60/154,764, filed September 20,1999, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION The present invention relates to methods for purification of aromatic polyethers, and more particularly to methods for purification of aromatic polyetherimides.

Various types of aromatic polyethers, particularly polyetherimides, polyethersulfones, polyetherketones, and polyetheretherketones have become important as engineering resins by reason of their excellent properties. These polymers are typically prepared by the reaction of salts of dihydroxyaromatic compounds, such as bisphenol A (BPA) disodium salt, with dinitroaromatic molecules or dihaloaromatic molecules. Examples of suitable dihaloaromatic molecules include bis (4-fluorophenyl) sulfone, bis (4-chlorophenyl) sulfone, and the analogous ketones and bisimides as illustrated by 1,3-bis [N- (4-chlorophthalimido)] benzene.

According to U. S. Pat. No. 5,229,482, the preparation of aromatic polyethers by displacement polymerization may be conducted in the presence of a relatively non- polar solvent, using a phase transfer catalyst which is substantially stable under the temperature conditions employed. Suitable catalysts include ionic species such as guanidinium salts. Suitable solvents disclosed therein include o-dichlorobenzene, dichlorotoluene, 1,2,4-trichlorobenzene and diphenyl sulfone.

It is desirable to isolate aromatic polyether from a reaction mixture free from contaminating species that may affect the polymer's final properties in typical applications. In a typical halide displacement polymerization process contaminating species often include alkali metal halide and other alkali metal salts, residual

monomer species, and residual catalyst species. For maximum efficiency of operation it is desirable to recover any solvent employed and other valuable compounds such as catalyst species, and to provide waste streams which do not contaminate the environment. In particular it is often desirable to recover alkali metal halide, especially sodium chloride, for recycle to a brine plant for production of sodium hydroxide and chlorine.

Many conventional techniques are used to purify polymer-containing organic solutions. For instance, extraction with water and settling by gravity in a mixer/settling tank have been used for removal of aqueous-soluble species. However, water extraction methods will not work when the water phase emulsifies with or does not phase separate efficiently from the organic phase. The particular case of polyethers in chlorinated aromatic hydrocarbon solvents often presents special difficulties when mixing with water and separating by settling. Depending upon such factors as polymer concentration and temperature, the organic solution may be particularly viscous making efficient washing with an aqueous phase difficult.

Variations in either temperature of operation in the range of about 20-180°C or in polymer concentration may promote settling due to density differences, but the presence of surface-active functional groups on the polymer may still promote emulsification, particularly the presence of ionic end-groups such as phenoxide and/or carboxylate left uncapped from the polymerization process. Another constraint is that the time for separation of the aqueous and organic phases must be fast, preferably on the order of minutes, so that separation rates do not slow down production. A method is needed that minimizes emulsification and is relatively fast for phase separation of the water and organic phases.

Dry filtration via filters or membranes has also been employed for the removal of relatively large suspended solids from polymer-containing organic solutions. The advantage is that no process water is needed, but the disadvantage is that the filter type has to be chosen carefully to avoid a high pressure drop as the solids cake builds.

Filtration is not feasible if the solid particles plug, blind, or go through the porous

filter media. Easy back flushing of the filter is also required for fast turn-around and repeated use. Alkali metal halides, such as sodium chloride, are typically insoluble in organic solvents such as chlorinated aromatic hydrocarbons, but such halides may be present as small suspended solid crystals that are difficult to remove by standard filtration methods. Furthermore, residual monomer species such as alkali metal salts of monomer or complexes of catalyst and monomer may also be present which often cannot be efficiently removed by filtration alone.

Because of the unique separation problems involved, new methods are needed for efficiently separating aromatic polyether products from contaminating species in chlorinated aromatic hydrocarbons. Methods are also required for recycling the solvent and for recovering useful catalyst and alkali metal halide species from any final waste stream.

BRIEF SUMMARY OF THE INVENTION After careful study the present inventors have discovered methods for purifying aromatic polyethers prepared in water-immiscible chlorinated aromatic hydrocarbons. These new methods also provide efficient recovery of solvent, alkali metal halide, and valuable catalyst species.

In one of its aspects the present invention provides a method for purifying a mixture comprising (i) an aromatic polyether reaction product made by a halide displacement polymerization process, (ii) a catalyst, (iii) an alkali metal halide, and (iv) a substantially water-immiscible organic solvent with boiling point at atmospheric pressure of greater than 110°C and a density ratio to water of greater than 1.1: 1 at 20-25°C, comprising the steps of: (a) quenching the reaction mixture with acid; and (b) extracting the organic solution at least once with water.

In another of its aspects the present invention provides a method for purifying a mixture comprising (i) an aromatic polyether reaction product made by a halide displacement polymerization process, (ii) a catalyst, (iii) an alkali metal halide, and.

(iv) a substantially water-immiscible organic solvent with boiling point at atmospheric pressure of greater than 110°C and a density ratio to water of greater than 1.1: 1 at 20-25°C, comprising the steps of: (a) filtering the reaction mixture at least once; (b) quenching the reaction mixture with acid; and (c) extracting the organic solution at least once with water.

In still another of its aspects the present invention provides a method for purifying a mixture comprising (i) an aromatic polyether reaction product made by a halide displacement polymerization process, (ii) a catalyst, (iii) an alkali metal halide, and (iv) a substantially water-immiscible organic solvent with boiling point at atmospheric pressure of greater than 110°C and a density ratio to water of greater than 1.1: 1 at 20-25°C, comprising: at least one filtration step, and at least one ion exchange step.

In still another of its aspects the present invention provides a method for purifying a mixture comprising (i) an aromatic polyether reaction product made by a halide displacement polymerization process, (ii) a catalyst, (iii) an alkali metal halide, and (iv) a substantially water-immiscible organic solvent with boiling point at atmospheric pressure of greater than 110°C and a density ratio to water of greater than 1.1: 1 at 20-25°C, comprising the steps of : (a) providing 0.5-5.0 volume % water to the reaction mixture; (b) heating to a temperature in a range between about 110°C and about 180°C at atmospheric pressure, wherein a portion of alkali metal halide is in a form that can be filtered following the application of heat; and

(c) filtering the reaction mixture at least once.

DETAILED DESCRIPTION OF THE INVENTION The polyethers of the present invention are typically derived from combining at least one dihydroxy-substituted aromatic hydrocarbon moiety and at least one substituted aromatic compound of the formula (I) Z (A'X) 2 wherein Z is an activating radical, A'is an aromatic radical and X'is fluoro, chloro, bromo, or nitro, in the presence of a catalytically active amount of a phase transfer catalyst. In one suitable procedure at least one alkali metal salt of the at least one dihydroxy-substituted aromatic hydrocarbon is combined with the at least one substituted aromatic compound of generic formula (I). The alkali metal salts of dihydroxy-substituted aromatic hydrocarbons which are employed are typically sodium or potassium salts. Sodium salts are frequently preferred by reason of their availability and relatively low cost. Said salt may be employed in anhydrous form.

