AU678732B2 - Coherent method for preparing water-soluble sulfonated polymer - Google Patents

Description

45880 AWT:MH P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

V Name of Applicant: LION CORPORATION Actual Inventors: SHOJI SASAKI MASANORI KOMATSU MASAYUKI IDE TAKESHI YAMADA e Address for ServApplicant: :CO LION CORPORATION11 King William Street Adelaide SA 5000 Actual Inventors: COHERENT METHOD FOR PREPARING WATER-SOLUBLE SULFONATED POLYMER The following statement is a full description of this invention, including the best method of performing it known to u:SASAKI MASANORI KOMATSU MASAYUKI IDE TAKESHI YAMADA Address for Service: COLLISON CO.,117 King William Street, Adelaide, S.A. 5000 Invention Title: COHERENT METHOD FOR PREPARING WATER-SOLUBLE SULFONATED POLYMER The following statement is a full description of this invention, including the best method of performing it known to us: ~sllb TITLE OF THE INVENTION Coherent Method for Preparing Water-Soluble Sulfonated Polymer BACKGROUND OF THE INVENTION The present invention relates to a method for coherently or continuously preparing a water-soluble sulfonated polymer such as polystyrenesulfonic acid or a salt thereof through an integrated operation from the polymerization of a polymerizable monomer to the sulfonation of the resulting polymer.

S" There have been known a variety of methods for preparing polymers and for sulfonating the resulting polymers. Examples of methods for preparing polymers include those which comprise polymerizing monomers in a solvent (such as those disclosed in, for instance, Japanese Un-Examined Patent Publication (hereinafter referred to as KOKAI") Nos. Sho 48-54189, Sho 53-24382, Sho 54- 38392 and Sho 56-152814), and those which comprise heat-polymerizing monomers in the absence of any solvent (such as those disclosed in e0 20" Japanese Examined Patent Publication (hereinafter referred to as "J.P.

KOKOKU") Nos. Sho 49-2340 and Sho 49-2341 and J.P. KOKAI Nos. Sho 48- 12887, Sho 49-22494 and Sho 54-17992). In either of these methods, the resulting polymers are withdrawn in the bulk states. In addition, as methods for sulfonating these polymers, there have general'y been adopted those which comprise dissolving each polymer thus prepared in a solvent, then sulfonating it with a sulfonating agent and recovering the solvent for recycling (see, for instance, J.P. KOKAI Nos. Sho 48- 12895, Sho 50-112481, Sho 58-11506 and Hei 2-294305). As has been discussed above, the preparation of a polymer and the sulfonation thereof have separately been performed in the conventional methods and this makes the efficient production of a sulfonated polymer difficult. Therefore, the conventional methods are unfavorable in view of profits.

On the other hand, there have also been known methods for directly preparing a polymer such as a sulfonated styrene oligomer starting from a monomer such as styrene (see, for instance, J.P.

KOKAI Nos. Sho 48-12895 and Sho 48-49745). However, these methods suffer from a problem in that they can prepare only oligomers each having a weight-average molecular weight ranging from 1200 to 5000 since the methods comprise adding a monomer such as styrene to a solvent and then polymerizing the monomer simultaneous with the sulfonation of the resulting polymer.

Moreover, if it is intended to carry out the preparation of a polymer and the sulfonation thereof in the same solvent, toluene as an example of such a solvent is suitably used for the preparation of

S

polystyrene KOKAI No. Sho 53-24382), but is unsuitable as a sulfonation solvent since the solvent per se is also sulfonated.

For this reason, there has not yet been reported any process which comprises carrying out the preparation of a polymer and the sulfonation thereof in the same solvent and recovering the solvent for recycling.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for preparing a water-soluble sulfonated polymer of high quality through an integrated operation from the polymerization of re I -a L' monomers to the sulfonation of the resulting polymer, a coherent method which comprises polymerizing a polymerizable monomer in a solvent, then sulfonating the resulting polymer still dissolved in the solvent without separating the polymer from the solvent in its bulk state and recovering the solvent for reuse.

