Kettenübertragung durch CBr4 bei der Polymerisation von Styrol und von Vinylacetat

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Polymerisationsanregung durch14C-markiertes Benzol

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Versuche zur Strahlungspolymerisation

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Das kathodische Verhalten von Acrylnitril in Gegenwart quartärer Ammonium- und Phosphoniumsalze

Zusammenfassung Zur Aufklärung der Elektrodenvorgänge bei der kathodischen Polymerisationsanregung von Acrylnitril in Gegenwart quartärer Ammonium- und Phosphoniumsalze wurden die Halbwellenpotentiale der entsprechenden Kationen an der Quecksilbertropfelektrode und an der rotierenden Platinelektrode in Acetonitril als Lösungsmittel in Gegenwart und Abwesenheit von Acrylnitril gemessen. Die Zugabe von Acrylnitril verändert weder die Lage noch die Höhe der Reduktionsstufe der Salze. Die Reduktionspotentiale der untersuchten Phosphonium- und Ammoniumionen liegen teils bei negativeren, teils bei positiveren Werten als das des Acrylnitrils. Copolymerisationsversuche ergaben, daß die Polymerisation in beiden Fällen nach anionischem Mechanismus verläuft. Reaktionsmechanismen werden für beide Fälle diskutiert.

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The electrode processes in the cathodic initiation of acrylonitrile polymerization in the presence of quaternary ammonium and phosphonium salts have been investigated by measuring the half wave potentials of the corresponding cations at the dropping mercury cathode and the rotating platinum electrode, acetonitrile with and without acrylonitrile being used as a solvent. By addition of acrylonitrile neither the position nor the height of the polarographic wave of the salt is changed. The phosphonium and ammonium ions investigated were reduced partly at more positive, partly at more negative potentials than acrylonitrile. Copolymerization experiments have shown that the polymerization mechanism is anionic in either case. Reaction mechanisms are discussed.

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Über Ordnungszustände in ataktischen,nicht kristallisierenden polymeren

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Rühreffekte bei der Vernetzungspolymerisation-Popcornpolymer-und Gelbildung

Stirring vinyl acetate—(1 Mol%) divinyl adipate mixtures during polymerization influences the gel formation. Popcornpolymer polymerization influences the gel formation. Popcorn-polymer formation is highly favored. To the contrary the growth of popcorn polymer particles in the stirred system is slowed down. An explanation of this behavior is offered.

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Oxygen‐Dependent Photochemistry and Photophysics of “MiniSOG,” a Protein‐Encased Flavin

Selected photochemical and photophysical parameters of flavin mononucleotide (FMN) have been examined under conditions in which FMN is (1) solvated in a buffered aqueous solution, and (2) encased in a protein likewise solvated in a buffered aqueous solution. The latter was achieved using the so‐called “mini Singlet Oxygen Generator” (miniSOG), an FMN‐containing flavoprotein engineered from Arabidopsis thaliana phototropin 2. Although FMN is a reasonably good singlet oxygen photosensitizer in bulk water (?_Δ = 0.65 ± 0.04), enclosing FMN in this protein facilitates photoinitiated electron‐transfer reactions (Type‐I chemistry) at the expense of photosensitized singlet oxygen production (Type‐II chemistry) and results in a comparatively poor yield of singlet oxygen (?_Δ = 0.030 ± 0.002). This observation on the effect of the local environment surrounding FMN is supported by a host of spectroscopic and chemical trapping experiments. The results of this study not only elucidate the behavior of miniSOG but also provide useful information for the further development of well‐characterized chromophores suitable for use as intracellular sensitizers in mechanistic studies of reactive oxygen species.