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  • Polymer and Materials Science  (11)
  • HPLC  (1)
  • 1995-1999  (3)
  • 1975-1979  (6)
  • 1965-1969  (3)
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  • 1
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: To prepare very narrow distributed polystyrene samples, a two step procedure of polymerization is proposed, which includes a change of solvent. The first solvent, used for the initiation step, has to be characterized by a high value of vst/vp, while the second one, used for the propagation step, should guarantee a good control of temperature during the polymerization reaction. In our case, tetrahydrofuran and benzene were chosen and n-Li-butyl has been used for the initiation.The polymerization products have been characterized by MW-averages and MW-distribution. Finally a preparative fractionation has been carried out to separate the low and high MW tail of the distribution thus leading to samples whose values for M̄w/M̄n can be shown to be about 1,01.
    Notes: Zur Herstellung hocheinheitlicher Polystyrole wird ein Verfahren angegeben, das auf einer zweistufigen Lösungspolymerisation mit Austausch des Lösungsmittel beruht. Die Lösungsmittel müssen so gewählt werden, daß bei der Vorpolymerisation die Startgeschwindigkeit wesentlich größer ist als die Wachstumsgeschwindigkeit, für die weitere Polymerisation jedoch die Reaktion thermisch gut kontrolliert werden kann; in dem beschriebenen Verfahren wurden Tetrahydrofuran und Benzol verwenigte Polymere entstehen sollten.Die Polymerisationsprodukte wurden durch ihr mittleres Molekulargewicht und ihre Molekulargewichts-Verteilungskurve charakterisiert. Nach einer Spitzenfraktionierung zur Abtrennung der hoch- und niedermolekularen Ausläufer liegt die erreichte Einheitlichkeit bei einem Wert M̄w/M̄n ≈ 1,01.
    Additional Material: 4 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 69 (1978), S. 189-210 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The solution instability (also called ageing or degradation) of high purity polyacrylamides(PAAm) was examined for a number of different molecular weights. This instability set in by a decrease of the solution viscosity and of [η] depending on time with simultaneous loss of flocculation activity.The instability appears only at molecular weights M̄ 〉 1,5 mill. in aqueous solutions; in formamide and ethyleneglycole PAAm-solutions however are stable. The viscosity loss was observed at a concentration range c = 0,001 to 5%. The standardization of several pH-values at a range from 1 to 12 by means of buffer substances as well as the addition of hydrochinone, chinone, NaNO2 and Na2SO3 do not lead to a stable solution. Only at pH = 5 a stable solution was obtained but by changing the buffer substance at the same pH the solution became instable again. Addition of isopropanol leads to stable aqueous PAAm-solutions from technical products as well as high purity polyacrylamides.The mechanism of the solution instability is not a decrease of the molecular weight due to chain scission but a change of conformation of the solution structure from single molecules based on hydrogen bonds.
    Notes: Die Lösungsinstabilität(auch Alterung oder Viskositätsabbau genannt) von hochreinen Polyacrylamiden (PAAm) verschiedener Molekulargewichte wurde untersucht. Diese Instabilität äßert sich durch eine Abnahme der Lösungsviskosität und des [η] in Abhängigkeit von der Zeit bei gleichzeitigem Flockungsverlust.Die Lösungsinstabilität tritt nur bei Molekulargewichten M̄ 〉 1,5 Mill. in wäßriger Lösung auf. PAAm.-Lösungen in Formamid und äthylenglykol sind stabil. Die Viskositätsabnahme erfolgt in einem Konzentrationsbereich von c = 0,001 bis 5%. Die Einstellung verschiedener pH-Werte im Bereich von pH = 1 bis 12 mittels Puffersubstanzen sowie die Zusätze von Hydrochinon, Chinon, NaNO2 und Na2SO3 führen nicht zu einer Lösungsstabilität. Nur pH = 5 zeigte sich eine Stabilisierung der Lösung, die jedoch beim Wechsel der Puffersubstanz bei gleichem pH wiederum in eine Instabilität überging. Zusätze von Isopropanol führen sowohl bei technischen Handelsprodukten als auch bei hochreinen Laborprodukten zu einer Stabilisierung wäßriger PAAm-Lösungen.Der Mechanismus der Lösungsinstabilität besteht nicht in einem Molekulargewichtsabbau durch Kettenbruch, sondern offenbar in einer änderung der Lösungsstruktur der Einzelmoleküle unter Beteiligung von Wasserstoff-Brücken.
    Additional Material: 14 Ill.
