Supported Zr-and Hf-cene Catalysts for Propylene Polymerization

The supported metallocene catalysts were obtained on the layered silicate montmorillonite (MMT), using AlMe₃ and AliBu₃ for synthesis of alkylaluminoxane directly on a support surface, followed by metallocene supporting. It was shown that the MMT-H₂O/AliBu₃ forms with ansa-Zr-cenes of C₁ and C₂-symmetry the significantly more active supported metal-alkyl complexes in propene polymerization, than MMT-H₂O/AlMe₃. The MMT-H₂O/AliBu₃ is the effective activator of the ansa-Hf-cenes, in contrast to MAO and MMT-H₂O/AlMe₃, giving the high active supported catalysts for synthesis of isotactic and elastic polypropene. The character of influence of metallocene fixation on support on the isotactic pentad [mmmm] content in polymer, compared to homogeneous analogues, depends on the metallocene nature. The introduction of borate Ph₃CB(C₆F₅)₄ in the case of both Zr-cene and Hf-cene catalysts increases significantly the activity at the reduced ratio of Al/Zr, Hf (100–500 instead of 2000–3000) and stabilizes the catalytic complexes.     

Polymerization of propylene with the [ArN(CH2)3NAr]TiCl2 (Ar = 2,6-iPr2C6H3) complex using R3Al/Ph3CB(C6F5)4 (R = Me,Et, iBu) as cocatalyst

Polymerization of propylene was conducted at 0 ∼ 150°C with the [ArN(CH₂)₃NAr]TiCl₂ (Ar = 2,6-ⁱPr₂C₆H₃) complex using a mixture of trialkylaluminium (AIR₃, R = methyl, ethyl and isobutyl) and Ph₃CB(C₆F₅₎₄ as cocatalyst. When AlMe₃ or AlEt₃ was employed, atactic polypropylene (PP) was selectively produced, whereas the use of Al(ⁱBu)₃ gave a mixture of atactic and isotactic PP. The isotactic index (I.I.; weight fraction of isotactic polymer) depended strongly upon the polymerization temperature, and the highest I.I. was obtained at ca. 40°C. The ¹³C NMR analysis of the isotactic polymer suggests that the isotactic polymerization proceeds by an enantiomorphic-site mechanism. It was also demonstrated that the present catalyst shows a very high regiospecificity.     

Ring-Opening Polymerization of Lactones Initiated with Metal Hydroxide-Activated Macrocyclic Ligands: Determination of Mechanism and Structure of Polymers

Anhydrous alkali metal hydroxide (KOH, NaOH, and LiOH)-activated macrocyclic ligand complexing metal cations, i.e., coronands 12C4, 15C5, 18C6, DCH24C8, and cryptand C222, were selected for initiation of β-butyrolactone (β-BL) and ε-caprolactone (ε-CL) polymerization. It was found that β-BL polymerizes in the presence of KOH/18C6, KOH/C222, and NaOH/C222 systems. The real initiators in this case are two salts, potassium 3-hydroxybutyrate and potassium trans-crotonate, which are responsible for the formation of two fractions of the obtained polymer. ε-CL underwent polymerization with KOH or NaOH activated by all ligands used or without the ligand but with LiOH/12C4. Using KOH-activated strong ligands, i.e., 15C5, 18C6, or C222, two polymer fractions were generated containing linear and, unexpectedly, also cyclic macromolecules. The mechanism of the studied processes is discussed.     

Polymerization of vinyl chloride by the Ti(O-n-Bu)4–AlEt3–epichlorohydrin catalyst system

The polymerization of vinyl chloride was carried out by using a catalyst system consisting of Ti(O-n-Bu)₄, AlEt₃, and epichlorohydrin. The polymerization rate and the reduced viscosity of polymer were influenced by the polymerization temperature, AlEt₃/Ti(O-n-Bu)₄ molar ratios, and epichlorohydrin/Ti(O-n-Bu)₄ molar ratios. The reduced viscosity of polymer obtained in the virtual absence of n-heptane as solvent was two to three times as high as that of polymer obtained in the presence of n-heptane. The crystallinity of poly(vinyl chloride) thus obtained was similar to that of poly(vinyl chloride) produced by a radical catalyst. It was concluded that the polymerization of vinyl chloride by the present catalyst system obeys a radical mechanism rather than a coordinated anionic mechanism.     

