Silvano Bresadola

MgCl2/TiCl4/AlEt3 catalytic system for olefin polymerisation: a XPS study

Abstract A variety of techniques have been applied for 40 years in order to characterise Ziegler–Natta catalysts, however, few studies report the use of surface science technologies in an effort to understand surface structure, composition and chemical bonding in MgCl2 supported catalytic system. In this paper, the synthesis and the characterisation of the MgCl2/TiCl4/AlEt3 catalyst in controlled conditions is reported. Our aim is to understand (1) the activation process of the magnesium chloride support; (2) the interaction between the magnesium chloride support and TiCl4; (3) the chemical structure of the titanium active centres formed by treatment of the procatalyst, MgCl2/TiCl4, with the co-catalyst, TEA (triethylaluminium ); (4) which Tin+ species is active in ethene and propene polymerisations. These experiments were performed in conditions as similar, as possible, to the ones used for laboratory synthesis and polymerisation. The experiment consists of different steps: (1) preparation of δ-MgCl2 under strictly inert atmosphere as previously reported [1] ; (2) activation of δ-MgCl2 in a UHV chamber by means of argon ion sputtering; (3) exposure to TiCl4 vapours; (4) exposure to TEA. The surface composition was checked during the experimental steps by means of XPS technique.

Catalytic systems supported on MgCl2 doped with ZnCl2 for olefin polymerization

Abstract Ziegler–Natta type catalysts for α-olefin polymerization supported on MgCl2–ZnCl2 mixtures were prepared and the effect of Zn doping on the catalyst performance was investigated. The supports were obtained by reacting a blend of powdered metallic magnesium and zinc with an excess of 1-Cl-n-butane under UV-visible radiations. Their treatment with TiCl4 yielded procatalysts, which were fully characterized and tested in propylene and ethylene polymerization. The effects of ZnCl2 as doping salt in MgCl2 supports were also investigated in dependence on the zinc concentration. In particular, in the propylene polymerization carried out at 70°C and 2 atm, the catalyst increased its activity on increasing the ZnCl2 content in the procatalyst up to 0.73 wt.% expressed as zinc. Going to a higher ZnCl2 content, it was found that the activity decreases. The isotactic index of polypropylene produced increases only slightly on increasing the zinc content up to a weight percentage of 0.73, but going to a higher zinc chloride content, the isotacticity decreases. In comparison with a reference commercial catalyst, the polydispersity was found to be very little affected, at least in the range of ZnCl2 content that we had investigated. The ZnCl2 doping was shown to cause a notable effect on the activity of the catalyst also in the ethylene polymerization (T=70°C, P=2 atm). In fact, in ethylene polymerization, a catalyst based on a support containing a doping amount of 0.73 wt.% of zinc exhibited an activity 2.5 times greater than that shown by the reference catalyst.

High yield MgCl2-supported catalysts for propene polymerization: effects of ethyl propionate as internal donor on the activity and stereospecificity

A series of MgCl 2 -supported Ziegler-Natta type catalysts containing different amounts of ethyl propionate (EP) as internal donor were prepared and tested in the propene polymerization in order to evaluate their activity and stereospecificity. These catalysts were obtained by treating chemically activated MgCl 2 supports bearing variable ethyl propionate contents with TiCl 4 . The supports and the derived catalysts so prepared were characterized by elemental analysis, XRD and FT-IR techniques. The polymerization tests were carried out at 70°C and 7.5 atm using dimethoxydiphenylsilane as external donor and hydrogen as chain transfer reagent. A correlation between the procatalyst structure and composition and their activity as well as stereoselectivity was obtained. On processing the obtained results it was possible to evaluate the trend of both the activity and the stereoselectivity on the simultaneous changes of the Ti/Mg, Ti/EP and EP/Mg molar ratios. Actually, these catalysts show the best performance with a composition corresponding to the following molar ratios: Ti/Mg = 0.03, Ti/EP = 0.14 and EP/Mg = 0.27. Finally, these studies confirm again that the active supports and the procatalysts are essentially based on a Cl-Mg-Cl chain structure model.

Synthesis and crystal structure of the MgCl2(CH3COOC2H5)2·(CH3COOC2H5) adduct

The reaction of α-MgCl2 with boiling ethyl acetate affords MgCI2(CH3COOC2H5)2·(CH3COOC2H5), which is obtained as crystals suitable for X-ray analysis only from the mother liquor. M=315.5, orthorhombic, space group P21221 (No. 18), a=25.077(3), b=8.616(1), c=7.345(1) A, V=1587.0(3) A3, Z=4, Dx=1.32 g cm−3,λ A(Mo Kα)=0.71069 A, μ=4.17 cm−1, F(000)=664, T=298 K, observed reflections: 1667, R=0.059 and Rw=0.069. The structure is composed of polymeric chains of MgCl2(CH3COOC2H5)2 and the ethyl acetate molecules occupy a mutually trans position.

