US4775474A
Expired / Lapsed
US
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Membranes containing microporous structure
Assignee: Dow Chemical Co
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Filing: 1986-12-01
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Granted: 1988-10-04
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Expires: 2006-12-01
Abstract
Abstract Asymmetric membranes are prepared by treating a major surface of a glassy polymer composition to render the surface resistant to solvent crazing and then contacting the glassy polymer composition with a crazing solvent. The crazing solvent permanently deforms the glassy polymer composition by forming a microporous structure on the untreated surface. The treated surface becomes the dense, discriminating layer of the membrane which achieves desirable permeation selectivity. The methods of treatment are (1) crosslinking, (2) providing an agent which renders the surface resistant to crazing, and (3) providing an agent which reacts with the surface. Additionally, the glassy polymer composition can be crosslinked before or after it is crazed to increase the mechanical strength of the membrane.
Inventors
- 👤 Chieh-Chun Chau
- 👤 Charles E. Reineke
- 👤 Lu H. Tung
- 👤 Edward J. Kramer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 08:09
CPC Classifications
B; B01; B01D; B01D67/00; B01D67/0002; B01D67/0023; B01D69/00; B01D69/02; C; C08; C08J; C08J7/00; C08J7/02; B01D2323/00; B01D2323/30; B01D2323/38; B01D2323/385; B01D2325/00; B01D2325/02; B01D2325/022
Claims Analysis
Total Claims: 27
Claim 1
Independent Claim
75 words
A process for preparing an asymmetric membrane having at least one dense layer comprising the steps of (a) selectively treating a major surface of a nonporous, glassy polymer composition to render the surface resistant to solvent crazing; and then (b) contacting the glassy polymer composition with a solvent so as to craze at least a portion of the composition and thereby provide at least one microporous layer and to leave at least one dense layer.
Claim 2
Dependent Claim
75 words
A process for preparing an asymmetric membrane having at least one dense layer comprising the steps of (a) selectively treating a major surface of a nonporous, glassy polymer composition to render the surface resistant to solvent crazing; and then (b) contacting the glassy polymer composition with a solvent so as to craze at least a portion of the composition and thereby provide at least one microporous layer and to leave at least one dense layer.
Claim 3
Dependent Claim
21 words
The process recited in claim 1 wherein the surface of the glassy polymer composition is treated in step (a) by crosslinking.
Claim 4
Dependent Claim
35 words
The process recited in claim 1 wherein the surface of the glassy polymer composition is treated in step (a) with an agent which prevents the crazing solvent from directly contacting the surface of the composition.
Claim 5
Dependent Claim
52 words
The process recited in claim 1 wherein the surface of the glassy polymer composition is treated in step (a) with an agent that exhibits a high flux for components to which the polymer is permeable, yet is capable of protecting the treated surface of the composition from attack by the crazing solvent.
Claim 6
Dependent Claim
43 words
The process recited in claim 1 wherein the surface of the glassy polymer composition is treated in step (a) with an agent which is capable of diffusing into the composition to a limited depth to render the surface layer resistant to solvent crazing.
Claim 7
Dependent Claim
35 words
The process recited in claim 1 wherein the surface of the glassy polymer composition is treated in step (a) with an agent which reacts with the surface thereby imparting a polar character to the surface.
Claim 8
Dependent Claim
13 words
The process recited in claim 2 wherein the crosslinking is provided by irradiation.
Claim 9
Dependent Claim
26 words
The process recited in claim 3 wherein the glassy polymer composition is crosslinked to a degree effective to increase the physical strength of the asymmetric membrane.
Claim 10
Dependent Claim
26 words
The process recited in claim 4 wherein the glassy polymer composition is crosslinked to a degree effective to increase the physical strength of the asymmetric membrane.
Claim 11
Dependent Claim
26 words
The process recited in claim 5 wherein the glassy polymer composition is crosslinked to a degree effective to increase the physical strength of the asymmetric membrane.
Claim 12
Dependent Claim
26 words
The process recited in claim 6 wherein the glassy polymer composition is crosslinked to a degree effective to increase the physical strength of the asymmetric membrane.
Claim 13
Dependent Claim
24 words
The process recited in claim 1 wherein the dense layer ranges up to about 50 percent of the total thickness of the asymmetric membrane.
Claim 14
Dependent Claim
33 words
The process of claim 1 wherein the dense layer is a continuous layer in close proximity to a first major surface of the membrane, which was rendered resistant to crazing in step (a).
Claim 15
Dependent Claim
26 words
The process of claim 1 wherein the crazing solvent is selected from the group consisting of aliphatic hydrocarbons, the halocarbons, the aliphatic ethers and carbonyl-containing solvents.
Claim 16
Dependent Claim
29 words
The process of claim 1 wherein the glassy polymer composition is selected from the group consisting of polystyrene, acrylonitrile, butadiene styrene resins, styrene-acrylonitrile copolymers and styrene acrylic acid copolymers.
Claim 17
Dependent Claim
55 words
The process of claim 1 wherein the membrane achieves at least a twofold increase in permeation flux relative to the flux achieved by the glassy polymer composition prior to treatment, while maintaining a selectivity for oxygen to nitrogen of at least 90 percent of the selectivity achieved by the glassy polymer composition prior to treatment.
Claim 18
Dependent Claim
53 words
An asymmetric membrane made from a glassy polymer composition by the process of claim 1, which comprises at least one dense layer at a first major surface of the membrane, which was rendered resistant to crazing in step (a), and at least one microporous layer at a second major surface of the membrane.
Claim 19
Dependent Claim
27 words
The asymmetric membrane recited in claim 17 wherein the glassy polymer composition is crosslinked to a degree effective to increase the physical strength of the asymmetric membrane.
Claim 20
Dependent Claim
27 words
The asymmetric membrane recited in claim 17 wherein the dense layer ranges up to about 50 percent of the total thickness of the untreated glassy polymer composition.
Claim 21
Dependent Claim
19 words
The asymmetric membrane recited in claim 17 wherein the dense layer is in the form of a continuous layer.
Claim 22
Dependent Claim
34 words
The asymmetric membrane recited in claim 17 wherein the glassy polymer composition is selected from the group consisting of a polystyrene, an acrylonitrile, a butadiene-styrene resin, a styrene-acrylonitrile copolymer and a styrene-acrylic acid copolymer.
Claim 23
Dependent Claim
22 words
The asymmetric membrane recited in claim 17 wherein the dense layer has a thickness ranging from 0.1 μm to about 25 μm.
Claim 24
Dependent Claim
23 words
The asymmetric membrane recited in claim 17 wherein the glassy polymer composition has a thickness ranging from 5 μm to about 100 μm.
Claim 25
Dependent Claim
57 words
The asymmetric membrane recited in claim 17 wherein the membrane achieves at least a twofold increase in permeation flux relative to the flux achieved by the glassy polymer composition prior to crazing, while maintaining a selectivity for oxygen to nitrogen of at least 90 percent of the selectivity achieved by the glassy polymer composition prior to treatment.
Claim 26
Dependent Claim
21 words
The process recited in claim 3 further comprising removing the agent from the asymmetric membrane after the desired crazing is complete.
Claim 27
Dependent Claim
37 words
The process recited in claim 6 wherein the glassy polymer composition is selected from the group consisting of a polystyrene, a styrene-acrylonitrile copolymer, a polycarbonate, a polysulfone, and a polyether sulfone and the agent is sulfur trioxide.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-10-04 | 1992-04-04 | 1992-10-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-10-04 | 1996-04-04 | 1996-10-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-10-04 | 2000-04-04 | 2000-10-04 | $7700.00 | Window Closed / Lapsed |