Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Organic compound containing
Reexamination Certificate
2001-10-16
2004-09-28
Rabago, Roberto (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Organic compound containing
C502S155000, C502S216000, C502S219000, C502S222000, C526S146000, C526S172000
Reexamination Certificate
active
06797664
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to catalysts, and more particularly to polyaddition catalysts.
2. Background Information
The present invention deals with a novel system of coordinated complexes, and their catalytic action for the preparation of polymers based on unsaturated monomers. High polymers belong to two great families, depending on the way in which their molecular weight is reached. One group is formed by polycondensation products, where functional groups in general eliminate a sub-product, typically water. The other group is made up of polymers resulting from polyaddition, reactions involving double bonds, which form a new bond between neighboring units. The catalysts described in the present invention are applicable for the obtainment of high polymers belonging to the second group, since they interact with the double bonds of unsaturated monomers, with the consequent catenation as new single bonds are formed. There are, nevertheless, synthetic resins of poly-condensation pre-polymers containing unsaturated sites which can be reacted in a poly-additive step that leads to crosslinking, which also fall in the scope of the present invention. Among the methods of polymerization of unsaturated monomers, there is a classification based on the chemical mechanism for the initiation and propagation of the polymer. The method most widely used in industry is the one employing free radicals, which are formed within the polymerizing medium starting from various agents. There are also anionic and cationic methods, with their respective initiating agents leading to the generation of carbanions or carbocations, according to each case. Finally, one must mention the methods involving coordination catalysts, which are based on the formation of metallic complexes of very diverse types, where the metallic nucleus is found surrounded by ligands, and incorporates the monomer as a coordinated ligand in a transitory form, thus transferring propagation to other monomer molecules. One should add that in any of the methods previously mentioned, it is possible to react not only one single type of monomer, but the method is extendible to mixtures of two or more monomers, leading to the obtainment of copolymers of very diverse types. The means to obtain polymers through any of the polyaddition methods mentioned above also varies considerably, and there is no single method with a universal advantage. Basically this aspect refers to the concentration and the medium of the monomer involved in the polymerization. In such a way, there are mass polymerizations, where the monomer is polymerized in the absence of diluents. Next, one finds solution polymerization, where the monomer is dissolved in a specific solvent, in which the polymer may or may not remain in solution. There are also convenient methods employing water as the medium where polymerization is carried out, and it can be in suspension, or in turn, in emulsion with the due presence of surface active agents, mainly those of anionic type. It is important to point out that polymerization techniques that make use of water as the medium, employ the free radical mechanism almost exclusively, since other initiation systems hydrolyze readily.
There are many polymer systems where traditionally free radical initiator systems are employed because of their many advantages in the industrial processes and because of their high hydrolytic stability. Even though there is relatively little control over the molecular weight in the polymer that is obtained, because of side reactions, chain transfers, and little control over stereoisomer factors, the fact that free radical methods are compatible with aqueous systems constitutes a great advantage when compared to the other polyaddition methods. Free radical methods start from inititators like potassium of ammonium persulphate, benzoyl peroxide, cumene hydroperoxide, tertiary butyl hydroperoxide, azo compounds, or hydroperoxides with ceric or ferrous ions, etc., neither of which are succeptible to hydrolysis, at least in an appreciable fashion, during the polymerization process. Such is the way in which free radical methods are compatible with all types of systems, not only anhydrous (in mass or in solution), but also highly aqueous ones (suspension and emulsion). On one hand, cationic systems as well as anionic ones, generally require anhydrous methods. This has to do with the fact that in an aqueous medium the strongest electrophilic agent that can be formed is H
3
O
+
, which would be the hydrolysis product of any carbocation that could have been formed. On the other hand, a strong nucleophilic agent would hydrolyze rapidly, forming OH
−
species, which in most polyaddition cases are not energetic enough to initiate anionic catenation. Next we have the cases involving coordination catalysts, which in great measure originate from organoaluminium or organotitanium complexes, or similar derivatives originating from some type of Lewis acid. Also in these catalysts, hydrolysis poses a serious limitation, and therefore, such polymerization must be conducted under strictly anhydrous conditions.
Synthetic resin type pre-polymers, either unsaturated polyesters, alkyl resins, or vinyl ester resins are another interesting case. When these resins are manufactured, an easy-to-handle material is made, un-crosslinked, which can be molded or laminated conveniently and its final curing be reached later under adequate catalysis. Unsaturation is made up of carbon—carbon double bonds present in the pre-polymer and also under the form of an unsaturated monomer which is also added as diluent. In the pre-polymer there can be structures with allylic hydrogens or maleic-fumaric units. Diluent monomers are usually styrene, alfa-methyl styrene, methyl methacrylate, and other similar ones. Catenation methods employed for crosslinking of the mentioned resins are essentially of the solution and mass type, and use redox methods based on ketone hydroperoxides or benzoyl peroxide with transition organometals or aromatic tertiary amines. Up to this moment no other catalytic method has been developed for the curing of the resins mentioned, with the exception of actinic radiation, which is applicable to films of minimum thickness.
SUMMARY OF THE INVENTION
A catalyst system and a method for preparing polymers using the catalyst system is provided. The catalyst system includes a complex represented by the formula [ML
y
(HSR)
ñ
]
n
, wherein M is a transition metal cation preferably in a low oxidation state, L is a ligand, Y is a whole number between 0 and 5, ñ is a whole number between 1 and 6, H is Hydrogen, S is sulphur and R is any organic group or hydrogen, and the complex has a charge of n. The catalyst system advantageously has high hydrolytic stability which allows it to be used in a variety of polymerization systems including mass, solution, suspension and emulsion.
The transition metal is preferably cobalt, but other transition metals such as chromium, manganese and iron can be used.
The catalyst system can be formed prior to contact with the compound to be polymerized or can be formed in situ in the medium where the polymerization takes place.
DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
As discussed above, the catalyst system disclosed in the present invention has wide applications and is made up of coordination complexes where the nucleus is formed by a transition metal selected from the group formed by chromium, manganese, iron and cobalt, preferably in a low oxidation, state and is surrounded by ligands derived from sulphur up to the limit of the coordination sphere, which generally lies in the number of six. Part of the coordination sphere can be occupied by a different type of ligand, but this can affect both the opening of the crystal field and the catalytic activity. In any case, a good level of reactivity is obtained, even though this is increased with a larger magnitude of 10 Dq, which measures the opening of the mentioned crystal field and reflects the funct
Cesari & McKenna LLP
Rabago Roberto
Rio Oeste, S.A.
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