Patent Publication Number: US-2015080537-A1

Title: Method for Preparing Polyethersulfone

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC Section 119 to and the benefit of Korean Patent Application 10-2013-0110720, filed Sep. 13, 2013, and Korean Patent Application No. 10-2014-0017315, filed Feb. 14, 2014, the entire disclosure of each of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a method for preparing a polyethersulfone. 
     BACKGROUND 
     Polyethersulfone (poly arylene ether sulfone, PES) is a super engineering plastic exhibiting excellent heat resistance and is widely used for materials for membranes, medical apparatuses, automotive parts, aircraft parts, infant feeding bottles, and the like. Moreover, demand for polyethersulfone is increasing in the field of secondary fuel cell membranes and general-purpose membranes. 
     Generally, polyethersulfone (PES) can be obtained, using a polar organic solvent, by condensation polymerization of a dihalogenodiphenylsulfone compound with a divalent phenol compound such as dihydroxydiphenylsulfone compounds and the like in the presence of an alkali metal compound, or by synthesis of a divalent alkali metal salt of the divalent phenol compound, followed by condensation polymerization with the dihalogenodiphenylsulfone compound. 
     However, such a method is typically performed at a high temperature of about 220° C. or more and requires addition of a strongly basic compound for reaction. Thus, there are drawbacks in that a side reaction, such as decomposition of polyethersulfone and the like, can occur at high reaction temperature, and that complicated post-treatment is required for separation of by-products from the polyethersulfone having poor solubility in a solvent after completion of the reaction. 
     Therefore, there is a need for a method which is performed under mild conditions, such as a polymerization temperature of about 190° C. or less, an oxidation temperature of about 70° C. or less and the like, and which allows preparation of polyethersulfone without complicated post-treatment. 
     SUMMARY 
     Exemplary embodiments of the present invention provide a method for preparing a polyethersulfone, which can be performed under mild conditions of a polymerization temperature of about 190° C. or less and an oxidation temperature of about 70° C. or less, and can allow preparation of polyethersulfone without complicated post-treatment, such as separation of by-products formed from a basic compound, and the like. 
     The method for preparing a polyethersulfone can include oxidation of a poly arylene ether sulfone-sulfide compound including a repeat unit represented by Formula 1 with an aqueous solution of an organic acid and an aqueous solution of hydrogen peroxide. 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2 , R 3  and R 4  are the same or different and are each independently a C 1  to C 10  hydrocarbon group, and a, b, c and d are the same or different and are each independently an integer from 0 to 4. 
     In one embodiment, the oxidation may be performed at about 30° C. to about 70° C. 
     In one embodiment, the oxidation may include adding the poly arylene ether sulfone-sulfide compound to the aqueous solution of the organic acid, followed by dropwise addition of the aqueous solution of hydrogen peroxide. 
     In one embodiment, the oxidation may include preparing an aqueous solution of a mixture of the organic acid and hydrogen peroxide by adding dropwise the aqueous solution of hydrogen peroxide to the aqueous solution of the organic acid, followed by addition of the poly arylene ether sulfone-sulfide compound. 
     In one embodiment, the organic acid may be present in an amount of about 10 parts by weight to about 100 parts by weight in the aqueous solution of the organic acid based on about 100 parts by weight of water; hydrogen peroxide may be present in an amount of about 3 parts by weight to about 20 parts by weight in the aqueous solution of hydrogen peroxide based on about 100 parts by weight of water; and the aqueous solution of the organic acid may be present in an amount of about 180 parts by weight to about 1,500 parts by weight and the aqueous solution of hydrogen peroxide may be present in an amount of about 200 parts by weight to about 600 parts by weight, based on about 100 parts by weight of the poly arylene ether sulfone-sulfide compound. 
     In one embodiment, a volume ratio of the organic acid to hydrogen peroxide (organic acid:hydrogen peroxide) may be about 0.1:about 1 to about 10:about 1 in the aqueous solution of the organic acid and the aqueous solution of hydrogen peroxide. 
