Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-02-20
2004-04-13
Lu, Caixia (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S139000, C526S165000, C526S335000
Reexamination Certificate
active
06720397
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for the synthesis of syndiotactic 1,2-polybutadiene.
BACKGROUND OF THE INVENTION
Syndiotactic 1,2-polybutadiene is a high-vinyl polybutadiene that has a stereoregular structure in which the side-chain vinyl groups are located alternately on the opposite sides in relation to the polymeric main chain. As a result, syndiotactic 1,2-polybutadiene is a crystalline thermoplastic resin that uniquely exhibits the properties of both plastics and rubber, and therefore it has many uses. For example, films, fibers, and various molded articles can be made from syndiotactic 1,2-polybutadiene. It can also be blended into and co-cured with natural or synthetic rubbers in order to improve the properties thereof.
Generally, syndiotactic 1,2-polybutadiene has a melting temperature within the range of about 80° C. to about 215° C., depending on the 1,2-linkage content and syndiotacticity. The physical properties and processing characteristics of syndiotactic 1,2-polybutadiene are affected by its melting temperature. Syndiotactic 1,2-polybutadiene having a relatively high melting temperature is generally characterized by having better mechanical properties but is more difficult to process due to the high temperature required to melt the polymer. On the other hand, syndiotactic 1,2-polybutadiene having a relatively low melting temperature is easier to process and can be readily mixed with elastomers, especially during mechanical mixing.
Very useful iron-based catalysts for the synthesis of syndiotactic 1,2-polybutadiene have recently been developed. Among the many advantages of these catalyst systems is their high activity in non-aromatic and non-halogenated solvents such as aliphatic and cycloaliphatic solvents, which are environmentally preferred.
Unfortunately, syndiotactic 1,2-polybutadiene has relatively low solubility in aliphatic and cycloaliphatic solvents, especially where the syndiotactic 1,2-polybutadiene has a melting temperature above about 100° C. In fact, when synthesized in aliphatic solvents, syndiotactic 1,2-polybutadiene quickly precipitates from solution and forms a highly swollen mass of polymer. As a result, a common technical difficulty is that the polymerization mixture is an extremely thick slurry or gelatin at commercially desirable polymer product concentrations, which is typically about 10% to about 25% by weight. These slurries or gelatins are difficult to stir and transfer, and thereby diminish heat transfer efficiency and interfere with proper process control. These slurries or gelatins also clog transfer lines, and contribute to reactor fouling due to the undesirable build-up of insoluble polymer on the baffles, agitator blades, agitator shafts, and walls of the polymerization reactor. The reactor must therefore be cleaned on a regular basis, which results in frequent shutdowns of continuous processes and serious limitations of the run length of batch processes.
One useful solution to this problem is to synthesize syndiotactic 1,2-polybutadiene within a rubber cement. For example, iron-based catalysts have recently been used to synthesize syndiotactic 1,2-polybutadiene within a polymer cement that includes a rubber, such as cis-1,4-polybutadiene, and an aliphatic solvent. The polymerization process alleviates the problems associated with the insolubility of syndiotactic 1,2-polybutadiene including reactor fouling. While this has proven to be a useful approach, there remains a need to develop a process for producing neat syndiotactic 1,2-polybutadiene within aliphatic solvents without the difficulties associated with polymer insolubility and reactor fouling.
SUMMARY OF THE INVENTION
In general the present invention provides a process for synthesizing syndiotactic 1,2-polybutadiene, the process comprising the steps of (1) polymerizing monomer consisting essentially of 1,3-butadeine monomer within an organic solvent that includes at least 50% by weight of aliphatic solvent by using an iron-based catalyst composition, where said step of polymerizing occurs at a temperature above about 65° C., thereby forming a supersaturated solution of syndiotactic 1,2-polybutadiene, (2) maintaining the supersaturated solution of syndiotactic 1,2-polybutadiene at a temperature above about 65° C. until isolation of the syndiotactic 1,2-polybutadiene is desired, and (3) isolating the syndiotactic 1,2-polybutadiene from the supersaturated solution.
The present invention also includes a process for synthesizing syndiotactic 1,2-polybutadiene, the process comprising the steps of (1) polymerizing 1,3-butadiene monomer within an aliphatic solvent by using an iron-based catalyst composition, where said step of polymerizing occurs at a temperature above about 65° C., thereby forming a supersaturated solution of syndiotactic 1,2-polybutadiene, (2) maintaining the supersaturated solution of syndiotactic 1,2-polybutadiene at a temperature above about 65° C. until isolation of the syndiotactic 1,2-polybutadiene is desired, and (3) isolating the syndiotactic 1,2-polybutadiene from the supersaturated solution.
The present invention further includes a process for synthesizing syndiotactic 1,2-polybutadiene wherein an iron-based catalyst system is employed to polymerize 1,3-butadiene monomer within an organic solvent comprising an aliphatic solvent, the improvement comprising (1) conducting the polymerization at a temperature above 65° C. to form a supersaturated solution of syndiotactic 1,2-polybutadiene, and (2) maintaining the supersaturated solution at a temperature above about 65° C. until isolation of the syndiotactic 1,2-polybutadiene is desired.
The discovery that a supersaturated solution of syndiotactic 1,2-polybutadiene can be achieved by synthesizing syndiotactic 1,2-polybutadiene at a high temperature overcomes the prior art problems associated with polymer insolubility within aliphatic solvents. Further, it has been discovered that this supersaturated solution can be maintained by maintaining the solution at the high temperature. The formation of this supersaturated solution offers many advantages including low cement viscosity, high polymer concentrations in the cement, improved heat transfer, increased production capacity, and improved transferability out of the reactor. Significantly, the long-term stability of the supersaturated solution alleviates the reactor fouling problem that is associated with the synthesis of syndiotactic polybutadiene 1,2-polybutadiene in aliphatic solvents. The supersaturated solution can be easily handled in a conventional solution polymerization reactor system. The process of this invention is particularly suitable for preparing syndiotactic 1,2-polybutadiene that has an intermediate melting temperature. This intermediate melting temperature syndiotactic 1,2-polybutadiene can be easily processed under mild conditions, and yet still possesses the adequate crystallinity that is required for mechanical properties.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The process of this invention includes polymerizing 1,3-butadiene monomer at a high temperature within an aliphatic solvent, which thereby forms a supersaturated solution of syndiotactic 1,2-polybutadiene. Following the polymerization, the supersaturated solution is maintained at a high temperature until the syndiotactic 1,2-polybutadiene is isolated from the solution. The process preferably employs an iron-based catalyst that is particularly suitable for preparing syndiotactic 1,2-polybutadiene having a melting temperature from about 120° C. to about 165° C.
The polymerization of 1,3-butadiene monomer into syndiotactic 1,2-polybutadiene according to this invention occurs within an organic solvent comprising an aliphatic solvent. The polymerization is conducted at a sufficiently high temperature so that the resulting polymer cement is a supersaturated solution that contains no appreciable amounts of polymer precipitate. This supersaturated solution is thermodynamically unstable because, once the polymer precipitates from the solution upon cooli
Bridgestone Corporation
Lu Caixia
Reginelli Arthur
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