Electrospinning of linear and highly branched segmented poly(urethane urea)s

Electrospun fibrous mats were formed from linear and highly branched poly(urethane urea)s. The highly branched poly(urethane urea)s were synthesized using an A₂+B₃ methodology, where the A₂ species is an oligomeric soft segment. Since the molecular weight of the A₂ oligomer is above the entanglement molecular weight, the highly branched polymers formed electrospun fibers unlike typical hyperbranched polymers that do not entangle. Stress-strain experiments revealed superior elongation for the electrospun fibrous mats. In particular, the highly branched fiber mats did not fail at 1300% elongation, making the electrospun mats promising for potential applications where enhanced tear strength resistance is required.     

A comparative study of the structure-property behavior of highly branched segmented poly(urethane urea) copolymers and their linear analogs

The solid-state structure-property behavior of highly branched segmented poly(urethane urea) (PUU) copolymers and their linear analog was investigated. A limited study of their solution rheological behavior was also undertaken. The linear PUUs were synthesized by the two-step prepolymer method, whereas the oligomeric A₂+B₃ methodology was utilized to synthesize the highly branched materials. The soft segments (SS) were either poly(tetramethylene oxide) (PTMO) or poly(propylene oxide) (PPO). All copolymers utilized in this study, with one exception, contained 28 wt% hard segment (HS) content. DMA, SAXS, and AFM studies indicated that the linear as well as the highly branched PUUs were microphase separated. The SS T_g of the highly branched PUUs was nearly identical to that of their respective linear analogs. However, the linear copolymers exhibited broader and less temperature sensitive rubbery plateaus, both attributed to one or both of two reasons. The first is better hydrogen bonding organization of the HS phase as well as greater HS lengths than in the highly branched analogs. The second parameter is that of a potentially higher chain entanglement for the linear systems relative to the branched analogs. Tapping-mode AFM phase images confirmed the microphase morphology indicated by SAXS and DMA. Ambient temperature strain-induced crystallization was observed in the PUU based on PTMO 2040 g/mol at a uniaxial strain of ca. 400%, irrespective of the chain architecture. Stress-strain, stress relaxation, and mechanical hysteresis of the highly branched copolymers were in general slightly poorer than that of their linear analogs. Ambient temperature solution viscosity of the highly branched materials in dimethyl formamide was substantially lower that that of the linear samples of nearly equal molecular weight.     

The effects of varied reactant ratios on the polymeric structures of stannous dicarboxylates

Some polymeric Sn(II) dicarboxylates have been produced with good yields from aqueous solution via a double decomposition reaction using varied nonstoichiometric molar proportions of the reactants. They were obtained as highly viscous pale yellow liquids formed into separate denser phases in the precipitation bath. The highly viscous precipitates were drawn directly into fibers. Meltspun polymeric stannous dicarboxylates produced fibers which were only flexible above the glass transition temperature, T_g. When the aliphatic dicarboxylic acids were replaced with their aromatic counterparts similar highly viscous liquids were obtained, but they solidified almost at the instant of formation.     

Improving heat ageing and thermal properties of silicone rubber using montmorillonite clay

Heat ageing and thermal stability of a silicone rubber (SR) filled with montmorillonite clay (MMT) was investigated. Three types of rubber nanocomposites were prepared with highly exfoliated Cloisite 30B (SR/C30B), intercalated/exfoliated Cloisite Na⁺ (SR/Na⁺MMT), and highly intercalated Cloisite 20A (SR/C20A). This study showed that the SR/C30B nanocomposite exhibited excellent heat resistance in comparison to the other two nanocomposites and neat SR as revealed by higher retention strength. The thermal stability of the rubber in air was strongly dependent on the clay morphology and increased in the following order: highly intercalated/exfoliated SR/Na⁺MMT < highly intercalated SR/C20A < highly exfoliated SR/C30B. The thermogravimetric analyses of the SR/C30B nanocomposite showed a substantial increase in the final residue in comparison with the neat SR. This indicated a major improvement in the thermal stability of the rubber containing the exfoliated clay, which was also supported by the higher activation energy of decomposition measured for the nanocomposite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41061.     

