Yanming Hu

Organoborane-containing polyacetylene derivatives: synthesis, characterization, and fluoride-sensing properties

Triarylborane-containing polyacetylene derivatives (2a–c) were synthesized by the polymerization of the corresponding monomers with Rh+(nbd)[C6H5B−(C6H5)3] catalyst. The anion sensing ability of 2a–c was examined by using tetra-n-butylammonium salts of a series of halide ions. UV-vis absorption and emission measurements revealed that these polymers could selectively detect F−, while they did not show any response for Cl−, Br−, and I−. The fluoride sensing properties of these polymers are highly dependent on the structure of the spacers between the conjugated main chain and boron atoms. Namely, 2a containing fluorenyl moieties exhibited a “turn on” fluorescence F− sensing ability. 2b having phenyl spacers displayed emission quenching upon addition of F− in solution, and a signal amplification phenomenon was observed compared to the corresponding monomer. Addition of F− changed the color of the biphenyl group-containing 2c in THF from yellow to orange, indicating that 2c can be used as a colorimetric sensor.

Highly Active and Cis-1, 4 Selective Polymerization of 1, 3-Butadiene Catalyzed by Cobalt(II) Complexes Bearing Α-Diimine Ligands

A series of cobalt(II) complexes bearing α‐diimine ligands were synthesized and characterized by elemental and spectroscopic analysis. These complexes had the general formulas [ArN = C(Me)-(Me)C = NAr]CoCl2 (Ar = C6H5, 3a; 4‐MeC6H4, 3b; 4‐MeOC6H4, 3c; 4‐FC6H4, 3d; 4‐ClC6H4, 3e; 2‐MeC6H4, 3f; 2‐EtC6H4, 3g; 2‐iPrC6H4, 3h; 2, 4, 6‐Me3C6H2, 3i; 2, 6‐Et2C6H3, 3j; 2, 6‐iPrC6H3, 3k). 2,6‐Bis[(2,6‐diisopropylphenylimino)ethyl]pyridine CoCl2 (4a) was also synthesized for comparison. The structures of complexes 3i, 3k, and 4a were further analyzed by X‐ray crystallography. When the Co(II) complexes were activated with ethylaluminum sesquichloride, they exhibited high catalytic activity for 1,3‐butadiene polymerization. The polymers produced have high cis‐1,4 stereoregularity (up to 98.0%) and high molecular weights (Mn = 1×10^4 - 1×10^5). The substituent ligand affected both catalytic activity and stereoselectivity through an electronic effect while steric hindrance by the substituent was not important. The effects of the polymerization conditions, such as polymerization time, temperature, different alkylaluminum compounds used as cocatalyst, and [Al]/[Co] molar ratio, on polymerization behavior were investigated.

Highly trans-1,4-stereoselective coordination chain transfer polymerization of 1,3-butadiene and copolymerization with cyclic esters by a neodymium-based catalyst system

trans-1,4-Selective coordination chain transfer polymerization of 1,3-butadiene was achieved by using a Nd(Oi-Pr)3/Mg(n-Bu)2 catalyst, affording polybutadienes having high trans-1,4 contents (ca. 96%), moderate molecular weight (Mn = 1.0–2.3 × 104), and narrow polydispersity (Mw/Mn ∼ 1.7). In the system, Mg(n-Bu)2 acted as both a co-catalyst and a chain transfer agent, and the calculated transfer efficiencies of Mg(n-Bu)2 were 27–34%. The produced living polybutadiene could further initiate the ring-opening polymerization of e-CL/lactide to give TPB-b-PCL/PLA copolymers in a controlled fashion. The crystalline amphiphilic copolymers (TPB-b-PCL/PLA) were subsequently applied to investigate their self-assembly behavior by adding a selective solvent into a polymer/co-solvent solution. The polymer plates composed of a crystallized TPB core and PCL/PLA brushes were obtained by the crystallization-driven self-assembly. Moreover, the morphology of the polymers underwent change from nano-sized plates to micro-sized plates with increasing addition of the selective solvent.

Preparation of PE/GO nanocomposites using in situ polymerization over an efficient, thermally stable GO-supported V-based catalyst

In the present article, an efficient and thermally stable vanadium (V)-based Ziegler–Natta catalyst supported on graphene oxide (GO) was synthesized. The resultant catalyst exhibited highly dispersed active sites along the surface, superior catalytic activity toward ethylene polymerization, and enhanced thermal stability, in contrast to the conventional VOCl3 catalyst. Interestingly, the resultant polyethylene (PE)/GO nanocomposite exhibited a higher thermal stability and better mechanical properties than PE obtained using VOCl3. Transmission electron microscopy reveals graphene homogeneously dispersed within the PE matrix.

Comparison of the properties of graphene- and graphene oxide-based polyethylene nanocomposites prepared by an in situ polymerization method

Here, we report a facile coagglomeration method for the preparation of graphene (G)/MgCl2- and graphene oxide (GO)/MgCl2-supported Ti-based Ziegler–Natta catalysts. The effects of the G-filler type on the ethylene polymerization behaviors and polymer properties were investigated. The morphologies of the resultant PE/G and PE/GO nanocomposites exhibited a layer-like shape and the G and GO fillers were well dispersed within the entire PE matrix. In addition, the thermal stability and mechanical properties of the PE were significantly enhanced by the introduction of a very small amount of G or GO fillers (0.02 wt%), due to the satisfactory dispersion of the G or GO in the PE matrix. Compared with the PE/G nanocomposites, the PE with the addition of GO exhibited superior toughness, while the stiffness of the PE was significantly enhanced by the G.

