Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From heterocyclic reactant containing as ring atoms oxygen,...
Reexamination Certificate
2000-04-10
2002-03-26
Lovering, Richard D. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From heterocyclic reactant containing as ring atoms oxygen,...
C560S240000, C568S617000
Reexamination Certificate
active
06362312
ABSTRACT:
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 acid-activated calcium montmorillonites.
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 a 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 water or telogens having two hydroxyl groups such as dialcohols. Examples of such dialcohols are ethylene glyco, 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 leads 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
57
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.
DE-B-1 226 560 describes a process for preparing polytetrahydrofuran diacetates. They are obtained by polymerizing tetrahydrofuran (THF) in the presence of bleaching earth catalysts. In particular, use is made of aluminum hydrosilicates or aluminum/magnesium silicates of the montmorillonite type which may be acid-activated. For example, an acidic montmorillonite earth having the trade name “Tonsil®” is used in conjunction with acetic anhydride as telogen.
PTHF diacetates obtained using the montmorillonites as described in DE-B-1 226 560 have a relatively high APHA color number. If a low color number product is desired, the mixture obtained according to DE-A-1 226 560 must be subjected to additional purification steps.
WO 94/05719 discloses a process for preparing polytetramethylene ether glycol diesters over an aluminum silicate catalyst. In addition to amorphous alumino-silicates or zeolites, acid-activated and calcined kaolins are used instead of known natural montmorillonites.
According to DE-C-195 13 493, polytetramethylene ether glycol diesters are prepared over magnesium/aluminum hydrosilicates of the attapulgite type as catalysts. It is claimed that the use of these catalysts instead of the known montmorillonite, zeolite or kaolin catalysts leads to higher polymerization rates and polymers having more uniform properties and a narrow molecular weight distribution.
U.S. Pat. No. 5,210,283 describes a process for preparing pTHF in the presence of acid anhydrides over an acid-activated bleaching earth that has been calcined at a temperature greater than 600° C. prior to use. The advantage of this process is a narrow molecular weight distribution of the resulting product, but the color number is not reduced thereby.
U.S. Pat. No. 4,127,513 describes a process for minimizing cyclic oligomers in THF/alkylene oxide copolymers over acid-activated montmorillonites having an acidity of from 0.1 to 0.9 milliequivalent of H
+
per g; an improvement in color number is not mentioned here either.
U.S. Pat. No. 4,228,272 describes an improvement over U.S. Pat. No. 4,127,513 which is achieved by using an acid-activated montmorillonite having a pore volume of 0.4-0.8 cm
3
/g, a surface area of 220-260 m
2
/g and an average pore volume of 0.1-0.3 &mgr;m. However, the catalyst used, KO® from Südchemie, only improves the color number in the initial stages of the polymerization.
However, the known catalyst systems are not sufficiently active to conduct the process on an industrial scale, in particular when technical grade THF is used.
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 coupled with a lower polymer color number, since the economic viability of a heterogeneously catalyzed PTHF process is critically dependent on the productivity of the catalyst and 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 polymerizing tetrahydrofuran in the presence of at least one telogen and/or comonomer over an. acid-activated calcium montmorillonite as catalyst having a BET surface area of at least 300 m
2
/g, an acidity of at least 0.02 mmol/g at pK
a
<−3 and a pore volume of at least 0.40 cm
3
/g for pore sizes in the range from 30 to 200 Å.
The montmorillonites used according to the invention are clays, in particular members of the smectite family. In the process of the invention, naturally occurring or synthetic montmorillonites may be used. Preference is given to using natural calcium montmorillonites.
Montmorillonite catalysts are preferably activated in acid prior to use in the process of the invention. The activation can be carried out according to processes as described, for example, in DE-B-10 69 583 or EP-A-0 398 636. Various acids can be used for the acid activation, preference being given to the conventional mineral acids or to organic carboxylic acids. The acids are preferably selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, formic acid, acetic acid or citric acid. Particular preference is given to sulfuric acid and/or hydrochloric acid.
The acid activation is effected by suspending the powdered montmorillonite in the acid, the solids content of the suspension being preferably from 1 to 70% by weight, particularly preferably from 20 to 60% by weight, based on the total weight of the suspension. The acid concentration depends on the acid and the type of clay used. It may vary within wide limits and is preferably in the range from 2 to 100%. When using sulfuric acid and hydrochloric acid, a concentration of from 20 to 50% is preferred. The suspension is preferably reacted at from 30 to 120° C., particularly preferably from 50 to 110° C., preferably for from 0.5 to 24 hours, particularly preferably from 1 to 15 hours, with stirring. The acid-activated montmorillonite is then separated off, for example by filtration, subsequently washed with distilled or deionized water to remove adhering traces of acid and then dried or calcined. The montmorillonite catalysts are advantageously dried at ambient pressure and at from 80 to 2
Becker Rainer
Eller Karsten
Hesse Michael
Rütter Heinz
BASF - Aktiengesellschaft
Keil & Weinkauf
Lovering Richard D.
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