杯[4]芳烃钛-Al(iBu)_3催化乙烯聚合

众所周知 ,茂金属催化剂用于烯烃聚合 ,不仅具有高的催化活性 ,而且能制得高规整度聚合物 ,在理论研究和工业应用中都有十分重要的意义 ,国际上已形成对茂金属催化剂的研究热潮 .人们在致力于研究茂金属催化剂的同时 ,并没有停止对非茂金属均相催化剂的研究 ,其中酚氧基钛、锆配合物的优良催化性能尤为引人注目 ,这类新型均相催化剂能高效地催化烯烃均聚[1 ] ,苯乙烯间规聚合[2 ] ,乙烯 苯乙烯共聚等[3] .杯芳烃是由若干个对叔丁基苯酚通过亚甲基经 2 ,6位连接而成的一类环状大分子 ,其结构与酚氧类配体相似 .李勇等曾发现杯芳烃钛化合物与…     

Comparative ethylene polymerization via imino-quinolinol catalysts

A series of zirconium catalysts based on tridentate 8-hydroxyquinoline Schiff base ligands were prepared and successfully used for polymerization of ethylene. The highest activities of the prepared catalysts were obtained at polymerization temperatures about 30–45ºC. By increasing the [Al]/[Zr] molar ratio productivity of all the catalysts enhanced to an maximum value then decrease at higher [Al]/[Zr] molar ratio with the exception of catalyst 4, which showed no optimum activity in the range studied. Also, the activities and selectivities to produce low-carbon olefins were profoundly influenced by the catalysts structure indicating the dramatic effects of the substitution on the polymerizations behavior. Fouling of the reactor was strongly related to polymerization parameters like as monomer pressure and [Al]/[Zr] ratio in the homogeneous polymerization. Heterogeneous polymerization of ethylene using the catalysts and the MAO modified silica decreased the fouling. The obtained polyethylenes have a melting point of about 125–130°C, crystallinities of about 45–55% and PDI of 2.45–3.45.     

Improvement of the Mo/TiO2-Al2O3 Catalyst by the Control of the Sol-Gel Synthesis

Traditional hydrotreating catalysts are constituted by molybdenum deposited on Al₂O₃ promoted by nickel and phosphorous. Several studies have shown that TiO₂-Al₂O₃ mixed oxides are excellent supports for the active phases. Results concerning the preparation, characterization and testing of molybdenum catalyst supported on titania-alumina are presented. The support was prepared by sol-gel route using titanium and aluminum isopropoxides, the titanium one chelated with acetylacetone (acac) to promote similar hydrolysis ratio for both the alcoxides. The effect of nominal molar ratio [Ti]/[Ti+Al] on the microstructural features of nanometric particles was analyzed by X-Ray Diffraction, N₂ Adsorption Isotherms and Transmission Electron Microscopy. The catalytic activity of Mo impregnated supports was evaluated using the thiophene hydrodesulfurization at different temperatures and atmospheric pressure. The pores size distribution curve moves from the micropores to the mesopores by increasing the Ti contents, allowing the fine tuning of average size from 2.5 to 6 nm. Maximal (367 m²·g^?1) and minimal (127 m²·g^?1) surface area were found for support containing [Ti]/[Ti+Al] ratio equal to 0.1 and 1, respectively. The good mesopore texture of alumina-titania support with [Ti]/[Ti+Al] molar ratio between 0.3 and 0.5 was found particularly valuable for the preparation of well dispersed MoS₂ active phase, leading to HDS catalyst with somewhat higher activity than that prepared using a commercial alumina support.     

