Metallocene polyethylenes with broad or bimodal molecular weight distribution

Seven new binuclear titanocenes with different linking bridges, unsubstituted or substituted on the Cp rings, were synthesized and tested for their effect on ethylene polymerization in the presence of MAO. The polyethylenes thus obtained had broad MWD or even bimodal GPC curves, as compared with that from two reference mononuclear titanocenes. This is explained by the difference in degree of steric hindrance around the active center sites imposed by the bulky substituted ligands assuming different configurations in the rotation of the catalyst molecules. Lower polymerization temperatures alleviate the effect of these configuration differences, as reflected in change in MW and (M) over bar(w)/(M) over bar(n). This effect is not caused by decomposition or disproportionation of the binuclear titanocenes as evidenced by the stability of the catalyst.

Crystallization of syndiotactic polypropylene (sPP) from oriented melts

The influence of the syndiotacticity on the crystallization behaviour of syndiotactic polypropylene (sPP) has been investigated. The syndiotacticity has been measured by C-13-NMR spectroscopy and the phase formation has been observed by electron diffraction of oriented samples. It is shown that the crystal phase formation depends strongly on the perfection of the tacticity of the macromolecules.

Preparação e caracterização da casca de banana prata particulada para aplicação com reforço em compósito de matriz de PEAD

The waste, exaggerated and incorrect disposal of biomass are common practices in modern times where everything is disposable. However the growing concern with the nature and the environment compel man to give nobler destinations for these products through sustainability and recycling of waste. Banana peel is a residual biomass, which is not consumed. It generates tons of waste per week in São Paulo city. This trash is disposed in dumps and landfills, which could be reduced by using it as reinforcement in natural composites. The high density polyethylene (HDPE) is a polymer derived from the ethylene polymerization and is easily recycled. Which makes it a sustainable material. In the present work characteristics of the natural composite composed with banana peel and high-density polyethylene were studied. It was noted that removing the lignin present in the banana peel, the fiber introduces a significant improvement in thermal resistance. The preparation of composite was made with a ratio of 5% and 10% of reinforcement in comparison with polymeric matrix mass. Composites were thermally, mechanically and microscopically characterized. The addition of fiber in the polymer increased the mechanical strength of the composite. The fiber surface treatment with distilled water removed the amorphous material present in the fibers, improving significantly thermal stability and increasing crystallinity of the celullose. The addition of 5% fiber in mass to the polymer increased significantly the tensile strength and elasticity modulus for the composite. With 10% of fiber addiction there were also an improvement when compared with pure HDPE, but when compared with 5% composite the mechanical properties are slightly lower. This may be due to the fiber particle size, which are small and eventually become a hub of tension ... (Complete abstract click electronic access below)

Rylenfarbstoffe in nanoskopischen Systemen

ZusammenfassungDurch die Funktionalisierung des Chromophors Tetraphenoxyperylendiimid mit vier Ethinylgruppen stand ein Farbstoff zur Verfügung, welcher sich als Kernmolekül für den Aufbau von Polyphenylendendrimeren eignet. Ausgehend von dem Farbstoffkern wurden drei Dendrimergenerationen synthetisiert. Durch die Dendronisierung wird die Aggregation des zentralen Farbstoffs im Festkörper verhindert, weshalb das G1-Dendrimer als aktive Schicht in LED´s eingesetzt wurde und zur Verbesserung dieser Bauelemente führte. Weiterhin wurde auch die Oberfläche der Polyphenylendendrimere mit 4, 8 bzw. 16 Perylenmonoimidfarbstoffen funktionalisiert. Durch zeitaufgelöste Absorptions- und Emissionsmessungen und Einzelmolekülspektroskopie des G2-Dendrimers wurde ein photophysikalisches Modell des multichromophoren Systems entwickelt.Neben Polyphenylendendrimeren dienten auch Emulsionspolymerisate, Miniemulsionspolymerisate und Halbleiterkristalle als nanoskopische Trägermaterialien für Rylenfarbstoffe. Für die Anknüpfung an Lartices wurden amino- und styrylfunktionalisierte Perylen- und Terrylenchromophore dargestellt, was zu einer statistischen Verteilung der Farbstoffe auf der Oberfläche bzw. im Inneren führte. Außerdem wurden Rylenfarbstoffe als stabile Fluoreszenzmarkierung von Metallocenkatalysatoren eingesetzt. Silica- und polymergeträgerte markierte Katalysatoren wurden zur Polymerisation von Ethylen verwendet und lieferten fluoreszente PE-Produkte, ohne Einfluß auf die Polymerisation zu nehmen. Zum Einen wurde mit Hilfe der Dotierung der heterogenen Polymerisationskatalysatoren der Verbleib des fragmentierten Trägermaterials in den PE-Produktpartikeln detektiert. Zum Anderen erlaubt der Einsatz unterschiedlich fluoreszierender Markierungsgruppen die Durchführung eines kombinatorischen Verfahrens zum Testen von Polymerisationskatalysatoren.

