Bulky iminophosphine-based nickel and palladium catalysts bearing 2,6-dibenzhydryl groups for ethylene oligo-/polymerization

A series of 2,6-dibenzhydryl substituted bulky Ni and Pd complexes containing P,N-chelating ligands, {[2,6-(Ph₂CH)₂-4-R-C₆H₂-N=CH-C₆H₄-2-PPh₂]MX₂; MX₂ =NiBr₂; R = Me ( Ni1 ); R = F ( Ni2 ); MX₂ =PdCl₂, R = Me ( Pd1 )}, have been prepared and used as catalyst precursors for ethylene oligo-/polymerization. Compared to the corresponding 2,6-diisopropyl Ni catalyst, these bulky Ni precatalysts activated by Et₂AlCl exhibited excellent catalytic performance toward ethylene polymerization with activity of up to 1.90 × 10⁵ g PE (mol Ni)⁻¹ h⁻¹, and result in semicrystalline PEs with high molecular weight. The catalytic performance of these bulky P,N-type complexes was significantly improved by introducing two ortho-dibenzhydryl on the N-aryl substituents. However, the formation of C₁₀–C₂₄ oligomers were generated using their palladium catalysts through ethylene oligomerization at high temperatures.     

Chromocene-based catalysts for ethylene polymerization: Kinetic parameters

The chromocene catalyst for ethylene polymerization shows a high response to hydrogen which leads directly to highly saturated polyethylenes containing methyl groups as the major terminal functionality in the polymers. At a polymerization temperature of 90°C the ratio of termination rate constants for hydrogen (k_H) and ethylene (k_M) is k_H/k_M = 3.60 × 10³. The ratio of k_H to the chain propagation constant (k_p) is k_H/k_p = 4.65 × 10^?1 A simple relation that can be derived from polymerization kinetics and the Quackenbos equation exists between melt index and hydrogen–ethylene ratio. A deuterium isotope effect (k_H/k_D) = 1.2 was calculated for the termination reaction. The overall polymerization process has an apparent activation energy of 10.1 kcal/mole. Oxygen addition studies show catalyst activity is proportional to initial divalent chromium content.     

Silolene-Bridged zirconocenium polymerization catalysts

A new silolene-bridged compound, racemic (1,4-butanediyl) silylene-bis (1-η⁵-in-denyl) dichlorozirconium ( 1 ) was synthesized by reacting ZrCl₄ with C₄H₈Si (IndLi)₂ in THF. 1 was reacted with trialkylaluminum and then with triphenylcarbenium tetrakis (penta-fluorophenyl) borate ( 2 ) to produce in situ the zirconocenium ion ( 1 ⁺). This “constraint geometry” catalyst is exceedingly stereoselective for propylene polymerization at low temperature (T_p = ?55°C), producing refluxing n-heptane insoluble isotactic poly(propylene) (i-PP) with a yield of 99.4%, T_m = 164.3°C, δH_f = 20.22 cal/g and M?_w = 350 000. It has catalytic activities of 10⁷?10⁸ g PP/(mol Zr · [C₃H₆] · h) in propylene polymerization at the T_p ranging from ?55°C to 70°C, and 10⁸ polymer/(mol Zr · [monomer] · h) in ethylene polymerization. The stereospecificity of 1 ⁺ decreases gradually as T_p approaches 20°C. At higher temperatures the catalytic species rapidly loses stereochemical control. Under all experimental conditions 1 ⁺ is more stereospecific than the analogous cation derived from rac-dimethylsilylenebis (1-η⁵-indenyl)dichlorozirconium ( 4 ). The variations of polymerization activities in ethylene and in propylene for T_p from ?55°C to +70°C indicates a Michaelis Mention kinetics. The zirconocenium-propylene π-complex has a larger insertion rate constant but lower thermal stability than the corresponding ethylene π-complex. This catalyst copolymerizes ethylene and propylene with reactivity ratios of comparable magnitude r_E ? 4r_p. Furthermore, r_E.r_p ? 0.5 indicating random copolymer formation. Both 1 and 4 activated with methylaluminoxane (MAO) exhibit much slower polymerization rates, and, under certain conditions, a lower stereo-selectivity than the corresponding 1 ⁺ or 4 ⁺ system. © 1994 John Wiley & Sons, Inc.     

