Cun-Yue Guo

Large-area, stretchable, super flexible and mechanically stable thermoelectric films of polymer/carbon nanotube composites

Recently, due to their unique advantages over inorganic materials, organic polymer thermoelectric (TE) materials have received considerable attention. However, most studies focus on TE performance enhancement. So far, little attention has been paid to large-area preparation, stretchability, super flexibility and mechanical stability, although these are the intrinsic advantages of polymer materials. Here we report for the first time large-area, stretchable, super flexible and mechanically stable TE films of polymer/carbon nanotube composites. Mechanically stretchable films with a diameter of ∼18 cm are achieved by common vacuum filtration, whose thicknesses and sizes can be conveniently adjusted. Despite direct observations of films under various deformations of bending, rolling or twisting, quantitative measurements of minimum bending radii (<0.6 mm) further confirm the super flexibility. More importantly, after mechanical bending or stretching, no obvious deterioration of TE performance is found. Our findings represent a novel direction of polymer TE materials, and will speed up their applications.

Poly(ethylene terephthalate) nanocomposites with a strong UV-shielding function using UV-absorber intercalated layered double hydroxides

A novel strategy has been developed to prepare poly(ethylene terephthalate) nanocomposites with a strong UV-shielding function. The nanoscale dispersion of UV-absorber intercalated layered double hydroxides (LDHs), and a combination of the chemical absorption and physical blocking of UV rays may account for the greatly enhanced UV-shielding ability, which remarkably depends on the interlayer anions, the content and the platelet size of the LDHs.

Enhancing thermo-stability to ethylene polymerization: synthesis, characterization and the catalytic behavior of 1-(2,4-dibenzhydryl-6-chlorophenylimino)-2-aryliminoacenaphthylnickel halides

A series of 1-(2,4-dibenzhydryl-6-chlorophenylimino)-2-aryliminoacenaphthylene derivatives (L1-L5) was synthesized and reacted with nickel halides to form the corresponding nickel complexes LNiX2 (X = Br, Ni1-Ni5; X = Cl, Ni6-Ni10). The molecular structures of representative complexes Ni2 and Ni5 were determined by single crystal X-ray diffraction, indicating the distorted square planar geometry around the nickel atom of complex Ni2 and the distorted tetrahedral geometry around the nickel atom of complex Ni5, respectively. Upon activation with low amounts of ethylaluminium sesquichloride (Et3Al2Cl3, EASC), all nickel complexes exhibited high activities up to 1.09 x 10(7) g of PE per mol of Ni per h toward ethylene polymerization, producing branched polyethylenes. Most importantly, these systems showed good thermo-stability, even at 80 degrees C maintaining the activity with 3.76 x 10(6) g of PE per mol of Ni per h.

Highly branched unsaturated polyethylenes achievable using strained imino-cyclopenta[b]pyridyl-nickel precatalysts

A new family of strained imino-cyclopenta[b]pyridines, 7-(ArN)-6-Me2C8H5N (Ar = 2,6-Me2Ph (L1), 2,6-Et2Ph (L2), 2,4,6-Me3Ph (L3), 2,6-Et2-4-MePh (L4), 2,6-i-Pr2Ph (L5)), have been synthesized in reasonable yield by a sequence of reactions from 2-chloro-cyclopenta[b]pyridin-7-one. Treatment of L1 and L3 with NiCl2·6H2O generates mononuclear bis-ligated [7-(ArN)-6-Me2C8H5N]2NiCl2 (Ar = 2,6-Me2Ph (Ni1), 2,4,6-Me3Ph (Ni3)), while with L2 and L4, the chloride-bridged binuclear complexes [7-(ArN)-6-Me2C8H5N]2Ni2(μ-Cl)2Cl2 (Ar = 2,6-Et2Ph (Ni2), 2,6-Et2-4-MePh (Ni4)), have been isolated; no apparent reaction occurred with L5. On activation with either MAO or MMAO, Ni1–Ni4 exhibited high activities towards ethylene polymerization with Ni3 the most active (5.02 × 106 g PE per mol Ni per h at 20 °C); rapid regeneration of the active species (3096–5478 h−1 at 20 °C) is a feature of their catalytic performance. A detailed microstructural analysis of the polyethylenes reveals the presence of vinyl and higher levels of internal vinylene groups indicative of high rates of chain isomerization, e.g., the ratio of (–CHCH–) to (H2CCH–) groups is 2.2 : 1 using Ni3/MAO at 60 °C. Agostic interactions involving γ-, δ- and higher-hydrogens are inferred in addition to β-hydrogen elimination to account for the vinylene groups and the longer chain alkyl branches. The molecular structures of Ni1 and Ni2·2MeOH are also reported.

Raising the N-aryl fluoride content in unsymmetrical diaryliminoacenaphthylenes as a route to highly active nickel(II) catalysts in ethylene polymerization

Five examples of selectively fluorinated unsymmetrical diiminoacenaphthylenes, 1-[2,6-{(4-FC6H4)2CH}2-4-FC6H4N]-2-(ArN) C2C10H6 (Ar = 2,6-Me2C6H3L1, 2,6-Et2C6H3L2, 2,6-iPr2C6H3L3, 2,4,6-Me3C6H2L4, 2,6-Et2-4-MeC6H2L5), have been synthesized and used to prepare their corresponding nickel(ii) halide complexes, LNiBr2 (Ni1-Ni5) and LNiCl2 (Ni6-Ni10). Both 1H and 19F NMR spectroscopy techniques have been employed to characterize paramagnetic Ni1-Ni10; an inequivalent fluorine environment is a feature of the tetrahedral complexes in solution. Upon activation with relatively low ratios (ca. 600 equiv.) of ethylaluminum sesquichloride (Et3Al2Cl2, EASC), all the nickel complexes displayed high activities toward ethylene polymerization at 30 °C with precatalyst Ni4 the standout performer at 2.20 × 107 g of PE per mol of Ni per h, producing highly branched polyethylenes. In comparison with related diiminoacenaphthylene-nickel catalysts, these current systems, incorporating a high fluorine content on one N-aryl group, display superior productivity. In addition, the molecular structures of Ni2 and Ni4 are reported and the active catalyst is probed using 19F NMR spectroscopy.

