Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-08-01
2003-12-02
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...
C526S088000, C526S173000, C526S204000, C526S209000, C526S346000
Reexamination Certificate
active
06657028
ABSTRACT:
TECHNICAL FIELD
This invention relates to processes for the production of anionic polymers of styrenic monomers.
BACKGROUND
Polystyrene has many uses in the production of plastic articles and materials. For instance, brominated polystyrene is known to be a useful flame retardant for use in thermoplastics, e.g., polybutylene terephthalate, polyethylene terephthalate and nylon. The characteristics of the brominated polystyrene typically are determined by the process by which it is made. Polystyrene produced by anionic polymerization has been less preferred in the past because of its high cost and scarce availability. At least to some extent, these problems with respect to anionic polystyrene are a function of the complexity of the previously known processes for producing such a polymer. The processes previously employed, particularly those involving a batch operation, in the anionic polymerization of styrenic monomers have suffered from difficulties caused by the large exotherm created upon the initiation of the reaction being conducted, and from the generation of a product with high molecular weights and, in the case of cationic or free radical styrenic polymers, unfavorable polydispersity.
Thus, a need exists for a facile process for the production of anionic polymers of styrenic monomers which results in a product having suitable molecular weight and polydispersity characteristics. In the case of anionic styrenic polymers for use in the preparation of brominated styrenic flame retardants, it would be highly advantageous if a way could be found to produce an anionic styrenic polymer which is essentially free or free of olefinic and indane end groups which are common to cationic or free radical styrenic polymers. The avoidance of such end groups has been found to markedly increase the thermal stability of the resultant brominated styrenic polymer.
SUMMARY OF THE INVENTION
This invention is deemed to satisfy the foregoing needs in unique and elegant way by providing, amongst other things, a batch process for producing anionic styrenic polymer. The process avoids the use of aromatic solvents, such as benzene or toluene, and thus results in a polymer product substantially free of trace levels of such compounds, thereby avoiding the undesirable byproducts such impurities can create in downstream production of, e.g., brominated styrenic flame retardants. The process allows for higher reaction temperatures, as compared to previously known batch processes, while still controlling the process exotherm. Relative to previously known batch processes, lower amounts of ether promoter can be used in processes of this invention. This is especially advantageous when the desired product is a low molecular weight polymer because of the resulting economic benefits and the avoidance of deleterious effects of excessive promoter impurities in downstream products made from the polymer. The process comprises:
A) charging a liquid saturated hydrocarbon diluent and an ether promoter into a reactor; and then
B) either
1) (i) charging a saturated hydrocarbon solution of organolithium initiator into the reactor, in an amount to provide in the range of about 1 to about 10 mol % of organolithium initiator based on the total amount of a styrenic monomer to be added followed by (ii) the controlled addition of the styrenic monomer such that the temperature of the resultant reaction mixture is maintained at or below about 55° C.; or
2) concurrently feeding separate feeds of (i) a styrenic monomer and (ii) a saturated hydrocarbon solution of organolithium initiator into the reactor, the feeds being maintained at rates to provide for the addition of an amount of organolithium initiator in the range of about 1 to about 10 mol % based on the total amount of styrenic monomer to be added, the temperature of the resultant reaction mixture being maintained at or below about 55° C. and feed (ii) being of a shorter duration than feed (i).
In a preferred embodiment of this invention, batch process for producing anionic styrenic polymer is provided. The process comprises charging cyclohexane and an ether promoter into a reactor, and then prefeeding about 1 percent of the total amount of styrene monomer to the reactor, and then concurrently feeding separate feeds of (i) the remaining styrene monomer and (ii) a saturated hydrocarbon solution of organolithium initiator into the reactor. When operating on a scale of about 3,000 to about 6,000 lbs. of styrenic monomer, it is desirable to maintain the concurrent feeds over a period of time in the range of about 2 to about 10 minutes and at rates to provide for the addition of an amount of organolithium initiator in the range of about 2.5 to about 3.5 mol % based on the total amount of the styrene monomer. The temperature of the resultant reaction mixture is maintained at or below about 55° C., and the styrene monomer is fed for a period of time not to exceed about 2 hours measured from initiation of the feeds (i) and (ii). The process is thus carried out so as to form an anionic styrenic polymer having a polydispersity index of about 1.2 or less.
These and still other embodiments, features and advantages of the present invention will become apparent from the following detailed description, examples and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The styrenic monomer of this invention may be any anionically polymerizable styrenic monomer. Suitable non-limiting examples include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, (&agr;-methylstyrene, ethyl-styrene, tert-butylstyrene, dimethylstyrene, and the like including mixtures of two or more of the foregoing. Preferably, the styrenic monomer consists essentially of styrene.
The liquid saturated hydrocarbon diluent of this invention may be any aliphatic or cycloaliphatic hydrocarbon, or a mixture of two or more of the same, which is liquid under reaction conditions. The saturated hydrocarbon preferably contains in the range of about 4 to about 12 carbon atoms in the molecule. The aliphatic hydrocarbon may be linear or branched. Non-limiting examples of suitable aliphatic hydrocarbons include pentane, isopentane, hexane, 2-methylpentane, octane, 2,2,4-trimethylpentane and the like. More preferably, the liquid saturated hydrocarbon is one or more liquid saturated cycloaliphatic hydrocarbons. Suitable non-limiting examples of such cycloaliphatic hydrocarbons are cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, cycloheptane, 1,3-dimethylcyclohexane, 1,4-dimethylcyclohexane and the like, with cyclohexane being particularly preferred as the liquid saturated hydrocarbon diluent.
The ether promoter of this invention may be a saturated aliphatic or cycloaliphatic monoether, a saturated aliphatic or cycloaliphatic diether or an aromatic ether. Thus, non-limiting examples of suitable ether promoters include tetrahydrofuran, methyl tert-butyl ether, ethyl tert-butyl ether, 1,4 dioxane, dimethoxyethane, methoxybenzene, and the like. The ether promoter is preferably a saturated cyclic or acyclic monoether having in the range of 4 to about 8 carbon atoms in the molecule. More preferably, the monoether is tetrahydrofuran (sometimes also referred to herein as “THF”), methyltetrahydrofuran or dimethyltetrahydrofuran, or a mixture of any two or more of these. Tetrahydrofuran is particularly preferred. In another particularly preferred embodiment of this invention, the monoether consists essentially of an alkyl tert-butyl ether. Suitable alkyl tert-butyl ethers include, e.g., linear and branched chain alkyl tert-butyl ethers such as, e.g., methyl tert-butyl ether (sometimes also referred to herein as “MTBE”) and ethyl tert-butyl ether, with methyl tert-butyl ether being particularly preferred. It is desirable to use an ether that is a liquid under the reaction conditions being used.
The organolithium initiator may be one of many lithium-containing hydrocarbons. Suitable non-limiting examples include methyllithium, ethyllithium, n- or sec-butyllithium, isopropyllithium, cyclohexyllithium orphenyllithium, includi
Aplin J. Todd
Klobucar W. Dirk
Kolich Charles H.
Maxwell Kimberly A.
Albemarle Corporation
Spielman, Jr. Edgar E.
Teskin Fred
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