The present invention has been completed on the basis of the finding that the foregoing problems associated with the conventional methods can effectively be solved by continuously carrying out the production of a polymer through polymerization of a monomer, the sulfonation of the resulting polymer and the separation of the resulting sulfonated polymer from the solvent according to specific methods; distilling the solvent thus separated from the reaction system, under specific conditions; and supplying the recovered solvent to the polymerization of the monomer for reuse.

The foregoing object of the present invention can effectively be accomplished by providing a coherent method for preparing a watersoluble sulfonated polymer which comprises the steps of (A) polymerizing a polymerizable monomer in a halogenated hydrocarbon solvent to form a polymer and then preparing a solution of the polymer with or without separation of solid matter present in the polymerization system; bringing the resulting polymer solution into contact with a sulfonating agent to thus sulfonate the polymer in the solution; allowing the resulting sulfonated polymer solution to stand after adding water thereto, with or without neutralization of the solution, to thus separate the suflonated polymer solution into an aqueous phase and a halogenated hydrocarbon solvent phase and to transfer the sulfonated polymer or a salt thereof to the water phase; distilling the separated solvent phase after adjusting the pH of the phase to a level of 4 to 10 to thus recover the halogenated hydrocarbon solvent; and supplying the solvent thus recovered to the step for recycling.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will hereinafter be described in more detail.

According to the method of the present invention, a polymerizable monomer is first polymerized in a halogenated hydrocarbon solvent to form a polymer in Step The polymerizable monomers usable in the present invention may 0**t Sbe, for instance, aromatic vinyl monomers having 8 to 12, preferably 8 to 10 carbon atoms such as styrene, a -methylstyrene, phydroxystyrene and vinyltoluene, which may be used alone or any combination. Examples of such monomers further include combinations of these aromatic vinyl monomers with isoprene, butadiene and/or acrylic acid derivatives.

Examples of the halogenated hydrocarbon solvents used herein are dichloroethanes such as 1,2-dichloroethane, chloroform, carbon tetrachloride, dichloromethane, tetrachloroethane and tetrachloroethylene which may be used alone or in any combination.

Among these solvents, preferred are dichloroethanes. In the present invention, the ratio of the polymerizable monomer to the halogenated hydrocarbon solvent may be arbitrarily be selected, but the weight ratio: polymerizable monomer/halogenated hydrocarbon solvent is preferably adjusted to the range of from 1/99 to 80/20 and more preferably 5/95 to 40/60. In addition, the concentration of the polymerizable monomer in the polymerization system is not restricted

I

to a specific range, but preferably ranges from 1 to 80% by weight and more preferably 10 to 60% by weight.

In the present invention, the polymerization of the polymerizable monomer may be carried out by the conventionally known polymerization method such as anionic polymerization, cationic polymerization or radical polymerization, with cationic polymerization being preferred. In this connection, it is preferred to use a Lewis acid as a catalyst, for instance, metal halides and particularly preferred metal halides are metal chlorides such as tin dichloride, tin tetrachloride, aluminum chloride and titanium tetrachloride. The amount of the catalyst to be used is not limited to a specific range, but preferably ranges from 0.01 to 1 part by weight per 100 parts by weight of the polymerizable monomer used. The catalyst may be added to

C.

the polymerization system in advance or may gradually be added thereto as the polymerization proceeds. Moreover, if a Lewis acid is *eo used as such a catalyst, it is preferred to add 50 to 1000 ppm, preferably 100 to 400 ppm of water to the halogenated hydrocarbon r0** solvent.

In the present invention, it is preferred to carry out the polymerization by introducing a halogenated hydrocarbon solvent, desired amounts of water and a polymerization catalyst into a reactor, then increasing the temperature of the mixtu):e to a desired level and dropwise adding a polymerizable moncmer to the mixture. The polymerization temperature suitably ranges from 30 to 150C preferably 40 to 150'C and more preferably 50 to 150°C.

