WO1998037940A1

WO1998037940A1 - Method of removing impurities from polymers utilizing facilitated ion exchange

Info

Publication number: WO1998037940A1
Application number: PCT/US1998/002540
Authority: WO
Inventors: Charles E. Forbes; Elizabeth E. Fernekess
Original assignee: Hoechst Celanese Corporation
Priority date: 1997-02-28
Filing date: 1998-02-10
Publication date: 1998-09-03
Also published as: AU6154298A

Abstract

A method for purifying polymers is disclosed and claimed. The method is generally directed to facilitated ion exchange wherein a complexing agent is added to a polymer solution prior to contacting the solution with an ion exchange resin.

Description

METHOD OF REMOVING IMPURITIES FROM POLYMERS UTILIZING FACILITATED ION EXCHANGE

Field of Invention

The present invention relates generally to a method for removing impurities from polymers and more specifically in preferred embodiments to a method of removing ionic impurities from polymers utilizing a complexing agent in combination with an ion exchange resin. In preferred embodiments, both an anionic and cationic ion exchange resin are employed.

Background of Invention Polymers and polymer resins substantially free of ionic impurities are required for a variety of uses, particularly in electronic and optical applications. Conventional means of monomer purification are typically employed to achieve such purity levels which generally require metal ion contents on the order of parts per billion (ppb) by weight. Such conventional methods include distillation, recrystallization, extraction and the like. These methods are expensive and do not always readily achieve the desired purity of the end product.

Ion exchange resins have been suggested for use in combination with complexing agents for purposes of preparing high purity metal halides. U. S. Patent No. 4,965,055 discloses a process wherein a complexing agent forms a species of a first charge with the desired metal halide as well as a species of a second charge with the undesired impurity, wherein the second charge is opposite the first charge. An ion exchange resin is then used to separate the two oppositely charged species. Unlike solutions of small molecules, high polymer solutions tend to be extremely viscous; in fact, conventional techniques useful in connection with dilute solutions of small molecules may be wholly inapplicable. It has been found in accordance with the present invention that a complexing agent greatly enhances the effectiveness of an ion exchange resin for removing metallic impurities from polymers, independently of the requirement of forming species of opposite charge as in the case with the '055 patent noted above.

Summary of Invention

There is provided in accordance with the present invention a method of purifying a polymer to remove ionic impurities. Generally speaking, the method of the present invention includes the steps of preparing a solution of the polymer to be purified, adding a complexing agent to the polymer solution and contacting the polymer/complexing agent solution with at least one ion exchange resin to remove ionic impurities. In particularly preferred embodiments, both an anionic and cationic ion exchange resin are used so as to immobilize both positively and negatively charged complexes from the polymer solution. The process of the present invention is based on the discovery that complexing agents can greatly facilitate ion exchange in polymer systems, as opposed to merely changing the selectivity of an ion exchange resin system. In other words, in accordance with the present invention, the efficiency of an ion exchange resin is greatly enhanced, not merely the selectivity toward a particular species.

Brief Description of Drawing The invention is described in detail with reference to the accompanying drawings in which: Fig. 1 is a schematic diagram illustrating the process of the present invention; and

Fig. 2 is characteristic plot of conductivity of a polymer solution vs. contact time with an ion exchange resin and complexing agent.

Detailed Description The foregoing process may be practiced in a variety of embodiments including with an additional step of filtering the solution to remove particulate contaminants. The filter employed is preferably a sheet-type microfilter with uniform holes less than about 1 micron in diameter, with less than 0.5 microns being preferred. Other types of media may be employed, preferably wherein their performance is substantially equivalent to the above, that is, wherein particles with diameters greater than the hole size are excluded. For purposes of convenience, the ability to exclude particles of above a certain diameter is referred to as the characteristic exclusion diameter of the filter in the accompanying claims. In other words, a filter made of one (1 ) micron fibers which excluded or removed all particles having a diameter above a micron or so is referred to herein as a filter with a characteristic exclusion diameter of one (1 ) micron. Likewise, a sheet-type filter with uniform pore size of 1 micron has a characteristic exclusion diameter of 1 micron.

The polymer solution may be prepared from polymer powder or may simply be a solution polymerization mixture which has not yet been precipitated to remove the polymer. Likewise, the inventive process as exemplified hereinafter includes the step of precipitating the filtered polymer in methanol or water, for example, as in reverse extraction. When using organic solvents, it is typically preferred to use macroporous, sometimes referred to as macroreticular ion exchange resins, since these resins generally perform better in organic solvents than do resins of the gel type, which depend upon swelling for their porosity. The preferred solvent will depend upon the polymer material to be purified, however, particularly useful solvents generally include dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide and mixtures of these solvents.

