Magnesium chloride supported high-mileage catalysts for olefin polymerization. XVII. Effect of lewis base on propylene polymerization

A systematic study has been made on the functions of external Lewis base (B_e, methyl-p-toluate, MPT) and internal Lewis base (B_i, ethyl benzoate, EB) for the CW-catalyst system MgCI₂/EB/PC/AlEt₃/TiCl₄–AlEt₃/MPT (PC, p-cresol). B_i is a nonstereoselective modifier. It increases the active site concentrations and rate constants of propagation, k_p, of both the isospecific and nonspecific sites, and thus the productivities of the stereoregular and irregular polypropylenes by five- to tenfold. It seems that B_i complexes with the MgCl₂ support to lower the electronegativity of the surface Mg atoms. It also acts to lower the rate constant of chain transfer to aluminum alkyl, k, by two- to fourfold. The action of B_e is highly stereospecific. The isotacticity index of polypropylene is ? 95% in the presence of B_e but ? 68% without it. Addition of B_e decreases nonspecific [Ti^*]_a by about (11 ± 2)-fold; there is only about a twofold reduction of the isospecific [Ti^*]_i. It decreases k_p,a about three times but has no effect on k_p,i, so that the latter is (21 ± 4) times the former. B_e decreases k for transfer with aluminum alkyl much more than it does to k; but it does not affect the rates of chain transfer with monomer and by β-hydride elimination or the rate of catalyst deactivation. The number of active sites without B_e is [Ti^*]_i = 15% and [Ti^*]_a = 55% for a total of 70%. In the presence of B_e they are both about 6%. Optimum performance in propylene polymerizations requires both B_i and B_e in the case of the CW-catalyst.     

Magnesium chloride supported high-mileage catalysts for olefin polymerization. X. Effect of hydrogen and catalytic site deactivation

The effect of H₂ on propylene polymerization initiated by a MgCl₂/EB/PC/AlEt₃/TiCl₄–3 AlEt₃/MPT catalyst was studied. Hydrogen increases significantly the initial rate during the early stage of the polymerization to give a higher yield of polymer than reactions without H₂. But H₂ reduces the yield toward the latter stages so that the net effect on the total yield can be quite small. There is no appreciable effect of H₂ on either the isotacticity index or polydispersity of the products. It decreases molecular weight proportional to (p_H2)^1/2. The chain transfer by H₂ resulted in a decrease of total metal polymer bond concentration with time of polymerization. The rate constants of hydrogen chain transfer for the two kinds of isospecific and nonspecific sites are = 5.1 × 10^?3, = 2.7 × 10^?3, = 7.5 × 10^?3, = 4.4 × 10^?3, in units of torr^1/2 sec^?1 at 50°. Hydrogen assists in the deactivation of the catalytic sites as does propylene; rates of the former and the latter vary with (p_H2)^1/2 and [C₃H₆]^1/2, respectively, with k = (12.1 ± 0.9) M^?1 torr^?1/2 sec^?1 and k = (65.3 ± 3.3) M^?3/2 sec^?1 at 50° and A/T = 167. The mechanism for deactivation of catalytic sites are discussed.     

Magnesium chloride supported high-mileage catalysts for olefin polymerization. IV. FTIR and quantitative analysis of modifiers in the catalysts

Fourier transform infrared (FTIR) spectra were obtained for a typical MgCl₂-supported, high-mileage catalyst for propylene polymerization. When ball-milling MgCl₂ with ethyl benzoate (EB), the latter is incorporated into the support (I) by Lewis acid-base complexation involving both oxygen atoms of the ester. Reaction of (I) with p-cresol (PC) resulted in a material (II) that contains all the characteristic IR bands of PC. The reaction of (II) that contains all the characteristic IR bands of PC. The reaction of (II) with AlEt₃ (TEA) resulted in (III) whose spectrum supports the reaction observed by product analysis and NMR spectroscopy. There was no evidence of any reaction between TEA and EB. Further reaction of (III) with an excess of TiCl₄ caused substantial removal of the p-cresol moiety as shown by the diminution of its characteristic bands. Finally, activation with 3TEA-1MT (methyl-p-toluate) complexes gave spectra that revealed the presence of MT in the activated catalyst without any visage of p-cresol moiety. The nondestructive FTIR method, however, is not quantitative. Quantitative analysis of the organic components in the support materials (I), (II), and (III) and the catalysts was accomplished by hydrolysis of the inorganic components, extraction with ether, and analysis by gas chromatography. The results are in good agreement with composition deducted from elemental analysis and substantiate the FTIR conclusions.     

