Radiation-Enhanced Thermal Depolymerization of Polytetrafluoroethylene

The initial stage of thermal and radiation-enhanced thermal depolymerization over the temperature range of 310–460°C in vacuum was studied for polytetrafluoroethylene specimens with different thicknesses. Conditions for the occurrence of depolymerization in the kinetic and diffusion regions were determined. The specific features of depolymerization kinetics for low-molecular-mass polytetrafluoroethylene specimens obtained by preliminary irradiation of virgin samples at room temperature were revealed. A possible role of depolymerization in radiation crosslinking of polytetrafluoroethylene irradiated above the crystallite melting point was considered.     

The effect of solvents and organic acids on the p-doping behaviors of poly(3′,4′-Ethylenedioxy-2,2′:5′,2″-terthiophene)

Poly(3??,4??-Ethylenedioxy-2,2??:5??,2??-terthiophene) was synthesized by chemical oxidative polymerization of 3??,4??-Ethylenedioxy-2,2??:5??,2??-terthiophene using FeCl₃ as an oxidant. The resulting polymer was characterized by FTIR and ¹H NMR. p-doping behaviors of substituted polyterthiophene with different organic sulfonic acids (methanesulfonic acid, p-toluene sulfonic acid, and ??-naphthalene sulfonic acid) in different solvents (CH₃CN, CHCl₃, THF and DMF) were studied by UV-VIS spectroscopy. The results from structural characterizations showed that the ??,????-bonding predominates in polyterthiophene. The spectroscopic changes in UV-VIS showed that ??-naphthalene sulfonic acid was an efficient doping acid for polymer while varying the solvents. Meanwhile, CH₃CN showed a high efficiency for p-doping of polyterthiophene while varying the doping acids.     

Dehydrogenation of nitro derivatives of bibenzyl to corresponding nitro stilbene with dioxygen catalyzed by 2,2,6,6-tetramethylpiperidine-1-oxyl

A simple and effective oxidative dehydrogenation of nitro derivatives of bibenzyl was developed using a mixture of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and metal salts as catalyst under an atmospheric pressure of oxygen. The oxidation of several nitro derivatives of bibenzyl led to corresponding nitro stilbene in good yields, and the yields increased with the increase in the substituted nitro group on the bibenzyl. For example, the aerobic dehydrogenation of 2,2??,4,4??,6,6??-hexanitrobibenzyl in the presence of a catalytic amount of TEMPO with metal salts gave 2,2??,4,4??,6,6??-hexanitrostilbene in 81?% yield and 4,4??-dinitrostilbene-2,2??-disulfonic acid (75?%) was obtained from 4,4??-dinitrobibenzyl-2,2??-disulfonic acid.     

Study on the preparation of Mg-Li-Ag Alloys by electrochemical deposition from LiCl-KCl-MgCl2-AgCl Melts

Electrochemical deposition of Mg, Li and Ag on molybdenum electrodes in LiCl-KCl-MgCl₂-AgCl melts at 943 K to form Mg-Li-Ag alloys was investigated. Cyclic voltammograms (CVs) showed that the potential of Li metal deposition, after the addition of MgCl₂ and AgCl, was more positive than that of Li metal deposition before the addition. ??, AgMg₄ + ??, and ?? + ?? + LiAg phases of Mg-Li-Ag alloys were obtained by galvanostatic electrolysis. The element Mg distributed homogeneously in the alloys while element Ag mainly located on the grain boundaries.     

Theoretical and experimental studies on the structure-antioxidant activity relationship of synthetic 4-methylcoumarins