In the present invention, after completion of the polymerization of the monomer and hence the formation of a desired polymer, the reaction system is preferably ripened for about 1 to 5 hours to thus control the degree of conversion to not less than 95% and preferably not less than 98%. In addition, the polymer thus prepared preferably has an average molecular weight ranging from 200 to 50,000 and preferably 2,000 to 30,000.

Incidentally, the polymerization of the foregoing polymerizable monomer may be carried out under the conditions as disclosed in J.P.

KOKAI Nos. Hei 3-52902, Hei 3-56509, Hei 3-56510 and Sho 53-24382 in addition to those discussed above. The disclosures of these patents are incorporated herein by reference.

After the preparation of an intended polymer, an alkaline agent such as calcium hydroxide is added to the reaction system to thus S" convert the polymerization catalyst into insoluble solid matter, followed by removing the catalyst from the reaction system through, for instance, filtration. For instance, this procedure is preferably carried out by adding an alkaline agent in an amount ranging from 0.1 to 2.0 parts by weight per 100 parts by weight of the polymer, then stirring the mixture for about 0.5 to 2.0 hours and filtering the mixture by the usual manner. The filtration is preferably carried out using a filter aid such as perlite or Celite.

*6* According to the method of the present invention, the polymer solution thus obtained is then brought into contact with a sulfonating agent to thus sulfonate the polymer present in the solution in Step In general, the sulfonation is suitably carried out by introducing the polymer solution withdrawn from the polymerizer into a sulfonation apparatus.

The sulfonation of the polymer may be carried out according to any method which permits close contact between the polymer solution and the sulfonating agent, but preferably by the method as disclosed in, for instance, J.P. KOKAI No. Sho 62-174205, Sho 63-172703, Hei 4- 264107, Hei 2-294305, Hei 3-14803 or Hei 3-66706. The disclosures of these patents are incorporated herein by reference.

More specifically, it is preferable that the polymer solution be continuously introduced into the sulfonation apparatus, simultaneously followed by addition of the sulfonating agent to the apparatus and carrying out the reaction of these reagents, with stirring, at a temperature ranging from 10 to 80 *C (preferably 25 to °C for residence time of 1 to 60 minutes (preferably 1 to minutes). In the sulfonation step, the sulfonating agent is added to the polymer solution having a polymer concentration ranging from 5 to by weight in an amount ranging from 0.5 to 2.0 moles, preferably 0.7 to 1.5 mole per mole of the monomer unit constituting the polymer, with or without addition of a halogenated hydrocarbon solvent to the Spolymer solution. The sulfonating agent usable herein may be, for instance, sulfuric acid anhydride (liquid or gas), gases containing sulfuric acid anhydride, fuming sulfuric acid or chlorosulfonic acid, with the use of sulfuric acid anhydride or a gas containing sulfuric 4 acid anhydride being preferred.

The sulfonation of the present invention may be carried out in the presence of a variety of auxiliary agent for sulfonation such as benzenesulfonic acid and alkylbenzenesulfonate. Such auxiliary agents for sulfonation are disclosed in, for instance, J.P. KOKAI Nos. Sho 61-250003, Sho 50-112480 and Hei 3-59005.

In Step of the method according to the present invention, the resulting sulfonated polymer solution is neutralized and then allowed to stand after addition of water, or allowed to stand after addition of water without neutralization to thus transfer the sulfonated polymer or a salt thereof to the resulting aqueous phase and then the aqueous phase is separated from the halogenated hydrocarbon solvent phase.

The neutralization of the sulfonated polymer solution can be carried out using an alkaline agent capable of forming a desired salt with the polymer. Examples of such alkaline agents are sodium hydroxide, potassium hydroxide and alkaline earth metal compounds.

