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

Abstract

ABSTRACT:25.0 MHz 13 C and 220 MHz 1 H NMR investigations were carried out on living anion chain ends of oligomeric 1-phenyl-1,3-butadiene (IPB) in order to reveal the anionic polymerization mechanism. The propagating species of IPB can be concluded to be the 4,1 anion. Lithiated 1-phenyl-2-butene (IP2B) was employed as a model anion of the propagating species of I PB. A negative charge on the chain end delocalizes at IX-carbon and phenyl ring, and delocalization to y-carbon is small regardless of the polymerization solvent. Therefore, the monomer attacks IXcarbon and consequently the in-chain I ,4 unit is predominant even in THF solvent. These behaviors are quite different from those observed in oligomeric butadiene and/or isoprene chain ends. In THF the living chain end is regarded as only trans-4, I, whereas in hydrocarbon media it is an almost equal mixture of trans-and cis-4, I structures.KEY WORDS 1-Phenylbutadiene I Anionic Polymerization I Living Oligomer/ 13 C NMR / 1 H NMR /1-Phenyl-2-butene I Metalation /Charge Distribution I Polymerization Mechanism / We have recently elucidated microstructures of poly(l-phenyl-1,3-butadiene) [poly(lPB)] and poly-(2-phenyl-1,3-butadiene) [poly(2PB)] prepared by anionic initiators. 1 • 2 These results lead to the conclusion that IPB and 2PB behave in quite different ways from butadiene (B) and isoprene (I) in anionic polymerization.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. A large number of investigations have been carried out on the adducts of alkyllithium and B or I, using NMR spectroscopic results to account for the polymerization mechanism. 3 -14 These results clearly revealed the structures of the living chain .ends and suggested the mechanism of the polymerizations. 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. 18 EXPERIMENTAL Materialstrans-1-Phenyi-1 ,3-butadiene (I PB) was synthesized by the method described in a previous paper 1 .

Characterization of Living Anion Chain End of Oligomeric 2-Phenyl-1,3-butadienyllithium

“…As reported previously, 3 a product distribution of one-to-one adducts of IPB with tBuLi after protonation was consistent with those 4 Sum of amounts of the one to one adducts is normalized to 100%. ' At higher temperatures over ooc one to one adducts could not be detected.…”

“…In the case of the lithia ted 1-phenyl-2-butene and the oligomeric IPBLi, 3 ortho carbon resonances at 24°C were extremely broader than the other resonances. Upon cooling, the broader resonances collapsed at ooc, then splitted into two peaks of equal intensity.…”

“…Anion chain ends of the oligomeric 1-phenyl-1 ,3-butadienyllithium (oligomeric lPBLi) were investigated to show the polymerization mechanism. 3 The charge distributions on the chain ends of the oligomeric lPBLi were hardly affected by the solvating power of a solvent and the negative charge was located at the ()(-carbon due to the resonance effect of the phenyl ring.In this study, we have investigated a charge distribution on a living chain end of the oligomeric 2PB under various conditions by means of 1 H-and 13 C-NMR spectroscopies. The results are compared with those of lPB as well as B and I, and the polymerization mechanism of 2PB is discussed.…”

“…Anion chain ends of the oligomeric 1-phenyl-1 ,3-butadienyllithium (oligomeric lPBLi) were investigated to show the polymerization mechanism. 3 The charge distributions on the chain ends of the oligomeric lPBLi were hardly affected by the solvating power of a solvent and the negative charge was located at the ()(-carbon due to the resonance effect of the phenyl ring.…”

Stable and Highly Regioselective Anionic Polymerization of (Z)-1-Phenyl[3]dendralene

“…6,7 Further, when tert-butyllithium (t-BuLi) reacts with these butadiene derivatives, nucleophilic addition of the t-Bu carbanion occurs mainly at the C1 position for 2PB but only at the C4 position for 1PB. 8,9 These results indicate that the olefinic carbon atoms are susceptible to nucleophilic addition and the microstructure of the resulting polymer is affected by the position of the phenyl substituent. Such a change in regioselectivity in nucleophilic addition is expected to occur in phenyl-substituted [3]dendralene, inspiring us to attempt the anionic polymerization of 1-phenyl[3]dendralene, a structural isomer of P3D.…”