The development of antioxidants as useful drugs for the treatment of neurodegenerative diseases such as Alzheimer??s is extremely challenging in medicinal chemistry. Coumarins have attracted great attention as possible therapeutic tools against oxygen radicals in human degenerative diseases. In order to establish the possible structure-antioxidant activity relationship, a series of twenty four 4-methylcoumarin derivatives were examined by employing reducing power measurements, and comparison with bond dissociation enthalpy and ionization potential calculations. Based on the reducing potency of 4-methylcoumarin derivatives with respect to trolox, these compounds were classified into five groups as ??most active??, ??more active??, ??moderately active??, ??less active?? and ??inactive?? derivatives. The presence of hydroxyl groups is an essential requirement for the activity, and substitution of hydroxyl groups by methoxy groups leads to non-active derivatives. The results revealed that dihydroxyl groups in the ortho position show a better antioxidant activity with respect to dihydroxyl groups in the meta position. This is ascribed to the ability to construct more stable 4-methylcoumarin radical intermediates by rearrangement of intra-molecular hydrogen bonding. Our findings indicate that other important factors to enhance the antioxidant activity of coumarins are the number of hydroxyl groups, the presence of ester substitutions and a thiono functional group on the pyrone ring. However, bond dissociation enthalpy and ionization potential calculations alone are not sufficient to identify the best antioxidant structures. As a result, chemical and functional properties of molecules such as 4-methylcoumarins should be examined as a whole entity, considering all substitutions versus a single substitution to design functional compounds with good antioxidant activity.     

Reaction of alicyclic reformatsky reagents with 2,5-bis(arylmethylidene)cyclopentanones

Reformatsky reaction of methyl 1-bromocyclobutane-, 1-bromocyclopentane-, 1-bromocyclohexane-, and 1-bromocycloheptanecarboxylates with 2,5-bis(arylmethylidene)cyclopentanones gave the corresponding 4??-aryl-7??-arylmethylidene-4??,5??,6??,7??-tetrahydro-2??H-spiro[cycloalkane-1,3-cyclopenta[b]pyran]-2??-ones.     

Active layer of fuel cell electrode with polymer electrolyte: Nature of proton and oxygen supply channels

The nature of proton and oxygen supply channels in the active layer of a cathode of fuel cell with polymer electrolyte is discussed. There are three types of electron, proton, and oxygen carriers in the active layer: agglomerates of carbon particles with supported platinum (support grains), agglomerates of Nafion molecules (Nafion grains), and void grains. In computer simulation of the active layer structure, the three types of grains were assumed equal-sized, cube-shaped and arranged into a cubic node lattice (in the terms of the percolation theory). Impossibility of forming on the basis solely the above three grain types of three percolation clusters (??electron??, ??proton??, and ??gas??) that could supply all that is required for the electrochemical process is proved. But in this, the following question arises: how can satisfactory operation of the cathode with polymer electrolyte be provided? The required supply of protons and oxygen can be provided only if the support grains can feature not only electronic conductivity, but can also participate in transport of both protons and oxygen. As a result, the transport of protons and oxygen is carried out via special combined percolation clusters that must include apart from the support grains either Nafion grains (combined ??proton?? cluster) or void grains (combined ??gas?? cluster). The paper describes the technique of calculation of effective specific conductivity of a combined ??proton?? cluster. The effective specific diffusion coefficient of a combined ??gas?? cluster can also be calculated in a similar way.     

Condensation of 2-naphthylamine or N-benzyl-2-naphthylamines with formaldehyde and methyl 2,2-dimethyl-4,6-dioxocyclohexane-3-carboxylate

Condensation of 2-naphthylamine with formaldehyde and methyl 2,2-dimethyl-4,6-dioxocyclohexanecarboxylate afforded depending on the reaction conditions methyl 9,9-dimethyl-11-oxo-8,9,10,12-tetrahydro-7H-benzo[a]acridine-10-carboxylate or 4-alkoxymethyl-1,4-dihydro-2??,6??-dioxo-4??,4??-dimethyl-2??H,3H,6??Hspirobenzo[f]quinoline-2,1??-cyclohexyl-3??-carboxylate. The condensation of N-benzyl-2-naphthylamines with formaldehyde and methyl 2,2-dimethyl-4,6-dioxocyclohexanecarboxylate provided with the quantitative yield the corresponding methyl 4-benzyl-1,4-dihydro-2??,6??-dioxo-4??,4??-dimethyl-2??H,3H,6??H-spirobenzo[f]quinoline-2,1??-cyclohexyl-3??-carboxylates.     

Transformations of tetrahydropyrido[4′,3′:4,5]thieno[2,3-d]pyrimidin-4(3H)-ones in the presence of alkynes bearing electron-withdrawing substituents

Tetrahydropyrido[4??,3??:4,5]thieno[2,3-d]pyrimidines in the presence of activated alkynes were transformed into mixtures of pyrimido[5??,4??:4,5]thieno[3,2-d]azocines and spiro[pyridine-4,5??-thieno[2,3-d]pyrimidines].     