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  • 3
    ISSN: 0887-6266
    Keywords: tensile drawing ; morphology ; polybutylene ; terephthalate ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The concept of the drawing of a molecular network has been employed to derive a total network draw ratio from the combination of the two deformations occurring in the production of poly(butylene terephthalate), PBT, fibers by the consecutive processes of melt spinning and cold drawing. The mechanical properties of PBT can then be more readily explained in terms of increases in this total network draw ratio. However, the preorientation and crystallization that occurs in the melt-spinning process can occur at different strain rates and temperatures, depending on the wind up speed employed, on the extensional viscosity of the polymer, and on the variation of the extensional viscosity with temperature. Therefore, for polymers such as poly(butylene terephthalate), which can exist in two crystalline forms, the morphology of the final drawn fiber might be expected to depend on the first melt-spinning stage of the process as well as on the total network draw ratio. In this work, density, birefringence, mechanical measurements, and WAXD measurements, which have been made on the melt-spun fibers and on the drawn fibers, are described. Small differences in some of the drawn yarn mechanical properties at the same overall network draw ratio are related to the crystallinity and in particular to differences in the proportion of the α and β phases present in the drawn yarn. These in turn are related to differences in the temperature and stress during melt spinning and drawing. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2465-2481, 1997
    Additional Material: 18 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It is proposed that the mobility of sufficiently long molecules undergoing translational diffusion through solid polyethylene is significantly reduced by tie molecules and fixed entanglements within the interlamellar regions of the matrix. The effect on the diffusion coefficient both of diffusant molecular length and of the host matrix morphology is considered, and a semiquantitative relation between them obtained. This indicates that the mobility of long diffusants is higher in polyethylene which has been cooled slowly from the melt than it is in quenched polyethylene, in marked contrast to the behavior of gaseous and other small diffusants.
    Additional Material: 4 Ill.
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  • 5
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The diffusion coefficient for two diffusants of the type n-(CH2)NX is measured, where N ≃ 25, 45 and X is a suitable label; the matrix is linear polyethylene cooled at two widely differing rates from the melt. The measuring technique used is a recently developed one based on infrared microdensitometry. The results indicate that these diffusants diffuse faster in the slowly cooled matrix, in marked contrast to the behavior of gaseous diffusants. They are in agreement with the predictions of the model developed in a previous paper (part I), in which the constraints imposed by interlamellar tie molecules on long diffusants were shown to be important.
    Additional Material: 3 Ill.
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  • 6
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Direct depth profiling techniques to date have largely lacked the necessary depth resolution to investigate interfacial phenomena of the order of the bulk correlation length (5 - 10 nm for a wide range of systems). Here we investigate the optimal spatial resolution and depth of probe that may be attained for composition  -  depth profiling of polymeric samples via nuclear reaction analysis (NRA) using the 2H(3He, 1H)4He reaction. We find that the spatial resolution can be greatly improved by using a grazing incidence geometry of the incident 3He beam on the sample, and analyzing the emitted protons in a backwards direction. This results in spatial resolutions down to about 3 nm at the sample surface, compared to a value of some 7 nm or more previously reported in earlier studies when emitted α-particles were detected in the forward direction. At the same time the depth to which samples can be profiled via the backwards emitted protons may be considerably extended relative to the α-particle detection mode, when the 3He beam impinges on the sample surface at normal incidence (up to about 4 μm into the sample for incident energies of 1.2 MeV in the proton-detection mode compared to only 1 μm for the equivalent α-particle detection mode).
    Additional Material: 5 Ill.
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  • 7
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The composition of sol- and gel-phases as formed during precipitation fractionation in various systems polymer-solvent-nonsolvent is examined analytically.It is shown that the polymer concentration in the gel-phase is independent of the initial concentration of polymer in the solution. The polymer concentration of the gel-phase increases with increasing molecular weight, if the nonsolvent-solvent-ratio is kept constant.The nonsolvent-solvent-ratio in the gel-phase is always smaller than in the corresponding sol-phase, it is constant during the early steps of fractionation and decreases slightly at the end of fractionation.
    Notes: Die Zusammensetzung der Sol- und Gelphasen, wie sie bei der Fällfraktionierung in verschiedenen Systemen Polymer-Lösungsmittel-Fällungsmittel gebildet werden, wird analytisch untersucht.Dabei zeigt sich, daß die Konzentration des Polymeren in der Gelphase unabhängig von der Ausgangskonzentration des Polymeren ist. Bei konstantem Fällungsmittelgehalt der Solphase nimmt die Polymerkonzentration in der Gelphase mit steigendem Molekulargewicht zu.Das Fällungsmittel-Lösungsmittel-Verhältnis in der Gelphase ist stets geringer als in der korrespondierenden Solphase. Es ist im Laufe einer Fraktionierung zunächst konstant und nimmt gegen Ende der Fraktionierung langsam ab.
