By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsTg that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems 相似文献
Thin films of rigid poly(p-phenylene pyromellitimide) (PMDA-PDA) and semi-rigid poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the respective poly(amic acid) and poly(amic ethyl ester) precursors, were characterized with respect to their optical, thermomechanical and structural properties. Both polyimides exhibit an unusually large anisotropy between the in-plane and out-of-plane refractive indices, with n ranging from 0.198 to 0.216 for PMDA-PDA and from 0.230 to 0.242 for BPDA-PDA, nearly independent of the nature of the initial polyimide precursor, film thickness, and film preparation method. PMDA-PDA films exhibit low coefficients of thermal expansion (CTE's) of 6.5 and 8.2 ppm/C for the acid-derived and the ester-derived polyimides, respectively. In comparison, the BPDA-PDA films show CTE values of 4.3 and 18.0 for the acid-derived and ester-derived samples, respectively, despite the small differences in their optical anisotropies. Wide-angle x-ray diffraction patterns obtained in reflection and transmission for the various samples reveal a strong in-plane chain orientation for both PMDA-PDA and BPDA-PDA polyimides, with somewhat better intermolecular packing order for the ester-derived polyimide films. These effects of chemical structure and precursor on properties and structures of the polyimide films are discussed in light of recent theoretical considerations of semiflexible polymers.Dedicated to Prof E. W. Fischer on the occasion of his 65th birthday 相似文献
Polyacetylene obtained by the dehydrochlorination of polyvinyl chloride in the NaOH—DMSO system undergoes sulfurization with elemental sulfur at 120—300 °C to liberate hydrogen sulfide and to form electroconducting (0.7·10–12—5.8·10–15Sm nm–1) and paramagnetic (1.5·1017—1.7·1019sp g–1, g = 2.0035—2.0045, H= 0.44—0.66 mT) dark powders with a metallic luster. Their IR spectra and comparison with the samples of sulfurized polyethylene show that sulfurized polyacetylene contains poly(vinylene polysulfide), poly(thienothiophene), and related structures. The polymers afford the cathode discharge capacity of lithium batteries up to 950 mA h g–1(in the first cycle) and stable cycling at a level of 500—300 mA h g–1(25 cycles). 相似文献
An investigation of the radial structure of composite latex particles by small-angle x-ray scattering (SAXS) is given. Measurements at different contrasts were done by addition of sucrose to the dispersion medium water. The latex particles investigated here consist of a poly(styrene) core and a shell of poly(methylmethacrylate) and were prepared by seeded emulsion polymerization. Since the electron density of both polymers can be easily matched by concentrated sucrose solution, a full analysis of the radial electron density by contrast variation can be given. Depending on the mode of monomer addition during the second polymerization step a very sharp or a diffuse interface between the two incompatible polymers may result.Respectfully dedicated to Prof. E. W. Fischer on the occasion of his 65th birthday 相似文献
Poly (caprolactone) membranes with addition of different poly (ethylene glycol) concentrations were prepared for separation of water/isopropanol azeotropic mixture by pervaporation process. Different characterization tests including Fourier transform infrared, scanning electron microscopy, water contact angle, and thermogravimetric analysis were carried out on the prepared membranes. In addition, the effect of poly (ethylene glycol) PEG content on the swelling degree and the performance of the prepared membranes in pervaporation process were investigated. According to the obtained results, all the membranes were water selective and the blend membrane containing 3 wt% PEG exhibited the best pervaporation performance with a water flux of 0.517 kg/m2 hour and separation factor of 1642 at the ambient temperature. Hydrophilicity improvement of the blend membranes was confirmed by constant decrease in water contact angle of the membranes as PEG content increased in the casting solution. Scanning electron microscopy cross‐sectional images indicated that the blend membranes containing PEG had a closed cellular structure. Furthermore, mechanical and thermal properties of the membranes decreased by adding PEG. 相似文献
Biodegradable poly(lactic acid) (PLA)/poly(butylene adipate‐co‐terephthalate) (PBAT) blends and films were prepared using melt blending and blowing films technique in the presence of chain extender‐Joncryl ADR 4370F. The ADR contains epoxy functional groups and used as a compatibilizer. The morphological, mechanical, rheological, thermal, and crystalline properties of the PLA/PBAT/ADR blown films were studied. Scanning electron microscopy micrographs of the films revealed more ductile deformation with increasing PBAT content. The addition of PBAT enhanced the toughness of the PLA film. Tensile tests indicated that the elongation at break increased from 20.5% to 334.6% in the machine direction and from 7.1% to 715.9% in the transverse direction. The Young modulus increased from 2690.5 to 395.6 MPa in the machine direction and from 2623.5 to 154.0 MPa in the transverse direction. The sealing strength of 40/60/0.15 PLA/PBAT/ADR film was the highest among all the samples up to 9.4 N 15 mm−1. These findings gave important implications for designing and manufacturing polymer packaging materials. 相似文献
