CA1315930C - Forming microporous polymeric articles by solvent extraction of one polymer - Google Patents

Abstract

Title: POLYMERIC ARTICLES AND METHODS OF MANUFACTURE THEREOF
Abstract Method for the preparation of an article from a blend of at least two molecularly compatible polymer, by treating the blend with a solvent which is a solvent for one of the polymers and a non-solvent for the other. The solvent can be re-moved while the article is restrained from undergoing substantial shrinkage, in which case a microporous article is ob-tained. Alternatively, the solvent can be removed while the article is permitted to shrink, In this case high shrinkage force (also referred to as recovery force) results which can be utilized to apply the article to a substrate. The final and intermedi-ate articles are novel. In a preferred embodiment, the invention provides a microporous article having an average pore size of about 0.005 microns to about 1 micron.

Description

~31~ 0 ~'qP 0 ~2 5 (~O~
MF.THOD OF MPKING ~ ~TCROPOROUS PRTTT.F~

This invention relates to a method of making a microporous polymeric article and to the resulting articles. In particular it relates to a method of making a microporous polymeric article from a blend comprising at least two polymers which are molecularly compatible, which involves treating the article with a solvent.

It is well known that most polymers are generally incompatible with each other. Most blends of two or more polymers contain the separate polymers as individual component domains or phases. Thus blends of what are termed compatible polymers generally are mechanically compatible only and exhibit properties which vary widely over the concentration range of the polymers. Such blends comprise a matrix polymer containing the other polymer as a dispersed or co-continuous phase. Such dispersed phases can be microscopic in size sometimes giving the resulting blend of multiple phases the appearance of being a single ~hase.
There are, however, a few pairs of polymers which are molecularly compatible, that is they form a molecularly dispersed mixture comprising a-singie amorphous phase when they are blended together. Not only do such blends not separate into their individual amorphous components, but they are also characterized by having a single glass transition ternperature (Tg). Mechanically compatible blends, on the other hand, exhibit two or more Tgls characteristic of the Tg~s of the individual components. By the term glass transition temperature is meant the temperature at which an amorphous polymer or the amorphous regions of a partially crystalline polymer changes to or from a hard and relatively brittle state to a more flexible or rubbery condition.
Measurement of glass transition temperatures of polymer systems is described, for example, in Ih~m~l aracteriza~ion Te~hniaues, Slade, et al., Marcel De~ker, Inc., New York (1970).

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As mentloned above, very few pol~rmeric blends are known wherein two or more polymers exhibit molecular compatibility. Reported in the literature are three basic classifications of compatible polymers represented by the followiny polymer pairs: poly(vinylidenefluoride) and poly~methyl methacrylate), poly(vinyl chloride) and poly(caprolactone), and poly(styrene) and poly-(phenyleneoxide). For examples of these type of compatible blends see Polymer Handbook, 2nd edition, Brandrup, et al.
page III 211-213.

Blends of polyetherimides and poly(aryl ethers) are described in U.S. Patent No. 4,293,670 to Robeson et al. The only specific blends reported in the patent are blends of a poly(aryl ether sulfone) and a poly(etherimide). Such blends exhibit mechanical compatibility with each blend having more than one glass transition temperature. Blends of a poly(etherimide) and a poly(aryl ether ketone) are discussed in general terms and no specific blend of a poly(aryl ether ketone) and a polyetherimide is reported. There is no mention that blends of these components would be molecularly compatible and therefore different from the poly(aryl ether sulfone~/polyetherimide blends specifically described.

Microporous articles prepared by blending one polymer with a pore forming additive which is then leached o.ut, generally have pore sizes considerably larger than the pore sizes of the articles of this invention. When a polymer is utilized as the pore forming component to be leached from the polymer system, it had been thought that the polymers used should be at least partially incompatible. This is taught, for example, in U.S. Patent No. 3,544,489 to Dowbenko, et al.
In the Dowbenko et al. patent, a composition comprising a thermosetting resin and a solvent extractable thermoplastic resin are applied to a substratej the thermosetting resin is ,, ~i .

,. . . .