Synthesis of functionalized 5H-spiro[furan-2,2′-indene]-1′,3′,5-triones from primary amines, acetylenic esters and ninhydrin

An effective route to functionalized 5H-spiro[furan-2,2??-indene]-1??,3??,5-triones is described via tandem reaction of primary amines, acetylenic esters and ninhydrin.     

1-Arylideneamino-2,2,2-trichloroethanols as synthetic equivalents of arylideneimines in the reaction with cyclopropenone derivatives

1-Arylideneamino-2,2,2-trichloroethanols react regiospecifically with cyclopropenones to form 2,2??-diaryl-1,1??,2,2??-tetrahydro-3H,3??H-2,2??-bipyrrole-3,3??-diones. A new preparative method was developed for the synthesis of 1-arylideneamino-2,2,2-trichloroethanols.     

Thermodynamic characteristics of complex formation reactions between d- and f-elements and alkylated dipyrrolylmethene in dimethylformamide

Thermal effects of the reactions of complex formation between d- and f-elements and 3,3??,5,5??-tetramethyl-4,4??-diethyl-2,2??-dipyrrolylmethene in dimethylformamide are determined from data of titration microcalorimetry and the temperature behavior of the complex formation equilibrium constants. The entropy and free energy changes of the complex formation reactions are calculated. It is shown that enthalpy-entropy compensation is observed for complex formation processes in all cases. Contributions from the enthalpy and entropy factors to the free energy change of the complex formation are analyzed, allowing us to confirm earlier conclusions as to the effect of the nature of a complexing agent on the relative percentage of covalent and ionic characters of the M-L bond. The dependence of the complex formation enthalpies on the inverse radius of a complexing agent is revealed for the lanthanide complexes.     

Modification of fluoropolymers by means of electron beam irradiation

High molecular weight polytetrafluoroethylene (PTFE) is transformed to free-flowing micropowder by treatment with electron beams. In case of irradiation in presence of air carboxylic acid fluoride groups are incorporated which rapidly hydrolyze to carboxylic groups in the surface-near regions due to atmospheric humidity. These polar groups reduce the hydrophobic and oleophobic properties so much that homogeneous compounding with other materials becomes possible. In addition to PTFE, copolymers of tetrafluoroethylene with hexafluoropropylene (FEP) and perfluoropropylvinylether (PFA) were modified. In case of identical irradiation conditions, the concentration of carboxylic groups is much higher in FEP and PFA than in PTFE, which is due to the lower crystallinity of the copolymers.

Electron beam irradiation of PTFE was performed in vacuum at elevated temperature above the melting point. The changes in the chemical structure were studied. The concentration of CF₃ branches was found to be much higher as compared to room temperature irradiation.

In a practical test PTFE micropowders functionalized by electron irradiation were compounded with epoxy resins, with polyoximethylene and with polyamides. Such compounds are characterized by very good frictional and wearing behaviour in dry-running tests.     

Physicochemical properties of ionic liquid analogue containing magnesium chloride as temperature and composition dependence

The ionic liquid analogue containing MgCl₂ based on choline chloride and glycerol was reported. The solubility of MgCl₂ in the ionic liquid analogue based on choline chloride and glycerol was measured from T?=?293?C393?K. The empirical equation about the solubility and temperature was obtained. Thermal analysis showed that the ionic liquid analogue was stable from room temperature to 140?°C. The physical properties such as conductivity ??, density ?? and viscosity ?? of ionic liquid analogue were measured as function of the content of MgCl₂ and temperature. An empirical equation about the density (??) and temperature was obtained. The ions transport behaviours are analyzed using hole-theory. It is shown that the conductivity of the ionic liquid analogues is controlled by the ion mobility and the suitable voids.     