However, in certain instances the employment of a hydrate, such as the hexahydrate of the bisphenol A sodium salt, may be advantageous provided water of hydration is removed before the substituted aromatic compound is introduced.

Suitable dihydroxy-substituted aromatic hydrocarbons include those having the formula (II) HO-A'-OH wherein A2 is a divalent aromatic hydrocarbon radical. Suitable A2 radicals include m- phenylene, p-phenylene, 4,4'-biphenylene, 4,4'-bi (3,5-dimethyl) phenylene, 2,2-bis (4- phenylene) propane and similar radicals such as those which correspond to the dihydroxy-substituted aromatic hydrocarbons disclosed by name or formula (generic or specific) in U. S. Pat. No. 4,217,438.

The A2 radical preferably has the formula

(III)-A'-Y-A4-, wherein each of A3 and A4 is a monocyclic divalent aromatic hydrocarbon radical and Y is a bridging hydrocarbon radical in which one or two atoms separate A3 from A4.

The free valence bonds in formula III are usually in the meta or para positions of A3 and A4 in relation to Y. Compounds in which A2 has formula III are bisphenols, and for the sake of brevity the term"bisphenol"is sometimes used herein to designate the dihydroxy-substituted aromatic hydrocarbons; it should be understood, however, that non-bisphenol compounds of this type may also be employed as appropriate.

In formula III, the A'and A4 values may be unsubstituted phenylene, or halo or hydrocarbon-substituted derivatives thereof, illustrative substituents (one or more) being alkyl, alkenyl, bromo or chloro. Unsubstituted phenylene radicals are preferred.

Both A'and A4 are preferably p-phenylene, although both may be o-or m-phenylene or one o-or m-phenylene and the other p-phenylene.

The bridging radical, Y, is one in which one or two atoms, preferably one, separate A'from A4. Illustrative radicals of this type are methylene, cyclohexylmethylene, 2- [2.2.1]-bicycloheptylmethylene, ethylene, isopropylidene, neopentylidene, cyclohexylidene, cyclopentadecylidene, cyclododecylidene and adamantylidene; gem-alkylene (alkylidene) radicals are preferred. Also included, however, are unsaturated radicals.

Also included among suitable dihydroxy-substituted aromatic hydrocarbons are the 2,2,2', 2'-tetrahydro-l, l'-spirobi [lH-indene] diols having formula IV:

wherein each R'is independently selected from monovalent hydrocarbon radicals and halogen radicals; each R2, R3, R4, and R5 is independently C, 6 alkyl; each R6 and R7 is independently H or C, 6 alkyl; and each n is independently selected from positive integers having a value of from 0 to 3 inclusive. A preferred 2,2,2', 2'-tetrahydro-l, l'- spirobi [1H-indene]-diol is 2,2,2', 2'-tetrahydro-3,3,3', 3'-tetramethyl-1,1'-spirobi [IH- indene]-6,6'-diol.

Some preferred examples of dihydric phenols of formula II include 6-hydroxy- 1- (4'-hydroxyphenyl)-1,3,3-trimethylindane, 5- trimethylcyclohexylidene) diphenol; 1,1-bis (4-hydroxy-3-methylphenyl) cyclohexane; 2,2-bis (4-hydroxyphenyl) propane (commonly known as bisphenol-A); 2,2-bis (4- hydroxy-3,5-dimethylphenyl) propane; 2,2-bis (4-hydroxy-3-methylphenyl) propane; 2,2-bis (4-hydroxy-3-ethylphenyl) propane; 2,2-bis (4-hydroxy-3- isopropylphenyl) propane; 2,4'-dihyroxydiphenylmethane; bis (2- hydroxyphenyl) methane; bis (4-hydroxy-phenyl) methane; bis (4-hydroxy-5- nitrophenyl) methane; bis (4-hydroxy-2,6-dimethyl-3-methoxyphenyl) methane; 1,1- bis (4-hydroxyphenyl) ethane; l, 1-bis (4-hydroxy-2-chlorophenyl) ethane; 2,2-bis (3- phenyl-4-hydroxyphenyl)-propane; bis (4-hydroxyphenyl) cyclohexylmethane; 2,2- bis (4-hydroxyphenyl)-1-phenylpropane; resorcinol; C, 3 alkyl-substituted resorcinols.

For reasons of availability and particular suitability for the purposes of this invention, the preferred dihydric phenol is bisphenol A in which the radical of formula III is the 2,2-bis (4-phenylene) propane radical and in which Y is isopropylidene and A'and A4 are each p-phenylene.

The substituted aromatic compounds of formula I which are employed in the present invention contain an aromatic radical A'and an activating radical Z. The A' radical is normally a di-or polyvalent C6, 0 radical, preferably monocyclic and preferably free from electron-withdrawing substituents other than Z. Unsubstituted C6 aromatic radicals are especially preferred for the A'radical.

The radical Z is one which activates a leaving group X on an aromatic radical for displacement by alkali metal salts of dihydroxy-substituted aromatic hydrocarbons. The Z radical is usually an electron-withdrawing group, which may be di-or polyvalent to correspond with the valence of A'. Illustrative examples of divalent radicals include carbonyl, carbonylbis (arylene), sulfone, bis (arylene) sulfone, benzo-1,2-diazine and azoxy. Illustrative examples of the moiety-A'-Z-A'- include bis (arylene) sulfone, bis (arylene) ketone, tris (arylene) bis (sulfone), tris (arylene) bis (ketone), bis (arylene) benzo-1,2-diazine or bis (arylene) azoxy radical and especially those in which A'is p-phenylene.

Also included are compounds in which-A'-Z-A'-is a bisimide radical, illustrated by those of the formula wherein R8 is a substituted or unsubstituted C6 20 divalent aromatic hydrocarbon radical, a C2 22 alkylene or cycloalkylene radical, or a C2 8 bis (alkylene- terminated) polydiorganosiloxane radical.

In one embodiment of the invention R8 is derived from a diamine selected from the group consisting of aliphatic, aromatic, and heterocyclic diamines.

Exemplary aliphatic moieties include, but are not limited to, straight-chain-, branched-, and cycloalkyl radicals, and their substituted derivatives. Straight-chain

and branched alkyl radicals are typically those containing from 2 to 22 carbon atoms, and include as illustrative non-limiting examples ethyl, propyl, butyl, neopentyl, hexyl, dodecyl. Cycloalkyl radicals are typically those containing from 3 to 12 ring carbon atoms. Some illustrative non-limiting examples of cycloalkyl radicals include cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, and cycloheptyl.