Polymerisationskatalysatoren auf Basis von Titan- und Vanadiumkomplexen mit Bisphenolato-Liganden

Die Synthese und Charakterisierung von Bisphenolato-Komplexen des Titans und Vanadiums werden beschrieben.Neben dem Methylkomplex wurde eine Reihe von Bisphenolato-Komplexen des Titan(IV) der Zusammensetzung (tbmp)(o-C6H4CH2NMe2)TiX (mit X = CH2SiMe3, CH2Ph, OTf) synthetisiert. Der Methylkomplex wurde mit B(C6F5)3 oder (tbmp)(tbmpH)Al zum Komplexkation [(tbmp)(o-C6H4CH2NMe2)Ti]+ umgesetzt und dessen Reaktivität gegenüber 1-Olefinen untersucht.Ausgehend von (tbmp)TiCl2 wurden der Dimethylkomplex (tbmp)TiMe2 und der Dibenzylkomplex (tbmp)Ti(CH2Ph)2 dargestellt und strukturell charakterisiert. Der Dibenzylkomplex liegt im Kristall als Dimer vor, verbrückt über ein Dioxan-Molekül, während der Dimethylkomplex auch im Feststoff monomer ist. Dies ist das erste Beispiel für die Koordinationszahl fünf bei Bisphenolato-Titan-Komplexen.Polymerisationsversuche mit (tbmp)TiMe2 und B(C6F5)3 weisen auf eine hohe Reaktivität und geringe Stabilität des aktivierten Komplexes hin, die zu geringen Polymer-Ausbeuten führt.Im Falle des Vanadiums konnten trotz Schwierigkeiten aufgrund der hohen Redoxaktivität dieses Elements mehrere Komplexe dargestellt werden. Synthetisiert und strukturell charakterisiert wurden der Komplex (mbmp)V(O)(CH2SiMe3)·B(C6F5)3, das erste Beispiel für ein Boranaddukt eines Oxokomplexes des fünfwertigen Vanadiums, und der erste Di(bisphenolato)-Komplex des vierwertigen Vanadiums, (tbmp)2V.Desweiteren gelang die Darstellung von (mbmp)V(O)(CH2SiMe2Ph)·B(C6F5)3, (tbmp)VCl(THF)2 und (mbmp)2V. Die Alkylkomplexe des fünfwertigen Vanadiums waren mit B(C6F5)3 für die Polymerisation von Ethen nicht aktivierbar. Hingegen bildete (tbmp)VCl(THF)2 mit DEAC ein sehr aktives System für die Polymerisation von Ethen.

Copolymerizations of ethylene with alpha-olefin-omega-ols by highly active vanadium(III) catalysts bearing [N,O] bidentate chelated ligands

The copolymerizations of ethylene with polar hydroxyl monomers such as 10-undecen-1-ol, 5-hexen-1-ol and 3-buten-1-ol were investigated by the vanadium(III) catalysts bearing bidentate [N,O] ligands (1, [PhN=C(CH3)CHC(Ph)O]VCl2(THF)(2): 2, [PhN=CHC6H4O]VCl2(THF)(2); 3, [PhN=CHC(Ph)CHO]VCl2(THF)(2)). The polar monomers were pretreated by alkylaluminum before the polymerization. High catalytic activities and efficient comonomer incorporations can be easily obtained by changing monomer masking reagents and polymerization conditions in the presence of diethylaluminium chloride as a cocatalyst. The longer the spacer group, the higher the incorporation of the monomer. Under the mild conditions, the incorporation level of 10-undecen-1-ol reached 13.9 mol% in the resultant copolymers was obtained. The reactivity ratios of copolymerization (r(1) = 41.4, r(2) = 0.02, r(1)r(2) = 0.83) were evaluated by Fineman-Ross method. According to C-13 NMR spectra, polar units were located both on the main chain and at the chain end.

