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  • Chemistry  (12)
  • ACC-independent  (1)
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  • 1
    Digitale Medien
    Digitale Medien
    Ethylene release from green spruce needles involves a combination of ACC-dependent and independent pathways (1991)
    Springer
    Plant growth regulation 10 (1991), S. 153-162 
    Details
    ISSN: 1573-5087
    Schlagwort(e): Picea abies L ; conifers ; ACC ; ACC-independent ; free radicals ; methionine ; peroxides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Aminoethoxyvinylglycine (AVG) and cobalt ions strongly inhibit the conversion of added methionine or aminocyclopropane-1-carboxylic acid (ACC) into ethylene by green-coloured, non-stressed Norway spruce (Picea abies L.) needles but only 30%–40% of basal ethylene formation is affected by such inhibitors. In addition, free radical-mediated ACC-independent ethylene formation (AIEF) of the type released by brown-coloured spruce needles also occurs in extracts from healthy green-coloured needles. Treatment with CdCl2 (10 mM), Na2S2O5 (5 mM) or FeSO4 (10 mM) induces 3–7 fold increases in the rates of ethylene evolution from green-coloured needles. However, only Cd2+-induced ethylene formation is inhibited by AVG while ethylene induced by S2O5 2- or Fe2+ is insensitive to added AVG although increased levels of ACC have also been detected in these treatments. Nevertheless, ethylene-forming decomposition of the precursors of AIEF is accelerated by S2O5 - or Fe2+ which indicates that the ethylene released from green-coloured spruce needles is formed by a combination of both the ACC-dependent and AIEF pathways.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00024961
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  • 2
    Digitale Medien
    Digitale Medien
    Interfacial phenomena controlling particle morphology of composite latexes (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 42 (1991), S. 1049-1063 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A thermodynamic analysis and a mathematical model were derived to describe the free energy changes corresponding to various possible morphologies in composite latex particles. Seeded batch emulsion polymerization was carried out at 70°C using as seed monodisperse polystyrene latex particles having different surface polarity. The surface polarity was estimated by contact angle measurement at the latex “film”/water interface for octane as the probe liquid. Methyl methacrylate and ethyl methacrylate were polymerized in a second stage seeded emulsion polymerization using polystyrene particles as seed in the presence of a nonionic stabilizer, nonyphenol polyethylene oxide (Igepal Co-990). Two types of initiators, potassium persulfate (K2S2O8) and azobisiobutyronitrile (AIBN), were used to change the interfacial tension between the second stage polymer (in monomer) and water interface. The values of the interfacial tension of polymer solutions in the second stage monomer vs. the aqueous phase, measured by drop-weight-volume method under conditions similar to those prevailing during the polymerization, correlated well with the determined particle surface polarity and the observed TEM particle morphology. The results showed that, rather than the polymer bulk hydrophilicity, the surface particle polarity is the controlling parameter in deciding which phase is inside or outside in the composite particle. The variation of the polymer phase interfacial tension with polymer concentration was also estimated. Based on experimentally measured interfacial tensions, composite particle configurations were predicted. The predicted morphologies showed good agreement with the observed particle morphologies of the composite latexes.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1991.070420418
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  • 3
    Digitale Medien
    Digitale Medien
    Particle morphology in artificial composite polymer latex systems (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 46 (1992), S. 691-706 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Artificial composite latex particles were prepared by direct emulsification of a toluene solution of a blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA). The morphology of the composite particles from the higher molecular weight polymers showed polystyrene particles partially encapsulated by PMMA on the surface. On the other hand, for the lower molecular weight polymers, the reverse morphology was observed. The morphologies of the artificial composite latex particles swollen with solvent were examined when kept under agitation. The degree of phase separation between the two polymers in the composite particles was found to be affected by agitation to different extent, depending on the viscosity of polymer phases, the interfacial tension, and degree of mixing at interface between the two polymers. Extended agitation of the composite latex particles of high molecular weight polymers resulted in mixed morphologies that included individual PS and PMMA particles along with the original morphology of the composite particles. On the other hand, composite latex particles with the lower molecular weight polymers resisted complete phase separation due to lower interfacial tension and better mixing at the interface between the two polymers.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/app.1992.070460416
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  • 4
    Digitale Medien
    Digitale Medien
    Soapless emulsion polymerization of methyl methacrylate. II. Simulation of polymer particle formation (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 61 (1996), S. 2235-2244 
    Details
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: In this work, a generalized mathematical model was developed to estimate the variation of particle concentration during the entire course of soapless emulsion polymerization of methylmethacrylate (MMA). All of the factors, such as oligomeric radical absorption or desorption by polymer particles, coagulation between polymer particles, and the termination effect on the formation mechanism of polymer particles, were considered and included in this model. When appropriate parameters were selected, this model could be successfully used to interpret the experimental behavior of particle concentration during the entire reaction. Under different conditions, the rate of polymerization, the number of radicals in each particle, the instantaneous average molecular weight of polymers, and the rate constant of termination were also calculated. All of them coincided with the experimental results quite well. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Transformation of the product set in separation sequence synthesis (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 1753-1757 
