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  • Polymer and Materials Science  (14)
  • 1995-1999  (5)
  • 1960-1964  (9)
  • 1950-1954
  • 1
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 1197-1212 
    ISSN: 0887-6266
    Schlagwort(e): block polyelectrolyte solutions ; micelles ; light scattering ; phase separation ; NaCl solutions ; extreme dilution ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Micellar solutions of polystyrene-b-poly(sodium acrylate) copolymers in aqueous NaCl were studied by static light scattering (SLS). It was found that micellar solutions of the copolymer, at concentrations of NaCl at, or above, 2.0 mol dm-3, became turbid on dilution at constant salt concentration and at constant temperature. Turbidity arose from highly dilute solutions (typically at a concentration three orders of magnitude lower than the overlap concentration of the micelle, C*), but at concentrations above the expected critical micellization concentrations (c.m.c.s). The observed turbidity was attributed to the phase separation of the micellar phase. A systematic investigation of the phase separation phenomenon was performed. The effects of various parameters on the solution behavior of the micellar solutions were studied, including the effect of the concentration of NaCl, the effect of temperature, and the effect of the length of the hydrophilic, corona-forming poly(sodium acrylate) block. Phase separation was attributed to the presence of a very large excess of NaCl in the dilute micellar solutions. It was proposed that phase separation arose because of the reduced hydration of the polyion, the decreased electrostatic repulsion between the micelles, and the increase in the amount of ion binding, which occur in highly dilute salt solutions. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1747-1755 
    ISSN: 0887-6266
    Schlagwort(e): kinetic sorption ; steady-state permeation/sorption ; polyimide ; carbon molecular sieve ; membrane separation processes ; Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Typically, materials with high-performance transport properties such as zeolites, carbon molecular sieves, or hyper rigid polymers are inherently difficult or impossible to characterize by steady-state membrane permeation experiments used for conventional polymers. Diffusion coefficients determined by transient sorption, a measurement easily performed on brittle media, are analyzed here and compared to those determined by steady-state permeation/sorption and transient permeation for a glassy polymer and a carbon molecular sieve. Average and local diffusion coefficients are extrapolated to zero upstream partial pressure to eliminate effects caused by concentration dependence. Good agreement between the techniques was observed for the glassy polymer. On the other hand, carbon molecular sieves, possessing a more complex morphology, exhibit a greater difference in diffusion coefficients determined by the various techniques. Nevertheless, comparison of the analysis techniques is shown to provide potentially valuable insights into the morphological features of such carbon molecular sieves. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1747-1755, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Biomaterials 6 (1995), S. 117-123 
    ISSN: 1045-4861
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The main function of the intervertebral disc is to transmit and attenuate compressive and torsional forces, and stabilize the intervertebral joint. Unfortunately, the disc may be displaced or damaged due to trauma or disease causing the nucleus to herniate and protrude into the vertebral canal or intervertebral foramen. Pressure on the spinal nerve may cause pain or paralysis in the area of its distribution. At present, the surgical procedures used to alleviate this condition include disc excision, and/or spinal fusion. A more desirable situation would involve removing the nucleus pulposus and part or all of the annulus fibrosis and implanting a suitable biofunctional equivalent. Such a prostheis should attenuate stresses and prevent abnormal stress at adjacent intervertebral joints. Maintenance of normal disc height would prevent impingement of the posterior facet joints and facet joint syndrome. In a previous companion paper (J. Applied Biomat. 5:125-132; 1994), the mechanical behavior of disc prostheses manufactured from fiber reinforced, elastomeric thermoset resins were examined. In order to develop devices which were more practical from a manufacturing standpoint and extremely reproducible, the fiber reinforced thermoset resins were replaced by multi-durometer thermoplastic elastomeric materials. In the present paper, the mechanical properties of thermoplastic multicomponent desings have been investigated. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 8 (1964), S. 2465-2478 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The relation between polymer and fiber structure and fiber properties is discussed. The specific effects of intermolecular forces, chain stiffness, monomer unit regularity, crystallinity, crosslinking, orientation, molecular weight, and chemical composition on the important fiber properties of melting point, modulus, elasticity, or recovery from strain, tensile strength, moisture adsorption, and dyeability are discussed in some detail. An example is given to illustrate the role of today's sophisticated engineering in further controlling and modifying fiber properties.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 1337-1348 
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The polymerization of desaminotyrosinetyrosylhexyl ester (DTH) with phosgene gives rise to poly(DTH carbonate), a new pseudopoly(amino acid). To evaluate the performance of this bioabsorbable material in orthopedic applications, the tissue responses elicited by compression-molded pins of poly(DTH carbonate) and clinically used polydioxanone pins (PDS; Orthosorb®) were compared. The two types of pins were implanted in the paravertebral muscle and in the metaphyseal proximal tibia and distal femur of 10 White New Zealand Rabbits for 1, 2, 4, and 26 weeks. The tissue response was evaluated using histologic staining of softand hard-tissue sections, fluorescent bone marker incorporation, and backscattered electron imaging. In soft tissue, both poly(DTH carbonate) and PDS elicited a mild inflammatory response resulting in encapsulation. During the disintegration phase, the PDS implants triggered a foreign body response involving the phagocytosis of polymeric debris by histiocytes and giant cells. No such response was observed for poly(DTH carbonate). In hard tissue, close bone apposition was observed throughout the 26-week test period for poly(DTH carbonate) implants. At the 26-week time point, the poly(DTH carbonate) implants exhibited surface erosion and were penetrated by new bone. In contrast, an intervening fibrous tissue layer was always present between the PDS pins and the bone. At 26 weeks, the PDS implants had partially resorbed and a foreign body response characterized by infiltration of inflammatory cells, and bone resorption was observed in several of the implantation sites. This study indicates that poly(DTH carbonate) and PDS exhibit fundamentally different interactions with hard tissue, and that poly(DTH carbonate) is a promising orthopedic implant material. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 31 (1996), S. 465-474 
