Selective propylene dimerization to 2,3-dimethylbutenes by homogeneous catalysts prepared by oxidative addition of α-nitroketones to nickel(0) complexes in the presence of phosphine ligands and organoaluminium co-catalysts

Novel nickel catalysts, prepared in situ by oxidative addition of α-nitroketones to nickel(0) complexes, in the presence of a phophine ancillary ligand and activated by organoaluminium co-catalysts were investigated in propylene oligomerization with the aim to selectively obtain 2,3-dimethylbutenes (DMB). In particular, the effect of the nature of the α-nitroketonate ligand as well as of the basicity and bulkiness of the phosphine on catalyst performances were studied. Finally, the influence of the type of organoaluminium co-catalyst and reaction temperature were examined.In particular, when the Ni(cod)₂/tricyclohexylphosphine (PCy₃)/α-nitroacetophenone (naph)/methylalumoxane (MAO) catalytic system was employed, the highest up to now reported regioselectivity within C₆ cut (>90%) was achieved. Moreover, the use of balanced mixtures of MAO and Et₂AlCl allowed to optimize the catalyst performances up to an overall yield to DMB of almost 70%, a significant productivity being also achieved (TOF=4500 h⁻¹).     

Modified preparation of HDPE/clay nanocomposite by in situ polymerization using a metallocene catalyst

In this study, preparation of high-density polyethylene (HDPE)/clay nanocomposite by in situ polymerization of ethylene using a zirconocene catalyst (bis-(cyclopentadienyl) zirconium dichloride (Cp₂ZrCl₂)) was investigated. To obtain higher efficiency, nanoclay particles (Na-montmorillonite) were modified by ammonia (NH₃), NH₃/methylaluminoxane (MAO), NH₃/dodecylamine (DDA), and NH₃/MAO/DDA systems. The results showed that the activity of the catalyst supported on the nanoclay particles modified by NH₃/MAO (762 g_p/mmol (Zr) t [atm]) was higher than that of the one supported on the unmodified nanoclay as well as the other prepared modified nanoclay-supported catalyst systems. The catalyst activities versus MAO concentration in NH₃/MAO treatment system and versus DDA concentration in NH₃/DDA system showed a maximum. Unexpectedly, a very low catalyst activity (180 g_p/mmol(Zr) t [atm]) was obtained using NH₃/MAO/DDA system. X-ray diffraction patterns showed that the HDPE/clay nanocomposites prepared by NH₃/MAO/DDA treatment system had less intercalated structure. Fourier transform infrared (FTIR) spectroscopy confirmed that water molecules of the nanoclay particles were reduced by NH₃ modification. DSC results revealed that crystallinity of the HDPE/clay nanocomposites increased with the modification of the nanoclay particles. The maximum degree of crystallinity of 80.8% was obtained for HDPE/clay nanocomposites prepared by the nanoclay modified by NH₃. In addition, nanoclay modification with NH₃, NH₃/MAO, and NH₃/DDA systems resulted in higher thermal decomposition temperature (~30 °C higher than 480 °C of the unmodified one). Such increase was not observed for the NH₃/MAO/DDA treatment system. Dynamic mechanical analysis showed an increase in the elastic modulus of the nanocomposite samples prepared by modified nanoclay particles, as well. Meanwhile, modification of the nanoclay particles by NH₃ led to the highest elastic behavior compared to the other modification systems. It was about 4.6 GPa which was 28% higher than the elastic modulus of the nanocomposite prepared by unmodified nanoclay particles.     