Vinylic polymerization of norbornene by neutral nickel(II)-based catalysts

Neutral Ni(II) salicylaldiminato complexes activated with modified methylaluminoxane as catalysts were used for the vinylic polymerization of norbornene. Catalyst activities of up to 7.08 x 10(4) kg(pol)/(mol(Ni) (.) h) and viscosity-average molecular weights of polymer up to 1.5 x 10(6) g/mol were observed at optimum conditions. Polynorbornenes are amorphous, soluble in organic solvents, highly stable, and show glass-transition temperatures around 390 degreesC. Catalyst activity, polymer yield, and polymer molecular weight can be controlled over a wide range by the variation of the reaction parameters such as the Al/Ni ratio, monomer/catalyst ratio, monomer concentration, polymerization reaction temperature, and time.

Preparation of polymer-supported zirconocene catalysts and olefin polymerization

A novel polymer-supported metallocene catalyst with crosslinked poly(styrene-co-acrylamide) (PSAm) as the support has been prepared and characterized. The probability of long sequences of acrylamide (Am) in PSAm is still low even at an Am amount of 32.8 mol %, implying the relatively homogeneous distribution of Am. The infrared spectra of PSAm and the supported catalyst substantiate that an amide group in PSAm coordinates with methylaluminoxane through both oxygen and nitrogen atoms. Ethylene/alpha-octene copolymerization showed that the catalytic activity is not markedly affected by adding alpha-octene. C-13 NMR analysis of the ethylene/alpha-octene copolymer indicated that the composition distribution of the copolymer is uniform. (C) 1999 John Wiley & Sons, Inc.

UNSTEADY DIFFUSION KINETICS OF ZIEGLER-NATTA HETEROGENEOUS CATALYST POLYMERIZATION .4. PREDICTION OF EXPERIMENTAL RESULTS OF PROPYLENE ETHYLENE 1-HEXADECENE TERPOLYMERIZATION

The prediction, based on unsteady diffusion kinetics, of the enhancement of reactivity and incorporation of 1-hexadecene in its copolymerization with propylene on adding a small amount of ethylene (increase from 5,2 mol-% to 10,8 mol-% when 2% of ethylene was added, and to 16,1 mol-% when 5% was added) was verified in the terpolymerization of propylene/1-hexadecene/ethylene on a commercial Solvay-type delta-TiCl3 catalyst. The catalyst efficiency was thus also increased. These augmentations originate from the increase in diffusion coefficient of 1-hexadecene at the catalyst surface when the PP crystallinity decreases on introduction of ethylene. Calculation based on unsteady diffusion kinetics showed that the order of diffusion coefficients ethylene > propylene > 1-hexadecene is reversed as the monomer concentration increases when the monomers are not at their equilibrium concentration. Sequence distribution as determined by means of C-13 NMR revealed a tendency of blocky structure rather than a Bernoullian one. The terpolymer compositions obtained by means of an IR method developed in this work conform rather well with the NMR results. Results in this work not only support the unsteady diffusion kinetics but also provide a new route to prepare olefinic copolymer rubbers with heterogeneous titanium catalysts.

SOME NEWER CONCEPTS OF ETHYLENE ALPHA-OLEFIN COPOLYMERIZATION ON HETEROGENEOUS ZIEGLER-NATTA CATALYSTS

Unsteady diffusion kinetic, recently advanced by this laboratory, is applied to the examination of some polymerization and molecular chain structure problems. Hitherto deemed "anomalous" phenomena, such as the faster rate of copolymerization of ethylene/alpha-olefin than the homopolymerization of ethylene and the enrichment in the incorporation of a higher alpha-olefin in its copolymerization with ethylene by a lower alpha-olefin, are reasonably explained by unsteady diffusion of monomers. Molecular chain structure of copolymers, such as compositional heterogeneity and its dependence on comonomer incorporation originates from the difference in diffusion coefficients of the monomers. A copolymer composition equation taking into consideration the unsteady diffusion was developed. In cases where simulated curves were compared with experimental curves, good agreements were found.