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cured resulting in the formation of minute discrete particles of the thermoplastic resin in the thermoset resin matrix. The thermoplastic is then extracted using a suitable solvent. It is specifically stated by Dowbenko, et al that the polymers must be at least partially incompatible.

In U.S. Patent No. 3,375,208, Duddy teaches the formation of microporous materials by treating a thermoplastic resin composition with a solvent which comprises intimately mixing under heat and pressure a particulate thermoplastic resin which is insoluble in said solvent with a substantially incompatible particulate thermoplastic resin which is soluble in said solvent to soften the resin into a plasticized mass, shaping the mass and thereafter contacting the shaped mass with said solvent to remove substantially all of the soluble thermoplastic resin and thereby render the insoluble thermoplastic resin microporous. It is specifically stated in U.S. Patent No.
3,375,208 that it is the incompatibility of the resins and the intimate milling and blending thereof which results in a porous material having thread-like pores of capillary size.

In U.S. Patent No. ~,096,099 to Koyama, et al., a-porous film having fine cylindrical holes from 70 to 2000 A
in diameter is disclosed. The resin film is prepared by treating a film of an AB or ABA type copolymer to decompose the copolymer to remove one of the components. It is clear that the polymer components used to make the block copolymers are incompatible with each other. Thus, the patentees resort to the use of block copolymers to obtain a microporous article in the desired film followed by decomposition of the block copolymer.

EP-A-91669 discloses a process for producing a porous film-like or fibrous structure of an aromatic polyester, , .

.

~31~30 which comprises melt-molding a blend of the polyester and a low molecular weight compound, and extracting at least a major part of the low molecular weight compound.

It has now been discovered that useful articles can be prepared from a blend of at least two molecularly compatible polymers by treating the blend with a solvent which is a solvent for one of the polymers and a non-solvent for the other. The resulting article is microporous, if the solvent is removed while restraining the article from shrinking. If the article is not restrained from shrinking, the force of shrinkage (recovery force) can be utilized to apply the article to a substrate. Depending on the degree of shrinkage permitted, the article may or may not be microporous.

In one aspect, the invention provides a method of making a microporous article, which comprises:

(a~ forming a blend of two molecularly compatible polymers, the blend existing as a single amorphous phase;
.
(b) forming the blend into an article of desired configuration; and (c) extracting at least some of one of the polymers by treatment with a solvent in which one of the polymers is soluble, while controlling shrinkage of the article.

The polymer systems utilized in accordance with this invention are blends comprising two or more polymers which are molecularly compatible with each other. Relatively few blends of this type are known and as the science of polymer ~i ,,,S, . z ~ -.. .;~ :
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blends develops others may he discovered that are also within the scope of this invention. The process of making an article of this application is applicable to any blend o~ two or more molecularly compatible polymers. Current known molecularly compatible classes of polymers comprise the following representative pairs:

1~ poly(vinylidene fluorides) and poly(methyl methacrylates) and other poly(ester methacrylates);

2) poly(vinyl chlorides) and pGly(caprolactones);

3) poly(styrenes) and poly(phenylenes) oxide; and 4) polyetherimide and poly(aryl ether ketones) and the molecularly compatible co-polymers of the above polymers. The use, in this application, of the generic term for a polymer, e.g. polyvinylidene fluoride, covers homopolymers and copolymers of the specified polymer.
-Of particular interest are microporous articles formedfrom a blend of a poly(aryl ether ketone) and a poly(etherimide).

The term poly(aryl ether ketone) refers to polymers having the repeat unit of the formula -CO-Ar-CO-Ar'-wherein Ar and Ar' are aromatic moieties at least one of which containing a diaryl ether linkage forming part of the polymer backbone and wherein both Ar and Arl are covalently linked to the carbonyl groups through aromatic carbon atoms.

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Preferably, Ar and Ar' are independently selected frorn substituted and unsubstituted phenylene and substituted and unsubstituted polynuclear aromatic moieties. The term polynuclear aromatic moieties is used to mean aromatic moieties containing at least two aromatic rings. The rings can be fused, joined by a direct bond or by a linking group. Such linking groups include for example, carbonyl, ether sulfone, sulfide, amide, imide, azo, alkylene, perfluoroalkylene and the like. As mentioned above, at least one of Ar and Ar' contains a diaryl ether linkage.