Isospecific Polymerization of Propylene By ansa-Zirconocene Diamide Compound Cocatalyzed by Mao

Abstract

The kinetics of propylene polymerization initiated by racemic ethylene-1,2-bis(1-indenyl) zirconium bis(dimethylamide) [rac-(EBI) Zr(NMe₂)₂(rac-1)] cocatalyzed by methylaluminoxane (MAO) were studied. The polymerization behaviors of rac-1/MAO catalyst investigated by changing various experimental parameters are quite different from those of rac-(EBI) ZrCl₂ (rac-2)/MAO catalyst, due to the differences in the generation procedure of cationic actives species of each metallocene by the reaction with MAO. The activity of rac-1/MAO catalyst showed maximum when [Al]/[Zr] is around 2000, when [Zr] is 137.1 μM, and when polymerization temperature is 30°C. The negligible activity of rac-1/MAO catalyst at a very low MAO concentration seems to be caused by the instability of the cationic active species. The meso pentad values of polymers produced by rac-1/MAO catalyst at 30°C are in the range of 82.8% to 89.7%. The rac-1/MAO catalyst lost stereorigid character at the polymerization temperature above 60°C. The molecular weight of polymer decreased as [Al]/[Zr] ratio, polymerization temperature, and [Zr] increased. The molecular weight distributions of all polymers are in the range of 1.8–2.3, demonstrating uniform active species present in the polymerization system.     

Polymerization and copolymerization of trioxane: Factors influencing molecular weight and end groups

In bulk polymerization and copolymerization of trioxane with ethylene oxide, it has been shown that p-chlorophenyldiazonium hexafluorophosphate is a superior catalyst as compared to boron trifluoride dibutyl etherate (BF₃ · Bu₂O). Polymers and copolymers of significantly higher molecular weight have been obtained. The higher molecular weight has been attributed primarily to less inherent chain transfer during propagation, which in turn can be attributed to the superior gegenion PF₆^?. The polymerization proceeds via a clear period followed by sudden solidification. Faster polymerization and higher molecular weight polymers have been observed for homopolymerization than for copolymerization. The polymer yield obtained after solidification is determined by both rate of polymerization and rate of crystallization of polymers. These rates, in turn, are dependent on the catalyst concentration. The molecular weight is determined both by polymer yield and extent of inherent chain transfer. In the range of monomer to catalyst mole ration [M]/[C] = (0.5–20) × 10⁴ investigated, it has been found that in the higher range, the polymer yield is independent of the catalyst concentration and the extent of inherent chain transfer is inversely proportional to the half power of catalyst concentration: [M]/[C] = (0.5–8) × 10⁴ for homopolymerization and (0.5–3) × 10⁴ for copolymerization with 4.2 mole % ethylene oxide. In the lower range, the yield decreases with catalyst concentration and the extent of inherent chain transfer is inversely proportional to higher power of catalyst concentration. The dependence of molecular weight of polymers on catalyst concentration has been shown to be a complex one. The molecular weight goes through a maximum as the catalyst concentration is decreased. The maximum molecular weights have been obtained at [M]/[C] ≈ 8 × 10⁴ for homopolymerization and ～3 × 10⁴ for copolymerization with 4.2 mole % ethylene oxide. Prior to reaching maximum the molecular weight is inversely proportional to the half power of catalyst concentration indicating it is primarily controlled by inherent chain transfer. Upon further decrease of catalyst, molecular weight decreases as a result of both a decrease in polymer yield and an increase in inherent chain transfer. In copolymerization of trioxane and ethylene oxide, it has been ascertained that methylene chloride exhibits a favorable solvating effect. Although higher inherent chain transfer takes place in copolymerization than in homopolymerization, the extent of chain transfer is independent of ethylene oxide concentration. The difference in polymer yield and molecular weight a t different ethylene oxide concentrations is attributed primarily to the difference in k_p/k_t ratio. It also has been demonstrated that end capping of polymer chains can be accomplished by the use of a chain transfer agent—methylal.     

