Synthesis, structural characterization, and ethylene polymerization behavior of the vanadium(III) complexes bearing salicylaldiminato ligands

Vanadium(III) complexes bearing salicylaldiminato ligands (2a-k) [RN=CH(Ar0)]VCl2(THF)2 (Ar C61714, R = Ph, 2a; p-CF3Ph, 2b; p-CH3Ph, 2c; 2,6-Me2Ph, 2d; 2,6-iPr2Ph, 2e; cyclohexyl, 2f; Ar = C6H3tBu(2), R = Ph, 2g; 2,6-iPr2Ph, 2h; Ar = C6H2tBU2(2,4), R = Ph, 2i; 2,6-iPr2Ph, 2j; Ar = C6H2Br2, R = Ph, 2k) were prepared from VC13(THF)3 by treating with 1.0 equiv of (RN=CH)ArOH in tetrahydrofuran (THF) in the presence of excess triethylamine (TEA).

Synthesis, Structural Characterization, and Olefin Polymerization Behavior of Vanadium(III) Complexes Bearing Tridentate Schiff Base Ligands

Vanadium(III) complexes bearing tridentate salicylaldiminato ligands (2a-f) [OC6H4CH=NL]VCl2(THF) (L = CH2CH2OMe, 2a; CH2CH2NMe2, 2b; CH2C5H4N, 2c; 8-C9H6N (quinoline), 2d; 2-MeSC6H4, 2e; 2-Ph2PC6H4, 2f) and tridentate beta-enaminoketonato ligands [OC6H8CH=N-2-Ph2PC6H4]VCl2(THF) (2g) and [O(Ph)C=CHCH=N-2-Ph2PC6H4]VCl2(THF) (2h) were prepared from VCl3(THF)(3) by treating with 1.0 equiv of the deprotonated ligands in tetrahydrofuran (THF). These complexes were characterized by FTIR and mass spectrometry as well as elemental analysis. Structures of complexes 2e, 2f, and 2h were further confirmed by X-ray crystallographic analysis. These complexes were investigated as catalysts for olefin polymerization in the presence of organoaluminum compounds. On activation with Et2AlCl, complexes 2a-h exhibited high catalytic activities toward ethylene polymerization (up to 20.64 kg PE/mmol(v) center dot h center dot bar) even at high temperature, suggesting these catalysts possess high thermal stability.

Ethylene Polymerization and Ethylene/Hexene Copolymerization with Vanadium(III) Catalysts Bearing Heteroatom-Containing Salicylaldiminato Ligands

A series of novel vanadium(III) complexes hearing heteroatoill-containing group-substituted salicylaldiminato ligands [RN=CH(ArO)]VCl2(THF)(2) (Ar = C6H4, R = C3H2NS, 2a; C7H4NS, 2c; C7H5N2, 2d; Ar = C(6)H(2)tBu(2) (2,4), R = C3H2NS, 2b) have been synthesized and characterized. Structure of complex 2c was further confirmed by X-ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et2AlCl. Complexes 2a-d exhibited high catalytic activities (up to 22.8 kg polyethylene/mmolv h bar), and affording polymer with unimodal molecular weight distributions at 25-70 degrees C in the first 5-min polymerization, whereas produced bimodal molecular weight distribution polymers at 70 degrees C when polymerization time prolonged to 30 min. The catalyst structure plays an important role in controlling the molecular weight and molecular weight distribution of the resultant polymers produced in 30 min polymerization. In addition, ethylene/hexene copolymerizations with catalysts 2a-d were also explored in the presence of Et2AlCl, which leads to the high molecular weight and unimodal distributions copolymers with high comonomer incorporation.