Magnesium chloride supported high-mileage catalysts for olefin polymerization. I. Chemical composition and oxidation states of titanium

The chemical composition of a MgCl₂-supported, high-mileage catalyst has been determined at every stage of its preparation. Ball milling of MgCl₂ with ethyl benzoate (EB) resulted in the incorporation of 95% of the EB present to give MgCl₂·EB_0.15. A mild reaction with a half-mole equivalent of p-cresol (PC) at 50°C for 1 h resulted in near quantitative retention of p-cresol by the support. The composition is now approximately MgCl₂·EB_0.15P?_0.5. Addition of an amount of AlEt₃ corresponding to half-mole equivalent of p-cresol liberated one mole of ethane per mole of p-cresol, thus signaling quantitative reaction between the two components. The support contains on the average one ethyl group per Al. Further reaction with TiCl₄ resulted in the incorporation of titanium of approximately 8, 38, and 54% in the oxidation states of +2, +3, and +4, respectively. The ratio of Al to Ti in the catalyst lies in the range of 0.5–1.0. Only 19% of all the Ti⁺³ species in the catalyst can be observed by electron paramagnetic resonance (EPR); these are attributable to isolated Ti⁺³ complexes. The remaining EPR silent Ti⁺³ species are believed to be bridged to another Ti⁺³ by Cl ligands. The total Cl content is equal to the sum of 2 × Mg + 3 × Al + 3.5 × Ti. Most of the p-cresol moiety apparently disappeared from the support, leaving much of ethyl benzoate in the catalyst. Activation with AlEt₃/methyl-p-toluate complex reduces 90% of the Ti⁺⁴ in the catalyst to lower oxidation states. The ester apparently moderates the alkylating power of AlEt₃ to avoid excessive formation of divalent titanium sites. There appears to be a constant fraction of 1/4–1/5 of the titanium which is isolated and the remainder is in bridged clusters independent of the oxidation states of titanium.     

Magnesium chloride supported high mileage catalysts for olefin polymerization. XII. Polymerization of ethylene

Polymerizations of ethylene by the MgCl₂/ethylbenzoate/p-cresol/AlEt₃ TiCl₄-AlEt₃/methyl-p-toluate (CW-catalyst) have been studied. The initially formed active site concentration, [Ti] has a maximum value of 50% of total titanium at 50°C and lower values at other temperatures. The Ti decays rapidly to Ti sites with conc. ca. 10 mol %/mol Ti. The rate constants for four chain transfer processes have been obtained at 50°C: for transfer with AlEt₃, k = 2.1 × 10^?4 s^?1 and k = 4.8 × 10^?4 s^?1; for transfer with monomer, k = 3.6 × 10^?3 (M s)^?1 and K = 8.3 × 10^?3 (M s)^?1; for β-hydride transfer, k = 7.2 × 10^?4 s^?1 and k = 4.9 × 10^?4 s^?1; and transfer with hydrogen, k = 4.0 × 10^?3 torr^1/2 s^? and k = 5.1 × 10^?3 torr^1/2 s^?1. The rate constants for the termination assisted by hydrogen is k = 1.7 (M^1/2 torr^1/2 S)^?1. If monomer is assisting termination as was observed for propylene polymerization, then k = 7.8 (M^3/2 s)^?1. Values of all the rate constants can be higher or lower at other temperatures. Detailed comparisons were made with the results of propylene polymerizations. There are more than four times as many Ti active sites for ethylene polymerization than there are for stereospecific polymerization of propylene; the difference is more than a factor of two for the Ti sites. Certain rate constants are nearly the same for both monomers while others are markedly different. Some of the differences can be explained by stereoelectronic effects.     

