Dielectric γ relaxation in polyethylene at low temperature

Dielectric γ relaxation in polyethylene with various degrees of branching and/or with various heat treatment has been measured in the ranges of frequency 10–10⁴ Hz and temperature?90 to?130°C. The difference between the dispersion maps obtained from the frequency dependence of the dielectric loss and from the temperature dependence suggests that the temperature dependence of the relaxation intensity in polyethylene is not negligible. With an increase in crystallinity owing to the decrease in branching, the relaxation time shifts to longer time or higher temperature side and the activation energy increases steeply, whereas the quite opposite tendency was observed for the heat treated polyethylene with different crystallinity. The distribution of relaxation times becomes narrower with increasing temperature. At higher temperatures, the distribution in the specimens with various degrees of branching becomes narrower with the increase in the crystallinity, whereas in the specimens with various heat treatments, the dependence of the distribution on crystallinity tends to cease. Defects in the crystalline phase increase with an increase in branching and in crystallinity through heat treatments, and the dielectric γ relaxation in polyethylene differs depending on the branching and/or heat treatments.     

Tensile failure of γ-ray irradiated blends of high-density polyethylene and natural rubber

The effect of ⁶⁰Co γ-radiation on the tensile properties of thermoplastic elastomer blends of natural rubber (NR) and high-density polyethylene (HDPE) has been investigated. The samples were irradiated to absorbed doses ranging from 0.1 to 100 Mrad in air at room temperature (25°C) at a dose rate of 0.21 Mrad/hr. The effect of blend ratio and addition of carbon black (N 330) dicumyl peroxide (DCP) on the radiation resistance of the blends has also been studied. High energy radiation at a high dose rate was found to cause extensive crosslinking in the bulk, which in effect, caused a minima in the ultimate tensile strength in the range of 10–25 Mrad and a continuous decline in the elongation at break in all the blends. Chain scission, on the other hand, was restricted to the surface under the above-mentioned experimental conditions. This contention was substantiated by the results of irradiation of the samples in a nitrogen environment. Scanning electron microscopy (SEM) studies on the tensile fracture surface morphology of the blends have also been undertaken in order to gain insight to the mechanism of failure.     

Preparation of polyethylene oxide/LixV2‐δO4‐δ nanocomposites

Polyethylene oxide (PEO)/LixV_2‐δO_4‐δ nanocomposites were prepared in aqueous solution. Characterization of the nanocomposites using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), powder X‐ray diffraction (XRD), and Fourier transform infrared spectrum (FTIR) shows that polymer chains intercalate inorganic host lamella and exhibit lattice expansion along the stacking direction of 4.2 Å. A possible model for the structure of the nanocomposite is also provided. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2162–2166, 2001     

Dielectric properties of poly(α-methyl α-n-propyl-β-propiolactone)/poly(vinyl chloride) blends

The dielectric properties of miscible blends of poly(vinyl chloride) (PVC) and poly(α-methyl-α-n-propy-β-propiolae-tone) (PMPPL) have been investigated at different temperatures above and below T_g. The results were analyzed using the Cole-Cole representation and lead to the conclusion that this mixture does not exhibit micro-scale heterogeneities. Dielectric constant and dielectric loss master curves were constructed using the stress relaxation shift factors determined previously; the same shift factors could be used for the homopolymers and their blends. Similarities between the dielectric master curves and the stress relaxation master curves of PVC, PMPPL, and their blends, are also discussed.     

Radiation-induced copolymerization of α,β,β-trifluoroacrylonitrile with α-olefin

Homopolymerization and copolymerization of α,β,β-trifluoroacrylonitrile (FAN) with γ-olefins were carried out in bulk by γ-ray irradiation at 25°C. FAN gives very small quantities of brown and greasy low molecular weight polymer. Cyano groups in FAN polymer were found to be readily hydrolyzed to acid amide groups in the atmosphere. FAN was found to copolymerize with ethylene, propylene, and isobutylene via a radical mechanism to form equimolar copolymers in a wide range of monomer compositions. The polymerization rate increases linearly with FAN fraction in the monomer mixture. These copolymers are also hydrolyzed in the atmosphere, and the hydrolysis proceeds with more difficulty for the copolymer with higher α-olefin. The reactivity ratios r₁ (FAN) and r₂ (α-olefin) were determined to be 0.01 and 0.12 for the FAN/ethylene copolymerization and 0.01 and 0.07 for the FAN/propylene copolymerization. These results confirm that an alternating copolymerization takes place in the FAN/α-olefin system.     

