Propylene polymerization with catalysts containing divalent titanium

The behavior in propylene polymerization of divalent titanium compounds of type [η⁶-areneTiAl₂Cl₈], both as such and supported on activated MgCl₂, has been studied and compared to that of the simple catalyst MgCl₂/TiCl₄. Triethylaluminium was used as cocatalyst. The Ti–arene complexes were active both in the presence and in the absence of hydrogen, in contrast to earlier reports that divalent titanium species are active for ethylene but not for propylene polymerization. ¹³C-NMR analysis of low molecular weight polymer fractions indicated that the hydrogen activation effect observed for the MgCl₂-supported catalysts should be ascribed to reactivation of 2,1-inserted (“dormant”) sites via chain transfer, rather than to (re)generation of active trivalent Ti via oxidative addition of hydrogen to divalent species. Decay in activity during polymerization was observed with both catalysts, indicating that for MgCl₂/TiCl₄ catalysts decay is not necessarily due to overreduction of Ti to the divalent state during polymerization. In ethylene polymerization both catalysts exhibited an acceleration rather than a decay profile. It is suggested that the observed decay in activity during propylene polymerization may be due to the formation of clustered species that are too hindered for propylene but that allow ethylene polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2645–2652, 1997     

State of titanium in supported titanium-magnesium catalysts for propylene polymerization

The oxidation state of titanium and the coordination state of Ti³⁺ ions in TiCl₄/D₁/MgCl₂ (D₁ is a phthalate) supported titanium-magnesium catalysts (TMCs) after the interaction with an AlEt₃/D₂ cocatalyst (D₂ is propyltrimethoxysilane or dicyclopentyldimethoxysilane) were studied by chemical analysis and EPR spectroscopy. Different oxidation state distributions of titanium ions were observed in the activated catalyst and mother liquor: Ti³⁺ and Ti²⁺ ions were predominant in the activated catalyst and mother liquor, respectively. The effects of interaction conditions (reaction temperature and time and Al/Ti and D₂/Ti molar ratios) of TMCs with the cocatalyst on the state of titanium in activated samples were studied. The interaction of TMCs with the cocatalyst decreased the titanium content and caused the appearance of aluminum in the activated sample, which was most clearly pronounced at a temperature of 25°C and occurred within the first 10 min of treatment. An increase in the temperature to 70°C and an increase in the interaction time to 60 min only slightly affected the concentrations of titanium and aluminum. The presence of D₂ as a cocatalyst constituent facilitated the removal of titanium compounds and restricted the adsorption of aluminum compounds on the catalyst surface. The main fraction of titanium consisted of Ti³⁺ ions (62–89%), and the rest was Ti⁴⁺ ions (22–35%) under mild interaction conditions (25°C; Si/Ti = 25) or Ti⁴⁺ (0–21%) and Ti²⁺ (9–21%) ions under more severe conditions (50 or 70°C; Si/Ti from 0 to 5). According to EPR-spectroscopic data, at D₂/Ti from 1 to 5, Ti³⁺ ions mainly occurred as associates, whereas they occurred as isolated ions at D₂/Ti = 25. The initial and activated catalysts were similar in activity in the reaction of propylene polymerization, and titanium compounds, which were removed from the catalyst upon interaction with AlEt₃/D₂, were inactive in this process.     

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.     

Highly active supported catalysts for olefin polymerization: Preparation and characterization of the catalyst

With use of the support prepared by the reaction¹ of a Grignard reagent with reaction mixture of AlCl₃ and CH₃Si(OC₂H₅)₃, an immobilized active stereospecific titanium catalyst was prepared by the three-step treatment of the support, first with TiCl₄, second with ethylbenzoate, and third with TiCl₄ again. The catalyst was also prepared by the two-step treatment of the support, with the mixture of TiCl₄ and ethylbenzoate, and with TiCl₄. Solids obtained in each step of the catalyst preparation were characterized by elemental and IR analysis, and their activities for propylene polymerization were determined with triethylaluminum as a cocatalyst under an atmospheric propylene pressure for 1 h at 60°C. The experimental data support the idea that both TiCl₄ and ethylbenzoate as donors are immobilized on the surface of the active stereospecific catalyst without any interaction between them.     

