Stephane Menoret

Retarded Anionic Polymerization of Styrene, 6. Influence of Zinc and Boron Derivatives on the Reactivity of Polystyryllithium

Zinc and boron derivatives were used as additives for the retardation of styrene polymerization initiated by sec-butyllithium. The formation of mixed complexes between polystyryllithium (PSLi) and alkyl zinc or boron derivatives as well as a transmetallation reaction between PSLi and alkoxyborane was studied by UV-vis spectroscopy. Kinetic studies performed in the presence of the additives show that the rate of polymerization is divided only by two with diethylzinc at [Zn]/[Li] = 8 suggesting the contribution of remaining non-complexed PSLi. On the contrary, the rate was found to decrease noticeably with triethylborane upon increasing the [B]/[PSLi] ratio, in agreement with the formation, at 20°C, of ate complexes more stable than than with diethylzinc. However, the dissociation constant of the complexation equilibrium between R 3 B and PSLi is higlhy dependent on the temperature, and the retardation is not so effective at T>100°C. The same retardation effect was observed with borane alkoxides. Transmetallation reaction involving PSLi and B-OR bonds is first observed yielding B(PS) x derivatives. Retardation is governed by the concentration of the remaining PSLi species.

Retarded styrene anionic polymerization. 8. Influence of dialkylphenoxyaluminum on the reactivity of polystyryllithium species

Abstract This paper discusses the influence of dialkylphenoxyaluminum additives on the retardation of styrene polymerization initiated by alkyllithium. Data are compared with results obtained with trialkylaluminum. Similar decreases of the propagation rate can be achieved with both types of compounds. Although with R 3 Al additives ( i -Bu 3 Al, Et 3 Al, Me 3 Al), reactivity extinction appears with the formation of inactive 1:1 (Al/Li) mixed complexes, at a ratio of [Al]/[Li]=1, in the presence of diisobutyl-2,6-di- tert -butyl-4-methyl-phenoxyaluminum, extinction occurs at a ratio of [Al]/[Li]=0.5. This was correlated to an irreversible ligand exchange between the polystyryllithium and the phenoxyaluminum derivative, as proved by the formation of the corresponding lithium phenoxide, prior to formation of a 1:1 complex.

Retarded styrene anionic polymerization, 7. Influence of mono- and diphenoxymagnesium derivatives on both the reactivity and thermal stability of polystyryllithium species at high temperature†

The influence of monophenoxymagnesium (2,6- di-tert-butyl-4-methylphenoxybutylmagnesium, BuMgOBT) and diphenoxymagnesium (bis(2,6-di-tert-butyl-4-methyl- phenoxy)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). Kinetic measurements were carried out in cyclohexane at 100 °C and the thermal stability of polystyryl end-groups was studied at 150 °C in decahydronaphthalene. The presence of BuMgOBT or Mg(OBT) 2 significantly increases the thermal stability of active species compared to dialkylmagnesium or alkylalkoxymagnesium derivatives. Unlike n,s-Bu 2 Mg, BuMgOBT and Mg(OBT) 2 do not contribute to the formation of new PS chains in addition to those produced by PSLi seeds.