Cp2TiCl2/坡缕石黏土负载型催化剂催化乙烯聚合的特性

利用浸渍法制备了两种二氯二茂钛（Cp₂TiCl₂）/坡缕石黏土负载型催化剂Cat-A 和Cat-B,并进行了乙烯淤浆聚合评价。对热活化黏土进行表征的结果表明,坡缕石黏土在热活化过程中由于配位结晶水的脱除表面主要由Lewis酸性位占据。黏土载体所具有的表面酸性使其具有完全不同于硅胶载体的负载茂金属催化剂聚合行为。在相同的聚合条件下,直接负载型催化剂的活性高于载体化学修饰型催化剂,甚至高于均相Cp₂TiCl₂催化剂。直接负载催化剂所得聚合产物的分子量和熔点低于载体化学修饰催化剂,且其产物性质受温度影响更为显著。以硅胶负载型茂金属催化剂作为对比,分析了表面具有较强Lewis酸性的载体活性中心性质,以此解释了直接负载型催化剂的乙烯聚合特性。对直接负载型催化剂不同时间段的聚合产物形态进行了扫描电镜观察,发现最终聚合产物中聚合物“纤维”和“纤维”聚集体形态的形成,并进一步分析了聚合物形态演化过程的特点。     

Late Transition Metal Catalyst Based on Cobalt for Polymerization of Ethylene

The late transition metal catalyst of [2,6-diacethylpyridinebis(2,6-diisopropylphenylimine)]cobalt(II) dichloride was prepared under controlled conditions and used for polymerization of ethylene. Methylaluminoxane (MAO) and triisobuthylaluminum (TIBA) were used as a cocatalyst and a scavenger, respectively. The highest activity of the catalyst was obtained at about 30°C; the activity decreased with increasing temperature. At polymerization temperatures higher than 50°C not only was a sharp decrease in the activity observed but also low molecular weight polyethylene product that was oily in appearance was obtained. The polymerization activity increased with increasing both of the monomer pressure and [MAO]:[Co] ratio. However, fouling of the reactor was strongly increased with increasing both of the monomer pressure and the amount of MAO used for the homogeneous polymerization. Hydrogen was used as the chain transfer. The activity of the catalyst and the viscosity average molecular weight (M_v) of the polymer obtained were not sensitive to hydrogen concentration. However, the viscosity average molecular weight of the polymer decreased with the monomer pressure. The (M_v), the melting point, and the crystallinity of the resulting polymer at the monomer pressure of 1 bar and polymerization temperature of 20°C were 1.2 × 10⁵, 133°C, and 67%, respectively. Heterogeneous polymerization of ethylene using the catalyst and the MAO/SiO₂ improved morphology of the resulting polymer; however, the activity of the catalyst was also decreased. Fouling of the reactor was eliminated using the supported catalyst system.     

Modification of a Ziegler-Natta catalyst with a metallocene catalyst and its olefin polymerization behavior

A Ziegler-Natta catalyst was modified with a metallocene catalyst and its polymerization behavior was examined. In the modification of the TiCl₄ catalyst supported on MgCl₂ (MgCl₂-Ti) with a rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)₂ZrCl₂, EIZ) catalyst, the obtained catalyst showed relatively low activity but produced high isotactic polypropylene. These results suggest that the EIZ catalyst might block a non-isospecific site and modify a Ti-active site to form highly isospecific sites. To combine two catalysts in olefin polymerization by catalyst transitioning methods, the sequential addition of catalysts and a co-catalyst was tried. It was found that an alkylaluminum like triethylaluminum (TEA) can act as a deactivation agent for a metallocene catalyst. In ethylene polymerization, catalyst transitioning was accomplished with the sequential addition of bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂)/methylaluminoxane (MAO), TEA, and a titanium tetrachloride/vanadium oxytrichloride (TiCl₄/VOCl₃, Ti-V) catalyst. Using this method, it was possible to control the molecular weight distribution (MWD) of polyethylene in a bimodal pattern. In the presence of hydrogen, polyethylene with a very broad MWD was obtained due to a different hydrogen effect on the Cp₂ZrCl₂ and Ti-V catalyst. The obtained polyethylene with a broader MWD exhibited more apparent shear thinning.     

