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Ring-Opening Polymerization (ROP) of lactides promoted by N,N-dialkylcarbamato complexes of group 4 metals
No full textN,N-Dialkylcarbamato Derivatives of Niobium and Tantalum as Precursors to Metal-Functionalized Silica Surfaces
No full textChemical implantation of Group 5 cations [Nb(III), Nb(V), and Ta(V)] has been carried out under mild conditions
by the reaction of N,N-dialkylcarbamato derivatives M(O2CNR2)n (M = Nb, Ta) with silanol groups
of amorphous silica, carbon dioxide, and secondary amine being released in the process. The amount of
supported cations depends on the metal and on the initial number of N,N-dialkylcarbamato ligands on M;
partial reduction to the +4 oxidation state occurs in the case of Nb(O2CNR2)5
Chemical Implantation of Group 4 Cations on Silica via Cyclopentadienyl- and N,N-Dialkylcarbamato Derivatives
No full textChemical implantation of Group 4 cations [Ti(III), Ti(IV), Zr(IV), Hf(IV)] has been carried out under mild
conditions by the reaction of polycyclopentadienyl- (MCpn; M = Ti, n = 3, 4; M = Zr, Hf, n = 4), mixed
cyclopentadienyl/N,N-dialkylcarbamato (MLx(O2CNEt2)y; M = Ti, L = Cp, C5Me5 (Cp*), x = 2, y = 1; M = Hf,
L = Cp, x = 1, y = 3), and N,N-dialkylcarbamato (M(O2CNR2)n, M = Ti, n = 3, R = iPr; M = Ti, Hf, n = 4,
R = Et; M = Zr, n = 4, R = iPr) derivatives, with the silanol groups of amorphous silica. Cyclopentadiene/
pentamethylcyclopentadiene and/or carbon dioxide and the secondary amine are released in the process.
The amount of implanted cations depends on the metal and on the ligands, the pentamethylcyclopentadienyl
complex being less reactive than the unsubstituted congener. The starting complexes and the final
products have been characterized by EPR or by 13C CP-MAS NMR spectroscopy
Solid catalyst component, catalyst comprising said solid component, and process for the (co)polymerization of alpha-olefins
No full textA solid catalyst component for the (co)polymn. of α-olefins having general formula (I): ZrnMA1xC1Mgp (I) wherein : M represents titanium (Ti), vanadium (V), or mixts. thereof; n is a no. ranging from 0.01 to 2; x is a no. ranging from 0.1 to 4; y is a no. ranging from 5 to 53; p is a no. ranging from 0 to 15; obtained by means of a process comprising putting at least one zirconium arene in contact with at least one metal compd. and, optionally, with at least one compd. of magnesium. Said solid catalyst component can be advantageously used as a solid component in a catalyst for the (co)polymn. of α-olefins. Said catalyst can be advantageously used in a process for the (co)polymn. of α-olefins
Ethylene Polymerization by Niobium(V) N,N-Dialkylcarbamates Activated with Aluminum Co-catalysts
No full textThe niobium N,N-dialkylcarbamates Nb(O2CNR2)n [n = 5, R = Me, 1, Et, 2; n = 4, R = Et, 3; n = 3, R = Et, 4], in combination with organoaluminum cocatalysts, were found to be active in the polymerization of ethylene. The effects of the main reaction parameters (solvent, ethylene pressure, time, temperature, cocatalyst, reactivator) on the polymerization reaction were investigated in detail. When 2 was used as precursor in combination with trimethylaluminum (TMA)-depleted MAO and 1,2-dichloroethane as reactivator, activity up to 110 kgpolyethylene molNb−1 h−1 bar−1 was ascertained and linear, high molecular weight polyethylene was produced. The catalytic activities related to the different precursors increase along the series 2 > 1 > 3 > 4. The 1:1 reaction of 2 with Al2Et3Cl3 proceeds via ligand exchange, giving the X-ray characterized mixed alkyl-carbamato derivative [Al3(μ-O2CNEt2)6Et2]Cl (6), in admixture with presumable species containing niobium in lower oxidation state. The latter and not the former seem to be responsible for directing the polymerization process, according to the evidence that 6, produced by ligand exchange between Al(O2CNEt2)3 and AlEt2Cl, is not active under analogous experimental conditions
Metal alkyl-arenes and processes for the preparation thereof
No full textMetal alkyl-arene, (η6-arene)2AlqXrRs (I) M (η6-arene)AlqXrRs (Ia) wherein: M = Zr, Hf, or mixts. thereof, preferably zirconium; arene represents a benzene, or a benzene 10 substituted with from 1 to 6 linear or branched C1-C6 alkyl groups, or mixts. thereof; X represents a halogen atom selected from chlorine, bromine, fluorine, iodine, preferably chlorine; R represents a linear or branched C1-C15 alkyl group; q is a no. ranging from 2 to 6, preferably 3 for a metal alkyl-arene I, 2 for a metal alkyl-arene Ia; r is a no. ranging from 1 to 20, preferably 9 for a metal alkyl-arene Ia, 6 for a metal alkyl-arene Ia; s is a no. ranging from 1 to 6, preferably 2. Said metal alkyl-arene can be advantageously used for the prepn. of solid components of catalysts for the (co)polymn. of α-olefins
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