Supported titanium‐magnesium catalysts for ethylene polymerization: A comparative study of catalysts containing isolated and clustered titanium ions in different oxidation states

Supported titanium–magnesium catalysts (TMC) comprising isolated and clustered titanium ions in different oxidation states, which are obtained using titanium compounds of different composition (TiCl₄, TiCl₃?nDBE (DBE – dibutyl ether), [η⁶–BenzeneTiAl₂Cl₈]), were synthesized and tested in ethylene polymerization. The state of titanium ions was studied by the ESR method both for the procatalysts and after their interaction with triisobutilaluminum. For identification of ESR‐silent Ti³⁺ ions and Ti²⁺ ions, special procedures of additional catalyst treatment with pyridine, water, and chloropentafluorobenzene were used to obtain Ti³⁺ ions that are observable in ESR spectra. In distinction to numerous earlier works performed with the TiCl₄/MgCl₂ catalyst comprising after the interaction with AlR₃ the Ti³⁺ surface compounds both as isolated ions and clusters (ESR‐silent), this work considers the [η⁶–BenzeneTiAl₂Cl₈]/MgCl₂ catalyst (TMC‐3) comprising mainly the isolated Ti²⁺ ions and a new catalyst TMC‐4 obtained by treating the TMC‐3 with chloropentafluorobenzene. This catalyst comprises only the isolated Ti³⁺ ions both before and after the interaction with triisobutylaluminum. It was shown that in spite of sharp distinctions between the catalysts under consideration concerning titanium oxidation state and the ratio of isolated Ti³⁺ ions to clustered ones, all these catalysts produce polyethylenes with similar molecular weights and molecular‐weight distributions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6362–6372, 2009     

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.     

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.     

Vanadium complex with tetradentate [O,N,N,O] ligand supported on magnesium type carrier for ethylene homopolymerization and copolymerization

Immobilization of 1,2‐cyclohexylenebis(5‐chlorosalicylideneiminato)vanadium dichloride on the magnesium support obtained in the reaction of MgCl₂·3.4EtOH with Et₂AlCl gives a highly active precursor for ethylene homopolymerization and its copolymerization with 1‐octene. This catalyst exhibits the highest activity in conjunction with MAO, but it is also highly active with AlMe₃ as a cocatalyst. On the other hand, when combined with chlorinated alkylaluminum compounds, Et₂AlCl and EtAlCl₂, it gives traces of polyethylene. Moreover, its catalytic activity is strongly affected by the reaction temperature: it increased with rising polymerization temperature from 20 °C to 60 °C. The kinetic curves obtained for the supported vanadium catalyst, in contrast to its titanium analogue, are of decay type, yet the reduction in the polymerization rate is rather moderate in the early stages of polymerization, and then it is relatively very slow. The vanadium catalyst gives copolymers at a lower yield than the titanium one does, but with the significantly higher 1‐octene content. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 471–478, 2010     

Studies on Ziegler-Natta catalysts. Part IV. Chemical nature of the active site

The determination of the number of sites active in the polymerization of ethylene on the surface of α-TiCl₃–Al(CH₃)₃ dry catalysts leads to the conclusion that this number is small in comparison to the total surface of the catalyst. Qualitatively this conclusion is also reached by two other independent methods. Infrared spectra of the catalyst before and after polymerization do not show a change in the type of bonds present in the surface. Electron microscopy proves that no active sites are formed on the basal plane of the α-TiCl₃ which constitutes 95% of the total surface. The results strongly favor the lateral faces of α-TiCl₃ as the preferred location of active centers. The lateral faces contain chlorine vacancies and incompletely coordinated titanium atoms. This must then be the essential conditions for the formation of active centers. The propagation of the polymer chain has been repeatedly shown to follow an insertion mechanism. The active site, therefore, necessarily contains a metal–carbon bond. The study of catalysts derived from TiCl₃CH₃ leads to the conclusion that a Ti? C bond on titanium of incomplete coordination is the active species in these cases. The alkylation of surface titanium atoms was proven to be an intermediate step in the catalyst formation from TiCl₃ and AlR₃. Survival of titanium–alkyl bonds on the lateral faces, where titanium atoms are incompletely coordinated explains best, in the light of our data, the activity of Ziegler-Natta catalysts. Coordination of aluminum alkyl compounds in or around the active center probably complicates the structure of the active centers.     