Head-to-head vinyl polymers. VII. Hydrolysis of head-to-head poly(methyl acrylate)

Head-to-head (H–H) and head-to-tail (H–T) poly(methyl acrylate)s (PMAs) were hydrolyzed in a mixture of acetone and water (4:1 by volume) at 30°C by using various alkali hydroxides as catalysts. For comparison, the H–T copolymer with 26% H–H units, dimethyl succinate (DMS), dimethyl glutarate (DMG), and dimethyl adipate (DMA) as model compounds were also hydrolyzed. It was found that the hydrolyses of all PMAs proceeded autocatalytically; i.e., the rates increased as a function of the reaction time. Both the initial rate constant k₀ and the autoaccelerating effect observed markedly depended on the structures of polymer chains and they decreased with increasing of the H–H sequences. The molecular weights of either H—H or H—T PMA did not show remarkable changes in either k₀ value or accelerating effect. The k₀ values were almost independent of the kinds of bases and were calculated to be 0.06 and 0.18 L mol^?1 min^?1 for H–H and H–T PMA, respectively. On the other hand, the autoaccelerating effect decreased in the order NaOH ? KOH > LiOH > CsOH for H–H PMA and NaOH > LiOH > KOH > CsOH for H–T polymer. When the ratio of acetone to water increased, the k₀ value was found to decrease, whereas the accelerating effect increased. The results obtained are described and discussed.     

Probing the roles of diethylaluminum chloride in propylene polymerization with MgCl2-supported ziegler-natta catalysts

In this article, the effect of diethylaluminum chloride (DEAC) in propylene polymerization with MgCl₂-supported Ziegler-Natta catalyst was studied. Addition of DEAC in the catalyst system caused evident change in catalytic activity and polymer chain structure. The activity decrease in raising DEAC/Ti molar ratio from 0 to 2 is a result of depressed production of isotactic polypropylene chains. The number of active centers in fractions of each polymer sample was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and fractionating the polymer into isotactic, mediumisotactic and atactic fractions. The number of active centers in isotactic fraction ([C_i*]/[Ti]) was lowered by increasing DEAC/Ti molar ratio to 2, but further increasing the DEAC/Ti molar ratio to 20 caused marked increase of [C_i*]/[Ti]. The number of active centers that produce atactic and medium-isotactic PP chains was less influenced by DEAC in the range of DEAC/Ti = 0–10, but increased when the DEAC/Ti molar ratio was further raised to 20. The propagation rate constant of C_i* (k _pi) was evidently increased when DEAC/Ti molar ratio was raised from 0 to 5, but further increase in DEAC/Ti ratio caused gradual decrease in k _pi. The complicated effect of DEAC on the polymerization kinetics, catalysis behaviors and polymer structure can be reasonably explained by adsorption of DEAC on the central metal of the active centers or on Mg atoms adjacent to the central metal.     

The effect of AlR3 on propylene polymerization by rac‐(EBI)Zr(NMe2)2/AlR3/[CPh3][B(C6F5)4] catalyst

