ISSN:0959-8103    

DOI:10.1002/pi.4990260402

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe dielectric absorption and dispersion of poly(vinyl chloride),MMv= 49 000, in THF and in cyclohexanone have been studied over a frequency range of 120 kHz to 11·0 MHz, at temperatures from −22·5 to 35°C, and at concentrations ranging from 4 to 12·0(w/v)% PVC/THF and from 2 to 8·0(w/v)% PVC/cyclohexanone. The viscosities of the two systems have also been measured at temperatures from 20 to 50°C. A single relaxation time was found (β = 0·8–1·0), which indicates that relaxation occurs by segmental rotation. The dielectric and viscous activation energies have been calculated. The dipole moment associated with the relaxation process has also been calculated. The relaxation time, dielectric and viscous activation energies and the dipole moment were found to be dependent on the type of solvent. The dipole moment also showed a molecular weight dependence. The influence of the concentration and temperature on the apparent dipole moment and on the relaxation time

ISSN:0959-8103    

DOI:10.1002/pi.4990260403

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractVulcanized bromobutyl, natural and nitrile rubbers were immersed in distilled water, or seawater, at 20, 40 or 60°C for up to 32 weeks and the resulting changes in weight and dynamic mechanical properties were monitored. Larger weight increases were observed for the specimens immersed in distilled water than for the equivalent specimens in seawater, and there was no sign of an equilibrium weight uptake being reached for the specimens immersed in distilled water at 60°C. Bromobutyl rubber showed increases in the magnitude of the loss tangent peak which could be related to the weight increases in both distilled water and seawater but the decreases in peak height observed for natural rubber and nitrile rubber were not well correlated with weight increase

ISSN:0959-8103    

DOI:10.1002/pi.4990260404

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractConductive polymeric films have been of great interest recently, although one major drawback to their use is environmental stability. Polypyrroles doped withp‐toluenesulfonate, tetrafluoroborate and perchlorate anions were examined under elevated temperatures and environments. The use of d.c. electrical conductivity decay measurements and fitting of kinetic models allows changes in bulk properties to be examined. Surface characterisation performed by X‐ray photoelectron spectroscopy (XPS) enables detailed investigation into changes in chemical states of surface atoms. The mechanisms described for the change in electrical and structural properties may be attributed to polymer backbone oxidation through free radical oxygen insertion and electrolyte dopant degradat

ISSN:0959-8103    

DOI:10.1002/pi.4990260405

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractSamples of polyaromatic amines were synthesised by chemical and electrochemical methods, using different amounts of electrolytes for the purpose of doping the polymer. These polymers were found to show electrical conductivity in the range 10−12–10−6S/cm. A study of conductivity at various temperatures indicates the semiconducting behaviour of these polymers. Thermal analysis shows that these polymers have high thermal stab

ISSN:0959-8103    

DOI:10.1002/pi.4990260406

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe palmitoyl ester ofN‐hydroxypyridine‐2‐thione displayed useful chain transfer properties in free radical polymerizations of methyl methacrylate and styrene. Retardation, however, accompanied the lowering of molecular weight in methyl acrylate and vinyl acetate polymerizations.4‐Methyl‐3‐palmitoyloxythiazol‐2(3H)‐thione had good chain transfer activity with methyl methacrylate, styrene and methyl acrylate. Although benzyl thionobenzoate exhibited virtually ‘ideal’ behaviour (chain transfer constantCx∼1) in styrene and methyl acrylate polymerizations, it was ineffective in lowering molecular weight of poly(methyl methacrylate). Severe retardation was observed with vinyl acetate.Addition‐fragmentation pathways are postul

ISSN:0959-8103    

DOI:10.1002/pi.4990260407

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPreliminary results are presented on the fabrication and analysis of junctions formed between metals and semi‐conducting and conducting polypyrrole. Rectifying junctions were observed between aluminium and indium with semi‐conducting polypyrrole in a sandwich geometry using current‐voltage (I‐V) and capacitance‐voltage (C‐V) analysis techniques, respectively. All planar junctions analysed were non‐rectifying, while both gold and platinum were observed to form ohmic junctions in both the sandwich and planar geometries. Preliminary analysis using ideal Schottky barrier theory was attempted with various junction parameters determined, with significant deviation from the ideal theory observed. It is proposed that this deviation is due to the synthesis history of the polymer and the presence of an insulating oxide layer between the polymer

ISSN:0959-8103    

DOI:10.1002/pi.4990260408

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractFormulations based on novel particulate ion‐exchange resins, containing a wide range of paramagnetic transition and rare‐earth metals bound to their surfaces, have been synthesised as potential contrast agents for the magnetic resonance imaging (MRI) of the gastro‐intestinal (GI) tract of man. They have been evaluated in terms of their effects upon the spin‐lattice (R1) and spin‐spin (R2) relaxation rates of the protons of water. Careful selection of the polymer, spacer‐arm, ligand and paramagnetic ion provides a means for subtle molecular tailoring.Further potential applications have been highlighted based on the observed properties of such f

ISSN:0959-8103    

DOI:10.1002/pi.4990260409

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn this study pyrrole was electropolymerized into polymers having three types of morphology. In the first case, convoluted tubes and dendrites were deposited on filled polymeric and roughened electrodes. Secondly, free‐standing fractals were formed, radiating from central anodes. In some instances the polymers were grown across filter papers located at the base of the anode and at the surface of the solvent. In the third instance, high surface area fibrillar forms were obtained by in‐situ polymerization within coated, γ‐alumina isoporous membrane hosts, followed by leaching in alkali. In all cases the morphology of these products is described by optical and scanning electron micr

ISSN:0959-8103    

DOI:10.1002/pi.4990260410

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe miscibility of styrene‐alt‐maleic anhydride (SMA) and a series of styrene‐acrylonitrile (SAN) copolymers in blends with either PMMA or PVC were examined by fluorescence and FTIR spectroscopic techniques. In the case of the alternating copolymerintra‐molecular excimer formation is precluded and changes in the excimer/monomer fluorescence intensity (IE/IM) reflect changes in the amount of inter‐chain excimer formation. The value ofIE/IMin blends, therefore, provides a sensitive measure of phase separation (miscibility). In the case of the acrylonitrile copolymers theIE/IMof the blend had to be corrected to account forintra‐molecular excimers formed between adjacent chromophores in the SAN. These results compared favourably with observed frequency shifts in the phenyl C—H out‐of‐plane

ISSN:0959-8103    

DOI:10.1002/pi.4990260411

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY