Weathering of low‐density polyethylene grafted with itaconic acid in laboratory tests

Polyethylene grafted with itaconic acid was subjected to weathering under laboratory accelerated conditions. The course of the photo‐oxidative degradation process of that material was studied by FTIR spectroscopy both through quantitative measurements of changes in absorbance values at selected wave numbers and through measurements of surface area values for absorption bands which were separated by means of deconvolution. The use of both those procedures of quantitative determinations resulted in a general conclusion that the oxidation process was initiated from the very first moment of irradiation, and it produced ketones, acids, esters (intramolecular and of acetate type), peracids, peresters, hydroperoxides, and alcohols. The molecular weight values and gel number values, which were established as well, pointed out that oxidation was accompanied by cracking of polymer macromolecules, and also by polymer crosslinking to a limited degree. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A supported titanium postmetallocene catalyst: Effect of selected conditions on ethylene polymerization

Ethylene polymerization with a titanium complex [N,N‐ethylenebis(3‐methoxysalicylideneiminato)titanium dichloride] immobilized on the magnesium support with the formula MgCl₂(THF)_0.32(Et₂AlCl)_0.36 was studied. In particular, the effects of polymerization temperature, monomer pressure, and polymerization time on the activity of the catalyst and on the polyethylene properties (molecular weight and its distribution, melting point, crystallinity, and bulk density) were evaluated. The findings of investigations prove that the studied supported titanium catalyst is highly active in ethylene polymerization, and its activity increases with increasing temperature and monomer pressure. Moreover, stability of the catalytic systems is dependent on the activator type used. Me₃Al, when employed as an activator, makes the catalytic system undergo no deactivation in practice. The catalyst coupled with MAO turned out less stable. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and catalytic properties for olefin polymerization of new vanadium complexes containing silsesquioxane ligands with different denticity

A series of new vanadium‐silsesquioxanes ( 2a ? 2d ) was prepared by reacting VCl₄ with not fully condensed silsesquioxanes (having from one to four silanol groups) and evaluated as pre‐catalysts in olefin polymerization. The activation of 2a ? 2d with EtAlCl₂ generated highly active catalysts for ethylene polymerization, yielding high molar mass polymers with narrow dispersity. Ultra‐high molar mass polyethylenes, M _w up to 4 × 10⁶ g mol^?1, were obtained with methylaluminoxane and Al(i Bu)₃/[Ph₃C][B(C₆F₅)₄] as activators. Upon treatment with methylaluminoxane and boron compounds, all vanadium pre‐catalysts were active in 1‐octene polymerization as well, and produced isotactic‐rich poly(1‐octene)s with moderate monomer conversion (up to 23%). The polymerization parameters were optimized and the effect of the silsesquioxane structure on the catalytic activity and polymer properties was studied. © 2017 Society of Chemical Industry     

Synthesis and activity of zirconocene catalysts supported on silica-type sol-gel carrier for ethylene polymerization

Summary Synthesis and activity of bis(cyclopentadienyl)zirconium dichloride catalyst supported on unconventional silica-type material obtained in sol-gel process and activated by organoaluminium co-catalyst were studied. The effect of support modification conditions (thermal dehydration and/or modification by organoaluminium compound) and a type of co-catalyst on an activity of the catalytic system in ethylene polymerization and properties of resulting polymers were investigated and compared with results obtained earlier for vanadium catalysts supported on mentioned sol-gel carrier. The most appropriate method of the sol-gel silica-type support preparation is thermal pre-treating (200°C) followed by modification with AlEt₂Cl. Metallocene catalyst supported on such sol-gel product and activated by MAO appeared to be most active among studied systems. Studied Cp₂ZrCl₂/MAO supported on silica-type sol-gel carrier allow to obtain polyethylene (at 50°C polymerization temperature) with yield up to 30·10⁶ g/(mol_Zr·h), molecular weight below 300 000 and MWD=2−4. Received: 4 September 2000/Revised version: 3 January 2001/Accepted: 3 January 2001     

The employability of older workers as teleworkers: An appraisal of issues and an empirical study

The aging of the population and, concomitantly, of the workforce has a number of important implications for governments, businesses, and workers. In this article, we examine the prospects for the employability of older workers as home‐based teleworkers. This alternative work could accommodate many of the needs and preferences of older workers and at the same time benefit organizations. However, before telework can be considered a viable work option for many older workers there are a number of issues to consider, including the ability of older workers to adapt to the technological demands that are typically associated with telework jobs and managerial attitudes about older workers and about telework. Through an integrated examination of these and other issues, our goal is to provide a comprehensive understanding of the challenges associated with employing older workers as teleworkers. We also present findings from a questionnaire study that assessed managers' perceptions of worker attributes desirable for telework and how older workers compare to younger workers on these attributes. The sample included 314 managers with varying degrees of managerial experience from a large variety of companies in the United States. The results presented a mixed picture with respect to the employability of older workers as teleworkers, and strongly suggested that less experienced managers would be more resistant to hiring older people as teleworkers. We conclude with a number of recommendations for improving the prospects for employment of older workers for this type of work arrangement. © 2009 Wiley Periodicals, Inc.     