Magnesium chloride supported high mileage catalysts for olefin polymerization. XIII. Effect of external Lewis base on ethylene polymerization

The effect of external Lewis base (B_e) on the polymerization of ethylene by the MgCl₂/ethyl benzoate/p-cresol/AlEt₃/TiCl₄ catalyst was studied by activation with AlEt₃ alone without the use of methyl-p-toluate. The initially formed active site concentration, [Ti], is about doubled in the absence of B_e; at 50°C about 93% of the total titanium became catalytic. The same increment of [Ti] was observed without B_e. The rate constants of propagation are not appreciably affected by B_e; the values are the same at 50° with and without B_e. At other temperatures the k_p values are somewhat smaller without B_e. One major effect was the very large k values for chain transfer with aluminum alkyls in the absence of B_e as compared to those with B_e. This can be attributed to the greater monomeric AlEt₃ concentration in the former, but in much smaller amounts in the presence of B_e due to complexation. The rate constants of chain transfer with hydrogen are not much affected by B_e. However, the termination rate constants are generally much smaller when Lewis base is not present.     

High activity magnesium chloride supported catalysts for olefin polymerization. XXIX. Molecular basis of hydrogen activation of magnesium chloride supported Ziegler–Natta catalysts

Hydrogen (pH₂ = 72 torr) increases the rate of propylene polymerization by a MgCl₂/ethyl benzoate/p-cresol/AlEt₃/TiCl₄-AlEt₃/methyl-p-toluate catalyst (CW-catalyst) by two-to three-fold which corresponds closely with the increase in the number of active sites as counted by radiolabeling with tritiated methanol. The oxidation states of titanium in decene polymerizations by the CW-catalyst were determined as a function of time of polymerization (t_p). In the absence of H₂, all [Ti⁺ⁿ] for n = 2, 3, 4 remain constant during a batch polymerization. In the presence of H₂ and within 5 min of t_p, [Ti⁺²] decreases by an amount, corresponding to 15% of the total titanium and [Ti⁺³] increases by the same amount, while [Ti⁺⁴] is not changed. Therefore, three-fourths of the H₂ activation result from oxidative addition processes. The remaining one-fourth of the H₂ activation may be attributed to the activation of previously deactivated Ti⁺³ ions by hydrogenolysis. Monomer converts some of the EPR silent Ti⁺³ sites to EPR observable species resulting in their activation.     

Magnesium chloride supported high mileage catalysts for olefin (decene-l) polymerization XIV. Propagation and chain transfer

Decene-l was polymerized with the MgCl₂/ethylebenzoate/p-cresol/AIEt₃/TiCl₄-AlEt₃/methyl-p-toluate catalyst at 50° using an A/T ratio of 167 and a range of monomer concentration. The concentration of the two kinds of active sites are [Ti] = 12% and [Ti] = 4% of the total titanium. The rate constants of propagation are 24 M^?1 s^?1. Chain transfers to AIEt₃, monomer, and by β-hydride elimination have rate constant values of 1.7 × 10^?3 M^?1 s^?1, 1.34 × 10^?2 M^?1 s^?1, and 1.7 × 10^?2 s^?1, respectively. Poly(decene-l) have relatively narrow MW which are unchanged during the course of a polymerization. Therefore, the active site concentrations in the CW catalyst for propylene and decene polymerization are identical and their rate constant values agree within a factor of 2. However, the rate of decene polymerization depends on fractional order of monomer concentration and decreases with the increase of activator concentration. Furthermore, the formation of metal polymer bonds has a rate independent of these concentrations. These kinetic behaviors are a manifestation of absorption processes of these species which are not seen in propylene polymerizations.     