Ansa‐zirconocene diamide complex rac‐(EBI)Zr(NMe₂)₂ [rac‐1, EBI = ethylene‐1,2‐bis(1‐indenyl)] reacted with AlR₃ (R = Me, Et, iBu) or Al(iBu₂)H and then with [CPh₃][B(C₆F₅)₄] (2) in toluene in order to perform propylene polymerization by cationic alkylzirconium species, which are in situ generated during polymerization. Through the sequential NMR‐scale reactions of rac‐1 with AlR₃ or Al(iBu₂)H and then with 2, rac‐1 was demonstrated to be transformed to the active alkyzirconium cations via alkylated intermediates of rac‐1. The cationic species generated by using AlMe₃, AlEt₃, and Al(iBu₂)H as alkylating reagents tend to become heterodinuclear complex; however, those by using bulky Al(iBu)₃ become base‐free [rac‐(EBI)Zr(iBu)]⁺ cations. The activity of propylene polymerization by rac‐1/AlR₃/2 catalyst was deeply influenced by various parameters such as the amount and the type of AlR₃, metallocene concentration, [Al]/[2] ratio, and polymerization temperature. Generally the catalytic systems using bulky alkylaluminum like Al(iBu)₃ and Al(iBu)₂H show higher activity but lower stereoregularity than those using less bulky AlMe₃ and AlEt₃. The alkylating reagent Al(iBu)₃ is not a transfer agent as good as AlMe₃ or AlEt₃. The polymerization activities show maximum around [Al]/[2] ratio of 1.0 and increase monotonously with polymerization temperature. The overall activation energy of both rac‐1/Al(iBu)₃/2 and rac‐1/Al(iBu)₂H catalysts is 6.0 kcal/mol. As the polymerization temperature increases, the stereoregularity of the resulting polymer decreases markedly, which is demonstrated by the decrease of [mmmm] pentad value and by the increase of the amount of polymer soluble in low boiling solvent. The physical properties of polymers produced in this study were investigated by using ¹³C‐NMR, differential scanning calorimetry (DSC), viscometry, and gel permeation chromatography (GPC). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1523–1539, 1999     

The kinetics of polymerization of cyclopentene by WCl6/AliBu3 catalyst

The kinetics of the polymerization of cyclopentene by WCl₆/AliBu₃ catalysts have been studied and the factors controlling the reproducibility of the rate of polymerization have been ascertained. A significant dependence of the rate of polymerization on the time between the additions of WCl₆ and AliBu₃ was observed. The dependence of the catalyst activity r,i this time delay suggested that WCl₆ reacted with cyclopentene to produce an unstable species (W₁) that could react with AliBu₃ to produce a catalytically active species (W₁¹) or that could react further with cyclopentene to produce another species W₂ that in turn would react with AliBu₃ to produce a much less active catalyst W₂¹. The detailed study of the kinetics of polymerization under controlled conditions suggested a kinetic chain mechanism initiated by two catalyst species; mechanism of polymerization based on the carbene system is suggested.     

Ethylaluminum oxide catalysts from Et2AlOLi–Et2AlCl binary system in relation to species of AlEt3–water catalyst

Equimolar reaction of Et₂AlOLi and Et₂AlCl gave Et₂AlOAlEt₂. The catalyst behavior for polymerization of acetaldehyde, propylene oxide, and epichlorohydrin was compared with that of the AlEt₃–H₂O (1:0.5) catalyst system. The thermal disproportionation product of Et₂AlOAlEt₂ derived from Et₂AlOLi–Et₂AlCl had the structure, ? (EtAlO)_n? , and it showed catalyst behavior quite similar to that of the product obtained by the same treatment of AlEt₃–H₂O (1:0.5). These ethylaluminum oxides can be regarded as species predominating in AlEt₃–H₂O (1:0.5) and AlEt₃–H₂O (1:1), respectively. Stereospecific or high molecular weight polymerizations of these species were investigated.     

Role of heterogeneous Cr(AcAc)3–AlEt3 catalyst system in isoprene polymerization

Polymerization of isoprene in presence of a heterogeneous Ziegler-type catalyst system, Cr(AcAc)₃–AlEt₃, has been studied in benzene medium. The rate of polymerization is first-order with respect to catalyst as well as monomer concentration. The rate studies, activation energy, and polymer microstructures are reported in order to follow the probable mechanism of polymerization.     