Syndioselective propylene polymerization: Comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

The kinetics and stereochemical control of propylene polymerization initiated by syndiospecific isopropylidene(1-η⁵-cyclopentadienyl)(1-η⁵-fluorenyl)-dimethylzirconium–methyl aluminoxane (1/MAO) and (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium–MAO (2/MAO) were investigated. The influence of MAO concentration and polymerization temperature (T_p) on polymerization kinetics and polypropylene properties, such as molecular weight, molecular weight distribution (MWD), and stereoselectivity, have been studied in detail. The activity of both catalytic systems is very sensitive to the concentration of MAO. The 1/MAO and 2/MAO catalysts record maximum activity when [Al]/[Zr] ratio is around 1300 and 2500, respectively. The activity and the degree of stereochemical control are also sensitive to T_p. The 2/MAO catalyst is much more thermally stable than 1/MAO catalyst; the former shows maximum activity at 80°C, whereas the latter shows maximum activity at 20°C. The cationic active species generated by 2/MAO is not so stereorigid as those by 1/MAO so that 2/MAO catalyst produces sPP of broad MWD (4.43–6.38) and low syndiospecificity at high T_p. When T_p is above 50°C, 2/MAO catalyst produces completely atactic polypropylene. The results of fractionation of sPP samples produced by 1/MAO and 2/MAO demonstrate that 1/MAO catalyst is characterized by uniform active sites, but 2/MAO is characterized by multiple active sites. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 973–983, 1998     

Isospecific polymerization of styrene with supported nickel acetylacetonate/methylaluminoxane catalysts

Summary The polymerization of styrene with catalysts based on Ni(acac)₂ supported on SiO₂ and Al₂O₃ was investigated. Using catalysts based on MAO supported on silica, a highly isotactic polystyrene was obtained. Nevertheless, the Al₂O₃-supported catalyst can promote isospecific polymerization activated by common. alkyl aluminum compounds even by any prior support treatment with MAO. Received: 3 March 1998/Revised version: 14 April 1998/Accepted: 14 April 1998     

In situ polymerization of ethylene with functionalized multiwalled carbon nanotubes using a zirconocene aluminohydride system in solution

This study reports nanocomposite synthesis based on high-density polyethylene with carbon nanotubes through in situ polymerization by coordination, and the use of an aluminohydride zirconocene/MAO system as a catalyst. Nanocomposites of linear polyethylene exhibit higher molar masses than pure high-density polyethylene synthesized under similar conditions; where multiwalled carbon nanotubes (MWCNTs) acted as nucleating agents, shifting the crystallization temperature to higher values than neat high-density polyethylene. Well-dispersed MWCNTs in the HDPE matrices of the obtained nanocomposites are observed by SEM, where most of the nanocomposites showed an improvement in their thermal stability and electric conductivity, besides it is possible to obtain nanocomposites containing up to 41 wt% of nanofiller in the polymeric matrix. The aluminohydride complex n-BuCp₂ZrH₃AlH₂, activated with MAO at Al/Zr ratios of 2000, produced homogeneous HDPE/MWCNT composites under in situ polymerization conditions, at 70°C and 2.9 bar of ethylene pressure, with minimal residual alumina in the HDPE matrix.     

Investigation of styrene/1‐hexene copolymerization by homogeneous and heterogeneous bisindenyl ethane zirconium dichloride catalyst system

Homogeneous copolymerization of styrene and 1‐hexene was carried out in toluene at room temperature using bisindenyl ethane zirconium dichloride/methylaluminoxane (MAO). The supported catalyst was prepared with immobilization of Et(Ind)₂ZrCl₂/MAO on silica (calcinated at 500°C) with premixed method. Heterogeneous copolymerization of styrene/1‐hexene with different mole ratios was carried out in the presence of supported catalyst system. The copolymers obtained from homogeneous and heterogeneous catalyst system were characterized by ¹H NMR and ¹³C NMR. Composition of the resulting copolymers was determined by ¹H NMR data. Analysis of ¹³C NMR spectra of obtained copolymers by homogeneous and heterogeneous catalyst systems present isotactic olefin‐enriched copolymers. Molecular weight and thermal behavior of resulting copolymers was investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4008–4014, 2007     