     In one embodiment, the organic acid may include at least one of formic acid, acetic acid, propionic acid, oxalic acid, and glycolic acid. 
     In one embodiment, the poly arylene ether sulfone-sulfide compound may be a polymer prepared by condensation of a dihydroxydiarylsulfide compound represented by Formula 2 and a dihalogenodiarylsulfone compound represented by Formula 3. 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2 , R 3 , R 4 , a, b, c and d are defined as set forth in Formula 1, and X is a halogen atom. 
     In one embodiment, condensation may be performed by heating the dihydroxydiarylsulfide compound and the dihalogenodiarylsulfone compound to about 160° C. to about 190° C. in an organic solvent in the presence of an alkali metal salt or an alkali earth metal salt. 
     In one embodiment, preparation and oxidation of the poly arylene ether sulfone-sulfide compound may be a one-pot reaction. 
     In one embodiment, the poly arylene ether sulfone-sulfide compound may have a number average molecular weight from about 7,000 g/mol to about 90,000 g/mol. 
     In one embodiment, the polyethersulfone may have a number average molecular weight from about 7,500 g/mol to about 110,000 g/mol. 
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments now will be described more fully hereinafter in the following detailed description, in which some, but not all, embodiments of the invention are described. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. 
     In accordance with exemplary embodiments of the present invention, a method for preparing a polyethersulfone (poly arylene ether sulfone, PES) includes oxidation of a poly arylene ether sulfone-sulfide compound (PES-S) including a repeat unit represented by Formula 1 with aqueous solutions of an organic acid and hydrogen peroxide. 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2 , R 3  and R 4  are the same or different and are each independently a C 1  to C 10  hydrocarbon group, for example, C 1  to C 10  alkyl, C 6  to C 10  aryl, or the like; and a, b, c and d are the same or different and are each independently an integer from 0 to 4. 
     According to the present invention, the oxidation is performed by the aqueous solution of the organic acid and the aqueous solution of hydrogen peroxide. Typically, a mixture of an (organic) acid and an oxidant forms a peracid, which can finally oxidize a sulfide group of the poly arylene ether sulfone-sulfide compound (PES-S) into a sulfone group via a sulfoxide group. 
     In one embodiment, the oxidation may be performed by adding the polymer (poly arylene ether sulfone-sulfide compound) to the aqueous solution of the organic acid, followed by dropwise addition of the aqueous solution of hydrogen peroxide, without being limited thereto. 
     In another embodiment, the oxidation may be performed by preparing an aqueous solution of a mixture of the organic acid and hydrogen peroxide through dropwise addition of the aqueous solution of hydrogen peroxide to the aqueous solution of the organic acid, followed by adding the polymer to the aqueous solution of the mixture, without being limited thereto. 
     For reference, since an exothermic reaction occurs when the aqueous solution of hydrogen peroxide is added to the aqueous solution of the organic acid, the aqueous solution of hydrogen peroxide can be added as slowly as possible. 
     Examples of the organic acid in the aqueous solution of the organic acid may include without limitation formic acid, acetic acid, propionic acid, oxalic acid, glycolic acid, and the like, and mixtures thereof. In exemplary embodiments, the organic acid may be formic acid, acetic acid, or a mixture thereof. 
     The organic acid may be present in an amount of about 10 parts by weight to about 100 parts by weight, for example, about 15 parts by weight to about 30 parts by weight, in the aqueous solution of the organic acid based on about 100 parts by weight of water. In addition, hydrogen peroxide may be present in an amount of about 3 parts by weight to about 20 parts by weight, for example, about 5 parts by weight to about 10 parts by weight, in the aqueous solution of hydrogen peroxide based on about 100 parts by weight of water. That is, according to the present invention, the aqueous solution of the organic acid and the aqueous solution of hydrogen peroxide may include an excess of water as compared with aqueous solutions of acid/oxidant used in typical oxidation of a polyarylene sulfide, and oxidation may be performed in the aqueous solution. 
