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  • Polymer and Materials Science  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 62 (1996), S. 2039-2051 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this paper, we present some new results of our work in a novel polymerization process (called the free-radical retrograde precipitation polymerization, or FRRPP, process) that occurs at temperatures above the lower critical solution temperature. Our polymerization experiments basically involve the methacrylic acid-poly(methacrylic acid)-water system. Experimental results indicate a gradual increase in conversion with time after what seemingly is the onset of phase separation. In an equivalent solution polymerization system, conversion of methacrylic acid reaches almost 100% at a much shorter time than in the FRRPP system. Molecular weights of poly(methacrylic acid) at different times for the FRRPP system are not dramatically different from those obtained in the solution system. However, the FRRPP system yields a relatively narrow molecular weight distribution at a wide range of conversion compared to that obtained in the equivalent solution system. The unique characteristics of the FRRPP process is shown in the asymptotic time behavior of the free-radical concentration compared to the decay behavior in other polymerization systems. © 1996 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 55 (1995), S. 753-759 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We studied the late-stage spinodal decomposition of the polystyrene-cyclohexanol system in relation to membrane formation. Phase separation was effected by the removal of thermal energy from the homogeneous polymer solution. The ultimate morphology of the phase-separated systems has been studied using electron microscopy and has been found to be strongly affected by the quenching time. A shift from a highly interconnected open-cell structure to a closed-cell structure has been observed, indicating the transition of the spinodal decomposition from early to late stages. The cell growth in the late stage has been quantitatively analyzed and a power-law relationship between the cell size and quenching time has been found. The resulting exponent of 0.61 is consistent with literature values from light-scattering measurements, as well as from theoretical derivations. © 1995 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Advances in Polymer Technology 10 (1990), S. 237-242 
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We are studying the use of PS-PMMA block copolymer systems to improve the mechanical properties of immiscible PS-PVC blends. For a particular PS-PMMA block copolymer system, we found that effective compatibilization occurs at compatibilizer levels of 1-5 wt % in a 50/50 PS-PVC blend. In the samples, storage and stress relaxation moduli were at least midway between those of pure PS and PVC. On the other hand, the equivalent uncompatibilized blend exhibited storage and stress relaxation moduli that are much lower than those of the soft PVC component. Stress relaxation moduli of pure PS remained fairly constant with time, while a 25% drop was observed for pure PVC after 120 sec. Also after 120 s, stress relaxation moduli for the uncompatibilized blend exhibited a 20% drop, while a less than 10% drop was observed for the compatibilized PS-PVC blends.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0730-6679
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this article, we present a newly discovered polymerization process, called the freeradical retrograde-precipitation polymerization (FRRPP) process, that is shown to have certain desirable features not normally found in free-radical polymerization processes. Here, free radical polymerization occurs with an unusual but widely applicable polymer precipitation phenomenon. Local heating is observed in the vicinity of the radical sites, which results in the controlled rate of propagation with a decrease in the rate of radical-radical termination reactions. In the case experiments, the existence of hot spots in the reactor fluid is shown to occur. There is also evidence of slowdown of the growth of polymer radicals after initiator decomposition. The polymer radicals, shown to have a relatively narrow molecular weight distribution, continue to grow at a controlled rate long after all the initiator molecules have decomposed. The addition of a second monomer results in the formation of a thermoplastic elastomer triblock copolymer. © 1992 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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