Room temperature polymerization of alkyl isocyanates catalyzed by rare earth Schiff base complexes

The polymerization of alkyl isocyanates catalyzed by rare earth chloride salen complexes/triisobutyl aluminum (Ln(H₂salen)₂Cl₃·2C₂H₇OH/Al(i-Bu)₃) at room temperature was investigated. The influences of ligand structure, catalyst composition, polymerization temperature, polymerization time, the concentration of catalyst and monomer, and the polymerization solvent on the polymerization of isocyanates were studied. It was found that under the polymerization conditions, examined La(H₂salen_A)₂Cl₃·2C₂-H₇OH/Al(i-Bu)₃ (H₂salen_A= N,N′-disalicylideneethylene diamine) is a fairly high efficient catalyst for the polymerization of n-hexyl isocyanate (n-HexNCO) to prepare high molecular weight poly(n-hexyl isocyanate) (PHNCO) with narrower molecular weight distribution at room temperature. PHNCO could be prepared with yield of 74.0%, number-average molecular weight (M _n) of 40.20×10⁴ and MWD of 1.79 under the following optimum conditions: [Al]/[La] = 30 (molar ratio), [n-HexNCO]/[La] = 100 (molar ratio), [n-HexNCO] = 3.43 mol/L polymerization at 20°C for 12 h in toluene. In the same polymerization conditions, poly (n-octyl isocyanate) (PONCO) with yield of 67.3%, and poly(n-butyl isocyanate) (PBNCO) with yield of 45.5%, could be prepared respectively. The kinetics of the polymerization of n-HexNCO was also investigated and found to be first-order with respect to both monomer and catalyst concentrations.     

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.     

Synthesis of isotactic polystyrene with a rare-earth catalyst

Polymerization of styrene with the neodymium phosphonate Nd(P₅₀₇)/H₂O/Al(i-Bu)₃ catalytic system has been examined. The polymer obtained was separated into a soluble and an insoluble fraction by 2-butanone extraction. ¹³C-NMR spectra indicate that the insoluble fraction is isotactic polystyrene and the soluble one is syndiotactic-rich atactic polystyrene. The polymerization features are described and discussed. The optimum conditions for the polymerization are as follows: [Nd] = (3.5–5.0) × 10⁻² mol/L; [styrene] = 5 mol/L; [Al]/[Nd] = 6–8 mol/mol; [H₂O]/[Al] = 0.05–0.08 mol/mol; polymerization temperature around 70°C. The percent yield of isotactic polystyrene (IY) is markedly affected by catalyst aging temperature. With increase of the aging temperature from 40 to 70°C, IY increases from 9% to 48%. Using AlEt₃ and Al(i-Bu)₂H instead of Al(i-Bu)₃ decreases the yield of isotactic polystyrene. Different neodymium compounds give the following activity order: Nd(P₅₀₇)₃ > Nd(P₂₀₄)₃ > Nd(OPrⁱ)₃ > NdCl₃ + C₂H₅OH > Nd(naph)₃. With Nd(naph)₃ as catalyst, only atactic polystyrene is obtained. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1773–1778, 1998     

Novel neodymium (III) isopropoxide‐methylaluminoxane catalyst for isoprene polymerization

A novel catalyst composed of neodymium (III) isopropoxide [Nd(OiPr)₃] and methylaluminoxane (MAO) was examined in isoprene polymerization. The Nd(OiPr)₃‐MAO catalyst proved to be highly effective in heptane even at low [Al]/[Nd] ratios (ca. 30) to give polyisoprene that possessed high cis‐1,4 stereoregularity (> ca. 90%), a high number‐average molecular weight (M_n ～10⁵), and relatively narrow molecular weight distributions (M_w/M_n = 1.9–2.8). The catalyst activity increased with an increasing [Al]/[Nd] ratio from 10 to 80 as well as temperature of aging and polymerization from 0 to 60 °C. The polymerization proceeded in the first order with respect to the monomer concentration. Aliphatic solvents (heptane and cyclohexane) achieved a higher yield and M_n of polymer than toluene as a solvent. The M_w/M_n ratio remained around 2.0, and the gel permeation chromatographic curve was always unimodal, indicating that this system is homogeneous and involves a single active site. The microstructure of polyisoprene was determined by IR, ¹H NMR, and ¹³C NMR. The cis‐1,4 contents of the final polymers stayed in the range of 90–92%, regardless of reaction conditions, indicating the high stability of stereospecificity of the catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1838–1844, 2002     

