EFFICIENCY OF THE SEC-BUTYLLITHIUM M-DIISOPROPENYLBENZENE DIADDUCT AS AN ANIONIC-POLYMERIZATION INITIATOR IN APOLAR SOLVENTS

The 2/1 sec-butyllithium/1,3-diisopropenylbenzene adduct has been prepared and evaluated as an effective, hydrocarbon soluble, difunctional initiator for the synthesis of polystyrene-polybutadiene-polystryene (SBS) thermoplastic elastomers in cyclohexane or benzene solution. The molecular weight distribution of both the PBD central block and the final block copolymer is narrow,and the expected molecular weight is obtained. However, mechanical testing, degradation of the PBD component, and use of an excess of s-BuLi compared to DIB suggest that the final copolymers are diblock instead of triblock as expected. The stoichiometric reaction of s-BuLi with DIB in an apolar solvent essentially results in the expected Li diadduct. This organolithium compound does not however react as a difunctional anionic initiator in a hydrocarbon solvent, but rather as a monofunctional compound more likely due to an association process. Addition of enough THF can make approximately two species active per DIB molecule. The addition of small amounts of triethylamine (<10 molecules per organolithium site) does not contribute to the formation of an acceptable difunctional initiator. The 1/1 addition of lithium tert-butoxide to the Li diadduct of DIB does not perturb the 1,4-microstructure of PBD, but it does not promote the activity of each metalated site of the initiator.