Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From heterocyclic reactant containing as ring atoms oxygen,...
Reexamination Certificate
2000-06-08
2001-08-14
Killos, Paul J. (Department: 1623)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From heterocyclic reactant containing as ring atoms oxygen,...
C528S413000, C528S409000, C502S062000, C560S103000, C560S240000
Reexamination Certificate
active
06274700
ABSTRACT:
The present invention relates to an improved process for preparing polytetrahydrofuran, polytetrahydrofuran copolymers, diesters or monoesters of these polymers by polymerization of tetrahydrofuran in the presence of at least one telogen and/or comonomer over an acid-activated montmorillonite.
Polytetrahydrofuran (PTHF), also called polyoxybutylene glycol, is a versatile intermediate in the plastics and synthetic fiber industries and is employed, inter alia, for preparing polyurethane, polyester and polyamide elastomers, being used as a diol component for the preparation of these. Furthermore, it is, like some of its derivatives, a valuable auxiliary in many applications, for example as a dispersant or in the deinking of waste paper.
PTHF is advantageously prepared industrially by polymerization of tetrahydrofuran over suitable catalysts in the presence of reagents whose addition makes it possible to control the length of the polymer chains and thus to set the mean molecular weight to the desired value (chain termination reagents or “telogens”). This control is effected by selection of the type and amount of the telogen. In addition, selection of suitable telogens enables functional groups to be introduced at one end or both ends of the polymer chain. Thus, for example, use of carboxylic acids or carboxylic anhydrides as telogens enables the monoesters or diesters of PTHF to be prepared.
Other telogens act not only as chain termination reagents, but are also incorporated in the growing polymer chain of the PTHF; they thus have not only the function of a telogen but also that of a comonomer and can therefore be equally justifiably referred to as a telogen or as a comonomer. Examples of such comonomers are water or telogens having two hydroxyl groups, e.g. dialcohols. Examples of such dialcohols are ethylene glycol, butylene glycol, 1,4-butanediol, 1,6-hexanediol, or low molecular weight PTHF. Further suitable comonomers are 1,2-alkylene oxides such as ethylene oxide or propylene oxide, 2-methyltetrahydrofuran or 3-methyltetrahydrofuran. The use of such comonomers leads, with the exception of water, 1,4-butanediol and low molecular weight PTHF, to the preparation of tetrahydrofuran copolymers. The PTHF can be chemically modified in this way. An example of this is the use of the telogen 2-butyne- 1,4-diol whose addition leads to the presence of a proportion of C≡C triple bonds in the polymer chain of the PTHF. PTHF modified in this way can be further modified chemically at these points as a result of the reactivity of these triple bonds, for example by hydrogenation of the triple bonds to double bonds, by subsequent grafting of other monomers to adjust the properties of the polymer, crosslinking for building up polymers having a comparatively rigid structure, or other customary procedures of polymer chemistry. The complete hydrogenation of the triple bonds present is likewise possible and generally leads to PTHF having a particularly low color number.
DE-A-1 226 560 describes a process for preparing polytetrahydrofuran diacetates. These are obtained by polymerization of tetrahydrofuran (PTHF) in the presence of bleaching earth as catalyst. In particular, use is made of aluminum hydrosilicates or aluminum magnesium silicates of the montmorillonite type, which can be activated by means of acid. By way of example, an acid montmorillonite having the trade name “Tonsil®” is used. Acetic anhydride is used as telogen.
Use of the montmorillonites as described in DE-A-1 226 560 gives PTHF diacetates which have a relatively high APHA color number. If a product having a low color number is desired, the mixture obtained as described in DE-A-1 226 560 has to be subjected to additional purification steps.
WO94/05719 relates to a process for preparing polytetramethylene ether glycol diesters using a catalyst of the aluminum silicate type. Instead of known natural montmorillonites, use is made of amorphous aluminum silicates or zeolites and also acid-activated and calcined kaolins.
According to DE-A-195 13 493, acid-activated magnesium aluminum hydrosilicates of the attapulgite type are used as catalyst for preparing polytetramethylene ether glycol diesters. The use of these catalysts in place of the known montmorillonite, zeolite or kaolin catalysts is said to lead to higher polymerization rates and more uniform properties and a narrow molecular weight distribution of the polymers obtained.
However, the known catalyst systems still do not have sufficient activity for industrial implementation of the process, in particular when using technical-grade THF.
It is an object of the present invention to provide a catalyst for a PTHF process which makes it possible to achieve higher polymer yields at a lower color number of the PTHF obtained, since the economics of a heterogeneously catalyzed PTHF process are critically dependent on the productivity of the catalyst and on the purity of the products obtained.
We have found that this object is achieved by a process for preparing polytetrahydrofuran, polytetrahydrofuran copolymers or diesters or monoesters thereof by polymerization of tetrahydrofuran in the presence of at least one telogen and/or comonomer over acid-activated montmorillonite catalysts, wherein the montmorillonite catalyst after acid activation has a ratio of montmorillonite structure to the sum of muscovite and kaolin structures, determined from the intensities of the reflections at 2&thgr;=5.5° for montmorillonite, 2&thgr;=9.0° for muscovite and 2&thgr;=12.5° for kaolin measured in the X-ray powder pattern, of at least 5:1.
In the acid-activated montmorillonites of the prior art, there are no montmorillonites or only a very small proportion of montmorillonites present in the montmorillonite structure after acid activation. The proportion of the catalyst which can be detected by X-ray diffraction consists predominantly or completely of the muscovite or kaolin structure. In addition, there are X-ray-amorphous constituents and natural impurities such as quartz.
According to the present invention, it has been found that montmorillonite catalysts can be used particularly advantageously in the preparation of polytetrahydrofuran or polymers derived therefrom if the ratio of montmorillonite structure to other structures after acid activation is large. Such catalysts have a high activity and selectivity, so that polytetrahydrofurans which have a low color number are also obtainable from technical-grade THF. Prepurification of the THF as described, for example, in DE-A-28 01 792 or hydrogenation to reduce the color number as described, for example, in EP-A-0 061 668 is not necessary according to the present invention.
The catalysts used according to the present invention are selected and activated with acid in such a way that after acid activation the ratio of montmorillonite structure to the sum of muscovite and kaolin structures, determined from the intensities of the reflections at 2&thgr;=5.5° for montmorillonite, 2&thgr;=9° for muscovite and 2&thgr;=12.5° for kaolin measured in the X-ray powder pattern, is at least 5:1, preferably at least 7.5:1, particularly preferably at least 20:1. Compared to the known catalysts which contain little if any montmorillonite structure, such catalysts have the abovementioned advantages.
The measurement by X-ray powder diffraction is carried out in customary ways, using copper K
&agr;
radiation. The angles given for the reflections can vary slightly depending on the apparatus and measurement method used. The procedure for carrying out the determination is known to those skilled in the art.
The montmorillonite catalyst preferably has more than 90% by weight of its crystalline constituents in the form of montmorillonite, muscovite and kaolin structures. Particularly preferably, the catalyst consists essentially or completely of montmorillonite, muscovite and kaolin structures. The proportion of other sheet structures or of quartz should be as low as possible.
The surface area of the montmorillonite catalyst is pre
Becker Rainer
Eller Karsten
Hesse Michael
Rutter Heinz
BASF - Aktiengesellschaft
Keil & Weinkauf
Killos Paul J.
Oh Taylor V.
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