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The copolymerization of ethylene with butadiene at -25°C. in the presence of co-ordinated anionic catalytic systems, prepared a t -78 "C. from a vanadium compound, organometallic compounds of aluminum and a weak LEWIS base, yields copolymers with particular crystalline structure.By fractionation of crude products, crystalline ethylene-butadiene copolymers were obtained, the crystalline structure of which was attributed to a succession of ethylene units regularly alternating with trons-buta-1,4-dienic units. Z US AM 31 E N F A S S U N G :Die Copolymerisation von k h y l e n und Butadien bei -25 "C ergibt Copolymere mit besonderer kristalliner Struktur; die koordinativ-anionischen Mischkatalysatoren fiir diese Reaktion wurden bei -78 "C aus einer Vanadium-Verbindung, Al-organischen Komponenten iind einer schwachen LEWIS-Base hergestellt.Bei der Fraktionierung der Rohprodukte wurden kristalline bthylen-Butadien-Copolymere erhalten, deren kristalline Struktur einer Folge von hhyleneinheiten, die regelmaaig mit trans-Butadien-l,4-Einheiten abwechseln, zugeschrieben wird.

Several methods of infrared analysis of polyisoprenes have been described in the literature'-3); they all are potentially good for the determination of the isoprene units having 1,2 and 3,4 enchainment. However, unsatisfactory results and several difficulties are found for the determination of trans-1,4 and cis-1,4 units. The best results are obtained with the method proposed by BINDER and RAMSOW3), who suggested the use of the bands at 8.68 and 8.84 microns for the determination of trans-1,4 and cis-1,4 units respectively. Whereas these bands are clear and well detectable in hevea, balata, and in their artificial mixtures, they become hardly measurable in the various synthetic polyisoprenes, especially in those rich in 3,4 units.Unreliable results have been obtained for several samples because the total % found *) was too far from 100.Another method has been devided by cORISH4) who uses the near infrared spectrum. His method can only be used for the determination of the cis-1,4 units.In a careful study of the infrared spectrum of several polyisoprenes we have noticed that the methyl bending absorptions near 3.25 microns OCcur a t different positions with variable intensities, namely at 7.22 microns for the trans-1,4, a t 7.26 micronsfor the cis-1,4 and a t 7.265 for the 3,4 units.At the present state of our research no statement can be made for the 1,2 units because we did not yet succeed in obtaining polyisoprenes with a content of 1,2 units larger than some percent. C (cis) + C (tram) + C (3,4) C (conc. of solution)*) Total yo found = .loo. 250

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