VARIOUS TYPES OF AGGREGATES IN MONOFUNCTIONAL OR BIFUNCTIONAL POLYISOPRENYLLITHIUM IN HYDROCARBONS

The addition of tert-butyllithium on 1,2-bis(isopropenyl-4 phenyl)etha ne in pure hexane leads to the quantitative synthesis of a dilithium c ompound as shown previously by analysis of the reactional mixture. Its characteristics of difunctional initiator for the synthesis of polydi enes in pure hydrocarbon solvents was proved by indirect methods. In t his study it is shown by mass spectrometry that difunctional oligopoly isoprene is solely obtained at the first stages of the initiation reac tion. Viscosimetric measurements show that, for low degree of polymeri zation and low concentration in Li, cyclic aggregates are preferential ly formed by intramolecular association. A Li-7 n.m.r. study in hexane of various mono- and difunctional organolithium compounds confirms th eir trend to associate in hydrocarbon solvents and, for alpha,omega-di lithiopolyisoprene, the influence of the chain length on the formation of aggregated species involving more than four lithium atoms. A chang e in the concentration in Li has little influence on the distribution of the various aggregates in the 4 x 10(-4) x 10(-3) mol l(-1) Li conc entration range. The addition of LiCl reduces the amount of the most a ssociated species, while the presence of 15 vol% THF leads to their di sappearance. Copyright (C) 1996 Elsevier Science Ltd.