The two amino groups in diamine-derived aliphatic moieties are preferably each separated from each other by at least two and most preferably by at least three carbon atoms. In especially preferred embodiments for diamines, the two amino groups are in the alpha, omega positions of a straight-chain or branched alkyl radical, or their substituted derivatives; or in the 1,4-positions of a cycloalkyl radical or its substituted derivatives. Preferred substituents for said aliphatic moieties include one or more halogen groups, preferably fluoro, chloro, or bromo, or mixtures thereof ; or one or more aryl groups, preferably phenyl groups, alkyl-or halogen-substituted phenyl groups, or mixtures thereof. Most preferably substituents for aliphatic moieties, when present, are chloro or unsubstituted phenyl.

Aromatic moieties suitable for R8 in formula V include, but are not limited to, monocyclic, polycyclic and fused aromatic compounds having from 6 to 20, and preferably from 6 to 18 ring carbon atoms, and their substituted derivatives.

Polycyclic aromatic moieties may be directly linked (such as, for example, biphenyl) or may be separated by 1 or 2 atoms comprising linking moieties as in formula VI in which Q is

or a covalent bond. Representative linking moieties may also include phosphoryl, S, and C, 6 aliphatic, such as isopropylidene and methylene. Illustrative non-limiting examples of aromatic moieties include phenyl, biphenyl, naphthyl, bis (phenyl) methane, bis (phenyl)-2,2-propane, and their substituted derivatives.

Preferred substituents include one or more halogen groups, preferably fluoro, chloro, or bromo, or mixtures thereof; or one or more straight-chain-, branched-, or cycloalkyl groups having from 1 to 22 carbon atoms, preferably methyl, ethyl, propyl, isopropyl, tert-butyl, or mixtures thereof. Most preferably, substituents for aromatic moieties, when present, are at least one of chloro, methyl, ethyl or mixtures thereof.

The two amino groups in diamine-derived aromatic moieties are preferably separated by at least two and most preferably by at least three ring carbon atoms.

When the amino group or groups are located in different aromatic rings of a polycyclic aromatic moiety, they are preferably separated from the direct linkage or from the linking moiety between any two aromatic rings by at least two and most preferably by at least three ring carbon atoms. Especially preferred diamines for the embodiments of the present invention include meta-phenylenediamine; para- phenylenediamine; mixtures of meta-and para-phenylenediamine; isomeric 2-methyl- and 5-methyl-4,6-diethyl- 1, 3-phenylenediamines or their mixtures; bis (4- diaminophenyl)-2,2-propane; and bis (2-chloro-4-amino-3,5-diethylphenyl) methane.

Heterocyclic moieties suitable for R8 in formula V include, but are not limited to, monocyclic, polycyclic and fused heterocyclic compounds having from 3 to 30, preferably from 5 to 13 ring carbon atoms, and 1 to 4 ring heteroatoms. The ring heteroatoms include, but are not limited to, oxygen, nitrogen, sulfur, or combinations thereof. Preferably, ring heteroatoms are nitrogen. Polycyclic heterocyclic moieties may be directly linked (such as, for example, bipyridyl) or may be separated by 1 or 2 atoms comprising linking moieties. Representative linking moieties include, but are not limited to, carbonyl, phosphoryl, O, S, SO2, C, 6 aliphatic, such as isopropylidene and methylene.

The two amino groups in diamine-derived heterocyclic moieties are preferably

separated by at least two and most preferably by at least three ring atoms. When the amino group or groups are located in different heterocyclic rings of a polycyclic heterocyclic moiety, they are preferably separated from the direct linkage or from the linking moiety between any two heterocyclic rings by at least two and most preferably by at least three ring atoms. Exemplary heterocyclic moieties include, but are not limited to, furyl, pyridyl, bipyridyl, pyrryl, pyrazinyl, pyrimidyl, pyrazolyl, thiazyl, thienyl, bithienyl, and quinolyl.

Most often, R8 is at least one of m-phenylene, p-phenylene, 4,4'- oxybis (phenylene) or Polyvalent Z radicals include those in which Z together with A'form part of a fused ring system such as benzimidazole, benzoxazole, quinoxaline or benzofuran.

Also present in the substituted aromatic compound of formula I are two displaceable X'radicals which may be fluoro, chloro, bromo, or nitro. In most instances, fluoro and especially chloro atoms are preferred by reason of the relative availability and effectiveness of the compounds containing them. The relative positions of the two X'radicals on two aromatic rings are such that they are activated for displacement by alkali metal salts of dihydroxy-substituted aromatic hydrocarbons. The two X'radicals are preferably each in the para position or each in the meta position or one substituent is in the para position and one in the meta position relative to the an activating group Z on an aromatic ring (or relative to a second aromatic group attached to an activating group Z on an aromatic ring).

Preferred substituted aromatic compounds of formula I include but are not limited to bis (4-fluorophenyl) sulfone and the corresponding chloro compound; bis (4- fluorophenyl) ketone and the corresponding chloro compound; and 1,3- and 1,4-

bis [N- (4-fluorophthalimido)] benzene, and [N- (3- fluorophthalimido)] benzene; and 4,4'-bis [N- (4-fluorophthalimido)] phenyl ether, and 4,4'-bis [N- (3-fluorophthalimido)] phenyl ether; and the corresponding chloro and bromo compounds, especially at least one of 1,3-bis [N- (4- chlorophthalimido)] benzene, 1,4-bis [N- (4-chlorophthalimido)] benzene, 1,3-bis [N- (3- chlorophthalimido)] benzene, 1,4-bis [N- (3-chlorophthalimido)] benzene, 1- [N- (4- chlorophthalimido)]-3- [N- (3-chlorophthalimido) benzene, or 1- [N- (4- chlorophthalimido)]-4- [N- (3-chlorophthalimido) benzene.

Also present in the reaction mixture is at least one phase transfer catalyst, preferably one which is substantially stable at the temperatures employed; i. e., in the range of about 125-250°C. Various types of phase transfer catalysts may be employed for this purpose. They include quaternary phosphonium salts of the type disclosed in U. S. Pat. No. 4,273,712, N-alkyl-4-dialkylaminopyridinium salts of the type disclosed in U. S. Pat. No. 4,460,778 and 4,595,760, and guanidinium salts of the type disclosed in the aforementioned U. S. Pat. No. 5,229,482. Said patents are incorporated by reference herein. The preferred phase transfer catalysts, by reason of their exceptional stability at high temperatures and their effectiveness to produce high molecular weight aromatic polyether polymers in high yield are the hexaalkylguanidinium and alpha, omega-bis (pentaalkylguanidinium) alkane salts, particularly the chloride salts. A preferred catalyst is hexaethylguanidinium chloride.

