Use of ultrafiltration on the analysis of low molecular weight complexing molecules. Analysis of iminodiacetic acid at constant ionic strength

Low molecular weight complexing molecules may be indirectly analyzed by ultrafiltration with the aid of a water-soluble polymer. The theory concerned is developed and the analysis of iminodiacetic acid (IDAA) is performed by ultrafiltration of aqueous solutions containing poly(sodium-4-styrenesulfonate) (PSS), Cu(NO3)2, and IDAA in variable concentrations. The technique allows measuring IDAA in a range of concentrations between 10(-4) M and 10(-5) M when a 1.6 x 10(-4) M Cu2+ solution is ultrafiltered in the presence of PSS and IDAA.     

Host-Plant Chemicals and Distribution of Neuquenaphis on Nothofagus

Extractable metabolites from leaves (EM) and volatiles released from six Nothofagus species were analyzed by TLC and GC-MS, respectively. Aphids of the genus Neuquenaphis, closely associated to Nothofagus, were sampled on each Nathofagus species. Cluster analyses of Nothofagus species were performed based on the presence or absence of EM and volatiles. Dissimilarity distances, from the cluster analyses of EM and volatiles, were used to evaluate their association with the aphid distribution. A major component identified from EM and volatiles of three species of Nothofagus, -agarofuran, was attractive to alates of the oligophagous Neuquenaphis sensoriata, which use them as hosts. These results suggest that chemicals play a significant role in the host-plant associations between Neuquenaphis and Nothofagus.     

Ethylene polymerization catalyzed by diamide complexes of Ti(IV) and Zr(IV)

In this research, we describe the application of the complexes o‐C₆H₄(NSiMe₃)₂ZrCl₂ ( 1 ), o‐C₆H₄(NSiMe₃)₂TiBr₂ ( 2 ), o‐C₆H₄(NSiMe₃)₂TiCl₂ ( 3 ), C₂H₄(NSiMe₃)₂ZrCl₂ ( 4 ), in the ethylene polymerization with different Al/M ratios and temperatures. These complexes presented significant catalytic activities in the presence of methyaluminoxane (MAO) as cocatalyst and toluene as solvent, producing high molecular weight linear polyethylenes. Zirconium complexes were more active at 60°C and titanium complexes at 40°C. Zirconium complex ( 1 ) showed the best values of activity (347 kg PE/mol Zr h atm) for Al/Zr ratio of 340 and 60°C of temperature. In ethylene‐1‐hexene copolymerization, the best result was also reached with catalyst 1 , at the same conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of high‐density polyethylene/rGO‐CNT‐Fe nanocomposites with outstanding magnetic and electrical properties

Semi‐conducting polyethylene (PE) nanocomposites with outstanding magnetic properties at room temperature were synthesized. These exceptional properties, for a diamagnetic and insulating matrix as PE, were obtained by polymerizing ethylene in the presence of a catalytic system formed by a metallocene catalyst supported on a mixture of reduced graphene oxide (rGO) and carbon nanotubes with encapsulated iron (CNT‐Fe). It was used a constant and very low amount of CNT‐Fe, obtained by vapor chemical deposition using ferrocene. The percolation threshold, to achieve conductivity, was obtained using a variable amount of rGO. The nanocomposites were semiconductors with the addition of 2.8 wt % and 6.0 wt % of the filler, with electrical conductivities of 4.99 × 10^?6 S cm^?1 and 7.29 × 10^?4 S cm^?1, respectively. Very high coercivity values of 890–980 Oe at room temperature were achieved by the presence of only 0.04–0.06 wt % of iron in the nanocomposites. The novelty of this work is the production of a thermoplastic with both, magnetic and electric properties at room temperature, by the use of two fillers, that is rGO and CNT‐Fe. The use of a small amount of CNT‐Fe to produce the magnetic properties and variable amount of rGO to introduce the electrical conductivity in PE matrix let to balance both properties. The encapsulation strategy used to obtain Fe in CNT, protect Fe from easy oxidation and aggregation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45382.     

Polymerization of ethylene by (α‐Diimine) nickel catalyst and statistical analysis of the effects of reaction conditions

This article regards the ethylene polymerization catalyzed by a nickel catalyst and activated by ethylaluminum sesquichloride (EASC). The effects of the reaction conditions [polymerization temperature, cocatalyst (EASC) concentration, and ethylene concentration] on the average molecular weights of the final polymers and reaction yields were evaluated with the help of empirical statistical models. It is shown that reaction temperature and cocatalyst (EASC) concentration exert the most important effects on average molecular weights and catalyst activity. The polydispersities of the obtained polyethylenes are larger than the polydispersities of polyethylenes obtained with typical Brookhart catalysts. The analysis of polymer branching frequencies shows new types of short branching and significant amounts of long branches, which may explain the relatively large polydispersities of the obtained polymer samples. POLYM. ENG. SCI., 50:1797–1808, 2010. © 2010 Society of Plastics Engineers     

Fabrication and application of Nafion®-modified boron-doped diamond electrode as sensor for detecting caffeine

The surface of boron-doped diamond (BDD) electrodes has been modified by Nafion^®. The polymer film was applied onto the BDD electrode surface by solvent evaporation. Nafion^®-BDD electrode was used as a sensor for caffeine detection in e.g. cola beverage samples. In cyclic voltammetric measurements, favorable ionic interaction between the Nafion^® film and caffeine enhances the current response, and thus the sensitivity, compared to that at the bare electrode. The modified electrode exhibits a stable and sensitive response to caffeine and may represent a new analytical tool, offering a significant improvement over other electroanalytical methods (e.g.: Nafion^®-modified glassy carbon electrode) and the accepted method for caffeine analysis (HPLC-MS). The analysis of residuals from the linear regression proved that a linear response exists from 2.0 × 10^? 7 to 1.2 × 10^? 5 M, obtaining a limit of detection of about 1.0 × 10^? 7 M. The findings presented in this study are described and discussed in the light of the existing literature.     

Analysis of traffic accident severity using Decision Rules via Decision Trees

A Decision Tree (DT) is a potential method for studying traffic accident severity. One of its main advantages is that Decision Rules (DRs) can be extracted from its structure. And these DRs can be used to identify safety problems and establish certain measures of performance. However, when only one DT is used, rule extraction is limited to the structure of that DT and some important relationships between variables cannot be extracted. This paper presents a more effective method for extracting rules from DTs. The method’s effectiveness when applied to a particular traffic accident dataset is shown. Specifically, our study focuses on traffic accident data from rural roads in Granada (Spain) from 2003 to 2009 (both included). The results show that we can obtain more than 70 relevant rules from our data using the new method, whereas with only one DT we would have extracted only five relevant rules from the same dataset.