     If the amount of the organic acid is less than about 10 parts by weight in the aqueous solution of the organic acid based on about 100 parts by weight of water, the poly arylene ether sulfone-sulfide compound may not be oxidized into polyethersulfone at high yield. If the amount of the organic acid is greater than about 100 parts by weight, there may be dissociation of some polymer chains. In addition, if the amount of hydrogen peroxide is less than about 3 parts by weight in the aqueous solution of hydrogen peroxide based on about 100 parts by weight of water, the poly arylene ether sulfone-sulfide compound may not be oxidized into polyethersulfone at high yield. If the amount of the organic acid is greater than about 20 parts by weight, there may be promotion of exothermic reaction. 
     In some embodiments, the aqueous solution of organic acid may include the organic acid in an amount of about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 parts by weight. Further, according to some embodiments of the present invention, the amount of organic acid can be in a range from about any of the foregoing amounts to about any other of the foregoing amounts. 
     In some embodiments, the aqueous solution of the hydrogen peroxide may include the hydrogen peroxide in an amount of about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 parts by weight. Further, according to some embodiments of the present invention, the amount of hydrogen peroxide can be in a range from about any of the foregoing amounts to about any other of the foregoing amounts. In the oxidation, the aqueous solution of the organic acid may be present in an amount of about 180 parts by weight to about 1,500 parts by weight, for example, about 190 parts by weight to about 1,000 parts by weight, and as another example, about 200 parts by weight to about 300 parts by weight, and the aqueous solution of hydrogen peroxide may be present in an amount of about 200 parts by weight to about 600 parts by weight, for example, about 300 parts by weight to about 400 parts by weight, based on about 100 parts by weight of the poly arylene ether sulfone-sulfide compound. 
     If the amount of the aqueous solution of the organic acid is less than about 180 parts by weight based on about 100 parts by weight of the poly arylene ether sulfone-sulfide compound, the poly arylene ether sulfone-sulfide compound may not be oxidized into polyethersulfone at high yield. If the amount of the aqueous solution of the organic acid is greater than about 1,500 parts by weight, there may be dissociation of some polymer chains. 
     In addition, if the amount of the aqueous solution of hydrogen peroxide is less than about 200 parts by weight based on about 100 parts by weight of the poly arylene ether sulfone-sulfide compound, the poly arylene ether sulfone-sulfide compound may not be oxidized into polyethersulfone at high yield. If the amount of the aqueous solution of hydrogen peroxide is greater than about 600 parts by weight, there may be loss of an excess of hydrogen peroxide due to exothermic reaction of the organic acid and hydrogen peroxide. 
     In one embodiment, in the aqueous solution of the organic acid and the aqueous solution of hydrogen peroxide, a volume ratio of the organic acid to hydrogen peroxide (organic acid:hydrogen peroxide) may be about 0.1:about 1 to about 10:about 1, for example, about 0.1:about 1 to about 0.5:about 1, and as another example about 0.25: about 1 to about 0.5:about 1. Within this range, the poly arylene ether sulfone-sulfide compound can be oxidized into polyethersulfone at high yield of about 98% or more. 
     In one embodiment, the oxidation can be performed under mild conditions of a temperature from about 30° C. to about 70° C., for example, from about 30° C. to about 40° C. and atmospheric pressure for, for example, about 1 hour to about 14 hours. Within this temperature range, the polyethersulfone can be prepared (oxidized) with minimal or no side reactions, such as decomposition of the polyethersulfone due to high temperature, and the like. 
     According to the present invention, the poly arylene ether sulfone-sulfide compound (PES-S) may be any compound including the repeat unit represented by Formula 1. For example, the poly arylene ether sulfone-sulfide compound may have a solid form such as fibers, powders, and the like, or may have a solution form obtained by dissolution in an organic solvent. 
