Thermally Stable and Optically Active Poly(amide-imide)s Derived from 4,4’–(Hexafluoroisopropylidene)-N,N’-bis-(phthaloyl-L-methionine) Diacid Chloride and Various Aromatic Diamines: Synthesis and Characterization

Summary Thermally stable and optically active poly(amide-imide)s (PAIs) have been synthesized and their properties such as optical activity, solubility, thermal stability were studied. Polymers were synthesized by solution polymerization of 4,4’–(hexafluoroisopropylidene)-N,N’-bis-(phthaloyl-L-methionine) diacid chloride and various aromatic diamines by three different methods. The compounds obtained were characterized by elemental C, H and N analysis, solubility, FTIR, ¹H NMR and ¹⁹F NMR spectroscopy. Thermogravimetric curves were also recorded. All data agree with the proposed structures.     

Direct Polyamidation of N,N’-(4,4’-Hexafluoroisopropy-lidendiphthaloyl)-bis-L-isoleucine with Different Aromatic Diamines via Vilsmeier Adduct Derived from Tosyl Chloride and N,N-Dimethylformamide

Summary Various approaches have been carried out in the synthesis of poly(amide-imide)s. A well-developed solution polycondensation method has been used to prepare such copolymers either from a dianhydride containing a preformed amide group with a diamine or from a dicarboxylic acid containing a preformed imide ring with a diamine. Direct polycondensations of carboxylic acids and aromatic diamines can be a more useful technique for synthesis of poly(amide-imide)s PAIs. In this work, direct polymerization reaction of N,N’-(4,4’-hexafluoroisopropylidendiphthaloyl)-bis-L-isoleucine with several aromatic diamines such as 4,4’-diaminodiphenylsulphone (4a), 4,4’-diaminodiphenylmethane (4b), 4,4’-diaminodiphenylether (4c), 1,4-phenylenediamine (4d), 4,4’-diaminobiphenyl (4e), 1,3-phenylenediamine (4f), 2,4-diaminotoluene (4g), was performed in the presence of tosyl chloride (TsCl)/dimethylformamide (DMF)/pyridine (Py) as a condensing agent. The resulting PAIs were obtained in high yield and inherent viscosity. Some structural characterization and physical properties of these polymers have been studied and will be reported.     

A Multi-Objective Optimization Approach for Joint Channel Assignment and Multicast Routing in Multi-Radio Multi-Channel Wireless Mesh Networks

Multicast routing is an effective mechanism for delivering data to a group of receivers. Due to intrinsic property of air medium in wireless mesh networks (WMN), interference is an important issue in determining the data rate for multicast services. Interference reduction is handled by assigning multiple orthogonal channels to multiple radios in multi-radio multi-channel WMNs. Channel assignment is known to be a NP-complete problem. Most prior methods have solved multicast routing and channel assignment problems sequentially and have not considered the interplay between these two problems. Focusing on this issue, we address joint channel assignment and routing problem for multicast applications. In this paper, a novel technique based on a multi-objective genetic algorithm is proposed to build a delay constrained minimum cost multicast tree with minimum interference. We have examined the proposed algorithm on different network configurations. Experimental results demonstrate that our method finds better trees in terms of cost, delay, and interference compared to prior methods.     

Effect of milling time and clay content on the thermal stability of polyethylene‐clay nanocomposite

The aim of the paper was to investigate the thermal properties of polyethylene (PE)‐clay nanocomposites prepared via the high energy ball milling (HEBM) method. The structure and morphology of the nanocomposites were examined by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Thermal stability of all milled samples, including pure PE and PE‐clay nanocomposites was measured by thermal gravimetric analysis (TGA). The effect of milling time and clay contents on the thermal stability of PE was investigated. The results show that the thermal stability of PE promotes with increasing milling time. Clay has two opposed functions in the thermal stability of the nanocomposite, the first one is the barrier effect to improve the thermal stability, and another one is the catalysis effect leading to a decrease of the thermal stability. J. VINYL ADDIT. TECHNOL., 22:285–292, 2016. © 2014 Society of Plastics Engineers     

Investigating the characteristics of two different methods in nanofiber yarn coloration

Today nanofibers are used widely in a variety of applications. Among many investigations of nanofiber characteristics, their color features have been studied scarcely. In this study, nanofiber yarns were colored using two different methods: exhaustion dyeing and colored solution electrospinning or dope dyeing. In the first method, nylon66 nanofiber yarns were produced and then dyeing process was followed at different dye concentrations. In the second method, colored nanofiber yarns were produced directly using the yarn electrospinning setup. Through the spectrophotometric measurements, it was illustrated that the color saturation increases by increasing the dye content in the dyeing bath and electrospinning colored solution. At the end, the nanofiber yarns with equal dye content were produced using two mentioned methods. It was observed that the color strength of dope-dyed samples was lower than the dyeing process samples, but their levelness was better than the samples of dyeing process. Chromatic values showed that the produced nanofiber yarns with equal dye content using different methods have different hues.     