Iminopyridine-Based Cobalt(II) and Nickel(II) Complexes: Synthesis, Characterization, and Their Catalytic Behaviors for 1,3-Butadiene Polymerization

A series of iminopyridine ligated Co(II) (1a–7a) and Ni(II) (1b–7b) complexes were synthesized. The structures of complexes 3a, 4a, 5a, 7a, 5b, and 6b were determined by X-ray crystallographic analyses. Complex 3a formed a chloro-bridged dimer, whereas 4a, 5a, and 7a, having a substituent (4a, 5a: CH3; 7a: Br) at the 6-position of pyridine, producing the solid structures with a single ligand coordinated to the central metal. The nickel atom in complex 5b features distorted trigonal-bipyramidal geometry with one THF molecule ligating to the metal center. All the complexes activated by ethylaluminum sesquichloride (EASC) were evaluated in 1,3-butadiene polymerization. The catalytic activity and selectivity were significantly influenced by the ligand structure and central metal. Comparing with the nickel complexes, the cobalt complexes exhibited higher catalytic activity and cis-1,4-selectivity. For both the cobalt and nickel complexes, the aldimine-based complexes showed higher catalyst activity than their ketimine counterparts.

Synthesis and extremely high gas permeability of polyacetylenes containing polymethylated indan/tetrahydronaphthalene moieties

Polymethylated poly(diphenylacetylene) derivatives, a new category of substituted polyacetylenes, were successfully synthesized, and proved to show extremely high gas permeability.

Polymerization of 1,3-butadiene catalyzed by cobalt(II) and nickel(II) complexes bearing pyridine-2-imidate ligands

Cobalt and nickel complexes (1a-1d and 2a-2d, respectively) supported by 2-imidate-pyridine ligands were synthesized and used for 1,3-butadiene polymerization. The complexes were characterized by IR and element analysis, and complex 1a was further characterized by single-crystal X-ray diffraction. The solid state structure of complex 1a displayed a distorted tetrahedral geometry. Upon activation with ethylaluminum sesquichloride (EASC), all the complexes showed high activities toward 1,3-butadiene polymerization. The cobalt complexes produced polymers with high cis-1,4 contents and high molecular weights, while the nickel complexes displayed low cis-1,4 selectivity and the resulting polymers had low molecular weights. The catalytic activities of the complexes highly depended on the ligand structure. With the increment of polymerization temperature, the cis-1,4 content and the molecular weight of the resulting polymer decreased.

Mono- and Binuclear Cobalt(II) Complexes Supported by Quinoline-2-imidate Ligands: Synthesis, Characterization, and 1,3-Butadiene Polymerization

A series of mono- and binuclear Co(II) complexes (Co1–Co7) supported by quinoline-2-imidate ligands were synthesized and thoroughly characterized. Measured by single crystal X-ray crystallography, complexes Co1 and Co3 adopted distorted tetrahedral structures around the cobalt center. Upon activation by ethylaluminium sesquichloride (EASC), these cobalt complexes exhibited high catalytic activity and cis-1,4-selectivity towards 1,3-butadiene polymerization. The effects of ligand environment, polymerization temperature, and cocatalyst types on the polymerization were investigated in detail. Interestingly, the binuclear Co(II) complexes exhibited high thermal stability, and the polymer yields were up to 97.2% even at a high temperature of 70 °C.

Morphology and properties of PP in-reactor alloys prepared with a MgCl 2 /TiCl 4 /diisobutyl phthalate/phosphate tris-methylphenyl ester catalyst system

A series of polypropylene(PP)/poly(ethylene-co-propylene) in-reactor alloys with different ethylene con-tents was prepared through a two-stage polymerization process using a MgCl2/TiCl4/diisobutyl phthalate/phosphate tris-methylphenyl ester catalyst system. The ethylene content, particle shape, fractured surface, and glass-transition temperature(Tg) of the obtained PP in-reactor alloys were characterized by means of nuclear magnetic resonance, scanning electron microscopy(SEM), and dynamic mechanical analysis(DMA). The ethylene content of the PP alloys increased from 2.34% to 26.69% when the propylene/ethylene feed ratio was increased from 66/34 to 54/46(molar ratio). Morevoer, the increment in ethylene content increased the notched Izod impact strength of the resulting PP al-loys. The impact strength of the PP alloy with an ethylene content of 26.69% was 55.8 kJ/m2, which is 12.7 times that of isotactic polypropylene. The results of DMA and SEM analysis reveal that ethylene-propylene random copoly-mer(EPR) in the PP alloy has a low Tg of ca.‒50 °C and a high interface compatibility with the PP matrix. The ex-cellent impact performance of the PP alloy can be attributed to the uniform dispersal of EPR in the alloy particles and PP matrix.