Chemistry of hydrocarbon compounds – Product blend – e.g. – composition – etc. – or blending process... – Component of indefinite molecular weight greater than 150
Reexamination Certificate
2000-07-10
2002-08-20
Howard, Jacqueline V. (Department: 1764)
Chemistry of hydrocarbon compounds
Product blend, e.g., composition, etc., or blending process...
Component of indefinite molecular weight greater than 150
C585S507000, C525S236000, C525S237000, C525S241000, C525S242000, C526S153000, C526S164000, C526S335000, C526S340400
Reexamination Certificate
active
06437205
ABSTRACT:
FIELD OF INVENTION
The present invention relates to low molecular weight high-cis polybutadienes synthesized with a catalyst system that comprises a neodymium-containing compound, an organoaluminum hydride, and a halide source in combination with either an alkyl aluminoxane or a trialkyl aluminum compound. Blends of these low molecular weight high-cis polybutadienes and high molecular weight high-cis polybutadienes are further disclosed for use in tire tread compounds to enhance fracture properties, snow traction, wet traction, and rolling resistance of a tire.
BACKGROUND OF THE INVENTION
In the past, low molecular weight polybutadienes have generally been prepared using Nickel- and Cobalt-based Ziegler catalysts with specific molecular weight regulators. These molecular weight regulators have been problematic. More particularly, it is generally accepted that these molecular weight regulators broaden the molecular weight distribution or reduce the rate of polymerization. For example, as shown in an article in Bull. Chem. Soc. Jpn., 65, pp.1307-1312 (1992) at Tables 3 and 4, the use of these molecular weight regulators in combination with co-ordination catalysts has in the past generally resulted in a decrease in the cis-1,4 content.
Japanese Patent Publication 8-73515 discloses the polymerization of dienes with Group 3B metal (including neodymium) catalyst systems, wherein molecular weight regulators are not used in the polymerization process. The methods taught therein are applicable to a situation for making a high molecular weight high-cis polybutadiene with a narrow molecular weight distribution. But the method taught therein, as shown in the examples, generally produced a very broad molecular weight distribution if used to form a low molecular weight high-cis polybutadiene.
More particularly, while the data in that application indicated that narrow molecular weight distributions were possible at number average molecular weights of 250,000 and above (see Table 1 Practical Examples 1-5), all of the examples producing number average molecular weights below 150,000 resulted in broad molecular weight distributions (e.g. 5.5-6.3). Molecular weight distributions are the weight average molecular weight divided by the number average molecular weight. Narrow molecular weight distributions are generally achieved by controlling the initiation of polymer chains, termination of polymer chains and the lifetime of each polymer chain so that each and every polymer chain grows for the same period of time and consequently grows to approximately the same molecular weight.
Moreover, it is known that low molecular weight polybutadienes can be blended with high molecular weight high-cis polybutadienes. These known low molecular weight polybutadienes, however, having a broad molecular weight distribution and/or a reduced cis-1,4 content, cannot be readily used in these blends. For example, because of the broad molecular weight distribution, it is difficult to determine and/or optimize properties. In addition, miscibility becomes a problem when these liquid polybutadienes, varying significantly in the cis-1,4 content from a higher molecular weight polybutadiene, are used together in blends.
The effects of blends of these high molecular weight/low molecular weight (HMW/LMW) high-cis polybutadiene on the properties of a rubber compound have not been thoroughly investigated. Japanese Patent Publication No. 7-5789, published on the Aug. 6, 1987, disclosed blends of HMW/LMW polybutadiene for use in impact modified polystyrene. Further, Bridgestone Corporation has examined the use of HMW/LMW blends of low-cis polybutadiene for improved wet/snow properties. But nothing has disclosed blends of HMW/LMW blends of low-cis polybutadiene particularly beneficial for use in tread compositions.
Thus, there presently exists a need for a low molecular weight high cis-1,4 polybutadiene having properties suitable for blending with a high molecular weight high-cis polybutadiene, the resultant blend being useful in tire tread compounds.
