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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Plant cell, tissue and organ culture 4 (1985), S. 111-122 
    ISSN: 1573-5044
    Keywords: alfalfa ; somatic embryogenesis ; germplasm ; genotypic variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Seventy-six cultivars of alfalfa (Medicago sativa L., M. falcata L. and M. varia Martyn) were tested in vitro for their capacity to produce callus and somatic embryos. A three-step media protocol was used to survey the response of the cotyledons and hypocotyl of each genotype while the epicotyl region was conserved in order to recover highly responding genotypes. The best regeneration response was observed in creepingrooted cultivars which contained a strong genetic contribution of two landrace germplasm sources, defined as M. falcata and Ladak, in their ancestry. The callus and embryogenesis responses showed a high degree of variation both between cultivars and among the plants of many of the 76 cultivars tested. A higher number of plants produced somatic embryos in the high regenerating cultivars compared to the low regenerating cultivars regardless of the media protocol or explant.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant cell, tissue and organ culture 9 (1987), S. 121-130 
    ISSN: 1573-5044
    Keywords: Medicago sativa ; direct embryogenesis ; genotypic variation ; mesophyll protoplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Clones of three cultivars of Medicago sativa (‘Rambler’, ‘Regen S’ and ‘Rangelander’) were used as sources of mesophyll protoplasts. Although all three clones readily produced protoplasts, the subsequent development patterns in culture varied greatly among genotypes, with protoplasts from ‘Regen S’ and ‘Rambler’ forming calli which could be induced to form embryos, and protoplasts from ‘Rangelander’ undergoing direct embryogenesis. Protoplasts of ‘Regen S’ exhibited high rates of division while those of ‘Rangelander’ tended to aggregate with only a few cells per aggregate surviving. The surviving cells gave rise to proembryos within the aggregates; these proembryos developed into differentiated embryos after 5–7 weeks of culture. Based on the initial protoplast population, the efficiency of embryo formation averaged 0.13% and ranged from 0.001–0.4%. Observations during the early stages of culture indicated that cell aggregation was a prerequisite for direct embryogenesis.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 7 (1969), S. 601-608 
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The glass transition temperatures Tg of several fluorine-containing polymers were determined by use of the differential scanning calorimeter. Values between -3 and 230°C were obtained. In polymers of α-olefins, Tg increases with the fluorine content of the backbone and the length of the n-perfluoroalkyl branch. In styrene polymers Tg also is higher if the backbone contains fluorine but nearly the same Tg's are found for polymers with phenyl and pentafluorophenyl groups. Saturated polymers of perfluoro-α,ω-dienes have lower Tg's than polyperfluoro-α-olefins. The Tg's of chloroperfluoropolymers are higher than those of perfluoropolymers. Polyperfluoropentadiene-1,3 has the lowest Tg of the polymers examined. Polyperfluoropentadiene-1,3 forms by 1,4-addition.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Copolymers of tetrafluoroethylene and propylene were prepared that contained 30-65 mole-% of the former. Reactivity ratios of tetrafluoroethylene- and propylene-ended radicals are 0.008 and 0.06, respectively, resulting in formation of highly alternating copolymers. The glass temperatures, Tg, were determined using a differential scanning calorimeter. Values ranged from 260 to 275°K. A plot of Tg versus composition has a low maximum centered about the equimolar composition. Copolymers of tetrafluoroethylene and isobutylene were prepared that contained 30-56 mole-% of the former. Reactivity ratios of tetrafluoroethylene- and isobutylene-ended radicals are 0.005 and 0.021, respectively. The glass temperatures of these copolymers range from 257 to 313°K. A higher maximum at the equimolar composition is obtained when Tg is plotted versus composition. Isobutylene-containing copolymers having 45-54 mole-% tetrafluoroethylene are crystalline. Melting temperatures range from 416 to 476°K and have their maximum value at the equimolar composition. It is thought that long sequences of alternating units behave as a third entity in these copolymers, the other two being nonalternating units of the two monomers. Unless inhibited, ionic homopolymerization of isobutylene can be appreciable, sometimes resulting in the polymer having two Tg.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radiation-induced polymerization of cis- and trans-1,3,3,3-tetrafluoropropene in bulk and with tetrafluoroethylene was studied at pressures between 5000 and 15000 atm and temperatures between 21 and 100°C. At 103 rad/hr the homopolymerization rates range from about 10-4 to 1%/hr. The activation enthalpy and volume are about 8 kcal/mole (33 kJ/mole) and -10 cm3/mole, respectively, for both isomers. The cis isomer polymerizes about twice as rapidly as the trans isomer. The latter freezes in the experimental range of temperature and pressure; the polymerization rate is very low in solid phase. Polymer intrinsic viscosities increase with polymerization pressure and decrease with polymerization temperature; the largest value obtained was 0.23 dl/g. In the copolymerizations all reactivity ratios favor incorporation of tetrafluoroethylene by factors of 6-16. The preference is stronger when the trans isomer is used.