Search

In the search for more efficient single-center ethene/α-olefin copolymerization catalysts, metallocenes bearing a 2-indenyl substituent pattern have largely been ignored in the past. Here, we show that such a structural motif yields competent linear low-density polyethylene (LLDPE) catalysts. They are also relatively easy to synthesize, allowing for a wide structural amplification. A screening of 28 catalysts reveals that the lead catalyst in this study displays high comonomer affinity and molecular weight capability at industrially relevant temperatures. QSAR models show that steric factors likely contribute stronger than electronic factors to the observed substituent trends, both for comonomer affinity and MW capability.

A series of Me2Si-bridged bis(2-Me-indenyl) ansa-zirconocenes containing N-pyrrolyl, N-indolyl, N-carbazolyl, and P-dibenzophospholyl substituents in position 4 of the indenyl moieties has been syn...

In the search for more efficient single-center ethene/α-olefin copolymerization catalysts, metallocenes bearing a 2-indenyl substituent pattern have largely been ignored in the past. Here, we show that such a structural motif yields competent linear low-density polyethylene (LLDPE) catalysts. They are also relatively easy to synthesize, allowing for a wide structural amplification. A screening of 28 catalysts reveals that the lead catalyst in this study displays high comonomer affinity and molecular weight capability at industrially relevant temperatures. QSAR models show that steric factors likely contribute stronger than electronic factors to the observed substituent trends, both for comonomer affinity and MW capability.

New ansa-zirconocene with bis(inden-2-yloxy)dimethylsilane ligand was synthesized and characterized by NMR spectroscopy and X-ray crystallography. The zirconocene was found to be highly active catalyst of ethylene polymerization and ethylene/hex-1-ene copolymerization upon methylaluminoxane activation.

In the title compounds, [Zr2Br6(C11H12N)2], (I) and [ZrBr2(C11H12N)2], (II), the positions of the η5-binding 2-dimethylaminoindenyl units are fixed by intramolecular C—H...Br interactions involving aromatic or dimethylamino H atoms. The binuclear molecule of (I) is located on a general position, while the mononuclear molecule of (II) is situated on a twofold rotation axis. Both ZrIVatoms in (I) are ligated by one cyclopentadienyl (CP) ring and four Br ligands (two bridging, two terminal), while in (II) the ZrIVatom is ligated by two CP rings and two terminal Br ligands. The crystal structures of both (I) and (II) comprise of strands of π–π- and N–π-bonded molecules, which in turn are linked by C—H...Br interactions.

Mol­ecules of di[(μ-bromido)(η5-2-di­methyl­amino­inden­yl)di­bromido­zirconium(IV)], (I), and bis­(η5-2-di­methyl­amino­inden­yl)di­bromido­zirconium(IV), (II), are dinuclear with one CP ligand and four Br ligands for each of the ZrIV atoms and mononuclear with two CP and two Br ligands for the ZrIV atom, respectively., In the title compounds, [Zr2Br6(C11H12N)2], (I) and [ZrBr2(C11H12N)2], (II), the positions of the η5-binding 2-di­methyl­amino­indenyl units are fixed by intra­molecular C—H⋯Br inter­actions involving aromatic or di­methyl­amino H atoms. The binuclear mol­ecule of (I) is located on a general position, while the mononuclear mol­ecule of (II) is situated on a twofold rotation axis. Both ZrIV atoms in (I) are ligated by one cyclo­penta­dienyl (CP) ring and four Br ligands (two bridging, two terminal), while in (II) the ZrIV atom is ligated by two CP rings and two terminal Br ligands. The crystal structures of both (I) and (II) comprise of strands of π–π- and N–π-bonded mol­ecules, which in turn are linked by C—H⋯Br inter­actions.