    Additional Material: 11 Ill.
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  • 8
    ISSN: 1432-1912
    Keywords: Key words Ethanol ; Acetylcholine ; Scopolamine ; Hippocampus ; Microdialysis ; HPLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Using the microdialysis technique and sensitive HPLC procedures for the determination of acetylcholine (ACh) and ethanol, we investigated the release of ACh in rat hippocampus after acute ethanol administration. Systemic administration of ethanol (0.8 and 2.4 g/kg i.p.) led to peak ethanol concentrations of 21 and 42 mM in the hippocampus, respectively. The high dose caused a long-lasting inhibition of basal ACh release by up to 33%. Local infusion of scopolamine (1 µM) enhanced hippocampal ACh release up to eightfold in the presence of neostigmine (10 µM), and this stimulated release was also inhibited after systemic ethanol administration (by up to 45%). The low dose of ethanol (0.8 g/kg) led to a delayed stimulation of hippocampal ACh release. A stimulatory effect on ACh release was also observed when ethanol (50–100 mM) was infused directly into the hippocampus or into the septal area, i.e. to the origin of the cholinergic septohippocampal pathway; thus, the stimulatory effect may be mediated by a direct effect on cholinergic fibres. We conclude that ethanol exerts dual modulatory effects on the activity of the septohippocampal cholinergic fibres, depending on the dose and the site of administration. It is suggested that the inhibition of hippocampal ACh release by intoxicating doses of ethanol may contribute to the well-known cognitive and amnesic effects of ethanol intake.
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  • 9
    ISSN: 0449-2986
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 69 (1978), S. 169-188 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The present manuscript describes a solution polymerization representing uniform, unbranched, ultrahigh molecular weight polyacrylamides (PAAm) which are free of additives and rest initiator. In addition to the determination by time-conversion-curves, molecular weight and molecular weight distribution of the polymers were characterized definitely by infrared spectroscopy, elemental analyses and thermogravimetry. Among other things it was established that PAAm binds about 2-9% water in spite of intensiv drying. This amount of water is extensively independent of the morphologie of the samples. Orientating measurements of the unknown [η]-M-relationships in formamide and ethylene glycol were made, showing an exponent in ethylene glycol of a 〈0,5. The [η]-M-relationships of H2O, formamide and ethylene glycol cut each other in a molecular weight range from 3·105 to 4·105 (g/mol). The determined ηsp/c-c-functions from ultrahigh molecular weight PAAm in water are not straight lines. By plotting after the Schulz-Blaschke-equation one gets straight lines, the constant KSB = 0,24 being independent from the solvent.
    Notes: In der vorliegenden Arbeit wird eine Lösungspolymerisation zur Darstellung von einheitlichen, linearen, ultrahochmolekularen Polyacrylamiden (PAAm) beschrieben, welche frei von Zusätzen sowie frei von Restinitiator sind. Neben der Bestimmung von Zeitumsatzkurven, Molekulargewicht sowie Molekulargewichtsverteilung wurden die erhaltenen Polymeren mittels IR-Spektroskopie, Elementaranalyse sowie thermogravimetrischen Untersuchungen eindeutig charakterisiert. Unter anderem wurde dabei festgestellt, daß PAAm trotz intensiver Trocknung (Gefriertrocknung etc.) ca. 2 bis 9% Wasser bindet. Dieser Wassergehalt ist weitgehend unabhängig von der Morphologie der Proben. Zu den bisher unbekannten [η]-M-Beziehungen in Formamid und äthylenglykol wurden orientierende Messungen durchgeführt, wobei sich in äthylenglykol ein Aufweitungsparameter a 〈0,5 ergab. Die [η]-M-Beziehungen in Wasser, Formamid und Äthylenglykol schneiden sich danach in einem Molekulargewichtsbereich von 3 · 105 bis 4 · 105 (g/mol). Die in Wasser ermittelten ηsp/c-c-Funktionen von ultrahochmolekularem PAAm stellen keine Geraden dar. Bei der Auftragung nach der Schulz-Blaschke-Gleichung ergeben sich wieder Geraden, wobei die Konstante KSB = 0,24 lösungsmittelunabhängig ist.
    Additional Material: 6 Ill.
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