These alkaline agents are preferably added to the sulfonated polymer solution in the form of an aqueous solution. The neutralization leads to the formation of a salt of the sulfonated polymer. The neutralization may be carried out by, for instance, a method as disclosed in J.P. KOKAI No. Sho 52-33993, Sho 63-189405, Hei 2-240116

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or Hei 2-296804. More specifically, the neutralization is preferably carried out by adding a 5 to 15% aqueous solution of sodium hydroxide for 1 to 2 hours with stirring.

The halogenated hydrocarbon solvent can be separated from the sulfonated polymer or the salt thereof by a method as disclosed in, for instance, J.P. KOKAI No. Sho 63-189404 or Hei 2-258802 or Japanese Patent Application Serial No. Hei 5-87218. The disclosures of these patents are incorporated herein by reference.

More specifically, water is added to the neutralized sulfonated polymer solution or the sulfonated polymer solution free of neutralization and then the mixture is allowed to stand to thus transfer the sulfonated polymer or the salt thereof to the aqueous 2- phase. Water is added to the sulfonated polymer solution in such an amount that the concentration of the sulfonated polymer or the salt thereof in the aqueous phase obtained after the transfer of the polymer thereto ranges from about 10 to 30% by weight. The mixture may be allowed to stand at any temperature and time insofar as the sulfonated polymer or the salt thereof is transferred to the aqueous phase, but in general at a temperature ranging from 20 to 60°C for minutes to 4 hours, preferably 1 to 2 hours. If dichloroethane is used 3s the halogenated hydrocarbon solvent and the sulfonated polymer or the salt thereof is sulfonated polystyrene or a salt thereof, the mixture is separated into the lower dichloroethane phase and the upper aqueous phase containing the sulfonated polstyrene or the salt thereof. According to another embodiment of the present invention, the aqueous phase containing the sulfonated polymer may be separated from the halogenated hydrocarbon solvent phase followed by addition of an alkaline agent such as sodium hydroxide, potassium hydroxide or an alkaline earth metal compound to thus recover the sulfonated polymer in the form of a salt.

In Step of the method according to the present invention, an alkaline agent is added to the halogenated hydrocarbon solvent phase thus separated to adjust the pH value thereof to the range of from 4 a to 10, preferably 6 to 8.0 and then the phase is distilled to recover the halogenated hydrocarbon solvent. Examples of the alkaline agents *-0 used in this step are sodium hydroxide, potassium hydroxide or an alkaline earth metal compound, which is preferably used in the form of an aqueous solution. In the present invention, the halogenated hydrocarbon solvent having a water content ranging from 10 to 150 ppm is preferably recovered by distillation under ordinary pressure or reduced pressure or/and by fractionating it using a fractionating column. If the pH is less than 4, the solvent thus recovered through distillation is contaminated with a trace amount of acidic substances such as the polymerization catalyst and substances each having a low I degree of sulfonation and a problem arises when such a solvent is reused in the polymerization, for instance, the resulting polymer does not have a constant molecular weight. On the other hand, if the pH is highe- than 10, the dichloroethanes are severely decomposed.

According to the method of the present invention, the halogenated hydrocarbon solvent thus recovered can be supplied to Step for polymerizing the monomer in order to reuse the same as the halogenated hydrocarbon solvent. In this respect, it is recommendable that the water content of the recovered halogenated hydrocarbon solvent is set at a level less than that required for the polymerization step and that the water content thereof is adjusted to the range of from 50 to 1,000 ppm prior to the polymerization by addition of an appropriate amount of water.

On the other hand, the aqueous solution of the sulfonated polymer or the salt thereof separated in Step may be used as such or after concentration by the usual method. Alternatively, the volatile components present in the solution may be removed by, for 4 instance, flash distillation to give a powdery product.

According to the method of the present inventi'on, a polymerizable monomer is polymerized in a solvent and then the resulting polymer in the reaction solution is sulfonated subsequent to the polymerization without isolating the polymer in the bulk state. Therefore, the method has various industrial advantages such as high operating efficiency.