At least one substantially water-immiscible organic solvent may also be present in the reaction mixture. Said at least one solvent may completely or at least partially dissolve reaction ingredients. Within the context of the present invention suitable solvents are those which have with a boiling point at atmospheric pressure of greater than 110°C (preferably greater than about 125°C) and a density which is in a ratio of greater than 1.1: 1, preferably greater than 1.15: 1, and more preferably greater than 1.2: 1 compared to the density of water at 20-25°C (which is 0.997 grams per cubic centimeter). Substantially water-immiscible means that the organic solvent dissolves to the extent of less than about 10 wt. % and preferably less than about 5

wt. % in water. Preferred solvents are aromatic hydrocarbons, and particularly halogenated aromatic hydrocarbons. Chlorinated benzenes, such as chlorobenzene, dichlorotoluene, 1,2,4-trichlorobenzene, and especially o-dichlorobenzene (hereinafter often referred to as ODCB), are particularly preferred. Mixtures of such solvents may also be employed.

In one embodiment the method of the present invention comprises extracting the polyether-containing organic phase with water so that contaminating species may be transferred from the organic to the aqueous phase. Extraction with water typically comprises three secondary processes: creation of sufficient surface area between water and organic phases for optimum contact while minimizing emulsion formation; transfer of water-soluble species from organic to water phases; and separation of water and organic phases. Typical water-soluble species which may be transferred include alkali metal halide and other alkali metal salts, ionic catalyst species and catalyst decomposition products, and residual monomer species. Extraction with water may be performed using known methods, including known methods for liquid-liquid contacting. Preferably contact with water is performed using a counter-current contact method with fresh water first contacting organic phase containing the lowest concentrations of water-soluble species (such as sodium chloride and ionic catalyst species). Any known method for performing counter-current extraction of a heavier- than-water organic phase with water may be used. Extraction methods also include those which employ, either separately or in series, one or more of mixer/settling tanks, in-pipe static mixers, liquid droplet coalescers, extraction columns, homogenizers, and liquid-liquid centrifuges, or combinations thereof. Temperatures at which extraction may be performed refer to the entire process and particularly to the secondary process of separation.

Prior to any purification step which involves extraction with water, a polyether-containing reaction mixture is preferably quenched with acid. Quenching with acid may be performed either before or after any filtration step that may be employed. The acid can be in solid, liquid, gaseous, or solution form. Suitable acids

include organic acids such as acetic acid, and inorganic acids such as phosphorous acid, phosphoric acid, or anhydrous hydrochloric acid. A gaseous acid, such as anhydrous hydrochloric acid, can be bubbled into the reaction mixture through a sparger or delivered as a solution in a convenient solvent such in the same organic solvent as used in the reaction mixture. The quantity of acid added is preferably at least sufficient to react with the calculated amount of phenoxide end-groups that will be present for a given molecular weight of polyether product. Preferably the quantity of acid added is greater than the calculated amount and more preferably about twice the calculated amount of phenoxide end-groups that will be present for a given molecular weight of polyether product.

The acid may be added using any convenient protocol. Typically, a gaseous acid is added over time, said time being dependent upon factors known to those skilled in the art, including the volume of the reaction mixture and the concentration of polyether product among other factors. The time of addition is typically less than about 60 minutes, more typically less than about 20 minutes, and still more typically less than about 10 minutes. The temperature of the reaction mixture during acid addition may vary from about room temperature to a temperature above the boiling point of the organic solvent (in which latter case the mixture is under pressure), and more typically from about room temperature to about the boiling point of the organic solvent, preferably from about 50°C to about 210°C, and more preferably from about 90°C to about 180°C. Following acid quenching, the reaction mixture may be taken directly to any subsequent steps or may be stirred for a convenient period, typically about 30-60 minutes.

The quenching step typically converts surface-active species, for example phenoxide salts of alkali metal and/or catalyst cationic species, to non-surface-active phenolic groups. This quenching step also permits more efficient recovery of any polymer-bound catalyst cationic species by converting them to salts which are more easily recovered from the reaction mixture, such as chloride salts. In the case of polyetherimide-containing reaction mixtures quenching is also important in

converting any residual carboxylate salts to carboxylic acids which can ring-close to imide during subsequent processing steps resulting in higher polymer stability. The quenching step also helps deter emulsion formation during subsequent water extraction through removal of surface active species.

In one embodiment the method of the present invention comprises subjecting the polyether-containing reaction mixture to at least one extraction with water following acid quenching. Water extraction may be performed using a mixer and settling tank combination. An advantage of this combination is that the required equipment is simple, requiring an impeller or other dynamic mixing device, and a tank of proper geometry.

In a preferred embodiment a mixer/settling tank is filled with a polyetherimide/o-dichlorobenzene solution comprising sodium chloride and at least one catalyst, preferably a hexaalkylguanidinium chloride. The mixture is brought to a temperature preferably in the range of about 25-205°C, more preferably in the range of about 60-180°C, and still more preferably in the range of about 80-100°C. Water is added to the tank and stirring is applied. If desired, water may be preheated before addition to the organic phase, or a water-organic mixture may be reheated to a desired temperature range. When temperatures above the effective boiling point (at atmospheric pressure) of the mixture are employed, then the tank is typically enclosed under pressure during any water addition and extraction step. In these cases typical pressures are about 1 to about 280 psi.

Brine formation is desirably achieved under conditions which minimize the amount of water used and which favor rapid phase separation of aqueous and organic phases. Typical phase ratios are preferably about 0.5-6 parts of ODCB to one part water by weight. A preferred phase ratio is about 5 parts of ODCB to one part water by weight. The desired stirring rate is below the rate at which emulsification of the reaction mixture occurs. More particularly, the stirring rate must provide sufficient contact between the phases so that adequate mass transfer occurs without too large an

interfacial area being generated. Typical stirring rates are such as to provide Reynolds numbers of about 25-500 and preferably about 50-100.

In a preferred embodiment the stirrer is stopped after a few minutes of stirring and the ODCB/water mixture is allowed to settle. The ODCB layer is typically the bottom layer. Some of the sodium chloride dissolves in the water and some remains in the ODCB phase, typically as crystals. This first extraction typically achieves up to 70-99.9% sodium chloride removal from an ODCB phase, and more typically 90- 99.9%. The first extraction also typically removes about 50-99.9% of any ionic catalyst present. In particularly preferred embodiments the first extraction achieves greater than 99.9% removal of sodium chloride and of ionic catalyst.

