Volume 88, Issue 12

It is well-known that the properties of cross-linked rubbers are strongly affected by the cross-link density. In this work it is shown that for thermoreversibly cross-linked elastomers, the type and length of the cross-linker also have a significant effect. A homologous series of diamine and bismaleimide cross-linkers was used to cross-link maleic-anhydride-grafted EPM irreversibly and furan-modified EPM thermoreversibly, respectively. Bismaleimide cross-linkers with a polarity close to that of EPM and a relatively low melting point have a better solubility in the rubber matrix, which results in higher chemical conversion and, thus, higher cross-link densities at the same molar amount of cross-linker. Samples cross-linked with different spacers (aromatic and aliphatic spacers of different lengths) were compared at the same cross-link density to interpret the effects on the material properties. The rigid character of the short aliphatic and the aromatic cross-linkers accounts for the observed increase in hardness, Young´s modulus and tensile strength with respect to the longer, more flexible aliphatic cross-linkers. In conclusion, the structure of the cross-linking agent can be considered as an alternative variable in tuning the rubber properties, especially for thermoreversibly cross-linked rubber.

The overall performance of alkoxysilanes as stone consolidants is constrained by stone mineralogy (particularly in the carbonate varieties) and by their tendency to crack during drying. In an attempt to overcome these problems, polyethylene glycol “chains” with two carboxylic acid end-groups (PEG-CA) were introduced in siloxane sols obtained by sol-gel chemistry using tetraethoxysilane (TEOS) as precursor. Different pre-condensation degrees (by varying the stirring times of sol-gel reaction: 10 min, 2, and 24 h) and PEG-CA chains with different molecular weights were studied as variables affecting the initial efficacy of the consolidants when applied into a limestone. The sol containing siloxanes with the lowest pre-condensation degree (10 min stirring) was quite susceptible to the carbonate media and thus a poor consolidation was achieved. The sol with the highest pre-condensation degree (24 h stirring) together with the PEG-CA chains with intermediate molecular weight produced significant and uniform strength gains along the stone depth. The consolidation also showed to be highly dependent on the molecular weight of the PEG-CA chains, the PEG-CA with highest molecular weight produced a non-uniform strength increase with potential harmful side effects. The results confirmed the role of carboxylic acid end-groups as efficient sol-gel catalysts and their ability to be incorporated into the silica matrix in the presence of carbonate stone.

A new multicomponent method for the synthesis of N -alkyl-2-( Z -1,2-diferrocenylvinyl)-4,5-dihydrooxazolinium salts 3a–f , 5-( N -alkyl-2′,3′-diferrocenyl-acryloylamido)-3-aza-3-alkylpentanols 4a–d , ( E )- N -alkyl- N -(2-morpholinoethyl)-2,3-diferrocenylacrylamides 9a,b,e,f and ( E )- N -alkyl- N -(2-piperidinoethyl)-2,3-diferrocenylacrylamides 10a,c from reactions of 2,3-diferrocenylcyclopropenone 1 with bis -1,4- N,O -nucleophiles in the presence of triethyloxonium tetrafluoroborate, alkyl iodides, morpholine, piperidine and Et 3 N is described. The characterization of the new compounds was done by IR, 1 H- and 13 C-NMR spectroscopy, mass-spectrometry, elemental analysis and X-ray diffraction studies.

This paper presents the sorption properties of a new adsorbent material prepared by impregnating Amberlite XAD 7 polymer with sodium β-glycerophosphate. For impregnation, the pellicular vacuum solvent vaporization method was employed. The functionalization was evidenced by energy dispersive X-ray analysis. The usefulness of this material and its performances were studied for the adsorption of the rare earth element La(III) in batch experiments. The influence of various parameters affecting the adsorption of lanthanum like contact time, initial concentration, pH value, and temperature was studied. The kinetic of the adsorption process was best described by the pseudo-second-order model. Sips isotherm was found to be the best fit of the equilibrium data. The maximum adsorption capacity of the functionalized material was of 33.8 mg La(III)/g. The values of thermodynamic parameters (Δ G o , Δ H o , Δ S o ) showed that the adsorption process was endothermic and spontaneous. The results proved that Amberlite XAD 7 functionalized with sodium β-glycerophosphate is an efficient adsorbent for the removal of La(III) ions from aqueous solutions. Quantum chemistry was performed using Spartan software.

A high molecular weight chitosan was chemically modified to quantitatively incorporate quaternary ammonium groups. Its efficiency was evaluated in the liquid-solid separation for various liquors, and compared with the one of a polyelectrolyte usually used for this utilization. The performance of the liquid-solid separation was estimated through the determination of two parameters measured after the screening- settling of the mixture liquor/flocculating agent: the separation efficiency (EV) and the TS removal efficiency (ETS). Apart for liquor 6, TS removal was always better after an addition of functionalized chitosan. Furthermore, whatever the type of liquor, the distribution was modified by an increased presence of high-size particles when functionalized chitosan was added. Moreover, chitosan addition tended to homogenize the size of the particles, which could facilitate the choice of the liquid-solid separation process. This homogenization was particularly observed for the liquor initially highly dispersed in size, i.e. liquors 1, 4, 6 and 8.