    Details
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/aic.690371123
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  • 6
    Digitale Medien
    Digitale Medien
    Degradation of medical-grade polyurethane elastomers: The effect of hydrogen peroxide in vitro (1993)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 27 (1993), S. 345-356 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: Treatment of Pellethane 2363-80A - a medical-grade poly(tetramethylene oxide)-based polyurethane elastomer - with 25% (w/w) hydrogen peroxide at 100°C for times ranging from 24 h to 336 h led to significant decreases in ultimate tensile properties and decreases in molecular weight, both at the surface and in the bulk. IR spectral changes were similar to those observed after degradation in vivo. Differential scanning calorimetry showed that hydrogen-peroxideinduced degradation was associated with greater order in the hard domain and greater mobility in the soft domain. Studies conducted with low-molecular-weight model compounds for the hard and soft segments confirmed that methylene groups adjacent to oxygen were susceptible toward oxidation. The extent of degradation of a series of commercial polyurethanes on treatment with hydrogen peroxide (25%, 24 h, 100°C) correlated well with their reported susceptibility to environmental stress cracking in vivo. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820270308
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  • 7
    Digitale Medien
    Digitale Medien
    Interpenetrating polymer network (IPN) as a permanent joint between the elements of a new type of artificial cornea (1994)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 28 (1994), S. 745-753 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Notizen: The combination at the interface between two chemically identical polymers was investigated by light and electron (scanning, transmission) microscopy. The polymers constitute elements of a new type of artificial cornea in which the peripheral skirt is made from spongy poly(2-hydroxyethyl methacrylate) (PHEMA) and the central optical zone from homogeneous, transparent PHEMA. Their two-phase combination along the boundary fulfill formally the requirements for an interpenetrating polymer network (IPN). The procedure for the manufacture of prosthesis was described in detail. Thin and ultrathin sections excised from the interface region were investigated using microscopic techniques. Light microscopy allowed the measurement of the diffusion path length of transparent PHEMA into sponge, which was approximately 0.5 mm. Transmission electron microscopy revealed a cellular-like morphology as well as larger segregated zones, which indicated network interpenetration on a molecular level and also a relatively poor miscibility of the two polymers despite their identical chemical structure. The latter was interpreted as a result of the submicroscopic restraints imposed by polymer I (sponge) upon polymer II. This study provides evidence that the interface combination of the prosthetic elements should be regarded as a gradient homo-IPN. This system offers a union between elements much stronger than those previously reported in artificial corneas. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820280612
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  • 8
    Digitale Medien
    Digitale Medien
    Enhancement of mechanical strength of poly(2-hydroxyethyl methacrylate) sponges (1995)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 1029-1032 
    Details
    ISSN: 0021-9304
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Medizin , Technik allgemein
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbm.820290815
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  • 9
    Digitale Medien
    Digitale Medien
    Influence of thionoesters on the degree of polymerization of styrene, methyl acrylate, methyl methacrylate and vinyl acetate (1992)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 193 (1992), S. 369-378 
    Details
    ISSN: 0025-116X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The aromatic thionoester 3 (benzyl thionobenzoate) was an effective chain transfer agent in polymerizations of styrene (Cx = 1,0) and methyl acrylate (Cx = 1,2) at 60°C. This activity was close to the ideal for obtaining narrow molecular-weight distributions in batch polymerizations. The thionoester 3 showed no activity in polymerizations of methyl methacrylate, but was too reactive to be useful in vinyl acetate polymerizations. Ring-substituted thionoesters 9-11 and 14 and 1H NMR spectroscopy of the resulting polymers were used to establish the type and quantity of end-groups. The thionoester 12 was used to produce low-molecular-weight polystyrene that was terminated at one end with a hydroxy group and at the other end by a thioloester moiety.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/macp.1992.021930209
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  • 10
    Digitale Medien
    Digitale Medien
    A general secular equation for cooperative binding of n-mer ligands to a one-dimensional lattice (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 1113-1121 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The binding of n-mer ligands to a one-dimensional lattice involving many ligand species and complex multiple-binding mechanisms is studied. We show that, when derived using the sequence-generating function method of Lifson, the secular equation of any binding system with a finite number of “elementary units” can be expressed in a matrix determinant form that is very symmetric and easy to construct. In other words, for any binding system whose elementary units are known, the secular equation of the system can be obtained readily without going through the formal derivation of the equation. We also show that the “determinant” secular equation obtained using the present procedure can be employed directly to the calculation of binding isotherms.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bip.360301111
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