Organocatalytic Highly Enantioselective Conjugate Addition of Aldehydes to Alkylidine Malonates

The first highly enantioselective, direct organocatalytic conjugate addition of unmodified aldehydes to alkylidinemalonates is presented. The reaction gives access to β‐formyl‐substituted malonates and highly functionalized lactones with up to 14:1 dr and generally 94 to >99% ee.     

Dynamic mechanical properties of highly loaded ferrite-filled thermoplastic elastomer

The dynamic mechanical properties in terms of the storage modulus E′, loss modulus E″, and the loss tangent δ has been studied for highly filled magnetic polymer composites. The effect of surface treatment on the relaxation spectra has been clearly elucidated and quantitative values indicating the extent of polymer–filler interactions have been given. Various models have been tested for describing the viscoelastic behavior of such highly filled systems. The Wiechert model using a single-arm with a Cole–Cole parameter has been shown to effectively fit the Argand diagram in the case of the present highly filled systems.     

Effect of electrolyte environment and Pt crystallite size on hydrogen adsorption—V

The role of Pt crystallite surface morphology on hydrogen adsorption isotherms in H₂SO₄ and alkaline electrolytes was examined by a potentiodynamic sweep technique. By varying the crystallite size (40–280Å) of highly dispersed Pt electrocatalysts, the relative concentrations of edges, vertices and crystallite faces which contribute to the surface morphology are changed. The potentiodynamic i-V profiles for adsorbed hydrogen oxidation on highly dispersed Pt electrocatalysts in 0.05 and 1 M H₂SO₄ showed similar changes with Pt crystallite size. Only two states of adsorbed hydrogen on highly dispersed Pt were observed in 0.05 M H₂SO₄, compared to four states reported by Angerstein-Kozlowska et al on smooth polycrystalline Pt electrodes.In 1 M NaOH and 35 wt % KOH, less than a monolayer of adsorbed hydrogen was present on highly dispersed Pt electrocatalysts at the reversible hydrogen potential. Two states of chemisorbed hydrogen were observed at 23–91°, while at low temperature (?47°) in 35 wt % KOH, an additional adsorbed hydrogen species was evident in the potentiodynamic i-V curves. A Pt crystallite size effect on the adsorption of hydrogen on highly dispersed Pt in alkaline electrolytes was not deduced.     

Simple synthesis of highly ordered mesoporous carbon by self-assembly of phenol–formaldehyde and block copolymers under designed aqueous basic/acidic conditions

In view of the low reactivity of phenol with formaldehyde under acidic condition in the synthesis of ordered mesoporous carbons, a strategy to accelerate the polymerization of phenol and formaldehyde by using designed aqueous basic/acidic conditions (first weakly basic condition then highly acidic condition) is developed. The first weakly basic condition benefits the formation of hydroxymethyl phenols at 313 K. The latter highly acidic condition mainly induces the condensation reaction between the formed hydroxymethyl phenols, as well as the self-assembly of phenol–formaldehyde and block copolymer template. After removal of the template, the obtained carbon exhibits highly ordered hexagonal mesostructure with a surface area of 760 m² g⁻¹, large pore volume (0.64 cm³ g⁻¹) and uniform pore size (3.32 nm). This developed strategy affords a simple and highly reproducible approach for the synthesis of ordered mesoporous carbon from the less expensive phenol under strong acidic condition, which also provides a wide and easily accessed synthesis condition for the further functionalization, such as the in situ introducing of metal ions.     

Determination of the strength anisotropy of oriented man-made fibres

Conclusions To investigate the transverse strength of highly oriented man-made fibres it is advisable to use the strength anisotropy method.The strength anisotropy of highly oriented fibres (Kevlar-49, Terlon, polyheteroarylene) is approximately two decimal orders of magnitude and is close to the anisotropy of the modulus of deformation.Translated from Khimicheskie Volokna, No. 3, pp. 47–48, May–June, 1983.     