The phenylene and polynuclear aromatic moieties can contain substituents on the aromatic rings. These substituents should not inhibit or otherwise interfere with the polymerization reaction to any significant extent. Such substituents include, for example, phenyl, halogen, nitro, cyano, alkyl, 2-alkynyl and the like.

Poly(aryl ether ketones) having the following repeat units ~the simplest repeat unit being designated for a given polymer) are preferred:

. ~~'C-~O~O~C~O'-{3 O~C~O~C~'OC-~O~O~C-.
.. ...... ~

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~O~C~C-Poly(aryl ether ketones) can be prepared by known methods of synthesis. Preferred poly(aryl ether ketones) can be prepared by Friedel-Crafts polymerization of a monomer system comprising:

I) (i) phosgene or an aromatic diacid dihalide together with (ii) a polynuclear aromatic comonomer - comprising:

(a) H-Ar"-O-Ar"-H

(b) H-(Ar -O)n-Ar"-H wherein n is 2 or (c) H-Ar"-O-Ar"-(CO-Ar"-O-Ar")m-H
~ wherein m is 1, 2 or 3 or (d) H-(Ar"-O)n-Ar"-CO-Ar"-(O-Ar")m-H
wherein m is 1, 2 or 3, and n is 2 or 3 or .

II): an acid halide of the formula:
: H-Ar"-O-[(Ar"-CO)p-(Ar'l-O)~-(Ar'l-CO) r~ k-Ar"-CO-Z wherein Z is halogen, : : k is 0, 1 or 2, p is 1 or 2, q is 0, 1 o. 2 and r is 0, 1 or 2;

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or III) an acid halide of the formula:
H-(Ar"-O)n-Ar"-Y
wherein n is 2 or 3 and Y is CO-Z or CO-Ar"-CO-Z where Z is halogen;

wherein each Ar" is independently selected from substituted or unsubstituted phenylene, and substituted and unsubstituted polynuclear aromatic moieties free of ketone carbonyl or ether oxygen groups, in the presence of a reaction medium comprising:

A) A Lewis acid in an amount of one equivalent per equivalent of carbonyl groups present, plus one equivalent per equivalent of Lewis base, plus an amount effective to act as a ~ catalyst for the polymerization;

B) a Lewis base in an amount from O to about 4 equivalents per equivalent of acid halide groups present in the monomer system;

and :
C~ a non-protic diluent in an amount from O to about 93% by weight, based on the weight of the totaI reaction mixture.

The a~romatic diacid dihalide employed is preferably a .~ dichloride or dibromide. Illustrative diacid dihalides which can~be used '~e~, for example ' ,~
~a' ~ " i , . . ' ''" .

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Cl-Q~C-a Cl-,C,J~ ~,C,-C~

Cl-C~C-C~

Cl-C-e30~0~ C-C-O

Cl-C~ Cl-C~C-~I
O O O

Cl-C~C-CI -o O
:
~: O
~ ~C-C~
. O o whelein a is~O 4.
:: : :
Illustrated polynuclear aromatic comonomers : wh~ich can~be~used with such diacid halides~are: :

a) H-Ar"-O-Ar"-H, which includes~ or example:

~ , : , __ .

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(b) H~(Ar"-O)n-Ar"-H, which include, for example:
~30~o-~
and ~o~~3 (c) H-Ar"-O-Ar"-(CO-Ar"-O-Ar")m-H, which includes, - for example:
~0~1~O~

and : , ;
(d) H-(Ar"~O~n-Ar"-CO-Ar"-(O-Ar")m-H which includes, for example:
~ ~ ~30~o~C~o~O~

Monomer systems II and III comprise an acid halide. (The term : acid halide is used herein to re~er to a monoacid monohalide.) In ~monomer system II, the acid halide is of the formula:

H-Ar"-O-[(Ar"-CO)p-(Ar"-O)q-(Ar"~CO) r] k-Ar"-CO-Z

Suoh nomers itR~ for example,~where k = O

,, : ',',"~,,, .... . ,. , ,,, -,, - ~ .

