Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2001-03-30
2003-05-06
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S403000, C528S408000, C568S617000, C560S240000
Reexamination Certificate
active
06559278
ABSTRACT:
The present relation relates to a method for discontinuously or continuously producing tetrahydrofuran polymers by homopolymerization of tetrahydrofuran (THF) or copolymerization of tetrahydrofuran with alkyl-substituted tetrahydrofurans and/or 1,2-alkylene oxides using non-acidified or acid-activated and calcined aluminum silicate, whereby homopolymers and copolymers are obtained which have a particularly narrow molecular weight distribution, contain a negligible amount of oligomeric cyclic ether contaminants and have a low color index and acid number.
The catalytic synthesis of tetrahydrofuran polymers on aluminum silicates has been known for a long time. British patent No. 845 948 describes a process for copolymerizing tetrahydrofuran with alkylene oxides, in which the polymerization is carried out in the presence of compounds containing reactive hydrogen, using bleaching-earth catalysts. In this process, relatively large amounts of low-molecular products consisting predominantly of oligomeric cyclic ethers are obtained as byproducts. The molecular weight distribution of the tetrahydrofuran polymers is very broad. Depending on the average molecular weight, it can correspond to a heterogeneity quotient M
w
/M
n
of 3 to 4 for the molecular weight range from 1000 to 2000 (M
w
=weight-average molecular weight; M
n
=number-average molecular weight). The polymers are altogether yellowish in color, are for the most part not strictly bifunctional, and have a high acid number (usually >0.1 mg KOH/g) which makes them unsuitable for further processing to polyesters and polyurethanes. An improved process is described in the PCT application WO 96/23833. Here, the use of acid-treated, calcined synthetic amorphous aluminum silicates, kaolin or zeolites is suggested for homo- and copolymerizing tetrahydrofuran. The polymers obtained in this way, especially the copolymers, show a significant deviation of more than 1-2% from strict bifunctionality, and thus have only limited suitability as soft-segment diol components of, for example, spandex fibers. In particular, the activity of these catalysts is not constant, but fluctuates from batch to batch. Despite their low price, this poses a serious disadvantage with regard to the commercial use of these catalysts. A further disadvantage is that only extremely pure THF produces usable polymers.
The homopolymerization of tetrahydrofuran by means of oxonium ion catalysis became known as the result of fundamental work done by H. Meerwein et al. (Angew. Chemie 72, (1960), 927), and is dealt with comprehensively in the monograph “Polytetrahydrofuran” by P. Dreyfu&bgr;, Gordon and Breach Sc. Publishers, New York, London, Paris 1982. The German published examined application No. 1226560 describes the homopolymerization of tetrahydrofuran to polyoxybutylene glycol diacetates using montmorillonite catalysts. Powdered catalysts prove superior to granular ones (cf. column 4, lines 34-36). This process, however, results in products which, on account of their poor color, just to give one reason, require costly purification if they are to be processed further. These problems are described in the unexamined German laid open patent application No. 3935750.
Oligomeric cyclic ethers formed during the homo- and copolymerization reactions constitute undesirable impurities in the polymers, since they represent inert material and lower the quality of the final polymers made from polymeric glycols. Various suggestions for reducing their content have already been made. For example, it is suggested in the EP-A 6107 that the copolymers could be treated at an elevated temperature with an activated montmorillonite. In U.S. Pat. No. 4,127,513 it is suggested to use a specially activated montmorillonite as catalyst. Disadvandageously of this process are high color indices of the polymers, a relatively slow rate of polymerization and an oligomeric cyclic ether content which is still as high as 5 to 6 wt. %.
A further proposal for improving the copolymerization of alkylene oxides with tetrahydrofuran under the catalytic influence of activated bleaching earth is to be found in the U.S. Pat. No. 4,228,272, which describes the use of bleaching earths with a given specific pore volume, a defined catalytic surface area and a given pore diameter. The oligomer content of 4 wt. % (cf. column 5, lines 14-15) is, however, still too high to permit use of the copolymers for the production of polyurethanes, which have to satisfy special mechanical demands.
As is known, all processes for copolymerizing alkylene oxides with tetrahydrofuran in the presence of bleaching earths result in high-molecular-weight polymers with terminal hydroxyl groups. The latter are always contaminated with a variable proportion of macrocyclic ethers without hydroxyl groups. Hence it has also been suggested that the cyclic ethers should be removed by way of extraction with hydrocarbons, water or supercritical gases (U.S. Pat. Nos. 4,500,705, 4,251,654 and 4,306,056).
According to the teaching of the EP-A-104 462, moreover, the formation of cyclic ethers is for the most part an inevitable side reaction of the cationic ring opening polymerization, and is little influenced by the catalyst used. Accordingly, one would not have assumed that the choice of a specific catalyst would suppress the formation of cyclic ethers.
All catalysts described so far have the disadvantage that their life span depends heavily on the purity of the tetrahydrofuran used. In particular, their life span is reduced considerably if tetrahydrofuran is contaminated with even low concentrations, e.g., 2 to 10 ppm of carbonyl compounds such as esters, ketones or aldehydes. In the processes described until now, a poor-quality monomer of this kind, as it is obtained, for example, from the decarbonylation and subsequent hydrogenation of furfural or the hydrogenation of maleic anhydride, must always be subjected to tedious refining so that the catalyst's life span is not shortened.
The unexamined German laid open patent application 3 346 136 describes a process for the copolymerization of alkylene oxides and tetrahydrofuran, in which the formation of cyclic oligomeric ethers is prevented from exceeding 2 wt. % by polymerizing continuously in a reactor and adding to the circulating reaction mixture less than 30 wt. % of fresh feed comprising tetrahydrofuran and 1,2-alkylene oxide. The disadvantage of this process is that the resulting polymers have a broad molecular weight distribution, with a heterogeneity quotient M
w
/M
n
in excess of 4.
From the EP-A-O 104 609 it is known that diesters of polyoxybutylen oxy—alkylene glycol diester with a low content of oligomeric cyclic ethers are obtained if the copolymerization of tetrahydrofuran and a 1,2-alkylene oxide is carried out in the presence of carboxylic acid anhydride and bleaching earth with a water content of less than 3 wt. %. However, in this process too, the molecular weight distribution of the copolymers is not sufficiently narrow. Recently, two other methods of polymerizing with bleaching earths or amorphous aluminum silicates (U.S. Pat. Nos. 5,208,385 and 5,210,283) have been published but are not satisfactory either. Only very heterogeneous polymers are obtained, which have the further disadvantages of being colored and having acid numbers >0.1 mg KOH/g.
The EP-A-0 239 787 contains a proposal for narrowly limiting the molecular weight distribution and reducing the formation of oligomeric cyclic ethers by means of a discontinuous copolymerization on bleaching earth catalysts in the presence of telogenes containing reactive hydrogen and a constant but low concentration of 1,2-alkylene oxide.
Nevertheless, there is still a need to reduce the molecular weight distribution of both homo- and copolymers to a value lower than 1.3 to 2.5 for molecular weights between 1000 and 2000, for example to a value between 1.1 and 2.0, and to limit the formation of oligomeric cyclic ethers to less than 1 wt. %. Methods are needed whereby low-molecular polymers with an average molecular
Fulbright & Jaworski L.L.P.
Truong Duc
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