In a preferred embodiment the aqueous phase is separated without including any emulsified layer (hereinafter sometimes referred to as"rag layer") that may be present, and saved for catalyst, monomer species, and sodium chloride recovery by conventional means (for instance, using a coalescer). Any rag layer, if present, may be separated and transferred to a separate vessel for later addition to the next batch of polymer reaction mixture for purification, or left together with the ODCB solution for a second extraction. The organic phase remaining may be subjected to a second extraction or other purification step, if further purification is desired, or sent to a polymer isolation step where the solvent is completely removed from the solution.

If higher levels of purification are desired, one or more additional water extraction steps may be performed, for example in a preferred embodiment using mixing/settling, for example in the same vessel. A ratio of about 0.5-6: 1 (weight/weight) ODCB to water and preferably about 5: 1 (weight/weight) ODCB to water is used. The desired stirring rate is below the rate at which emulsification of the reaction mixture occurs. More particularly, the stirring rate must provide sufficient contact between the phases so that adequate mass transfer occurs without too large an interfacial area being generated. Typical stirring rates are such as to provide Reynolds numbers of about 25-500 and preferably about 50-100.

In addition, any extraction after a first extraction is preferably performed in the temperature range of about 25-205°C, more preferably in the range of about 60- 180°C, and still more preferably in the range of about 80-100°C. A second water extraction process typically achieves up to 90-99.9% and preferably greater than 99.9% residual sodium chloride and ionic catalyst removal from an ODCB phase (based on the weight sodium chloride and catalyst remaining after a first extraction).

In another preferred embodiment a second (or subsequent) water extraction step can be carried out by a process which comprises sparging steam through the ODCB phase under pressure. The steam temperature has a value of less than the boiling point of ODCB under the process conditions, preferably a value of about 110- 175°C, and more preferably a value of about 140°C. The ODCB mixture preferably has a temperature of about 25-175°C, and more preferably about 110°C. The amount of steam sparged per minute is typically such as to provide about 1-7: 1 (vol./vol.) ODCB to steam ratio and more preferably about 2: 1 ODCB to steam ratio. In a typical process steam is sparged for about 10-60 minutes and preferably for about 30 minutes. Steam may be vented from the container through a pressure relief valve. Any ODCB that happens to be removed along with the escaping steam may be recovered using standard methods.

As the steam rises, it will typically carry upwards any residual entrained water droplets remaining from a first (or subsequent) extraction, thus further increasing the sodium recovery efficiency. As described above, the aqueous phase may typically collect at the top of the ODCB phase. The ODCB phase may then be removed from the bottom of the vessel leaving the aqueous phase behind after which said aqueous phase may be treated in a manner as described hereinafter. More than one step comprising steam sparging of an ODCB phase may be employed.

In another embodiment a static mixer can be used in conjunction with or as an alternate approach to a dynamic mixer/settling tank in a purification process comprising water extraction. The advantages of static mixers are that a milder degree of mixing is often possible by minimizing shear forces and avoiding smaller droplet

formation and possible emulsification. Various process configurations can be employed when at least one step in the process uses a static mixer. For example, a static mixer can be used for a first extraction with water, or for all extractions with. water, or for one or more subsequent extractions with water following a first extraction that employs a dynamic mixer/settling tank combination.

The usefulness of a static mixer may be greater for performing a second or subsequent extraction following a first water extraction, since often with second and/or subsequent extractions the emulsification tendencies may be greater.

Employing a static mixer for at least one extraction step may be particularly useful when a reaction mixture produces a larger than usual rag layer or emulsifies abnormally, or when the purification process comprises adding rag layer either to a subsequent extraction after a first extraction or to a next reaction mixture, and the volume of rag layer continues to increase as the number of batches increases. Since rag layers typically represent about 10% or less of any aqueous phase volume (or typically less than about 2% of the organic phase), the use of additional water injected into any rag layer as it is removed from a holding tank, for example, for pumping through a static mixer is not a serious penalty to the process operation. The two phases can then be separated and recovered by such means as in a coalescer filter medium. A static mixer/coalescer combination can also be used in parallel to the hereinabove described processes of one or more water extraction steps (including the steam sparging option), optionally with a subsequent filtration step. In one embodiment a dynamic mixer/settling tank combination may separate the bulk of the two phases while a static mixer/coalescer reclaim the polymer solution from any rag layer formed.

In another embodiment a dynamic mixer/settling tank combination may separate the bulk of the two phases and the organic phase (optionally with rag layer) may then be passed at least once through a recycle loop comprising a static mixer with water injection at a level of about 0.5-6: 1 organic: water (weight/weight). The treated mixture may then return to a tank for settling or other treatment as described hereinabove. An advantage of such processes is that a static mixer can be used to perform the mixing in a transfer pipe in a matter of seconds, rather than minutes as in

a mixer tank, and a liquid-liquid coalescer filter can be used in parallel with or instead of a settling tank to perform the separation of organic from water.

In a preferred embodiment a polyetherimide-containing ODCB solution may be pumped out of a holding tank to a static mixer, where it may be combined with a stream of water in a predetermined ratio and put through a static mixer. The amount of water added may be for example about 0.5-6: 1 and preferably about 5: 1 ODCB: water weight/weight ratio. The speed of pumping is determined by the desired Reynolds number in the static mixer. Reynolds numbers less than 500 will typically result in mild interphase contact approaching laminar flow as the Reynolds number goes to zero. More vigorous contacting will be obtained in turbulent flow above 2000 Reynolds Number. By adjusting the length of the static mixer the contact time between the two phases can be controlled. The contact time is typically on the order of seconds. Because of the action of the static mixer resembles end-over-end or side-by- side motion rather than a shearing motion as in a stirrer, emulsification is inhibited.

In a preferred embodiment contact between ODCB phase and water phase in a static mixer is performed at temperatures of about 25-175°. Typical pressures are about 1-280 psi. The mixed system may then be sent directly to a coalescer, particularly if the time for phase separation in a settling tank is longer than desired.

The coalescer may be operated at a temperature similar to or different from that of the mixture to be separated. The use of a coalescer may require a temperature as high as possible (for example, as high as about 90°C) to reduce viscosity, and an ODCB-to- water ratio of less than 1: 1, for instance, since coalescers are typically only effective for oil-in-water emulsions. A prefilter may be required to remove solid particles, for example of residual monomer, prior to using a coalescer. Alternatively, a settling tank can be used instead of a coalescer. In the settling tank, the aqueous phase is continuously decanted at the top, the organic phase is continuously sent to polymer isolation where the ODCB may be evaporated from the polymer.

The aqueous phase from any extraction step by any method may be removed and sent for recycling, waste water treatment, and/or to at least one recovery step (for

example, processing in a coalescer) for recovery of such species as catalyst and traces of organic solvent. In one embodiment two or more aqueous fractions from different extractions are combined for recovery of such species as catalyst, monomer, and any traces of organic solvent. Any small, water-insoluble particles that may remain in the ODCB phase after separation from a water phase may be removed by filtration as described hereinafter.