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¢~ ~C-C~ ~30~C-C~

~30~1Co-~ ~C-C~

and where k = 1 O
C~
o ~30~3c{~10 cl In monomer system III, the acid halide is of the formula H-(Ar"-O)n-Ar"-Y

Examples of such acid halides include O ~ ~ G-Cl O
and O
0~ C-C~

O

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It is to be understood that combinations of monomers can be employed. For example, one or more diacid dihalides can be used with one or more polynuclear aromatic comonomers as long as the correct stoichiometry i5 maintained. Further, one or more acid halides can be included. In addition monomers which contain other linkages such as those specified above, can be employed as long a one or more of the comonomers used contains at least one ether oxygen linkage. Such comonomers include for example: ~
~O~}SI~O~

and ~3_C~

which can be used as the sole comonomer with an ether containing diacid dihalide or with phosgene or any diacid dihalide when used in addition to a polynuclear aromatic comonomer as defined in I(ii)(a), I(ii)(b), I(ii)(C) or I(ii)(d). Similarly ~CH2~

can be used as a comonomer together with an ether-containing polynuclear aromatic acid halide or as an additional comonomer together with a monomer system as defined in I.

The monomer system can also contain up to about 30 mole % of a comonomer such as a sulfonyl chloride which polymerizes under Friedel-Crafts conditions to provide .

1315~30 - - 13 - Mæ0925 COM

ketone/sulfone copolymers.

Further details of thls process for producing poly~aryl 'u s. Pat~znt ~/ ~ 70~ ~0'~
ether ketones) can be found in U.S. ~a~ 8e~a~-*~.
,503,-filcd-3~-U~eb-~44.

The polyetherimides suitable for use in this invention are well known in the art and described in, for example, U.S.
Patent Nos. 3,847,867, 3,838,097 and 4,107,147. A preferred polyetherimide has the structùre:

~ ~Lo~c;~o~N--~ L

For example, one or more polyetherimides and one or more poly (aryl ether ketones) can be present in the blend to provide the desired physical properties of the final article. The polymers or co-polymers can be used in any of the various commercial grades which may vary in average molecular weights, molecular weight distributions and may contain minor amounts of comonomer residues.

Blends of molecularly compatible polymers are characterized in that they comprise a single amorphous phase although individual polymers may have both an amorphous portion and a crystalline portion where any crystalline portion may exist as a separate phase. One aspect of this degree o~ compatibility is that the amorphous phase exhibits a single glass transition temperature as defined above.

Blends suitable for use in preparing articles in , ~ ,. . .

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accordance wlth this invention comprise preferably frorn about 5 to about 95 weight percent of one of the molecularly compatible components preferably and from about 95 tO about 5 weigh~ percent of the second molecularly compatible component (either of the components can comprise more than one polymer as indicated above).

The polymer soluble in the solvent is referred to as the leachable component and the polymer removed by the process is referred to as the polymer leached out or extracted from the blend or article. The amount of leachable component utilized depends on the proposed use of the ~inal shaped article. Generally either polymer may be leached out as desired by selecting the appropriate solvent. In a preferred embodiment, the non-leached polymer should be in a partly crystalline state. This has been found to be particularly advantageous in preparing microporous articles of this invention to reduce or control shrinkage of the pore size of the article.

- The weight percent of the polymer component to be leached out is generally in the amount of from about 10% to about 90% and preferably from about 30% to about 70%, by weight based on the combined weight of the molecularly compatible polymers.

The blends can contain various additives in addition -to the molecularly compatible polymer components in order to give any desired property to the non-leached polymer.
For example, stabilizers, flame retardants, pigments, plasticizers~, and the like can be present. Other polymers may also be added to give a desired property.

The bIends can be prepared by any convenient technique. For example, the components can be mixed on a , ,'~:,' ~ ''~'''' ' .

