New perfectly difunctional organolithium initiators for block copolymer synthesis: Synthesis of dilithium initiators in the absence of polar additives

New types of difunctional organolithium initiators have been prepared by addition of sec or tert-butyl lithium on two families of non polymerizable precursors having two non-conjugated double bonds. They were made in pure hydrocarbon solvents such as n-hexane, the dilithium adducts being insoluble and easily purified by elimination of monofunctional species. However, they easily initiate the polymerization of monomers such as conjugated dienes, giving soluble and stable difunctional living polymers in the complete absence of any polar additive.