     In one embodiment, the poly arylene ether sulfone-sulfide compound may be a polymer prepared by condensation of a dihydroxydiarylsulfide compound represented by Formula 2 and a dihalogenodiarylsulfone compound represented by Formula 3. 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2 , R 3 , R 4 , a, b, c and d are defined as set forth in Formula 1, and X is a halogen atom such as a chlorine atom (Cl), a fluorine atom (F), a bromine atom (Br), an iodine atom (I) and the like. 
     In one embodiment, the condensation may be performed by heating the dihydroxydiarylsulfide compound and the dihalogenodiarylsulfone compound to about 160° C. to about 190° C. in an organic solvent in the presence of an alkali metal salt or an alkali earth metal salt. 
     In the condensation, a mole ratio of the dihydroxydiarylsulfide compound to the dihalogenodiarylsulfone compound may be about 1:about 0.9 to about 1:about 1.1, for example, about 1:about 0.95 to about 1:about 1.05. Within this range, the poly arylene ether sulfone-sulfide compound (PES-S) can be obtained at high yield. 
     Examples of the alkali metal salt and/or the alkali earth metal salt may include without limitation potassium carbonate (K 2 CO 3 ), sodium carbonate (Na 2 CO 3 ), calcium carbonate (CaCO 3 ), potassium hydroxide (KOH), sodium hydroxide (NaOH), and the like, and mixtures thereof. The alkali metal salt and/or the alkali earth metal salt may be present in an amount of about 100 parts by mole to about 220 parts by mole, for example, about 110 parts by mole to about 210 parts by mole, based on about 100 parts by mole of the dihydroxydiarylsulfide compound and the dihalogenodiarylsulfone compound. For example, sodium hydroxide, calcium hydroxide and the like may be present in an amount of about 200 parts by mole to about 210 parts by mole. Within this range, the poly arylene ether sulfone-sulfide compound (PES-S) can be obtained at high yield. 
     The organic solvent may be any polar and/or non-polar organic solvent used in the art without limitation. Examples of the organic solvent may include without limitation N-methylpyrrolidone (NMP), toluene, dimethylformamide (DMF), dimethylacetamide (DMAc), sulfolane, diphenyl sulfone (DPS), propylene carbonate, ethylene carbonate, and the like, and mixtures thereof. The organic solvent may be present in an amount of about 80 parts by weight to about 150 parts by weight, for example, about 90 parts by weight to about 110 parts by weight, based on about 100 parts by weight of the dihydroxydiarylsulfide compound and the dihalogenodiarylsulfone compound. Within this range, a poly arylene ether sulfone-sulfide compound having a high molecular weight can be obtained. 
     In one embodiment, condensation may be performed at a temperature from about 160° C. to about 190° C., for example, from about 170° C. to about 190° C., and at atmospheric pressure for, for example, about 1 hour to about 5 hours. Within this range, a poly arylene ether sulfone-sulfide compound having a high molecular weight can be obtained. 
     In one embodiment, the poly arylene ether sulfone-sulfide compound may have a number average molecular weight from about 7,000 g/mol to about 90,000 g/mol, as measured by gel permeation chromatography (GPC), without being limited thereto. 
     In one embodiment, as shown in Reaction Formula 1, the method for preparing a polyethersulfone according to the present invention may be a method for preparing a polyethersulfone including a repeat unit represented by Formula 4 by preparing the poly arylene ether sulfone-sulfide compound (PES-S), which corresponds to an intermediate product and includes the repeat unit represented by Formula 1, through condensation polymerization of the dihydroxydiarylsulfide compound represented by Formula 2 and the dihalogenodiarylsulfone compound represented by Formula 3 using the alkali metal salt and/or alkali earth metal salt and the organic solvent (base/solvent), followed by oxidation of the PES-S with the aqueous solution of the organic acid and the aqueous solution of hydrogen peroxide (acid/H 2 O 2  aqueous solution), as described above. In addition, preparation and oxidation of the poly arylene ether sulfone-sulfide compound may be one-pot reaction. 