Novel catalyst systems based on Ni(II), Ti(IV), and Cr(III) complexes for oligo-and polymerization of ethylene

The complex of Brookhart Ni(α-diimine)Cl2 (1) (α-diimine = 1,4-bis(2,6- diisopropylphenyl)-acenaphthenediimine) has been characterized after impregnation on silica (S1) and MAO-modified silicas (4.0, 8.0 and 23.0 wts.% Al/SiO2 called S2, S3 and S4, respectively). The treatment of these heterogeneous systems with MAO produces some active catalysts for the polymerization of the ethylene. A high catalytic activity has been gotten while using the system supported 1/S3 (196 kg of PE/mol[Ni].h.atm; toluene, Al/Ni = 1000, 30ºC, 60 min and atmospheric pressure of ethylene). The effects of polymerization conditions have been tested with the catalyst supported in S2 and the best catalytic activity has been gotten with solvent hexane, MAO as cocatalyst, molar ratio Al/Ni of 1000 and to the temperature of 30°C (285 kg of PE/mol[Ni].h.atm). When the reaction has been driven according to the in situ methodology, the activity practically doubled and polymers showed some similar properties. Polymers products by the supported catalysts showed the absence of melting fusion, results similar to those gotten with the homogeneous systems by DSC analysis. But then, polymers gotten with the transplanted system present according to the GPC’s curves the polydispersity (MwD) varies between 1.7 and 7.0. A polyethylene blend (BPE/LPE) was prepared using the complex Ni(α-diimine)Cl2 (1) (α-diimine = 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine) and {TpMs*}TiCl3 (2) (TpMs* = hydridobis(3-mesitylpyrazol-1-yl)(5-mesitylpyrazol-1-yl)) supported in situ on MAO-modified silica (4.0 wts. -% Al/SiO2, S2). Reactions of polymerization of ethylene have been executed in the toluene in two different temperatures (0 and 30°C), varying the molars fraction of nickel (xNi), and using MAO as external cocatalyst. To all temperatures, the activities show a linear variation tendency with xNi and indicate the absence of the effect synergic between the species of nickel and the titanium. The maximum of activity have been found at 0°C. The melting temperature for the blends of polyethylene produced at 0 °C decrease whereas xNi increases indicating a good compatibility between phases of the polyethylene gotten with the two catalysts. The melting temperature for the blends of polyethylene showed be depend on the order according to which catalysts have been supported on the MAO-modified silica. The initial immobilization of 1 on the support (2/1/S2) product of polymers with a melting temperature (Tm) lower to the one of the polymer gotten when the titanium has been supported inicially (1/2/S2). The observation of polyethylenes gotten with the two systems (2/1/S2 and 1/2/S2) by scanning electron microscopy (SEM) showed the spherical polymer formation showing that the spherical morphology of the support to been reproduced. Are described the synthesis, the characterization and the catalytic properties for the oligomerization of the ethylene of four organometallics compounds of CrIII with ligands ([bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]amine] chromium (III) chloride (3a), [bis[2-(3,5- dimethyl-l-pyrazolyl)ethyl]benzylamine] chromium (III) chloride (3b), [bis[2-(3,5-dimethyl-lpyrazolyl) ethyl]ether] chromiun(III)chloride (3c), [bis[2-(3-phenyl-lpyrazolyl) ethyl]ether]chromiun(III)chloride (3d)). In relation of the oligomerization, at exception made of the compounds 3a, all complex of the chromium showed be active after activation with MAO and the TOF gotten have one effect differentiated to those formed with CrCl3(thf)3. The coordination of a tridentate ligand on the metallic center doesn't provoke any considerable changes on the formation of the C4 and C6, but the amount of C8 are decrease and the C10 and C12+ have increased. The Polymers produced by the catalyst 3a to 3 and 20 bar of ethylene have, according to analyses by DSC, the temperatures of fusion of 133,8 and 136ºC respectively. It indicates that in the two cases the production of high density polyethylene. The molar mass, gotten by GPC, is 46647 g/mols with MwD = 2,4 (3 bar). The system 3c/MAO showed values of TOF, activity and selectivity to different α-olefins according to the pressure of ethylene uses. Himself that shown a big sensibility to the concentration of ethylene solubilized.

Catalytic Dehydration of Ethanol to Ethylene on TiO2/4A Zeolite Composite Catalysts

TiO2/4A zeolite composite catalysts were prepared by coating TiO2 on 4A zeolite via liquid phase deposition. The TiO 2/4A zeolite composite catalysts wtih higher surface weak acidity and lower mediate strong acidity exhibit much better catalytic performance on ethanol dehydration to ethylene compared with 4A zeolite. It is suggested that the TiO2 promoter could improve the effective Lewis acidity of composite catalyst which consequently enhanced the catalytic performance.