Aged lanthanide-based catalyst systems and their use in the preparation of cis-1,4-polydienes

A method for preparing a functionalized polymer, the method comprising:

• (a) preparing a catalyst composition by combining a lanthanide-containing compound, an alkylating agent, and a halogen source;
• (b) aging the catalyst composition to form an aged catalyst composition, where said step of aging includes aging for from 12 days to 15 days, where said step of aging the catalyst composition consists only of aging the catalyst composition prior to combining the aged catalyst composition with additional alkylating agent;
• (c) combining the aged catalyst composition with additional alkylating agent to thereby form a premixture of the aged catalyst system and the additional alkylating agent;
• (d) combining the premixture of the aged catalyst system and the additional alkylating agent with conjugated diene monomer to be polymerized to form a polymerization system that produces a polydiene having a reactive chain end, wherein said step of combining the premixture of the aged catalyst system and the additional alkylating agent with the conjugated diene monomer to be polymerized occurs within 24 hours of said forming the premixture of the aged catalyst system and the additional alkylating agent;
• wherein an amount of total aluminum employed in the aged catalyst composition relative to a total amount of the conjugated diene monomer is less than 5 mmol per 100 grams of the conjugated diene monomer, where said step of combining the premixture of the aged catalyst system and the additional alkylating agent with the conjugated diene monomer to be polymerized includes combining from about 0.001 to about 2 mmol of the lanthanide-containing compound per 100 grams of the conjugated diene monomer to be polymerized;
• and
• (e) introducing a functionalizing agent to the polymerization system to thereby prepare the functionalized polymer.