For the detection of unstable intermediates during rapid chemical reactions an experimental technique has been developed which allows tracing of reactions with reaction times of minutes or seconds by nuclear magnetic resonance spectroscopy. By this technique series of NMR spectra were taken during thermal decomposition of peroxides and azo-compounds, and the following unexpected effect was observed: During some reactions the proton resonance lines of reaction products appear intermediately in emission instead of absorption. The emission lines in the decomposition reactions of dibenzoylperoxide and di-p-chlorbenzoylperoxide are treated in detail, and are shown to be due to benzene and chlorobenzene molecules formed in the reactions. Obviously these molecules are formed initially with a negative spin polarization of their proton spin systems which is assumed to be a consequence of a chemically induced dynamic nuclear polarization.

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ZUS AMMENFASSUN G:Methylmethacrylat kann durch alkalimetallorganische Verbindungen zu Produkten mit sehr verschiedener sterischer Struktur polymerisiert werden. Es wird der E i d 3 desKations des Initiators, des Losungsmittels und der Temperatur a d die Taktizitit der Polymeren untersucht. I n apolaren Losungsmitteln entstehen vornehmlich isotaktische Polymerisate, wobei der Anteil an isotaktischen Verkniipfungen in den mit lithiumorganischen Verbindungen hergestellten Produkten am hochsten ist und mit natrium-und kaliumorganischen Initiatoren in dieser Reihenfolge abfiillt. In polaren Losungsmitteln entstehen hauptsachlich syndiotaktische Polymere, wobei Lithiumalkyle die hochste Zahl syndiotaktischer Verkniipfungen liefern. Der EinfluB der Polymerisationstemperatur ist dagegen nur sehr gering. Ebenfalls untersucht wird die Polymerisation in Gemischen aus polaren und apolaren Losungsmitteln. Die dabei entstehenden Produkte unterscheiden sich in ihrem sterischen Aufbau nicht grundsitzlich von den in den jeweils reinen polaren Losungsmitteln erhaltenen.Die Struktur der Polymeren wird mit Hilfe der magnetischen Kernresonanzabsorptiou untersucht. Damit sind gleichzeitig Aussagen iiber die mittlere Lange von Segmenten gleicher Taktizitlt und iiber die Verteilung der Grundbausteine auf die einzelnen Sequenzen gleicher Tqktizitat moglich. SUMMARY:By means of alkali organometallic compounds, methyl methacrylate can be polymerised to products with varying steric structures. The influence of the cation of the initiatorb the solvent and temperature on the tacticity of the polymers were investigated. In apolar solvents mainly, isotactic polymeristttes were obtained, whereby, the portion of isotactic linkages produced by means of lithium organic compounds was the highest and decreasing when uwig the sodium and potassium organic compounds in this sequenee. I n polar solvents, syndiotactic polymers are chiefly produced, with lithium alkyls yielding the largest number of syndiotactic linkages. The influence of the polymerisation temperature is insignificant.Likewise, polymerisations were conducted in mixed solvents, polar and apolar. The resulting polymers differed very little in their steric structure from those obtained in the pure solvents.The structures of the polymers were investigated by means of the nuclear magnetic resonance absorption. Thereby, it was possible to make a declaration simultaneously over the average lengths of segments of the same tacticity and the distribution of the monomer units in segments of the same tacticity.

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