MgCl2‐supported catalysts for the propylene polymerization: effects of triethers as internal donors on the activity and stereoselectivity

The effects of triethers as internal donors on the activity and stereoselectivity of MgCl 2 -supported Ziegler-Natta type catalysts in the propylene polymerization were studied. In particular, we prepared and fully characterized some procatalysts of the type δ-MgCl 2 /ID/TiCl 4 , where ID are internal donors such as di(ethyleneglycol) diethyl ether (DEGDEE) and di(ethyleneglycol) dimethyl ether (DEGDME). By aging these procatalysts with AlEt 3 (cocatalyst) we obtained δ-MgCl 2 /ID/TiCl 4 /AlEt 3 catalytic systems, which were tested in the propylene polymerization in order to evaluate their catalytic performance. All polymerizations were carried out in the absence of both external donors (ED) and hydrogen. The productivity and the properties (M w , M n , M w /M n , and isotacticity index (I.I.)) of the polymers obtained were determined and the results compared with those obtained by using catalysts either lacking an internal donor or with ethyl benzoate as internal donor. The comparison pointed out that the presence of triethers lowers the productivity of the catalysts and increases their stereoselectivity. Polydispersity is also remarkably enhanced suggesting that a multiplicity of active catalytic sites characterized by different environments is present.

Crystal structure of a magnesium chloride-ethylformate adduct

The crystal structure of [MgCl 2 (HCOOC 2 H 5 ) 2 ] 3 , obtained by slow crystallization at room temperature from a solution of α-MgCl 2 in dry ethyl formate, has been determined by X-ray diffraction. The structure was solved by direct and Fourier methods and refined by least-squares technique. This polymeric adduct is formed by asymmetric units having the formula [MgCl 2 (HCOOC 2 H 5 ) 2 ] 3 and crystallizes in an orthorhombic cell, space group Pbca (no. 61), a = 20.96(2) A, b = 37.02(2) A, c = 9.518(4) A, V= 7385(8) A 3 , Z = 8 and d c = 1.31 g cm #753

A kinetic investigation of ethyl formate elimination from the [MgCl2(HCOOC2H5)2]n adduct using thermoanalytical data

Abstract A kinetic investigation of ethyl formate elimination from the polymeric adduct [M g Cl 2 (HCOOC 2 H 5 ) 2 ] n (V. Di Noto, G. Bandoli, S. Bresadola, R. Zannetti and M. Viviani, submitted to Z. Kristallogr) has been carried out under a rigorously inert atmosphere at reduced pressure by means of thermogravimetric measurements. The elimination appears to occur in two steps which agree well with rate laws of the first and second order of reaction, respectively. The activation energies of these elimination reactions have been also determined and a reaction mechanism is proposed.

Rate study on the redistribution reactions of organotin compounds

Abstract The redistribution reactions between R 3 SnMe (R = Me, Et, n–Pr, iso–Pr, Bu) and Me 2 SnCl 2 in methanol, have been investigated. The reactivity order is: Me>Et>n–Pr>Bu>iso–Pr. The second order observed rate constants and the activation parameters are reported. A reaction mechanism involving the electrophilic attack on the carbon centre of the methyl group by the Me 2 Sn 2+ species, assisted by the solvent, is proposed.

Determination of ethyl acetate, acetone or ethanol in magnesium chloride used as a Ziegler-Natta catalyst support by Fourier transform infrared attenuated total reflectance spectrometry

Fourier transform infrared spectrometry with attenuated total reflectance was used for the determination of ethyl acetate, acetone and ethanol, intercalated or co-ordinated, in inorganic matrices such as magnesium chloride. The spectra were recorded directly on solutions obtained by dissolving the inorganic supports in ethanol or water. The proposed method is sensitive and rapid and appears to be very reliable when compared with other methods, such as solvent extraction followed by gas chromatographic or ultraviolet spectrophotometric analysis.

A three-membered ring formed through internal metallation in a diphenylmethylphosphine—platinum(II) complex

Abstract Prolonged treatment of cis-(MePh2P)2PtCl2 with a large excess of 1-Li-2-C6H5-1,2-B10C2H10 in ether gives the internally metallated complex cis-1-[(MePh2P) Pt(PC H2Ph2)]-2-C6H5-1,2-(σ-B10C2H10) in which a methyl group of one coordinated phosphine is involved in the ring formation.