Cooperative effect through different bridges in nickel catalysts for polymerization of ethylene

A series of mononuclear (M₁ and M₂) and dinuclear (C₁–C₆) Ni α‐diimine catalysts activated by modified methylaluminoxane were used in polymerization of ethylene. Catalyst C₂ bearing the optimum bulkiness showed the highest activity (1.6 × 10⁶ g PE (mol Ni)^?1 h^?1) and the lowest short‐chain branching (32.5/1000 C) in comparison to the dinuclear and mononuclear analogues. Although the mononuclear catalysts M₁ and M₂ polymerized ethylene to a branched amorphous polymer, the dinuclear catalysts led to different branched semicrystalline polyethylenes. Homogeneity and heterogeneity in the microstructure of the polyethylene samples was observed. Different trends for each catalyst were assigned to syn and anti stereoisomers. In addition, thermal behavior of the samples in the successive self‐nucleation and annealing technique exhibited different orders and intensities from methylene sequences and lamellae thickness in respect of each stereoisomer behavior. Higher selectivity of hexyl branches obtained by catalyst C₂ showed a cooperative effect between the centers. The results also revealed that for catalysts C₅ and C₆, selectivity of methyl branches led to very high endotherms and crystalline sequences with melting temperatures higher than that of 100% crystalline polyethylene indicating ethylene/propylene copolymer analogues. For catalysts C₃ and C₄, more vinyl end groups were a result of the long distance between the Ni centers. Kinetic profiles of polymerization along with a computational study of the precatalysts and catalysts demonstrated that there is a direct relation between rate constant, energy interval of catalyst and precatalyst, and interaction energy of Et···methyl cationic active center (Et···MCC or π–Comp.). Based on this, narrow energy interval (activation energy) of precatalyst and catalyst leads to fast and higher activation rate (catalyst M₂), and strong interaction of ethylene and catalyst leads to high monomer uptake and productivity (catalyst C₂). Moreover, theoretical parameters including electron affinity, Mulliken charge on Ni, chemical potential and hardness, and global electrophilicity showed optimum values for C₂.     

Transition metal complexes bearing 2,6-bis(imino)pyridyl: Synthesis,structure, ethylene polymerization/ oligomerization studies

A series of new complexes {2,6-bis[1-((2-methyl-4-methoxyphenyl)imino)ethyl]pyridine}Cl₂ [M=Fe(II) (2), Co(II) (3), Ni(II) (4), Cu(II) (5), Zn(II) (6)] have been synthesized. At 25°C, using 500 equiv of methylaluminoxane (MAO), the activities of Fe(II), Co(II) catalysts can reach 4.02 ×10⁶ g/mol-Fehatm for ethylene polymerization and 3.98×10⁵ g/mol-Cohatm for ethylene oligomerization. The effects of polymerization conditions such as reaction temperature, Al/M molar ratio and time on the activity of catalyst have been explored.

     

Transition metal complexes bearing 2,6-bis(imino)pyridyl: Synthesis,structure, ethylene polymerization/ oligomerization studies

A series of new complexes {2,6-bis[1-((2-methyl-4-methoxyphenyl)imino)ethyl]pyridine}Cl₂ [M=Fe(II) (2), Co(II) (3), Ni(II) (4), Cu(II) (5), Zn(II) (6)] have been synthesized. At 25°C, using 500 equiv of methylaluminoxane (MAO), the activities of Fe(II), Co(II) catalysts can reach 4.02 ×10⁶ g/mol-Fehatm for ethylene polymerization and 3.98×10⁵ g/mol-Cohatm for ethylene oligomerization. The effects of polymerization conditions such as reaction temperature, Al/M molar ratio and time on the activity of catalyst have been explored.     

