Effect of aluminum derivatives in the retarded styrene anionic polymerization

This paper reports on the influence of various aluminum derivatives, i.e. trialkyl aluminum, diisobutylaluminum hydride and diethylaluminum alkoxides, on the anionic polymerization of styrene in hydrocarbons at high temperature. The importance of the structure of the aluminum additives and of the ratio [Al]/[Li] on both the formation of ‘ate’ complexes, the retardation effect and the reactivity profile of the polymerization are investigated by UV–visible spectroscopy and polymerization studies. The presence of bulky alkyl groups and/or alkoxide ligands onto aluminum allows the retarded polymerization to proceed for [Al]/[Li] ratios higher than one. Some of these systems offers a broad polymerization window in which the rate of polymerization is strongly reduced and remains almost constant over a large range of [Al]/[Li] ratios. While for trialkylaluminum and diethylaluminum alkoxide the number of PS chains formed can be related directly to the initial amount of lithium initiator, for diisobutyl aluminum hydride and diisobutylpolystyryl aluminum, the hydride and polystyryl groups act as second chain carrier, thus yielding the formation of up to two polymer chains per ‘ate’ complex.