In a preferred embodiment hexaalkylguanidinium chloride catalyst from a polyetherimide preparation may be recovered for reuse from one or more aqueous fractions by mixing with ODCB and removing water by distillation until substantially all the water is removed. The distillation may be further continued until a desired concentration of catalyst in ODCB and a desired residual water level are obtained. If necessary, additional ODCB may be added to the distillation as required.

Concentrations of residual water are typically less than 100 ppm, and preferably less than 50 ppm. If there are any water-insoluble particles in the catalyst-containing ODCB phase after distillation, they may be removed by filtration as described hereinafter.

The purification methods of the present invention may comprise one or more filtration steps. Any known filtration method may be used. For example, filtration may be performed using at least one of a dead-end filter, cross-flow filter, liquid-solid cyclone separator, vacuum drum filter, centrifuge, or vacuum conveyor belt separator.

In particular, suitable filtration methods include those described in"Chemical Engineer's Handbook", (Robert H. Perry and Cecil H. Chilton, editors; McGraw Hill, publishers). In one embodiment a purification process may comprise at least one dry filtration step (that is, a filtration of a polyether-containing organic phase essentially free of water) as described hereinafter.

In another embodiment a purification process may comprise at least one filtration step which comprises providing a small amount of water to a polyether- containing organic phase before filtration. Typically water is provided after quenching the reaction mixture with acid, and at a temperature preferably in the range of about

25-105°C, more preferably in the range of about 60-105°C, and still more preferably in the range of about 80-100°C. Water is added to the tank and stirring is applied. If desired, water may be preheated before addition to the organic phase, or a water- organic mixture may be reheated to a desired temperature range. The amount of water added is typically about 0.1-5.0 vol. % based on polymer solution volume, preferably about 0.5-5.0 vol. % and more preferably about 1 vol. %. In this case the added water interacts with the hydrophilic sodium chloride crystals and forms liquid bridges that promote further agglomeration. The agglomerated crystals can then be filtered using any known filtration method, typically at a temperature in a range of about 25-105°C, more preferably in a range of about 60-105°C, and still more preferably in a range of about 80-100°C. One effect of using elevated temperature is to decrease the mixture viscosity to facilitate filtration. In a preferred embodiment a polyetherimide- containing ODCB reaction mixture is treated with water and filtered as described, and the permeate from said filtration can then be subjected to further purification steps, if so desired, including, for example, extraction one or more times with water as described above.

In another embodiment a purification process may comprise at least one filtration step which comprises providing a small amount of water to a polyether- containing organic phase and then heating the mixture to a temperature of at least the boiling point of water under the process conditions and subsequently filtering. The amount of water added is typically about 0.1-5.0 vol. % based on polymer solution volume, preferably about 0.5-5.0 vol. % and more preferably about 1 vol. %. The temperature of the organic phase may be raised to a temperature between the boiling point of water and the boiling point of the organic phase under the prevailing pressure, preferably to at least about 100°C, more preferably to a temperature between about 110°C and the boiling point of the organic phase and still more preferably to a temperature between about 120°C and the boiling point of the organic phase under the process conditions. Alternatively, the mixture can be heated under partial vacuum, in which case the temperature may also be less than 100°C as well as in the ranges given above. Under these conditions water generates small bubbles of steam that escape the

organic phase and evaporate. Any organic solvent that escapes with the steam may be recovered using conventional means. In the process of water evaporation species dissolved in the aqueous phase recrystallize, grow in size, and form agglomerates so that they may sediment to the bottom of the tank when stirring is stopped. Typically any alkali metal halide recrystallizes during evaporation of water to form agglomerates. Said agglomerates are typically larger in size than any crystallites or agglomerates that may be present before an evaporation step. Essentially all or at least a portion of alkali metal halide is now typically in a form that can be filtered following application of heat. The polyether-containing reaction mixture is typically held at a temperature in the desired range until most of or essentially all of the water has evaporated, or preferably until essentially all or at least a portion of alkali metal halide is in a form that can be filtered. The mixture may now be subjected to filtration.

The organic permeate from filtration may be subjected to further purification steps and/or sent to equipment for recovery of polymer. The filter cake itself may be treated to recover any entrained polymer and other valuable species by standard techniques, such as by extracting with organic solvent.

In a preferred embodiment a reaction mixture comprises (i) an aromatic polyetherimide, (ii) hexaethylguanidinium chloride catalyst, (iii) sodium chloride, and (iv) o-dichlorobenzene. Water is provided in the prescribed amounts and the temperature of the ODCB phase is raised to a temperature between the boiling point of water and the boiling point of ODCB under the prevailing pressure, preferably to at least 110°C, more preferably to a temperature between about 110°C and the boiling point of ODCB and still more preferably to a temperature between about 120°C and the boiling point of ODCB under the process conditions (wherein the normal boiling point of ODCB is 180°C at one atmosphere pressure). Alternatively, the mixture can be heated under partial vacuum, in which case the temperature may also be less than 110°C as well as in the ranges given above. Any ODCB that escapes with the steam may be recovered using conventional means. In the process of water evaporation sodium chloride dissolved in the aqueous phase recrystallizes, and the crystallites grow in size, and form agglomerates so that they may sediment to the bottom of the

tank when stirring is stopped. For instance, the initial size of sodium chloride crystals produced during a typical polyetherimide polymerization may typically be in the range of about 0.5 to about 20 pm in diameter in an ODCB phase. The agglomerates are typically larger in size than any crystallites or agglomerates that may be present before an evaporation step. A portion of residual sodium chloride is now typically in a form that can be filtered. The reaction mixture is filtered using known methods. The ODCB permeate from filtration may be subjected to further purification steps and/or sent to equipment for recovery of polyetherimide from organic solvent. The filter cake itself may be treated to recover any entrained polyetherimide and other valuable species by standard techniques, such as by extracting with ODCB.

Water may be provided to a polyether-containing reaction mixture by any convenient method. In one embodiment at least one filtration step may be included following one or more water extraction steps in which case water is provided as residual water remaining after extraction. Additional water may be added if desired.

This embodiment may be preferred for polyether-containing reaction mixtures in which the initial particle size of solids present in the organic phase may be such that filtration prior to extraction is not feasible or cost effective. The combination of one or more water extraction steps followed by a filtration step may be used to treat polyether/organic solvent reaction mixture, or rag layers therefrom, or the combination of polyether/organic solvent reaction mixture and rag layer. Thus, in a preferred embodiment a polyetherimide/ODCB reaction mixture comprising sodium chloride, residual monomer, and catalyst is subjected to one or more water extraction steps to remove the bulk of water-soluble species, and then subjected to at least one filtration step comprising heating the reaction mixture as described.

