Some peculiarities in ESR spectra of titanium complexes in catalysts for isoprene polymerization in excess A1R3

It has been established that at low temperatures of TiCl₄+AOC catalyst preparation in solution (with Ti/Al1/15), ESR spectra exhibit rhombic anisotropy of the g-factor. Experiments with the sample having 61 % concentration of⁴⁷Ti isotopes suggest the formation of associates of Ti³⁺ with magnetic ordering, apparently due to the Jahn-Teller cooperative effect.

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TiCl₄+ AOC ( Ti/Al1/15) g-. ⁴⁷Ti (61%) Ti³⁺ , , -.

     

Observation of109Ag NMR spectra of supported silver catalysts

The first observation of¹⁰⁹Ag NMR spectra from Ag metal particles dispersed on alumina and silica, in some cases at Ag contents as low as 0.1 wt.% is reported. The Knight shifts and relaxation times are found to be typical for Ag bulk metal. The distortions of the Ag metal crystal lattice were found to contribute to¹⁰⁹Ag NMR line width. The estimation of Ag crystal size at which the metal-to-nonmetal transformation takes place was made from studies of samples with different size distribution of supported Ag particles.

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¹⁰⁹Ag , , 0,1 .%. . , ¹⁰⁹Ag . , , , -.

     

ESR investigation of the adsorption of13CO on CoO?MgO catalysts

Adsorption of CO enriched with¹³C isotope was investigated on a CoO–MgO catalyst containing 3 at.% Co. It is argued that the ESR signal with g_1,2=2.0054±0.0005; g₃=2.0020±0.0005; A₁=33 0e^*; A₂=11 0e; A₃=63 0e, appearing in the course of adsorption may not be ascribed to CO ₂ ^– or CO ₃ ^– anion radicals but should be attributed to surface X–CO complexes of a carbonyl-like structure.

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CO, C¹³, CoO–MgO, 3 .%-a Co. , g _1,2 ¹ =2,0054±0,0005, g₃=2,0020±0,0005, A₁=33 , A₂=11 A₃=63 , , - CO ₂ ^– CO ₃ ^– , X–CO , .

     

ESR identification of formation stages for TiCl3 particles in catalysts for isoprene polymerization

The analysis of ESR spectra from the system TiCl₄+ TIBA in solution under defreezing from 77 to 200 K permitted to identify formation stages of TiCl₃ particles. At first well-ordered Ti ₂ ⁷⁺ structures, and upon subsequent reduction [Ti ₂ ⁶⁺ ]_n are formed. It is the crystallization of the latter that produces TiCl₃ particles.

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TiCl₄+ 77 200 K TiCl₃: Ti ₂ ⁷⁺ , -[Ti ₂ ⁶⁺ ]_n, TiCl₃.

     

CO LMR spectrum of14N16O and its analysis with spectra of14N17O and14N18O

LMR spectra for v=1←0 transitions of¹⁴N¹⁶O in X²II_{1/2, 3/2} states were observed at 5.6 μm and 5.4 μm of CO laser. Introducing the advanced isotopic molecular constant scaling function to Hund’s case (a) diatomic structure model, these spectra were analyzed and fitted together with all reliable previous spectral data of¹⁴N¹⁶O as well as¹⁴N¹⁷O and¹⁴N¹⁸O. A full set of precise molecular parameters and their vibrational dependencies have been determined with much higher precision (1–2 orders for most parameters). Many of them have been obtained for the first time. Using isotopic scaling function, the molecular constants of¹⁴N¹⁷O and¹⁴N¹⁸O were deduced.     

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.     

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     

ESR studies of the state of Ti3+ and Ti2+ in Ti?Mg catalysts for olefin polymerization

ESR studies have revealed that in Ti–Mg catalysts after interaction with organoaluminium compounds, the Ti³⁺ ions formed are present mainly as TiCl₃ associates. Isolated Ti³⁺ ions of various types are also detected. Part of titanium ions is in the divalent state and provides an ESR signal after oxidation by water to the trivalent state in the form of Ti³⁺ ordered by cooperative Jahn-Teller interaction.

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, - , Ti³⁺ TiCl₃. Ti³⁺ . Ti³⁺ - -.

     

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.     

Soluble magnesium–titanium catalysts for ethylene polymerization. I

A study has been made of a catalyst system comprising the heptane-soluble magnesium and titanium compounds in combination with an organoaluminum compound for ethylene polymerization at a high temperature. The productivity for ethylene polymerization of the catalyst system, n-butylethyl magnesium (BEM)-2-ethyl hexanol (C₈H₁₇OH)-tetra-n-butoxytitanium[Ti(OBu)₄]/diethyl aluminum chloride (DEAC) is higher than for MgCl₂-Cl₂-C₈H₁₇ OHTi(OBu)₄/DEAC and much higher than MgCl₂-Ti(OBu)₄/DEAC. The nature of the three different catalyst systems have been discussed in comparison with experimental data on polymerization behavior and the data of the elemental and x-ray diffraction analysis of the solid products obtained from the reactions between the catalyst components.     

Comparison between ESR spectra and activities of bismuth tungstate catalysts

Electron spin resonance absorptions have been studied in bismuth tungstate catalysts with Bi/W ratios of 2/3, 1/1, 2/1 and 6/1. The first three systems exhibit a mean g value of 2.07±0.04 while the last one does not show any ESR signal. All the systems are diamagnetic. The signals at g=2.03–2.11 are attributed to oxygen ion-radicals chemisorbed (O ₂ ^– ) on W⁶⁺. An attempt has been made to correlate these whith the catalytic activities of the bismuth tungstates in the oxidation of propylene and 1-butene.

