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
1998-07-24
2001-01-09
Lipman, Bernard (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...
C525S327400, C525S329600, C525S329700, C525S333300, C525S338000, C525S339000
Reexamination Certificate
active
06172165
ABSTRACT:
The present invention is directed to a process for hydrogenating a high molecular weight aromatic polymer.
BACKGROUND OF THE INVENTION
Aromatic polymers have been previously hydrogenated using a variety of catalysts and conditions. Historically, typical hydrogenation catalysts have low reactivity, require high catalyst to polymer ratios and hydrogenate low molecular weight (less than 20,000) aromatic polymers. Hydrogenation of high molecular weight (Mw) aromatic polymers have also required high temperature and/or pressure conditions in order to achieve high hydrogenation levels. However, these conditions may cause polymer degradation.
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 Mw 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.
Accordingly, it remains highly desirable to provide a process of hydrogenating an aromatic polymer at high levels which does not exhibit the foregoing disadvantages.
SUMMARY OF THE INVENTION
The present invention is a process for hydrogenating an aromatic polymer 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 surface area of at least 10 m
2
/g and a pore size distribution such that at least 98 percent of the pore volume is defined by pores having diameter of greater than 600 angstroms, and at least 80 percent aromatic hydrogenation is achieved.
A second aspect of the present invention is a silica supported metal catalyst characterized in that the silica has a surface area of at least 10 m
2
/g and a pore size distribution such that at least 98 percent of the pore volume is defined by pores having diameter of greater than 600 angstroms.
A third aspect of the present invention is the hydrogenated polymers produced by the process previously described.
Because of the high efficiency of the present catalysts, this process can be used in hydrogenating polystyrene to produce polyvinylcyclohexane without the disadvantages of the prior art.
DETAILED DESCRIPTION OF THE INVENTION
The aromatic polymers useful in the process of the present invention include any polymeric material containing pendant aromatic functionality. Preferably the Mw is from 100,000 to 3,000,000, more preferably from 100,000 to 1,000,000, and most preferably from 100,000 to 500,000. Although high molecular weight aromatic polymers are preferred, aromatic polymers below 100,000 molecular weight may also be hydrogenated by the process of the present invention. 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 anthrcenyl, 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, 3,734,973, 3,390,207, 3,231,635, and 3,030,346. Blends of polymers including impact modified, grafted rubber containing aromatic polymers may also be used.
The silica support used in the process of the present invention has a narrow pore size distribution and surface area greater than 10 meters squared per gram (m
2
/g).
The pore size distribution, pore volume, and average pore diameter can be obtained via mercury porosimetry following the peedings of ASTM4 D-428483.
The pore size distribution is typically measured using mercury porosimetry. However, this method is only sufficient for measuring pores of greater than 60 angstroms. Therefore, an additional method must be used to measure pores less than 60 angstroms. One such method is nitrogen desorption according to ASTM D-4641-87 for pore diameters of less than about 600 angstroms. Therefore, narrow pore size distribution is defined as the requirement that at least 98 percent of the pore volume is defined by pores having pore diameters greater than 600 angstroms and that the pore volume measured by nitrogen desorption for pores less than 600 angstroms, be less than 2 percent of the total pore volume measured by mercury porosimetry.
The surface area can be measured according to ASTM D-3663-84. The surface area is typically between 10 and 50 m
2
/g, preferably between 12 and 20 with most preferred between 14 and 17 m
2
/g.
The desired average pore diameter is dependent upon the aromatic polymer which is to be hydrogenated and its molecular weight. It is preferable to use supports having higher average pore diameters for the hydrogenation of polymers having higher molecular weights to obtain the desired amount of hydrogenation. Average pore diameters are typically between 1000 and 5000 angstroms, preferably between 3000 and 4000 angstroms, most preferably between 3500 and 4000 angstroms. Pore diameters of greater than 5000 angstroms may also be used if the surface area is maintained at the levels specified.
The silica used as the support in the process of the present invention can be made by combining potassium silicate in water with a gelation agent, such as formamide, polymerizing and leaching as exemplified in U.S. Pat. No. 4,112,032. The silica
Hahn Stephen F.
Hucul Dennis A.
Lipman Bernard
The Dow Chemical Company
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