Novel vanadium(III) complexes with bidentate N,N-chelating iminopyrrolide ligands: synthesis, characterization and catalytic behaviour of ethylene polymerization and copolymerization with 10-undecen-1-ol

A series of novel vanadium(III) complexes bearing iminopyrrolide chelating ligands [2-(RN=CH)C4H3N]V(THF)(2)Cl-2 (2a: R = cyclohexyl; 2b: R = Ph; 2c: R = 2,6-iPr(2)C(6)H(3); 2d: R = p-CF3C6H4; 2e: R = C6F5) have been synthesized and characterized. Single-crystal X-ray diffraction revealed that complexes 2a, 2c and 2e adopt an octahedral geometry around the vanadium center. In the presence of Et2AlCl as a co-catalyst, these complexes displayed high catalytic activities up to 48.6 kg PE mmol(V)(-1) h(-1) bar(-1) for ethylene polymerization, and produced high molecular weight polymers. 2a-e/Et2AlCl catalytic systems were tolerant to elevated temperature (70 degrees C) and yielded unimodal polyethylenes, indicating the single site behaviour of these catalysts. By pre-treating with equimolar amounts of alkylaluminums, functional alpha-olefin 10-undecen-1-ol can be efficiently incorporated into polyethylene chains. 10-Undecen-1-ol incorporation can easily reach 15.8 mol% under the mild conditions.

Effect of swelling response of the support particles on ethylene polymerization

Macroporous and modified macroporous poly(styrene-co-methyl methacrylate-co-divinylbenzene) particles (m-PS and mm-PS) supported Cp2ZrCl2 were prepared and applied to ethylene polymerization using methylaluminoxane (MAO) as cocatalyst. The influences of the swelling response of the support particles on the catalyst loading capabilities of the supports as well as on the activities of the supported catalysts were studied. It was shown that the Zr loadings of the supports and the activities of the supported catalysts increased with the swelling extent of the support particles. The m-PS or mm-PS supported catalysts exhibited very high activities when the support particles were well swollen, whereas those catalysts devoid of swelling treatment gave much lower activities. Investigation on the distribution of the supports in the polyethylene by TEM indicated that the swelling of the support particles allowed the fragmentation of the catalyst particles. In contrast, the fragmentation of the support particles with poor swelling was hindered during ethylene polymerization.

Zirconocene catalyst well spaced inside modified montmorillonite for ethylene polymerization: role of pretreatment and modification of montmorillonite in tailoring polymer properties

Zirconocene catalyst was heterogenized inside an organosilane-modified montmorillonite (MMT) pretreated by calcination and acidization, for supported catalyst systems with well-spaced alpha-olefin polymerization active centers. The varied pretreatment and modification conditions of montmorillonite are efficient for supported zirconocene catalysts in control of polyethylene microstructures, in particular, molecular weight distribution. In contrast to other supported catalyst systems, Cp2ZrCl2/modified montmorillonite(MMT-7)-supported catalysts with a distinct interlayer structure catalyzed ethylene homopolymerization and copolymerization with I-octene activated by methylaluminoxane (MAO), resulting in polymers with a bimodal molecular weight distribution (MWD).

Ethylene polymerization with porous polystyrene spheres supported Cp2ZrCl2 catalyst

A catalyst with porous polystyrene beads supported Cp2ZrCl2 was prepared and tested for ethylene polymerization with methylaluminoxane as a cocatalyst. By comparison, the porous supported catalyst maintained higher activity and produced polyethylene with better morphology than its corresponding solid supported catalyst. The differences between activities of the catalysts and morphologies of the products were reasonably explained by the fragmentation processes of support as frequently observed with the inorganic supported Ziegler-Natta catalysts. Investigation into the distribution of polystyrene in the polyethylene revealed the fact that the porous polystyrene supported catalyst had undergone fragmentation during polymerization.