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two-roll mlll, ln an lnternal mlxer such as a Brabender* mlx~r or Banbury* mlxer, or ln a twln-screw extruder. They may al80 be prepared from a solvent, or case from solutlon or the llke.
The shaped artlcle can be formed by known technlques de-pending on the de~ired shape. Fllms of the blend can be formed by extrusion or castlng, hollow fibers by melt splnning or the llke.
Other articles may be in~ectlon molded, compre~slon molded, pour molded, blow molded or the llke.
The shaped article ls treated wlth a solvent whlch should not substantlally dlssolve, extract or leach one of the compatlble components, l.e. lt must be a "non-solvent" for sald polymer. The non-solvent may, however, cause the non-leach~d component to swell whlle ln 3ald solvent. Further, the non-solvent may remove low molecular weight fractlons of the non-leached component. If lt ls deslrable that a particular solvent whlch is a solvent for both component~ be used, one of the component~ may be rendered non-soluble by crosslinklng the polymer u~lng known method such as irradlation or chemlcal curlng for example. It ls then necessary of course that the polymer lnvolved be crossllnkable. Treatment with the solvent preferably takes place by immerslng the shaped artlcle ln a bath contalnlng the solvent. The shaped artlcle ls lmmersed ln the bath for a perlod of time suf~lclent to remove the desired amount of the soluble polymer. Generally, the shaped article wlll be malntalned in contact wlth the solvent for about 1 mln. to about 8 hours or more, pre~erably from about 10 mln. to about 4 hours. Alterna-tlvely the artlcle may be suspended ln the vapors of the bolllng *Trade-Mark ..,",~
,~ .

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16 228g5-174 solvent.
The temperature at whlch th solvent treatment stsp i3 carried out depends on the solv~nt used and the polymer system utillzed. In most instances the solvent wlll be maintain~d at temperatures from about amblent temperature to about the boillng polnt of the solvent.
Those skllled in the art wlll readlly be able to select solvents whlch are non-solvents for at least one of the compatible polymer components. For example, methyl~ne chlorlde at amblent temperature could be used to leach polymethylmethacrylate (P~MA) from a polyvinylldlnefluorlde (PVF2)/polymethylmethacrylate blend or methylene chlorlde at 40-50C could be used to leach polyether-lmide from polyetherlmideipolyetherketone blends. Other examples -are polyetherlmide removed from poly(ether ketone) by dimethyl formamide at 100C and PMMA removed from PVF2 wlth refluxing toluene.
In preparln~ mlcroporous ar~lcles of thls inventlon, the proportion of soluble polymer component utillzed ln the blend ~nd the amount oE that polymer whlch ls leached out depends on the desired deyree of poroslty and other properties deslred of the ~lnal artlcle. Generally, lt ls desirable to leach out substan-tlally all o~ the soluble polymer resulting in an article havlng the physlcal and mechanical propertles of the non-soluble polymer.
In certaln clrcumstances, however, it may be advantageous to leach out a portlon only of the soluble polymer. Presence of the solu-ble polymer can, for example, result ln an artlcle of greater flexlbility, greater wettability or the llke than exhlblted by an article substantially free of the non-soluble polymer. Generally, ~b 16a 22885-174 however the flnal porou~ ~haped article should contaln no more than about 5 welght percent, based on the welght of the porous shaped article, of the soluble polymer.

.

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It is not necessary to remove the solvent to use the microporous articles of the invention. For example, a membrane article of the invention leached with dimethyl formamide (DME) may be placed directly in an aqueous solution for filtration purposes without removal of the solvent involved. Optionally however, the solvent i5 removed from the article. The removal can be accomplished by continu~ous removal e.g. distillation while the article is being treated by the solvent or subsequent to the completion of extraction by evaporation, vacuum, heat, filtration, freeze drying or any other technique known to one skilled in the art for removal of solvents.

Where the leaching solvent may weaken, cause to shrink or otherwise change the non-soluble polymer it may be desirable to "exchange" solvents in order to prevent such an occurrence. After treatment with the solvent, the treating solvent and dissolved pol~mer is removed from the shaped article by washing the shaped article with a second solvent.

The second solvent is miscible with the first and on washing with the second solvent the treating solvent and dissolved polymer is removed. The porous member can then be dried if desired to remove the second solvent. The selection of the second solvent depends on the first solvent used for leaching ~and the nature of the polymer component being leached from the shaped article).

