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
2002-01-07
2004-06-29
Wilson, D. R. (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...
C525S339000, C525S328300, C525S329300, C524S093000, C524S099000, C524S251000, C524S254000, C524S323000, C524S565000
Reexamination Certificate
active
06756451
ABSTRACT:
The invention relates to a process for the hydrogenation of a polymer composed of conjugated diene monomer units and nitrile group-containing monomer units, in which hydrogenation is carried out in the presence of hydrazine and an oxidizing compound.
It is possible to wholly or partially hydrogenate the double bonds present in the polymer chain of polymers that are composed of conjugated diene monomer units and nitrile group-containing monomer units, such as for instance nitrile butadiene rubber (NBR). After hydrogenation, the polymers are, for instance, less susceptible to oxidative degradation at elevated temperature and the polymers can be applied, for instance, under the bonnet in cars or even in the engine block.
Current commercial processes for hydrogenating such polymers are very cumbersome and costly. NBR is for instance dissolved in a suitable solvent and then hydrogenated with hydrogen at a high pressure and a high temperature in the presence of a noble metal catalyst. The catalyst and the solvent must subsequently be removed in a separate process step.
In addition, when high degrees of hydrogenation are achieved, side reactions take place that result in undesired branching of the polymer and even give rise to gelation.
U.S. Pat. No. 4,452,950 discloses the hydrogenation of NBR in the form of an aqueous dispersion in the presence of hydrazine, an oxidizing compound and a metal compound as catalyst. Following polymerization, NBR in itself is usually already present as an aqueous dispersion in the form of a latex. The polymer may also be formed as an aqueous dispersion. A metal compound of for example copper or iron is used as catalyst.
This in itself yields a simplified process for the hydrogenation, but a high degree of hydrogenation is difficult to achieve.
It is the aim of the invention to provide a process that does not have the above-mentioned drawback or has that drawback only to a much lesser extent.
Surprisingly, this aim is achieved by the hydrogenation being carried out in the presence of an antioxidant comprising more than 6 carbon atoms and chosen from a derivative of a substituted aromatic alcohol, of dihydroquinoline, of benzimidazole or of an aromatic secundary amine.
In the process of the invention, a higher degree of hydrogenation is attained under otherwise equal conditions. A further advantage of the process of the invention is that, in comparison with the known process, side reactions are at least strongly suppressed or even absent. Consequently, the development of undesired branching of the polymer or even the development of undesired gelation is avoided, so that the polymer can readily be compounded and can readily be processed to form moulded parts.
U.S. Pat. No. 5,221,714 discloses the teaching of Zhong and Lim whereby o-phenylenediamine can be utilized to catalyse the reaction of oxygen with residual hydrazine in an aqueous emulsion of rubber. However the above teaching learns the use of compounds with less than 6 carbon atoms which form complexes with the catalyst and further catalyse the hydrogenation reaction. These compounds have no effect on the formation of crosslinks.
While U.S. Pat. No. 5,424,356 discloses hydrogenation of NBR which is polymerized in the presence of a polymerizable antidegradant, it does not appear from that patent that the use of such NBR may have a favourable effect on how the hydrogenation reaction proceeds. The use of NBR that is polymerized in the presence of an antidegradant is excluded in the process of the invention, except in the case where the hydrogenation is carried out in the presence of a compound which contains an element from group 13 of the periodic system as catalyst the use of such NBR is not excluded.
Crosslinking of the latex during the hydrogenation process as described in U.S. Pat. No. 4,452,950 is mentioned in U.S. Pat. Nos. 5,039,737 and 5,442,009. Both patents disclose a process for breaking up the gel structures through post-treatment with ozone.
The unsaturated polymers that can be hydrogenated via the process of the present invention contain for example 5-95% by weight of the conjugated diene-monomer unit and 95-5% by weight of the nitrile group-containing monomer unit. Preferably, the polymer contains 50-80% by weight of the conjugated diene-monomer unit and 20-50% by weight of the nitrile group-containing monomer unit. More preferably, the polymer contains 60-70% by weight of the conjugated diene-monomer unit and 30-40% by weight of the nitrile group-containing monomer unit. Specific examples of conjugated diene-monomer units are 1,3-butadiene, 2,3-dimethyl butadiene, isoprene and 1,3-pentadiene. It is preferred for 1,3-butadiene to be used. Specific examples of a nitrile group-containing monomer units are acrylonitrile and methacrylonitrile. It is preferred for acrylonitrile to be used.
It is preferred for NBR to be used as polymer.
The polymers used in the process of the invention can be prepared by various processes such as emulsion polymerization, solution polymerization or bulk polymerization. Preferably, the polymers are prepared by emulsion polymerization, because in that case the polymer becomes available as a latex right away.
During hydrogenation, the polymers preferably are present in the latex form. The latex form is an aqueous emulsion of polymer, in which sundry additives such as soap and stabilisers may be present. A description of the latex form which is suitable for, for example, the hydrogenation of unsaturated polymers via the process of the invention is given in U.S. Pat. No. 5,442,009.
The polymer content of the latex is in the range from for example 1 to 70% by weight, preferably between 5 and 40% by weight.
It is possible for hydrazine to be present during the process of the invention in asmuch as it is added as such. It is also possible for a hydrazine-releasing compound to be added, such as hydrazine hydrates, hydrazine acetate, hydrazine sulphate and hydrazine hydrochloride. If the unsaturated polymer is hydrogenated in latex, use is preferably made of hydrazine and hydrazine hydrate.
Hydrazine preferably is present in a molar ratio of from 0.1:1 to 100:1 relative to the double bonds in the polymer chain. Preferably, this ratio lies between 0.8:1 and 5:1, most preferably between 0.9:1 and 2:1.
Examples of oxidizing agents that are suitable for use in the process of the invention are air, oxygen, ozone, peroxides, hydroperoxides, iodine, iodates, hypochlorite and similar compounds. Particularly suitable oxidizing agents are chosen from the group comprising peroxides and hydroperoxides. Most preferably, use is made of hydrogen peroxide.
The oxidizing compound is present in the polymer chain at a molar ratio of between 0.1:1 and 100:1 relative to the double bonds. This ratio preferably is between 0.8:1 and 5:1, most preferably between 0.9:1 and 2:1.
Examples of suitable antioxidants are given in Rubber Technology Handbook (ISBN 1-56990-145-7 (US), (Hanser/Gerdner Publications Inc., Cincinatti Ohio 1996), page 269. Specific examples of derivatives of a substituted aromatic alcohol, of dihydroquinoline, of benzimidazole or of an aromatic secundary amine, comprising more than 6 carbon atoms are derivatives of p-phenylenediamine, of trimethyl-dihydroquinoline, of naphthylamine and of mercaptobenzimidazole. It is preferred for a derivative of p-phenylenediamine to be used. Most preferably, N-isopropyl-N′-phenyl-p-phenylenediamine is used.
As antioxidant use is preferably made of a compound that is insoluble in water. Preferably, the antioxidant is added to the polymer prior to hydrogenation. It is preferred for the antioxidant to be added to the aqueous dispersion of the polymer in the form of an emulsion.
Good results are achieved when the antioxidant is added in an amount of 0.1-1.0% by weight relative to the amount of polymer. Preferably, the antioxidant is added in an amount of 0.1-0.5% by weight relative to the amount of polymer. The hydrogenation preferably is carried out in the presence of a catalyst. Suitable catalysts are compounds which contain an elemen
Aagaard Olav M.
Belt Johannes W.
DSM IP Assets B.V.
Pillsbury & Winthrop LLP
Wilson D. R.
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