Synthesis and characterization of polypropylene/montmorillonite nanocomposites via an in-situ polymerization approach

Polypropylene/montmorillonite (PP/MMT) nanocomposites were prepared by in-situ polymerization using a MMT/MgCl2/TiCl4-EB Ziegler-Natta catalyst activated by trietbylaluminum (TEA). The enlarged layer spacing of MMT was confirmed by X-ray wide angle diffraction (WAXD), demonstrating that MMT were intercalated by the catalyst components. X-ray photoelectron spectrometry (XPS) analysis proved that TiCl4 was mainly supported on MgCl2 instead of on the surface of MMT The exfoliated structure of MMT layers in the PP matrix of PP/MMT composites was demonstrated by WAXD patterns and transmission electron microscopy (TEM) observation. The higher glass transition temperature and higher storage modulus of the PP/MMT composites in comparison with pure PP were revealed by dynamic mechanical analysis (DMA).

HELIX-INDUCED ASYMMETRIC POLYMERIZATION

Asymmetric polymerization could be induced by an already formed optically active living prepolymer with one-handed screw sense helix conformation. The usually formed anionic active centre on the prepolymer could be changed to cationic, radical and even of Ziegler-Natta type. These living prepolymers with various kinds of active centre were all effective to induce a consequent asymmetric polymerization of a monomer which may be other than that in the prepolymer, to afford an optically active helical chain with the same screw sense as that of the prepolymer. Eight monomers have been used in the work. Optical rotation, circular dichroism and gelpermeation chromatography have been taken to prove the helix-induced asymmetric polymerization.

Nanosized polymer carriers for metallocene catalysts in heterogeneous olefin polymerization

Das Ziel der vorgelegten Arbeit war die Synthese von definierten, sphärischen Polystyrolpartikeln im Größenbreichen von Nanometern, die als Träger für die Immobilisierung von Metallocenkatalysatoren verwendet werden sollten. Ein wichtiger Anspruch an das System war dabei die Möglichkeit einer homogene Verteilung des Metallocenes auf dem Träger and eine homogene Fragmentierung des geträgerten Katalysators während der Polymerisation im Polymerprodukt. Für diese Zielsetzung wurden unterschiedliche Polystyrolnanopartikel hergestellt. Die Polystyrolnanopartikel waren mit unterschiedlichen funktionellen Gruppen wie Polyethylenoxid- und Polypropylenoxidketten oder Hydroxygruppen auf der Oberfläche versehen, um den Metallocenkatalysator und den Cokatalysator MAO immobilisieren zu können. In verschiedenen Experimenten wurde der Einfluss dieser Polystyrolnanopartikel als Träger auf die Katalysatoreigenschaften wie Aktivität oder Produktivität und die Eigenschaften des produzierten Polyolefins wie z.B. Molekulargewicht und Morphologie untersucht. Im Vergleich zu den PS- Nanopartikeln wurden außerdem PS-Mikropartikel, Silica und Dendrimere als Träger in der heterogenen Olefinpolymerisation eingesetzt. Von all diesen Trägersystemen wurde das Fragmentierungsverhalten durch konfocale Fluoreszenzmikroskopie untersucht. Aus den erhaltenen Ergebnissen kann geschlossen werden, dass die hergestellten Polystyrolnanopartikel neuartige und leistungsfähige Träger für heterogene Polymerisationsprozesse darstellen. Die hergestellten Polystyrolnanopartikel besaßen eine wohldefinierte sphärische Struktur, die eine homogene Verteilung des immobilisierten Metallocenkatalysators und somit auch eine vollständige Fragmentierung des geträgerten Katalysators im hergestellten Polyolefin ermöglichte. Die Katalysatorsysteme, die aus den PS- Nanopartikeln und dem Metallocenkatalysator zusammengesetzt waren, wurden in verschiedenen Polymerisationen wie der Ethylen- oder Propylenhomopolymersation und der Copolymerisation von Ethen mit α- Olefinen getestet. Die Oberflächen- funktionalisierten PS Nanopartikel immobilisierten den Metallocenkatalysator ausreichend gut, so dass kein „Leachen“ (Ablösen) des Katalysators von der Trägeroberfläche festgestellt werden konnte und deshalb Polymer von sehr guter Morphologie erhalten wurde. Um die Fragmentierung des Katalysators und den inneren Aufbau des Polymers näher untersuchen zu können, wurde die konfocale Fluoreszenzmikroskopie für das PS- Nanopartikelträgersystem angewendet. Durch farbstoffmarkierte Trägerpartikel konnte die Verteilung des fragmentierten Katalysators innerhalb des Polymers sichtbar gemacht und analysiert werden. Dabei wurde festgestellt, dass sich PS- Nanopartikel und auch Dendrimere als Träger ähnlich verhalten wie Ziegler- Natta- Katalysatoren, die auf MgCl2 immobilisiert für die heterogene Olefinpolymerisation verwendet werden. Das Fragmentierungsverhalten der Silica oder PS- Mirkopartikel geträgerten Systeme entsprach dagegen dem schichtweisen Fragmentierungsverhalten wie es bereits von Fink und Mitarbeitern beschrieben wurde.

