Synthesis of polyisoprene with neodymium catalyst

Neodymium salts activated with aluminum alkyl co-catalysts catalysts have been known to catalyze the polymerization of conjugated dienes since the early 1960's. To date, many papers and patents have been published which describe variations and improvements to the original systems (see U.S. Pat. Nos. 3,297,667, 3,676,441, and 3,794,604). Much of this work was driven by the eventual commercialization of high cis-polybutadiene in the 1980s for the use in tire applications (see U.S. Pat. Nos. 4,242,232, 4,260,707, 4,699,960, and 4,444,903). The neodymium catalyst system prepared by the technique of this invention can be used in the polymerization of isoprene monomer into polyisoprene rubber that is clear (transparent) and of high purity. This invention more specifically discloses a process for the synthesis of polyisoprene rubber which comprises polymerizing isoprene monomer in the presence of a neodymium catalyst system, wherein the neodymium catalyst system is prepared by (1) reacting a neodymium carboxylate with an organoaluminum compound in the presence of isoprene for a period of about 10 minutes to about 30 minutes to produce neodymium-aluminum catalyst component, and (2) subsequently reacting the neodymium-aluminum catalyst component with a dialkyl aluminum chloride for a period of at least 30 minutes to produce the neodymium catalyst system.