Properties of urethane elastomers

Summary The dielectric relaxation processes in poly(azourethaneurea) prepared from diphenylmethane-4,4-diisocyanate (MDI) and poly(ethylene adipate) glycol were studied in the range 200–390 K using thermally stimulated depolarization currents (TSDC). The TSDC spectra obtained on original sample, annealed sample, and both annealed and stretched sample showed significant differences which were explained in terms of the supramolecular structure of polymers. It was accepted that the polymers have a multiphase supramolecular structure.     

Electrical Condultion and Polarization in Lead Silicate Glasses

Thermally stimulated polarization and depolarization current (TSPC/TSDC) and dc conductivity measurements on a series of lead silicate glasses were made between −196° and 190°C. The general composition of the glasses was xPbO·(100 − x )SiO₂, where x = 30, 40, 45, 50, and 65. The dc conductivity exhibits a monotonic increase with increasing PbO content. For x > 45, the rise in conductivity with increasing PbO content is much less than for x < 45. Two TSDC peaks have been observed in all the glasses. The smaller of the two TSDC peaks, occurring at lower temperatures, increases linearly in size with increasing concentrations of PbO. The high-temperature TSDC peak does not saturate from −196° to 190°C. Direct current conductivity in these glasses is ionic and due to the motion of Pb²⁺ ions. The behavior of the low-temperature TSDC peak is consistent with the hypothesis that it is caused by short-range motion (orientational polarization) of Pb²⁺ ions. The origin of the high-temperature TSDC peak is tentatively attributed to space charge polarization of Pb²⁺ ions.     

Sodium Motion in Phase-Separated Sodium Silicate Glasses

The thermally stimulated polarization and depolarization current (TSPC/TSDC) technique was used to study Na^plus; ion motion in phase-separated silicate glasses containing between 10.3 and 20 mol% Na₂O. Generally, two TSDC peaks and a high-temperature background (HTB) current were observed. The two TSDC peaks were attributed to different types of Na^plus; motion, i.e. a short-range reorientation process and a longer-range translational motion. Changes in the microstructure affected only the size of the larger TSDC peak located at higher temperatures.     

Effect of K0.5Na0.5NbO3 filling particles on the charge carrier trap distribution of polyimide films

Polyimide (PI) films filled with K_0.5Na_0.5NbO₃ (KNN50) particles at different weight 0, 5, 10, and 15 wt % had been prepared by in‐situ dispersion polymerization process. The thermally stimulated current (TSDC) method was used to investigate the charge carrier trap levels and their distribution of the composite films. The TSDC spectra show that pure film has ‐peaks and ‐peak, but the composite films only have ‐peaks and an extraordinary peak at high temperature region. The trap parameters were calculated by an approximate model, and the results indicate that charge released of the shallow traps show a nonlinear behavior. The trap energies decrease from 0.879–0.968 eV to 0.549–0.839 eV with the increase of the KNN50 content. The surface and interface between KNN50 and PI matrix was considered to the variation of the trap levels. The extraordinary peak of the composite films was correlated with the phase transition of the KNN50 particles. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39828.     

Polarization and Conduction Mechanism in Mixed-Alkali Glasses

Thermally stimulated polarization and depolarization current (TSPC/TSDC) measurements on mixed alkali (Li-Na) silicate glasses show two TSDC peaks along with a dc conduction current at high temperatures, similar to single-alkali silicate glasses. The activation energies for the two TSDC peaks and for dc conduction increase with the addition of a second alkali. The first TSDC peak does not change in size but the second becomes substantially smaller when the second alkali is added. The reduction in size of the second TSDC peak correlates well with the reduction in the dielectric loss hi mixed-alkali glasses. A model is proposed to account for the behavior of the two TSDC peaks.     

Properties of urethane elastomers

Summary The dielectric relaxation processes in polyurethanes based on 4,4-dibenzyle diisocyanate and saturated polyester in the temperature range of 250–400°K using thermally stimulated depolarization currents method have been investigated. The structure of the relaxation thermograms, location and intensity of the constituent peaks depend both on the precipitation temperature and thermal history of the polymer. The relaxation processes have been associated with the molecular motions within domains with distinct morphological structures. The morphological structure of the samples was evidenced using electron microscopy method.     

