Towards the control of the reactivity in high temperature bulk anionic polymerization of styrene, 1 - Influence of n,s-dibutylmagnesium on the reactivity of polystyryllithium species

The influence of n,s-dibutylmagnesium on the kinetics of styrene polymeriza tion initiated by s-butyllithium was investigated in cyclohexane at 50 degr ees C. The presence of n,s-dibutylmagnesium, in molar ratios ranging from 0 to 20 with respect to polystyryllithium, leads to a drastic and continuous reduction of the reactivity of the propagating species. The living charact er of the polymerization, especially the control of the molar mass is prese rved over the entire range studied. The experimental molar masses are in ag reement with the formation of one polystyrene chain per lithium and 0.5 to 0.8 chains per magnesium atom, indicating that both alkyllithium and dialky lmagnesium species are involved in the polymerization process through the f ormation of "ate" complexes. The UV-visible study of the PSLi/n,s-dibutylma gnesium systems shows that several types of "ate" complexes with different stoichiometry are formed depending on the proportion of the two metal deriv atives.