Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-02-29
2002-09-24
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C528S405000, C528S408000, C528S413000, C528S409000, C560S012000
Reexamination Certificate
active
06455711
ABSTRACT:
DESCRIPTION
The present invention relates to an improved process for preparing polytetrahydrofuran, polytetrahydrofuran copolymers or diesters or monoesters of these polymers by polymerizing tetrahydrofuran in the presence of at least one telogen and/or comonomer over a hectorite polymerization catalyst.
Polytetrahydrofuran (“PTHF”), also known as poly(oxybutylene glycol), is a versatile intermediate in the plastics and synthetic fibers industry, inter alia for the preparation of polyurethane, polyester and polyamide elastomers, for which it is used as diol component. In addition, polytetrahydrofuran and also some of its derivatives are valuable auxiliaries in many applications, for example as dispersants or for deinking waste paper.
In industry, PTHF is advantageously prepared by polymerization of tetrahydrofuran over suitable catalysts in the presence of reagents which make it possible to control the length of the polymer chains and thus to adjust the mean molecular weight to the desired value (chain terminators or telogens). The control is provided through choice of type and amount of telogen. Additional functional groups at one end or both ends of the polymer chain may be introduced by selection of suitable telogens. Thus, for example, the monoesters or diesters of PTHF can be prepared by using carboxylic acids or carboxylic anhydrides as telogens.
Other telogens act not just as chain terminators, but are also incorporated into the growing PTHF polymer chain. So they can be thought of as comonomers as well as telogens. Examples of such comonomers are telogens having two hydroxyl groups such as dialcohols. Examples for such dialcohols are ethylene glycol, butylene glycol, 1,4-butanediol, 1,6-hexanediol or low molecular weight PTHF. Suitable comonomers are furthermore 1,2-alkylene oxides, for example ethylene oxide or propylene oxide, 2-methyltetrahydrofuran or 3-methyltetrahydrofuran. With the exception of water, 1,4-butanediol and low molecular weight PTHF, the use of such comonomers gives rise to the formation of tetrahydrofuran copolymers. In this way, the PTHF can be chemically modified. An example is the use of the telogen 2-butyne-1,4-diol which leads to the presence of a proportion of C≡C triple bonds in the PTHF polymer chains. PTHF modified in this way can be further chemically modified at these sites owing to the reactivity of these triple bonds, for example by hydrogenation of the triple bonds to double bonds, by subsequent grafting with other monomers to adjust the properties of the polymer, by crosslinking to form polymers having a comparatively rigid structure, or by other conventional methods of polymer chemistry. Complete hydrogenation of the triple bonds present is likewise possible and generally leads to PTHF having a particularly low color number.
As extensive studies have shown, acidic catalysts are suitable for the polymerization of THF on an industrial scale, but has the disadvantage of giving polymers with a yellow to brownish discoloration. The discoloration increases with the polymerization temperature and increasing conversion.
For instance, PCT/WO 94/05719 discloses a process for preparing polytetrahydrofuran diesters, by polymerization of THF over acid-activated kaolin, zeolites or amorphous alumosilicates.
DE-A 19 513 493 teaches a process for preparing polytetrahydrofuran esters by polymerization of tetrahydrofuran in the presence of a carboxylic anhydride over an acid-activated attapulgite polymerization catalyst. However, the conversions obtainable with the catalysts known from PCT/WO 94/05719 and DE-A 19 513 493 are poor. DE-A 12 26 560 discloses a process for preparing polytetrahydrofuran diesters over acid montmorillonites in the presence of acetic anhydride. It is true that acid montmorillonites give a higher conversion, but the color number of the polymers is correspondingly higher.
The purity of the PTHF also depends on the quality of the THF used.
The technical grade contains small amounts of impurities in a concentration of from 10 to 500 ppm. The chemical nature of these impurities is not known in every respect. Although this THF is of very high purity (it normally has a purity of 99.9%), even traces of impurities cause the abovementioned discoloration on polymerization. In addition, at the same time as the discoloration, a changed reactivity is observed in the preparation of polyesters or polyurethanes from the polytetramethylene ether glycols. These deficiencies are serious, since color and reproducible processing are among the most important properties of a polymer which is to be used industrially.
Numerous treatment methods have therefore been proposed to improve the quality of technical grade THF. For instance, DE-A-2 801 792 describes a process in which THF is treated with bleaching earths before polymerization. Although this gives polymers having an improved color number, this method of treatment cannot in every case be applied reproducibly to every available technical grade of THF.
Processes for decolorizing polymers obtained over acidic heterogeneous catalysts in a separate decolorization process following the polymerization are also known.
According to EP-A 61 668, polytetramethyl ether glycol or diesters thereof having a low color number are prepared by subjecting the polymers obtained by a cationic polymerization of THF to a hydrogen treatment in the presence of a hydrogenation catalyst. If the polymerization is carried out using a commercially available THF grade, the hydrodecolorization has to be effected at very high hydrogen pressures of, for example, from 50 to 300 bar.
It is an object of the present invention to provide a process for preparing polytetrahydrofuran, tetrahydrofuran copolymers or diesters or monoesters of these polymers which enables the preparation of THF polymers and copolymers having a low color number in a simple and economical manner. Since the economic viability of a heterogeneously catalyzed PTHF process is critically dependent on the productivity of the catalyst, it is also an object of the present invention to improve the catalyst activity compared to the known catalysts while maintaining a low color number for the polymers.
We have found that this object is achieved by a process for preparing polytetrahydrofuran, polytetrahydrofuran copolymers or diesters or monoesters of these polymers by polymerizing tetrahydrofuran in the presence of at least one telogen and/or comonomer over a heterogeneous catalyst comprising hectorite.
Hectorite is a clay and in particular a member of the smectite family. In the process of the invention, naturally occurring or synthetic hectorite may be used, preference being given to using synthetic hectorite. Replacement of the hydroxyl groups by fluorine yields fluorohectorites which may likewise be used as synthetic hectorites in the process of the invention. Synthetic smectites are described, for example, in GB-A 2 164 636 and synthetic hectorites are sold, for example, under the tradename Laponit®RD by Laporte, (Laponite Technical Bulletin L 104/90/A). Synthetic hectorites may include, from their process of production, varying amounts of water. On drying, hectorites give off absorbed water. Calcination also liberates water by dehydroxylation. Hectorites used according to the invention preferably contain less than 1% by weight of alkali metal ions.
Preference is given to essentially water-free hectorites obtained from commercially available water-containing hectorites by drying at from 80° C. to 200° C., preferably from 100° C. to 150° C., under atmospheric pressure for from 1 hour to 20 hours. However, drying may also be effected at reduced pressure and low temperatures. Dried hectorites may additionally be calcined at from 150° C. to 600° C., preferably from 200° C. to 500° C., for from 0.5 hour to 12 hours, preferably from 1 hour to 5 hours.
Hectorites used in the process of the invention are preferably activated prior to use by acid treatment, preferably using mineral acids, such as hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid, partic
Becker Rainer
Eller Karsten
Hesse Michael
Höhn Arthur
Rütter Heinz
BASF - Aktiengesellschaft
Keil & Weinkauf
Oh Taylor V.
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