Polymérisation anionique des diènes. V. Configurations des oligopolyisoprènyl–lithium en milieu benzènique et en présence de dioxanne. Étude par résonance magnétique protonique: Haute résolution (RMP‐HR)

Abstract

By PMR, three dioxane–Li+ complexes have been detected for the oligopolyisoprenyl–lithium–dioxane mixtures in benzene solution. The (4‐1) living end isomerizes into the cis configuration when the sample temperature or the dioxane concentration is increased, but the isomerization phenomenon is reversible only if dioxane/Li+ ratios are smaller than unity. The specificity of the vinyl addition (86%), mainly (4‐3) (70%), due to the stronger negative charge at the Cγ carbon atom is effective only at low temperature (+15°C). At higher temperature, because of the steric hindrance of the methyl group, this stereospecificity decreases.

Characterization of Living Anion Chain End of Oligomeric 1-Phenyl-1,3-butadienyllithium

“…Small resonances at 17.8 and 39.0 ppm show the presence of a small quantity of unreacted 1P2B. 13 C chemical shifts and 13 C-H coupling constants of phenylallyllithium compounds were first reported by van Dongen et a/. 16 The assignments were carried out by comparing the observed spectra with those reported in the literature, with the aid of the off-resonance spectra.…”

“…In some cases THF was used in the place of THF-d 8 to eliminate the appearance of multiplet solvent peaks due to 13 C-D coupling. Very strong absorptions of solvent peaks compared with sample signals were carefully recorded within the dynamic range of the AD converter of the istrument (12 bits).…”

“…Figure 3 shows the 13 C NMR spectra of the living oligomeric 1 PB. Although resonances are broader and more complicated due to in-chain units, they are essentially the same as that of Figure 3B).…”

“…In this study we have investigated 13 C and 1 H NMR spectra of living anions of oligomeric IPB under various conditions. It is of interest to see how the charge distributes in the anion chain end (covalent or ionic) and how the microstructure of poly-(IPB) is controlled in a homogeneous polymerization system.…”

“…Recently Bywater et a!. have studied benzylic alkali metal compounds by 13 C NMR spectroscopy in order to discuss the charge distribution of benzylic anions corresponding to the propagating species of styrene derivatives in anionic polymerizationY On the other hand, several NMR studies have been reported on phenyl allyl anions. 16 • 17 Living anion chain ends of polymeric and oligomeric I PB are considered to be quite similar to the phenyl allyl anion.…”