The exact mechanism of the invention is not known and may vary from system to system; however, it is clear that a complexing agent may greatly enhance the performance of an ion exchange resin to remove impurities. It is thus most preferred to use a complexing agent with both a cationic and anionic ion exchange resin present, since both positive and negatively charged ions will be removed. It is believed the complexing agent greatly enhances the ability of the solvent to solvate ions which may be immobilized on the polymeric material. Strong acid cationic ion exchange resins and strong or weak base anionic resins are believed particularly preferred for metallic impurities.

The amount of polymer present in the solution is generally from about 0.5 to about 50 weight percent, typically from about 1 to about 25 weight percent and preferably from about 2 to about 10 weight percent. The amount of complexing agent will depend on the nature of the complexing agent itself and the ratio and concentration of the impurity. As a starting point, one might employ from about 10 to about 3000 ppm (by weight) complexing agent or perhaps more typically from about 20 to about 1000 ppm complexing agent or perhaps preferably from about 50 to about 500 ppm complexing agent.

Relatively concentrated solution of polymer, for example, 20 weight percent polymer and more tend to have viscosities of 1000 centipoise and move at room temperature at shear rates of 75 sec^"1 or so. More dilute solutions are not quite so viscous, but still many times more viscous then the solvent alone. For example, a 12% solution of Hoechst Celanese's PBI polybenzimidazole polymer exhibits a viscosity of about 35 centipoise at room temperature at a shear rate of 8.6 sec^"1. The complexing agent may be nitrogen containing ring-like structures referred to as ligands in United States Patent No. 4,965,055. Suitable ligands may include phen [orthophenanthroline,

2,2'-dipyridyl (dpy)

CιoH₈N₂), bathophenanthroline (bathophen)

(C₂₄Hι₆N₂) or 3(2-pyridyl)-5,6-diphenyl-1 ,2,4-triazine,

C₂₀Hι₄N₄-(PDT)

bathophen and

Particularly suitable are conventional chelating agents such as ethylene diamine, ethylene diaminetetraacetate acetic acid (EDTA) and ethyleneglycol-bis (beta-amino-ethylether)-N,N-tetra acetic acid. So also salts of EDTA such as EDTA diammonium salt abbreviated herein as EDTA(NH₄)₂ may be employed. The complexing agent used in accordance with the present invention needs to be capable of forming a coordination compound with the ionic impurity to be removed, which coordination compound, in turn, has an affinity for the ion exchange resin. The process of the present invention is usually employed with any polymer material such as high polymers or resins used in photoresists of the Novalak type, for example. As used herein, high polymers generally are those with a degree of polymerization greater than about 20. The present invention is particularly useful for removing impurities from nitrogen or oxygen containing polymeric materials such as Novalaks, polyester, poly(hydroxystyrene), polyamides and the like and is believed to be particularly preferred for polymers containing a heterocycle such as polybenzoxazoles, polyimides and polybenzimidazoles. The foregoing lists are merely classes of resins, for example, any suitable polybenzimidazole, typically with a molecular weight between 1000 and 100,000 may be purified. These polymers may be prepared from an aromatic diacid and an aromatic tetramine. Such polymers include: poly- 2,2'-(m-phenylene)-5,5'-bibenzimidazole; poly-2,2'-(pyridylene-3",5")- bibenzimidazole; poly-2,2'-(furylene-2",5")-5,5^,-bibenzimidazole; poly-2,2'- (naphthalene-1",6")-5,5'-bibenzimidazole; poly-2,2'-(biphenylene-4",4")- 5,5'-bibenzimidazole; poly-2,2'-amylene)-5,6'-bibenzimidazole; poly-2,2'- octamethylene-5,5'-bibenzimidazole; poly-2,6'-(m-phenylene)diimidazo- benzene; poly-2'2-(m-phenylene)5,5'-di(benzimidazole)ether; poly-2'2'-(m- phenylene)5,5'-di(benzimidazole)sulfide; poly-2'2'-(m-phenylene)5,5'- (benzimidazole)sulfone; poly-2'2-(m-phenylene)5,5'-di(benzimidazole)- methane; poly-2'2"-(m-phenylene)5,5"-di(benzimidazole)-propane-2,2; and poly-2,2'-(m-phenylene)-5',5"-di(benzimidazole)-ethylene-1 ,2. The most preferred commercially available polybenzimidazole is poly^^'^m-phenylenej-δ.δ'-bibenzimidazole as characterized by the recurring monomeric unit:

This polymer is marketed by Hoechst Celanese as PBIJ polybenzimidazole polymer.