SUMMARY OF THE INVENTION
In part, the present invention relates to a low molecular weight high cis-1,4 polybutadiene and an improved process for polymerization of dienes to a low molecular weight high-cis polybutadiene using either of two neodymium-based catalyst systems. One such catalyst system is referred to throughout as an MAO catalyst system-and comprises: (a) a neodymium-containing compound; (b) an aluminoxane; (c) an organoaluminum hydride compound; and (d) a halide source. While neodymium-based catalyst systems are known to produce high-cis polybutadiene, the use of these four catalyst components to yield a liquid high-cis polybutadiene with a narrow molecular weight distribution was not known. The catalyst system is operational under a variety of conditions.
The resulting polydiene has (a) at least 80 mole percent cis-1,4-butadiene microstructure; (b) a molecular weight distribution of less than 3.1; and (c) a number average molecular weight from about 2000 to about 50,000.
Another such neodymium-based catalyst system disclosed herein, and referred to throughout as a TIBA catalyst system, comprises: (a) a neodymium-containing compound; (b) a trialkyl aluminum compound; (c) an organoaluminum hydride compound; and (d) a halide source. At least 80 weight percent of the resulting polydiene has a molecular weight less than 100,000. In addition, the polydiene has a number average molecular weight less than 35,000; and a ratio of Mp (peak molecular weight) to Mn (number average molecular weight) between about 0.9 and about 2.0. This catalyst system is useful where environmental considerations dictate against the use of hexane-insoluble aluminoxanes in the polymerization process.
Moreover, the present invention also relates to low molecular weight/high-cis polybutadiene blends containing either of these low molecular weight high-cis polybutadienes. In this regard, the present invention relates to a high-cis polybutadiene blend, which comprises: (a) from about 20 to about 80 percent by weight of a first polybutadiene having a number average molecular weight from about 2000 to about 50,000 and a cis-1,4 microstructure content of at least 70 percent; and (b) from about 20 to about 80 percent by weight of a second polybutadiene having a number average molecular weight from about 90,000 to about 300,000, and a cis-1,4 microstructure content of at least 92 percent.
The present invention further relates to a rubber compound, which comprises at least 30 parts by weight of a high cis-1,4-polybutadiene based upon 100 parts by weight rubber wherein a) from about 20 to about 80 weight percent of the high cis-1,4-polybutadiene is a low molecular weight high-cis polybutadiene of the present invention has a molecular weight from about 2,000 to about 50,000 and a cis-1,4 content of at least 70 percent; and b) from about 20 to about 80 weight percent of the high cis-1,4-polybutadiene is a high molecular weight high-cis polybutadiene having a molecular weight from about 90,000 to about 300,000 and a cis-1,4- microstructure of at least 92 percent. Desirably these two fractions of high-cis polybutadiene represent distinct peaks (or modes) in the molecular weight distribution of the high-cis polybutadiene. Desirably the molecular weight distribution of the lower molecular weight peak is from about 1.1 to about 5 and the molecular weight distribution of the higher molecular weight peak in the distribution is from about 1.8 to about 6. These rubber characteristics facilitate achieving a balance of good fracture resistance, snow traction, wet traction, and low rolling resistance.
DETAILED DESCRIPTION OF THE INVENTION
A process is disclosed below for producing low molecular weight high-cis polybutadiene with a specific molecular weight distribution by polymerizing 1,3-butadiene in the presence of either of two catalyst systems comprising: (a) a neodymium-containing compound; (b) an aluminoxane in the MAO catalyst system or a trialkyl aluminum compound in the TIBA catalyst system; (c) an organoaluminum hydri
Hamada Tatsuro
Miller H. Jerrold
Ozawa Yoichi
Pakdel Peyman
Bridgestone Corporation
Fry Jude
Howard Jacqueline V.
Palmer Meredith
LandOfFree
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