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Branched-Polyethylene Produced by Asymmetric Metallocene Catalyst Using Ethylene as Monomer  [PDF]
分子催化 , 1999,
Abstract: Continuousfundamentalinvestigationsonmetalocenehaveledtothebasicunder-standingandthecontrolofpolymerizationactivesites,thusca...
The influence of the metal net charge of non-metallocene early transition metal catalyst on the ethylene polymerization activity
ChunHong Wu,HuaYi Li,YuQi Feng,YouLiang Hu
Chinese Science Bulletin , 2008, DOI: 10.1007/s11434-008-0460-9
Abstract: The net charges on central metals of a serial non-metallocene early transition metal catalysts (FI catalyst) with similar steric hindrance were caculated with MM-QEq (molecular mechmism-charge equilibration) method and associated with ethylene polymerization activities of these FI catalyts. It was found that the activity increased with the net charge on metal if ignoring the influence of the steric hindrance. In other words, introduction of strong and/or more electron-withdrawing groups onto the ligand of FI catalyst would enhance the activity of the catalyst. This conculsion gave a direction to designing new FI catalyst with higher activity.
Lldpe prepared byin situ polymerization using a dualfunctional catalytic system of Ti(On-Bu)4 /ALEt3-Et(Ind)2-ZrCl2/MAO
Liu Zhongyang,Xu Demin,Guo Cunyue,Wang Jun,He Dawei,Hu Youliang
Chinese Science Bulletin , 2001, DOI: 10.1007/BF02901130
Abstract: Linear low-density polyethylene (LLDPE) was prepared byin situ polymerization using a dual-functional catalytic system containing Et(Ind)2ZrCl2/MAO and Ti(OnBu)4/AlEt3 used as co-polymerization catalyst and dimerization catalyst, respectively. The catalytic system showed high activity and the polymer with low melting point, narrow molecular weight distribution (MWD) and low crystallinity was produced.
Thermal and Mechanical Properties of Polyethylene/Doped-TiO2 Nanocomposites Synthesized Using In Situ Polymerization  [PDF]
S. H. Abdul Kaleel,Bijal Kottukkal Bahuleyan,J. Masihullah,Mamdouh Al-Harthi
Journal of Nanomaterials , 2011, DOI: 10.1155/2011/964353
Abstract: Ethylene polymerization was carried out using highly active metallocene catalysts (Cp2ZrCl2 and Cp2TiCl2) in combination with methylaluminoxane. Titanium (IV) oxide containing 1% Mn as dopant was used as nanofillers. The effects of filler concentration, reaction temperature, and pressure on the thermal and mechanical properties of polymer were analyzed. The improvement of nanoparticles dispersion in the polyethylene matrix was checked by WAXD. The thermal properties were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The filler impact on the melting temperature of polyethylene synthesized using Cp2ZrCl2 was very minimal which is due to the degree of short-chain branching. The ash content was also analyzed for each nanocomposite and found to be in line with the activity of the catalyst. There was a significant increase in the mechanical properties of the polyethylene by addition of filler. 1. Introduction The inorganic mineral fillers help in fulfilling polymer performance properties, such as increasing the stiffness, heat distortion temperature, dimensional stability, hardness, and toughening of the products [1–4]. The properties of polymer composites depend on the particles shape, size, loading, interfacial bonding, and dispersion of the fillers [5–8]. Polymer nanocomposites are a new class of materials incorporating an ultrafine dispersion of nanomaterials in a polymeric matrix. Inorganic nanoparticles such as silicon dioxide (SiO2) [9–12], titanium dioxide (TiO2) [13–16], Aluminium trioxide (Al2O3) [17, 18], and Zirconium dioxide (ZrO2) [19, 20] have been used to improve polymer properties. TiO2 primarily served as a pigment than as filler for improving mechanical strength. TiO2 was found to be well dispersed in polyvinyl alcohol using solution-mixing technique and these samples acted as efficient optically transparent UV filters due to the photo-responsive properties of TiO2 [13]. In the recent past, TiO2-filled polymers prepared by melt compounding have been reported to exhibit markedly improved properties over neat polymers and micron-sized particle-filled polymer composites [21, 22]. Different kinds of polymer-based TiO2 composites have been reported in the literature, such as high-impact polystyrene (HIPS)/nano-TiO2 [23] and polyamide/nano-TiO2 composite [24]. Polyethylene/TiO2 composites were prepared, and it was found that the introduction of TiO2 increased the viscosity of composites and produced a better dispersion of TiO2 in the melt compounding with significant improvement in the impact
Polypropylene Nanocomposites Obtained by In Situ Polymerization Using Metallocene Catalyst: Influence of the Nanoparticles on the Final Polymer Morphology
Paula Zapata,Raúl Quijada
Journal of Nanomaterials , 2012, DOI: 10.1155/2012/194543
Abstract: Polypropylene nanocomposites containing silica nanospheres based on the sol-gel methods were produced via in situ polymerization using a rac-Et(Ind)2ZrCl2/methylaluminoxane (MAO) system. Two different routes were used depending on the interaction between the silica nanoparticles with the catalytic system. In route 1 the nanoparticles were added together with the catalytic system (rac-Et(Ind)2ZrCl2)/(MAO) directly into the reactor, and in route 2 the metallocene rac-Et(Ind)2ZrCl2 was supported on silica nanospheres pretreated with (MAO). SEM images show that when the nanospheres were added by both routes, they were replicated in the final polymer particle morphology; this phenomenon was more pronounced for PP obtained by route 2. The polypropylene (PP) nanocomposites obtained by both routes had a slightly higher percent crystallinities and crystallinity temperatures than pure PP. Transmission electron microscopy (TEM) images show that the nanospheres were well dispersed into the polypropylene matrix, particularly in the nanocomposites obtained by the support system (route 2).
