Patent ID: 7288611

Claim:
A method for preparing a cis-1,4-polybutadiene rubber with a controlled molecular weight distribution, comprising polymerizing butadiene monomer using a rare-earth catalyst system comprising: (a) at least one aliphatic hydrocarbon-soluble organometallic compound comprising at least one metal element selected from the group consisting of the elements of atomic numbers 51-71 in the periodic table; (b) at least one organoaluminum compound of the formula: AlR 1 R 2 2 , wherein R 1 and two R 2 groups, which may be identical or different, are each selected from the groups consisting of alkyl groups, or when R 1 is H, two R 2 groups are the same and selected from the group consisting of alkyl groups; (c) at least one aliphatic hydrocarbon-soluble halogen-containing compound selected from the group consisting of metal haloalkyl compounds, metal halides, and haloalkyl compounds; (d) at least one alkylaluminum alkoxide; and (e) at least one conjugated double bond-containing organic compound, further comprising premixing the catalyst components according to a feeding order of (a)+(e)+(b)+(d)+(c) or (a)+(e)+(b)+(c)→(d) and aging the mixture of the catalyst components (a), (e), (b) and (d) before adding the catalyst component (c) or aging the mixture of the catalyst components (a), (e), and (b) before adding the catalyst component (c) and the catalyst component (d), wherein the aging temperature is above 30° C.