On the Development of Titanium κ1-Amidinate Complexes,Commercialized as Keltan ACE™ Technology,Enabling the Production of an Unprecedented Large Variety of EPDM Polymer Structures

ARLANXEO Elastomers has developed and commercialized Keltan ACE™ technology, a class of half-sandwich cyclopentadienyl κ¹-amidinate metal complexes, which are extremely active for the production of first-class ethylene/propylene/diene copolymers (EPDM). In this review, the development and some of the key features of the Keltan ACE™ catalyst system are presented. Many different ACE catalysts have been synthesized over the past years, including bridged and bimetallic catalysts. With Keltan ACE™, a complete range of EPDM products with similar polymer characteristics as their Ziegler–Natta (ZN) counterparts can be produced, including variations containing very high 5-ethylidene-2-norbornene (ENB) contents, controlled long chain branching, very high molecular weight, as well as oil-extended products. Moreover, other EPDM structures can be polymerized. The Keltan ACE™ catalyst technology also allows the production of EPDMs with very high amounts of dicyclopentadiene (DCPD) or 5-vinyl 2-norbornene (VNB) without excessive gelation and reactor fouling, that is, products that cannot or are extremely difficult to obtain via classical ZN catalysis. In a next step, high-VNB-EPDM can be postreactor modified, for example, via metathesis chemistry. In addition, EPDM polymers with a very broad or even bimodal molecular weight distribution can be obtained in a single reactor with certain ACE catalyst structures at particular activator/precatalyst ratios. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2877–2891     

Thermal photoionization in resonance ionization spectroscopy

In Resonance Ionization Spectroscopy, neutral atoms are usually produced by thermal effects, using an oven or a hot surface at high temperature. The radiation from these thermal sources is intense enough to effectively contribute to the photoionization of atoms excited by laser pumping. We show that, for the most common experimental conditions, the ratio of thermal to laser photoionization can be higher than one for excited levels which lie as far as a few thousand cm^–1 below the ionization threshold. This result is obtained with the use of the analytic expression for the photoionization cross-section of a hydrogen-like atom. We suggest two applications of this thermal photoionization. Namely, the study of highly excited states and Quasi Resonance Ionization Spectrometry, using only one laser of low radiance.Commissariat à l'Energie Atomique, Centre d'Etudes Nucléaires de Fontenay-aux-Roses DERDCA/DCAEA/SEA, BP no 6, F-92265 Fontenay-aux-Roses Cedex, France (Visiting scientist at Ecole Polytechnique from Commissariat à l'Energie Atomique)Commissariat à l'Energie Atomique, Centre d'Etudes Nucléaires de Saclay, IRF/DPHG/PAS. Bât 462, F-91191 Gif-sur-Yvette Cedex, France     

Direct determination of traces of lanthanide ions in aqueous solutions by laser-induced time-resolved spectrofluorimetry

The most convenient spectral regions for dye laser excitation are presented for seven lanthanide ions. Fluorescence lifetimes are given for 0.5 M sulphuric acid and 3 M potassium carbonate media. With the excimer-pumped dye laser, the detection limits are in the range 0.1 μg 1^?1 (Eu) to 50 μg 1^?1 (Gd). Examples of the resolution of mixtures are given.     

Literatur

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Influence of the particle size of the MgCl2 support on the performance of Ziegler catalysts in the polymerization of ethylene to ultra‐high molecular weight polyethylene and the resulting polymer properties

A highly systematic size series of Ziegler catalysts with similar porosities and surface textures are synthesized by varying the stirring speed during the MgCl₂ support synthesis. Besides the mean particle size, the only substantial difference observed between the various catalysts is the size and number of nodules per particle. Varying the mean diameter of the catalyst particles between 1.5 and 11.9 µm, leads to a pronounced impact on the activity in ultra‐high molecular weight polyethylene (UHMWPE) polymerization, while the M_w capabilities are only affected to a limited extend. In addition, it is observed that both the M_ws as the polymer bulk density (BD) increases during the course of the polymerization. This particularity allows to optimize the M_w and/or BD at a set polymer size, by tuning the catalyst particle size. This is particularly interesting in UHMWPE production, as control of the morphological and structural properties of the UHMWPE reactor powders are critical for efficient processing as well as the performance of the final product. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2679–2690     

Real-time quantitative polymerase chain reaction methods for four genetically modified maize varieties and maize DNA content in food

Quantitative detection methods are needed for enforcement of the recently introduced labeling threshold for genetically modified organisms (GMOs) in food ingredients. This labeling threshold, which is set to 1% in the European Union and Switzerland, must be applied to all approved GMOs. Four different varieties of maize are approved in the European Union: the insect-resistant Bt176 maize (Maximizer), Btl 1 maize, Mon810 (YieldGard) maize, and the herbicide-tolerant T25 (Liberty Link) maize. Because the labeling must be considered individually for each ingredient, a quantitation system for the endogenous maize content is needed in addition to the GMO-specific detection systems. Quantitative real-time polymerase chain reaction detection methods were developed for the 4 approved genetically modified maize varieties and for an endogenous maize (invertase) gene system.     

Dramatic enhancement of the alkene metathesis activity of Mo imido alkylidene complexes upon replacement of one tBuO by a surface siloxy ligand

[(triple bond SiO)Mo(triple bond NAr)(=CHCMe2R)(OtBu)], a well-defined silica supported alkene metathesis catalyst precursor, shows a dramatic enhancement of activity and selectivity compared to [Mo(triple bond NAr)(=CHCMe2R)(OtBu)2] and [(triple bond SiO)Mo(triple bond NAr)(=CHCMe2R)(CH2tBu)], respectively.