Radiation grafting of α,β,β-trifluoroethylenesulfonyl fluoride onto low-density polyethylene film by simultaneous irradiation method. I. Kinetic study of simultaneous-irradiation grafting

α,β,β-Trifluoroethylenesulfonyl fluoride (TFESF) was grafted onto polyethylene (PE) film by a simultaneous-irradiation method. The influences of the grafting conditions were analyzed kinetically. The dependencies of the grafting rate on the dose rates and monomer concentrations ranging from 10 to 75% were found to be of 1 and 0 order, respectively. The overall activation energy for the graft polymerization was 2.05 × 10⁴ J/mol. The grafting rate was found to be independent of the film thicknesses ranging from 25 to 100 μm.     

Mechanistic studies of adhesion promotion by γ-aminopropyl triethoxy silane in α-Al2O3/polyethylene joint

In order to understand the mechanism of adhesion promotion by organo silane in joints where its chemical reaction with a polymer matrix may be negligible, we studied the role of γ-aminopropyl triethoxy silane (γ-APS) in α-Al₂O₃/ polyethylene joints. When adsorbed or deposited on α-A1₂O₃/ and moderately dried, γ-APS forms a multimolecular film that is not fully cured. Drying at elevated temperatures for an extended time leads to further curing, resulting in a glassy silane film with a T_g around 108°C, while prolonged dry may cause some degradation. Joint strength is markedly improved by the application of a γ-APS film with a maximum peel strength of 2.3 kg/cm when the silane is applied from a 2 percent aqueous solution. Drying the silane at an elevated temperature prior to joint formation reduces joint strength and also changes the failure mode from cohesive failure through the polyethylene to a mixed mode. Evidence of interdiffusion between γ-APS film and polyethylene at a temperature (149°C) that is above the melting point of polyethylene and the T_g of the silane film was obtained by measuring the Si concentration profile across the interface of the laminate of polyethylene/γ-APS/polyethylene. Diffusion constants in the order of 10^?12 cm²/s were obtained, with a teridency toward reduced diffusion as a consequence of extensive drying. DSC results indicate at least partial miscibility of the silane polymer in the amorphous region of polyethylene. It is proposed that the interdiffusion between γ-APS silane film and polyethylene is an important mechanism for adhesion promotion of the joints investigated in this study.     

Studies on γ‐Fe2O3–high‐density polyethylene composites and their additives

γ‐Fe₂O₃–high‐density polyethylene (HDPE) composite films are prepared by a gel‐casting technique. To understand the effect of additives, rice husk ash and thiourea are made to disperse in the HDPE matrix to obtain the composite films with additives. The as‐prepared γ‐Fe₂O₃–HDPE composite films with their additives are subjected to characterization and study through X‐ray diffraction, thermal, scanning electron microscopy, and dielectric measurements. The results are qualitatively treated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1527–1533, 2004     

β-Fur-2-yl-α-halogenacrylonitrile. I. Darstellung von β-Fur-2-yl-ß-aminoacrylonitrilen und β-Fur-2-yl-α-aminoacrylonitrilen

β-Fur-2-yl-α-halogenacrylonitriles. I. Preparation of β-Fur-2-yl-ß-aminoacrylonitriles and β-Fur-2-yl-α-aminoacrylonitriles β-Fur-2-yl-α-halogenacrylonitriles 1 react with secondary amines to yield β-fur-2-yl-ß-aminonitriles 2 and β-fur-2-yl-α-aminoacrylonitriles 3 . The ¹ H-n.m.r. spectra of the E/Z isomers are discussed.     

Reactions of α-Arylhydrazono-β-oxo-β-phenyl-propionitriles

ω-Cyanoacetophenone was coupled with a variety of aromatic diazonium chlorides to give the corresponding arylazo derivatives 1 a – g . Analysis of the IR and UV spectra of these compounds indicated that they exist mainly as the corresponding arylhydrazones. Compounds 1 a – d, f, g reacted with diazomethane to yield the N-methyl-arylhydrazones 2 a – f . 3-Amino-4-arylazo-5-phenylpyrazoles 5 a – g and 4-arylazo-5-imino-1,3-diphenyl-2-pyrazolines 6 a – g were obtained by the interaction of 1 a – g with hydrazine hydrate and with phenylhydrazine, respectively.     