Ni/Al2O3改性催化剂催化重整生物油模拟物制氢研究

制备了Ni/Al₂O₃、Ni-Cu/Al₂O₃、Ni-Co/Al₂O₃和Ni-Co-Cu/Al₂O₃催化剂,研究了Co和Cu对生物油水蒸气催化重整的影响。实验表明,Co 能促进水汽变换(WGS)反应,提高氢气的产率,Cu能抑制反应中焦炭的形成,提高催化剂的稳定性。对催化剂Ni-Co-Cu/Al₂O₃进行工艺条件考察,当900 ℃、水油比为6 g/g、质量空速(WHSV)为1 h^-1时,碳选择性达到87.5%,氢气产率达到84.2%,潜在氢气产率达到92.4%。     

A novel zirconocene/ultradispersed diamond black powder supported catalytic system for ethylene polymerization

A novel carrier of ultradispersed diamond black powder (UDDBP) was used to support metallocene catalyst. Al₂O₃ was also used as carrier in order to compare with UDDBP. Supported catalysts for ethylene polymerization were synthesized by two different reaction methods. One way was direct immobilization of the metallocene on the support, the other was adsorption of MAO onto the support followed by addition of the metallocene. Four supported catalysts Cp₂ZrCl₂/UDDBP, Cp₂ZrCl₂/Al₂O₃, Cp₂ZrCl₂/MAO/UDDBP and Cp₂ZrCl₂/Al₂O₃/MAO were obtained. The content of the zirconium in the supported catalyst was determined by UV spectroscopy. The activity of the ethylene polymerization catalyzed by supported catalyst was investigated. The influence of Al/Zr molar ratio and polymerization temperature on the activity was discussed. The polymerization rate was also observed.     

Influences of steric bulkiness in hydrotris(pyrazolyl)borate ligands on ethylene polymerization reaction

Manganese(II) complex catalysts with hydrotris(pyrazolyl)borate ligands have been examined on their catalytic performance in ethylene polymerization and ethylene/1‐hexene copolymerization. The activities of [Mn(L6)(Cl)(NCMe)] ( 1 ) and [Mn(L10)(Cl)] ( 2 ) activated by Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄] for ethylene polymerization go up to 326 and 11 kg mol (cat^?1) h^?1, respectively, (L6^? = hydrotris(3‐phenyl‐5‐methyl‐1‐pyrazolyl)borate anion, L10^? = hydrotris(3‐adamantyl‐5‐isopropyl‐1‐pyrazolyl)borate anion). In particular, for ethylene/1‐hexene copolymerization, complex 1 gives high‐molecular‐weight poly(ethylene‐co‐1‐hexene)s with the highest M_w of 439,000 in manganese olefin polymerization catalyst systems. Moreover, the 1‐hexene incorporation by complex 1 seems more efficient than that by [Mn(L3)(Cl)] ( 4 ) (L3^? = hydrotris(3‐tertiary butyl‐5‐isopropyl‐1‐pyrazolyl)borate anion). In this work, we demonstrated that the coordination geometry and coordination number are also important factors for ethylene polymerization reaction as well as steric hindrances and ligand frameworks in our manganese(II) catalysts. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5720–5727, 2009     

Ethylene polymerization with novel phenoxy-imine catalysts bearing 4-vinylphenyl group