Further, the result of any shrinkage when the solvent is optionally removed-is to reduce the porosity or pore size of the article. Since porosity of the article is the desired property sought in the preparation of the article, steps should be taken to eliminate or control shrinkage of the article. This can be achieved by clamping the article -- -- ..... .. . .... ..

---` 1315930 - 18 - MeO925 C~)M

during the porosity forming steps, replacing the leachiny solvent with one which is less plasticizing to the nonsoluble polymer (2s described above), annealing the article before or after removal of the solvent, or freeze drying of the solvent. In general the shrinkage of the article advantageously may be from about 10 to 30%.

Articles of the invention will have an average pore size preferably from about 5 x 10-9 to 1 x 10~6m ~0.005 microns to 1 micron) in diameter, more preferably from 1 x 10-8 to 1 x 10~7m (0.01 microns to 0.1 microns). However, the average pore size will be determined as desired, by for example, selection of the amount of polymer leached out, the contact time for the solvent, the solubility of the polymer in the solvent, the amount of polymer originally in the article, the above being readily ascertainable by one skilled in the art.

Membranes may be made from about 1 x 10-6 to about 5 x 10-4 m (about 1 micron to about 500 microns) thick and - preferably from about 1 x 10-5 to about 1 x 10~4m (about 10 to about~100 microns) thick. Films used in the manufacture of membranes of the invention refer to sheets or flat objects of optional width and length and a thickness of not greater than about 2.5 x 10-4 m ~250 microns). Membrane articles of the invention are desirable as they would not require mechanical support as, for exampIe, an inversion cast microfilter would.
oros;~ ry ,~ Mercury intrusion ~ is used to measure pore size as descr1bed by H.M.~Roatare under the title "A Review of Mercury Porisimetry" in "Advance Experimental techniques in Powder Metallurgy" (Perspect Powder Met. (19~0) pp 225-252 (Plenum Press)).

-, ' 131~g3~
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In preparation of recoverable shaped articles from molecularly compatible polymers in the manner described steps can be taken if desired to substartially control shrinkage of the article. This can be achieved by clamping the article during the porosity forming steps, replacing the leaching solvent with one which is less plasticising to the non-so]uble polymer (as described above for "exchange of solvents"~, annealing the article before or after removal of the solvent, or removing of the solvent by freeze drying.

PREPARATION OF FILM

The following materials were used to prepare microporous films.

'~l, Ultem D2000 (General Electric) - a high molecular weight poly(etherimide) which is amorphous and melt-- processable.

Vitrex PEEK~(ICI Americas) poly(carbonyl-p-phenylenep-oxy-phenylene-p-oxy-phenylene) - a high molecular weight poly(aryl ether ketone), which is semi-crystalline and melt processable.

The PEEK and Ultem resins were dried in air circulating ovens at 150C for a minimum of four hours before processing. Blends from 10 to 90 percent of each ~component by weight were then compounded on counter-rotating twinscrew extruder. The extrusion conditions were as follows.

acle~ fk ~ ~) ~; . .
. .

.. ... . . .. . . .. . .... .. .... . . . . . ... . ... . .. .. .. ... . .. . ...... . . . . . . . . ....
.

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Zone $1 - 330C
Zone ~2 - 340C
Zone ~3 - 350C
Zone #4 - 350C
Zone #5 - 360C
Zone #6 - 370C
Die - 380C
Screw Speed - 75 rpm A one-hole die was used on ~he extruder and the emerging strand was passed through a water bath and then pellitized.
.
Differential scanning calorimetry was used to : determine if molecular compatabilty had been achieved. Table #l lists the Tg's recorded on the ;DSC for various composition. The DSC's were recorded on the second heating scan at 20C/minute.
, : ~ ComDosition (~e'.~ht ~) Tg (C) 80 ; 20 164 ~ 70 30 169 : : 60 40 178 50. 50 189 40~ 60 : 195 ~30~ 70 : 204 :20;~ 80 211 ~:
~ ~220 :
O~ 100 222~

~ :The~mGlecular PEE~/Ultem blends were redried and then : ~ blown into film uslng a 1.9 x 10~3m (3/4") Brabender ; ' ~ : :

'.':'1.,, ~,, ~/, , 131~30 - 21 - MP0925 CO~

Extruder equipped with a circular blown film die. Four inch diameter tubes were formed with various wall thickness ranging from 1.27 x 10-5 to 2.54 x 10~4m (.0005"
to .010"). The films were transparent and had a slight yellow tint.

