Polymerization of butadiene and styrene initiated by tributyltin lithium

The reactions of polymerization of butadiene and styrene initiated by Bu3Sn Li were studied. It was found that the different behavior of initiators bea ring Sn-Li and C-Li bonds is predominantly determined by the nature of mono mer, Polymerization of butadiene catalyzed by Bu3SnLi in hexane proceeds si milarly to the same process initiated by n-BuLi. A quite different picture is observed in the polymerization of styrene. In toluene, the reactivity of a Sn-Li bond in the reaction of styrene addition is several orders of magn itude lower than that of a C-Li bond. As a result, polymerization initiated by Bu3SnLi proceeds extremely slowly, and the molecular mass of the polyme r is many times higher than the calculated value. In THF, styrene undergoes a rapid polymerization without any pronounced induction period when Bu3SnL i is used as an initiator, and only a small fraction of the initial initiat or is involved in the process. For the reaction of chain propagation, the r ate is not only many times lower than that in the case of "usual" poly(styr yllithium), which is determined by a contribution of free ions, but is almo st two orders of magnitude lower than the rate of chain propagation involvi ng poly(styryllithium) contact ion pairs. It is suggested that the specific features of styrene polymerization carried out in a nonpolar medium are ma inly related to a difference in the rates of initiation involving Sn-Li and C-Li bonds, whereas a decreased reactivity of active centers due to comple x formation with organotin groups is the determining factor in the case of THF.