High‐Speed Living Polymerization of Polar Vinyl Monomers by Self‐Healing Silylium Catalysts

This contribution describes the development and demonstration of the ambient‐temperature, high‐speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (≤ 0.05 mol % relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal (^RSKA) initiator (I) with a strong Brønsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near‐precise polymer number‐average molecular weight (M_n, controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain‐termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well‐defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst “self‐repair” involved in this living polymerization system have been elucidated, chiefly featuring a propagation “catalysis” cycle consisting of a rate‐limiting C? C bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et₂O)₂]⁺[B(C₆F₅)₄]^? is the most effective activator, which spontaneously delivers the most active R₃Si⁺, reaching a high catalyst turn‐over frequency (TOF) of 6.0×10³ h^?1 for methyl methacrylate polymerization by Me₃Si⁺ or an exceptionally high TOF of 2.4×10⁵ h^?1 for n‐butyl acrylate polymerization by iBu₃Si⁺, in addition to its high (>90 %) to quantitative efficiencies and a high degree of control over M_n and MWD (1.07–1.12). An intriguing catalyst “self‐repair” feature has also been demonstrated for the current living polymerization system.     

Novel organosoluble polynorbornene bearing a polar,pendant, ester‐bridged epoxy group via living ring‐opening metathesis polymerization

A novel organosoluble polynorbornene bearing a polar, pendant, ester‐bridged epoxy group [poly(oxiran‐2‐ylmethyl 2‐methylbicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate) (polyOMMC)] was prepared via the living ring‐opening metathesis polymerization (ROMP) of active norbornenes with a Ru catalyst. PolyOMMC exhibited excellent solubility in a variety of solvents. The number‐average molecular weight of polyOMMC linearly increased with the [M]/[I] ratio (where [M] is the monomer concentration and [I] is the initiator concentration), and a narrow polydispersity of 1.09–1.19 was observed; this was considered a living polymerization. When ROMP of oxiran‐2‐ylmethyl 2‐methylbicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate with [M]/[I] = 350 was carried out at 30 °C in CH₂Cl₂, the number‐average molecular weight (7.01 × 10⁴; polydispersity index = 1.07) was close to the calculated molecular weight (7.28 × 10⁴), and a diblock copolymer was observed after the addition of another monomer ([M]/[I] = 350) with an increase in the number‐average molecular weight (1.60 × 10⁵; polydispersity index = 1.11), which was close to the calculated molecular weight (1.61 × 10⁵). The modified polynorbornenes retained good solubility in methylene chloride, tetrahydrofuran, dimethyl sulfoxide, dimethylformamide, N,N‐dimethylacetamide, and N‐methyl‐2‐pyrrdione. High‐performance polynorbornenes with active epoxy groups could be designed with great potential for applications in photoresists, UV curing, and elastomers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4428–4434, 2006     

Unsymmetrical N-Heterocyclic Carbene: 1-Isopropyl-3-benzylimidazol-2-ylidene as Catalyst for Ring-Opening Polymerization of ϵ-Caprolactone

An unsymmetrical N-heterocyclic carbene, namely 1-isopropyl-3-benzylimidazol-2-ylidene, is a highly active catalyst for ring-opening polymerization of ?-caprolactone (CL) to give polycaprolactone (PCL) with number average molecular weight (Mn) as high as 2.66 × 10⁴ at 0°C in 100 min in tetrahydrofuran (THF). The effects of monomer/initiator molar ratio ([M]/[I]), catalyst/initiator molar ratio ([C]/[I]), monomer concentration, as well as polymerization temperature and time have been investigated. The kinetic studies of CL polymerization have indicated that the polymerization rate is first-order with respect to both monomer and catalyst concentrations. The apparent activation energy amounts to 56.04 kJ/mol. The proposed mechanism is a monomer-activated process.     

n-Octyloxyallene homopolymerization and random copolymerization with styrene using catalyst system composed of lanthanide Schiff-base complexes and Al(i-Bu)3

