Silicoaluminates as “support activator” systems in olefin polymerization processes

In this work we report the polymerization behaviour of natural clays (montmorillonites, MMT) as activating supports. These materials have been modified by treatment with different aluminium compounds in order to obtain enriched aluminium clays and to modify the global Brönsted/Lewis acidity. As a consequence, the intrinsic structural properties of the starting materials have been changed. These changes were studied and these new materials used for ethylene polymerization using a zirconocene complex as catalyst. All the systems were shown to be active in ethylene polymerization. The catalyst activity and the dependence on acid strength and textural properties have been also studied. The behaviour of an artificial silica (SBA 15) modified with an aluminium compound to obtain a silicoaluminate has been studied, but no ethylene polymerization activity has been found yet

Titanium-catalyzed synthesis of polymyrcene and polyanethol and application as sustainable additives for poly(lactic acid)

The replacement of fossil-derived plastics with those obtained from bio-based resources, which present suitable performance to be employed as commodity plastics is currently an important field of research, given the urgent need to transition from a fossil-based to a more sustainable economy. In this context, this work is focused on the application of a catalytic system based on silsesquioxane-cyclopentadienyl titanium complexes for the preparation of bio-based polymers, which can be used as additives to improve the poor material properties of a biodegradable polymer such as poly(lactic acid) (PLA). These titanium complexes, when activated with methylaluminoxane or with triflate salts, are shown to be capable of the polymerization of two bio-based monomers: myrcene and anethole. It is notable that polymerizations with these two distinct monomers take place through different mechanisms. The resulting polymyrcene (PMy) and polyanethol (PAN) have been applied as modifiers for PLA. Binary blends of PMy and PLA exhibited a considerable decrease in Tg and the promotion of PLA crystallization for a PMy content below 15 wt%. The mechanical properties of the PLA/PMy blends also displayed plasticization, with a decrease in the elastic modulus and enhanced plasticity, which resulted in less fragile systems compared to pure PLA. Morphological analysis has indicated a partially miscible, phase-separated system with micron-sized domains. In contrast, PAN completely inhibited PLA crystallization and the PLA/PAN blends were immiscible, but well-dispersed, a phase-separated system was obtained in solvent-casting film preparation with very small PAN domains. The blends showed higher tensile modulus than pure PLA and an absence of plastic behaviour, resulting in more fragile systems upon the addition of PAN to PLA

Prácticas de laboratorio avanzado en últimos cursos de grado

Resumen de los autoresGrado en Química (Universidad de Alcalá de Henares)Hemos desarrollado unas prácticas de laboratorio en una asignatura de Química Avanzada. El planeamiento es combinar la experimentación práctica con un trabajo de búsqueda bibliográfica centrado en el tema de la experimentación. Así, los alumnos buscarán información relacionada en las fuentes bibliográficas que habitualmente se utilizan en investigación como son las revistas especializadas listadas en el JCR. Al final del laboratorio, los alumnos expondrán a sus compañeros sus resultados y la información encontrada en la búsqueda bibliográfica. Así se logra que el alumno se implique en la generación de su propio conocimiento y en la transferencia del mismo a sus compañeros. Los temas escogidos pertenecen a áreas de investigación punteras y permiten complementar las clases expositivas tradicionales.ES

Studies on the active species in olefin polymerisation generated from phenoxo-amido titanium “<i>chiral-at-metal</i>” compounds

Treatment of RHN-CH2-(3,5-tBu2C6H2-2-OH) (R = C6H5 1a, p-MeC6H4 1b, Cy 1c; Cy = cyclohexyl) with 1 equiv of TiCp*Cl3 (Cp* = &#x3b7;5-C5Me5) in the presence of 2.5 equiv of NEt3 in pentane or hexane at room temperature gives the monocyclopentadienyl phenoxo-amido monochloro complexes [TiCp*&#x7b;RN-CH2-(3,5-tBu2C6H2-2-O)}Cl] (R = C6H5 2, p-MeC6H4 4, Cy 5). In a more polar solvent the phenoxo-amino complex [TiCp*&#x7b;(C6H5)(H)N-CH2-(3,5-tBu2C6H2-2-O)}Cl2] (3) is obtained from the reaction with 1a. The reaction of TiCp*Cl3 with tBu(H)N-CH2-(3,5-tBu2C6H2-2-OH) (1d) affords the complex [TiCp*&#x7b;tBu(H)N-CH2-(3,5-tBu2C6H2-2-O)}Cl2] (6) in which no coordination of the amino group to the metal centre is observed as a consequence of the high steric requirements of the amino substituent in the phenol-amine. All the reported compounds were characterised by the usual analytical and spectroscopic methods and the molecular structures of 2 and 5 were determined by X-ray diffraction analysis from suitable single crystals.Studies of catalytic activity for ethylene or propylene polymerisation using boron or aluminium reagents as cocatalysts were performed under different conditions. In general the trends observed for the phenoxo-amido precatalysts with the aluminium reagent as cocatalyst in the &#x3b1;-olefin polymerisation reactions might suggest a catalyst decomposition process through ligand abstraction by sMAO. The activity found for ethylene or propylene polymerisation when B(C6F5)3 or [CPh3][B(C6F5)4] are used as cocatalysts is related to the strength of the cation-anion interactions

