Umlagerungen bei der durch Lithiumbutyl initiierten Polyreaktion der Diene Isopren und Butadien

Abstract

ZUSAMMENFASSUNG:Bei der Reaktion von Lithiurnbutyl mit Isopren in Diathylather entstehen Lithiumnonenyle, die bei der Zersetzung mit Wasser 36% 2-Methylocten-(1) und die cis-trans-Isomeren des 3-Methyl-octens-(2) irn Verhaltnis 63 : 1 ergeben. Nach Entfernung des Diathylathers vom Lithiumnonenyl durch Abkondensation nach wiederholterZugabevon n-Heptanwerden dieKohlenwasserstoffe imverhaltnis 26 : 74 gefunden, wghrend nach erneuter Zugabe von Diathylather wieder das Verhaltnis 36 : 64 auftritt. Das Verhaltnis der verschiedenen isomeren Lithiumnonenyle ist vom Losungsmittel abhlngig. Die Isomeren lagern sich reversibel um; auch in Diathylather findet in erheblichem Umfange 1.4-Addition von Isopren an Lithiumbutyl statt. Wahrend bei -1OOC fur die Polyreaktion des Isoprens mit Lithiumbutyl als Initiator die Geschwindigkeitskonstanten ks = 1,6.10-4I/Mol.sec und k, = 1,5.10-2l/Mol.sec gefunden werden, betragen die entsprechenden Werte fur die Polyreaktion des Butadiens k, = 4,5.10-5l/Mol.sec und k , = 2,4.10-3 I/Mol.sec. Das kinetisch erfanbare Assoziationsverhalten von Lithiumpolyisoprenyl wird durch KI = 1,86.10-9 MoP/P und Kg = 2,80.10-21 Mo15/15 beschrieben, wahrend Lithiumpolybutadienyl durch Ks = 2,98.10-9 Mo12/12 und KO = 2,76.:0-20 Mo15/15 beschrieben wird. Die Vermutung, daB primar immer 1.4-Verknupfung erfolgt, deren Produkt dann unter der Wirkung des Initiators isomerisiert, wird gestutzt durch die Zunahme der 1.4-13s-Struktur mit fallender Initiatorkonzentration : 1.4-cis-Struktur Isopren I Butadien 80 % 35 ?' o 95 yo 70% -98 %

Anionic polymerization of dienes using oligobutadienyl-lithium as initiator

“…In addition to the structures considered in Table 3, small amounts of oxygenated functions are present in commercial HTPB samples as hydroxyl end-groups or in the middle of the chain.6 It is interesting to note that the vinyl content (1,2 and 3,4 enchainments for polybutadiene and polyisoprene, respectively) obtained under the conditions employed here was much greater than those reported for usual anionic conditions.19 This Ðnding can be explained in terms of the mechanism of Gerbert et al 50 depicted schematically in Fig. 3, where three isomeric forms coexist in equilibrium with a n-complex.…”

Electronic excitation in anionic polymerization of butadiene: Nonempirical calculations of reaction complexes

“…Actually, this state does not exhibit chemical activity in contrast to the electronically excited state (on the complex) in which acts of chemical bond breaking and formation take place 1. In extensive literature on BD polymerization 5–30, such an important characteristic as the content of 1,4‐ cis, 1,4‐ trans, and 1,2 units in its chain depending on polymerization conditions and the nature of the active center (AC) is discussed. According to the data of 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy 18–23, the structure of the AC terminal unit in both hydrocarbon (HCS) and electron‐donating (EDS) solvents is similar to the π‐allyl structure in which the negative charge is distributed between C α and C γ carbon atoms (Structure 1).…”

“…According to traditional concepts of the mechanism of anionic polymerization, the monomer molecule is inserted into the polymer chain on the CMet bond 5–30. Moreover, the content of 1,2‐ and 1,4‐( cis, trans ) units is determined by the probability that butadiene would attack the AC carbon atom bearing the maximum negative charge.…”

Influence of the concentration of growing chains on the polymerization rate of butadiene and the microstructure of the polymer formed in the polybutadienyllithium‐butadienealiphatic hydrocarbon system

“…Many authors [4,8,9,[11][12][13][14][15] have reported that the fraction of 1,2-units in polybutadiene increases with the concentration of living chains. GLAZE and coworkers [12] have explained this by the bonding of butadiene t o the Cs atom of the terminal unit in the associate.…”

“…GLAZE and coworkers [12] have explained this by the bonding of butadiene t o the Cs atom of the terminal unit in the associate. However, neither the specific character of the dependence of the microstructure on GC concentration, nor the state of the associate taking part in polymerization have been considered in references [4,[13][14]. Moreover, most authors regard polymerization as process occuring only under the influence of the monomeric form of GC and assume that only isomerization takes place in associates [4, 9, 161. I t is shown in the present work that both the kinetics of the formation of polybutadiene and its microstructure can he described by a single kinetic reaction scheme.…”