Moreover, the method of the present invention permits the effective reuse of the halogenated hydrocarbon solvent and the production of a highly pure water-soluble sulfonated polymer showing uniform quality in a high yield.

The method of the present invention will hereinafter be described in more detail with reference to the following nonlimitative working Examples.

Example 1 A stirring machine, a thermometer, a droppng funnel and a condenser were fitted to a 5 liter volume 4-necked flask. To this reactor, there were added 2 Kg of 1,2-dichloroethane (EDC), 2 g of tin tetrachloride as a catalyst and 0.7 g of pure water.

The temperature of the content of the reactor was raised up to the boiling temperature of EDC with stirring and then 2 Kg of styrene was dropwise added to the reactor through the dropping funnel over hours to thus polymerize the monomer. Then 4 g of tin tetrachloride was additionally added to the reaction system followed by stirring for S16 additional 2 hours to give a polymer solution, adding 2 Kg of EDC and then 20 g of calcium hydroxide to the polymer solution, thereafter stirring the mixture for one hour and finally removing the solid S matter from the solution through filtration to thus give a

B

polystyrene solution.

B.

The polystyrene solution was diluted by addition of 8 Kg of EDC. The starting solution, the diluted polystyrene solution was supplied to a sulfonation reactor along with sulfuric acid anhydride at a molar ratio of the sulfonating agent to the starting material of 1.16 and the sulfonation reaction was carried out under conditions of a reaction temperature of 40°C and a residence time of 10 minutes.

Water was added to the reaction system in such an amount that the concentration of the resulting sulfonated product in the aqueous phase was 20% by weight to thus dissolve the sulfonated product in the aqueous phase, followed by transferring the mixture to a separatory funnel and allowing the mixture to stand for 2 hours to separate the mixture into the aqueous phase and the halogenated hydrocarbon solvent phase.

Then the separated lower phase, the haiogenated hydrocarbon solvent phase was removed, followed by neutralization through addition of 1.7 g of a 5% NaOH aqueous solution and distillation of the mixture to give bottom solutions concentrated to 60% and 8C% respectively. Then each concentrated bottom solution was further distilled to give a distillate, distilled

EDC.

The same procedures for the polymerization reaction and the sulfonation reaction described above were carried out using the recovered halogenated hydrocarbon solvent as a reaction solvent, S: followed by neutralization of the upper phase containing the sulfonated product, which was removed from the separatory funnel, with a 10% NaOH aqueous solution to give an Na salt of the polystyrenesulfonic acid. The pH value of the solvent observed when it was recovered, conditions for sulfonation and properties of the resulting sodium polystyrenesulfonate (PSS-Na) are summarized in the following Table 1 (Sample Nos. 1 to Moreover, the weight-averaga molecular weight of the sodium polystyrenesulfonate obtained when neutralizing the sulfonated product present in the aqueous phase separated in Step with the 10% NaOH aqueous solution was found to be 13,200.

Comparative Example 1 The same procedures used in Example 1 were repeated except that distilled EDC was obtained by removing the separated lower phase, then I @0O* O 4* 4i *r concentrating it to 60% or 80% without neutralization to give a bottom solution and then further distilling the bottom solution and that the resulting distilled EDC was used in the polymerization, to thus give sodium polystyrenesulfonate (Sample Nos. 4 and Table 1: Properties of Sodium Polystyrenesulfonate Sample No. 1 2 3 4 5 pH of Solvent Bottom EDC 7.0 5.0 4.0 2.9 2.4 Recovered EDC 6.5 6.1 5.1 3.5 Conditions for Sulfonation SOa Molar aatio 1.16 1.15 1.10 1.15 1.10 Temperature (C 40 40 41 40 41 Residence Time of Reaction (min) 10 5 15 5 PSS-Na Weight-Average Molecular Weight 13200 13300 12900 8500 7000 Yield 99.9 99.9 99.9 99.9 99.9 Sample Nos. 4 and 5 correspond to Comparative Examples.