The catalyst system composed of lanthanide Schiff-base complexes with [3,5-tBu2 -2-(O)C6H2 CH=NC6H5]3 Ln(THF)(Ln(Salen)3 , Ln = Sc, Y, La, Nd, Sm, Gd, Yb) and triisobutyl aluminum shows high activity for n-octyloxyallene (A) homopolymerization with narrow molecular weight distribution (MWD). The influences of reaction conditions on polymerization behavior are investigated, and poly(n-octyloxyallene) has a weight average molecular weight (M w ) of 20.6 × 10 3 with MWD of 1.39 and 100% yield is obtained under the optimum conditions: [Al]/[Y] = 50 mol/mol, [A]/[Y] = 100 mol/mol, with polymerization at 80 ℃ for 16 h in bulk. The kinetic studies of n-octyloxyallene homopolymerization indicate that the polymerization rate is first-order with respect to the monomer concentration and shows some controlled polymerization characteristics. Random copolymer of n-octyloxyallene with styrene is obtained by using the same binary catalyst system; the reactivity ratios of the comonomer determined by Kelen Tüd s method are r A = 1.20 and r St = 0.35, respectively, the ratio of each segment and M w of the resulting copolymer could be controlled by varying the feed ratio of each monomer. Determined by differential scanning calorimetry, the copolymers obtained show only one glass transition temperature, which increases gradually with the increase of styrene content in the copolymer.     

Polymer-supported titanium catalysts for syndiotactic polymerization of styrene

Poly(styrene-co-acrylamide)(PSAm)-titanium complexes (PSAm · Ti) were prepared and characterized. It is found that the coordination number of acrylamide (Am) to Ti in the complexes is strongly dependent on Am content in PSAm, but not on [Am]/[Ti] ratio in the feed. The infrared and x-ray photoelectron spectra suggest that the polymer-supported complexes possess the structure The catalytic behavior of the complexes in styrene polymerization is described. The catalytic activity is markedly affected by [Al]/[Ti] ratio in the complexes. ¹³C NMR, IR, and DSC data indicate that the polystyrene obtained with PSAm · Ti/MAO (MAO = methylaluminoxane) is highly syndiotactic. Use of Et₃Al and i-Bu₃Al in place of MAO gives atactic polystyrene. The activities of the various aluminum compounds used as the cocatalysts decrease in the order: MAO > Et₃Al > i-Bu₃Al. The polymer-supported complexes show relatively high activity even after the complexes had been exposed to air for 19 h or higher polymerization temperature. © 1996 John Wiley & Sons, Inc.     

茂钛均相催化剂丁二烯聚合研究

由五甲基单茂钛化合物Cp TiL3 和甲基铝氧烷 (MAO)组成的催化体系进行丁二烯聚合 .考察具有不同辅助配体L的主催化剂Cp TiL3 及外加三异丁基铝 (TIBA)对聚合的选择性 ;讨论了聚合温度、AlMAO Ti摩尔比和催化剂浓度对聚合反应的影响 .发现外加适量TIBA有助于提高催化活性 ,而且随着TIBA用量的增加聚丁二烯分子量增加 .结合钛氧化态分析 ,说明催化体系中Ti(Ⅲ )活性中心更有利于丁二烯聚合     

The composition of catalysts prepared from tri-n-propylaluminum,anisole, and titanium tetrachloride