Syndiotactic polymerization of styrene: Study of catalyst components and polymerization conditions

Syndiotactic polystyrene (s‐PS) was prepared using monotitanocene catalyst of cyclopentadienyl titanium trichloride (CpTiCl₃) activated by methylaluminoxane (MAO). Solution polymerization was carried out in toluene using different polymerization conditions. Syndiotacticity index (SI) between 68 and 91.6% was obtained. Increasing Al/Ti molar ratio shows an increase in both conversion percentage and SI. The conversion increased linearly with increasing Al/Ti molar ratio in the range studied. The conversion reached to an optimum value of about 65% at styrene/Al molar ratio of 2.83, while no regular behavior of SI was observed with changing the ratio. Effect of temperature of the range 50–80°C on polymerization was studied. The most favorable temperature for the polymerization regarding activity is 70°C; however SI decreased with temperature up to 80°C. H₂ value to 140 mL/100 mL solvent increased the productivity of the catalyst, however further increase of H₂ reduced the activity of the catalyst. Polymerization time of 15 to 125 min shows a decrease in activity. The decrease was sharper for about 30 min of polymerization than longer time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2216–2221, 2006     

Effect of cocatalyst on the chemical composition distribution and microstructure of ethylene-hexene copolymer produced by a metallocene/Ziegler-Natta hybrid catalyst

A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for metallocene/Ziegler-Natta hybrid catalyst. The SMB was treated with methylaluminoxane (MAO) prior to the immobilization of TiCl₄ and rac-Et(Ind)₂ZrCl₂. The prepared rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO/SMB catalyst was applied to the ethylenehexene copolymerization with a variation of cocatalyst species (polymerization run 1: triisobutylaluminum (TIBAL) and methylaluminoxane (MAO), polymerization run 2: triethylaluminum (TEA) and methylaluminoxane (MAO)). The effect of cocatalysts on the chemical composition distributions (CCDs) and microstructures of ethylene-hexene copolymers was examined. It was found that the catalytic activity in polymerization run 1 was a little higher than that in polymerization run 2, because of the enhanced catalytic activity at the initial stage in polymerization run 1. The chemical composition distributions (CCDs) in the two copolymers showed six peaks and exhibited a similar trend. However, the lamellas in the ethylene-hexene copolymer produced in polymerization run 1 were distributed over smaller sizes than those in the copolymer produced in polymerization run 2. It was also revealed that the rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO/SMB catalyst preferably produced the ethylene-hexene copolymer with non-blocky sequence when TEA and MAO were used as cocatalysts.     

Partially hydrolyzed trimethylaluminum (PHT) as heterogeneous cocatalyst for the polymerization of olefins with metallocene complexes

A method for the preparation of a novel heterogeneous cocatalyst, partially hydrolyzed trimethylaluminum (PHT), has been developed and optimized for ethylene polymerization reactions. It is possible to generate PHT on nearly any support without much loss of catalyst activity. The carrier material can be SiO₂, AlF₃, B₂O₃, starch, cellulose, active carbon, polyethylene, polypropylene, polystyrene, etc. This new type of partially hydrolyzed trimethylaluminum (PHT) is synthesized by reacting such a carrier material with trimethylaluminum (TMA) in toluene to block all surface Lewis basic centers that could poison a cationic metallocene polymerization center. The subsequent addition of a calculated amount of water gives a heterogeneous PHT that is different from the common methylalumoxane (MAO). Various PHT cocatalysts were studied by ¹³C and ²⁷Al MAS NMR, scanning electron microscopy (SEM), and infrared spectroscopy (IR), and compared with solid MAO. Surface areas and porosities were determined according to the BET method. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 454–466, 2001     