In Table 1, each pH value of the solvent was determined by adding an equivalent volume of water to the solvent, sufficiently stirring the mixture to thus transfer any acidic components to the aqueous phase and then measuring the pH of the aqueous phase.

On the other hand, the molecular weight of PSS-Na was determi-ned according to the method detailed below.

The molecular weight of each PSS-Na was determined by the GPC method using a standard sodium polystyrenesulfonate as a reference substance, TSK G3000SW (7.5mmIDX 30cm) and TSK G4000SW oooo, I available from Tosoh Corporation as fractionation columns and an ultraviolet detector (detection wavelength: 238 nm). In this respect, when a styrenesulfonate was detected in the sample, the styrenesulfonate was removed prior to the determination of the weight-average molecular weight.

Example 2 To the same reactor used in Example 1, there were added 2 Kg of 1,2-dichloroethane (EDC), then 4 g of tin tetrachloride as a catalyst and 0.7 g of pure water.

*0 The temperature of the content of the reactor was raised up to 65 °C with stirring and then 2 Kg of styrene was dropwise added to the reactor through the dropping funnel over 5 hours, while 00 00 maintaining the temperature of the content at 65°C to thus polymerize the monomer. After stirring the reaction system for 4 hours, 2 Kg of EDC was additionally added to the resulting polymer solution, followed by addition of 10 g of calcium hydroxide, stirring the mixture for one hour and finally removing the solid matter through 0 filtration to thus give a polystyrene solution.

0* The polystyrene solution was diluted by addition of 12 Kg of EDC. The starting solution, the diluted polystyrene solution was supplied to a sulfonation reactor together with sulfuric acid anhydride at a molar ratio of the sulfonating agent to the starting material of 1.10 and the sulfonation reaction was carried out under conditions of a reaction temperature of 45°C and a residence time of minutes.

The resulting sulfonated product was neutralized with a NaOH aqueous solution such that the pH of the aqueous phase was neutral, followed by transferring the neutralized, sulfonated polymer solution to a separatory funnel and allowing the solution to stand for one hour to separate the solution into the aqueous phase and the halogenated hydrocarbon solvent phase.

Then the separated lower phase, the halogenated hydrocarbon solvent phase was removed, followed by neutralization of the phase through addition of 1.2 g of a 5% NaOH aqueous solution and distillation of the mixture to give bottom solutions concentrated to 60% and 80% respectively. Then each concentrated bottom solution was further distilled to give a distillate, distilled EDC.

The same procedures for the polymerization reaction and the sulfonation reaction described above were carried out using the 5** recovered halogenated hydrocarbon solvent as a reaction solvent, followed by neutralization of the upper phase containing the j.1 sulfonated product, which was removed from the separatory funnel, with a 10% NaOH aqueous solution to give an Na salt of the polystyrenesulfonic acid. The pH value of the solvent observed when it was recovered, conditions for sulfonation and properties of the resulting sodium polystyrenesulfonate (PSS-Na) are summarized in the following Table 2 (Sample Nos. 6 to Moreover, the weight-average molecular weight of the sodium polystyrenesulfonate obtained when neutralizing the sulfonated product present in the aqueous phase separated in Step with the 10% NaOH aqueous solution was found to be 26,000.

Comparative Example 2 The same procedures used in Example 2 were repeated except that distilled EDC was obtained by removing the separated lower phase, then 1 I" concentrating it to 60% or 80% without neutralization to give a bottom solution and then further distilling the bottom solution and that the resulting distilled EDC was used in the polymerization, to thus give sodium polystyrenesulfonate (Sample Nos. 9 and Table 2: Properties of Sodium Polystyrenesulfonate 0**oe* 20 Sample No. 6 7 8 9 10 pH of Solvent Bottom EDC 9.2 7.4 5.5 2.9 2.4 Recovered EDC 6.8 6.8 6.5 3.5 PSS-Na Weight-Average Molecular Weight 26000 25600 25500 18200 14500 Yield 99.9 99.9 99.9 99.9 99.9 Sample Nos. 9 and 10* correspond to Comparative Examples.