Phase-structure analysis of brass by anodic linear-sweep voltammetry

Anodic linear-sweep voltammetry (ALSV) was applied to electrodeposited alloy layers and to metallurgically obtained Cu–Zn alloys of different composition and structure. Metallurgically obtained samples covered the range of composition in which , (+), and (+) intermediate phases were detected by X-ray. The ALSV of samples containing less than 30 wt % Zn exhibited a single peak at –0.08 to –0.1 V/SCE before massive dissolution, starting at about –0.05 V/SCE. The presence of the -phase gave another peak at a significantly more negative potential (–0.25 to –0.35 V/SCE). The ALSV of electrodeposited alloys were significantly more complex than the former, depending on the deposition potentials, with peaks attributable to pure Zn, to the -phase, to the -phase as well as to the -phase, present in most cases and dissolving at potentials similar to that of pure Cu. ALSV was shown to be a reliable and practical method for a fast determination of both the composition and the phase structure of electrodeposited brass.     

Structure,Microwave Dielectric Properties and Thermally Stimulated Depolarization Currents of (1 − x)Ba0.6Sr0.4La4Ti4O15–xBa5Nb4O15 Solid Solutions

(1 ? x)Ba_0.6Sr_0.4La₄Ti₄O₁₅–xBa₅Nb₄O₁₅ (x = 0.05, 0.1, 0.15 and 0.2, BSLT–BN) ceramic samples were prepared by co‐firing the mixtures of Ba_0.6Sr_0.4La₄Ti₄O₁₅ and Ba₅Nb₄O₁₅ powders. Crystal structure, microwave dielectric properties and thermally stimulated depolarization currents (TSDC) of the BSLT–BN series ceramics were investigated. X‐ray diffraction patterns reveal that all the samples exhibit a hexagonal perovskite structure, which implies that the BSLT–BN mixtures form solid solutions. With increasing Ba₅Nb₄O₁₅ content, the diffraction peaks shift to low angles and the sintering temperature of BSLT–BN decreases. Raman spectra analysis reveals the shifting and splitting of the vibration modes. The microwave dielectric properties of the well‐sintered (1 ? x)BSLT–xBN ceramics vary with Ba₅Nb₄O₁₅ content. The dielectric permittivity of the ceramics exhibits a slight decreasing trend. The quality factor varies in the range of 45 000–11 200 GHz, whereas near‐zero temperature coefficients of the resonant frequency may be achieved by changing the Ba₅Nb₄O₁₅ content. TSDC was utilized to explore the extrinsic loss mechanism associated with defects. TSDC relaxation peaks are mainly generated by oxygen vacancies, and the Ba₅Nb₄O₁₅ content has a significant influence on the TSDC spectra.     

Thermally Stimulated Currents and Alkali-Ion Motion in Silicate Glasses

The thermally stimulated polarizatioddepolarization (TSPC/TSDC) current technique is used to investigate alkali-ion motion in silicate glasses. lbo TSDC peaks are observed in all these glasses along with the dc conduction current at high temperatures. The low-temperature TSDC peak magnitude is essentially constant, but the second TSDC peak magnitude varies with the type of alkali ion present in these glasses. Based on a proposed model, the two TSDC peaks are interpreted in terms of the localized alkali-ion motion around the nonbridging oxygen ion and through the limited conduction pathways, respectively.     

Thermal Studies of Polyaniline Doped with Dodecyl Benzene Sulfonic Acid Directly Prepared via Aqueous Dispersions

In this paper, polyaniline (PANI) doped with dodecyl benzene sulfonic acid (DBSA) was directly prepared by chemical oxidation in aqueous dispersions. The temperature and color changes of the polymerization reaction solution were examined. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were used to analyze thermal characteristics of the doped PANI (PANDB). These results indicated that the PANDB powder had discernible moisture content. Moreover, in the first run of DSC thermal analysis, two endothermic peaks were found. The first endothermic peak (at around 120°C) represented the evaporation of moisture. The second endothermic peak (at around 280°C) represented the starting evaporation of DBSA. The XRD examination further confirmed the chemical crosslinking reaction during thermal treatment. The TGA result illustrated that there were three major stages for weight losses of the PANDB powder sample. The first weight loss at the lower temperature resulted from the evaporation of moisture. The second weight loss at the higher temperature was due to evaporation of DBSA. And the third weight loss at around 420°C–450°C was due to the chemical structure degradation of PANI. The electrical conductivity of PANDB has a plateau at the heating time around 30 min when the heating temperature was set at 100°C.     

