Process for preparing hydrogenated aromatic polymers

Details Process for preparing hydrogenated aromatic polymers Process for preparing hydrogenated aromatic polymers

2001-02-26

2002-09-24

Lipman, Bernard (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C525S332900, C525S333300, C525S339000

Reexamination Certificate

active

06455656

ABSTRACT:

The present invention is directed to a process for preparing hydrogenated aromatic polymers.
BACKGROUND OF THE INVENTION
Hydrogenated aromatic polymers have been produced by a variety of processes and hydrogenation techniques. Methods of hydrogenating aromatic polymers are well known in the art, such as that described in U.S. Pat. No. 5,700,878 by Hahn and Hucul, wherein aromatic polymers are hydrogenated by contacting the aromatic polymer with a hydrogenating agent in the presence of a heterogeneous metal hydrogenation catalyst. Typically, this process includes hydrogenation of a previously prepared and isolated polymer. The polymer is then dissolved in a hydrogenation processing solvent and purified prior to hydrogenation. However, this process suffers from poor catalyst efficiency due to catalyst poisoning from toxins, such as stabilizers, introduced during the polymerization process or finishing steps.
Therefore, there remains a need for a process of producing hydrogenated aromatic polymers with increased hydrogenation catalyst efficiency.
SUMMARY OF THE INVENTION
The present invention is directed to a process for producing a hydrogenated polymer or copolymer comprising:
a) preparing a solution comprising at least one vinyl aromatic monomer and a solvent;
b) subjecting the solution to polymerization conditions such that the vinyl aromatic monomer polymerizes, forming an aromatic polymer solution of an aromatic polymer and a solvent;
c) optionally, purifying the aromatic polymer solution, and
d) subjecting the aromatic polymer solution to hydrogenation conditions such that aromatic hydrogenation is achieved,
wherein the aromatic polymer is not isolated prior to hydrogenation.
Surprisingly, this integrated process has lower hydrogenation catalyst poisoning when compared to processes wherein hydrogenation of an isolated aromatic polymer occurs. Thus the hydrogenation catalyst can be isolated and re-used in other hydrogenation reactions.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to an integrated process wherein polymerization is followed by hydrogenation without isolation of the polymer prior to hydrogenation. The polymers to be hydrogenated can be made by any acceptable polymerization process, but are typically prepared by anionic polymerization. Anionic polymerization of vinyl aromatic monomers is known in the art and exemplified in U.S. Pat. Nos. 4,942,209 and 4,871,814, which are herein incorporated by reference. Anionic suspension polymerization is disclosed in WO96/27623. Anionic polymerization is well known in the art as a polymerization wherein a color change occurs when polymerization takes place under the influence of an anionic initiator. Representative polymerization systems are set forth in the following U.S. Pat. Nos.: 2,975,160; 3,030,346; 3,031,432; 3,139,416; 3,157,604; 3,159,587; 3,231,635; 3,498,960; 3,590,008; 3,751,403; 3,954,894; 4,183,877; 4,196,153; 4,196,154; 4,200,713; 4,205,016; 4,859,748; the teachings of which are hereby incorporated by reference thereto.
Vinyl aromatic monomers to be polymerized include, but are not limited to those described in U.S. Pat. Nos. 4,666,987, 4,572,819 and 4,585,825, which are herein incorporated by reference. Preferably, the monomer is of the formula:
wherein R is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyl substitution, wherein any alkyl group contains 1 to 6 carbon atoms and haloalkyl refers to a halo substituted alkyl group. Preferably, Ar is phenyl or alkylphenyl, wherein alkylphenyl refers to an alkyl substituted phenyl group, with phenyl being most preferred. Typical vinyl aromatic monomers which can be used include: styrene, alpha-methylstyrene, all isomers of vinyl toluene, especially paravinyltoluene, all isomers of ethyl styrene, propyl styrene, vinyl biphenyl, vinyl naphthalene, vinyl anthracene and the like, and mixtures thereof. Homopolymers may have any stereostructure including syndiotactic, isotactic or atactic; however, atactic polymers are preferred.