Silicoaluminates as “Support Activator” Systems in Olefin Polymerization Processes

In this work we report the polymerization behaviour of natural clays (montmorillonites, MMT) as activating supports. These materials have been modified by treatment with different aluminium compounds in order to obtain enriched aluminium clays and to modify the global Brönsted/Lewis acidity. As a consequence, the intrinsic structural properties of the starting materials have been changed. These changes were studied and these new materials used for ethylene polymerization using a zirconocene complex as catalyst. All the systems were shown to be active in ethylene polymerization. The catalyst activity and the dependence on acid strength and textural properties have been also studied. The behaviour of an artificial silica (SBA 15) modified with an aluminium compound to obtain a silicoaluminate has been studied, but no ethylene polymerization activity has been found yet

Enhanced activity of clays and its crucial role for the activity inethylene polymerization

This paper presents a study of the effects of different treatments on the polymerization activity of mod-ified clays as cocatalysts. To achieve this goal, an intercalating cation was introduced into two smectitesand these clays were then modified with trimethyl aluminium. The results for ethylene polymeriza-tion, when a zirconocene complex was used as catalyst, and the structure analysis, allow us to obtaininteresting deductions about the generation mode of the active species. All active materials employedas support activators presented aluminium in a pentahedral environment together with acidic hydrogenatoms. These two features were detected only after TMA treatment and they seem to be crucial elementsin active cocatalyst generation. Moreover, a material without structural aluminium displayed the bestactivity pointing to the new aluminium species generated in the solid matrix as the determining factorfor the activity. We proposed a synergic effect between Lewis acid aluminium centres and acidic Brönstedprotons that generate the SiOHAl groups that activate the zirconium compound.Peer Reviewe

Stereospecific synthesis of chiral titanium complexes bearing a bifunctionalized cyclopentadienyl-terpenoid ligand derived from α-pinene

11 pags., 6 figs., 6 schs.The reaction of the complexes [Ti(η5- C5H3R′SiMe2Cl)Cl3] (R′ = H, SiMe3 ) with the terpenoid preligand C7H6Me3(OH)(NCH2CH2NH2) affords the stereospecific synthesis of the constrained-geometry chiral titanium complexes [Ti{(η5-C5H3R′SiMe2N(CH2)2NC7H6Me3O)- κ3N,N′,O}Cl] (R′ = H, 1; R′ = SiMe3 2), bearing a new cyclopentadienyl-terpenoid ligand derived from α-pinene. The corresponding alkyl derivatives [Ti{(η5-C5H4SiMe2N- (CH2)2NC7H6Me3O)-κ3N,N′,O}R] (R = Me, 4; R = nBu, 5) have been prepared by treatment with suitable alkylating reagents. The reactivity of the methyl complex 4 with different protonic reagents such as alcohols and thiols proceeds via protonation of the amido nitrogen to stereospecifically give the corresponding strain-free alkoxide- and thiolate-methyl compounds [Ti{(η5- C5H4SiMe2NH(CH2)2NC7H6Me3O)-κO}Me(XR)] (X = O, R = iPr, 6; X = S, R = Et, 7; R = p-MeC6H4, 8). The reversibility of this protonation reaction is observed in the case of the thiolate compounds, which are thermically converted, via methane release, into the corresponding constrained-geometry thiolate derivatives [Ti{(η5-C5H4SiMe2N(CH2)2NC7H6Me3O)-κ3N,N′,O}(SR)] (R = Et, 9; R = C6H4-p-Me, 10). However, the analogous alkoxide-methyl compound 6 does not undergo a similar transformation. To gain further insights into the results reached in the reactions of 4 with alcohols and thiols and to understand the different behavior of the strain-free alkoxide- and thiolate-methyl complexes with regard to the thermal decomposition, calculations using DFT methods have been performed.Ministerio de Ciencia, Innovacion y Universidades (project RTI2018−094840−B-C31) and Universidad de Alcalá (project UAH-AE-2017−2

