Increased throughput in the manufacture of block copolymers...

Details Increased throughput in the manufacture of block copolymers... Increased throughput in the manufacture of block copolymers...

1998-08-06

2001-02-13

Mullis, Jeffrey C. (Department: 1711)

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

Synthetic resins

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

C525S333300, C525S338000, C525S339000

Reexamination Certificate

active

06187873

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the manufacture of block copolymers of conjugated dienes and/or vinyl aromatic hydrocarbons by anionic polymerization of these monomers 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/slurry/suspension of the anionic polymer in the hydrocarbon solvent).
BACKGROUND OF THE INVENTION
Polymers of conjugated dienes and/or vinyl aromatic hydrocarbons have been produced by numerous methods. However, anionic polymerization of such dienes 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 conjugated diene blocks of the block copolymers which usually form the largest part of the block copolymers.
As the polymer is created from the monomers, a solution/slurry/suspension of the polymer forms in the inert hydrocarbon solvent. This solution/slurry/suspension 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 these block copolymers, one of the most significant rate limiting aspects is the viscosity of the polymer cement. For instance, in order to achieve a reasonable efficiency in the removal of hydrogenation catalyst residue from the polymer cement, the viscosity of the polymer cement must not be more than 1000 cp at 80° C. Some of the desired hydrogenated block copolymers can achieve this viscosity requirement so hydrogenation catalyst residue can be efficiently removed at 20% solids, some at 15% solids, but there are other block copolymers that can only achieve the viscosity requirement in polymer cements at close to 10% solids. The manufacturing cost of such hydrogenated block copolymers is therefore much higher. It can be seen that there would be a significant advantage achieved if a way could be found to utilize the current manufacturing technology but decrease the polymer cement viscosity for enhanced catalyst residue removal at higher solids contents so more polymer can be produced in a given amount of time.
It would be desirable to operate the process at a higher solids content in the cement if the same amount of catalyst removal could be achieved in the same amount of time. More polymer would be produced then in a given amount of time. Alternatively, it would be advantageous to be able to decrease the time it takes to remove the desired amount of catalyst residue while operating at the same solids content. The total throughput time would thus be decreased. Another result which would be highly advantageous would be to operate at the same conditions as are presently used (time, solids content, etc.) and thus remove more of the residual hydrogenation catalyst. The present invention provides a method for achieving these goals.
SUMMARY OF THE INVENTION
This invention is an improvement upon the current process for the production of block copolymers, especially hydrogenated block copolymers, of conjugated dienes and/or vinyl aromatic hydrocarbons which comprises anionically polymerizing the monomers in an inert hydrocarbon solvent in the presence of an alkali metal initiator whereby a polymer cement is produced and then contacting the cement with hydrogen under hydrogenation conditions in the presence of a hydrogenation catalyst, and separating the metal residues from polymerization and hydrogenation from the polymer cement. This invention and the improvement to the foregoing process comprises reducing the viscosity of the polymer cement by adding to it, preferably prior to hydrogenation (if the polymer is to be hydrogenated), from 2 to 50% by weight (% wt) of a polar compound. The polar compound must be a poorer solvent for the rubber block than the inert hydrocarbon solvent from polymerization and effect a contraction of the rubber (polymer) coil. Preferred polar compounds include diethyl ether, tetrahydrofuran, diethoxyethane, monoglyme, diglyme, diethoxypropane, dioxane, ortho-dimethoxybenzene, and the like.
DETAILED DESCRIPTION OF THE INVENTION
As is well known, polymers containing both ethylenic and/or aromatic unsaturation can be prepared by copolymerizing one or more polyolefins, particularly a diolefin, by themselves or with one or more alkenyl aromatic hydrocarbon monomers. The polymers may, of course, be random, tapered, block or a combination of these, as well as linear, star or radial.
Polymers containing ethylenic unsaturation or both aromatic and ethylenic unsaturation may be prepared using anionic initiators or polymerization catalysts. Such polymers may be prepared using bulk, solution or emulsion techniques. In any case, the polymer containing at least ethylenic unsaturation will, generally, be recovered as a solid such as a crumb, a powder, a pellet or the like. Polymers containing ethylenic unsaturation and polymers containing both aromatic and ethylenic unsaturation are, of course, available commercially from several suppliers.
In general, when solution anionic techniques are used, conjugated diolefin polymers and copolymers of conjugated diolefins and alkenyl 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, napthalides, biphenyls and anthracenyl derivatives. It is preferred to use an organoalkali metal (such as sodium or potassium) compound in a suitable solvent at a temperature within the range from about −150° C. to about 300° C., preferably at a temperature wit hin the range from about 0° C. to about 100° C. Particularly effective anionic polymerization initiators are organolithium 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.
Conjugated diolefins which may be polymerized anionically include those conjugated diolefins containing from 4 to about 12 carbon atoms such as 1,3-butadiene, isoprene, piperylene, methylpentadiene, phenylbutadiene, 3,4-dimethyl-1,3-hexadiene, 4,5-diethyl-1,3-octadiene and the like. Conjugated diolefins containing from 4 to about 8 carbon atoms are preferred for use in such polymers. Alkenyl aromatic hydrocarbons that may be copolymerized include vinyl aryl compounds such as styrene, various alkyl-substituted styrenes, alkoxy-substituted styrenes, 2-vinyl pyridine, 4-vinyl pyridine, vinyl naphthalene, alkyl-substituted vinyl naphthalenes and the like.
In general, any of the inert hydrocarbon solvents known in the prior art to be useful in the preparation of such polymers may be used. Suitable solvents, then, include straight- and branched-chain hydrocarbons such as pentane, hexane, heptane, octane and the like, as well as, alkyl-substituted derivatives thereof; cycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane and the like, as well as, alkyl-substituted derivatives thereof; aromatic and alkyl-substituted derivatives thereof; aromatic and alkyl-substituted aromatic hydrocarbons such as benzene, naphthalene, toluene, xylene and the like; hydrogenated aromatic hydrocarbons such as tetralin, decalin and the like.
The polymers of this invention may be hydrogenated as disclosed in U.S. Patent Reissue 27,145, which is herein incorporated by reference. The hydrogenation of

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