Polybenzimidazoles can also be prepared by autocondensation of at least one aromatic compound having a pair of amine substituents in an ortho position relative to each other and carboxylate ester group positioned upon an aromatic nucleus. Examples of such compounds are esters of diaminocarboxylic acids which include 2,4-diaminonaphthalene acid; 5, 6-diaminonaphthalene-1 -carboxylic acid; 5,6-diamino-napthalene- 2-carboxylic acid; 6, 7-diaminonaphthalene-1 -carboxylic acid; 6,7- diaminonaphthalene-2-carboxylic acid; and the like. A preferred compound is 4-phenoxycarbonyl-3',4'-diaminodophenyl ether:

The polymer obtained with 4-phenoxycarbonyl-3',4'- diaminodophenyl ether is poly-5-(4-phenyleneoxy)benzimidazole.

The solvents utilized to form polybenzimidazole polymer solution in connection with the examples herein of the present invention include those solvents which are commonly recognized as being capable of dissolving typical unsubstituted polybenzimidazole polymers. For instance, the solvents may be selected from those commonly utilized in the formation of polybenzimidazole dry spinning solutions including N,N- dimethylacetamide, N,N-dimethylformamide, dimethylsulfoxide, and N- methyl-2-pyrrolidone. The particularly preferred solvents are N,N- dimethylacetamide and N-methyl-2-pyrrolidone.

The following specific examples are provided for illustration purposes which are not intended to limit in any way the present invention, which is defined in the appended claims. The specific examples were performed on an apparatus shown schematically as Fig 1. Polymer solutions were prepared from 100 mesh powder of Hoechst Celanese's PBI polybenzimidazole polymer which is a polymer of tetraaminobiphenyl and isophthalic acid by dissolving the polymer in dimethylacetamide in stainless steel pressure containers at 288°C for 1.5 hours to provide a

7.5%) by weight polymer dope. Ion exchange beds were prepared by adding 5 grams of Amberlyst 15 (a strong-acid, macroporous cationic ion exchange resin, Rohm and Haas) followed by adding 5 grams of Amberlyst 21 (a strong-base, macroporous anionic ion exchange resin) to vessel 10 shown on Fig 1. The PBI solution 5 prepared as above was placed in vessel 20 and recirculated through line 30, and filter 40, and ion exchange bed 10 overnight. Filter 40 is a one micron glass fiber filter which removes all particles having a diameter of 1 micron or so.

After recirculation solution 5 is passed through a sheet-type polypropylene filter 50 with uniform pores of 0.2 microns and into a water or methanol bath 60 to precipitate the polymer, i.e., by a reverse extraction technique. The bath 60 may preferably contain EDTA(NH₄)₂. Comparative Example A.

An "as received" sample of Hoechst Celanese's 100 mesh PBI polybenzimidazole polymer was analyzed and found to have the following metals content (ppm): Cu 21

Cr 3 Ni 3 Fe 31 Na 51 Ca 19

Mg 2

Comparative Example B

An "as received" sample of Hoechst Celanese's 100 mesh PBI polybenzimidazole polymer was dissolved and treated in the apparatus of Fig 1 , using the general procedure described above, except that no ion exchange resin was employed and no chelating agent was used during recirculation. The resulting polymer was found to have the following metals content (ppm): Cu 11.9

Cr < 1.2 Ni < 1.2 Fe 2.9 Na 7.9 Ca 1.6

Mg < 1.2

Comparative Example C

An "as received" sample of Hoechst Celanese's 100 mesh PBI polybenzimidazole polymer was dissolved and treated in the apparatus of Fig 1 using the general procedure described above including using both anionic and cationic ion exchange resins (i.e., no chelating agent used in connection with recirculation). The resulting polymer had the following metals content (ppm): Cu 14

Cr < 0.6

Ni O.8

Fe 3

Na 0.8 Ca 3

Mg < 0.6

Comparative Example D

An "as received" sample of Hoechst Celanese's 100 mesh PBI polybenzimidazole polymer was dissolved and treated as described in

Example B, except that a small amount of EDTA(NH )₂ was added (i.e., no ion exchange resin was used.) The treated polymer had the following metals content (ppm): Cu 13 Cr < 1.0