In addition, a comonomer(s) can be polymerized with the vinyl aromatic monomer to prepare copolymers including random, pseudo random, block and grafted copolymers. For example, hydrogenated copolymers of at least one vinyl aromatic monomer(s) and at least one comonomer selected from: nitrites, acrylates, acids, ethylene, propylene, maleic anhydride, maleimides, vinyl acetate, and vinyl chloride may also be prepared. Exemplary copolymers include styrene-acrylonitrile, styrene-alpha-methylstyrene and styrene-ethylene. Block copolymers of vinyl aromatic monomers and conjugated dienes such as butadiene, isoprene may also be prepared. The conjugated diene monomer can be any monomer having 2 conjugated double bonds. Such monomers include for example 1,3-butadiene, 2-methyl-1,3-butadiene, 2-methyl-1,3 pentadiene, isoprene and similar compounds, and mixtures thereof. Further examples of block copolymers may be found in U.S. Pat. Nos. 4,845,173, 4,096,203, 4,200,718, 4,210,729, 4,205,016, 3,652,516, 3,734,973, 3,390,207, 3,231,635, and 3,030,346. Blends of such polymers with other polymers including impact modified, grafted rubber containing aromatic polymers may also be prepared. In addition, the polymerization of the vinyl aromatic monomer may be conducted in the presence of predissolved elastomer to prepare impact modified, or grafted rubber containing products, examples of which are described in U.S. Pat. Nos. 3,123,655, 3,346,520, 3,639,522, and 4,409,369, which are incorporated by reference herein.
In one embodiment, the polymer is a vinyl aromatic-conjugated diene block copolymer, wherein the conjugated diene polymer block is chosen from materials which remain amorphous after the hydrogenation process, or materials which are capable of crystallization after hydrogenation. Hydrogenated polyisoprene blocks remain amorphous, while hydrogenated polybutadiene blocks can be either amorphous or crystallizable depending upon their structure. Polybutadiene can contain either a 1,2 configuration, which hydrogenates to give the equivalent of a 1 -butene repeat unit, or a 1,4-configuration, which hydrogenates to give the equivalent of an ethylene repeat unit. Polybutadiene blocks having at least approximately 40 weight percent 1,2-butadiene content, based on the weight of the polybutadiene block, provides substantially amorphous blocks with low glass transition temperatures upon hydrogenation. Polybutadiene blocks having less than approximately 40 weight percent 1,2-butadiene content, based on the weight of the polybutadiene block, provide crystalline blocks upon hydrogenation. Methods of modifying the 1,2-butadiene content are well known by those skilled in the art. Depending on the final application of the polymer it may be desirable to incorporate a crystalline block (to improve solvent resistance) or an amorphous, more compliant block. The conjugated diene polymer block may also be a copolymer of a conjugated diene, wherein the conjugated diene portion of the copolymer is at least 50 weight percent of the copolymer.
A block is herein defined as a polymeric segment of a copolymer which exhibits microphase separation from a structurally or compositionally different polymeric segment of the copolymer. Microphase separation occurs due to the incompatibility of the polymeric segments within the block copolymer. Microphase separation and block copolymers are widely discussed in “Block Copolymers-Designer Soft Materials”, PHYSICS TODAY, February, 1999, pages 32-38.
The vinyl aromatic monomer is contacted with an anionic initiator which is typically an organometallic anionic polymerization initiating compound. The initiator is typically an alkyl or aryl alkali metal compound, particularly lithium compounds with C
1-6
alkyl, C
6
aryl, or C
7-20
alkylaryl groups. Such initiators can be monofunctional or polyfunctional metal compounds including the multifunctional compounds described, in U.S. Pat. Nos. 5,171,800 and 5,321,093, which are incorporated herein by r

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