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
2000-06-01
2002-06-11
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...
C524S555000, C524S556000, C524S565000, C524S572000, C524S574000, C524S575000, C524S575500, C525S332800, C525S333400, C525S333100, C525S333200, C525S339000
Reexamination Certificate
active
06403727
ABSTRACT:
The present invention relates to a process for selectively hydrogenating ethylenically unsaturated double bonds in addition polymers by reacting the polymers with hydrogen in the presence of at least one hydrogenation catalyst selected from salts and complex compounds of rhodium a nd/or of ruthenium.
The hydrogenation of ethylenically unsaturated double bonds is an important method of derivatizing polymers containing such bonds. A range of polymers of this kind are produced on the industrial scale, examples being butadiene- and/or isoprene-based polymers. The ethylenically unsaturated double bonds in these polymers are starting points for the aging processes as may occur under the action of light, oxygen and/or heat. Depending on the degree of exposure, such aging processes often entail a dramatic deterioration in the mechanical properties of the polymers and/or the articles produced from the polymers, and are also the cause of instances of very obvious and disruptive discoloration. By hydrogenating the double bonds it is intended to remove such weak points. Furthermore, hydrogenation makes it possible in principle to provide classes of polymer which are new or which can otherwise be prepared only by a very much more complex method.
In developing hydrogenation processes for polymers a fundamental consideration is that the polymer hydrogenation substrates may include not only the ethylenically unsaturated double bonds but also other hydrogenation-reactive functionalities. A feature of the hydrogenation process must therefore be, in general, a high level of selectivity toward the target double bonds. Further, an intrinsic risk of hydrogenation is that there may be generated on the polymer reactive intermediates which have the capacity to react with remaining double bonds and so cause crosslinking.
Techniques for hydrogenating polymers that contain ethylenically unsaturated double bonds are fundamentally known. An overview of such techniques is given by N. T. McManus et al. (J. Macromol. Sci., Rev. Macromol. Chem. Phys. (C 35(2), 1995, 239-285). A common feature of all of the techniques described is that the reaction is conducted in an organic medium. This includes the homogeneous reaction of the dissolved polymer in the presence of a homogeneously dissolved catalyst in an organic solvent, and heterogeneous reactions of polymers in suspension in an organic solvent in the presence of homogeneously dissolved catalysts, and also the hydrogenation of polymer solutions and/or polymer melts in the presence of heterogeneous catalysts. However, gelling is generally observed in the course of the hydrogenation, which points to crosslinking reactions.
EP-A 588 097 discloses the hydrogenation of polymers based on butadiene/acrylonitrile. In these processes the polymers are reacted in the form of aqueous dispersions in at least five times the amount, based on the dispersion, of an organic solvent and in the presence of ruthenium catalysts. Special additives are added to suppress the formation of crosslinked polymers. A disadvantage of this process is the large quantities of solvent that are employed.
Fundamentally there is great interest in the transfer of the catalytic hydrogenation of polymers containing ethylenically unsaturated double bonds to aqueous reaction systems. For instance, some industrially important butadiene polymers are available commercially as aqueous polymer dispersions. Furthermore, the use of solvents in the course of production is a not insignificant cost factor. Solvent avoidance also appears desirable on the grounds of workplace safety and environmental protection.
It is an object of the present invention to provide a process for selectively hydrogenating ethylenically unsaturated double bonds in polymers which firstly operates without the use of large amounts of solvent and secondly ensures high selectivity of the hydrogenation reaction of the ethylenic double bond over the hydrogenation of other functionalities and over crosslinking reactions.
We have found that this object can be achieved, surprisingly, by a process in which the polymers are hydrogenated in the presence of rhodium and/or ruthenium compounds or their salts, as hydrogenation catalysts, in an aqueous dispersion of the polymers that contains little if any organic solvent.
The present invention therefore provides a process for selectively hydrogenating ethylenically unsaturated double bonds in polymers P by reacting the polymers with hydrogen in the presence of at least one hydrogenation catalyst selected from the salts and complex compounds of rhodium and/or of ruthenium, which comprises conducting the hydrogenation in an aqueous dispersion of the polymers that comprises not more than 20% by volume of an organic solvent.
The hydrogenation of polymers in aqueous dispersion has to date been considered an impossibility. For successful hydrogenation it has been assumed that the polymers must be present in the dissolved or melted state, or at least in a swollen state, so that the catalytically active species can get to the reactive sites, in other words the ethylenically unsaturated double bonds in the polymers. In organic reaction media, hydrophobic polymers will naturally be present in dissolved or at least swollen form, but this is not the case in water or aqueous reaction systems. For this reason the hydrogenation of hydrophobic polymers, as already mentioned, has to date always been conducted in an organic medium or in the melted state.
This opinion is confirmed, inter alia, by B. Cornils, Angew. Chem. 107, 1995, 1709-1711. This reference states that catalytic reactions in two-phase systems where the substrate is the hydrophobic phase and the catalyst is in the aqueous phase come up against their limits when the starting materials, in this case the polymers, are of inadequate solubility in water and, consequently, when the transfer of organic substrate into the aqueous phase or to the interface is hindered. The ruthenium- and/or rhodium-comprising catalyst systems employed in accordance with the invention, on the other hand, appear able under the reaction conditions to penetrate at least partly into the polymer phase/water interface or to cross said interface.
In the process of the invention the hydrogenation catalysts or catalyst precursors that can be employed are all salts and/or complex compounds of ruthenium or of rhodium which are able under the respective reaction conditions—that is, hydrogen partial pressure, reaction temperature, reaction mixture pH, and any coligands present (or inorganic or organic compounds that act as coligands)—to form active hydrogenation species of low molecular mass. Examples of rhodium and ruthenium salts suited to this purpose are their hydrides, oxides, sulfides, nitrates, sulfates, halides, such as their chlorides, carboxylates, such as their acetates, propionates, hexanoates and benzoates, their salts with sulfonic acids, and mixed salts, ie. salts with different anions, such as the oxide chlorides. Also suitable are salts of complex ions of rhodium and/or ruthenium, examples being the salts of rhodium or ruthenium oxoacids, the salt of haloruthenates and halorhodates, especially the chlororuthenates and chlororhodates, the ammine and aqua complexes of rhodium halides and of ruthenium halides, especially the chlorides, and the salts of nitroruthenates. Examples of the above salts and complex salts are ruthenium(III) chloride, ruthenium(III) nitrosylchloride, ammonium pentachloroaquaruthenate(III), hexaammineruthenium(II) and -(III) chloride, dichlorobis(2,2′-bipyridyl)ruthenium(II), tris(2,2′-bipyridyl)ruthenium(II) chloride, pentaamminechlororuthenium(III) chloride, potassium pentachloronitrosylruthenium(II), ruthenium(IV) oxide, tetraacetatochlorodiruthenium(II,III), hexakisacetatotriaqua-&mgr;-oxotriruthenium(III) acetate, rhodium(III) chloride, rhodium(III) hydroxide, rhodium(III) nitrate, rhodium(III) sulfate, ammonium pentachloroaquarhodate(III), potassium pentachlororhodate(III), sodium hexachlororhodate(III), triamminetrichlororhodium(III), tr
Leube Hartmann F.
Maas Heiko
Schmidt-Thümmes Jürgen
Zeller Edgar
BASF - Aktiengesellschaft
Lipman Bernard
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