This contribution reports ethylene polymerization behavior of titanium complexes incorporating bis(phenoxyimine) ligands. Six phenoxy-imine Ti(IV) complexes {6-R1-2-[CH=N(2,6-difluoro-3,5-diR2-4-R3Ph)]C6H3O}2TiCl2(1: R1 = H, R2 = H, R3 = H; 2: R1 = H, R2 = H, R3 = 4-vinylphenyl; 3: R1 = CH3, R2 = H, R3 = H; 4: R1 = CH3, R2 = H, R3 = 4-vinylphenyl; 5: R1 = CH3, R2 = F, R3 = H; 6: R1 = CH3, R2 = F, R3 = 4-vinylphenyl) have been synthesized and evaluated for ethylene polymerization using dried MAO(simplified as DMAO) as cocatalyst. An obvious catalytic heterogeneity of Cat 2(Complex 2/DMAO) towards ethylene polymerization was observed, which was illustrated by decreased activity, multimodal molecular weight distribution and partially improved particle morphology comparing with Cat 1. Moreover, Cat 3 exhibits "living" characteristics in the process under certain conditions(25 °C, less than 20 min). Otherwise, the moderate to high ethylene polymerization activity of ca. 105-106 g PE/(mol Ti·h) and high molecular weight(Mw = 105-106) of polyethylene can be obtained by changing the skeleton structure of these complexes.     

Olefin polymerization and copolymerization with soluble transition‐metal complex catalysts

Olefin polymerizations catalyzed by Cp′TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 1 – 5 ; Cp′ = cyclopentadienyl group), RuCl₂(ethylene)(pybox) { 7 ; pybox = 2,6‐bis[(4S)‐4‐isopropyl‐2‐oxazolin‐2‐yl]pyridine}, and FeCl₂(pybox) ( 8 ) were investigated in the presence of a cocatalyst. The Cp*TiCl₂(O‐2,6‐ⁱPr₂C₆H₃) ( 5 )–methylaluminoxane (MAO) catalyst exhibited remarkable catalytic activity for both ethylene and 1‐hexene polymerizations, and the effect of the substituents on the cyclopentadienyl group was an important factor for the catalytic activity. A high level of 1‐hexene incorporation and a lower r_E · r_H value with 5 than with [Me₂Si(C₅Me₄)(N^tBu)]TiCl₂ ( 6 ) were obtained, despite the rather wide bond angle of Cp Ti O (120.5°) of 5 compared with the bond angle of Cp Ti N of 6 (107.6°). The 7 –MAO catalyst exhibited moderate catalytic activity for ethylene homopolymerization and ethylene/1‐hexene copolymerization, and the resultant copolymer incorporated 1‐hexene. The 8 –MAO catalyst also exhibited activity for ethylene polymerization, and an attempted ethylene/1‐hexene copolymerization gave linear polyethylene. The efficient polymerization of a norbornene macromonomer bearing a ring‐opened poly(norbornene) substituent was accomplished by ringopening metathesis polymerization with the well‐defined Mo(CHCMe₂Ph)(N‐2,6‐ⁱPr₂C₆H₃)[OCMe(CF₃)₂]₂ ( 10 ). The key step for the macromonomer synthesis was the exclusive end‐capping of the ring‐opened poly(norbornene) with p‐Me₃SiOC₆H₄CHO, and the use of 10 was effective for this polymerization proceeding with complete conversion. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4613–4626, 2000     

Solvay type VCl3 isospecific catalysts

Solvay type S –VCl₃ catalyst has 7% of catalytically active vanadium sites ([C^*]) with k_p (rate constant of propagation) = 31 (M s)^?1 for ethylene polymerization. Addition of a comonomer, propylene of 4-methylpentene-1 (4-MP) significantly raised the ethylene polymerization activity. S –VCI₃ catalyst has very small amounts of catalytically active vanadium for propylene polymerizations: [C] = 0.19% with k_p,i = 857 (M s)^?1 and [C] = 0.45% with k_p,a = 23 (M s)^?1 for isospecific and nonspecific sites, respectively. Addition of a conomer, ethylene or 4-MP. lowered the propylene polymerization activity. S –VCI₃ is more easily reduced to the divalent ion by AIR₃ than S –TiCl₃. Methyl-p-toluate moderates the reducting power of AIR₃; it increase the productivity and stereoselectivity of the S –YiCl₃ catalyst, VCI₃ supported on MgCl₂ (CW–V catalyst) has enhanced rate constant of propylene polymerization but has the opposite effects on the S –TiCl₃ Catalyst. VCI₃ supported on MgCl₂ (CW–V catalyst) has enhances rate constant of propylene polymerization but only a minute fraction of the supported vanadiums are catalytically active: [C] = 0.019% and k_p,i = 1580 (Ms)^?1, [C] = 0.057% and k_p,i = 58 (M s)^?1. This is compared with far greater number of catalytically active titanium sites in the TiCl₃ supported on MgCl₂ catalyst: [C] = 6% and k_p,i = 200 (M s)^?1, [C] = 6% and k_p,a = 16(M s)^?1. Therefore, both the S –VCI₃ and CW–V catalysts are highly stereoselective but low in efficiency with respect to the utilization of the vanadium ion in the catalysis.     