Kinetics of propylene polymerization in the initial acceleration stage

The kinetics of propylene polymerization catalyzed over a superactive and stereospecific catalyst for the initial build-up period was investigated in slurry-phase. The catalyst was prepared from Mg(OEt)₂/benzoyl chloride/TiCl₄ co-activated with AlEt₃ in the absence or presence of external donor. Despite a very fast activation of the prepared catalyst the acceleration stage of polymerization could be identified by the precise estimation of polymerization kinetics for a very short period of time after the commencement of polymerization (ca. 2 min). The initial polymerization rate, (dR_p/dt)₀ extrapolated to the beginning of the polymerization was second order with respect to monomer concentration. The dependence of initial polymerization rate on the concentration of AlEt₃ could be represented by Langmuir adsorption mechanism. The initial rate was maximum at about Al/Ti ratio of 20. The activation energy for the initiation reaction was estimated to be 14.3 kcal/mol for a short-time polymerization. The addition of a small amount of p-ethoxy ethyl benzoate (PEEB) as an external donor increased the percentage of isotactic polymer, which was obtained after 120 s of polymerization, to 98% and the initial polymerization rate decreased sharply as [PEEB]/[AlEt₃] increased. © 1994 John Wiley & Sons, Inc.     

Magnesium chloride modified with organoaluminium compounds as a support of the zirconocene catalyst for ethylene polymerisation

This work describes the influence of the modification of the MgCl₂(THF)₂ and MgCl₂ magnesium supports with the AlEt₂Cl, MAO, AlEt₃, AlMe₃, and AlEt₂Cl alkylaluminium compounds on heterogenisation of the bis(cyclopentadienyl) zirconium(IV) dichloride Cp₂ZrCl₂ catalyst. It was found that only the MgCl₂(THF)₂ support modified with AlEt₂Cl gave the heterogeneous catalyst. On the contrary, application of a magnesium carrier modified by AlEt₃, AlMe₃, and MAO compounds only results in a homogeneous zirconocene catalyst.     

The influence of cations on the dissociation behaviour of copolymers of propene and maleic acid and their modified products with taurine in salt-free solution

Potentiometric and conductometric titrations were used to study the dissociation behaviour of poly(propene-co-maleic acid) and poly(propene-co-maleic acid) modified with various contents of taurine (2-aminoethanesulfonic acid) in salt-free solution. Copolymers of propene and maleic acid with different molecular weights were titrated with LiOH, NaOH, and KOH. The influence of molecular weight on pK_a is ascertainable in both the first and second dissociation step. Of the various alkali metal cations studied, lithium had the most significant effect on the dissociation behaviour. The acidic strength decreased in the order lithium > sodium ≥ potassium. After insertion of sulfonic acid groups into poly(propene-co-maleic acid), the influence of strong acidic groups on the dissociation behaviour of carboxylic groups was studied. The contents of taurine were 10, 25, and 50 mol%. The second dissociation step was analyzed in this case. The pK_a values increased with increasing content of taurine for titrations with LiOH and KOH, but not NaOH. When NaOH was used, the pK_a decreases if the polymer was modified with 10% taurine. Higher taurine contents had no influence on the magnitude of pK_a. The results demonstrate the strong influence of short-range electrostatic interactions on the dissociation behaviour of weak polyacids. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1949–1955, 1999     

Improvement by heating of the electronic conductivity of cobalt spinel phases, electrochemically synthesized in various electrolytes

The nature of the alkaline electrolyte (based on KOH, NaOH, LiOH), in which Co₃O₄ spinel type phases are synthesized by electrooxidation of CoO, is shown to play a key role on the composition, the structure and the electronic conductivity of the materials. In the materials, prepared in pure LiOH electrolyte or in mixed ternary electrolyte (KOH, NaOH, LiOH), Co⁴⁺ ions are present in the octahedral framework, which entails electronic delocalization in the cobalt T_2g band and a high conductivity. The structure of the sample, synthesized in KOH, is on the opposite closer to that of ideal Co₃O₄, with only Co³⁺ in the octahedral sublattice, which leads to a semi-conducting behavior. Whatever the initial material, a thermal treatment induces an increase of the Co⁴⁺/Co³⁺ ratio in the octahedral network, resulting in a significant increase of the electronic conductivity.     

