Thermolytic behavior of polydienyllithium and polystyryllithium

Abstract

UV absorption spectra of thermolyzed polybutadienyl‐ and polyisoprenyl‐lithium reveal a chromophore group previously not recognized for such systems; its absorption band at 271 nm has been assigned to a structure with three conjugated double bonds. A two‐step mechanism for the formation of this trienic structure is proposed: an intermolecular metallation of associated living ends is followed by lithium hydride (LiH) elimination. Along thermolysis the presence of a dienic structure was also recognized, the latter arising from intramolecular elimination of LiH. The trienyllithium structure is also considered to be an effective species for the observed molecular weight distribution (MWD) variations. The observed different extent of high molecular weight (HMW) for polyisoprenyl‐ and polybutadienyl‐lithium is explained on the basis of a different stability of the intermediates present along the proposed reaction mechanism. The thermolytic behavior of polystyryllithium does not provide any significant change in MWD: the disappearance of the living chain ends, UV detected, is due to an intramolecular LiH elimination which obeys first‐order kinetics. The influence of temperature and of the tetrahydrofuran (THF) level on kinetic rate constants was investigated. © 1996 John Wiley & Sons, Inc.

Retarded styrene anionic polymerization, 7Part 6: A. Deffieux, S. Ménoret, S. Carlotti, M. Fontanille, P. Desbois, C. Schade, Macromol. Chem. Phys. 2002, 203, 862.

“…This behavior is in agreement with Schué data concerning thermal degradation of PSLi alone in ethylbenzene at 80 8C. [8] Half-life times of polystyryl species were calculated assuming a first order kinetics for the termination process (R t ¼ k t [PS*]) [5,6] in the presence and in the absence of additives.…”

“…The main results are summarized in Figure 5 in Table 2. The half-life time of PSLi without additives at 150 8C was extrapolated from data of Viola [6] using an Arrhenius law (k t : E a ¼ 63 kJ Á mol À1 , A ¼ 1.1 Â 10 7 L Á mol À1 Á min À1 ).…”

“…This was shown during the initial stage of the process by Kern. [5] At 120 8C in cyclohexane, PSLi half-life time was estimated to be 0.5 h. Recently, Viola, [6] using Full Paper: The influence of monophenoxymagnesium (2, BuMgOBT) and diphenoxymagnesium (bis(2,6-di-tert-butyl-4-methylphenoxy)magnesium, Mg(OBT) 2 ) derivatives used as additives, on the structure and reactivity of polystyryllithium (PSLi) species in hydrocarbons was studied. The impact of these compounds on the thermal stability of active species and on the reactivity in the styrene anionic polymerization at high temperature was investigated and was compared with that of n,s-dibutylmagnesium (n,s-Bu 2 Mg).…”

Synthesis of Polymer/Silica Hybrid Nanoparticles Using Anionic Polymerization Techniques

“…Poly(butadienyl)lithium is known to cross-link in hydrocarbon solvents at higher temperatures. 34,35 However, although the solution turned yellow during time, in SEC no indication for cross-linking was noticeable even in LS detection, which is sensitive toward traces of higher molecular weight products.…”

Ionic Polymerization

“…Polybutadienyllithium is somewhat more stable than polystyryllithium (k tt ¼ 6:7 Â 10 À5 s À1 versus 1:9 Â 10 À4 s À1 at 93 C [13]), but contrary to styrene, the side reactions here may cause coupled and branched polymers [95][96][97][98].…”