In another embodiment the method of the present invention comprises initial treatment of a polyether-containing reaction mixture by at least one non-aqueous or dry filtration step, in which contaminating species are removed as solid particles or

adsorbed species in the essential absence of water. Typical species which may be removed by dry filtration include alkali metal halide and residual monomer salts.

In a preferred embodiment polyetherimide-containing ODCB mixtures are treated by filtration to remove such filterable species as sodium chloride and bisphenol A monomer species as solid particles from the ODCB phase without initially adding water. Other insoluble species will also be removed from the ODCB phase. Following filtration, catalyst species and other non-filterable, water-soluble species may be separated and recovered via aqueous methods such as those employing a dynamic or static mixer or any of the aqueous configurations previously discussed.

In one embodiment acid quenching is postponed until after filtration so that bisphenol A salts can be removed by filtration; otherwise, bisphenol A formed during quenching may become soluble in the organic phase and may not be efficiently removed by solids filtration. In another embodiment quenching may be preferably done before filtration, for example if bisphenol A salts are not present. The permeate from the filtration step is typically a clean solution of polymer and catalyst in ODCB. The stream that is rejected by the filter is typically a concentrated slurry of sodium chloride, residual monomer species, and some catalyst in ODCB. The primary filter may be at least one of either a dead-end filter or a cross-flow filter. If a dead-end filter is used, a back-washing step is required to remove the solids from the filter. Since flux through a dead-end filter is indirectly proportional to viscosity, decreasing the solution viscosity will typically increase the flux by a proportionate factor. The viscosity is largely determined by temperature and polymer concentration. Therefore, increasing the temperature or decreasing the polymer concentration may typically result in increased flux through a filter. In a preferred embodiment a 15 wt. % polyetherimide solution in ODCB may be conveniently filtered at a temperature up to about the boiling point of ODCB, and preferably at a temperature of about 90-180°C.

If a cross-flow filter is used, nearly continuous operation is possible but at least one secondary filter is typically required to minimize product loss. Process time and costs will determine which filtration method is best. If needed, the secondary

filter can concentrate the slurry to a cake. The secondary filter may be a dead-end filter (such as a candle filter or a belt press) or a liquid cyclone. A liquid cyclone can perform the separation because the concentration of particles that occurs during cross- flow filtration induces solid particles to agglomerate and the inertial forces that promote separation in a liquid cyclone are often more effective for separation of larger agglomerates.

The permeate stream (from both the primary and, if necessary, the secondary filters) that is particle-free can be quenched with acid and sent for catalyst recovery.

Because catalyst is typically more soluble in water than in ODCB, this stream can be processed with any of the aqueous methods described above. Similarly, catalyst can be processed via the dry method of ion exchange described hereinafter. Again, multiple combinations of aqueous and dry purification configurations are possible, depending on the relative process conditions and the desired level of purification.

In still another embodiment the method of the invention comprises at least one dry filtration step in the presence of a solid medium that may adsorb or absorb soluble species from a polyether-containing reaction mixture. Insoluble species such as an alkali metal halide may be removed by simple physical filtration in the same process.

The mechanism of adherence to a solid medium is not important provided that the medium serves to remove selected species in one or more filtration steps while passing essentially all polyether and any other species not selected. The medium may be contacted with the reaction mixture either by addition of all or a portion of the medium to the reaction mixture followed by stirring, typically at a temperature in a range of about 25-105°C, and more preferably in a range of about 60-105°C. Less preferably, the heated reaction mixture can be filtered through all or a portion of medium not previously contacted with the reaction mixture. Suitable media include, but are not limited to, alumina, silica, diatomaceous earth, fuller's earth, commercial filter agents such as CELITE, and other media typically employed in adsorption chromatography. In a preferred embodiment a polyetherimide reaction mixture in ODCB may be contacted with an appropriate medium to adsorb essentially all or a

portion of soluble species (other than polyetherimide) such as ionic catalyst species, preferably hexaethylguanidinium chloride. A preferred medium is silica. The treated reaction mixture can then be filtered one or more times to remove essentially all or a portion of insoluble sodium chloride and adsorbed catalyst species on the medium.

Following filtration, catalyst species may be recovered from the solid medium using methods known in the art, and any non-polyether soluble species, if still present in the filtrate, may be separated and recovered, for example by further filtration steps or by aqueous methods such as those employing a dynamic or static mixer or any of the aqueous configurations previously discussed.

In still another embodiment the method of the present invention comprises at least one dry filtration step followed by at least one ion exchange step for catalyst recovery. The dry filtration step may be accomplished by any combination of filtration methods described hereinabove. For the second step, ion exchange on a resin bed can be used after filtration to reclaim cationic catalyst remaining in the organic phase. Following ion exchange, the process solution may be sent for further purification and/or to an isolation step for polyether recovery by standard methods.

A purification process comprising any combination of at least one dry filtration step followed by at least one ion exchange step may be employed. In one embodiment the polyether reaction mixture is not quenched with acid before the at least one dry filtration step and the at least one ion exchange step. In this case the reaction mixture following at least one filtration step may be contacted at least once with an ion exchange resin in the sodium form to remove ionic catalyst and release sodium chloride. In an alternative embodiment an unquenched reaction mixture is contacted at least once with ion exchange resin in the hydrogen form and the resin itself serves entirely or at least partially as an acid quencher for the reaction mixture, adsorbing ionic catalyst in the process. In another embodiment the reaction mixture is quenched with acid after at least one dry filtration step. In this case the reaction mixture following at least one filtration step and acid quenching may be contacted at least once with an ion exchange resin in the hydrogen form to remove ionic catalyst

and release hydrogen chloride. In a preferred embodiment a polyetherimide reaction mixture containing hexaalkylguanidinium chloride catalyst in ODCB, after at least one filtration step and acid quenching, is contacted at least once with an ion exchange resin in the sodium form.

A packed column of ion exchange resin can be used to exchange ionic catalyst for recovery. The identity of the ion exchange resin is not critical so long as the ion exchange resin is effective for recovering cationic catalyst for the reaction mixture.

AMBERLYST 36 or AMBERLYST 15 resins available from Rohm and Haas Co. can be used for this purpose. In a preferred embodiment a polyetherimide-containing ODCB reaction mixture is passed through a resin bed operated below about 90°C.

Depending on the mode of operation, the resin column will adsorb the catalyst cation and typically release sodium chloride or hydrochloric acid.

The ion exchange process may be performed in a batch, semi-continuous, or continuous mode. In a preferred embodiment a column saturated with catalyst cation is regenerated off-line with hydrochloride acid and the catalyst chloride salt is recovered from the aqueous phase for reuse. While a saturated column is being regenerated, at least one fresh column may be in use for recovering catalyst cation from further process solution.