Intermediates of Prostanoid Synthesis. Stereospecific conversion of (+)-5β-hydroxycyclopenten-2-yl-1β-acetic acid γ-lactone into (+)-1β-methoxycarbonylmethyl-2β,3β-(p-nitrobenzylidene)-dioxycyclopentan-5-one

Starting from (+)-5β-hydroxycyclopenten-2-yl-1β-acetic acid γ-lactone ( 1 ), (+)-1β-methoxycarbonylmethyl-2β, 3β-(p-nitrobenzylidene)-dioxycyclopentan-5-one ( 7 ) was prepared within 4 steps. Subsequent cleavage of the latter gives (−)-3β-hydroxy-1-methoxy-carbonylmethylcyclopent-1-en-5-one ( 8a ). Hydroxylation of the lactone ( 1 ) was found to give (+)-2β,3β,5β-trihydroxycyclopentyl-1β-acetic acid γ-lactone ( 2a ) with cis-oriented hydroxy groups in respect to the lactone ring. No formation of the trans-isomer, as has been reported earlier [4], was observed.     

TGA analysis of γ‐irradiated linear low‐density polyethylene

Linear low‐density polyethylene (LLDPE), based on butene‐1 or hexene‐1, was irradiated with γ‐rays under vacuum or in the presence of air. The study focused on the influence of the dose rate and the γ‐dose on the thermal properties of LLDPE. Differential scanning calorimetry, thermogravimetric analysis (TGA), and TGA/FTIR techniques were used to address the thermal behavior as a result of γ‐irradiation. During this irradiation, competition between crosslinking and scission reactions, subsequent to oxidation reactions, occurred in the polymeric material, which strongly depends on the experimental conditions. A decrease of the crystallinity for γ‐irradiated samples was observed in particular for samples irradiated under vacuum. This observation may be explained by increased hindrance of segment mobility due to crosslinking reactions that prevent crystal growth. TGA investigations revealed an enhancement of the thermal stability for samples irradiated under vacuum but not for those irradiated in air. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2790–2795, 2006     

Acetylcholine Promotes Binding of α‐Conotoxin MII at α3β2 Nicotinic Acetylcholine Receptors

α‐Conotoxin MII (α‐CTxMII) is a 16‐residue peptide with the sequence GCCSNPVCHLEHSNLC, containing Cys2–Cys8 and Cys3–Cys16 disulfide bonds. This peptide, isolated from the venom of the marine cone snail Conus magus, is a potent and selective antagonist of neuronal nicotinic acetylcholine receptors (nAChRs). To evaluate the impact of channel–ligand interactions on ligand‐binding affinity, homology models of the heteropentameric α₃β₂‐nAChR were constructed. The models were created in MODELLER with the aid of experimentally characterized structures of the Torpedo marmorata‐nAChR (Tm‐nAChR, PDB ID: 2BG9) and the Aplysia californica‐acetylcholine binding protein (Ac‐AChBP, PDB ID: 2BR8) as templates for the α₃‐ and β₂‐subunit isoforms derived from rat neuronal nAChR primary amino acid sequences. Molecular docking calculations were performed with AutoDock to evaluate interactions of the heteropentameric nAChR homology models with the ligands acetylcholine (ACh) and α‐CTxMII. The nAChR homology models described here bind ACh with binding energies commensurate with those of previously reported systems, and identify critical interactions that facilitate both ACh and α‐CTxMII ligand binding. The docking calculations revealed an increased binding affinity of the α₃β₂‐nAChR for α‐CTxMII with ACh bound to the receptor, and this was confirmed through two‐electrode voltage clamp experiments on oocytes from Xenopus laevis. These findings provide insights into the inhibition and mechanism of electrostatically driven antagonist properties of the α‐CTxMIIs on nAChRs.     

Ruthenium(II)‐Catalyzed Protocol for Preparation of Diverse α,β‐ and β,β‐Dihaloenones from Diazodicarbonyls

Efficient one‐step syntheses of α,β‐ and β,β‐dihaloenones were achieved by ruthenium(II)‐catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers several significant advantages, which include ease of handling, mild reaction conditions, one‐step reaction, and the use of an effective and non‐toxic catalyst. The synthesized compounds were further transformed into highly functionalized novel molecules bearing aromatic rings on the enone moiety using the Suzuki reaction.