Synthesis and thermal behavior of [Li(thf)_3(μ-Cl)La{N(SiMe_3)_2}_3] and its investigation as spin-coating precursor for lanthanum-based layer formation

The lanthanum(Ⅲ) complex [Li(thf)_3(μ-CI)La{N(SiMe_3)_2}_3](3) was obtained by the reaction of LaCl_3 with three equiv of Li[N(SiMe_3)_2]_3 in a tetrahydrofuran solution. The molecular structure of 3 in the solid state was characterized by a tetracoordinated anionic lanthanide(Ⅲ) amide in form of an adduct with LiCl(thf)_3 as evidenced by single crystal X-ray structure analysis. In order to study the suitability of 3 as a precursor for the deposition of La_2O_3/LiLaSiO4 by thin layer deposition techniques,its thermal behavior was investigated by thermogravimetry(TG) and TG-MS-coupled studies. TG studies show a two-step decomposition process, whereby volatile decomposition products can be detected during the second decomposition step. TG measurements under an atmosphere of oxygen produced La_2O_3, Calcination processes of 3 under ambient atmosphere for 10 h at 1000 ℃ gave La_2O_3 and LiLaSiO_4,which was confirmed by PXRD studies. Metal-organic 3 was applied as spin-coating precursor for La_2O_3 thin film formation giving the as-deposited layers nearly crack-free.     

Tetranuclear yttrium and gadolinium 2-acetylcyclopentanoate clusters: Synthesis and their use as spin-coating precursors for metal oxide film formation for field-effect transistor fabrication

Lanthanide clusters [Ln_4(μ_3-OH)_2(η~2-accp)_4((μ-O)-η~2-accp)_6](Ln = Y(4),Gd(5); accp = 2-acetylcyclopentanoate) are accessible by treatment of [M(NO_3)_3·6 H_2 O](M = Y(1),Gd(2)) with 3 equiv. of Haccp(3) in presence of NaOH. The molecular structures of 4 and 5 in the solid-state are discussed. The thermal behavior of 4 and 5 was studied by TG under Ar and O_2, showing multistep decomposition processes. Additionally, DSC studies were carried out under an atmosphere of O_2. PXRD measurements of the TG residues confirm the formation of Ln_2 O_3.Spin-coating experiments were carried out with 4 and 5 for Ln_2 O_3 film deposition on silicon substrates. The layers are smooth, close and are of thicknesses of 18.87±1.13 nm and 25.59 ± 4.55 nm for Ln = Y and Gd, which was evidenced by SEM and EDX studies. Field-effect transistors were successfully fabricated by deposition of carbon nanotubes on top of the Y_2 O_3 films and formation of palladium contacts by a lift-off procedure. An on/off ratio of more than 4 orders of magnitude is achieved without considerable leakage currents. These results demonstrate the potential use of spin-coated Y_2 O_3 as a gate dielectric in electronic devices.     

Enhancing the durability of multi-walled carbon nanotube supported by Pt and Pt–Pd nanoparticles in gas diffusion electrodes

This work tries to improve the durability of electrocatalysts of gas diffusion electrodes (GDEs) by using multi-walled carbon nanotube supported Pt–Pd bimetallic (Pt–Pd/MWCNT). The durability investigation of multi-walled carbon nanotube supported metals was evaluated by a repetitive potential cycling (RPC) corrosion test and by extended constant potential (ECP) experiments. Potential cycling tests were performed from −0.3 to 1.2 V at 50 mV s⁻¹ in 1 mol L⁻¹ H₂SO₄. Extended constant potential (ECP) durability test were also carried out on the GDEs by 30 h of constant potential operation at 0.8 V vs. Ag/AgCl. The smaller performance loss was observed on the GDE using Pt–Pd/MWCNT as electrocatalyst compared with GDE using Pt/MWCNT during both durability tests. ICP analysis also suggests that the dissolution of Pt nanoparticles from the carbon nanotube surface is hindered when Pd is present.     

Comparative study of the factors affecting the generativity of office spaces

This study investigated the categories of generative and conservative offices by using syntactic theories and conducting a comparativean alysis of two different layout configurations. Generativity depends on several features that include but are not limited to spatial criteria. Generativity is also affected by aspects that extend beyond the physical, such as the symbolic relationship between the social organism of an organization and the internal structure of a workplace. Results show that no consistent relationship exists between spatial variables and behaviors even though the examined layouts satisfy an organization's basi ccultural require-ments, including privacy, territoriality, and hierarchy. Spatial parameters increase the potential for generativity, but such increase is not guaranteed without necessary changes in the attitudes, programs, and policies of organizations. Recognizing the limits of spatial variables requires evidence-based field research on office settings to determine operational and tailor-made solutions.