This study reports a detailed analysis of an electrode material containing poly(phenolphthalein), carbon nanotubes and gold nanoparticles which shows superior catalytic effect towards to hydrazine oxidation in Britton–Robinson buffer (pH 10.0). Glassy carbon electrode was modified by electropolymerization of phenolphthalein (PP) monomer (poly(PP)/GCE) and the multiwalled carbon nanotubes (MWCNTs) was dropped on the surface. This modified surface was electrodeposited with gold nanoparticles (AuNPs/CNT/poly(PP)/GCE). The fabricated electrode was analysed the determination of hydrazine using cyclic voltammetry, linear sweep voltammetry and amperometry. The peak potential of hydrazine oxidation on bare GCE, poly(PP)/GCE, CNT/GCE, CNT/poly(PP)/GCE, and AuNPs/CNT/poly(PP)/GCE were observed at 596 mV, 342 mV, 320 mV, 313 mV, and 27 mV, respectively. A shift in the overpotential to more negative direction and an enhancement in the peak current indicated that the AuNPs/CNT/poly(PP)/GC electrode presented an efficient electrocatalytic activity toward oxidation of hydrazine. Modified electrodes were characterized with High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Amperometric current responses in the low hydrazine concentration range of 0.25–13 µM at the AuNPs/CNT/poly(PP)/GCE. The limit of detection (LOD) value was obtained to be 0.083 µM. A modified electrode was applied to naturel samples for hydrazine determination. 相似文献
X-ray diffraction, scanning electron microscopy, and infra-red spectroscopy are applied to study the evolution of films electrodeposited from acidic tungstate solutions. Structural inhomogeneity is found to be responsible for the difference in rechargeability of films of different thickness. Voltammetric responses demonstrate pronounced sensitivity to the nature of crystalline phases, thus throwing light on the defects of the lattice features of nonstoichiometric W(V)–W(VI) oxides. One crystalline phase observed in the films under study and attributed to the layered nonstoichiometric oxohydroxide was never reported for oxotungstate films fabricated by other techniques. This phase is believed to be special to electrocrystallized films and to keep some structural features of dissolved isopolytungstate molecular precursors.Dedicated to Prof. G.Horanyi with the highest respect to his experimental talents, remarkable papers and important contributions in various fields of modern electrochemistry. 相似文献
General purpose poly(styrene) prepared by conventional radical techniques contains a head-to-head unit as a consequence of
polymerization termination by radical coupling. As has been previously demonstrated, thermal stress promotes homolysis of
the bond linking the head-to-head components. The macroradicals generated depolymerize rapidly to generate styrene monomer.
This decomposition during processing can lead to finished articles containing objectionable levels of styrene monomer, particularly
for food packaging applications in which even low levels of monomer can promote objectionable taste and aroma. Polymer containing
no head-to-head units should not be prone to this facile decomposition. In this instance, poly(styrene) has been prepared
by nitroxyl-mediated polymerization of styrene monomer followed by reductive removal of nitroxyl end groups. Polymer prepared
in this manner contains no head-to-head units and displays thermal stability much greater than that observed for conventional
poly(styrene). A direct comparison of the stability for the two polymers is readily available by thermogravimetric techniques.
A quantitative reflection of the difference in stability is available from the rate constants for the respective decomposition. 相似文献
Polyacetylene functionalized by sulfoxide groups was synthesized from poly(methyl vinyl sulfoxide) by the elimination of methanesulfenic acid under the action of a strong base at 20—50 °C.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 774–776, March, 2005. 相似文献
Summary: The unusual structure of poly(ethylene oxide) (PEO) and Laponite clay in transparent nanocomposite films was investigated using scanning electron, atomic force, and optical microscopy, and X‐ray scattering. Each method is sensitive to different aspects of structural features and together they measure the resulting morphology and shear‐induced orientation. On nanometer length scales, clay platelets were found to orient in bundles while polymer crystallinity was suppressed. Microscopy led to the observation of unexpected and highly oriented multilayers on the micron length scale.
Scanning electron microscopy image of the freeze‐fractured surface of a poly(ethylene oxide)–Laponite film: the view on top of the x–y plane. 相似文献
Thermal oxidation of poly(1-trimethylsilylprop-1-yne) was studied by IR spectroscopy in the 20—245 °C temperature interval. In the 20—160 °C temperature range, the reaction proceeds predominantly at the C—Me group as revealed by the decrease in the intensity of the bands of the methyl group bound to the C atom and the appearance of the bands of the hydroperoxide and methylene groups. The decomposition of hydroperoxides produces aldehydes and ethers. At 160—200 °C, oxidation occurs via two routes: at the C—Me and C=C groups, while the Me3Si group remains unchanged. At 230—240 °C, the rate of the reaction occurring at the C=C bond is higher than the rates of the processes involving the MeC and Me3Si groups. The relative content of the structural units was calculated for the samples oxidized at different temperatures. Plausible mechanisms of thermal oxidation of poly(1-trimethylsilylprop-1-yne) were considered on the basis of the data obtained. 相似文献
The orientation and relaxation behavior of compatible blends of poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) was investigated. The deformation was performed at 9 K above the glass transition temperature. Based on birefringence and IR-dichroic measurements, it was found that the orientation of PMMA is strongly increased in the blends as compared to pure PMMA at identical draw ratios.The orientation of PVC, on the other hand, is not changed by blending. The results are discussed in terms of friction coefficients and their enhancement by molecular interactions.Dedicated to Prof. E. W. Fischer on the occasion of his 665th birthday 相似文献