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
1999-06-23
2001-04-10
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S094000, C525S316000, C524S505000, C523S106000
Reexamination Certificate
active
06214936
ABSTRACT:
The present invention relates to the use of microphase-separated polymer blends consisting of A-B-C triblockcopolymers having an elastomeric middle block B, and A′-C′ diblockcopolymers, for the preparation of permeable membranes. Furthermore, the invention relates to these membranes and also to their use for the separation of gas mixtures.
There has now become available a broad range of methods for the separation of mixtures of substances in fluid phase with the aid of membranes. For example, elektrolyte/water mixtures can be separated by means of reverse osmosis, dialysis, electrodialysis or membrane distillation, mixtures of organic substrate and water or of colloid and water by means of ultrafiltration, and mixtures of different organic substrates by means of pervaporation, it being necessary to use in each case membrane types or membrane materials that are compatible with the task to be performed (cf E. Staude, Membranen und Membranprozesse, VCH Verlagsgesellschaft, Weinheim, 1992, pp
1-7
).
In order to separate gases, particularly supercritical gases such as oxygen, carbon dioxide or hydrogen, from mixtures thereof, membranes composed of polymers having a high glass transition temperature T
g
, ie for example polyvinyl chloride, cellulose acetate or polysulfone, are frequently used. When these membranes are used, separation takes place under diffusion control, ie smaller particles show better penetrativeness.
If, on the other hand, volatile organic compounds or higher hydrocarbons such as propane or n-butane are to be separated selectively from eg naturally occurring gas or hydrogen, recourse is made to polymer materials having elastic properties such as cis-polyisoprene or polydimethylsiloxanes. That the volatile organic compounds are easier to separate than, say, supercritical gasses, is due to the higher solubility of the volatile organic compounds in the specified membrane material. On the other hand, it has been found that volatile organic compounds can also be selectively separated when use is made of membranes of poly(1-trimethyl-silyl-1-propyne), a material characterized by a T
g
above 250° C. (cf B. Freeman, J. Pinnau, TRIP, 1997, pages
167-173
).
All of the the described membrane materials are homopolymeric compounds.
Freeman and Pinnau (ibid, page 169) propose to effect optimization of the separating characteristics by changing the polymeric backbone of the homopolymer such that the torsional movements are minimized. This is usually accomplished by the inclusion of sterically demanding side branches. However, sterically protected monomers cannot be polymerized very efficiently and also tend, eg in the case of cationic or free-radical polymerizations, toward rearrangement reactions, as a result of which a non-uniform polymer backbone is formed, the structure of which cannot be predicted with any reliability. Membrane morphologies having suitable properties cannot be obtained or cannot be obtained as reproducible entities in this manner.
Homogenous polymer blends composed of polyetherimides, polyethersulfones or polyimides as the major component of the mixture and polyvinylpyrrolidone as the minor component, are described as being suitable membrane materials in Marcel Mulder, “Basic Principles of Membrane Technology”, Kluwer Academic Publishers, 1991, page 40, 41, but without going into structural features or special separation properties. A feature common to the specified components is that they show a high glass transition temperature of more than 170° C.
U. Breiner, Dissertation 1997, University of Mainz, chapter 9, describes binary mixtures of triblockcolymers comprising poly(styrene-block-butadiene-block-methyl methacrylate) and dibockcopolymers comprising poly(styrene-block-methyl methacrylate) and makes statements on the lamellar morphology of the specified polymer blend. However, no reference is made to possible fields of application of the mixtures obtained.
It would be desirable to be able to make use of membranes based on polymer blends for the separation of fluid mixtures, if said membranes could be adapted at moderate expense to each particular separation problem, and if they could be obtained in a simple manner with good reproducibility and showed a defined morphology.
It is thus an object of the present invention to provide a membrane composed of a polymeric ingredient, by means of which the permeability characteristics can be adjusted to solve different separation problems.
Accordingly, there has been found a method of using microphase-separated polymer blends, consisting of A-B-C triblockcopolymers and A′-C′ diblockcopolymers for the preparation of permeable membranes. We have also found these membranes and the use thereof for the separation of fluid mixtures.
Block A of the A-B-C triblockcopolymer used is substantially composed of vinylaromatic monomer units. Particularly suitable are compounds which comply to the general formula
R
1
and R
2
independently denote hydrogen, halogen or linear or branched C
1
-C
8
alkyl, m is an integer from 1 to 3. As examples of suitable compounds (I) there may be mentioned styrene, p-chlorostyrene, &agr;-methylstyrene, p-methylstyrene, vinyl toluene and p-tert-butylstyrene. Block A can also be composed of arbitrary mixtures of said compounds. Preferably however, block A is composed of only styrene as the monomer unit.
The average molecular weight of block A can be varied within wide limits. Suitable average molecular weights M
n
generally range from 2,000 to 120,000 and preferably from 5,000 to 70,000 g/mol.
Suitable A-B-C triblockcopolymers are generally compounds such as have an elastomeric middle block B, ie component B has as homopolymer or copolymer a glass transition temperature T
g
of less than 20° C., preferably less than 0° C. and more preferably less than −20° C. Theoretically, all olefinically unsaturated monomer units can be used for the preparation of block B, provided the criterion concerning the value of T
g
is satisfied. In addition, mixtures of olefinically unsaturated monomers are possible.
Preferably conjugate dienes are used as monomers for block B, where those containing from 4 to 16 carbon atoms are preferred. Particularly suitable are conjugate dienes containing from 4 to 8 carbon atoms. Not only linear but also cyclic conjugate dienes can be used. The said conjugate dienes can be substituted by alkyl groups, preferably C
1
-C
3
alkyl, particularly methyl.
As examples there may be mentioned 1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene and also conjugate hexadienes, preferably 1,3-hexadiene. Particularly suitable monomers for block B are 1,3-butadiene and 2-methyl-1,3-butadiene. If desired, the aforementioned compounds may be used in the form of arbitrary mixtures for the preparation of block B.
Block B of the A-B-C triblockcopolymer may also exist in hydrogenated or partially hydrogenated form. Of these blocks preference is given to a block B which comprises hydrogenated 1,3-butadiene units.
Hydrogenated blocks B generally include those blocks in which at least half of all possible double bonds originally present have been hydrogenated, ie the degree of hydrogenation is in the range of from 50 to 100%, preferably from 70 to 100% and more preferably from 90 to 100%.
The average molecular weight of block B can be varied within wide limits. It is usually adjusted such that the desired properties of the polymer blends and thus the corresponding desired properties of the membrane are obtained. The number-average molecular weight M
n
of block B can generally assume values ranging from 5,000 to 200,000 g/mol and preferably from 10,000 to 150,000 g/mol
Block C of the A-B-C triblockcopolymer is usually composed of C
1
-C
18
alkyl esters of (meth)acrylic acid or arbitrary mixtures of these compounds.
Examples of suitable acrylates are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, lauryl and stearyl acrylates. Preferably methyl acrylat
Breiner Ulrike
Goldacker Thorsten
Gottschalk Axel
Mehler Christof
Stadler Eric Paulino Pereira
Asinovsky Olga
Seidleck James J.
Stadler Eric Paulino Pereira
Stadler Marilena Martina Pereira
Stadler Wolfgang Matthias
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