In situ synthesis of nanoclay filled polyethylene using polymer supported metallocene catalyst system
Murthy, Z. V. P;Parikh, Parimal A;Rajesh, Smitha;
Química Nova , 2011, DOI: 10.1590/S0100-40422011000700010
Abstract: in situ ethylene polymerizations were performed using bis(cyclopentadiene)titanium dichloride supported on polyethersulfone as catalyst. the bis(cyclopentadiene)titanium dichloride supported on polyethersulfone catalyst activity estimated by ethylene polymerization was 360 kgpe/molti/h. during polymerization the fillers used were montmorillionite nanoclays having surface modifications with 35-45 wt% dimethyl dialkyl(14-18)amine (fa) and 25-30 wt% trimethyl stearyl ammonium (fb). these fillers were pretreated with methylaluminoxine (mao; cocatalyst) for better dispersion onto the polymer matrix. the formation of polyethylene within the whole matrix was confirmed by ftir studies. it was found that the nature of nanofiller did not have any remarkable effect on the melting characteristics of the polymer. tga study indicates that nanoclay fb filled polyethylene has higher thermal stability than nanoclay fa filled polyethylene. the melting temperature of the obtained polyethylenes was 142 oc, which corresponds to that synthesized by the polyether sulfone supported catalyst.
Dual catalyst system composed by nickel and vanadium complexes containing nitrogen ligands for ethylene polymerization
Furlan, Luciano G.;Casagrande Jr., Osvaldo L.;
Journal of the Brazilian Chemical Society , 2005, DOI: 10.1590/S0103-50532005000700024
Abstract: branched polyethylene/high-density polyethylene blends (bpe/hdpe) were prepared using the combined [nicl2(a-diimine)] (1) (a-diimine = 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine) and [tpms*vcl2(ntbu)] (2) (tpms* = hydridobis(3-mesitylpyrazol-1-yl)(5-mesitylpyrazol-1-yl)) catalysts. the polymerization reactions were performed in hexane or toluene at three different polymerization temperatures (0, 30 and 50 °c) and several nickel molar fractions (xni), using mao as cocatalyst. at all temperatures, the activities show an approximate linear correlation with xni, indicating a non-synergistic effect between the nickel and the vanadium species. higher activities were found in toluene at 0 °c. the melting temperatures for the polyethylene blends produced at 0 °c decrease as xni increases in the medium indicating good miscibility between the polyethylene phases made by both catalysts. the surface morphology of the bpe/hdpe blends studied by scanning electron microscopy (sem) revealed low miscibility between the pe phases mainly in the case of the polymer blends produced at high temperature (50 oc).
Comparative investigations of surface instabilities ("sharkskin") of a linear and a long-chain branched polyethylene  [PDF]
Teodor I. Burghelea,Hans J. Griess,Helmut Muenstedt
Physics , 2010,
Abstract: An experimental study of the physical origin and the mechanisms of the sharkskin instability is presented. Extrusion flows through a slit die are studied for two materials: a linear low density polyethylene (LLDPE) and a low density polyethylene (LDPE). By combining laser-Doppler velocimetry (LDV) with rheological measurements in both uniaxial extension and shear, the distributions of tensile and shear stresses in extrusion flows are measured for both materials.
Análise de copolímeros de etileno alfa-olefinas por meio de técnicas de fracionamento
Escher, Fernanda F. N.;Silva, Luciana P.;Galland, Griselda B.;Benetti, Adriana;
Polímeros , 2000, DOI: 10.1590/S0104-14282000000400007
Abstract: samples of ethylene 1-butene copolymer, produced in laboratory by different processes using ziegler-natta catalysts, ethylene-1-hexene and metallocene catalysts, were fractionated according to molecular size by direct extraction by different solvents and at different temperatures. these samples were also fractionated by differences on crystallinity using a dsc calorimeter. the obtained fractions were characterized by 13c-nmr , ftir, gpc and dsc. the polyethylene copolymers produced by ziegler-natta catalyst were found more heterogeneous when compared with the one produced by metallocene catalysts. the commercial resin produced by ucc process with ziegler-natta catalysts showed a more homogeneous incorporation of comonomer compared with the one obtained by the spherilene process. the supported metallocene catalyst gave a more homogeneous product than the homogeneous metallocene one.
Polietileno: principais tipos, propriedades e aplica??es
Coutinho, Fernanda M. B.;Mello, Ivana L.;Santa Maria, Luiz C. de;
Polímeros , 2003, DOI: 10.1590/S0104-14282003000100005
Abstract: the structure of each polymer has a direct influence on its density and mechanical properties. long-chain branches, such as those present in low density polyethylene, for example, increase its impact strength, decrease density and improve processing. short-chain branches present in linear low density polyethylene, on the other hand, increase crystallinity and tensile strength in comparison to low density polyethylene (produced by free radical initiators). the main applications and the type of processing used for each type of polyethylene are also presented in this work. a comparison between ziegler-natta and metallocene catalysts is carried out. the polyethylene produced by metallocene catalysts presents narrow molecular weight distribution and a uniform distribution of comonomer incorporated into the polymer chain. those characteristics provide an enhancement on the tensile properties and impact strength of final products.
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