Polymerization of α-piperidone with M–AlEt3, MAlEt4, or KAlEt3(piperidone) as catalysts and N-acetyl-α-piperidone as initiator

Low-temperature polymerization of α-piperidone was carried out by using MAlEt₄, KAlEt₃(piperidone), and M–AlEt₃ (where M is Li, Na, or K) as catalysts and N-acetyl-α-piperidone as initiator. The behavior in polymerization of these catalysts was superior to alkali metal or aluminum triethyl, and a polymer having an intrinsic viscosity of 0.8 dl./g. was obtained. Polymerization results and infrared analyses of the metal salts of lactams suggest that a complex, the structure of which was analogous to the one formed from M–AlEt₃, is formed in the case of the alkali metal piperidonate–ethyl aluminum dipiperidonate catalyst system and that it is changed to another complex having a different composition and lower catalytic activity by heat treatment. The infrared absorption band of the metal salts of lactams and of KAlEt₃(piperidone) at 1570–1590 cm.^?1, which is attributable to the C?N group in enolate form, may be considered to be related to the catalytic activities of alkali metals and the polymerizabilities of lactams. Such special catalysts as MAlEt₄, alkali metal–AlEt₃, or KAlEt₃(piperidone) are supposed to suppress the consumption, by alkali metal, of N-acyl-α-piperidone group of growing polymer end. A prolonged polymerization required for obtaining a high molecular weight polymer, even when such catalysts are used, is ascribable to a greater difficulty in re-forming lactam anion from α-piperidone, the basicity of which is higher than that of the other lactams.     

Crown ethers as ligands for stereospecific polymerization by Ziegler–Natta catalysts

Some new TiCl₄/Crown ether complexes were synthesized and used as polymerization catalysts with AlEt₃ or AlEt₂Cl as cocatalyst for the stereospecific polymerization of 1,3-butadiene. As with most of the nucleophilic ligands the addition of crown ethers to Ziegler–Natta catalytic systems results in a decrease of the polymer conversion. But the Al/Ti molar ratio appears to be less critical for the complexed systems than for the uncomplexed ones. The presence of the crown ether in the surroundings of the catalytic sites presumably protects them from an excess of the organoaluminum cocatalyst. The side groups of the crown ether do not influence the microstructure of the polybutadiene obtained but they change the activity of the catalytic systems. Thus, the electron-donating effect of the macrocyclic ligands seems to be less important than the sterical effect due to the rigidity and to the hole size of the crown ether.     

Multicenter nature of titanium‐based Ziegler–Natta catalysts: Comparison of ethylene and propylene polymerization reactions

This article discusses the similarities and differences between active centers in propylene and ethylene polymerization reactions over the same Ti‐based catalysts. These correlations were examined by comparing the polymerization kinetics of both monomers over two different Ti‐based catalyst systems, δ‐TiCl₃‐AlEt₃ and TiCl₄/DBP/MgCl₂‐AlEt₃/PhSi(OEt)₃, by comparing the molecular weight distributions of respective polymers, in consecutive ethylene/propylene and propylene/ethylene homopolymerization reactions, and by examining the IR spectra of “impact‐resistant” polypropylene (a mixture of isotactic polypropylene and an ethylene/propylene copolymer). The results of these experiments indicated that Ti‐based catalysts contain two families of active centers. The centers of the first family, which are relatively unstable kinetically, are capable of polymerizing and copolymerizing all olefins. This family includes from four to six populations of centers that differ in their stereospecificity, average molecular weights of polymer molecules they produce, and in the values of reactivity ratios in olefin copolymerization reactions. The centers of the second family (two populations of centers) efficiently polymerize only ethylene. They do not homopolymerize α‐olefins and, if used in ethylene/α‐olefin copolymerization reactions, incorporate α‐olefin molecules very poorly. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1745–1758, 2003     