Emulsion polymerization of styrene. III. Effect of Ti(III) and Cl(1) on the polymerization of styrene initiated by potassium persulfate

The emulsion polymerization of styrene initiated by potassium persulfate catalyzed by Ti⁺³ ions was studied. Two sources of Ti⁺³ ions were used: the titanium trichloride and titanium sulfate. It was found that the titanium ions used in conjunction with potassium persulfate decrease both the reaction rate and the average molecular weight. An even greater drop of reaction rate was noted when chlorine anions (TiCl₃) were present. The presence of these ions had a stabilizing effect on the polydispersity.     

Ti complex catalysts including thiobisphenoxy group as a ligand for olefin polymerization

Titanium complexes were prepared by the reaction of 2,2′-thiobis(6-tert-butyl-4-methylphenol) (TBP) with TiCl₄ or Ti(OPrⁱ)₄. These complexes in combination with methyalumoxane as cocatalyst are highly active towards ethylene and propene, giving polymers having high molecular weights. The polymerization activities for ethylene and propene are comparable to those of Cp₂ZrCl₂-MAO catalyst. Polypropylene obtained had extremely high molecular weight (Mw>6 million) and low regioregularity (30% of head-to-head and tail-to-tail linkages). Highly syndiotactic polystyrene was obtained with these catalysts with activity up to 27 kg polymer per g Ti and hour. Copolymerization of styrene with ethylene gave highly alternating copolymer with isotactic styrene units. These catalysts are also active toward both conjugated and nonconjugated dienes such as butadiene and 1,5-hexadiene. Polybutadiene had mainly cis-1,4-structure (98%). The structure of poly(1,5-hexadiene) is rather complicated, which is quite different from that prepared with heterogeneous TiCl₃ catalysts.     

The roles of oxidation state,Lewis acid cocatalyst and solvent polarity in activating titanium compounds for olefin polymerization

The polymerization activity of the following three catalyst systems towards ethylene has been investigated and compared: 1) methyltitanocene chloride-Me₂AlCl 2) η³-allyltitanocene-Me₂AlCl and 3) titanium dichloride tetrahydrofuranate-Me₂AlCl. The first two catalysts formed homogeneous phases and produced linear polymer; the last catalyst functioned in a heterogeneous medium and formed crosslinked polymer. The titanium(IV) catalyst was about 30 times more active than the titanium(III) system and the titanium(II) catalyst on MgCl₂ could be made 8 times more active than the titanium(IV) system. A novel mechanism is proposed to explain the behavior and activity of the titanium(II) system.     

Polymerization of vinyl chloride catalyzed by a titanium complex with an anionic oxygen tripod ligand

Poly(vinyl chloride) (PVC) was prepared using a titanium complex with an anionic oxygen tripod ligand [CpCo{P(O)(OEt)₂}₃]⁻ () as catalyst and methyl aluminoxane (MAO) as cocatalyst. The polymerization behavior was compared with that of pentamethyl cyclopentadienyl titanium trichloride (Me₅CpTiCl₃). It is observed that L_OEtTiCl₃ can polymerize vinyl chloride with activity comparable to that of Me₅CpTiCl₃. The PVC samples prepared with L_OEtTiCl₃/MAO exhibit bimodal molecular weight distribution and the fraction of high molecular weight peak decreases with polymerization temperature. The microstructure and thermal decomposition of the PVC obtained were studied. Five types of structural defect were detected by ¹H-NMR. Only saturated structural defects are found at low polymerization temperature, but at high polymerization temperature unsaturated structural defects, possibly resulting from dehydrochlorination of the saturated structural defects, appear as well. No head-to-head structural defect is observed. ¹³C-NMR shows that the PVC prepared by L_OEtTiCl₃ has an atactic stereostructure. Compared with the PVC from radical polymerization and anionic polymerization, the PVC samples prepared with L_OEtTiCl₃ show improved thermal stability.     

