The synthesis in a liquid propene phase of ethylene-propylene copolymers of low molecular weights (3 000-20 000 g mol(-1)) is accomplished using three different metallocenes containing bridged bis(indenyl) moieties: (A) rac-dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride, (B) rac-ethylenebis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride, and (C) racethylenebis(indenyl) zirconium dichloride. Hydrogen pressures higher than 1 bar were required to drop the molecular weight below 25 000 g mol(-1). Metallocene B gives rise to the copolymers with lower molecular weights (< 5 000 g mol(-1)), irrespective of the ethylene content, due to the presence of a hydrogenated six membered ring in the indenyl moiety as well as a -CH2-bridge. DSC experiments indicate that for low ethylene contents (below 4 wt%), metallocene A gives rise to copolymers with the highest melting temperatures and the lowest melting enthalpies, suggesting the existence of longer isotactic propylene sequences into the copolymer backbone.

Los complejos TpTiCl2(OR) (Tp = Hidrotris(pirazolil)borato; R = Et, i-Pr, n-Bu) fueron evaluados en la copolimerizacion de etileno con 1-hexeno. La activacion de estos complejos con polimetilaluminoxano (P-MAO) mostro un buen desempeno catalitico para la produccion de copolimeros; sin embargo, la inclusion del comonomero afecto negativamente la actividad catalitica respecto a la obtenida en la homopolimerizacion. Estos sistemas fueron capaces de producir polietilenos con un porcentaje de incorporacion molar de 1-hexeno maximo del 6%. ABSTRACT The TpTiCl2 (OR) (Tp = Hydrotris (pyrazolyl) borate; R = Et, i-Pr, n-Bu) complexes were evaluated according to their efficiency towards the copolymerization of ethylene with 1-hexene. A good precatalyst response to copolymerization was observed when they were activated with P-MAO. However, the catalytic activity was negatively affected with regard to homopolymerization. Polyethylenes with a maximum of 6 mol-% of a-olefin incorporation were obtained by this catalytic system.Keywords: Hydrotris (pyrazolyl) borate, Alcoxy group, Copolymerization, Ethylene, 1-Hexene.

Poly(1-butene) low molecular weight macromolecules with molecular weights within 1000-20,000 gmol(-1) and isotacticities around 50-90% were prepared by the polymerization of 1-butene in liquid phase with n-butane as solvent using two metallocene catalysts: rac-dimethyl-silyl-bis-(2-methyl-4,5-benzoindenyl)zirconium dichloride (A) and rac-dimethylsilyl-bis-(2-methylindenyl)zirconium dichloride (B). Catalyst A showed higher yields and productivities than catalyst B, as well as better isotacticity values, which were ascribed to the presence of an additional aryl substituent in the indenyl moiety which increases its stability and hinders deactivation phenomena by aggregation. Kinetic experiments with catalyst A showed a continuous increase in conversion along the time so no strong deactivation was observed. With catalyst A, an increase in the hydrogen pressure at 75 degrees C up to 6.0 bar led towards low molecular weight macromolecules with 3000-4000 g mol(-1) and a isotacticity of 75-80%. An enhancement in temperature up to 105 degrees C decreased the yields, molecular weights and isotacticity for both catalysts. Additionally, increasing the hydrogen partial pressure to 1.0 bar at 95 and 105 degrees C decreased the molecular weight within the 3000-5500 gmol(-1) range. XRD patterns of the majority of low molecular weight macromolecules showed the presence of mixed phases, although some low molecular weight macromolecules with pure phase I (twined hexagonal) were obtained. Additionally, the DSC thermograms showed a decrease in the melting temperatures of the crystalline phases of poly(1-butene) low molecular weight macromolecules with regard to the corresponding ones of poly(1-butene) polymers (M-w > 100,000 g mol(-1)), due to their lower molecular weight. (c) 2013 Elsevier B.V. All rights reserved.

Mesoporous silica-alumina functionalized with propyl sulfonic acid groups was synthesized and used as a support for MAO-(nBuCp(2))ZrCl2 for the ethylene polymerization. Mesoporous silica-alumina (Si/Al = 25) functionalized with 10 wt% propyl sulfonic exhibited remarkable activity with negligible leaching, due to the presence of tetrahedral aluminum, incorporated into the framework.

Ethylene polymerization over heterogeneous [Ph2C(Cp)(2,7‐t‐Bu2Flu)ZrCl2] supported on SiO2‐MAO is studied. The influence of the main reaction variables is determined in ethylene homopolymerization: TEA concentration (88–702 ppm), temperature (55–85 °C) and pressure (3–12 bar). An optimum in the catalytic activity is achieved at TEA a concentration of 351 ppm, 85 °C and 8 bar of ethylene. At this ethylene pressure, all the polyethylenes show molecular weights above 400 000 g · mol−1. Using hydrogen as transfer agent, the activity is distinctly lower but it is possible to attain molecular weights below 40 000 g · mol−1. Regarding 1‐butene, it is observed good catalytic response in copolymerization, observing remarkable activities, higher than those obtained in homopolymerization.