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Bi/W=2/3, 1/1, 2/1 6/1. g=2,07±0,04, . . g=2,03 2,11 - (O₂ ^–), W⁺⁶. 1-.

     

Studies of Ziegler-type catalysts for the polymerization of ethylene and propylene—III the polymerization of propylene with TiCl4-MgCl2-based catalysts

It has been confirmed that a reaction product of TiCl₄ and MgCl₂ is an extremely active catalyst for the polymerization of propylene. This catalyst is markedly different from the usual Ziegler-Natta TiCl₃ catalyst in the dependence of its reactivity on additions of aluminium alkyl co-catalyst and Lewis base.     

ESR characteristics of paramagnetic species on Pd/La2O3 catalysts

Reduction of Pd/La₂O₃ catalysts by H₂ and CO at room temperature leads to the formation of Pd⁺ ions stabilized in bulk and the subsurface layer. Hydrogen spillover seems to enhance the process. O ₂ ^– and (CO) ₂ ^– radicals are formed after adsorption of CO and O₂ at 295 K.

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Pd/La₂O₃ CO Pd⁺ . . CO O₂ (CO) ₂ ^– O ₂ ^– La₂O₃.

     

ESR and optical spectra of Cu2+:NH4Br

ESR and optical studies of Cu²⁺ ions doped in NH₄Br single crystals have been carried out at room temperature. A new centre has been identified for the crystal grown from acidic medium. The room temperature data reveal that Cu²⁺ ions go to interstitial sites having square planar coordination of four Br^? ions.     

Self-immobilized catalysts for ethylene polymerization based on various phenoxyimine titanium halide complexes

The kinetic features of ethylene polymerization on ten methylalumoxane-activated self-immobilized bis(phenoxyimine) complexes of titanium chloride of various structure containing oxyallyl functional groups were studied. The catalytic activity of the systems was determined in the temperature range 20–60 °C under ethylene pressure 0.4 MPa. The positions and structures of the oxyallyl group and substituents in the phenoxy groups of the complexes substantially change the activity of the catalytic systems based on these complexes, the rate of the self-immobilization of the catalysts on the polymer, and molecular weights and molecular weight distributions of the obtained polyethylenes.     

Studies of Ziegler-type catalysts for the polymerization of ethylene and propylene II The polymerization of ethylene with VOCl3-Et3Al2Cl3 (chlorinated activator) catalysts

VOCl₃-Et₃Al₂C1₃(chlorinated activator) catalysts have been employed for the polymerization of ethylene at T between 15 and 85° in n-hexane. Using butylperchlorocrotonate as the activator, the following catalyst efficiencies (g polymerization, hr, atmosphere ethylene in the cap gas) were achieved: 10^6,1 MFI = 0-00; 10^5,8, e.g. MFI = 1 0 (with 9 per cent H₂ present in the cap gas) and 10^6–9 MFI = 0?4 (with 44 mmole/1 styrene in the hexane medium). Reactions between the aluminium alkyl and the activator molecules produced other chlorinated species of high average activator effectiveness. The catalyst system could be reactivated by further additions of Et₃Al₂Cl₃. The minimum value of the polymerization propagation rate constant is estimated to be 10¹²²?6x10,461 cm³/mole sec.     

Bis(alkylphenylaminopyridinato) titanium dichlorides as ethylene polymerization catalysts

Four titanium complexes derived from 2-(2-ethylanilino)-, 2-(3,5-dimethylanilino)pyridine, 2-(4-n-butylanilino)- and 2-(2-t-butylanilino)pyridine were synthesized and characterized by spectroscopic methods. These complexes were used to catalyze the polymerization of ethylene in the presence of MAO as cocatalyst. The effect of the complex structures on the polymerization behavior was studied. All the alkylphenylaminopyridinato titanium complexes used in this study yielded higher molar masses than the unsubstituted bis(phenylaminopyridinato) titanium dichloride complex. Correspondingly, activities were lower and molar mass distributions were broader than those in the case of the unsubstituted bis(phenylaminopyridinato) titanium catalyst. The fluxional behavior of alkylphenylaminopyridinato titanium catalysts is probably the reason for the broad molar mass distributions. This might be due to the electron-donating effect from the alkyl substituent because the alkyl substituent enhances the active site isomerization rate.     

Olefin polymerization with titanium tetrachloride catalysts supported on surface-modified silica

After modification of silica with benzoyl chloride (BC) to obtain BC-modified SiO₂ (BC-SiO₂), BC-SiO₂/TiCl₄ and BC-SiO₂/BEM/TiCl₄ catalysts were prepared by treating the BC-SiO₂ with TiCl₄ directly or with butylethylmagnesium (BEM) followed by TiCl₄, respectively. During the modification, BC reacts with hydroxyl groups of silica. In this way the corresponding ester is anchored on the silica surface and the CO group is coordinated with Ti and/or Mg. In addition, BEM is converted to MgCl₂ in the reaction with TiCl₄. These catalysts have reasonable activities for ethylene or propene polymerization.     

Cyclopentadienyl titanium hydroxylaminato complexes as highly active catalysts for the polymerization of propylene

Half sandwich complexes of titanium bearing eta1 or eta2 bound nitroxide ligands are highly active catalysts for the polymerisation of propylene to high molecular weight atactic poly(propylene).