Ti7Cl16 und Ti7Br16 sowie weitere Untersuchungen mit Titanhalogeniden. Al2X6 als Komplexbildner

Ti₇Cl₁₆ and Ti₇Br₁₆ and Further Investigations with Titanium Halides. Al₂X₆ as a Complex Forming Agent TiCl_3,s can be transported with Al₂Cl₆ via TiAlCl_6,g in a temperature gradient. The equilibrium of this reaction was studied by mass spectroscopy. There is no indication of the existence of a TiAl₂Cl₉ molecule as assumed in the literature. β-TiBr₃ was prepared from the elements in the presence of the transporting agent Al₂Br_6,g. The transport of TiCl₂ with Al₂Cl_6,g involves, as an important step, the disproportionation which is favoured by the reaction of Ti with the glass wall. If the disproportionation is made impossible by addition of Ti the novel compound Ti₇Cl₁₆ is obtained. Independent of Ti₇Cl₁₆, a phase TiCl_{(2 + x)} with a broad range of homogeneity exists. The compound Ti₇Br₁₆, being isostructural with Ti₇Cl₁₆, was also prepared. Results of magnetic measurements and observations on the thermal decomposition of the compounds are reported.     

1‐Hexene Polymerization over Supported Titanium–Magnesium Catalyst: The Effect of Composition of the Catalytic System and Polymerization Conditions on Temperature Dependence of the Polymerization Rate

The effect of temperature on the rate of 1‐hexene polymerization over supported titanium–magnesium catalyst of composition TiCl₄/D₁/MgCl₂ + AlR₃/D₂ (D₁ is dibutyl phthalate, D₂ is propyltrimethoxysilane, and AlR₃ is an organoaluminum cocatalyst) is studied. The unusual data that the polymer rate decreases when temperature is increased from 30 to 70 °C are obtained. The 1‐hexene polymerization rate and the pattern of changes in polymerization rate with temperature depend on a combination of factors such as cocatalyst (AlEt₃ or Al(i‐Bu)₃) and presence/absence of hydrogen and an external donor in the reaction mixture. These factors differ in their effects on catalytic activity at different polymerization temperatures, so the temperature coefficient (E_eff) values calculated using the Arrhenius dependence of the polymerization rate on polymerization temperature vary greatly. The “normal” Arrhenius plot where polymerization rate increases with temperature is observed only for polymerization with the Al(i‐Bu)₃ cocatalyst in the presence of hydrogen and without an external donor. Formation of high‐molecular‐weight polyhexene at low polymerization temperatures results in catalyst particle fragmentation, which may additionally contribute to the increase in polymerization rate as polymerization temperature is reduced.     

Monomer-Isomerization polymerization. XXVIII. Catalytic activity of transition metals and alkylaluminums in monomer-isomerization polymerization of 2-butene

Monomer-isomerization polymerization of cis-2-butene (c2B) with Ziegler–Natta catalysts was studied to find a highly active catalyst. Among the transition metals [TiCl₃, TiCl₄, VCl₃, VOCl₃, and V (acac)₃] and alkylauminums used, TiCl₃? R₃Al (R = C₂H₅ and i-C₄H₉) was found to show a high-activity for monomer-isomerization polymerization of c2B. The polymer yield was low with TiCl₄? (C₂H₅)₃Al catalyst. However, when NiCl₂ was added to this catalyst, the polymer yield increased. With TiCl₃? (C₂H₅)₃Al catalyst, the effect of the Al/Ti molar ratio was observed and a maximum for the polymer yields was obtained at molar ratios of 2.0–3.0, but the isomerization increased as a function of Al/Ti molar ratio. The valence state of titanium on active sites for isomerization and polymerization is discussed.     

Olefin polymerization and copolymerization by complexes bearing [ONNO]‐Type salan ligands: Effect of ligand structure and metal type (titanium,zirconium, and vanadium)