Magnesium chloride supported high mileage catalysts for olefin (decene-1) polymerization XV. Termination and energetics

Polymerizations of decene-1 were carried out from 0° to 70° at A/T = 167 and [M] = 0.75 M initiated by 0.17, 0.34, and 0.69 mM of Ti contained in the MgCl₂/ethylbenzoate/p-cresol/AlEt₃/TiCl₄-AlEt₃/methyl-p-toluate catalyst. The rate of polymerization is directly proportional to the catalyst concentration. About 12% of the Ti in the catalyst is initially active at 50°; they are 1.4%, 8.8%, and 9.4% at 0°, 25°, and 70°, respectively. The changes of R_p with temperature parallels the variations in the active site concentration. The decline of R_p with time has second-order plots with slopes which are inversely proportional to the catalyst concentration, but the rate constants for these deactivations are nearly the same for decene and propylene polymerizations. These results strongly support a mechanism of deactivation involving two adjacent sites in the catalyst particle surfaces. The rate constants of propagation and of chain transfer to AlEt₃, the energetics for these processes, and MW and MW distribution data have been obtained.     

Polystyrene-supported metallocene catalysts for olefin polymerizations

Several kinds of polystyrene-supported metallocene catalysts were prepared and used in the polymerizations of propylene and ethylene with methylaluminoxane (MAO) as cocatalyst. It was found that these catalysts are stable even at 70°C. They display fairly high activities when the polymerizations are conducted at high temperatures.     

Magnesium chloride supported high mileage catalysts for olefin polymerization. XXI. Isospecific and regiospecific vanadium catalyst for propylene polymerization

Several CW–V catalysts were prepared by supporting VCl₄ on Mg Cl₂ with ethyl benzoate and CH–V catalysts prepared by reacting MgCl₂.ROH, phthalic anhydride, and VCl₄. These vanadium catalysts, activated with TEA (triethyl aluminum)/MPT (methyl-p-toluate) produce mainly (88–96%) refluxing n-heptane insoluble isotactic PP. The active site has $ k_{p,i} = 1580 \left( M {\rm s} \right)^{ - 1}, k_{tr,i}^{\rm A} = 2 \times 10^{ - 3} {\rm s}^{ - 1} , k_{tr}^{\rm H} = 3.8 \times 10^{ - 2} \left( {\rm torr} \right)^{ - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{ - 1}$ for the isospecific ones and $ k_{p,a} = 58 \left( M {\rm s} \right)^{ - 1} ,k_{tr,a}^{\rm A} = 3 \times 10^{ - 3} {\rm s}^{ -1}$ for the nonspecific sites. Catalyst of VCl₃ supported on MgCl₂ has comparable productivity as the VCl₄/MgCl₂ catalyst but catalyst of VCl₂ supported on MgCl₂ exhibit only one-ninth of the productivity. Extensive comparison has been made between the CW–V and the CW–Ti systems which revealed striking similarities between their polymerization behaviors. MgCl₂ exerts profound influence on the stereochemical control of the vanadium ion on its activity for monomer coordination and insertion.     

Magnesium chloride-supported,high-mileage catalysts for olefin polymerization. V. BET,porosimetry, and x-ray diffraction studies

