Increased throughput in the manufacture of anionic polymers...

Details Increased throughput in the manufacture of anionic polymers... Increased throughput in the manufacture of anionic polymers...

2002-03-26

2002-12-10

Henderson, Christopher (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S370000, C526S078000, C526S173000

Reexamination Certificate

active

06492469

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to the manufacture of polymers by anionic polymerization of monomers, especially conjugated dienes and/or vinyl aromatic hydrocarbons, in a hydrocarbon solvent. More particularly, this invention relates to an improvement in such a process whereby the throughput of the manufacturing system is increased by reducing the viscosity of the polymer cement (the solution of the anionic polymer in the hydrocarbon solvent).
Anionic polymers, including polymers of conjugated dienes and/or vinyl aromatic hydrocarbons, have been produced by numerous methods. However, anionic polymerization of such or other monomers in the presence of an anionic polymerization initiator is the most widely used commercial process. The polymerization is carried out in an inert solvent such as hexane, cyclohexane, or toluene and the polymerization initiator is commonly an organo alkali metal compound, especially alkyl lithium compounds. The solvent used is almost always a non-polar hydrocarbon because such solvents are much better solvents for the polymers of such monomers, especially conjugated diene polymers or blocks when they form a part of block copolymers.
As the polymer is created from the monomers, a solution of the polymer forms in the inert hydrocarbon solvent. This solution is called the polymer cement. These polymerizations may be carried out at a variety of solids contents and it is reasonably obvious that if the process can be run at high solids content, the manufacturing cost will be decreased because the cost of solvent will be decreased and more polymer can be produced in a given amount of time.
Unfortunately, with polymer cements of anionic polymers, one of the most significant rate limiting aspects is the viscosity of the polymer cement. This is especially true in the manufacture of block copolymers of conjugated dienes such as butadiene or isoprene and vinyl aromatic hydrocarbons such as styrene.
Solutions of living anionic polymers, living polymer cements, tend to be higher in viscosity than their terminated analogs, terminated polymer cements. The higher viscosity of living polymer cements in polymerization tends to limit the production capacity of equipment used to make these products. Higher concentrations of terminated polymer solutions could be pumped and mixed with the existing equipment but polymerization at these higher concentrations is not possible due to the prohibitively high viscosities of the living polymer solutions. Production rates are limited by the viscosity of the living anionic polymer solutions in polymerization since the polymer chain must be kept “living”, i.e., not terminated, until the desired molecular weight is achieved.
SUMMARY OF THE INVENTION
The present invention is an improvement upon the known method of anionically polymerizing monomers by contacting the monomers with an anionic polymerization initiator which is an organo-substituted alkali metal compound. The improvement comprises decreasing the viscosity of the polymer cement by adding at least 0.01 equivalent of a metal alkyl compound per equivalent of alkali metal initiator if the metal alkyl is added before or at the beginning of polymerization. If the metal alkyl is added during the polymerization or after but before the living polymer is terminated, then at least 0.01 equivalent of the metal alkyl compound per equivalent of living polymer chain ends (i.e., styryl-lithium or dienyl-lithium moiety) should be used. Preferably, in both cases, from 0.01 to 1.5 equivalents is used and most preferably, 0.01 to 1.0 equivalents.
The metal alkyl is preferably added during the polymerization but it can be added before polymerization begins. It can also be added subsequent to polymerization before termination if desired. The alkyl groups of the metal alkyl are chosen such that they do not exchange with the organo substituents of the alkali metal, which can be the living polymer chain ends or the organo substituents of the initiator. To avoid this undesired exchange reaction, the alkyl groups of the metal alkyl compound are selected to be more basic and/or less bulky or both than the organo substituents of the alkali metal compound. The organo substituents of the alkali metal compound are aliphatic, cycloaliphatic, aromatic, or alkyl-substituted aromatic and include multi-functional initiators such as the sec-butyl lithium adduct of diisopropenyl. In a preferred embodiment of the invention, the organo-substituted alkali metal species at the time of the addition of the metal alkyl is a styryl-lithium or dienyl-lithium moiety. The preferred metal alkyl for use herein is triethyl aluminum.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to anionic polymers and processes for polymerizing them by anionic polymerization using mono- or di- or multi-alkali metal, generally lithium, initiators. Sodium or potassium initiators can also be used. For instance, polymers which can be made according the present invention are those from any anionically polymerizable monomer, including random and block copolymers with styrene, dienes, polyether polymers, polyester polymers, polycarbonate polymers, polystyrene, acrylics, methacrylics, etc. Polystyrene polymers hereunder can be made in the same manner as the polydiene polymers and can be random or block copolymers with dienes.
In general, when solution anionic techniques are used, copolymers of conjugated diolefins, optionally with vinyl aromatic hydrocarbons, are prepared by contacting the monomer or monomers to be polymerized simultaneously or sequentially with an anionic polymerization initiator such as group IA metals, their alkyls, amides, silanolates, naphthalides, biphenyls or anthracenyl derivatives. It is preferred to use an organo alkali metal (such as lithium or sodium or potassium) compound in a suitable solvent at a temperature within the range from about −150° C. to about 150° C., preferably at a temperature within the range from about −70° C. to about 100° C. Particularly effective anionic polymerization initiators are organo lithium compounds having the general formula:
RLi
n
wherein R is an aliphatic, cycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbon radical having from 1 to about 20 carbon atoms and n is an integer of 1 to 4. The organolithium initiators are preferred for polymerization at higher temperatures because of their increased stability at elevated temperatures.
Other initiators that can be used herein include multifunctional initiators. There are many multifunctional initiators that can be used herein. The di-sec-butyl lithium adduct of m-diisopropenyl benzene is preferred because of the relatively low cost of the reagents involved and the relative ease of preparation. Diphenyl ethylene, styrene, butadiene, and isoprene will all work well to form dilithium (or disodium) initiators by the reaction:
Still another compound which will form a diinitiator with an organo alkali metal such as lithium and will work herein is the adduct derived from the reaction of 1,3-bis(1-phenylethenyl)benzene (DDPE) with two equivalents of a lithium alkyl:
Related adducts which are also known to give effective dilithium initiators are derived from the 1,4-isomer of DDPE. In a similar way, it is known to make analogs of the DDPE species having alkyl substituents on the aromatic rings to enhance solubility of the lithium adducts. Related families of products which also make good dilithium initiators are derived from bis[4-(1-phenylethenyl)phenyl]ether, 4,4′-bis(1-phenylethenyl)-1,1′-biphenyl, and 2,2′-bis[4-(1-phenylethenyl)-phenyl]propane (See L. H. Tung and G. Y. S. Lo, Macromolecules, 1994, 27, 1680-1684 (1994) and U.S. Pat. Nos. 4,172,100, 4,196,154, 4,182,818, and 4,196,153 which are herein incorporated by reference). Suitable lithium alkyls for making these dilithium initiators include the commercially available reagents (i.e., sec-butyl and n-butyl lithium) as well as anionic prepolymers of these reagents, polystyryl l

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