A series of novel titanium(IV) complexes bearing tetradentate [ONNO] salan type ligands: [Ti{2,2′‐(OC₆H₃‐5‐t‐Bu)₂‐NHRNH}Cl₂] (Lig¹TiCl₂: R = C₂H₄; Lig²TiCl₂: R = C₄H₈; Lig³TiCl₂: R = C₆H₁₂) and [Ti{2,2′‐(OC₆H₂‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴TiCl₂) were synthesized and used in the (co)polymerization of olefins. Vanadium and zirconium complexes: [ M{2,2′‐(OC₆H₃‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴VCl₂: M = V; Lig⁴ZrCl₂: M = Zr) were also synthesized for comparative investigations. All the complexes turned out active in 1‐octene polymerization after activation by MAO and/or Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄]. The catalytic performance of titanium complexes was strictly dependent on their structures and it improves for the increasing length of the aliphatic linkage between nitrogen atoms (Lig¹TiCl₂ << Lig²TiCl₂ < Lig³TiCl₂) and declines after adding additional tert‐Bu group on the aromatic rings (Lig³TiCl₂ < Lig⁴TiCl₂). The activity of all titanium complexes in ethylene polymerization was moderate and the properties of polyethylene was dependent on the ligand structure, cocatalyst type, and reaction conditions. The Et₂AlCl‐activated complexes gave polymers with lover molecular weights and bimodal distribution, whereas ultra‐high molecular weight PE (up to 3588 kg mol^?1) and narrow MWD was formed for MAO as a cocatalyst. Vanadium complex yielded PE with the highest productivity (1925.3 kg mol_v^?1), with high molecular weight (1986 kg mol^?1) and with very narrow molecular weight distribution (1.5). Copolymerization tests showed that titanium complexes yielded ethylene/1‐octene copolymers, whereas vanadium catalysts produced product mixtures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2111–2123     

Mesoporous silica as nanoreactor for olefin polymerization

Various metal-containing MCM-41(Metal-MCM-41) were prepared by the post-synthesis method with organometallic compound or alkoxide and used as a nanoreactor for olefin polymerization. Strong Lewis acid sites generated on Metal-MCM-41 could activate the metallocene catalyst rac-ethylene(bisindenyl)zirconium dichloride (rac-Et(Ind)₂ZrCl₂) effectively, resulting in the formation of active sites for polymerizations of ethylene and propylene. This suggests that Metal-MCM-41 is useful as a heterogenized cocatalyst. Ti-, Zr-, Hf-, Mn- and Zn-MCM-41 combined with alkylaluminum (without metallocene catalyst) were also found to provide isotactic polypropylene with a broad molecular weight distribution. By analyzing the characteristics of polypropylenes both inside and outside the mesopores, the polymerization behavior under extreme confined geometry was discussed.     

Probing the Coordinative Unsaturation and Local Environment of Ti3+ Sites in an Activated High‐Yield Ziegler–Natta Catalyst

The typical activation of a fourth generation Ziegler–Natta catalyst TiCl₄/MgCl₂/phthalate with triethyl aluminum generates Ti³⁺ centers that are investigated by multi‐frequency continuous wave and pulse EPR methods. Two families of isolated, molecule‐like Ti³⁺ species have been identified. A comparison of the experimentally derived g tensors and ^35,37Cl hyperfine and nuclear‐quadrupole tensors with DFT‐computed values suggests that the dominant EPR‐active Ti³⁺ species is located on MgCl₂(110) surfaces (or equivalent MgCl₂ terminations with tetra‐coordinated Mg). O₂ reactivity tests show that a fraction of these Ti sites is chemically accessible, an important result in view of the search for the true catalyst active site in olefin polymerization.     

Copolymerization of poly(propylene) macromonomer and ethylene with metallocene catalysts

Copolymerization of ethylene and poly(propylene) macromonomer(PPM) with Mn⇋710 was conducted with the (t-butylamido)dimethyl(tetramethyl-η⁵-cyclopentadienyl)silanetitanium dichloride(CGC-Ti), ethylenebis(tetrahydroindenyl)zirconium dichloride(Et[IndH₄]₂ZrCl₂), bis(cyclopentadienyl)zirconium dichloride(Cp₂ZrCl₂) and bis(cyclopentadienyl)titanium dichloride(Cp₂TiCl₂) catalysts using methylaluminoxane as cocatalyst. From the detail analysis of resulting copolymers by DSC, IR and ¹³C NMR, it was proved that PPM is copolymerized with ethylene to give poly(ethylene-co-PPM). The ability of incorporating PPM in the copolymer was found to increase in the following order: Cp₂ZrCl₂ «Cp₂TiCl₂ < Et[IndH₄]₂ZrCl₂ «CGC-Ti.