Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-08-24
2001-04-17
Boykin, Terressa M. (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...
C525S339000, C525S333200, C525S333300
Reexamination Certificate
active
06218478
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to anionic polymerization of monomers to produce functionalized polymers with silyloxy reagents used as protected functional initiators for the synthesis of these polymers. More particularly, the present invention relates to an improved process for deprotection of such polymers made with silyloxy protected functional initiators.
BACKGROUND OF THE INVENTION
Anionic polymerization of conjugated dienes with lithium initiators, such as sec-butyllithium, and hydrogenation of residual unsaturation has been described in many references including U.S. Pat. No. Re. 27,145 which teaches a relationship between the amount of 1,2-addition of butadiene and the glass transition temperatures of the hydrogenated butadiene polymers. The capping of living anionic polymers to form functional end groups is described in U.S. Pat. Nos. 4,417,029, 4,518,753, and 4,753,991. Of particular interest for the present invention are anionic polymers that are capped on one or more ends with hydroxyl, carboxyl, phenol, epoxy, or amine groups.
Anionic polymerization using protected functional initiators having the structure R
1
R
2
R
3
Si—O—A′—Li is described in WO 91/12277 wherein R
1
, R
2
, and R
3
are preferably alkyl, alkoxy, aryl, or alkaryl groups having from 1 to 10 carbon atoms, and A′ is preferably a branched or straight chain bridging group having at least 2 carbon atoms. R
1
, R
2
, and R
3
are preferably not all CH
3
. The bridging group (A′) is most preferably a straight chain alkyl having from 3 to 10 carbon atoms. A preferred protected initiator wherein all of the R groups are methyl groups is described in U.S. Pat. No. 5,416,168. The polymers produced by these initiators are readily endcapped and hydrogenated to form anionic polymers having one or more terminal functional groups under commercially attractive conditions.
As described in U.S. Pat. No. 5,416,168, deprotection has preferably been accomplished by acid-catalyzed hydrolysis although contact with dilute aqueous base solution is also possible. One preferred process involves dissolving methane sulfonic acid in water in an alcohol and then adding this to the polymer cement (the solution/slurry/suspension of the polymer in the polymerization solvent). Under appropriate conditions, deprotection is also known to be able to be accomplished by contacting the polymer with aqueous mineral acid.
These deprotection processes are robust and are capable of achieving satisfactory results. However, the acid catalyzed method suffers from two significant deficiencies. The principle coproduct of this reaction, hexamethyldisiloxane (HMDS), is difficult to remove from the process solvent which is normally used, cyclohexane, greatly complicating solvent recycle. In addition, the extent of hydrolysis generally fails to exceed 97 percent. This appears to be an equilibrium limitation. Removal of the solvent and volatile silicon compounds, followed by addition of clean cyclohexane and a second aqueous acid contact, results in complete hydrolysis but this process is expensive and time consuming.
It can be seen that there is a need for a process that accomplishes a high degree of deprotection without the formation of difficult to remove silicon compounds. The present process provides these advantages.
SUMMARY OF THE INVENTION
The present invention provides a process for making functionalized polymers comprising the steps of
(a) initiating polymerization of an unsaturated monomer with a lithium initiator having the structure R
1
R
2
R
3
Si—O—A—Li wherein A is a branched or straight chain bridging group having at least two carbon atoms, R
1
,R
2
, and R
3
are alkyl, preferably methyl, alkoxy, aryl, or alkaryl groups having from 1 to 10 carbon atoms, thus producing a functionalized polymer which has a protecting silyl group at one end thereof; and
(b) contacting the protected polymer with aqueous acid to remove residual lithium, and
(c) contacting the protected polymer with from 1 to 10 equivalents of an organic or inorganic hydride; and
(d) contacting the resulting solution with aqueous acid, and
(e) recovering a linear or branched deprotected polymer having one or more terminal functional groups.
This novel deprotection process generates an easily separated co-product and proceeds to completion in one step. Preferably, the hydride is a hydrocarbon soluble hydride including aluminum hydrides and boranes. Diisobutyl aluminum hydride is particularly preferred. Less soluble hydride reducing agents, such as lithium aluminum hydride and sodium borohydride, and simple hydride salts, such as LiH, should also work in the presence of polar solvents.
DETAILED DESCRIPTION OF THE INVENTION
The polymerization of unsaturated monomers with protected functional initiators as described above is described in detail in U.S. Pat. No. 5,416,168, which is herein incorporated by reference. Following those teachings, a polymer is produced which has a functional group on one end and on the other end has a functional group which has been reacted with a silyl alkoxy protected functional initiator which serves as a “masked” or “protected” alcohol, capable of conversion to a primary, neopentyl-type alcohol group after polymerization is completed by reaction with acids or bases under mild, low cost conditions.
The lithium initiator process is well known as described in U.S. Pat. No. 4,039,593 and Re. No. 27,145 which descriptions are incorporated herein by reference. Typical living polymer structures that can be made with lithium initiators such as Structure (2) include:
X—B—Li
X—B/A—Li
X—A—B—Li
X—B—A—Li
X—B—B/A—Li
X—B/A—B—Li
X—A—B—A—Li
wherein B represents polymerized units of one or more conjugated diene hydrocarbons, A represents polymerized units of one or more vinyl aromatic compounds, B/A represents random polymerized units of the conjugated diene hydrocarbons and the vinyl aromatic monomers, and X is the residue of the lithium initiator. The living polymers are terminated as linear polymers, coupled to form branched polymers, or capped to add an additional terminal functional group by conventional means such as addition of methanol, silicon tetrachloride, divinylbenzene, or ethylene oxide. If the polymer is to be capped, the capping step is usually between polymerization and contact with aqueous acid to remove lithium. In the present invention, X is a trimethylsilyl ether group and cleavage of the trimethylsilyl ether leaves a neopentyl-like primary alcohol group in this position.
The initiators of the present invention are very active at room temperature and polymerization is preferably initiated at a temperature from 15° C. to 60° C., most preferably from 30° C. to 40° C. Polymerizations can be carried out over a range of solids levels, preferably from about 5% to about 80% wt polymer, most preferably from about 10% to about 40% wt.
Anionic polymerization is often terminated by addition of water to remove the lithium as lithium hydroxide (LiOH) or by addition of an alcohol (ROH) to remove the lithium as a lithium alkoxide (LiOR). Polymers prepared from initiators of the present invention and terminated in this way will be monohydroxy functional materials (mono-ols) after removal of the trimethylsilyl protecting group. To prepare polymers having additional terminal functional groups, the living polymer chains are preferably reacted (end capped) with hydroxyl (—OH), carboxyl (—CO
2
H), phenol (ArOH), epoxy, or amine groups by reaction with ethylene oxide (—OH), oxetane (—OH), 2,2-dimethyloxetane (—OH), carbon dioxide (—CO
2
H), a protected hydroxystyrene monomer (ArOH), ethylene oxide plus epichlorohydrin (epoxy), or the aziridine compounds listed in U.S. Pat. No. 4,791,174 (amine). For the preparation of telechelic diols, the preferred process is to terminate with 1 to 10 equivalents, most preferably 1 to 2 equivalents, of ethylene oxide at 30° C.-50° C. This reaction is quite rapid; reaction times from 5 to 30 minutes yield acceptable results.
Hydrogenation of at least 90%, preferably at least 95%, of the unsaturation
Bening Robert Charles
Willis Carl Lesley
Boykin Terressa M.
Haas Donald F.
Shell Oil Company
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