Dong-ho Lee

Synthesis, characterization, and reactivities of the polysiloxane-bridged binuclear metallocenes tetramethyldisiloxanediylbis(cyclopentadienyltitanium trichloride) and hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride)

Abstract The reaction of dithallium salts of tetramethyldisiloxanediylbis(cyclopentadienyl), 3, and hexamethyltrisiloxanediylbis(cyclopentadienyl), 4, with two equivalents of TiCl4 gives the title compounds tetramethyldisiloxanediylbis(cyclopentadienyltitanium trichloride), 5 and hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride), 6 respectively. The stoichiometric reaction of 5 and 6 with water results in the formation of new oxygen-bridged metallocenes [(TiCl2)2(μ2-O)-(η5-C5H4)2-μ2-(SiMe2)2O], 7, and [(TiCl2)2(μ2-O)-(η5-C5H4)2-μ2-(SiMe2)3O2}], 8. In addition, further reaction of 7 and 8 with another one equivalent of water or the treatment of 5 and 6 with an excess amount of water gives rise to the formation of the metallocene compounds having Ti4O4 rings [(TiCl)2(μ2-O)-(η5-C5H4)2-μ2-(SiMe2)2O]2(μ2-O)2, 9, and [(TiCl)2(μ2-O)-(η5-C5H4)2-μ2-(SiMe2)3O2]2 (μ2-O)2, 10. All the new kinds of metalocenes prepared have been characterized by IR, NMR, mass spectrometry, or elemental analysis. Especially an investigation of the Δδ values in 1H NMR and a comparison between the theoretical and observed isotopic ratio in a mass spectra among the synthesized bridged compounds have been very conveniently utilized to study their structures. Polymerization experiments with the dinuclear complexes in the presence of methylaluminoxane as a cocatalyst indicate that the compounds 5 and 6 do exhibit catalytic activity for syndiotactic polymerization of styrene.

Effects of GO oxidation degree on GO/BuMgCl-supported Ti-based Ziegler–Natta catalyst performance and nanocomposite properties

In the present research, three graphene oxide (GO)/n-butyl-magnesium chloride (BuMgCl)-supported Ti-based Ziegler–Natta catalysts were synthesized by the reaction of Grignard reagent with GO at various oxidation degrees, followed by anchoring of TiCl4. The effects of GO oxidation degree and of the reaction conditions on in situ ethylene polymerization were investigated. The obtained PE/reduced GO (rGO) product was subsequently used as a masterbatch for melt-blending with commercial PE. The resultant PE/rGO nanocomposites, even at low rGO loads, due to the good dispersion and to the good interface adhesion of the graphene sheet and the PE matrix, exhibited significant increase in heat distortion temperature, thermal decomposition temperature, tensile strength and modulus, in addition to acceptable reduction in elongation at break.

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.

A phenomenological model for linear viscoelasticity of monodisperse linear polymers

Although the reptational model of Doi and Edwards gives a successful description of viscoelasticity of flexible linear polymers, the success is restricted to the terminal region.1 There have been several attempts to modify the Doi-Edwards model to describe wider range of time or frequency.2–6 This paper suggests a simple phenomenological model which can describe wider range of molecular weight than such molecular models can. Although our model is a phenomenological one, it is practical and convenient to predict the effect of molecular weight distribution on linear viscoelastic data because of its simple mathematical form.