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  • Articles  (327)
  • Physics  (296)
  • Electron microscopy  (31)
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  • 1970-1974  (327)
  • 1
    Electronic Resource
    Electronic Resource
    Normal coordinate analysis of cis-1,4-polybutadiene (1974)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 12 (1974), S. 445-454 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The fundamental vibrational frequencies of an isolated chain of cis-1,4-polybutadiene have been calculated. Infrared and polarized Raman data are used in the force constant refinement routine. The assignments of the vibrational frequencies are discussed in terms of the potential energy distribution.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1974.180120301
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  • 2
    Electronic Resource
    Electronic Resource
    Cationic starch-polyacrylonitrile graft copolymer latexesPresented at the 8th Great Lakes Regional Meeting, American Chemical Society, West Lafayette, Indiana, June 3-5, 1974. (1974)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 12 (1974), S. 2683-2692 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acrylonitrile (AN) was graft-polymerized onto gelatinized cationic starch (CS) possessing diethylaminoethyl ether groups by cerium (IV) initiation to give stable latexlike copolymer dispersions. Dispersions of the latex copolymers, having up to 50% grafted polyacrylonitrile (PAN), air- and heat-dry on glass to clear, adhesive films. Sonification of up to 8% dispersions at 20 Khz reduced their viscosities from 1500-3000 cP to 15-40 cP. Scanning electron microscopy revealed that both nonsonified and sonified dispersions consist of ball-like particles measuring about 0.05-0.15 μ in diameter when dry. The films are formed by coalescence of these particles. The degree to which AN grafts onto CS at ambient temperature is related to the nitrogen content of CS, gelatinization time of CS at 95°C, sequence of AN and cerium(IV) addition, concentration of cerium (IV), concentration of AN, and severity of reaction agitation. Number-average molecular weight values of PAN were about 106 when grafting was conducted under stirring and about 5 × 105 when conducted under shaking action.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1974.170121122
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  • 3
    Electronic Resource
    Electronic Resource
    Organometallic polymers. XXV. Preparation of polyvinylferrocene (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 11 (1973), S. 1213-1224 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthetic details of solution polymerization in benzene and bulk polymerization of vinylferrocene are reported. In benzene solutions, with azobisisobutyronitrile (AIBN) as the initiator, small yields of low-polydispersity low molecular weight (M̄n ≃ 5000) polyvinylferrocene is obtained. However, high yields can be obtained by continuous or multiple AIBN addition. Higher molecular weight polymers and binodal polymers can be obtained as the monomer concentration is increased. In bulk polymerizations, yields of 80% can be obtained. The molecular weight increases as temperature decreases from 80 to 60°C in bulk polymerizations, and an increasing amount of insoluble polymer results. The soluble portion is often binodal, the higher molecular weight node consisting of an increasingly branched structure. Lower molecular weight polymer was readily fractionated into narrow fractions from benzene-methanol systems, but higher molecular weight polymer proved impossible to fractionate into narrow fractions due to branching.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.170110609
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  • 4
    Electronic Resource
    Electronic Resource
    The fine structure of oogonia and oocytes in the rhesus monkey (Macaca mulatta) (1972)
    Springer
    Cell & tissue research 126 (1972), S. 53-74 
    Details
    ISSN: 1432-0878
    Keywords: Oogenesis ; Rhesus monkey ; Meiotic chromosomes ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The ovaries of foetal and neonatal rhesus monkeys have been examined with the electron microscope. The fine structure of the germ cells (oogonia; oocytes at the preleptotene, leptotene, zygotene, pachytene and diplotene stages of meiotic prophase) closely resembles that of corresponding human cells. Stages in spontaneous atresia are also described. Cytoplasmic organelles in oogonia are sparse and are grouped mainly at one pole of the nucleus, but become dispersed and more abundant as oogenesis proceeds. The nuclei of oogonia contain a random fibrillar matrix which becomes organized into threads at pre-leptotene. At leptotene these chromosomal threads each contain a dense axial “core”; during zygotene they become loosely paired in a “bouquet” arrangement and at pachytene the bivalents contain synaptinemal complexes. “Single” cores reappear at diplotene, surrounded by a complex fibrillar sheath organized into lateral projections and loops with associated granules: such chromosomes resemble those in human primordial oocytes although they are more diffuse. These findings support the view that at the diplotene stage mammalian oocytes contain chromosomes of the lampbrush type. Observations on the monkey are compared with those on other species, and the ways in which chromosomal organization may influence the radiosensitivity of oocytes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00306780
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of colchicine on the fine structure of the neuromuscular junction (1972)
    Springer
    Cell & tissue research 135 (1972), S. 439-448 
    Details
    ISSN: 1432-0878
    Keywords: Neuromuscular junction ; Triturus ; Colchicine ; Axoplasmic flow ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Repeated injections of colchicine into the forearms of normal adult newts led to the disappearance of microtubules within some nerves and a concomitant loss of specialized morphological features at the neuromuscular junction. Within 2 weeks, the postsynaptic folds decreased in height and number, became flattened and eventually disappeared. In addition, nerve terminals in drug-treated animals became separated from the muscle surface and were highly congested with masses of synaptic vesicles. The present findings show that colchicine has an effect on the structural integrity of the neuromuscular junction. These effects could be direct; secondary to retraction of the nerve from the muscle surface; or the result of interference with the proper transport and/or release of neurotrophic substances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00583428
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  • 6
    Electronic Resource
    Electronic Resource
    Electron microscope studies of radiation-induced degeneration in oocytes of the sexually mature rhesus monkey (1972)
    Springer
    Cell & tissue research 133 (1972), S. 435-454 
    Details
    ISSN: 1432-0878