Preparation of hydrocellulose fibres from highly concentrated solutions of cellulose in N-methylmorpholine-N-oxide

Conclusions -- The conditions in preparation of highly concentrated cellulose solutions can greatly affect the structure and properties of the fibres obtained.-- In the preparation of fibres from highly concentrated solutions of cellulose in MMO, a number of complications arise which hinder practical realization of the process.VNIIPV (Mytishchi). Translated from Khimicheskie Volokna, No. 5, pp. 24–27, September–October, 1992.     

Special features of the formation of the structure of highly porous cellular materials based on reaction-sintered silicon carbide

Special features of the structure of highly porous cellular materials containing reaction-sintered silicon carbide are investigated. The effect of the ratio of the initial components of the synthesis (silicon and carbon) on the quantitative and qualitative characteristics of micropores formed during the reaction sintering of silicon carbide is studied. Formulas for calculating the microporosity are presented. The distribution of micropores in the structure components of highly porous cellular materials is analyzed. The influence of the chemical composition and the macro- and microporosity on the strength parameters of highly porous materials is investigated. It is established that despite the maximum microporosity, the strength of highly porous silicon carbide is the highest as compared to the investigated materials containing free silicon or carbon.Translated from Ogneupory, No. 2, pp. 8 – 12, February, 1995.     

Interaction of MgAl2O4 and MgCr2O4 spinels with calcoferruginous melts

Conclusions The interaction was studied between MgAl₂O₄ and MgCr₂O₄ spinels (and their solid solutions and compositions with periclase) with calcoferruginous melts, which are the essential constituents of various slag reagents.On exposure to a highly basic calcoferruginous melt, the magnesium-aluminum spinel forms magnesio-ferrite, brownmillerite, and some calcium aluminate.On interaction of magnesiochromite with calcium ferrite, chiefly high-temperature compounds form.With the action of highly ferruginous melts on magnesiochromite, the resulting solid solution increases in volume, and a distortion is observed at the boundary of the reaction and little-change zones of the samples.The addition of granular MgO to spinels or their solid solutions improves the chemical stability of the compositions against calcoferruginous melts [4].During use in contact with highly basic calcoferruginous melts, the addition of periclase to chromium spinellide additives is recommended; for use in contact with highly ferruginous melts, periclase and aluminum spinellide compositions are recommended.Translated from Ogneupory, No. 7, pp. 44–47, July, 1969.     

Formation of low-resistance contact between titanium and lightly doped polycrystalline diamond using highly doped interlayer

A low-resistance ohmic contact between lightly doped polycrystalline diamond (poly-C) and metal was achieved for piezoresistive sensor applications using highly doped poly-C thin interlayer in the contact area for the first time for poly-C. Two Trimethylboron (TMB) doping concentrations were used during the growth of poly-C films using microwave plasma chemical vapor deposition (MPCVD), which yielded a 0.2 μm highly doped layer on top of 1.8 μm lightly doped layer. The resistivities of the highly and lightly doped poly-C layers are 0.022 and 151 Ω cm, respectively. The contacts were defined by partially etching the highly doped poly-C layer beyond the contact area. Kelvin bridges are fabricated to test the contact resistance. It is demonstrated that the contact resistivities are 0.0028 and 0.0083 Ω cm² for contacts with and without interlayer, respectively. This method reduced the contact resistance to one third of the original value and improved the performance of the piezoresistive sensor.     

Rheology and Dispersion Behavior of Highly Filled Propylene-Ethylene Copolymer/Calcium Carbonate Composites

The rheology and dispersion behavior of commercial propylene-ethylene copolymer, highly filled propylene-ethylene copolymer/CaCO₃ composites and highly filled propylene-ethylene copolymer/HDPE/CaCO₃ composites prepared by melt-compounding were investigated. The pure propylene-ethylene copolymer exhibits pseudoplastic flow behavior obviously. The CaCO₃ particles in the composites have achieved a homogeneous dispersion and the increasing shear rate has almost no influence on the dispersion behavior of CaCO₃ particles. The high loading of CaCO₃ particles influences the rheology behavior of propylene-ethylene copolymer slightly. For the highly filled propylene-ethylene copolymer/CaCO₃ composites, the extensional viscosity only decreases slightly throughout the entire range of extension rates.     