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrafluoroethylene (A) and 1,2,3,4,5-pentafluorostyrene (B) were irradiated at 15°C at autogenous pressure by use of 30-92 mole-% A and at 5000 atm by use of 42-99.9 mole-% A. The high-pressure results indicate that the reactivity ratio rA for monomer addition to A-ended radicals is 0.005; the other reactivity ratio rB appears to vary from 15 to 60 generally increasing with the A content of the charge. At autogenous pressure rA is small, but a precise determination is not possible because of the very low polymerization rate when the A content of the charge is high. However, if rA is less than 0.01, then values of rB vary from 15 to 50, again generally increasing with the A content of the charge. Mixtures of A and B exhibit positive deviations from Raoult's Law. Activity coefficients were measured at autogeneous pressure and used in an attempt to correct rB for the nonideality of solution. The range of rB was reduced only slightly to 8-27, and charges with high A contents now generally gave low values of rB; consequently, this approach was not regarded as a success. Another attempt was made to account for the apparent variation in rB by ascribing influence to the penultimate units of the radicals. Improved agreement between theoretical and observed compositions resulted, but significant discrepancies remained unexplained. Rate data agreed well with those calculated from a theoretical copolymer rate equation using values of rA and rB of 0.0045 and 40, respectively. The equation predicts an almost proportional decrease in rate with increasing proportions of A in the charge from 0 to 99 mole-% A.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 15 (1977), S. 2623-2639 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Henry's law and diffusion constants of vinyl chloride in poly(vinyl chloride) were determined at temperatures of 24, 90, 120, 150, and 170°C for weight fractions of vinyl chloride between 0.2 × 10-3 and 0.8 × 10-3. Above 90°C, Henry's law applies; values of the constant increase with temperature from 1.8 × 102 to 5.5 × 102 atm per unit weight fraction of dissolved vinyl chloride. The heat of desorption is about 15 kJ/mole. At 24°C, the nominal Henry's law constant was smaller than would have been obtained by extrapolating the values found at higher temperature. The diffusion constants increase with temperature from about 2 × 10-13 to 3 × 10-7 cm2/sec. The activation energy for diffusion is about 110 kJ/mole between 90 and 170°C. Although all values were determined in the absence of air, it is likely that they apply to polymer in air. They may, therefore, be used to calculate the vinyl chloride content in the gas above poly(vinyl chloride) under specific processing conditions.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 17 (1979), S. 759-768 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radiation-induced copolymerization of tetrafluoroethylene (A) and styrene (B) was studied in bulk and in perfluorotoluene at 22°C at autogenous pressure and 260 and 510 MPa. The reactivity ratio for addition to A-ended radicals, rA, is effectively zero at the two lower pressures and is in the range 0.002-0.008 at 510 MPa. The other reactivity ratio, rB, is 6 at autogenous pressure and also at 260 and 510 MPa if the A content of the charge is less than 50%. If the A content is greater than 95%, rB appears to be 100 at pressures of 260 and 510 MPa. The apparent variation in rB cannot be explained by invoking a penultimate unit effect for B-ended radicals. Polymerization rates scatter somewhat, but all rates are quite small when the A content of the charge is in the range 95-99.8%. Polymers containing as much as 66% A appear to be inherently benzene soluble but frequently contain some gel because of radiation-induced crosslinking after their formation. No very high polymers were formed that contained more than a few percent A, even at high pressure. Features that complicated the study were immiscibility of the liquid monomers, extreme variation of the monomer - copolymer compatibility with charge composition, and freezing of B at high pressure.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 4 (1966), S. 131-140 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Perfluoro-1,4-pentadiene was prepared by pyrolysis of sodium 3,5,6-trichloroperfluorohexanoate and subsequent dehalogenation. The monomer was polymerized under a number of conditions of temperature and pressure using various periods and various dose rates of γ-ray initiation. The compound was found to undergo doublebond migration producing perfluoro-1,3-pentadiene. The polymer samples, some of them rubbery, others grainy, are assumed to be copolymers of the 1,4-pentadiene and the 1,3 pentadiene, the 1,4-diene polymerizing according to a cyclic mechanism and the 1,3-diene undergoing the 1,4-addition that is characteristic of butadienes under certain conditions. Infrared and nuclear magnetic resonance studies tend to support these assumptions. Under polymerization conditions the monomer also produced four distinct dimers and traces of two monomeric substances.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 6 (1968), S. 1367-1379 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study was made of the gamma-ray-induced copolymerization of tetrafluoroethylene and 3,3,3-trifluoropropene. Copolymerizations were carried out at 100°C. and 5000 atm. pressure and at 21°C. and various pressures up to 8000 atm. The reactivity ratios calculated from the composition data indicate that the propagation rate constants favor addition of trifluoropropylene by a factor of 3-7; individual values depended little on the polymerization pressure and temperature. Polymerization rates changed little with monomer composition between 0 and 75% tetrafluoroethylene; between 75 and 95% tetrafluoroethylene they increased by a factor of 10. As many as 850,000 molecules were polymerized per 100 e.v. absorbed. The copolymers are soluble in hexafluorobenzene at 29.6°C. if they contain less than 70% tetrafluoroethylene. Intrinsic viscosities range from 0.1 to about 10 dl./g. From various considerations it appears likely that the degree of polymerization is about equal to the kinetic chain length in high-pressure polymerizations at 21°C.; at autogenous pressure or at 5000 atm and 100°C., monomer transfer reduces the value considerably.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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