Ni < 1.0 Fe 2.0 Na < 1.0 Mg 2.0 Ca 120

Example 1

Following the procedure of Example C above, PBI polybenzimidazole polymer was treated in accordance with the invention by adding a small amount of ethylenediamine during the step of dissolving the polymer followed by re-circulation overnight. The purified polymer had the following metals content (ppm):

Cu <1

Cr < 1

Ni < 1

Fe 2

Na 2

Ca 2

Mg < 1

Example 2

Following the procedure of Example C above, PBI polybenzimidazole polymer was treated in accordance with the invention by adding a small amount (100 ppm or so) of EDTA(NH₄)₂ after dissolution of the polymer and prior to re-circulation overnight. The purified polymer had the following metals content (ppm): Cu 0.4 Cr 0.9 Ni 0.3 Fe > 0.3

Na 3 Ca 2 Mg O.δ There is shown in Fig 2 a plot of conductivity vs. time for a PBI polymer solution being recirculated and treated in accordance with the present invention as in examples 1 and 2 above. The actual apparatus employed was as depicted in Fig 1 with a 1 ft³ (7.5 gallon) ion exchange resin (50:50, cationic:anionic) and a 55 gallon batch of polymer solution at a flow rate of 0.5 gal /minutes. Thus, one day actually involves approximately 14 minutes of treatment time for the solution, assuming plug flow through the bed.

As can be seen, the conductivity of the solution drops by a factor of 10 in about 14 minutes of treatment time, indicative of a ninety percent reduction in ionic impurities.

Claims

1. A method of purifying a polymeric material comprising the steps of:

(a) preparing a solution including a solvent and said polymeric material;

(b) adding a complexing agent in an amount effective to facilitate ion exchange processes when said solution is contacted with an ion exchange resin; and

(c) contacting said solution including the aforesaid solvent, polymeric material, and complexing agent with at least one ion exchange resin whereby the amount of ionic impurities present in the system is reduced.

2. The process according to claim 1 , wherein said process further includes the step of filtering said solution.

3. The process according to claim 1 , wherein the filter has substantially all of its openings of a characteristic exclusion diameter of less than above two microns.

4. The process according to claim 3, wherein said filter has substantially all of its openings of a characteristic diameter of less than about 0.5 microns.

5. The process according to claim 1 , further comprising the step of separating said polymeric material from said solution.

6. The process according to claim 5, wherein said step of separating said polymeric material from said solution comprises precipitating said polymer by contacting said solution with water.

7. The process according to claim 5, wherein said step of separating said polymeric material from said solution comprises precipitating said polymer by contacting said solution with methanol.

8. The process according to claim 1 , wherein said solvent is an organic solvent and said ion exchange resin is a macroporous ion exchange resin.

9. The process according to claim 8, wherein said organic solvent is selected from the group consisting of dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone and mixtures thereof.

10. The process according to claim 1 , wherein said ion exchange resin comprises a strong or weak acid cationic ion exchange resin.

11. The process according to claim 1 , wherein said ion exchange resin comprises a strong or weak base anionic ion exchange resin.

12. The process according to claim 1 , wherein said solution is from about 1 to about 25 weight percent polymer.

13. The process according to claim 1 , wherein said complexing agent is a chelating agent selected from the group consisting of ethylene diamine, ethylenediaminetetraacetic acid, ethyleneglycol-bis (beta-amino- ethyl ether)-N,N-tetraacetic acid, and salts thereof.

14. The process according to claim 13, wherein said chelating agent is selected from the group consisting of ethylene diamine and ethylenediaminetetraacetic acid and salts thereof.

15. The process according to claim 1 , wherein said complexing agent is added in an amount of from about 10 to about 1 % ppm based on the weight of solution.

16. The process according to claim 1 , wherein said polymeric material is a high polymer having a degree of polymerization greater than about 20.

17. The process according to claim 16, wherein said polymer is a nitrogen or oxygen containing polymer.

18. The process according to claim 17, wherein said polymer is a polymer containing a heterocycle.

19. The process according to claim 17, wherein said polymer is selected from the group consisting of polybenzimidazoles and polybenzoxazoles.

20. A method of purifying a polymeric material comprising the steps of:

(a) preparing a solution including a solvent and said polymer material;

(b) adding a complexing agent in an amount effective to facilitate ion exchange processes when said solution is contacted with an ion exchange resin;

(c) contacting said solution including the aforesaid solvent, polymeric material, and complexing agent with an anionic ion exchange resin; and

(d) contacting said solution including the aforesaid solvent, polymeric material and complexing agent with a cationic ion exchange resin.