Ziegler catalytic systems in cationic polymerization

The ternary catalytic system AlBuⁱ ₃-TiCl₄-CCl₄ initiates the cationic polymerization of isobutylene in toluene at room temperature, whereas the binary combinations of these components do not induce isobutylene polymerization. At low CCl₄ concentrations, the polymerization rates decrease sharply with time, and the quantitative yield of the polymer is achieved at an excess of CCl₄ with respect to the titanium and aluminum components. The molecular weights of the polymers range within 1300–4000, and the index of polydispersity, as a rule, does not exceed 2.7. The influence of the conditions of component mixing (order of addition, duration of exposure prior to addition of the third component) on the yield and molecular weight of the polymerization product was found. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 711–714, April, 1999.     

Investigation of the composition of Co(0) complexes in Ziegler type catalytic systems

Upon the interaction of cobalt chelate compounds (containing a carbonyl or imino group) with Al, Mg and Li organic compounds in aromatic hydrocarbons, Co(0) complexes are formed. The coordination sphere of Co(0) includes an arene molecule, an organometallic molecule and a chelate ligand of the initial cobalt complex.

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, , Al-, Mg-, Li- Co(0). Co(0) , lql .

     

ESR studies of methallyl monomers with redox systems

The effects of three types of free radical initiators (HO·, H₂N·, and H₃C·) from redox systems, have been studied for four types of methallyl monomers, by use of ESR with a flow system. The structure, the relative concentrations, and the steric conformations of the monomer radical intermediates have been derived from the ESR spectra. In the case of H₂N · and HO · addition to methallyl alcohol (MAA), methallyl amine (MAAm), and sodium methallyl sulfonate (SMAS), the ESR spectra of the reacting species are interpreted as monomer head radicals only (H₂N · and HO · are added to the monomer tail). Methallyl acetate (MAAc) with HO ·, is an exception, giving hydrogen abstraction to form an allyl type radical. This reaction may influence the polymerization behavior of MAAc. The methallyl monomers behave differently from the allyl monomers, where appreciable amounts of monomer tail radicals were found in addition to the head radicals which were the main species. For methallyl monomers, this may be due to steric hindrance caused by the two substituents on the α carbon. The CH₃ radicals add only to positively polarized reactive double bonds, i.e., in SMAS in this study, and allyl alcohol in a previous study. The coupling constants of β CH₂ protons vary considerably with the substituents. For β₁ protons, the coupling constants decrease in the order OH > CH₃ > NH₂. For β₂ protons (allyl hydrogen), the coupling constants decrease in the order CH₂OH > CH₂NH₂ > CH₂OCOCH₃Na, i.e., the constants decrease in the order of increased bulkiness of the groups. Some exceptions are interpreted as due to complex formation with Ti⁴⁺. The effects of pH of the reaction medium are largely those expected.     

Phosphorylation of heptafluorobutanol in the presence of metal chloride-ether catalytic systems

Catalytic activity of complex catalysts based on Li, Na, K, and Cs chlorides and polydentate ligands, viz., dibenzo-18-crown-6, mono-, di-, and tetraglymes, and poly(ethylene glycols) PEG-600 and PEG-1000 was examined in the phosphorylation of heptafluorobutanol with phosphorus oxychloride. The introduction of an organic ligand into a catalytic system leads to improvement in solubility of the salt used as a catalyst and to an increase in the reaction rate by a factor of 1.3—2.8. The catalytic systems based on LiCl and poly(ethylene glycols) proved to be most efficient.     

Kinetic and ESR studies on radical polymerization of methyl methacrylate in the presence of fullerene

The effect of fullerene (C₆₀) on the radical polymerization of methyl methacrylate (MMA) in benzene was studied kinetically and by means of ESR, where dimethyl 2,2′-azobis(isobutyrate) (MAIB) was used as initiator. The polymerization rate (R_p) and the molecular weight of resulting poly(MMA) decreased with increasing C₆₀ concentration ((0–2.11) × 10⁻⁴ mol/L). The molecular weight of polymer tended to increase with time at higher C₆₀ concentrations. R_p at 50°C in the presence of C₆₀ (7.0 × 10⁻⁵ mol/L) was expressed by R_p = k[MAIB]^0.5[MMA]^1.25. The overall activation energy of polymerization at 7.0 × 10⁻⁵ mol/L of C₆₀ concentration was calculated to be 23.2 kcal/mol. Persistent fullerene radicals were observed by ESR in the polymerization system. The concentration of fullerene radicals was found to increase linearly with time and then be saturated. The rate of fullerene radical formation increased with MAIB concentration. Thermal polymerization of styrene (St) in the presence of resulting poly(MMA) seemed to yield a starlike copolymer carrying poly(MMA) and poly(St) arms. The results (r₁ = 0.53, r₂ = 0.56) of copolymerization of MMA and St with MAIB at 60°C in the presence of C₆₀ (7.15 × 10⁻⁵ mol/L) were similar to those (r₁ = 0.46, r₂ = 0.52) in the absence of C₆₀. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2905–2912, 1998     

Polymerization of ethylene in the presence of novel single-site titanium phenolate catalytic systems

The polymerization of ethylene has been studied in the presence of novel catalytic systems based on various sterically hindered phenol precursor complexes of titanium containing grafted phenoxyammonium ligands. The presence of the grafted ammonium salt in the phenolate ligand leads to an increase in the activity of the catalyst and originates single-site catalytic systems. As evidenced by IR and ¹³C NMR studies and DSC measurements, the resulting polymers are linear, possess a narrow molecular-mass distribution (M _w/M _n = 2–4), and are characterized by a wide range of thermal properties.     