EXTRACTION

Sections were cut from the films and their weight recorded. Then they were placed into a resin kettle containing dimethyl formamide (DMF) which was fitted with a thermometer and condensor. The kettle was heated to 100C for two hours. The resulting films were white and opaque indicating they were porous. The weight changes of the films are listed below.
Initial Concent~ation % Weiaht Loss E~ / ~ Ul~8m 48~
58%

PRESERVATION OF PORES BY SO~VENT EXTRACTION

~ After forming the pores by extraction in DMF, a solvent exchange procedure was followed to minimize shrinkage. The first step was to transfer the solvent filled PEEK film into a nonplasticizing solvent such as ethanol. The sample was allowed to soak for an hour or untiI the ethanol displaced the DMF in the membrane. The film was then placed into water at which time it floated until the water displaced the ethanol, at which time the sample sank to the bottom. The water filled membrane was then vacuum dried with very little shrinkage occurring. For 1.27 x 10~4m ,, .. . .. .. .. . . . . . . .
:

1 31~930 (0.005") 40% PEEK / 60% Ultem samples that have been ex~racted using the procedure described above typical volume shrinkage was 42 to 51 percent. After using tne solvent exchange procedure described in this Example typical volume shrinkage was 8 to 12 percent.

~m~

PREPARATION OF FILM

The following materials were used to form polyvinylidene fluoride/(PVF2) polymethylmethacrylate (PMMA) blends.

A high molecular weight PMMA supplied by Rohm and Haas which is melt processable.

solef#1012 (Sol~ay Corp.) - a high molecular weight PVF2 which is melt processable.

- A 70% PVF2/30% PMMA blend was mixed in a ~rabender Plasticorder at 200CC. The molten polymer was removed from the mixing bowl and immediately compression molded into a ~lat slab at 200C and then cooled in a cooling press. The resulting slab was 5.08 x 10~4m (0.020") thick and was transparent.

2.54 x 10~2m (one inch) squares PVF2/PMMA were cut from the slabs. The~slabs were weighed and then extracted in both boiling under reflux methylene chloride at room temperature~and toluene. Weight losses ranged from 26 to 28 percent. The samples were opaque and white indicating porosity. ~ -::
P Y~IC~ ANA~YSIS
~:
~f JraJc~ 2rk .
~, ~ ." ,, . .. . , , ~ .. . . . . , . ... .. ... , . , , ., .. , . , .. , . , . . ... ... ,, . . . . . ~ .. ... .. .. ... ..
. . .

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A: Mercury intrusion porosimetry (MIP) was done on blends of 55% PEEK / 45% Ultem that were extracted by the rnethods detailed in Example 1. The MIP results confirmed a voided structure with an average pore size of 0.03 microns. The largest pores detected were 0.07 microns.

B: A Scanning F,lectron Microscope Study on the membranes formed in Examples 1 and 2 was undertaken.
Extracted 60% Ultem / 40% PEEK membranes exhibited a very fine porous structure visible above 20,000X. Pore sizes were measured at less than 0.1 microns. The extracted PVF2 "~_e ,` membrane from Example 2 had pores of about 0.1 microns in , ~ ,, s~owed ~o~eS
diameter. The surface structure ~M ~}~ of fairly even size and distribution.

USE QF A MEM~R~NE IN AN ELE~TRQCHE~IC~L CE~L

Diffusion of KOH through an extracted PEEK / Ultem membrane was examined. A cell was constructed with a - ~ resevoir of dilute potassium hydrooxide of pH 12 separated from a reservoir of dilute hydrochloric acid of pH 2 by an extracted 40% PEEK / 60% Ultem membrane. The pH change was monitored as a function of time on the acidic side using a pH meter. E~uilibrium was reached in approximately four hours. This shows the permeability of the material.