The polymerization of propadiene by Ni(acac)2, C3H4, RnAlX3−n catalysts

Catalyst formation in the system Ni(acac)₂, C₃H₄, R_nAlX_3?n was studied. Polymerization experiments showed that, by replacing ionic groups such as acac^?, Br^?, Cl^? with alkyl or hydride groups, an active catalyst is obtained. Electrolysis of Ni(acac)₂ in tetrahydrofuran also gives an active catalyst. Lewis acids like (iBu)₃Al and Et₃Al increase the polymerization rate, while Lewis bases like pyridine and triphenylphosphine not only decrease the rate but also change selectivity. The selectivity is not changed if different transition metals (e.g. Co, Pd, Ni) are used. Kinetic measurements show a first order dependence on Ni. The dependence on (iBu)₃Al changes from first to zero order with increasing $\text{Al}\text{Ni}$ ratio. This can be explained by assuming that the very active catalyst is formed via an equilibrium between a nickel complex and (iBu)₃Al. A first order deactivation of the nickel catalyst is observed; it is faster during polymerization than during ageing of the catalyst.     

Crystalline titanium dichloride—an active catalyst in ethylene polymerization. I. Catalyst activation

Crystalline titanium dichloride, in the absence of organometallic cocatalyst, is a very poor catalyst for the polymerization of ethylene. It is transformed into a very active catalyst through mechanical activation (ball-milling). This catalyst is active in the absence not only of organometallic cocatalysts, but also metals and compounds (such as aluminium and AlCl₃) capable of forming organometallic compounds in situ (i.e., with ethylene, before polymerization starts). Ball-milling causes not only the expected increase in surface area but also disproportionation of Ti⁺⁺ to Ti⁺⁺⁺ and metallic titanium, as well as a crystal phase change to a structure not previously identified with those of TiCl₂ or TiCl₃. Catalyst activity (polymerization rate) is shown to be proportional to surface area and a direct function of Ti⁺⁺ content of the catalyst; an empirical equation relates catalyst activity to surface area and to Ti⁺⁺ lost through disproportionation. Titanium trichloride was found to be inactive in the absence of organometallic cocatalyst, even after ball-milling. The difference in structure of the catalytically active species in the conventional Ziegler (organometallic cocatalyst) and in the titanium dichloride catalyst are discussed. The mechanism of polymerization is compared with that of the supported (CrO₃ on SiO₂/Al₂O₃ and MoO₃ on Al₂O₃) catalyst systems.     

Various silyl-substituted cyclopentadienyl titanium complexes [CpSi(CH3)2X]TiCl3 as catalysts for syndiotactic polystyrene

Three silyl-substituted titanium trichloride complexes [CpSi(CH₃)₂X]TiCl₃ [X=Cl(1), Me(2), PhOMe(3)] were tested as catalyst precursors for the syndiospecific polymerization of styrene. The catalytic activity increased in the order 1 > 2 > 3. The highest activity was 2.42 × 10⁷ g s-PS/mol Ti mol S h using complex 1/MAO catalytic system at molar ratio of Al/Ti=2000. The effects of variation on polymerization temperature and Al/Ti ratio on the polymerization of styrene were also studied.     