The physical state of the material obtained during the various stages of preparation of a typical MgCl₂-supported, high-mileage propylene polymerization catalyst was studied by BET, mercury porosimetry, and x-ray diffraction techniques. The starting MgCl₂ and the substance after HCl treatment have negligible BET surface areas. Mercury porosimetry showed that they have large pores with radii > 200 nm which are probably crevices between MgCl₂ crystallites. The most pronounced physical changes occur during dry porcelain ball milling in the presence of ethyl benzoate. After 60 h or more of ball milling the material had a 5.1–7.3 m² g^?1 BET surface area, twice the pore surface area, and a smaller pore radius than before ball milling and a large reduction in crystallite sizes to almost ultimate dimensions. The crystallites were probably held together by complexation with ethyl benzoate in the form of large agglomerates. Subsequent reactions with p-cresol and triethyl aluminum had minor effects in further reduction of the MgCl² crystallite size but efficiently brokeup the agglomerates. The final refluxing with TiCl₄ increased the BET surface area to 110–150 m² g^?1 but may have increased the crystallite size somewhat due to cocrystallization of TiCl₃ and AlCl₃ with MgCl₂. There may have been only 8–10 crystallites in each catalyst particle. The surface structure of the catalyst resembled those of the classical Ziegler-Natta γ-TiCl₃·0.33 AlCl₃ catalyst.     

Magnesium-chloride-supported high-mileage catalysts for olefin polymerization. III. Electron paramagnetic resonance studies

Electron paramagnetic resonance (EPR) was used to study a MgCl₂-supported, high-mileage olefin polymerization catalyst. Anhydrous Toho MgCl₂ was the starting material. Treatment with HCl at an elevated temperature, ethyl benzoate by ball-milling, p-cresol, AlEt₃, and TiCl₄produced a catalyst that contained a single EPR observable Ti⁺³ species A, which was strongly attached to the catalyst surface, had a D_3h symmetry, and no other Ti⁺³ ion in an immediately adjacent site. Species A constitutes only 20% of all the trivalent titaniums; the remainder is EPR-silent and may be attributed to those Ti⁺³ ions that have adjacent sites occupied by one or more Ti⁺³ ions. Activation with preformed AlEt₃/methyl-p-toluate complexes produced a single Ti⁺³ species (C) with rhombic symmetry and displaying ²⁷Al superhyperfin splitting which has attributes for a stereospecific active site. This species is unstable under polymerization conditions and is transformed to another species with axial symmetry and solubilization. Both processes could lead to catalyst deactivation and loss of stereospecificity. Catalysts activated by AlEt₃ and methyl-p-toluate separately in various sequential orders produced a multitude of EPR-observable Ti⁺³ species with varying degrees of motional freedom deemed detrimental to stereospecific polymerization of α-olefins.     

Magnesium chloride supported catalysts for olefin polymerization. XIX. Titanium oxidation states,catalyst deactivation,and active site structure

A precise method for the determinations of Ti⁺², Ti⁺³ and Ti⁺⁴ was developed. The CW-procatalyst before activation contains mostly Ti⁺⁴ ions with 6% Ti⁺³ and 4% Ti⁺² ions. Activation with AlEt₃ alone at room temperature reduced all the titaniums to lower valence states consisting of 71% Ti⁺³ and 29% Ti⁺². Reduction is incomplete when methyl-p-toluate was present as external Lewis base during activation: at 25°C the distribution of Ti⁺⁴ : Ti⁺³ : Ti⁺² is 36% : 25% : 38%; the distribution at 50°C is 37% : 22% : 40%. Aging of the activated catalyst caused little or no changes in the distribution of [Ti⁺ⁿ]; whereas the catalytic activity decays rapidly with aging. The aged catalysts have polymerization activity comparable to the decreased activity of the catalyst during a polymerization. The [Ti⁺ⁿ] was determined for the CW-catalyst during the course of a decene polymerization; they were found to be Ti⁺⁴ : Ti⁺³ : Ti⁺² = 30% : 27% : 43%, which did not change with polymerization time. These results suggest that the reducibility of Ti⁺⁴ species by AlEt₃ or 3AlEt₃/MPT to different valence states is predicated by their structures. These species do not undergo further changes in their oxidation states during either aging or polymerization. Their decays probably involve nonreductive metathesis reactions like those known for zirconium alkyls. Possible structures for the stereospecific and nonspecific sites are proposed.     

