, which will be a convenient method for new material design and performance prediction. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47335.     

Cucurbitacins fromCucurbita texana: Evidence for the role of isocucurbitacins

In addition to cucurbitacins E andI, cucurbitacins D,1, 3-epi-isocucurbitacin D,2, and B,3, were isolated from the fruits ofCucurbita texana and structurally identified by UV, IR,¹H NMR,¹³C NMR, and MS, and 2-O--glucopyranosylcucurbitacin I was identified. These compounds have not been reported previously as constituents of this species. The isolation of 3-epi-isocucurbitacin D2 together with normal cucurbitacins suggests that isocucurbitacins occur naturally. Evidence is also discussed that isocucurbitacins are biosynthesized one step ahead of normal cucurbitacin.