Kinetic features of ethylene polymerization over supported catalysts [2,6‐bis(imino)pyridyl iron dichloride/magnesium dichloride] with AlR3 as an activator

The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl₂/MgCl₂‐Al(i‐Bu)₃ (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007     

Kinetic study of ethylene polymerization with chromium oxide catalysts by a radiotracer technique

The quenching of polymerization with a chromium oxide catalyst by radioactive methanol ¹⁴CH₃OH enables one to determine the concentration of propagation centers and then to calculate the rate constant of the propagation. The dependence of the concentration of propagation centers and the polymerization rate on reaction time, ethylene concentration, and temperature was investigated. The change of the concentration of propagation centers with the duration of polymerization was found to be responsible for the time dependence of the overall polymerization rate. The propagation reaction is of first order on ethylene concentration in the pressure range 2–25 kg/cm². For catalysts of different composition, the temperature dependence of the overall polymerization rate and the propagation rate constant were determined, and the overall activation energy E_ov and activation energy of the propagation state E_p were calculated. The difference between E_ov and E_p is due to the change of the number of propagation centers with temperature. The variation of catalyst composition and preliminary reduction of the catalyst influence the shape of the temperature dependence of the propagation center concentration and change E_ov.     

Highly active copolymerization of ethylene with 10‐undecen‐1‐ol using phenoxy‐based zirconium/methylaluminoxane catalysts

Activated with methylaluminoxane (MAO), phenoxy‐based zirconium complexes bis[(3‐^tBu‐C₆H₃‐2‐O)‐CH?NC₆H₅]ZrCl₂, bis[(3,5‐di‐^tBu‐C₆H₂‐2‐O)‐PhC?NC₆H₅] ZrCl₂, and bis[(3,5‐di‐^tBu‐C₆H₂‐2‐O)‐PhC?N(2‐F‐C₆H₄)]ZrCl₂ for the first time have been used for the copolymerization of ethylene with 10‐undecen‐1‐ol. In comparison with the conventional metallocene, the phenoxy‐based zirconium complexes exhibit much higher catalytic activities [>10⁷ g of polymer (mol of catalyst)^?1 h^?1]. The incorporation of 10‐undecen‐1‐ol into the copolymers and the properties of the copolymers are strongly affected by the catalyst structure. Among the three catalysts, complex c is the most favorable for preparing higher molecular weight functionalized polyethylene containing a higher content of hydroxyl groups. Studies on the polymerization conditions indicate that the incorporated commoner content in the copolymers mainly depends on the comonomer concentration in the feed. The catalytic activity is slightly affected by the Al_(MAO)/Zr molar ratio but decreases greatly with an increase in the polymerization temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5944–5952, 2005     

The polymerization of ethylene with a highly active Ziegler-Natta catalyst

A soluble ethylene catalyst were obtained by mixing a methylene dichloride solution of dichlorobis(γ-cyclopentadienyl) titanium (Cp₂TiCl₂) with a heptane solution of ethylaluminium sesquichloride (Al₂Et₃Cl₃) or of diethylaluminium chloride (AlEt₂Cl). Ethylene was polymerized using these catalysts; the solution was examined by electron spin resonance technique before the polymerization and during the reaction. The catalyst activity remained constant for a long period, and the polymerization went on at the same rate for 6–8 hr. The mechanism of the reaction is discussed.     

A kind of novel nonmetallocene catalysts for ethylene polymerization

A kind of novel bridged nonmetallocene catalysts was synthesized by the treatment of N,N‐imidazole and N,N‐phenylimidazole with n‐BuLi, and MCl₄ (M = Ti, Zr) in THF. Those catalysts were performed for ethylene polymerization after activated by methylaluminoxane (MAO). The effects of polymerization temperature, Al/M ratio, pressure of monomer, and concentration of catalysts on ethylene polymerization behaviors were investigated in detail. Those results revealed that the catalyst system was favorable for ethylene polymerization with high catalytic activity. The polymer was characterized by ¹³C NMR, WAXD, GPC, and DSC. The result confirmed that the obtained polyethylene featured broad molecular weight distribution around 20, linear structure, and relative low melting temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 33–37, 2008