Relaxation processes in barium strontium titanate glass-ceramics by thermally simulated depolarization current

Thermally stimulated depolarization current (TSDC) experiments were carried out to investigate the effect of polarization temperature on different relaxation processes in barium strontium titanate glass-ceramics. It was found that all the TSDC curves are composed of four relaxation peaks. From the characteristics of peak temperature and peak current intensity with various polarization temperatures, the origin of these four peaks are identified as from defect dipole orientation, charge carrier detrapping, in-crystal oxygen vacancy migration, and trans-interface oxygen vacancy migration respectively. In addition, both the dipole concentration and trap density for the glass-ceramic samples were estimated.     

Thermally Stimulated Currents in Sodium Silicate Glasses

Sodium-ion motion in three sodium silicate glasses and a sodium aluminosilicate glass was investigated by the thermally stimulated polarization (TSPC) and depolarization (TSDC) current techniques. The two TSDC peaks found in the sodium silicate glasses were attributed to localized sodium-ion movement around a nonbridging oxygen ion, a type of dipolar orientational polarization, and to a longer-range sodium motion leading to interfacial polarization at the immiscible phase boundaries. The high-temperature background (HTB) current corresponded to the sodium motion for dc conductivity and diffusion. The commonly observed dc absorption current was found to be related to the two TSDC peaks.     

Polyimides based on “multiring” flexible diamines

The five benzene rings-containing (hereafter for convenience, referred to as five-ringrd) diamines ad-bis[4-(4-aminophenoxy)phenyl]-1,4 (or 1,3)-diisopropylbenzene (p- or m-3) were prepared by a nucleophilic substitution of ,-bis(4-hydroxyphenyl)-1, 4 (or 1,3)-diisopropylbenzene (p- or m-1) with p-chloronitrobenzene in the presence of K₂CO₃ and then hydro-reduced. The polyimides were synthesized from diamine 3 and various aromatic dianhydrides via the two-stage procedure that include ring-opening polyaddition in DMAc to give poly(amic acid)s, followed by thermal conversion to polyimides. The poly(amic acid)s had inherent viscosities of 0.63–1.54 dL/g depending on the dianhydrides used. Almost all the poly(amic acid)s could be solution-cast and thermally converted into transparent, flexible, and tough polyimide films. These polyimides have glass transition temperatures in the range of 186–290°C and almost no weight loss up to 500°C in air or nitrogen atmosphere. The polyimide obtained from pyromellitic dianhydride and diamine m-3 showed two endothermic peaks of 270 and 300°C on the diagram of differential scanning calorimetry (DSC), and the other polyimides showed no endotherms on their DSC traces.     

Spectroscopic and thermal analyses of α′ and α crystalline forms of poly(l-lactic acid)

Poly(lactic acid) samples rich in α′ or α crystals have been characterized using spectroscopic and thermal methods. Cryogenic infrared and Raman spectroscopy were used to probe the differences in chain conformation and packing. Compared to the α crystal, the α′ crystal has weakened specific carbonyl and methyl interactions. Experimental spectroscopic analysis in conjunction with simulation studies have shown that the α′ crystal has uniform conformational disorder in the C_α-C torsion angle. This disorder in chain conformation and packing leads to different crystalline forms with different stabilities. The difference in thermal stability was quantified by measuring enthalpic change at melting for both crystalline forms. Significantly different values for the two crystalline forms were obtained ( and ). The transformation from the less stable α′ to the more stable α phase has been characterized. This analysis provides an explanation to the double melting peaks usually found in PLLA samples.     

Thermally stimulated depolarization currents in poly (ethyleneterephthalate‐ran‐p‐hydroxybenzoates)

Thermally stimulated polarization (TSPC) and depolarization currents (TSDC) are measured on polyethylene terephthalate (PET) copolymerized with p‐hydroxy benzoic acid (PHB). These systems are important since they comprise components of many commercial polymer liquid crystals (PLCs). There has been some speculation about the origins of the multiple transition peaks in TSDC of PLCs and secondary peaks have frequently been designated as resulting from Maxwell‐Wagner interphase polarization. The applicability of this designation for main chain PLCs has been investigated. TSDC as a function of field strength and window polarization has been conducted and the transitions have been identified as glass transition peaks as opposed to space charge relaxations. A comparison of the TSDC current versus the polarization current (TSPC) reveals that TSPC is not generated for transitions associated with the PHB component.     

