Abstract
Diene elastomers, in particular, high cis polybutadiene (BR) and high cis polyisoprene (IR), are widely used as synthetic rubber. Industrially, Ziegler-Natta catalyst systems using Ni, Co, and Nd metals have been employed for the production of BRs which have high 1,4-cis contents (94-98%), but the molecular weight and molecular weight distribution of the resulting polymers in these systems can not be well controlled (MWD 3-4). Since homogeneous catalysts can better control molecular weight, d-block transition metal metallocene/MAO catalyst systems, e.g. , have been developed recently. In such "single-site" catalyst systems, cis-specific living polymerization (sharp MWD) of 1,3-butadiene have been realized. This article is a brief introduction of recent topics, including modification of the system. Mechanistic studies of the 1,4-polymerization of butadiene affected by organometallic catalysts are also described.

Keywords:
d-Block Transition Metal, Organometallic Catalyst, Metallocene Catalyst, Single-Site Catalyst, Diene Polymerization, Polymerization Mechanism

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