Process for manufacture of a porous polymer by use of a porogen

Details Process for manufacture of a porous polymer by use of a porogen Process for manufacture of a porous polymer by use of a porogen

1999-05-10

2000-05-09

Foelak, Morton

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

264 41, 523106, G02C 204, B29D 1100, C08J 928, B29C 6500

Patent

active

060605308

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for producing porous polymers, in particular to a process for polymerising or copolymerising monomers incorporating perfluoropolyethers to form porous polymers and to porous polymers comprising perfluoropolyethers obtained according to said process.
In many applications it has been found advantageous for polymers to be porous. The degree of porosity required depends on the application. For example, membrane filtration depends on the use of microporous polymers to effect separations of various materials. Also macroporous sheets of chemically resistant polymers find extensive use as cell dividers in cells for electrolysis or electricity storage.
Pores may be formed in the polymer during the process of manufacturing an article of the desired shape or may be formed in the article after manufacture. There are a variety of methods known in the art for the introduction of porosity into synthetic polymers, such as those described in WO 90/07575, WO 91/07687, U.S. Pat. No. 5,244,799, U.S. Pat. No. 5,238,613, U.S. Pat. No. 4,799,931. Some rely on a drilling or etching process after the polymer has been formed. Thus, high energy particles or electromagnetic radiation, such as that emitted from lasers, have been used as described in WO91/07687. These processes are generally labour intensive and time consuming.
Less commonly, the porosity may be an inherent property of the polymer and the porosity maintained as the polymer is formed into the desired shape for a particular application. It is particularly advantageous for the porosity to be introduced during the polymer forming steps. This is generally economical and, in appropriate cases, good control over the porosity and pore size can be achieved.
Polymers based on perfluoropolyethers, in general, have many unique and desirable properties. These include resistance to fouling by proteinaceous and other materials, outstanding flexibility, transparency, high resistance to temperature extremes, and exceptional chemical and oxidation resistance. These properties would make perfluoropolyether based polymers particularly suitable for a variety of applications and would be particularly suited for use as membranes if methods were available for the economic introduction of porosity. Indeed, there has been a long-felt need for membrane materials with the above attributes. Polytetrafluoroethylene-based (PTFE) membrane materials provide a partial solution to this need. However, unlike perfluoropolyether-based polymers, which can be readily cured and formed into articles by in-situ polymerisation, PTFE-based materials suffer from the disadvantage of being difficult to fabricate and manufacture into articles. In addition, stretching processes such as those described in U.S. Pat. No. 3,953,566 (Gore) give a somewhat limited range of size and shape of the porosities and are difficult to control.
Because of the properties mentioned above perfluoropolyether based polymers are highly desirable materials for contact lenses and other ophthalmic devices (U.S. Pat. No. 4,440,918, U.S. Pat. No. 4,818,801); if such materials could be made porous to allow transfer of tear fluids or nutrients their usefulness would be considerably enhanced.
Despite the obvious potential advantages of these materials, porous perfluoropolyether polymers have not previously been available.
In certain polymers porosity may be an interpenetrating network of holes, closed cells or a combination thereof. This may be achieved by polymerization in the presence of an insoluble material often referred to as a porogen. Subsequent leaching of the porogen gives rise to interstices throughout the formed polymer material. Sodium chloride is one such material that has been used. A disadvantage of this process is the difficulty of stabilising the suspension of porogen in the polymerisation mixture. Unstable suspensions can lead to an inhomogeneous and unacceptable product. In many cases, extensive optimisation of the viscosity of the system and the type of porogen is needed to obtain a s

REFERENCES:
patent: 4806291 (1989-02-01), Susa
patent: 4818801 (1989-04-01), Rice
patent: 4902456 (1990-02-01), Yen et al.

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