Hydroformylation of styrene in the presence of rhodium-2,4,6-trialkylphenyl-phosphole in situ catalytic systems

The hydroformylation of styrene was carried out in the presence of in situ rhodium catalysts containing 1-arylphospholes with different substituents in position 2 or 3. The aryl substituents were varied from phenyl to different sterically hindered 2,4,6-trialkylphenyls. The structures and Bird-indices (BIs) of the phospholes with different steric and electronic properties were determined by DFT calculations. High chemoselectivities towards hydroformylation, as well as regioselectivities towards the branched formyl regioisomer (2-phenyl-propanal) were obtained at a temperature of 40 °C. Similarly, high chemoselectivity was accompanied by a decreased regioselectivity at 100 °C. The phospholes with an exocyclic P-function in position 2 or 3 showed higher catalytic activity.     

Oligomerization of ethylene in the presence of heterogenized complex catalytic systems based on ionic liquid‐type substituted zirconium phenolates

The oligomerization of ethylene was investigated in the presence of novel catalytic systems consisting of alkylaluminium chlorides and heterogenized zirconium phenolates containing amino and imino hydrochloride substituents. It was determined that the composition of a synthesized oligomer and the activity or selectivity of the catalyst systems depend on various parameters such as the molar ratio of Zr:Al, the composition of alkylaluminium, the temperature of the reaction, the pressure of ethylene and the structure of zirconium phenolates. The results showed that C₄‐C₁₀ linear α‐olefins were obtained with high selectivity when diethylaluminium chloride was used as a co‐catalyst. The process of the separation of a synthesized oligomer from the catalyst containing amino and imino hydrochloride ionic liquid substituents was carried out by simple decantation, and after this process zirconium complexes could be reused several times for successive ethylene oligomerizations.     

Promotion by supports of the reactivity of propagating species of Ziegler supported catalytic systems for the polymerization and copolymerization of olefins

Kinetics for the polymerization of ethylene and the copolymerization of ethylene and propylene were studied by using highly effective heterogeneous metal organic catalysts produced by coating different organic and inorganic supports with the components of Ziegler systems. The activity of a supported Ziegler catalyst is characterized by the physical parameters of the support structure and its chemical nature. The active role of magnesium-containing supports was established for the formation and functioning of the propagating species on their surfaces. This role is expressed not only by an increase in the portion of transition metal included in the propagating species, compared with typical Ziegler catalysts, but also by an increase in the reactivity of the propagating species, change in the nature of the elementary processes for polymerization and copolymerization, including control of copolymerization constants, and modification of the molecular structure of the polymers and copolymers. It was shown that by choice of support it is possible to control the activity of the same catalytic system and characteristics of the structure and properties of the polymers it produces under identical polymerization conditions.     

Isotope effects in the oxidative functionalization of methane in the presence of rhodium-containing homogeneous catalytic systems

The combined oxidation of carbon monoxide, CH₄, and CD₄ by molecular oxygen (¹⁶O₂ and ¹⁸O₂) in aqueous solutions of trifluoroacetic acid labeled with ¹⁸O in the presence of rhodium and copper compounds and potassium iodide has been studied. The distribution of ¹⁸O in isotopically substituted products suggests that oxygen entered into the methane molecule from an active oxidizing agent. This oxidizing agent was produced from molecular oxygen under the action of reagents and catalytic system components. The kinetic isotope effect observed for methane (k _H/k _D=3.9?4.3) suggests a nonradical character of the step at which the oxygen atom passes from an active oxidizing agent to the methane molecule or its fragments—transition-state components of the corresponding step.     

Non-Cp type homogeneous catalytic systems for olefin polymerization

Development of homogeneous metallocene catalysts for olefin polymerization has been briefly overviewed prior to detailed examination of the chemistry of non-Cp type homogeneous catalytic systems. In order to emphasize the structural characteristics of non-Cp catalysts, they were initially classified according to the coordination numbers of 4-7 and then further subclassified according to the ligand types. Over 100 line drawings and 200 references are utilized.     

Electrochemical and ESR studies of the oxidation mechanism of pyrazine-di-N-oxides in the presence of methanol and its deuterated derivatives

The mechanism of oxidation of pyrazine-, 2,5-di-Me-, and 2,3,5,6-tetra-Me-pyrazine-di-N-oxides in the presence of methanol and its deuterated derivatives (CH₃OD, CD₃OD), i.e., compounds exhibiting the high energy of C-H bond dissociation, is studied by the methods of cyclic voltammetry, ESR electrolysis, and quantum chemical modeling. The study is carried out on a glassy carbon (GC) electrode in acetonitrile and on an Au electrode in solutions of different alcohols (methanol and its deuterated derivatives CH₃OD, CD₃OD). In alcohol solutions, the ESR spectra of radical cations and radical anions of the tested aromatic di-N-oxides are observed. The quantum chemical simulation of the reaction of the pyrazine-di-N-oxide radical cation with the MeOH C-H bond is carried out. The results obtained are explained within the framework of the E₁C₁E₂C₂ mechanism for a two-stage electrode process determined by the catalytic current of the second electrode stage. The overall two-electron catalytic oxidation of an alcohol within its complex with the pyrazine-di-N-oxide radical cation is proposed.