Poly(vinyl ethers)

Sandler, Stanley R.; Karo, Wolf

doi:10.1016/b978-0-08-092555-4.50011-6

Cited by 2 publications

(1 citation statement)

References 61 publications

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“…Acrylamide is well known as one of the most reactive of all acrylic monomers, i.e. it has one of the highest k p /k t ratios among acrylic monomers, where k p and k t are propagation and termination rate constants respectively (Brandrup andImmergut 1989, Sandler andKaro 1992).…”

Section: Two Factors Of Sensitivity: Reactivity Of Monomers and Relax...mentioning

confidence: 99%

Untitled

1997

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The effects of varying the weight fraction (%C) of the crosslinker N, N'-methylene-bisacrylamide (bis) per total amount of monomer (6% w/w), and the NMR measurement temperature, on the dose response of the transverse relaxation rate (R2) of bis-acrylamide-nitrogen-gelatin (BANG) aqueous polymer gel dosimeters have been investigated. The gel samples were irradiated in test tubes with 250 kV x-rays, and the water proton NMR transverse relaxation rates were measured at 0.47 T using a Carr-Purcell-Meiboom-Gill multiecho pulse sequence. Both the dose sensitivity (slope of the linear portion of an R2-dose response) and the maximum rate at which the R2-dose response saturated (R2max), were found to depend strongly on the crosslinker fraction and on the temperature of the R2 measurement. The dose sensitivity peaked at approximately 50% C, and, for this composition, varied from 0.14 s-1 Gy-1 at 40 degrees C to 0.48 s-1 Gy-1 at 10 degrees C. The maximum transverse relaxation rates ranged from 0.8 s-1 at 33% C and 40 degrees C to 11.8 s-1 at 83% C and 5 degrees C. These results suggest that water proton transverse relaxation in the gel is controlled by an exchange of magnetization between the aqueous phase and the semi-solid protons associated with the polymer, and that the latter experience spectral broadening from immobilization which increases with crosslinking or cooling. Theoretical and practical implications of the above findings are discussed in the paper.

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Section: Two Factors Of Sensitivity: Reactivity Of Monomers and Relax...mentioning

confidence: 99%

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1997

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The Polymerization of Free Enols with Electron-Deficient Comonomers

Novak¹,

Cederstav²

1997

Journal of Macromolecular Science, Part A

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The balance between kinetics and thermodynamics is illustrated herein by the first direct polymerization of vinyl alcohol, the thermodynamically unstable tautomer of acetaldehyde, at a rate faster than it can tautomerize. Vinyl alcohol was formed through the acid catalyzed hydrolysis of ketene methyl vinyl acetal. With excess water present, the kinetics of tautomerization first order dependence upon vinyl alcohol (kobs = 2.73 x 10 -4 s -1). Under water starved conditions, however, the kinetics now show a zero order dependence upon the concentration of vinyl alcohol (kobs = 3.5 x 10-6 Mis). Under these latter conditions, the half life of vinyl alcohol is nearly 24 hours at room temperature. Although cationic and homo free radical polymerization of vinyl alcohol failed, we found that this meta-stable species could be quantitatively polymerized in a copolymerization (AIBN, hu , -10 to 25°C) with maleic anhydride. The k,b, for copolymerization was found to be 4.41 x 10-4 sec-1 at -10°C. Since the rate of polymerization is far greater than that of tautomerization under these conditions (ca. 30 times faster at -lO°C), there is no significant increase in acetaldehyde concentration during polymerization. 1815

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Poly(vinyl ethers)

Cited by 2 publications

References 61 publications

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The Polymerization of Free Enols with Electron-Deficient Comonomers

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