Zur Natur der durch katalytische Mengen von N,N,N′,N′‐Tetramethyläuthylendiamin in Organolithium/Isopren Systemen bedingten Effekte

Abstract

ZUSAMMENFASSUNG: N,N,N',N'-Tetramethylathylendiamin (TMD) ruft in den Systemen Organolithium (RLi)/Isopren schon beim Molverhaltnis [TMD]/[RLi] z 1 eine betrachtliche Zunahme der Polymerisationsgeschwindigkeit und bevorzugte Bildung von 3,4-Kettengliedern in den Polymeren hervor. Um die Natur dieser Effekte zu klaren, wurden Fraktionen der Polymeren untersucht, die sich beim parallelen Verlauf der Wachstumsreaktion an RLi-Agenzien und deren Komplexen mit TMD bilden, was durch die Wahl des Verhaltnisses [TMD]/[RLi] = 0,Ol erreicht wurde. Der hochste Gehalt an 3,4-Gliedern in dem unter dieser Bedingung erhaltenen Polyisopren wurde fur die Fraktion mit dem kleinsten Molekulargewicht festgestellt. Es wird ein moglicher Mechanismus fur diese Erscheinung vorgeschlagen. SUMMARY: N,N,N',N'-Tetramethylethylenediamine (TMD) causes a significant increase of the polymerization rate and of the content of 3,4-links in the polymers formed in the systems organolithium (RLi)/isoprene already at a mole-ratio [TMD]/[RLi] r 1. In order to clear the nature of these effects fractions of the polymers formed at a ratio [TMD]/[RLi] = 0,Ol which secured parallel propagation reactions by the RLi-speciesand their complexes with TMD were investigated. The highest content of 3,4-links was found in the polyisoprene fraction with the lowest molecular weight. A possible mechanism of this phenomenon is discussed.

Anionic Polymerization of (Meth)acrylic Monomers. 22. Anionic Polymerization of tert-Butyl Methacrylate in Toluene/THF Mixtures: A Preliminary Approach to the Role of Solvation/Ligation Equilibria

“…It is worth recalling that in his kinetic studies Müller has already suggested that an "intramolecular solvation" equilibrium between several active species possibly dominates the tBMA anionic polymerization in pure toluene,lb whereas an association equilibrium between THF-solvated dimeric and THF-solvated monomeric living chain ends is mostly operative in pure THF.lb'6b On these bases, we feel strongly justified in proposing that THF nonsolvated (P*ns) and THF-solvated active species (P*s) may reasonably coexist in tBMA anionic polymerization in toluene/THF mixtures at -78 °C. Since that polymerization has already been established to be by one order of magnitude faster in toluene than in THF,lb biand even multimodal MWD's must result,6 provided the exchange between (P*ns) and (P*s) is slow compared to the monomer addition rate; i.e., we deal here with a solvation equilibrium mechanism (Scheme It is worthwhile to recall here that a similar solvation effect on MWD has been previously reported by Erussalimsky et al,7 who demonstrated that isoprene anionic polymerization in cyclohexane results in a unimodal and narrow MWD, whereas addition of 0.01 molar equiv of TEMDA gives rise to a broad and even bimodal MWD. The author has attributed this effect to a coexistence of slowly exchanging TEMDA-free and -complexed active species.…”

The effect of TMEDA on the kinetics of the anionic polymerization of methyl methacrylate in tetrahydrofuran using lithium as counterion

“…[23,24] In anionic polymerizations, either an increase or a decrease in reactivity was observed when adding TMEDA, depending on the monomer, the solvent, and the concentration. [25][26][27][28][29] Hélary et al [28] observed that the addition of TMEDA in the polymerization of styrene in cyclohexane leads to a deaggregation of polystyryllithium dimers into TMEDA-coordinated unimers. However, these unimers are less reactive than the non-chelated unimers which are formed from the dissociation of dimers in absence of TMEDA, presumably due to steric hindrance.…”

Allylidene Monomers: Anionically Polymerizable 1,1-Disubstituted 1,3-Diene Derivatives

“…TMEDA was then used as a polar additive to further study the anionic polymerization of DMBd. In the anionic polymerization, either an increase or a decrease in the reactivity is observed with TMEDA addition, which depends on the monomer type, concentration, and the solvent used. − In addition, the microstructure of the diene polymer is often dramatically changed. , In the case of DMBd polymerization, TMEDA addition resulted in an extremely low conversion (∼6%) with only oligomers formed even after 48 h (Figure b), implying the deceleration of the polymerization reaction (run 3).…”