The triazine-based herbicides removal from aqueous solution on specific polymeric adsorbent was studied. Poly(divinylbenzene) modified with maleic anhydride in Diels-Alder reaction was selected for the sorption experiments because molecular structures of triazine derived herbicides exhibit complementarity to the arrangement of functional groups in the polymer. The presence of carboxyl groups in adsorbent structure resulted in specific directional interactions, such as hydrogen bonds, which can intensify adsorption ability towards triazines. In the case of both atrazine and terbuthylazine the effect is more intensive, whereas in sorption of simazine and propazine the non-specific interactions have higher importance than hydrogen bonds. Specific interactions in investigated systems are between the hydrogen atom of the amino group of triazine and the carbonyl oxygen atom of the carboxyl group of the modified poly(divinylbenzene) (O…H–N). Only in the case of terbuthylazine the creation of hydrogen bonds between hydroxyl hydrogen atom of carboxylic group and nitrogen atom containing free electron pair from triazine (O–H…N) was observed. The sorption of simazine, atrazine and propazine does not depend on pH in the acidic region, whereas in the case of terbuthylazine an increase in sorption efficiency is observed while pH decreases.

The porous material containing carboxyl groups was investigated in fixed bed system for the triazine-based herbicides removal from aqueous solution. In order to obtain adsorbent capable of generating specific interactions with triazines, the poly(divinylbenzene) was synthesized in radical suspension polymerization and then was modified with maleic anhydride in Diels-Alder reaction with subsequent base hydrolysis. The introduction of carboxyl groups into polymer structure resulted in obtaining specific interactions, such as hydrogen bonds between modified poly(divinylbenzene) and triazines, therefore the selectivity and the high adsorption capacity towards terbuthylazine, propazine, atrazine and simazine was observed. The total and usable adsorptive capacities, the breakthrough and exhaustion times, the coefficients of sphericity of isoplanes, the heights of adsorption fronts and the mass exchange moving rates were calculated based on the analysis of the breakthrough curves. Results show that the best sorption parameters in dynamic conditions were achieved for terbuthylazine and propazine. For them the highest values of adsorptive capacities, the smallest heights of mass transfer fronts and their slow movement along the bed height were obtained. The use of ethanol for herbicides elution provided a high recovery degree of adsorbed substances. Reusability of investigated polymer bed was studied in three adsorption/desorption cycles.

New copolymers of ε-caprolactone with three hydroxy-fatty acids, 12-hydroxy stearic acid, 16-hydroxyhexadecanoic acid and ricinoleic acid, were synthesized by catalytic polyesterification. The reactions were carried out in solvent-free systems and in organic solvents as well, using tin(II) 2-ethylhexanoate as catalyst, at different temperatures and molar ratios of the comonomers. Cyclic and linear polymeric products with medium molar weight of about 2000 Da have been synthesized and their chemical structures were confirmed by FT-IR, NMR and MALDI-TOF MS analysis. The synthesis parameters were optimized and the ε-caprolactone/hydroxy acid molar ratio was set as 5:1, according to mass spectrometry results. The biodegradability of the newly synthesized polymers was studied in the presence of Candida antarctica B lipase in phosphate buffer solutions (pH=7.4), at 37°C. The weight-loss profile emphasized the degradation of the 16-hydroxyhexadecanoic acid based polymer samples at more than 50% of their initial weight in 18 days of incubation in the presence of the lipase. The composition of the degradation products was assessed using the GC-MS technique and displayed residues of the comonomers moieties.

There are 63 chemical elements that have two or more isotopes that are used to determine their standard atomic weights. The isotopic abundances and atomic weights of these elements can vary in normal materials due to physical and chemical fractionation processes (not due to radioactive decay). These variations are well known for 12 elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, bromine, and thallium), and the standard atomic weight of each of these elements is given by IUPAC as an interval with lower and upper bounds. Graphical plots of selected materials and compounds of each of these elements have been published previously. Herein and at the URL http://dx.doi.org/10.5066/F7GF0RN2, we provide isotopic abundances, isotope-delta values, and atomic weights for each of the upper and lower bounds of these materials and compounds.

A joint IUPAC/IUPAP Working Party (JWP) has confirmed the discovery of the elements with atomic numbers ( Z ) 113, 115, 117 and 118. In accordance with the 2016 IUPAC guideline for naming new elements, the discoverers were invited to propose names and symbols for the elements. Claims have been assigned to them and the following are proposed: (a) nihonium and symbol Nh, for the element with Z =113, (b) moscovium with the symbol Mc, for the element with Z =115, (c) tennessine with the symbol Ts, for the element with Z =117, and oganesson with the symbol Og, for the element with Z =118. After careful deliberation on these names and symbols, considering the 2016 rules and a public review period, the Inorganic Chemistry Division recommended these proposals for acceptance by the IUPAC Council.