Following any of the purification procedures illustrated hereinabove, a polyether-containing organic solution may be sent to a polymer isolation step where the polyether may be isolated free of organic solvent by standard methods, such as by anti-solvent precipitation, filtration, and drying, or by devolatilization, for example, in an appropriate extruder with recovery and recycling of the organic solvent. In a preferred embodiment a polyetherimide is isolated from an ODCB solution and the ODCB is recovered and recycled for further use. The isolated polyetherimide typically contains less than about 100 ppm sodium and preferably less than about 50 ppm sodium. A preferred polyetherimide comprises the reaction product of a bisphenol A moiety, particularly bisphenol A disodium salt, with at least one of [N- (4-chlorophthalimido)] benzene.

Embodiments of the invention are illustrated by the following non-limiting examples. The terms"extraction"and"wash"are used interchangeably.

EXAMPLE 1 A polyetherimide was prepared in o-dichlorobenzene through the reaction of bisphenol A disodium salt and 1,3-bis [N-4-chlorophthalimido] benzene in the presence of hexaethylguanidinium chloride catalyst (HEG). The reaction mixture was quenched at 120°C with glacial acetic acid and diluted to about 15% solids (wt. polymer/wt. polymer + wt. solvent) through addition of more o-dichlorobenzene. The reaction mixture (about 10 liters; about 13 kilograms) was washed with about 4.1 kilograms water (3: 1 organic: aqueous) at a temperature of about 85-90°C and fed to a liquid/liquid continuous centrifuge at about 90°C at different rates. All of the organic phase was collected and washed with a second portion of water (about 4.1 kilograms), and the organic phase fed to the centrifuge a second time. All of the organic phase was collected and washed with a third portion of water (about 4.1 kilograms), and the organic phase fed to the centrifuge a third time. For each set of conditions the organic phase was analyzed by ion chromatography for sodium, HEG and PEG (pentaethylguanidinium chloride, a decomposition product of HEG); duplicate analyses were run on the same sample. Conditions and analyses are summarized in Table 1. In each case the data are reported vs. polymer rather than vs. the entire mixture. The centrifuge employed had a maximum rating of 10,000 rpm.

TABLE 1 Org.+Aq.Sodium HEG PEG Flow Centrifug analyses, ppm analyses,analyses, RunNo.*grams/minute e vs. polymer ppmvs.ppmvs. rpm polymer polymer firstpass1000 75% 890/905 333/335 150/150 firstpass900 100% 690/712 327/322 141/142 firstpass450 100% 769/828 292/293 134/132 firstpass600 100%785/809 290/288 131/131 secondpass800 100% 251/310 31/32 19/21 secondpass400 100% 224/192 38/41 24/25 thirdpass800 100%'165/177 9/8 6/5

The data show that the sodium and catalyst level decreases with each successive wash.

The sodium level may be further decreased using evaporation and filtration process steps.

EXAMPLE 2 The same quenched, diluted polyetherimide reaction mixture used in Example 1 (4 liters) was fed simultaneously along with water through a concentric tube assembly to a homogenizer at flow rates of 450 grams per minute for the organic phase and 150 grams per minute for the aqueous phase. Both the organic and aqueous phases were at a temperature of about 85-90°C. The homogenizer, comprising a rotor assembly with blades and a stator with outlet orifices on the periphery and an exit port leading to a centrifuge, was operated at different rpms. The homogenized mixture from the homogenizer was fed directly to a liquid/liquid centrifuge operated at 100% rpm capability. All of the organic phase was collected and fed to the homogenizer along with water under the same conditions as for the first pass, and the output fed to the centrifuge a second time. All of the organic phase was collected and fed to the homogenizer along with water under the same conditions as for the first pass, and the output fed to the centrifuge a third time. For each set of conditions the organic phase was analyzed by ion chromatography for sodium, HEG and PEG (pentaethylguanidinium chloride, a decomposition product of HEG); duplicate analyses were run on the same sample. Conditions and analyses are summarized in Table 2. In each case the data are reported vs. polymer rather than vs. the entire mixture.

TABLE 2 Homogenizer Sodium HEGPEGanalyses, RunNo.*rpm analyses, ppm analyses,ppmppmvs. vs.polymer vs.polymerpolymer first pass 1500 1592/1583 242/239 81/80 first pass 3000 2306/2320 261/261 100/99 first pass 4000 2010/1996 182/188 77/77 secondpass 2000 670/682 15/15 9/9 thirdpass 1500 129/125 8/9 4/4

The data show that the sodium level decreases with each successive wash. The sodium level may be further decreased using evaporation and filtration process steps.

EXAMPLE 3 A similar polyetherimide reaction mixture to that used in Example 1 was held in a 10 gallon reactor, quenched at about 120°C with glacial acetic acid, and diluted to about 8% solids (wt. polymer/wt. polymer + wt. solvent) through addition of more o- dichlorobenzene. The reaction mixture was transferred to clean containers and the reactor rinsed with a small amount of o-dichlorobenzene and deionized water to remove any salts that might have adhered to the walls of the reactor. The polymer reaction mixture was returned to the rinsed reactor and heated to 80°C. The mixture was then extracted three times, each time with nine liters deionized water also at 80°C. The phases were mixed each time for ten minutes with gentle agitation. The first two washed were allowed to settle for one hour, and the third wash was allowed to settle for two days at 80°C. For each set of conditions the organic phase was analyzed for sodium by ion chromatography. The sodium content after the first wash was 797 ppm; after the second wash, 223 ppm; and after the third wash, 32 ppm vs. polymer.

EXAMPLE 4 A similar polyetherimide reaction mixture to that used in Example 1 and containing about 800 ppm soluble ionic chloride in the form of hexaethylguanidinium chloride was quenched at about 43°C with anhydrous hydrochloric acid, and diluted to about 5% solids (wt. polymer/wt. polymer + wt. solvent) through addition of more o- dichlorobenzene. The mixture was treated with silica (60-200 mesh; 0.5 grams per 10 g.. of polymer in solution) and stirred at 60°C. The mixture was filtered and the filtrate

analyzed for soluble ionic chloride by titration. The soluble ionic chloride value was 75 ppm.

Described hereinabove are several modular configurations of procedures that will achieve the required level of polyether purification. These represent illustrative examples of the invention and many other process combinations are also possible within the scope of the present invention. Although the preferred embodiments of the invention concern methods for purification of a polyetherimide in an ODCB solution, it is to be understood that the invention discloses methods which are suitable for the purification of any polyether made by a halide displacement polymerization method in a water-immiscible solvent with boiling point at atmospheric pressure of greater than 110°C and a density ratio to water of greater than 1.1: 1 at 20-25°C.