Ring‐opening metathesis polymerization of dicyclopentadiene catalyzed by titanium tetrachloride adduct complexes with oxygen‐containing ligands

Ring‐opening metathesis polymerization of dicyclopentadiene catalyzed by TiCl₄ · 2L/CH₃Li system [where L is tetrahydropyran (1), dioxane, 2,5‐dimethylfuran, or tetrahydrofurfyl alcohol] is reported. The obtained polymer was characterized by IR and ¹H‐NMR. These catalytic systems effectively promoted the polymerization reaction. Seven influencing factors are discussed. When the aging temperature was 0°C, the aging time was 90 min, the polymerization temperature was 60°C, Li/Ti was 1.5–2, and the monomer/catalyst molar ratio ranged between 30 and 50, the polymerization reaction catalyzed by complex 1 yielded better results within a shorter period of time. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 662–666, 2001     

Polymerization of ethylene by supported zirconium alkoxide complex

Dichlorobis(3‐hydroxy‐2‐methyl‐4‐pyrone)Zr(IV) was grafted onto different inorganic supports, namely SiO₂, MAO‐modified SiO₂, MCM‐41, Al₂O₃, and MgO. The resulting supported catalysts were shown to be active in ethylene polymerization using methylaluminoxane (MAO) as the catalyst. Catalysts were characterized by Rutherford Backscattering Spectrometry (RBS) and nitrogen adsorption method. The highest catalyst activities were observed for the zirconium complex supported on MCM‐41. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cocatalytic activities of methylaluminoxane prepared by direct water addition method in ethylene polymerization over Cp2ZrCl2

The characterization of ethylene polymerization behaviors catalyzed over Cp₂ZrCl₂/MAO homogeneous system using methylaluminoxanes prepared by the direct hydrolysis of AlMe₃ (Me=methy1) were reported. The MAO was prepared at the ratio of [H₂O]/[A1]=1 and 0.5 and at three different temperatures, i.e., −40, −60 and −80 °C. The polymerization rate was not decreased with polymerization time when the MAO prepared at the ratio of [H₂O]/[AlMe₃]=l at −60 °C was used as a cocatalyst regardless of the ratio of Al/Zr and the polymerization temperature. The polymerization rate drastically decreased with polymerization time above 60 °C in case of using MAO prepared at the ratio of [H₂O]/[AlMe₃]=l at −80 °C. However, in case of the MAO prepared at the ratio of [H₂O]/ [AlMe₃]=0.5 at −80 °C, the rate continuously increased with polymerization time at the polymerization temperature of 70 °C and 80 °C. The amount of MAO needed to activate Cp₂ZrC1₂ was larger than that of MAO prepared at the ratio of [H₂O]/[A1]=1. The viscosity molecular weight of polyethylene (PE) cocatalyzed with MAO prepared at the ratio of [H₂O]/[Al]=0.5 was lower than that of polyethylene obtained with MAO prepared at the ratio of [H₂O]/[A1]=1.     

Methylaluminoxane‐activated neodymium chloride tributylphosphate catalyst for isoprene polymerization

The polymerization of isoprene was examined by using a novel binary catalyst system composed of neodymium chloride tributylphosphate (NdCl₃·3TBP) and methylaluminoxane (MAO). The NdCl₃·3TBP/MAO catalyst worked effectively in a low MAO level ([Al]/[Nd] = 50) to afford polymers with high molecular weight (M_n ～10⁵), narrow molecular weight distribution (M_w/M_n = 1.4–1.6), and high cis‐1,4 stereoregularity (> 96%). The catalytic activity increased with an increasing [Al]/[Nd] ratio from 30 to 100 and polymerization temperature from 0 to 50°C, while the M_n of polymer decreased. The presence of free TBP resulted in low polymer yield. Polymerization solvent remarkably affected the polymerization behaviors; the polymerizations in aliphatic solvents (cyclohexane and hexane) gave polymer in higher yield than that in toluene. The M_w/M_n ratio of the producing polymer remained around 1.5 and the gel permeation chromatographic curve was always unimodal, indicating the presence of a single active site in the polymerization system. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40153.     