Catalysts were prepared from titanium tetrachloride and tri-n-propylaluminum or tri-n-propylaluminum anisole at [Al]/[Ti] molar ratios of 0.20–1.10. They were aged and filtered, and the solid and liquid portions were analyzed for aluminum, titanium, chlorine, and certain organic constituents. The analyses indicate that the solid of the nonetherate catalyst is predominantly TiCl₃, some AlCl₃ or aluminum alkyl chlorides being included. Only at [Al]/[Ti] = 1.10 was any alkyl group found in the solid. The same general results were found for the etherate catalyst, but the solid had a somewhat lower [Cl]/[Ti] ratio, indicating greater reduction or alkylation, or both, of the titanium species than in the nonetherate catalyst. The solid also contained some anisole at the higher [Al]/[Ti] ratios. The results lend general support to proposed reactions for the catalyst formation. The main differences in the etherate catalysts relative to the non-etherate system, particularly at the higher [Al]/[Ti] ratios, are the apparently greater reduction or alkylation of the titanium in the solids, the presence of anisole in the liquid and solid portions, and the presence of phenol in the liquid portion. The phenol presumably comes from cleavage of the anisole during the catalyst formation. Not all of the anisole has been accounted for in a materials balance, nor has all of the chlorine in the etherate catalysts. No propyl or isopropyl chloride was found in the catalysts; there is no significant amount of polypropylene in any of the catalyst solids. Hence the fate of the alkyl groups remains undetermined at present.     

Poly(4‐vinylpyridine)‐supported cationic bis(cyclopentadienyl)zirconocene catalyst: Development of a new simple method to prepare polymer‐supported cationic zirconocene and its application to ethylene polymerization

Bis(cyclopentadienyl)zirconocene dimethyl (Cp₂ZrMe₂) combined with triphenylcarbenium tetrakis(pentafluorophenyl)borate ([Ph₃C][B(C₆F₅)₄]) was brought into contact with a suspension of 2% cross‐linked poly(4‐vinylpyridine) to give a new type of polymer‐supported cationic zirconocene catalyst. The resulting polymer‐supported catalyst system combined with Al(i‐Bu₃) showed markedly high activity for ethylene polymerization in even a non‐polar solvent like hexane at 25–60°C and [Al]/[Zr] molar ratio 40–200. By the analysis of Zr content of the hexane solution, it was found that no Zr was detected in the solution, i. e. no leaching of the cationic catalyst into the hexane medium. The catalytic activity was found to increase with an increase of polymerization temperature and showed the highest at [Al]/[Zr] = 100. The molecular weight, crystalline melting temperature, crystallinity, and bulk density of polyethylene formed were higher than those of the polymer obtained from the homogeneous system.     

Reduced titanium dioxide as support for Ziegler–Natta catalysts

Titanium tetrachloride heterogenized on reduced TiO₂ has been studied as a catalyst for ethylene polymerization. The catalyst has good storage stability and exhibits good activity for ethylene polymerization. The polymer chains grow linearly during ca. 1 h, giving an average molecular weight of up to 2.5 × 10⁶ which indicates that practically no β-elimination occurs. The activity of the catalyst at 50°C, based on Ti(III), is 7.6 × 10⁶ PE/mol Ti h bar and based on the quantity of polyethylene formed it is 1.25 × 10⁶ g PE/mol Ti h bar. The molecular weight of the polymer can be controlled with the addition of hydrogen, under 0.5 bar hydrogen, polyethylene with a molecular weight of 411,000 and a relatively low polydispersity index of 2.2 is obtained. The catalyst shows good thermal stability; the Arrhenius activation energy is 31.8 kJ/mol for the polymerization. The catalyst is also active for propylene polymerization, giving 3 × 10⁶ g PP/mol Ti h bar with the high isotacticity of 93%. © 1994 John Wiley & Sons, Inc.     

A Novel Highly Active Iron/2,6‐Bis(imino)pyridyl Catalyst for Ethylene Polymerization

A novel highly active catalyst 2,6‐bis[1‐(2‐methylnaphthylimino)ethyl]pyridineiron(II) chloride ( 1 ) is reported for ethylene polymerization. Compared with 2,6‐bis[(1‐naphthylimino)ethyl]pyridineiron(II) chloride ( 2 ) reported recently, catalytic activities of this new complex are high with maximum activity 6.51×10⁶ g PE·mol^–1·Fe·h^–1·bar^–1 at 40°C. The activity of the catalyst, and the molecular weight and melting temperature of the polymers depend on the methylaluminoxane/ 1 molar ratio and polymerization temperature.