FTIR investigation of the influence of diisocyanate symmetry on the morphology development in model segmented polyurethanes

Novel segmented polyurethanes with hard segments based on a single diisocyanate molecule with no chain extenders were prepared by the stoichiometric reactions of poly(tetramethylene oxide)glycol (M_n=1000 g/mol) (PTMO-1000) and 1,4-phenylene diisocyanate (PPDI), trans-1,4-cyclohexyl diisocyanate (CHDI), bis(4-isocyanatocyclohexyl)methane (HMDI) and bis(4-isocyanatophenyl)methane (MDI). Time dependent microphase separation and morphology development in these polyurethanes were studied at room temperature using transmission FTIR spectroscopy. Solvent cast films on KBr discs were annealed at 100 °C for 15 s and microphase separation due to self organization of urethane hard segments was followed by FTIR spectroscopy, monitoring the change in the relative intensities of free and hydrogen-bonded carbonyl (CO) peaks. Depending on the structure of the diisocyanate used, while the intensity of free CO peaks around 1720-1730 cm⁻¹ decreased, the intensity of H-bonded CO peaks around 1670-1690 cm⁻¹, which were not present in the original samples, increased with time and reached saturation in periods ranging up to 5 days. Structure of the diisocyanate had a dramatic effect on the kinetics of the process and the amount of hard segment phase separation. While PPDI and CHDI based polyurethanes showed self-organization and formation of well ordered hard segments, interestingly no change in the carbonyl region or no phase separation was observed for MDI and HMDI based polyurethanes. Quantitative information regarding the relative amounts of non-hydrogen bonded, loosely hydrogen bonded and strongly hydrogen bonded and ordered urethane hard segments were obtained by the deconvolution of CO region and analysis of the relative absorbances in CO region.     

Microwave Dielectric Properties and Thermally Stimulated Depolarization Currents Study of (1−x)Ba0.6Sr0.4La4Ti4O15–xTiO2 Ceramics

Microwave dielectric properties and thermally stimulated depolarization currents (TSDC) of (1?x)Ba_0.6Sr_0.4La₄Ti₄O₁₅–xTiO₂ (x = 0, 0.01, 0.02, 0.05, and 0.1) ceramics were studied. X‐ray diffraction analysis indicates that the specimens show a hexagonal perovskite structure; however, with an increase of x to 0.1, TiO_2?δ as a secondary phase can be detected in the ceramics. The variation of TiO₂ content has a significant effect on the dielectric properties of (1?x)Ba_0.6Sr_0.4La₄Ti₄O₁₅–xTiO₂ at microwave frequency. The dielectric permittivity of ceramics increases from 44 to 49 with the increase of TiO₂ content. The Qf value is in the range of 39 300–53 400 GHz. However, the temperature coefficient of resonant frequency (τ_f) changes from ?7.5 to–9.4 ppm/°C, and then turns to +3.9 ppm/°C. A near zero τ_f value can be obtained by tuning the content of TiO₂ addition. TSDC was also employed to analysis the extrinsic loss mechanism. Utilizing a fixed polarization condition, the TSDC relaxation peaks are present, which are generated by oxygen vacancies. And the concentration of oxygen vacancies increases with the increase of TiO₂ content. It can be concluded that the extrinsic dielectric loss is dominated by microstructure and oxygen vacancy defects.     

Identification of compounds in an HPLC fraction from female extracts that elicit mating responses in male screwworm flies,Cochliomyia hominivorax

When hexane extracts of mature screwworm females were chromatographed on a silica gel column, mating stimulant activity was concentrated in a fraction that eluted with hexane-ether (946, v/v). Separation of this fraction with HPLC (acetonitrile-acetone; 6040, isocratic) resulted in a chromatogram of some 20 peaks. Only peaks 4–11 elicited mating responses. Peaks 5–10 had most of the activity, with peak 8 producing the highest response. Sixteen compounds were characterized from peak 8 by gas chromatography-mass spectrometry: six unbranched secondary acetates (C₃₁H₆₂O₂); seven previously unreported methyl-branched secondary acetates (C₃₂H₆₄O₂); one unbranched ketone (C₃₁H₆₂O); and one methyl-branched ketone (C₃₂H₆₄O). The isomeric acetates were not completely resolved from each other by capillary gas chromatography (CGC) on methyl silicone columns. The sixteenth compound was an aldehyde (C₃₀H₆₀O) that was present only in occasional peak 8 preparations. These compounds and several derivatives were characterized by capillary gas chromatography-mass spectrometry (CGC-MS). The position of the acetate group was ascertained by conversion to a keto group or by replacement of the acetate with a methyl group. Pheromone activity was not observed in peaks trapped either from CGC or by recombination of the trapped CGC peaks from HPLC peak 8. This apparent loss of activity from CGC peaks or from TLC cannot currently be explained.Mention of a proprietary or commercial product does not constitute an endorsement by the U.S. Department of Agriculture.