Organotitanium and niobium chemistry. I. Structure and reactivity of a titanium ethylene complex. II. Reactivity of decamethyl niobocene derivatives

The synthesis and X-ray diffraction study of bis(pentamethylcyclopentadienyl) ethylene titanium (I) are reported. This complex represents the first example of an isolable ethylene adduct of a group IV metal, a key intermediate in Ziegler-Natta olefin polymerization schemes. While treatment of I with ethylene leads to only traces of polymer after months, I participates in a wide range of stoichiometric and catalytic reactions. These include the catalytic conversion of ethylene specifically to butadiene and ethane and the catalytic isomerization of alkenes. Detailed studies have been carried out on the stoichiometric reactions of I with nitriles and alkynes. At low temperatures, nitriles react to form metallacycloimine species which more slowly undergo a formal 1,3-hydrogen shift to generate metallacycloeneamines. The lowest energy pathway for this rearrangement is an intramolecular hydrogen shift which is sensitive to the steric bulk of the R substituent. The reactions of I with alkynes yield metallacyclopentene complexes with high regioisomer selectivity. Carbonylation of the metallacyclopentene (η-C₅Me₅5)₂TiC(CH₃)=C(CH₃)CH₂ under relatively mild conditions cleanly produces the corresponding cyclopentenone and [C₅(CH₃)₅]₂Ti(CO)₂. Compounds derived from CO₂ and acetaldehyde have also been isolated.

The synthesis and characterization of bis-(η-pentamethylcyclopentadienyl) niobium(III) tetrahydroborate (II) are described and a study of its temperature-dependent proton NMR spectroscopic behavior is reported. The complex is observed to undergo a rapid intramolecular averaging process at elevated temperatures. The free energy of activation, ΔG^≠ = 16.4 ± 0.4 kcal/mol, is calculated. The reinvestigation of a related compound, bis(η-cyclopentadienyl)niobium(III) tetrahydroborate, established ΔG^≠ = 14.6 ± 0.2 kcal/mol for the hydrogen exchange process. The tetrahydroborate complex, II reacts with pyridine and dihydrogen to yield (η-C₅Me₅5)₂NbH₃ (III). The reactivity of III with CO and ethylene is reported.

Copolimerização de 1,3-butadieno e alfa-olefinas com catalisadores à base de versatato de neodímio