A number of new alkoxy- and phenylsulfanyl-substituted 1,1-dihalospiro[2.2]pentanes bearing different halogen atoms were synthesized. 1,1-Dihalo-4-tert-butoxyspiro[2.2]pentanes reacted with methyllithium at −55 to −10°C to give exclusively 1-tert-butoxy-2-vinylidenecyclopropane. The reaction of 1-bromo-1-fluoro-4-phenylsulfanylspiro[2,2]pentane with methyllithium resulted in replacement of the fluorine atom by methyl group.

A series of novel gem-bromofluorospiropentanes were synthesized and investigated in the reaction with methyllithium. Either substitution of the fluorine atom for a methyl group or rearrangement into methylated cyclobutene derivatives occurred under these conditions.

This paper reviews the literature data on mercury-less electrodes for determining traces of transition elements by stripping voltammetry after the adsorption enrichment of these elements as dimethylglyoxime complexes on the surface of the electrode. A brief discussion of the design and characteristics (detection limit, adsorption time) of mercury-less electrodes and mercury-based electrodes is given.

A series of novel gem-bromofluorospiropentanes were synthesized and investigated in the reaction with methyllithium. Either substitution of the fluorine atom for a methyl group or rearrangement into methylated cyclobutene derivatives occurred under these conditions.

The present research deals with the digital synthesis of the multiview diffractive image elements, or simply the Multiview Diffractive Images (MDIs), also known as stereographic diffractive images or holographic stereograms. These images are designed to be included in Diffractive Op tically Variable Image Devices (DOVIDs) in order to make them more spectacular and visually impressive and to improve their security properties. In the present paper there are considered the computation of parameters for Diffractive Gratings (DGs) composing the MDI topology. The innovative DGs based on the curvilinear strokes are offered. They provide larger diffraction efficiency and better integrity of the scene for any variant of the Lighting and Observation (LO) as well as for the arbitrary parameters of LO geometry. There are described the original approach for computation and estimation of the polychromatic DGs intended to reproduce the complex spectral distribution of the diffracted light. There are proposed the powerful and flexible techniques for Diffractive Images (DIs) enco ding and for uniting different DIs within multichannel one. The distinctions in the modes of the MDI observation, which were escaping anyone’s attention until now, are discussed. The physical aspects of visu al perception for diffractive images are also concerned. So, the present investigations elucidate the main topics pertinent to the diffractive images synthesis and approach to master the creation of striking ones, particularly the multiview images. Keywords: Diffractive Optically Variable Image Device, Electron-Beam Lithography, Diffractive Image, Multiview Image, Polychromatic Curvilinear Diffractive Grating.

The present work deals with the Multiplex Images (MIs) including stereographic and animated ones with opportunity to predict their appearance and behavior before they are recorded by Electron-Beam Lithography Equipment (EBLE). On the one hand the presence of MI in Optical Security Device (OSD) increases its structure complexity improving security properties; on the other hand it makes it more spectacular and visually impressive. The analysis of MI behavior on a visual level is based on the theoretical estimations of the diffraction by the phase reflecting Elemental Diffracting Grating (EDG) under the arbitrary Conditions of Lighting and Observation (CLO). These estimations start from the strict quantitative formulation of the Huygens-Fresnel principle that was by Kirchhoff presented in 1883. They are also used for the assignment of encoding parameters for MI. The approach of middle wave zone is used, i.e. the distinctions in CLO for different points of MI topology are taken into account, which provides the integrity of the scene during observation. To represent the diffraction results in the RGB color system, it has been proposed to use the non-linear color compensation. It allows to obtain more expressive highlights together with shadows within one computed angle shot. Experimental results show viability of the proposed approach to visualization. Undoubtedly, the opportunity of predicting the look of any MI, provided by this utility, is a powerful tool, which will help to create vivid and impressive diffractive images.