     
       
         
         
             
             
         
       
     
     where R 1 , R 2 , R 3 , R 4 , X, a, b, c and d are defined as set forth in Formulae 1 to 3. 
     According to the present invention, one-pot reaction refers to a reaction process in which, during a 2-stage or more reaction process as described above, the intermediate product (PES-S) is continuously added to the next-stage (oxidation) reactants (aqueous solutions of organic acid and hydrogen peroxide) without separation and purification thereof, thereby obtaining a target polyethersulfone (PES) compound. 
     The oxidation of the poly arylene ether sulfone-sulfide compound (PES-S) is performed in a heterogeneous state, and PES-S exhibits a similar oxidation rate regardless of forms thereof. For example, PES-S exhibits almost the same oxidation rate when used in solid form such as fibers, powders and the like, and even when used in bead form formed by dissolving PES-S in an organic solvent (sulfolane, DMAc, DMF, NMP, and the like), followed by precipitation in water. 
     That is, in preparation of polyethersulfone (PES) by one-pot reaction, since the poly arylene ether sulfone-sulfide compound (PES-S) is precipitated in bead form when an organic solvent solution including the poly arylene ether sulfone-sulfide compound (PES-S) prepared by condensation polymerization is added to the aqueous solution of the organic acid or to the aqueous solution of the organic acid and the aqueous solution of hydrogen peroxide, oxidation can be performed as in oxidation of the purified PES-S. 
     In addition, since the method for preparing a polyethersulfone according to the present invention allows oxidation in an aqueous solution state, there are merits in that a salt can be more effectively removed from the obtained polymer, and in that an aqueous solution obtained by filtration after completion of oxidation can be used again in oxidation by adjusting the concentrations of the organic acid and the oxidant without post-treatment. 
     In one embodiment, the polyethersulfone prepared by the method according to the present invention may have a number average molecular weight from about 7,500 g/mol to about 110,000 g/mol as measured by gel permeation chromatography (GPC), without being limited thereto. 
     Hereinafter, the present invention will be described in more detail with reference to the following examples. However, it should be noted that these examples are provided for illustration only and are not to be construed in any way as limiting the present invention. 
     EXAMPLE 
     Preparative Example 1 
     120 mL of NMP and 60 mL of toluene are added to a mixture of 17.6 g (61.2 mmol) of dichlorodiphenyl sulfone (DCDPS), 13.1 g (60 mmol) of thiodiphenol (TDP) and 10.6 g (76.8 mmol) of potassium carbonate (K 2 CO 3 ), followed by removal of water and toluene generated in the course of heating the mixture to 130° C. for 4 hours. Next, the mixture is heated to 180° C. for 15 hours, followed by cooling to 60° C. and filtration. A brown viscous solution is precipitated in a water/methanol (3:7) solution and filtered, followed by drying in a vacuum oven, thereby obtaining a polyphenylene ether sulfone-sulfide compound (yield: 94%, number average molecular weight (Mn): 11,200 g/mol, polydispersity index (PDI): 3.46) in chip form. 
     Preparative Example 2 
     160 mL of NMP and 80 mL of toluene are added to a mixture of 25.93 g (102 mmol) of difluorodiphenyl sulfone (DFDPS), 21.8 g (100 mmol) of thiodiphenol (TDP) and 16.6 g (120 mmol) of potassium carbonate (K 2 CO 3 ), followed by removal of water and toluene generated in the course of heating the mixture to 130° C. for 2 hours. Next, the mixture is heated to 150° C. for 5 hours, followed by cooling to 60° C. and filtration. A pale yellow viscous solution thus obtained is precipitated in a water/methanol (3:7) solution and filtered, followed by drying in a vacuum oven, thereby obtaining a polyphenylene ether sulfone-sulfide compound (yield: 92%, number average molecular weight (Mn): 80,000 g/mol, polydispersity index (PDI): 1.7) in fiber form. 