Magnesium-chloride-supported high-mileage catalysts for olefin polymerization. II. Reactions between aluminum alkyl and promoters

The reactions between AlEt₃ and the modifiers, promoters, and coactivators of a typical magnesium-chloride-supported, high-activity propylene polymerization catalyst were studied. Infrared, MS analysis of the gas evolved, and GC–MS of the hydrolysis products for the reaction between AlEt₃ and p-cresol showed rapid and quantitative reactions with p-cresol either in the support or solution. The reaction products from AlEt₃ and esters were hydrolyzed, acidified, and dehydrated. The resulting carbonyl and olefinic compounds were identified by GC–MS. Proton and carbon nuclear magnetic resonance (NMR) techniques were also used to study these reactions. The expected intermediates were found in the PMR and CMR spectra. The mechanisms of reactions were proposed. The results of this study showed that when AlEt₃ and esters are used as coactivators reaction products that can significantly influence the performance of the catalyst are formed.     

Magnesium chloride-supported high-mileage catalysts for olefin polymerization XI. Determinations of poly(decene-1) molecular weight chain dimension and thermal transitions

Decene-1 was polymerized with the CW catalyst and fractionated by precipitation technique. Light-scattering and viscometric measurements on these fractions established the relationship [η] = 5.19 × 10^?3 M . The unperturbed mean square end-to-end distance is (〈R〉/M)^1/2 = (6.17 ± 0.34) × 10^?9. Light-scattering data is consistent with a relatively stiff molecule with length of L = 1.75 × 10^?5 cm for poly(decene-1) with MW = 397,000. Its mean square radius of gyration 〈R〉 is 2.79 × 10^?11 cm.² The ratio of L²/〈R〉 = 11 is close to the theoretical ratio of 12 for this kind of macromolecule.     

Magnesium chloride supported high mileage catalyst for olefin polymerization. VI. Definitive evidence against diffusion limitation

There has been continuing interest in the possible role of insoluble polymer products forming a barrier reducing rate of diffusion of monomer to the active site to cause decrease in rate of polymerization and broadening of molecular weight distribution. This possibility is more acute the higher the catalytic activity. We have now shown that diffusion limitation is unimportant for the MgCl₂ support high activity Ziegler–Natta catalyst by comparing its polymerization of propylene to isotactic insoluble polypropylene and of decene-1 to isotactic soluble polydecene. The rate constant of propagation is about eight times greater for propylene while the rate constants of termination, i.e, decay of R_p, are comparable for the two monomers.     

New organic supports for metallocene catalysts applied in olefin polymerizations

Nano-sized latex particles as organic supports for metallocenes applied in olefin polymerizations are introduced. The particles are functionalized with nucleophilic surfaces such as polyethylenoxide (PEO), polypropyleneoxide (PPO) or pyridine units allowing an immobilization of the metallocene catalysts via a non-covalent immobilization process. The latices are obtained by emulsion or miniemulsion polymerization with styrene, divinylbenzene as the crosslinker, and either PEO or PPO functionalized styrene or 4-vinylpyridine for surface functionalization. The supported catalysts, e.g. [Me₂Si(2MeBenzInd)₂ZrCl₂/MAO] on PPO containing latices or Cp₂ZrMe₂/([Ph₃C][B(C₆F₅)₄]) on pyridine functionalized materials were tested in ethylene polymerizations. Remarkably, high activities and excellent product morphologies were obtained. The influence of the degree of surface functionalization on activity and productivity was investigated. Furthermore, the fragmentation of the catalyst was studied by electron microscopy using bismuth-labeled latex particles or by fluorescence and confocal fluorescence microscopy using dye-labeled supports. Finally, a self-immobilizing catalyst/monomer system is presented. It is demonstrated that by using PEO-functionalized olefins, the metallocenes were immobilized on the monomers. Subjecting these mixtures to an ethylene copolymerization, again high activities and productivities as well as polyolefin beads with high bulk densities are observed, indicating that an extra supporting process for controlling the product size and shape of the polyolefins is not necessary for these monomers.