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The interfacial shear strength and bone tissue response was investigated for an arc deposited (AD) commercially pure titanium implant surface, with (AD/HA) and without (AD) plasma-sprayed hydroxyapatite (HA) coating. Ten purpose bred coonhounds received bilateral femoral stem implantation (AD and AD/HA) in the proximal femurs (hemiarthroplasty). The femoral prosthesis consisted of a modular CoCr alloy head, modular Ti-6A1-4V neck, and a 10-mm diameter cylindrical Ti-6A1-4V femoral stem. The AD surface had 30-35% greater surface roughness than the AD/HA surface. The HA coating had a purity greater than 90% and a crystallinity greater than 65%. After 6, 12, and 24 weeks, the implants were retrieved and analyzed with mechanical testing, qualitative and quantitative histology, and electron microscopy. The AD/HA implants had equivalent interfacial shear strengths to the AD implants at all time periods. The AD/HA implants had significantly greater linear bone contact than the AD implants. The 6-week implants had significantly thicker cortical bone than the 12- and 24-week implants. The HA coating was very stable in vivo, evidenced by no thickness reduction at any time period. Qualitatively, the AD/HA implants primarily had bone contacting the implant surface with little fibrous tissue present, and the AD implants had bone and fibrous tissue contacting the implant surface. The electron microscopy analysis showed that the mechanically tested implants exhibited a mixed failure mode at the bone, HA coating, and titanium interfaces. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 44 (1960), S. 107-116 
    ISSN: 0022-3832
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The molecular weight distributions of vinyl polymers grafted by irradiation have been deduced theoretically. The derivations are rigorous for cases where chain transfer is not important or in all cases where the radiation dose is high (〉1 Mrad). In the absence of chain transfer, the width of the distribution depends mainly on conversion of monomer to grafted polymer and on the ratio of the rate constant for propagation to that for termination (kp/2kt). As this ratio gets smaller, the molecular weight distribution becomes broader. For relatively small values of kp/2kt (e.g., 0.5 or less), the width of the distribution increases markedly with increasing conversion. In such cases, the occurrence of chain transfer tends to make the distribution narrower. For a monomer grafted to a substrate where kp/2kt = 0.9 (for example), the ratio of weight to number average molecular weight is ca. 2. In general, monomers which have lower rates of propagation should form grafted polymers with broader molecular weight distributions.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    ISSN: 0022-3832
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A simple kinetic model for the formation of a nucleotide homopolymer is presented and evaluated. It consists of an initial dinucleotide formation followed by growth through further monomer addition and a competitive phosphorolysis. The molecular weight distribution is narrow up to the first 10-30% conversion and broadens on approach to equilibrium. From the equilibrium amounts of phosphate liberated, the final average molecular weight, and the time pattern of the synthesis, it is possible to obtain estimates of the rate constants. Turning to copolymers, the analysis of experimental data on sequence frequencies in an AU polymer in terms of addition probabilities indicates the existence of a penultimate effect, and a consistent set of four such probability parameters is derived. Finally, we consider a set of rate equations for binary copolymer formation suggested by these results. Their solution will permit a calculation of sequence distributions by utilizing kinetic experimental results exclusively.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 46 (1960), S. 151-162 
    ISSN: 0022-3832
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The changes in relative viscosity which occur when nylon 66 is irradiated with 2 m.e.v. electrons under an oxygen-free atmosphere under various conditions have been observed. A mechanism is proposed which reconciles all of these observations, and on the basis of this postulated mechanism yields of chain breaks and crosslinks are calculated. The effect of the presence of a small concentration of a vinyl monomer (acrylic acid) in the polymer during irradiation on degradation and crosslinking is also considered. The rate of penetration of oxygen into irradiated polyamides has been measured. There is a marked reduction in penetration rate which results from the presence of free radicals in the fiber and the irreversible reaction which results. The data are treated by an approximate diffusion equation and estimates of true diffusion coefficients are given. The effect of filament diameter on the extent of degradation which occurs when fibers of nylon 66 are irradiated and then exposed to air has been investigated. The marked dependence of degradation on fiber thickness is related qualitatively to the data on rate of oxygen penetration.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 49 (1961), S. 247-252 
    ISSN: 0022-3832
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The kinetics of grafting of allylic monomers to a solid polymeric substrate are compared with those for normal vinyl monomers which have been treated in a previous paper. The particular case treated theoretically for both types of monomers (using well established basic principles) is the sequence where the polymer is soaked in a solution of the monomer, the excess monomer is removed from the surface, the polymer is then irradiated at -78°C. at a high dose rate, and the system subsequently allowed to condition at 25°C. under an oxygen free atmosphere. It was previously shown theoretically that with a normal vinyl monomer in a very viscous matrix, the conversion of monomer to polymer increases indefinitely with post-irradiation time and that radiation dose and post-irradiation time are interchangeable in the absence of inhibitors. It is shown here that under similar conditions with allylic monomers, the existence of degradative chain transfer to the monomer places a definite limit on the maximum conversion and makes this conversion quite dependent on dose. The theory for the case involving degradative chain transfer is applied to data on the grafting of itaconic acid to 66 nylon and values are deduced for the ratio of transfer to propagation constants and transfer to termination constants. Lower limits for the absolute values of these constants are also deduced. The ratio of propagation kp and termination kt rate constant in this very viscous medium is kp/2kt = 0.58.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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