Copolymerization of ethylene and 1-octene by homogeneous and different supported metallocenic catalysts

In this work, the performance of the homogeneous catalyst system based on Et(Flu)₂ZrCl₂/MAO was evaluated on the copolymerization of ethylene and 1-octene. Characteristics of some of the produced polymers were also investigated. A study was performed to compare this system with that of Cp₂ZrCl₂/MAO. The influence of different support materials for the Cp₂ZrCl₂ was also evaluated, using silica, MgCl₂, and the zeolite sodic mordenite NaM. An increase in activity was observed in relation to the comonomer addition for the two homogeneous catalysts. The copolymers produced by the Et(Flu)₂ZrCl₂/MAO system showed higher molecular weight and narrower molecular weight distribution. We verified that the catalyst supported on SiO₂ was the most active one, although the copolymers produced with the catalyst supported on NaM showed higher molecular weight and lower molecular weight distribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 724–730, 2001     

Ethylene polymerization with hafnocene adamantolate/MAO system

Summary A new alcoholate of cyclopentadienyl metallocene with voluminous group as ligand substituting chlorine atoms and formula Cp₂Hf(OMAd)₂ (where Cp = cyclopentadienyl and OMAd = derived of 2-methyl-2-adamantol) was synthesized and employed as catalyst for olefin polymerization. The compound was evaluated in ethylene polymerization activated by methylaluminoxane (MAO) using several experimental conditions. These conditions were determined by a statistic method, and a model for dependent variables like catalyst activity and average molecular weight of polymers were developed. The hafnocene alcoholate produced polyethylenes with molecular weights in the same range of the corresponding metallocene dichloride. The new catalyst system showed high stability under temperature of 100°C. In the presence of H₂ as molecular weight controlling agent, the catalyst showed a maximum of activity in the concentration range used. Received: 10 March 2000/Revised version: 13 September 2000/Accepted: 13 September 2000     

Characterization of MAO‐Modified Silicas for Ethylene Polymerization

A series of methylaluminoxane (MAO)‐modified PQ and EP 12 silicas, calcined at 110, 250, and 450°C, were prepared. The resulting MAO‐modified supports were characterized by a set of complementary techniques: Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy‐energy dispersive X‐ray spectroscopy (SEM‐EDX), small angle X‐ray scattering (SAXS), and thermal gravimetric analysis (TGA). The Al/Si ratios of the MAO‐modified PQ and EP12 silicas were in the ranges of 0.19–0.27 wt % and 0.17–0.30 wt %, respectively. MAO‐modified silicas were used in the polymerization of ethylene using an Et₂IndZrCl₂ catalyst. The MAO‐modified PQ silica showed higher activity in comparison to the MAO‐modified EP12. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4568–4575, 2013     

Poly(pent‐1‐ene) Synthesized with the Syndiospecific Catalyst i‐Pr(Cp)(9‐Flu)ZrCl2/MAO

1‐Pentene was polymerized with the syndiospecific catalyst system i‐PrC(Cp)(9‐fluorenyl)ZrCl₂/MAO. The molar mass of the resulting polymers depends strongly on the reaction temperature and decreases from M̄_w = 126 000 at 0°C to M̄_w = 46 000 at 100°C, but is more or less independent of the monomer and the MAO concentration. The influence of reaction temperature and concentrations of MAO and monomer on the type of end‐groups generated during the chain termination, as well as on the type of stereoerror, was investigated. The degree of tacticity was dependent on the polymerization temperature with [rrrr] > 0.99 at 0°C and [rrrr] = 0.75 at 100°C.