Elastomeric polyethylenes accessible via ethylene homo-polymerization using an unsymmetrical α-diimino-nickel catalyst

Five types of unsymmetrical bis(arylimino)acenaphthenes, 1-[2,4,6-(CHPh2)3C6H2N]-2-(ArN)C2C10H6 (Ar = 2,6-Me2Ph L1, 2,6-Et2Ph L2, 2,6-i-Pr2Ph L3, 2,4,6-Me3Ph L4 and 2,6-Et2-4-MePh L5), each containing a single N-2,4,6-tribenzhydrylphenyl group, have been prepared and fully characterized. The interaction of L1–L5 with (DME)NiBr2 (DME = 1,2-dimethoxyethane) afforded the corresponding 1 : 1 nickel(II) bromide chelates, LNiBr2 (Ni1–Ni5), in good yield. Distorted tetrahedral geometries are a feature of the X-ray structures of Ni1 and Ni3; broad paramagnetically shifted peaks are seen in the 1H NMR spectra for all the nickel complexes in solution. Upon activation with relatively low amounts of Et2AlCl or Me2AlCl (200–700 equivalents), Ni1–Ni5 exhibited exceptionally high activities for ethylene polymerization (up to 1.07 × 107 g of PE (mol of Ni)−1 h−1), displayed good thermal stability [2.97 × 106 g of PE (mol of Ni)−1 h−1 even at 90 °C] and produced hyperbranched polyethylenes. Dynamic mechanical analysis and stress–strain testing reveal that the polymeric materials possess good elastomeric recovery and high elongation at break, indicating a promising alternative material to thermoplastic elastomers (TPEs).

Polypyrrole nanostructures and their thermoelectric performance

Controlled synthesis of various nanostructures of polypyrrole (PPy) and their thermoelectric performances have been reported. First, the controlled synthesis and morphological characterization of PPy nanostructures are systematically studied by adjusting the experimental parameters. The effects of oxidant type, oxidant concentration, polymerization period as well as reaction medium are examined. Then, the thermoelectric performances of the as-obtained PPy nanostructures are measured in detail. Finally, the level of doping is calculated by X-ray photoelectron spectra. The relation between PPy nanostructures and their thermoelectric performances has been discussed. The present study will benefit the development of novel organic thermoelectric materials by a morphological design strategy, will deepen our understanding towards structure–thermoelectric function relationship, and will be helpful for the future application of organic polymer thermoelectric materials.

Metal complexes bearing 2-(imidazol-2-yl)phenol ligands: synthesis, characterization and catalytic performance in the fixation of carbon dioxide with epoxides

A series of metal complexes bearing 2-(imidazol-2-yl)phenol ligands (Zn, Cu, Ni, Co, Pb) were synthesized and their structures were characterized by IR, NMR, elemental analysis and X-ray. The catalytic activities of all complexes for the coupling reaction of CO2 and epoxide were then detected. The activity influence factors, such as temperature, time, pressure, substituents of ligands and metal centre, were systematically investigated. All these complexes were efficient to catalyze the coupling of CO2 and epoxide to generate cyclic carbonate in perfect yields (>90%) and selectivities (>99%) under optimized conditions of (2 MPa, 5 h, 110 °C) without any organic solvents. A 99.7% yield and >99% selectivity for propylene carbonate (PC) were obtained with C7/n-Bu4NI as catalyst system under the optimized conditions. The catalysts were also proved to be applicable to other terminal epoxides. It is worthy noted that the Pb(II) complex was firstly used to catalyze the coupling reaction of epoxides with carbon dioxide. Moreover, these metal catalysts were recyclable with only minor losses in catalytic activity after simple separation. Finally, a plausible mechanism was given.

Steam reforming of glycerol over Pt-MCM-41 synthesized in a one-step process

Pt-MCM-41 materials were synthesized by a simple method via simultaneous self-assembling and Pt incorporation using cetyltrimethylammonium chloride (CTAC) as a structure directing agent. Structural characterization of the sample was carried out by N2 sorption, XRD and TEM measurements. The highly ordered structure of MCM-41 was not appreciably affected by the formation of the Pt particles. Unlike related results, the Pt nanoparticles were incorporated into the mesopores and embedded into the pore walls as framework. The Pt-MCM-41 sample was tested as a catalyst in the steam reforming of glycerol in which it exhibited moderate activity, high selectivity to hydrogen, and very low selectivity to light alkanes.

Synthesis and characterization of spherical porous calcium carbonate with ordered secondary structures in the presence of polymer with double hydrophilic ionic moieties

Sulfonated poly(aspartic acid) (SPASP) of narrow polydispersity was successfully employed in the facile synthesis of porous calcium carbonate microspheres with regular trigonal star-like secondary structure units and significantly improved surface area (56.3 m2 g−1). Based on the CaCO3 particles morphology through different aging times, a mechanism for the formation of porous CaCO3 microspheres with trigonal star-like secondary structures in the presence of SPASP was proposed.