Processes for the preparation of high-cis polydienes

An improved solution polymerization process for producing a high-cis polydiene by polymerizing at least one conjugated diene monomer in an organic solvent charged with a pre-formed lanthanide-based catalyst composition, wherein the improvement comprises:

• polymerizing the at least one conjugated diene monomer in the presence of at least one thiol compound in the organic solvent charged with the pre-formed lanthanide-based catalyst composition to produce a polydiene having a cis-1,4-linkage content of 90-99%,
• wherein the at least one thiol compound is represented by the general formula R—S—H, where R is a hydrocarbyl group or a substituted hydrocarbyl group;
• wherein the polydiene produced has a higher cis-1,4-linkage content compared to a polydiene produced under the same polymerization conditions but without the at least one thiol compound;
• and
• wherein the molar ratio of the at least one thiol compound to the lanthanide compound ranges from 0.01:1 to 100:1.

A solution polymerization process for producing a high-cis polybutadiene, comprising:

• polymerizing 1,3-butadiene in an organic solvent in the presence of at least one thiol compound and a pre-formed lanthanide-based catalyst composition to produce a polydiene having a cis-1,4-linkage of 90-99%,
• wherein the at least one thiol compound is represented by the general formula R—S—H, where R is a hydrocarbyl group or a substituted hydrocarbyl group;
• wherein the pre-formed lanthanide-based catalyst composition comprises:
• (a) a lanthanide compound, (b) an alkylating agent, and (c) a halogen source, wherein (c) may optionally be provided by (a), (b), or both (a) and (b);
• and
• wherein the molar ratio of the at least one thiol compound to the lanthanide compound ranges from 0.01:1 to 100:1.