Nesta Dissertação, foram realizadas reações de copolimerização de 1,3-butadieno com diferentes alfa-olefinas (1-hexeno, 1-octeno e 1-dodeceno) utilizando-se um sistema catalítico do tipo Ziegler-Natta ternário constituído por versatato de neodímio, hidreto de diisobutilalumínio e cloreto de t-butila. O sistema catalítico também foi avaliado em reações de homopolimerização com cada alfa-olefina. As condições reacionais, tanto da síntese do catalisador como das reações de polimerização, foram mantidas constantes. Foi estudada a influência de diferentes teores de cada alfa-olefina (1, 3, 5, 10, 20 e 30 % em relação ao 1,3-butadieno) sobre a conversão da polimerização, a microestrutura, a massa molar, as propriedades viscosimétricas e a estabilidade térmica dos polímeros obtidos. Foi avaliada, ainda, a influência do tamanho da cadeia da alfa-olefina sobre as características da polimerização. Os polímeros foram caracterizados por espectroscopia na região do infravermelho (FTIR), cromatografia por exclusão de tamanho (SEC), viscosimetria capilar e termogravimetria (TG). A microestrutura dos polímeros, praticamente, não variou com a adição das alfa-olefinas. A massa molar numérica média (Mn) não sofreu alterações significativas, enquanto que a massa molar ponderal média (Mw) apresentou tendência ao aumento, quanto maior foi a incorporação de comonômero. A viscosidade intrínseca não apresentou uma tendência com a adição da alfa-olefina na reação, permanecendo na faixa de 2,015 a 3,557 dL/g. A estabilidade térmica do copolímero mostrou uma tendência a aumentar com a incorporação das alfa-olefinas

Effect of Copolymerization Time on the Microstructure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-Reactor Alloys

Three Polypropylene/Poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys produced by a two-stage slurry/gas polymerization had different ethylene contents and mechanical properties, which were achieved by controlling the copolymerization time. The three alloys were fractionated into five fractions via temperature rising dissolution fractionation (TRDF), respectively. The chain structures of the whole samples and their fractions were analyzed using high-temperature gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), C-13 nuclear magnetic resonance (C-13 NMR), and differential scanning calorimetry (DSC) techniques. These three in-reactor alloys mainly contained four portions: ethylenepropylene random copolymer (EPR), ethylene-propylene (EP) segmented and block copolymers, and propylene homopolymer. The increased copolymerization time caused the increased ethylene content of the sample. The weight percent of EPR, EP segmented and block copolymer also became higher.

DSC AND C-13 NMR-STUDIES OF ETHYLENE-PROPENE COPOLYMERS PREPARED BY A HIGHLY-ACTIVE AND STEREOSPECIFIC CATALYST

Ethylene-propene copolymers (EPR) were synthesized at different feed compositions using a highly active and isospecific MgCl2-supported Ti-based catalyst. The thermal behavior of EPR was studied by differential scanning calorimetry, the heterogeneity by f

STRUCTURE AND PROPERTIES OF SEQUENTIALLY POLYMERIZED PROPYLENE-B-[ETHYLENE-CO-PROPYLENE]-B-PROPYLENE COPOLYMERS

The structure and properties of presumed block copolymers of polypropylene (PP) with ethylene-propylene random copolymers (EPR), i.e., PP-EPR and PP-EPR-PP, have been investigated by viscometry, transmission electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, gel permeation chromatography, wide-angle x-ray diffraction, and other techniques testing various mechanical properties. PP-EPR and PP-EPR-PP were synthesized using delta-TiCl3-Et2AlCl as a catalyst system. The results indicate that the intrinsic viscosity of these polymers increases with each block-building step, whereas the intrinsic viscosity of those prepared by chain transfer reaction (strong chain-transfer reagent hydrogen was introduced between block-building steps during polymerization) hardly changes with the reaction time. Compared with PP / EPR blends, PP-EPR-PP block copolymers have lower PP and polyethylene crystallinity, and lower melting and crystallization temperatures of crystalline EPR. Two relaxation peaks of PP and EPR appear in the dynamic spectra of blends. They merge into a very broad relaxation peak with block sequence products of the same composition, indicating good compatibility between PP and EPR in the presence of block copolymers. Varying the PP and EPR content affects the crystallinity, density, and morphological structure of the products, which in turn affects the tensile strength and elongation at break. Because of their superior mechanical properties, sequential polymerization products containing PP-EPR and PP-EPR-PP block copolymers may have potential as compatibilizing agents for isotactic polypropylene and polyethylene blends or as potential heat-resistant thermoplastic elastomers.