L~L~h~ FORCE MFASURFME~

PVF2/PMMA blends were prepared as described in Example 1. Strips of~the blend were measured and weighed, then placed into~refluxing toluene or methylene chloride for four hours to remove the PMMA.

Once the solvent had cooled to ambient temperature the ~31a9~0 - 24 - ~0925 COM

strips were removed and quickly clamped into the jaws of an Instron tensile testing machine. The jaw separation ~ras held constant and the force the sample applied was measured as a function of time. As the solvent evaporated the force increased and then leveled off to a constant value when the evaporation was completed. The following Table lists these results.

Average Weight Average Stress Solvent B.T.T.o~s (%) _ Generated (PSI) Toluene 110.7 28.6 710 Methylene Chloride 40.1 31.6 852 USF. OF THE ARTICLE TO COIJPT.E OBJECTS

, A cylinder with a diameter of 3.175 x 10~4m (0.125 `' inches) and length of 1.27 x 10~2m (0.50 inches) was machined from an injection molded bar of 60% PEEK / 40%
Ultem. A 3.048 x 10~5m (0.0012 inch) hole was bored longitudinally through the cylinder. This specimen was extracted in PMF for four hours then allowed to cool in the solvent.
~ ' ' Two 2 x 10~4m (200 micron) plastic clad silica fiber optics (Maxlight Corp.) were ~ and then 6.35 x 10~3m :,, ,.. ~.
(0.25 inches) of cladding was stripped from their ends. The extracted cylinder was then removed from the solvent and , the fibers were inserted into the opposite ends until the cladding touched the cylinder. as the~solvent evaparated the cylinder ~ onto the~fibersc aligning them and applying force to hold them;in place. a white light source o. Je -~nork "

- ` 1 3 ~
- 25 - ~0925 COM

was applied to one fiber end and could be detected visibly through the other end.

.

.
~ ~, :

:

:

,,, .. ., . . ..... _, . _ _ . . ~ .
".,.,~,. ~ .

`. `

Claims (15)

1. A method of making a microporous article, which comprises:
(a) forming a blend of two molecularly compatible polymers, the blend existing as a single amorphous phase;

(b) forming the blend into an article of desired configuration; and (c) extracting at least some of one of the polymers by treatment with a solvent in which only one of the polymers is soluble, while restricting shrinkage of the article.

2. A method as claimed in claim 1, in which the polymers are a polyvinylidene fluoride and a poly(methyl methacrylate).

3. A method as claimed in claim 1, in which the polymers are a polyvinylchloride and a polycaprolactone.

4. A method as claimed in claim 1, in which the polymers are a polystyrene and a poly(phenylene oxide).

5. A method as claimed in claim 1, in which the polymers are a polyetherimide and a poly(aryl ether ketone).

6. A method as claimed in claim 5, in which the poly(aryl ether ketone) has a repeat unit selected from the group consisting of:

7. A method as claimed in claim 5, in which the poly(ether-imide) has the formula:

8. A method as cIaimed in claim 1, in which the article is a membrane having a thickness of from about 10-6 to about 5 x 10-4 m (about 1 micron to about 500 microns).

9. A method as claimed in claim 1, in which the article is a membrane having a thickness of from about 10-5 to about 10-4 m (about 10 microns to about 100 microns).

10. A method as claimed in claim 1, in which the pore size of the membrane is from about 5 x 10-9 to about 10-6 m (about 0.005 microns to about 1 micron).

11. A method as claimed in claim 1, in which the pore size of the membrane is from about 5 x 10-8 to about 10-7 m about 0.01 microns to about 0.1 micron).

12. A method as claimed in claim 1, in which the polymer which is insoluble in the solvent is partially crystalline.

13. A method as claimed in claim 1, in which the polymer which is insoluble in the solvent is crosslinked.

14. A method as claimed in claim 1, in which restricting shrinkage of the article is achieved by restraining the article physically.

15. A method as claimed in claim 1, in which restricting shrinkage of the article is achieved by displacement of the solvent in which the extracted component has been dissolved by another solvent.