The basic aspects of animated and stereographic rainbow images making technology are considered in this paper. These images are devoted to include in Optical Security Devices (OSDs) in order to increase its structure complexity and to improve its protective properties. They provide on the one hand the simple identification on the visual level of verification and on the other hand the sufficient reliability against counterfeit. The last one is achieved at first by the division of the elemental unit on the regions of any adjusted shape with outline of the precision that is inaccessible for recreation without Electron Beam Lithography Equipment (EBLE), which is used for OSDs recording, and, secondly, by the used encoding methods. In the context of the paper the theoretical discussion of the diffraction on elemental diffractive grating was carried out. The acquired results have been allowed to create the software utility that models the behaviour of the anigram or stereogram. The analysis of examples of the sythetized by the given methodology anigrams shows that there is peculiar for them the effects of the stereoscopic perception. So the investigations on combined methodology of animated stereographic images synthesis were carried out. There were recorded the stereographic, animated and the animated stereographic images as a parts of demonstrational holograms of STC “Optronics”, Ltd.

In the context of the paper there are represented the theoretical foundations and technological aspects of creation of the Optical Security Devices by Polygram technology. This technology implies the images of different types combining. There are generally discussed the Computer-Generated Rainbow Holograms (CGRHs) of 3D images. This type of holographic images is distinguished by its reliability against counterfeit, caused by the fact it requires matchless in this field precision of printing system, using extreme for the Electron Beam Lithography Equipment, which is applied for the recording, values of the stamp sizes. On the other hand CGRHs certainly distinguish from similar optical and stereographic images, so they can be easy recognized on the visual level of the verification and don’t need application of any tools. The theoretical basis of the CGRHs creation is strictly presented in this paper. The special attention is paid to the right choice of the non-linear quantization parameters. This paper is mainly concentrated on the investigation of the CGRH combining both with another CGRHs and with the other different images implying by the Polygram technology. The methods of the space restriction of the separate CGRH topology with the information loss and without it are compared. There are carried out the investigations of the influence of the additional images on visual perception of the CGRH.

This work deals with Computer-Generated Rainbow Holograms (CGRHs), which can restore the 3D images under white light. They are devoted to include in Diffractive Optically Variable Image Devices (DOVIDs) that are currently widely used for security needs. CGRHs prevent counterfeiting due to the complexity of recreation on the one hand and allow the simple identification at the first (visual) level of verification on the other hand. To record it the Electron Beam Lithography (EBL) is used. The CGRH computation process is conventionally divided on two parts: synthesis and recording. On the synthesis stage, firstly, the geometrical and optical constants of recording scheme are determined, secondly, the basic parameters accounting for discretization of ID in hologram plane are defined and, finally, the calculation of the Interferogram Data (ID) - the array of Bipolar Intensity (BI) values - is carried out. This calculation is performed separately in each independent horizontal slice of object space and hologram plane. On the recording stage a suitable quantization parameters are chosen and transformation of ID into the multilevel rectangle data appropriate for EBL is accomplished. The investigations on optimization of synthesis and recording of the multilevel CGRHs of 3D images integrated in Polygrams are presented here. So the rules for definition of the appropriate discretization parameters were finding out. Advantages of using non-linear quantization that implies condensing of quantization levels near the BI zero were explored. The random deviation of location and direction of elemental hybrid radiating area was applied.

Computer-generated holograms (CGHs) integrated within combined optical-digital security devices (CO/DSDs) are described in this work. They can restore the monochrome and color 3D images in white light. For their recording the Electron Beam Lithography (EBL) is used. Our investigations on optimization of synthesis and recording of the CO/DSDs with the integrated in it multilevel CGHs of 3D images possessed horizontal parallax only (HPO) are presented here. The CGH fabrication process is mainly composed of two parts: calculating of the interferogram data (ID) and their recording. Calculation of the ID is done as follows: firstly, the geometrical and optical constants of recording scheme and the object surface represented by the elemental self-radiating areas, are determined, secondly, the basic parameters accounting for discretization of ID in hologram plane is defined. The ID values can be derived by calculation of the necessary elemental object areas bipolar intensities sum. Next, over suitable quantization of ID, recording of the rectangle data appropriate for EBL onto glass coated with non-organic photoresist based on As40S40Se20 is performed. We have also investigated reciprocal influence of an optical part of the CO/DSD and a digital one.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.