    Keywords: Oocytes ; Monkey ; Radiation damage ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary This study describes the effects of acute X-irradiation of the ovaries upon the structure of primordial follicles in mature rhesus monkeys. Doses of 1000 r to 12000 r, and post-irradiation intervals of 7 hours to 30 days were used. Oocytes in biopsies from irradiated ovaries were compared with those removed from the same ovaries prior to treatment or from contra-lateral controls. The results of the treatment were assessed using light and electron microscopy. The fine structural features of normal primordial oocytes are described, with particular reference to mitochondria and dense granular bodies. Some observations on spontaneous degenerative changes are included. Irradiated ovaries are classified into four arbitrary groups according to the severity of cellular damage visible in primordial follicles with the light microscope. Effects are more marked following higher doses and/or longer intervals; the most obvious changes are pyknosis of nuclei and accumulation of dense granules in the follicle cell cytoplasm. Early changes in oocytes are relatively difficult to detect, but lead to clumping of cytoplasmic and nuclear contents at more advanced stages of degeneration. Alterations in oocyte fine structure consist mainly in swelling and disruption of membrane-bound organelles, and condensation of nuclear and nucleolar chromatin. They thus resemble those occurring during spontaneous atresia, although the damage to follicle cells is evident much sooner after irradiation. These findings are compared with those made for species in which primordial follicles are known to be destroyed by much lower doses of X-rays than were used here. The contribution to the radiation-response made by the relative radiosensitivities of oocytes and follicle cells in different species is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00307127
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  • 7
    Electronic Resource
    Electronic Resource
    Crystallization kinetics of dilute polyethylene solutions (1970)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 869-882 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystallization kinetics of a high molecular weight fraction of linear polyethylene was studied in dilute solutions of p-xylene, n-hexadecane, and decalin by dilatometric methods. For all solvents and temperatures, the experimental isotherms could be quantitatively described by the Avrami formulation for the complete transformation. This result is unique in the realm of polymer crystallization, since marked deviations from this theory are usually observed in more concentrated systems. The Avrami exponent is found to be n = 4 in all cases. The temperature coefficients of the rate constants are indicative of a nucleation controlled process. The data fit either a two-dimensional or three-dimensional nucleation mode, and a discrimination can not be made between these two cases. The interfacial free energies are found to be independent of the solvent medium. It is also shown that, irrespective of the type of nucleation control governing the kinetics, the same type governs the crystallite thickness of the lamella-like crystals that are formed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1970.160080604
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  • 8
    Electronic Resource
    Electronic Resource
    Fracture behavior in nylon 6 fibers (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 1415-1445 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A reaction rate model of fracture in polymer fibers is described. This model assumes that bond rupture is governed by absolute reaction rate theory with a stress-aided activation energy. It is demonstrated that the key in obtaining good agreement between the model and experiment lies in taking proper account of the variation of stress on the tie-chain molecules. The more taut chains rupture first, and the load is redistributed among the remaining unruptured tie chains. The effect of varying the temperature both in the model and in experiments on fracture in fibers is explored. Good agreement between predictions of the model and experiment is possible only with an undeterstanding of the distribution in stress on the tie chains. The distribution in stress on the chains was experimentally determined by monitoring the kinetics of bond rupture with electron paramagnetic resonance (EPR) spectroscopy. Temperature is found to have two effects on macroscopic strength. (1) The thermal energy aids the atomic stress in breaking the atomic bonds; as a consequence the rate of bond rupture of a family of bonds under a given molecular stress is increased. In this respect temperature might be viewed as decreasing the “strength” of a bond. (2) Temperature also serves to “loosen” the molecular structure and in this way modify the distribution in stress on the tie chains. To explain bond rupture and macroscopic fracture behavior quantitatively, account must be taken of both effects.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.160100802
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  • 9
    Electronic Resource
    Electronic Resource
    EPR studies of mechanically induced bond rupture in elastomersPaper presented at the Symposium on Mechano-Chemistry of Polymers, American Chemical Society National Meeting, Washington, D. C., September 16, 1971. (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 10 (1972), S. 599-606 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electron paramagnetic resonance (EPR) spectroscopy was used to compute the surface bond rupture density in polyurethane and to determine the phase experiencing fracture in styrene-butadiene block copolymers when these elastomers are subjected to mechanical degradation by grinding. The polyurethane grinding was done at temperatures above and below the glass transition Tg; 0.155 × 1013 radicals/cm2 of fracture surface area were formed above the Tg and 4.42 × 1013 radicals/cm2 for grinding below the Tg. These values are essentially equal to those found earlier for spherulitic polymers. In all cases the fracture appears able to progress along preferential paths so as to rupture significantly fewer molecular chains than one would expect on the basis of calculations of the number of chains passing through each square centimeter of cross section. Comparison of EPR spectra formed by grinding styrene-butadiene copolymer with those of styrene and butadiene above indicated that at cryogenic temperature, the fracture in the copolymer takes place in the butadiene phase.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.160100403
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  • 10
    Electronic Resource
    Electronic Resource
    A search for the mosaic block structure in polyethylene single crystals (1974)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 12 (1974), S. 1015-1022 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A diffraction contrast study with the aid of an image intensifier was undertaken to obtain direct evidence for the existence of a mosaic block structure in polyethylene single crystals grown by self seeding under isothermal conditions. Dark-field microscopy indicates that the crystals do not contain a mosaic block structure. High-resolution electron diffraction confirms that the crystal is coherent (i.e., mosaic block-free) over regions of several thousands of Angstroms. It is concluded that a mosaic structure on the scale of ∼300 Å does not exist in polyethylene single crystals grown under carefully controlled conditions from dilute solutions. Possible reasons for previous results that indicate the presence of a ∼300 Å mosaic block structure are discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1974.180120512
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