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
2001-02-20
2002-09-17
Truong, Duc (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...
C525S191000, C525S242000, C525S321000, C525S326100, C525S535000, C528S171000, C528S174000, C528S391000
Reexamination Certificate
active
06451921
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to block copolymers containing blocks of unsulfonated aromatic polyether sulfones and blocks of aromatic polyether sulfones sulfonated on the aromatics, as well as a process for the preparation thereof. In addition, the present invention pertains to membranes containing such block copolymers.
2. Discussion of Related Art
The use of synthetic polymers for membranes and separation processes based thereon has been known for a long time. In addition to typical fields of application, such as sea water desalination by means of reverse osmosis or the ultrafiltration of process waters from electric immersion painting for recovery of the lacquer, membrane processes in the fields of food technology, medicine, and pharmacy are becoming increasingly important. In the last-mentioned cases, membrane separation processes have the major advantage that the substances to be separated are not subjected to thermal load or indeed damaged at all.
In addition to the always necessary mechanical and thermal properties, polymers which are suitable for use as constituents and component parts for medical applications must also possess properties which are characteristic of medicine, such as
sterilizability in autoclaves
very good resistance, even to strong disinfectants
biocompatibility in contact with skin, tissue or blood.
Sterilizability is of essential importance when it comes to use as a membrane. Not least for safety reasons and on ecological grounds in that case steam sterilization is to be preferred over chemical sterilization through radiation, especially through gamma radiation.
Ordinarily, the steam sterilization takes place by means of the approximately 30-minute treatment of the membrane with superheated steam of >110° C. The criterion of steam sterilizability thus strongly reduces the number of potential polymers for membranes. For instance, membranes of polyacrylonitrile cannot be steam sterilized on principle, because exceeding the glass temperature of the polymer leads to the material or the membrane being irreversibly damaged. Polymers susceptible to hydrolysis, e.g., some polycarbonates and polyamides, likewise do not survive a superheated steam sterilization without being damaged.
Steam sterilizable membranes of, e.g., polyether imides, polyether sulfones or polyvinylidene fluoride are well-known.
Polyether sulfones fulfill the mechanical and thermal properties requirements and stand out as a result of an excellent resistance to chemicals.
A major drawback to membranes based on, e.g., polyether sulfone is the hydrophobicity of the membrane material, which excludes spontaneous wetting with aqueous media. Because of this it has to be prevented that the membrane dries out completely, or the membrane has to be treated with a hydrophilizing agent, such as glycerol, prior to being dried.
Hydrophilic membranes are remarkable for being wettable with water. A measure of wettability is the contact angle of a drop of water vis-a-vis the membrane surface. In the case of hydrophilic materials, this contact angle will always exceed 90 degrees. Phenomenologically, wetting of a dialysis membrane can also be inferred from the fact that a drop of water introduced onto the membrane surface will penetrate into the membrane after a short time.
A further substantial drawback to hydrophobic materials for use in membranes consists in that they often have a strong, nonspecific adsorption capacity. Hence when hydrophobic membranes are used, often a rapid, tightly adhering coverage of the membrane surface with preferably high-molecular weight solvent constituents takes place. This phenomenon known as fouling leads to a rapid deterioration of the membrane permeability. A subsequent treatment of the membrane with a hydrophilizing agent will not permanently prevent the fouling.
Proposals have been made for the use as membrane material of hydrophilic polymers/polymer systems said not to have the aforementioned drawbacks. Thus in German published application DE-OS 3 149 976, it is proposed that for the preparation of a hydrophilic membrane, use be made of a polymerizate mixture which in addition to polysulfone or polyamide contains at least 15 wt. % of polyvinyl pyrrolidone. For the hydrophilizing of, e.g., polyimide and polyether sulfone membranes, EP-A-0 228 072 claims the use of polyethylene glycol in amounts of 44 to 70 wt. %, calculated on the polymer solution.
The hydrophilizing of membranes by using large amounts of water-soluble polymers has the drawback, however, that the hydrophilicity of the membrane steadily declines when it is used in aqueous media, since the water-soluble polymer is washed out. This can lead to the membrane material regaining its original hydrophobicity and exhibiting the aforementioned negative secondary phenomena associated therewith.
The drawbacks can be avoided by the use of hydrophilic, yet water-insoluble polymers for the preparation of membranes. Thus in a series of patents, e.g., EP-A-0 182 506 and U.S. Pat. No. 3,855,122, the preparation of membranes from sulfonated polymers is claimed. However, the processes described there are suitable only for the preparation of flat membranes. The membranes have a high salt retention capacity and are primarily eligible for use in reverse osmosis.
DE-OS 3 149 976 proposes the preparation of aromatic polyether sulfones by sulfonation with the aid of a solution of sulfur trioxide in sulfuric acid, with the content of sulfur trioxide, calculated on the total amount of pure sulfuric acid present in the reaction mixture, being kept at a value of less than 6 wt. % during the entire period of sulfonation.
In this way the degree of sulfonation, i.e., the quotient of the total number of sulfonic acid groups in the polymer and the total number of repeating monomer units, should be easily controllable; however, it is not possible to set other than a random distribution of the sulfonic acid groups in the polymer.
However, for regulation of the biocompatibility, it is desirable when not only the total number of sulfonic acid groups in the polymer, but also their distribution in the polymer chain can be influenced. By the selective introduction of, e.g., domains with high and low degrees of sulfonation, the variational possibilities with respect to the functional polymer groups can be increased and thus, e.g., the hydrophilicity properties can be graded even more selectively.
Such block copolymers containing blocks of sulfonated and unsulfonated polyether sulfones are known, e.g., from JP 1009230. In this document, a block copolymer of polyether sulfone and sulfonated polyether sulfone is described which is prepared using &agr;,&agr;′-dichloro-p-xylene as coupling reagent and where the block transitions are made up of aliphatic groups, which may lead to inhomogeneities and, at worst, to weak points in the chain. Moreover, aliphatic groups may enter into unfavourable interactions with blood and for that reason their presence in, e.g., haemodialysis membranes is highly undesired.
Finally, EP-A-112724 describes a process for sulfonating polysulfones containing repeating units of the formula —Ph—SO
2
—Ph—O—, wherein the polysulfone is first of all suspended in a liquid halogenated hydrocarbon and then sulfonated with a sulfonating reagent, such as sulfur trioxide. According to EP-A-112724, the sulfonated product can resemble to a certain degree that of a block copolymer with alternating regions of highly sulfonated and unsulfonated chain sequences. The document does not pronounce on the length of the sulfonated and unsulfonated sequences, respectively. Moreover, EP-A-112724 does not disclose either whether and in which way these sequence lengths can be controlled. The document even leaves open whether in the described process it is actually block copolymers which are formed, since there is talk only of a resemblance to or the appearance of the existence of block copolymers. EP-A-112724 is consistently directed to the sulfonation of polysulfones, and not to a process for th
Höcker Hartwig
Keul Helmut
Weisse Hilmar
Membrana GmbH
Truong Duc
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