Biodegradable PHB from rac-β-Butyrolactone: Highly Controlled ROP Mediated by a Pentacoordinated Aluminum Complex

The diphenoxyimine five-coordinated aluminum complex [AlMeL2] (1), (L = N-(2,6-diisopropylphenyl)phenoxyimine), has been synthesized and fully characterized. The mononuclear structure observed in the solid state by X-ray diffraction analysis is maintained in solution, as shown by diffusion-ordered NMR spectroscopy (DOSY). Complex 1 is an active ROP catalyst able to provide well-controlled living ring-opening polymerization of rac-BBL at 100 °C, with PDI = 1.03, in the presence of BnOH to give the biodegrable polyester poly(hydroxybutyrate) (PHB). The suggested active species of this catalytic process, the aluminum complex [Al(OBn)L2] (2), has been synthesized and fully characterized. DFT calculations have been carried out to study the influence of the catalytic active species pocket over the polymer molecular weight control. Moreover, 1 is also active in the copolymerization of rac-β-butyrolactone and l-lactide to provide random copolymers

Chiral Titanium(IV) Complexes Containing Polydentate Ligands Based on α‑Pinene. Catalytic Activity in Sulfoxidation with Hydrogen Peroxide

The reaction of TiCl_4–<i>n</i>(O^<i>i</i>Pr)_<i>n</i> (<i>n</i> = 0, 2, 4) with various terpenoid preligands based on α-pinene, C₇H₆Me₃(OH)­(NCH₂CH₂G) (G = NH₂, <b>I</b>; NHMe, <b>II</b>; OH, <b>III</b>), stereoselectively affords a series of new chiral titanium­(IV) complexes. Such complexes are either octahedral, [TiCl₂X­(OC₇H₆Me₃NCH₂CH₂G-κ³<i>N</i>,<i>N</i>,<i>O</i>)] (X = Cl, G = NH₂, <b>1</b>; X = OⁱPr, G = NH₂, <b>2</b>; G = NHMe, <b>3</b>), or trigonal bipyramidal, [Ti­(OⁱPr)₃­(OC₇H₆Me₃­NCH₂CH₂­G-κ²<i>N</i>,<i>O</i>)] (G = NH₂, <b>4</b>; NHMe, <b>5</b>) and [TiX­(OⁱPr)­(OC₇H₆Me₃NCH₂CH₂O-κ³<i>N</i>,<i>O</i>,<i>O*</i>)] (X = Cl, <b>6</b>; OⁱPr, <b>8</b>), depending on the acidity of titanium, the reaction conditions and the nature of the pendant ending group of the terpenoid ligand. Density functional theory (DFT) calculations have been carried out to assess the stability of the multiple possible diastereoisomers allowing us to propose structural suggestions. The new titanium complexes efficiently catalyze the selective oxidation of various types of sulfides to either sulfoxides or sulfones using aqueous hydrogen peroxide, under mild conditions. All compounds have been characterized by multinuclear NMR spectroscopy and the molecular structure for some of them has been determined by X-ray diffraction

Synthesis and Structure of Homo- and Heterometallic Lithium–Magnesium Complexes and Their Reactivity in the ROP of <i>rac</i>-Lactide

The homometallic azo complexes of lithium [Li₂{(η²-O­(C₁₀H₆)­NN­(C₆H₅)}₂]_<i>n</i> and magnesium [Mg­{(η²-O­(C₁₀H₆)­NN­(C₆H₅)}₂]_<i>n</i> and the heterometallic lithium–magnesium derivative [Li₂Mg₂{(η²-O­(C₁₀H₆)­NN­(C₆H₅)}₆] have been synthesized. The heterometallic complex exhibits a novel structure described as two truncated cubes that share a Mg₂O₂ ring as one of the cube sides. These complexes have been studied in the polymerization of <i>rac</i>-lactide. In order to gain insight into the behavior of these compounds as catalysts, ¹H NMR experiments, diffusion-ordered spectroscopy, and X-ray studies have been used. DOSY NMR experiments support the notion that the structure of the mixed-metal complex <b>3</b> persists in benzene solution, and ¹H NMR studies show that it follows an activated monomer mechanism