Synthesis and characterization of aluminum complexes based on amino‐benzotriazole phenoxide ligand: luminescent properties and catalysis for ring‐opening polymerization

Aluminum complexes coordinated by a ^C1DEABTP ligand (^C1DEABTP‐H = 2‐(2H‐benzotriazol‐2‐yl)‐6‐((diethylamino)methyl)‐4‐methylphenol) were synthesized and structurally characterized. The formation of Al complexes is dependent on the stoichiometry of AlMe₃ to ^C1DEABTP ligand ratio. The reaction of ^C1DEABTP‐H with AlMe₃ (1.0 molar equiv.) in hexane produced mono‐adduct aluminum complex [(^C1DEABTP)AlMe₂] (1), but treatment of ^C1DEABTP‐H with 2.0 molar equiv. of AlMe₃ afforded mixtures of [(^C1DEABTP)Al₂Me₅] (2) and [(^C1DEABTP)Al₃Me₈] (3). The penta‐coordinated bis‐adduct aluminum complex [(^C1DEABTP)₂AlMe] (4) was synthesized through the reaction of AlMe₃ with ^C1DEABTP‐H (2.0 molar equiv.) in hexane. Tri‐adduct Al complex [(^C1DEABTP)₃Al] (5) resulted from treatment of AlMe₃ with ^C1DEABTP‐H (3.0 equiv.); the Al center is hexa‐coordinated with three N,O‐bidentate ^C1DEABTP ligands. X‐ray diffraction of single crystals indicates that the bonding modes of the ^C1DEABTP ligands in complexes 2–3 are greatly affected when excess AlMe₃ is coordinated. The optical properties and catalysis for lactone polymerizations of ^C1DEABTP coordinated to Al complexes were tested. Tri‐adduct Al complex 5 produced an intense green fluorescence in both solution and the solid state. Complex 4 is an active catalyst for the ring‐opening polymerization of ε‐caprolactone (ε‐CL) and L‐lactide (L‐LA) in the presence of 9‐anthracenemethanol (9‐AnOH). In ε‐CL polymerization, Al complex 4 catalyzes efficiently in both a 'controlled' and 'immortal' manner, giving polymers with the expected molecular weights and narrow polydispersity indexes. Copyright © 2012 John Wiley & Sons, Ltd.     

Theoretical study of structure and basicity of some alkali metal oxides,hydroxides, and amides

Ab initio (TZV *, SBK *, and 3–21G * or 6–31G * basis sets) calculations were performed to predict the geometries and gas-phase proton affinities of Li₂O, LiOH, LiNH₂, Na₂O, NaOH, NaNH₂, K₂O, KOH, and KNH₂. © 1994 John Wiley & Sons, Inc.     

Polymerization of styrene with VOCl3–aluminum alkyls

The polymerization of styrene with VOCl₃ in combination with AlEt₃ and with Al(i-Bu)₃ in n-hexane at 40°C. has been investigated. The rate of polymerization was found to be second order with respect to monomer in both systems. With respect to catalyst the rate of polymerization was first order for VOCl₃–AlEt₃ and second order for VOCl₃-Al(i-Bu)₃ systems. The activation energies for VOCl₃–AlEt₃ and VOCl₃–Al(i-Bu)₃ systems were 7.37 and 11.25 kcal./mole, respectively. The molecular weight of polystyrene in the AlEt₃ system was considerably higher than that in the Al(i-Bu)₃ system. The valence of vanadium obtained by a potentiometric method showed that the catalyst sites in the AlEt₃ system are different in nature from those in the Al(i-Bu)₃ system. The effect of diethylzinc as a chain-transfer agent in the AlEt₃ system was also studied.