He-Xin Zhang

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.

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.

Preparation and properties of isotactic polypropylene obtained from MgCl2-supported TiCl4 catalyst bearing bifunctional internal donor

In this research, a novel MgCl2-supported TiCl4 catalyst in conjunction with bifunctional internal donor was synthesized. The effects of internal donor on propylene polymerization behaviors and polymer properties (morphology, Mw and MWD) were investigated. It was found that the activity of novel catalyst was higher than that of the traditional DIBP-based Ziegler–Natta catalyst, while the catalyst activity was less influenced by the ether group length of the bifunctional internal donor. It was also observed that the MWD of PP obtained by bifunctional internal donor-based catalyst was broader than that of PP made by DIBP-based Ziegler–Natta catalyst.

In situ polymerization approach to functionalized MoS2/polyethylene nanocomposites with enhanced thermal stability and mechanical properties

Bulk MoS2 was chemically exfoliated and functionalized with a long alkyl amine (octadecylamine, ODA) and subsequently used as a component in the preparation of an (ODA)–MoS2/MgCl2/TiCl4 catalyst through a coagglomeration method. After in situ ethylene polymerization, flake shape polyethylene (PE)/ODA–MoS2 nanocomposites were obtained, and the ODA–MoS2 fillers were well dispersed in the PE matrix with strong interfacial adhesion. Additionally, the thermal stability and mechanical properties of PE were significantly enhanced by incorporation of the ODA–MoS2 fillers. Therefore, the in situ polymerization approach proposed here will open a new and exciting avenue for the development of transition metal dichalcogenide reinforced polyolefin nanocomposites.

PREPARATION AND PROPERTIES OF MMA/1-PROPYLMETHACRYLATE-POSS COPOLYMER WITH ATOM TRANSFER RADICAL POLYMERIZATION *

The methyl methacrylate (MMA)/1-propylmethacrylate-polyhedral oligomeric silsesquioxane (PM-POSS) copolymers were synthesized via atom transfer radical polymerization with CuBr as catalyst. The unreacted PM-POSS monomer could be removed completely by washing the copolymerization product with n-hexane. The copolymers were characterized with 1H-NMR, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and gel permeation chromatography. With increasing PM-POSS feed ratio, the total conversion increased while the glass transition temperatures of copolymer decreased. The thermogravimetric analysis demonstrated that the thermal stability of copolymer improved slightly with PM-POSS addition. The molecular weight of copolymers increased with incorporation of PM-POSS.

An efficient organic additive to control the crystallization rate of aliphatic polyketone: A non-isothermal crystallization kinetics study

Three types of organic compounds—two carboxylic acids and an anhydride, were used as additives for polyketone (PK). The effect of the additive structure and their feed ratios on the melting temperature, crystallization temperature, and crystallization rate of PK were studied. We found that the crystallization temperature could be reduced significantly by introducing a small quantity of organic additive, in particular, an anhydride. On addition of 1 phr of anhydride, the crystallization temperature was reduced by 10.7 °C. Therefore, the non-isothermal crystallization kinetics of aliphatic PK/anhydride blends with various feed ratios was investigated using DSC. The results were analyzed by various theoretical models, such as Avrami, Ozawa and combined Avrami-Ozawa models.

Preparation of ultra high molecular weight polyethylene with MgCl2/TiCl4 catalyst: Effect of hydrogen and cocatalyst on molecular weight and molecular weight distribution

The ultra high molecular weight polyethylene (UHMWPE) of a special class of HDPE was a linear polyethylene (PE) with a molecular weight numbering in the millions and was also known as high modulus PE or high performance PE. UHMWPE was a unique polymer with outstanding physical and mechanical properties. Most notable were its chemical inertness, lubricity, impact resistance and abrasion resistance. These properties of UHMWPE have been exploited in a wide range of industrial applications, including pickers for textile machinery, lining for coal chutes and dump trucks, runners for bottling production lines, as well as bumpers and siding for ships and harbors. Ethylene polymerization by typical MgCl2-supported Tibased catalysts, and trialkylaluminiums was the most commonly used cocatalyst. On the other hand, H2 is known to be the most efficient industrial regulator of the molecular weight of the olefin polymerization as a chain transfer agent. The use of H2 as a molecular weight regulator was based on the hydrogenolysis of metal to polymer bonds, and the rate of chain transfer to H2 was substantially higher than others. As reported by Hindryckx, the catalyst activity and the molecular weight drastically decreased with the introduction of H2 for ethylene polymerization, while the PDI increased with the increasing H2 pressure. It is well known that molecular weight distribution has a significant effect on the processability and end-use properties of olefin polymers. Therefore, it is necessary to control the molecular weight distribution of polyolefin to produce various grades suitable for the many end-use applications of polyolefin. However, the effects of H2 and cocatalyst on PDI value of UHMWPE have not been reported until now. Therefore, the aim of the present work was to study the effect of H2 feed ratio, H2 feeding time (tH) and cocatalyst on activity, thermal property, molecular weight and molecular weight distribution of UHMWPE produced by using MgCl2-supported Ti catalyst systems. The molecular weight distribution of UHMWPE was analyzed through both GPC and rheometry measurements in this study.

Dependence of performance of organic light-emitting devices on sheet resistance of indium-tin-oxide anodes

The dependence of the performance of organic light-emitting devices(OLEDs) on the sheet resistance of indium-tin-oxide(ITO) anodes was investigated by measuring the steady state current density brightness voltage characteristics and the electroluminescent spectra. The device with a higher sheet resistance anode shows a lower current density, a lower brightness level, and a higher operation voltage. The electroluminescence(EL) efficiencies of the devices with the same structure but different ITO anodes show more complicated differences. Furthermore, the shift of the light-emitting zone toward the anode was found when an anode with a higher sheet resistance was used. These performance differences are discussed and attributed to the reduction of hole injection and the increase in voltage drop over ITO anode with the increase in sheet resistance.