Aging, motor control, and the performance of computer mouse tasks

Because of the increased presence of computers in work and everyday life and the demographic "graying" of America, there is a need for interface designs that promote accessibility for older people. This study examined age differences in the performance of basic computer mouse control techniques. An additional goal of the study was to examine the influence of age-related changes in psychomotor abilities on mouse control. A total of 60 participants in 3 age groups (20-39 years, 40-59 years, and 60-75 years) performed 4 target acquisition tasks (pointing, clicking, double-clicking, and dragging) using a computer mouse. The data indicated that the older participants had more difficulty performing mouse tasks than the younger participants. Differences in performance attributable to age were found for the more complex tasks (clicking and double-clicking). Furthermore, age-related changes in psychomotor abilities were related to age differences in performance. We discuss applications to computer interface designs. Actual or potential applications of this research include specifications for computer mouse design to accommodate older populations.     

Lipopolysaccharide-neutralizing antibody reduces hepatocyte injury from acute hepatotoxin administration

OBJECTIVES: This study investigated the role of nitrate technetium-99m sestamibi imaging in predicting the postrevascularization outcome of chronically hypoperfused asynergic territories. BACKGROUND: Rest technetium-99m sestamibi myocardial scintigraphy underestimates the presence of viable myocardium in asynergic territories. Stimulation that improves coronary blood flow could increase tracer uptake in hibernating territories. METHODS: Nineteen patients with a previous myocardial infarction and left ventricular dysfunction scheduled for revascularization underwent quantitative technetium-99m sestamibi tomography under baseline conditions and during isosorbide dinitrate infusion. Global and regional function were assessed, respectively, before and after revascularization by radionuclide angiocardiography and two-dimensional echocardiography. RESULTS: Seven patients (group A) showed postrevascularization regional function recovery, and 12 (group B) showed no significant changes. In group A, nitrate infusion induced a decrease in the extent of the global uptake defect ([mean +/- SD] -37.4 +/- 21.6% of baseline value); in group B, no change or a slight increase was observed (+5.8 +/- 8.4%, p < 0.0005 vs. group A). The nitrate-induced changes in the extent of uptake defect correlated with postrevascularization changes in ejection fraction (r = -0.94, SEE 7.6). After revascularization, 11 asynergic vascular territories showed improvement (hibernating), and 34 remained unchanged (fibrotic). With administration of nitrates, 10 hibernating territories had a decrease in the extent of uptake defect, whereas only 4 of 34 of the fibrotic territories showed a nitrate-induced uptake improvement. CONCLUSIONS: Short-term administration of isosorbide dinitrate immediately before injection of technetium-99m sestamibi increases tracer uptake in some chronically hypoperfused asynergic territories. This finding correlates with the observation of post-revascularization functional recovery. Nitrate technetium-99m sestamibi myocardial scintigraphy could be a promising method for the noninvasive detection of viable hibernating myocardium.     

Ethylene/1-olefin copolymerization behaviour of vanadium and titanium complexes bearing salen-type ligand

Ethylene/1-olefin copolymerization using vanadium and titanium complexes bearing tetradentate [O,N,N,O]-type ligand and EtAlCl₂ or MAO as a cocatalyst is carried out. In the presence of the vanadium complex activated with EtAlCl₂ is observed (a) negative “comonomer effect”, (b) high comonomer incorporation and narrow chemical composition distribution (CCD), (c) unexpected copolymer microstructure, and (d) increased molecular weight of copolymers when compared with the homopolymer. In contrast, titanium catalyst gives copolymers with lower 1-olefin content and broad CCD. Supported complexes show higher activity, lower 1-olefins incorporation and give copolymers with ultra high molecular weights.     

Detection of B<Subscript>6</Subscript> Vitamers in Grain Products: Experimental and Computational Studies

A reversed phase high-performance liquid chromatography method (HPLC) with coulometric electrochemical detection has been applied and validated for the simultaneous analysis of pyridoxamine (PM), pyridoxal (PL), and pyridoxine (PN) in cereal products. Isocratic separation was achieved using a C₁₈ column with a mobile phase consisting of methanol-phosphate buffer (10:90) and 0.018 M trimethylamine adjusted to pH 3.55 with 85% orthophosphoric acid. The limits of detection for PM, PL, and PN were 0.28, 0.36, and 0.43 ng mL^?1, respectively, with vitamins recoveries ranging from 90.4 to 98.1%. The applied method for the analysis of B₆ vitamins naturally present in grain products, offers a simple and fast sample preparation without derivatization. To understand vitamer separation further, methods of computational chemistry were employed. Specifically, density functional theory (DFT) was used to determine electrostatic potentials, as well as the charges of each vitamer. A number of correlations were established between these properties and elution order.