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
2000-11-21
2002-04-23
Lipman, Bernard (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...
C502S240000, C502S258000, C502S259000, C502S260000, C502S261000, C502S262000, C525S332800, C525S332900, C525S333100, C525S333200, C525S339000
Reexamination Certificate
active
06376622
ABSTRACT:
BACKGROUND OF THE INVENTION
Aromatic polymers have been previously hydrogenated using a variety of catalysts and conditions. Historically, typical hydrogenation catalysts have low reactivity and require high catalyst to polymer ratios.
Japanese Patent Application 03076706 describes a process for hydrogenating an aromatic polymer using a silica supported metal hydrogenation catalyst. These catalysts use a silica support of small pore diameter (200 to 500 angstroms), high surface area (100-500 m
2
/g) and achieve hydrogenation levels of greater than 70 percent. However, to achieve high hydrogenation levels, large amounts of catalyst (1-100 weight percent based on resin) and high temperatures (170° C.) are required which cause polymer degradation as exemplified by the decrease in the Mn after hydrogenation.
U.S. Pat. No. 5,028,665 describes a process for hydrogenating an unsaturated polymer using a supported metal hydrogenation catalyst wherein the support contains a majority of pores having diameters greater than 450 angstroms. However, the catalyst is limited by a small surface area and enables 90 to 100 percent olefinic hydrogenation but less than 25 percent aromatic hydrogenation.
U.S. Pat. No. 5,352,744 issued to Bates et al. describes a process for hydrogenating poly(alkenyl aromatic) or poly(alkenyl aromatic)/polydiene block copolymers, that provides hydrogenated polymers with 99.5% or greater saturation, using a metal catalyst on an alkaline metal salt support. Although Bates teaches from 0.01 to 10 grams of catalyst per gram of polymer may be used, a ratio of greater than 1.0 gram of catalyst per gram of polymer is needed to reach high hydrogenation levels.
Silica has long been used as a support for metal catalysts. Typically, the silica used as a support has had high surface area (200-600 m
2
/g) and small average pore diameter (20 to 40 angstroms). Very low hydrogenation levels are obtained when hydrogenating high molecular weight aromatic polymers using metal hydrogenation catalysts supported by this type of silica.
U.S. Pat. No. 5,612,422 discloses a metal hydrogenation catalyst comprising a silica support characterized in that the silica has a pore size distribution such that at least 98 percent of the pore volume is defined by pores having a diameter of greater than 600 angstroms. However, these catalysts are typically used to hydrogenate polymers of 100,000 Mw or higher and offer lower than desired rates for the hydrogenation of lower Mw polymers.
Accordingly, it remains highly desirable to provide a hydrogenation catalyst and process of hydrogenating unsaturated polymers, particularly a low molecular weight aromatic polymer at high levels, which does not exhibit the foregoing disadvantages.
SUMMARY OF THE INVENTION
The present invention is therefore directed to a catalyst and a process for hydrogenating an unsaturated polymer. The catalyst is particularly useful in hydrogenating aromatic polymers as well as polymers containing olefinic unsaturation. The catalyst comprises a silica supported metal catalyst characterized in that the silica has a surface area of from 30 to 120 m
2
/g and a pore size distribution such that at least 95 percent of the pore volume is defined by pores having diameter of from 300 to 1000 angstroms, and less than 4 percent of the pore volume is defined by pores having a diameter of 200 angstroms or less.
Another aspect of the present invention is a process for hydrogenating an aromatic polymer having a number average molecular weight (Mn) of from 40,000 to less than 120,000 comprising contacting the aromatic polymer with a hydrogenating agent in the presence of a silica supported metal hydrogenation catalyst, characterized in that the silica has a pore size distribution such that at least 95 percent of the pore volume is defined by pores having diameter from 300 to 1000 angstroms, less than 4 percent of the pore volume is defined by pores having a diameter of 200 angstroms or less and at least 80 percent aromatic hydrogenation is achieved.
