Structure of chain-ends in polybutadiene produced with the CoBr_2(PPh_3)_2/MgCl_2/SiPh_2(OCH_3)_2-Al(CH_3)_3 catalyst system

摘要

Polymerization of 1,3-butadiene with the CoBr_2(PPh_3)_2/MgCl_2/SiPh_2(OCH_3)_2-Al(CH_3)_3 catalyst system was conducted in the presence of ethylene. It was found that addition of ethylene causes a marked decrease in the molecular weight of polybutadiene although ethylene is not incorporated at the chain-end. The structure of chain-ends was analyzed using very low molecular-weight polybutadiene produced in the presence of ethylene, which led to the conclusion that 1,2 and 2,1 insertion reactions predominate at the initiation and propagation steps, respectively.