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  • Physics  (6)
  • Animals
  • 1970-1974  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    Viscosity study of radiation chemistry of polystyrene (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 11 (1973), S. 2591-2600 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of γ-radiation on aqueous polystyrene emulsions were followed by measurements by intrinsic viscosities of soluble polymer in toluene. Estimates of incipient gel dose from intrinsic viscosity data do not coincide closely with those from measurements of gel content. This uncertainty and those in molecular weight averages make it difficult to assign a precise value to G(crosslink), even when the scission crosslinking ratio in the particular system is reliably known. The intrinsic viscosity of sol polymer in the postgel region decreases with increasing dose to an asymptotic value. The decrease is as expected if larger molecules are progressively linked into the gel network and the asymptote may be attributable to cyclization. Present theories of branching do not seem to be applicable for quantitative estimation of scission/crosslinking ratios caused by irradiation of polystyrene. This is probably connected with deficiencies in the theoretical connection between radius of gyration and intrinsic viscosity in good solvents. Diallyl fumarate and diallyl maleate increased crosslinking rates, but only at low doses. Chain scission was enhanced by addition of 1,2-dichloroethylene and 2,5-dimethylhexane-2,5-dihydroperoxide.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.170111013
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetics of free-radical copolymerization of α-methylstyrene and styrene (1974)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 12 (1974), S. 2235-2254 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The free-radical copolymerization of α-methylstyrene and styrene has been studied in toluene and dimethyl phthalate solutions at 60°C. Gas chromatography was used to monitor the rate of consumption of monomers. For styrene alone, the measured rate of polymerization Rp and M̄n of the polymer coincided with values expected from previous studies by other workers. Solution viscosity η affected Rp and M̄n of styrene homopolymers and copolymers as expected on the basis of an inverse proportionality between η1/2 and termination rate. The rate of initiation by azobisisobutyronitrile appears to be independent of monomer feed composition in this system. Molecular weights of copolymers can be accounted for by considering combinative termination only. The effects of radical chain transfer are not significant.A theory is proposed in which the rate of termination of copolymer radicals is derived statistically from an ideal free-radical polymerization model. This simple theory accounts quantitatively for Rp and M̄n data reported here and for the results of other workers who have favored more complicated reaction models because of the apparent failure of simple copolymer reactivity ratios to predict polymer composition. This deficiency results from systematic losses of low molecular weight copolymer species in some analyses. Copolymer reactivity ratios derived with the assumption of a simple copolymer model and based on rates of monomer loss can be used to predict Rp values measured in other laboratories without necessity for consideration of depropagation or penultimate unit effects. The 60°C rate constants for propagation and termination in styrene homopolymerization were taken to be 176 and 2.7 × 107 mole/l.-sec, respectively. The corresponding figures for α-methylstyrene are 26 and 8.1 × 108 mole/l.-sec. These constants account for the sluggish copolymerization behavior of the latter monomer and the low molecular weights of its copolymers. The simple reaction scheme proposed here suggests that high molecular weight styrene-α-methylstyrene copolymers can be produced at reasonable rates at 60°C by emulsion polymerization. This is shown to be the case.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1974.170121007
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of temperature on styrene-methacrylonitrile copolymerization (1971)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 9 (1971), S. 3009-3025 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The free-radical copolymerization of styrene and methacrylonitrile was studied in toluene solution at 60, 90, and 120°C. Copolymer composition was estimated from gas-chromatographic measurement of unreacted monomer concentrations. Reactions were carried to about 20% conversion to minimize analytical errors. Reactivity ratios were calculated by using an integrated form of the Mayo-Lewis simple copolymerization equation. Reactivity ratios were not sensitive to reaction temperature. The values at 90°C are r1 = 0.41 (methacrylonitrile) and r2 = 0.37 (styrene). The r1 values are higher than those reported by other workers, presumably because of advantages in the present analytical technique and calculation method. The negligible temperature dependence of reactivity ratios is in accord with theory. If monomer pairs exhibit pronounced dependence of reactivity ratios on polymerization temperature, this may indicate a change in mode of placement of units in the polymer chain.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1971.150091021
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  • 4
    Electronic Resource
    Electronic Resource
    Universal calibration in GPC (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 217-235 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The M[η]-elution volume calibration curve for gel-permeation chromatography (GPC) is based on the implicit assumption that the hydrodynamic volume of a solvated polymer species in the GPC columns is that which pertains at infinite dilution. This is not true of highly solvated high molecular weight fractions and results in apparent failure of this calibration in some instances. A model is presented to estimate hydrodynamic volumes of polymers at finite concentrations. The parameters required are polymer concentration, molecular weight, amorphous density, and the Mark-Houwink constants for the particular polymer-solvent combination. The calculated log (hydrodynamic volume)-elution volume relation provides a universal GPC calibration. The model accounts for the occasional shortcomings of the infinite dilution calibration and is essentially equivalent to it in noncritical cases. The use of the proposed calibration method is illustrated.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.150100120
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  • 5
    Electronic Resource
    Electronic Resource
    γ-Irradiation of polystyrene emulsions (1972)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 10 (1972), S. 3589-3603 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aqueous polystyrene emulsions were subjected to γ-irradiation at 30°C and 0.6 Mrad/hr dose rate. Analogy with water-soluble systems suggests that such conditions might suppress chain scission and favor crosslinking. The (extrapolated) infinite-dose gel content and gel-permeation analysis of the polymer in the pre-gel region indicate that the extent of chain scission was negligible. The G (crosslink) value obtained from the dose for incipient gelation and molecular weight variations in the pre-gel region is 0.051. Charlesby-Pinner plots were linear, but linearity cannot be construed as indicating that chain scission has produced an effective random molecular weight distribution. Our results are consistent with the conclusions that crosslinking events are random and directly proportional to dose. The probability that a given crosslink is effective in increasing the gel content decreases with dose past the incipient gel point, however, because of cyclization on preformed gel. The crosslink density/dose ratio is a decreasing function of dose in this range. Attempts to predict dose-gel relations with assumptions of various initial molecular weight distributions were unsuccessful, possibly because of the neglected influence of cyclization on the measured gel content.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1972.170101213
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  • 6
    Electronic Resource
    Electronic Resource
    Concentration effects in gel-permeation chromatography (1971)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 9 (1971), S. 2587-2604 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Peak elution volume in gel-permeation analysis of polymers depends on sample concentration as well as molecular weight. Elution volume is related to the logarithm of the hydrodynamic volume of the solvated polymer species. The hydrodynamic volume of a given species is, in turn, inversely related to the concentration. Since molecular weight and concentration are interacting variables, the elution volume-molecular weight relation is not uniquely determined. A model is presented which accounts quantitatively for concentration effects, using parameters which are available a priori. The data required are polymer molecular weight, concentration, and density and the Mark-Houwink relation for the particular polymer-solvent combination.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1971.150090914
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