Triorganotin lithium, process to prepare same and anionic polymerization initiated therewith

Solutions of triorganotin lithium are described having low residual concentrations (preferably less than 2,000 ppm) of halide. These are produced by a two-step process. Triorganotin halide is reacted with lithium to produce hexaorgano ditin and a precipitate of lithium halide. The lithium halide precipitate is removed by filtration and/or use of highly concentrated reaction conditions. Then the hexaorgano ditin is further reacted with lithium to form the triorgano substituted tin lithium. The lithium halide is less soluble in hot tetrahydrofuran (THF) and/or more concentrated solutions. THF is a preferred solvent for the reaction. The low-temperature reactions described result in low amounts of inactive and/or undesirable byproducts. These triorganotin lithium compounds are useful as anionic initiators that result in polymers with terminal tin compounds, e.g., triorganotin, attached to the terminal end of the polymer where initiation occurred. The polymers with terminal tin compounds have lower hysteresis in cured carbon black-filled elastomeric compounds. Low concentrations of residual halides in the initiators and consequently in the polymers has been associated with reduced amounts of volatile organotin compounds being generated during processing of polymers with organotin terminal groups.