Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-11-19
2001-06-05
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S065000, C526S088000, C526S346000
Reexamination Certificate
active
06242542
ABSTRACT:
The present invention relates to a process for producing syndiotactic vinylaromatic polymers.
Syndiotactic vinylaromatic polymers are typically prepared in the form of particulate polydispersed material, that is, powders. Such polymers can be made using various methods. For example, U.S. Pat. No. 5,037,907 describes a vertical tank reactor equipped with a stirring agitator for making particulate syndiotactic polystyrene. Another technique is described in U.S. Pat. No. 5,254,647, which is a process for preparing syndiotactic vinylaromatic polymers in a wiped surface reactor. In yet another example, in U.S. Pat. No. 5,484,862, a process for preparing syndiotactic vinylaromatic polymers in a horizontally disposed, continuously agitated cylindrically shaped reactor is described.
The catalysts used to make syndiotactic vinylaromatic polymers typically include a Group 4 metal complex and an activator, which are relatively expensive. However, the above mentioned prior art does not use catalysts as efficiently as is desired. It would be an advance in the art of syndiotactic vinylaromatic polymerization to provide a process which utilizes the catalyst more efficiently than in the above-mentioned prior art.
In one aspect, the present invention is a method for making a syndiotactic vinylaromatic polymer comprising mixing a first amount of a vinylaromatic monomer with a catalyst under well stirred, back-mixed polymerization conditions such that the first amount of vinylaromatic monomer polymerizes to a conversion of from 60 to 85 percent to form a polymer-containing mixture; and contacting the polymer-containing mixture with a second amount of the same or a different vinylaromatic monomer under well stirred, back-mixed polymerization conditions such that the syndiotactic vinylaromatic polymer is formed.
In a second aspect, the present invention is a method for making a syndiotactic vinylaromatic polymer comprising mixing a first amount of a vinylaromatic monomer with a catalyst in a first reaction zone under well stirred, back-mixed polymerization conditions such that the first amount of the vinylaromatic monomer polymerizes to a conversion of from 60 percent to 85 percent to form a polymer-containing mixture; passing at least a portion of the polymer-containing mixture to one of at least two parallel reactors; passing at least a portion of the polymer-containing mixture to the second parallel reactor; mixing the polymer-containing mixture in the first and second parallel reactors with additional amounts of the same or a different vinylaromatic monomer under welt stirred, back-mixed polymerization conditions to form the syndiotactic vinylaromatic polymer.
In a third aspect, the present invention is a method for making a syndiotactic vinylaromatic polymer comprising mixing a first amount of a vinyl aromatic monomer with a catalyst in a back-mixed first reaction zone of a reactor such that the vinylaromatic monomer polymerizes to a conversion of 60 percent to 85 percent to form a polymer-containing mixture; passing the polymer-containing mixture to at least one other back-mixed reaction zone of a reactor; and contacting the polymer-containing mixture with a second amount of the vinylaromatic monomer in the other reaction zone to form the syndiotactic vinylaromatic polymer.
REFERENCES:
patent: 5254647 (1993-10-01), Yamamoto et al.
patent: 5306790 (1994-04-01), Imabayashi et al.
patent: 5597879 (1997-01-01), Ase et al.
Teskin Fred
The Dow Chemical Company
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