The polymerization of ethylene in n-heptane with (nBuCp)2ZrCl2 supported over mesoporous SBA-15 catalysts functionalized with propyl or aryl sulfonic acid groups and impregnated with either MAO or TMA was investigated and compared with reference samples. All the supports showed mesoscopic ordering with pore sizes of 7.8–6.6nm, BET surface areas around 700m2g−1, sulfonic acid loadings between 10 and 20 wt% and an acidity of roughly 1–1.7mmol H+g−1. None of the catalysts were capable of polymerizing ethylene in the absence of MAO in spite of using TMA or TIBA as scavengers. The addition of MAO (Al/Zr=800 or 5000) led towards ethylene polymerization, being the activity dependent on Al/Zr molar ratio (higher for Al/Zr=5000). The catalysts treated with TMA during the impregnation exhibited considerable leaching, unlike those treated with MAO wherein the leaching was low (<9 wt%). The presence of the sulfonic acid moiety enhanced the activity of the catalysts. In addition, the activity was also augmented with the increase of the sulfonic acid content from 10 to 20 wt%. Interestingly, the molecular weight of the polyethylene synthesized with the SBA-15 functionalized with sulfonic acid groups were 1.5–2.5 times higher, especially with the propyl moiety which leads towards Mw∼350,000gmol−1 at 1.2barg. The results were explained through an interaction between the sulfonic acid moiety and the chlorinated MAO species, which activates the metallocene.

Nanocomposites of ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNT) were obtained by in situ polymerization of ethylene by TpTiCl(2)Et. This novel catalytic complex activated with polymethylaluminoxane (P-MAO) (Al:Ti = 200) allowed to incorporate the CNT at different compositions (0,1-1 w/w %) into the UHMWPE matrix. The filler addition produced an important enhancement of the catalytic activity when it was compared to that of homogeneous ethylene polymerization carried out under the same experimental conditions (30 min; 1bar; 25 degrees C). This fact was attributed to in situ support of TpTiCl2Et onto the CNT surface, which not only could induce the stabilization of the catalytic system but also allowed the growing of polymeric chains around the CNT structures. The characterization of these nanocomposites was carried out by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Thermal analysis showed that the incorporation of CNT (at the tested concentrations) did not produce changes in the polymer thermal stability, as revealed by the initial degradation temperature values. However, the CNT produced a nucleating effect in the crystallization of UHMWPE as observed by DSC, independently of the filler content. The crystallization temperature of the obtained nanocomposites increased and the crystallinity degree slightly increased as well.

The TpTiCl 2 (OR) (Tp = Hydrotris (pyrazolyl) borate; R = Et, i-Pr, n-Bu) complexes were evaluated according to their efficiency towards the copolymerization of ethylene with 1-hexene. A good precatalyst response to copolymerization was observed when they were activated with P-MAO. However, the catalytic activity was negatively affected with regard to homopolymerization. Polyethylenes with a maximum of 6 mol-% of a-olefin incorporation were obtained by this catalytic system.

Different kinds of polyethylene and ethylene-1-hexene copolymers were synthesized with TpTiCl(2)(OR) (Tp = hydrotris(pyrazolyl)borate; R=Et, i-Pr, n-Bu) catalysts with and without H-2. The polymers were characterized by C-13 NMR, capillary viscosimetry or GPC, and DSC. The homopolymers showed properties characteristic of ultra-high molecular weight polyethylenes (UHMWPE) with linear structure and high density polyethylenes (HDPE) with molecular weights in the range of commercial grades under hydrogen atmosphere. The copolymers showed a 1-hexene incorporation up to 6 mol-%. Important differences in the thermal properties were observed between the first DSC (nascent powders) and the second DSC heatings (melt-crystallized samples), which evidenced the molecular weights influence on the melt-crystallized samples.

Polyethylene was synthesized using iron(II) and cobalt(II) complexes stabilized by tris(2-pyridyl)X (X = N, P) ligands in the presence of methylaluminoxane (MAO) as cocatalyst. The catalysts showed activities ranging from moderate to high. The iron complexes showed higher activities than the cobalt analogous and it was found that the bridgehead atom of the ligand tpX (X = P, N) did not affect significantly the activity of the active species as well as the molecular weight of the polymers. The polyethylenes obtained were classified as HDPE with linear structure and broad monomodal distribution.

The TpTiCl2(OR) (where Tp = hydrotris(pyrazolyl)borate; R = Me, Et, i-Pr, n-Bu) and TpTiCl3 complexes activated with very low concentration of MAO (≥200 Al/Ti) showed very high activity in the ethylene polymerization. The substitution of one chlorine ligand in the TpTiCl3 for one alkoxyl ligand increases the catalytic activity up to 76 times and 3.4 times respect to Cp2ZrCl2 at the same reaction conditions. The TpTiCl2(OR) precatalysts activity decreases in the following order: TpTiCl2(OEt) > TpTiCl2(On-Bu) ≈ TpTiCl2(Oi-Pr) ≫ TpTiCl2(OMe) > TpTiCl3. The alkyl chain size of the alkoxyl ligands strongly affects the catalytic activity and the molecular weights of the polymers, prevailing the steric effect over the electronic effect. The resulting polymers can be classified as ultra-high molecular weight polyethylenes with basically linear structure.

The combination of TpTiCl2(OR) (Tp = Hidrotris(pyrazolyl)borate; R = Me, Et, i-Pr, n-Bu) precatalysts with methylaluminoxane (MAO) produced active catalysts for styrene polymerization. In general, these precatalysts showed higher activities than TpTiCl3. The activity and syndiospecificity of TpTiCl2(OR) were affected by alkoxyl ligands. The syndiotacticity of the polystyrenes (s-PS) obtained was in the range of 47–70%.