     Preparative Example 3 
     160 mL of NMP and 80 mL of toluene are added to a mixture of 25.93 g (102 mmol) of difluorodiphenyl sulfone (DFDPS), 21.8 g (100 mmol) of thiodiphenol (TDP) and 16.6 g (120 mmol) of potassium carbonate (K 2 CO 3 ), followed by removal of water and toluene generated in the course of heating the mixture to 130° C. for 2 hours. Next, the mixture is heated to 150° C. for 15 hours, followed by cooling to 60° C. and filtration. A pale yellow viscous solution thus obtained is precipitated in a water/methanol (3:7) solution and filtered, followed by drying in a vacuum oven, thereby obtaining a polyphenylene ether sulfone-sulfide compound (yield: 92%, number average molecular weight (Mn): 94,000 g/mol, polydispersity index (PDI): 1.7) in fiber form. 
     Example 1 
     2 g of the polyphenylene ether sulfone-sulfide compound (PES-S) prepared in Preparative Example 1 is pulverized and added to a mixture of 50 mL of water and 8 mL of formic acid, followed by heating the reactants to 40° C. Next, 4 mL of a 30% aqueous solution of hydrogen peroxide (H 2 O 2 ) is added dropwise to the reactants for 30 minutes, followed by stirring at the same temperature for 16 hours. After stirring, solids are filtered and washed with 20 mL of methanol three times. The washed white solids are dried in a vacuum oven at 80° C., thereby obtaining a polyethersulfone (PES, yield: 99%, number average molecular weight (Mn): 15,000 g/mol) as a final product. 
     Example 2 
     A polyethersulfone (PES, yield: 99%, number average molecular weight (Mn): 95,400 g/mol) is obtained in the same manner as in Example 1 except that the polyphenylene ether sulfone-sulfide compound (PES-S) prepared in Preparative Example 2 is used instead of the polyphenylene ether sulfone-sulfide compound (PES-S) prepared in Preparative Example 1. 
     Example 3 
     A polyethersulfone (PES, yield: 92%, number average molecular weight (Mn): 109,000 g/mol) is obtained in the same manner as in Example 1 except that the polyphenylene ether sulfone-sulfide compound (PES-S) prepared in Preparative Example 3 is used instead of the polyphenylene ether sulfone-sulfide compound (PES-S) prepared in Preparative Example 1. 
     Example 4 
     120 mL of NMP and 60 mL of toluene are added to a mixture of 17.6 g (61.2 mmol) of dichlorodiphenyl sulfone (DCDPS), 13.1 g (60 mmol) of thiodiphenol (TDP) and 10.6 g (76.8 mmol) of potassium carbonate (K 2 CO 3 ), followed by removal of water and toluene generated in the course of heating the mixture to 130° C. for 4 hours. Next, the mixture is heated to 180° C. for 15 hours, followed by cooling to room temperature, thereby preparing a PES-S in a viscous solution state. Next, the PES-S in a solution state is added to an aqueous solution of an organic acid, in which 800 mL of water and 200 mL of formic acid are mixed, followed by heating the reactants to 40° C. Next, 200 mL of a 30% aqueous solution of hydrogen peroxide (H 2 O 2 ) is added dropwise to the resulting material over 30 minutes, followed by stirring at the same temperature for 16 hours. After stirring, solids are filtered and washed with 20 mL of methanol three times. The washed white solids are dried in a vacuum oven at 80° C., thereby obtaining a polyethersulfone (PES, yield: 99%, number average molecular weight (Mn): 16,000 g/mol) as a final product. 
     Each of the polyethersulfones prepared in Examples 1 to 4 is subjected to  1 H-NMR measurement using an FT-NMR (Bruker Co., Ltd., 300 MHz). Results shown below confirm that the polyethersulfone is prepared. 
     ( 1 H-NMR, 300 MHz, DMSO-d 6 ): δ 7.98 (d, J=9.0 Hz, 4H), 7.27 (d, J=8.7 Hz, 4H) 
     Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing description. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.