Because of the high efficiency of the present catalyst, this process can be used in hydrogenating numerous unsaturated polymers, especially an aromatic polymer, such as polystyrene, to produce a hydrogenated polymer such as polyvinylcyclohexane without the disadvantages of the prior art.
DETAILED DESCRIPTION OF THE INVENTION
The polymers to be hydrogenated by the process of the present invention, include any unsaturated polymer containing olefinic or aromatic unsaturation. Such polymers include any amorphous saturated hydrocarbon thermoplastic. The term saturated refers to the amount of olefinic bonds within the chemical structure. As used herein, saturated refers to a polymer wherein less than 10 percent of the carbon-carbon bonds are olefinic or unsaturated in nature, generally less than 7.5 percent, typically less than 5 percent, advantageously less than 2 percent, more advantageously less than 1.5 percent, preferably less than 1 percent, more preferably less than 0.5 percent and most preferably less than 0.2 percent. These types of polymers include hydrogenated aromatic polymers, hydrogenated cyclic-olefin-(co)polymers and hydrogenated ring opening metathesis polymers. Specific hydrocarbon polymers include those produced from olefinic monomers, such as homopolymers of butadiene or isoprene, copolymers thereof, and aromatic polymers and copolymers. The aromatic polymers useful in the process of the present invention include any polymeric material containing pendant aromatic functionality. Preferably the Mn is from 40,000 to less than 120,000, more preferably less than 110,000 and most preferably less than 100,000. Pendant aromatic refers to a structure wherein the aromatic group is a substituent on the polymer backbone and not embedded therein. Preferred aromatic groups are C
6-20
aryl groups, especially phenyl. These polymers may also contain other olefinic groups in addition to aromatic groups. Preferably, the polymer is derived from a monomer of the formula:
wherein R is hydrogen or alkyl, Ar is phenyl, halophenyl, alkylphenyl, alkylhalophenyl, naphthyl, pyridinyl, or anthracenyl, wherein any alkyl group contains 1 to 6 carbon atoms which may be mono- or multisubstituted with functional groups such as halo, nitro, amino, cyano, carbonyl and carboxyl. More preferably Ar is phenyl or alkylphenyl with phenyl being most preferred. Homopolymers may have any stereostructure including syndiotactic, isotactic or atactic; however, atactic polymers are preferred. In addition, copolymers containing these aromatic monomers including random, pseudo random, block and grafted copolymers may be used. For example, copolymers of vinyl aromatic monomers and comonomers selected from nitrites, acrylates, acids, ethylene, propylene, maleic anhydride, maleimides, vinyl acetate, and vinyl chloride may also be used such as styrene-acrylonitrile, styrene-alpha-methylstyrene and styrene-ethylene. Block copolymers of vinyl aromatic monomers and conjugated dienes such as butadiene, isoprene may also be used. Examples include styrene-butadiene, styrene-isoprene, styrene-butadiene-styrene and styrene-isoprene-styrene copolymers. Further examples of block copolymers may be found in U.S. Pat. Nos. 4,845,173, 4,096,203, 4,200,718, 4,201,729, 4,205,016, 3,652,516 3,231,635, and 3,030,346. Blends of polymers including impact modified, grafted rubber containing aromatic polymers may also be used.
Cyclic-olefin-copolymers suitable for hydrogenation are copolymers of cycloolefin monomers with any other monomer containing aromatic and/or olefinic unsaturation. Cyclic-olefin copolymers include norbornene-type polymers as described in U.S. Pat. Nos. 5,115,041, 5,142,007, 5,143,979, all of which are incorporated herein by reference. The cycloolefin moiety may be substituted or unsubstituted. Suitable cycloolefin monomers include substituted and unsubstituted norbornenes, dicyclopentadienes, dihydrodicyclopentadienes, trimers of cyclopentadiene, tetracyclododecenes, hexacycloheptaciecenes, ethylidenyl norbornenes and vinyinorbornenes. Sub
Lipman Bernard
The Dow Chemical Company
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