Recent Trends of Polybutadiene and Polyisoprene

High cis-polybutadiene (BR) and high cis-polyisoprene (IR) are widely used in the industrial field such as materials for tire. High cis-BRs prepared from Ziegler-type catalyst system are effective to take a cis configuration in high levels, however, the molecular weight distributions (Mw/Mn) of obtained BRs are fairly broad. BR having both narrow Mw/Mn and high cis configuration levels are desirable for the purpose of better abrasion resistance, higher resilience and lower heat build-up, and so on. On the other hand, 1, 4-cis selectivity of IR synthesized with Li-, Ti- and Nd-based catalysts are still lower than NR, and their physical properties, e.g., Green strength, tensile strength or tear strength, are not satisfactory compared to NR. Recently, several kinds of catalysis systems were investigated to achieve simultaneous control of both molecular weight distribution and cis-1, 4 specificity in the polymerization of both butadiene and isoprene. In this paper, recent trends in research on the polymerization of cis-1, 4 polybutadiene and cis-1, 4-polyisoprene are reviewed.