Development of structural hierarchy during uniaxial drawing of PEEK/PEI blends from amorphous precursors

When poly(ether ether ketone)/poly(ether imide) (PEEK/PEI) blends are drawn in their rubbery region, prior to the critical draw ratio, they remain amorphous. Subsequent to the onset of strain hardening, the stress rises rapidly as a result of strain-induced crystallization of the chains highly oriented in the direction of strain. It is during this stage of deformation process that a highly structured physical network is formed where oriented crystallites act as nodes in the network structure. The wide angle X-ray scattering data indicate that chains in these ‘nodes’ are highly oriented and the three dimensional crystalline lattice is not well established due to poor axial registry of these highly oriented chains. This is evidenced by the absence of off-equatorial peaks. During this period, the effectiveness of drawing arises from the existence of the tie chains aligned in the direction of draw and forming the net between the crystallites. PEI, though a stiff and bulky chain, is found to delay the oriented crystallization rate of PEEK, but has little effect on its crystalline orientation in the composition range investigated.     

二硫化碳生产装置消防初探

二硫化碳为低闪点易燃液体,具有易燃、易爆、高毒、高挥发性,其蒸气与空气形成爆炸性混合物,遇明火、高温极易燃烧爆炸,与氧化剂能发生强烈反应,其蒸气比空气重,能在较低处扩散到相当远的地方,遇火源引着回燃。若遇高温,容器内压力增大,有开裂和爆炸的危险。二硫化碳一旦泄漏,需用大量水封其泄漏产品,发生火灾时,需用水、泡沫、干粉、砂土等灭火。     

Reforming of Methane with Carbon Dioxide over a Catalyst Consisting of Ruthenium Metal and Cerium Oxide Supported on Mordenite

Reforming of CH₄ with CO₂ proceeds at 400 °C over a catalyst consisting of ruthenium metal and CeO₂ highly dispersed on mordenite. The catalyst, Ru-CeO₂/MZ, is highly active for the reforming of CH₄ under the conditions at which a carbon formation reaction is thermodynamically apt to take place. The reforming selectively forms H₂ and CO. An increase in the weight of the catalyst resulting from carbon deposits was scarcely observed. IR spectra for the catalyst indicate that the reforming proceeds via the formation of the intermediate species such as Ru-CO and Ru-CH_x on the surface of ruthenium. The data of H₂ adsorption support the idea that ruthenium is highly dispersed in Ru-CeO₂/MZ.     

Highly Enantioselective Transfer Hydrogenation of α‐Imino Esters by a Phosphoric Acid

Chiral phosphoric acids have been identified as highly efficient organocatalysts for the asymmetric transfer hydrogenation of α‐imino esters and amide. Utilizing Hantzsch esters as the hydrogen donor, versatile highly enantioenriched α‐amino esters and their derivatives were obtained with up to 98 % ee.     

Synthesis and Photochemistry of Quantum-Size Semiconductor Particles in Solution and in Modified Layers

We describe the preparation of highly monodisperse, quantum-size CdS particles. In these samples a band splitting into discrete exciton-like states is observed. A mechanism for the excitonic fluorescence is presented involving shallow traps as a reservoir for electrons which finally recombine with free positive holes across the bandgap. Quantum-size CdS and PbS particles prepared in situ on highly porous, polycrystalline TiO₂ electrodes work as highly efficient sensitizers. Photocurrent yields of more than 70% are reported. In the case of PbS, it is shown that an efficient electron transfer is possible only with particles in the size of the quantization regime.     

Studies on the blends of polycarbonate and highly branched polystyrene

A highly branched polystyrene (HBPS) was synthesized via the copolymerization of 4‐(chloromethyl) styrene with styrene using the self‐condensing atom transfer radical polymerization method. The addition of this highly branched polystyrene as a melt modifier for polycarbonate (PC) was attempted. Indeed, the results show that the addition of highly branched polystyrene can decrease the melt viscosity of PC with little change in mechanical properties, although the blends do exhibit lower thermal stability compared with pure PC. Extrapolation shows that all of the blends have an initial weight loss temperature above 450°C with a statistic heat‐resistant index T_s above 225°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2425–2430, 2004