Thermal properties of novel polymers based on poly(hydantoin-methyl-p-styrene) and their substrates

The following compounds have been synthesized: (a) hydantoins 5,5-dimethylimidazolidine-2,4-dione (1), 1??,3??-dihydrospiro[imidazolidine-4,2??-indene]-2,5-dione (2), 3??,4??-dihydro-1??H-spiro[imidazolidine-4,2??-naphthalene]-2,5-dione (3); (b) monomers: 5,5-dimethyl-3-(4-vinylbenzyl)imidazolidine-2,4-dione (4), 1-(4-vinylbenzyl)-1??,3??-dihydrospiro[imidazolidine-4,2??-indene]-2,5-dione (5), 1-(4-vinylbenzyl)-3??,4??-dihydro-1??H-spiro[imidazolidine-4,2??-naphthalene]-2,5-dione (6), (two of them are unknown: 5 and 6); (c) macromolecular compounds: poly(chloromethyl-p-styrene) (7), used as reference, and three polymers (two of them are novel) obtained by substitution of hydantoins 1?C3 to poly(methyl-p-styrene) (8?C10). Their thermal properties have been studied by thermogravimetry. It was found that the chemical structure, tautomerization, and intermolecular interaction influence the thermal stability of substrates. The presence of phenyl rings causes the increase of resistance of studied hydantoins. The obtained polymers are characterized by significantly improved thermal stability comparing to poly (chloromethyl-p-styrene). The mechanism of thermal degradation of investigated polymers and explanation of their thermal resistance has been proposed. The relatively high temperatures of glass transition of polymers have been determined by DSC.     

Effect of the SO2 group in the diamine fragment of polyimides on their structural, thermophysical, and mechanical properties

Experimental and theoretical investigations, including an all-atom computer simulation, are performed for block samples of thermoplastic polyimides, amorphous R-BAPS (based on R dianhydride 1,3-bis(3??,4-dicarboxyphenoxy)benzene and diamine BAPS 4,4??-bis(4??-aminophenoxy)biphenyl sulfone), and crystallizable R-BAPB (based on R dianhydride and diamine BAPB 4,4??-bis(4??-aminophenoxy)biphenyl), which differ in either the presence or absence of the sulfone group in the repeating unit of the polyimide macromolecule. The features of thermophysical, structural, and mechanical properties of R-BAPS and R-BAPB are related to the formation of associates from sulfur and oxygen atoms of the sulfone group that are stabilized by electrostatic interactions.     

A new antifriction and sealing material based on radiation-modified polytetrafluoroethylene

The current situation with research into the effect of ionizing radiation exposure on the structure and properties of polytetrafluoroethylene was analyzed. New methods of radiation-induced modification, that improve the performance characteristics of polytetrafluoroethylene, were discussed. The results of research into properties of polytetrafluoroethylene irradiated at temperatures exceeding the melting point of its crystalline phase in media with different compositions were presented. It is shown that, under certain irradiation conditions, an extremely strong increase (up to 10 000-fold) in the wear resistance of polytetrafluoroethylene can be achieved, with the creepage decreased up to 100-fold. A conclusion was made that high-temperature radiation-induced modification can yield new modifications of the polymer, in which the advantages offered by untreated polytetrafluoroethylene are combined with high mechanical and triboengineering characteristics.     

Synthesis and crystal structures of copper(II) and silver(I) complexes of a biphenyl-bridged bipyrazolyl ligand

A semirigid bipyrazolyl ligand, 4,4??-bis[(3??,5??-diethyl-1H-pyrazol-4??-yl)methylene)]-1,1??-biphenyl (H₂L), and four of its Ag(I) and Cu(II) complexes have been prepared and structurally characterized. X-ray analysis demonstrates that the Ag(I) complexes are dinuclear molecular rectangle, while the Cu(II) complexes display a twisted rectangular structure. Two different conformations, namely cis and trans, have been observed for this bipyrazolyl ligand.     

IR-spectroscopic examination of polytetrafluoroethylene and its modified forms

The results of IR-spectroscopic examinations of the molecular and supramolecular structure of polytetrafluoroethylene and polymer materials thereof were summarized. It was shown that, upon heat, mechanical, and other treatment, as well as under radiation exposure, polytetrafluoroethylene preserves its chain-helical conformation, and the resulting modified forms consist of crystalline and amorphous phases in a ratio depending on the history of the sample. The degree of the structural ordering in the polymer decreases with increasing temperature and pressure. The formation of branched moieties and short macromolecules with double bonds (?CF=CF₂) in the terminal groups is specific for the process caused by thermal and radiation-induced degradation. The oxidation of the polymer macromolecules requires applying high irradiation doses and heating samples in an oxygen or air atmosphere.