Example 3 To the same reactor used in Example 1, there were added 2 Kg of EDC and then 1.0 Kg of styrene monomer. Further 40 g of benzoyl peroxide (BPO) was added as a polymerization initiator and immediately after the addition, the temperature of the content of the reactor was raised up to the boiling temperature of the solvent followed by polymerization over 10 hours. After completion of the polymerization, the unreacted monomer was removed by distillation under reduced pressure followed by addition of EDC to give a polystyrene solution having a polystyrene concentration of 8%.

The starting solution, the polystyrene solution prepared in Step was sulfonated at a molar ratio of the sulfonating agent to the starting material of 1.10, a reaction i temperature of 35*C and a residence time of 5 minutes and then the reaction product was continuously supplied to a stirring bath provided with a stirring blade in such a manner that the retention time in the bath was set at 30 minutes to give a sulfonated product.

Water was added to the reaction system in such an amount that the concentration of the resulting sulfonated product in the aqueous phase was 20% by weight to thus dissolve the sulfonated product in the aqueous phase, followed by transferring the mixture to a separatory funnel and allowing the mixture to stand for 2 hours to separate the mixture into the aqueous phase and the halogenated hydrocarbon solvent phase.

Then the separated lower phase, the halogenated hydrocarbon solvent phase was removed, followed by neutralization of the phase through addition of 0.6 g of a 5% NaOH aqueois sc.iation and distillation of the mixture to give bottom solutions tc,:;trated to 40%, 60% and 80% respectively. Then each concentrated bottom solution was further distilled to give a distillate, distilled EDC.

The same procedures for the polymerization reaction and the

U

sulfonation reaction described above were carried out using the *s 20 recovered halogenated hydrocarbon solvent as a reaction solvent, followed by neutralization of the upper phase containing the sulfonated product which was removed from the separatory funnel with a NaOH aqueous solution to give an Na salt of the p olystyrenesulfonic acid. The pH value of the solvent observed when it was recovered, conditions for sulfonation and properties of the resulting sodium polystyrenesulfonate (PSS-Na) are summarized in the following Table 3 (Sample Nos. 11 to 13). Moreover, the weightaverage molecular weight of the sodium polystyrenesulfonate obtained

I

when neutralizing the sulfonated product present in the aqueous phase separated in Step with the 10% NaOH aqueous solution was found to be 28,000.

S

4.

so 0*

S

5 Comparative Example 3 The same procedures used in Example 3 were repeated except that distilled EDC was obtained by removing the separated lower phase, then concentrating it to 60% or 80% without neutralization to give a bottom solution and then further distilling the bottom solution and that the resulting distilled EDC was used in the polymerization, to thus give sodium polystyrenesulfonate (Sample Nos. 14 and Table 3: Properties of Sodium Polystyrenesulfonate Sample No. 11 12 13 14 15 pH of Solvent Bottom EDC 7.0 5.0 4.0 2.8 2.3 Recovered EDC 6.6 6.1 5.0 3.4 2.9 PSS-Na Weight-Average Molecular Weight 28000 27000 27000 19000 13000 Yield 99.8 99.8 99.9 99.9 99.9 Sample Nos. 14* and 15* correspond to Comparative Examples.

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Claims (9)

1. A coherent method for preparing a water-soluble sulfonated polymer comprising the steps of polymerizing a polymerizable monomer in a halogenated hydrocarbon solvent to form a polymer and then preparing a solution of the polymer with or without separation of solid matter present in the polymerization system; bringing the resulting polymer solution into contact with a sulfonating agent to thus sulfonate the polymer in the solution; allowing the resulting sulfonated polymer solution to stand while adding water with or without neutralization of the solution to thus separate into the aqueous phase and the lalogenated hydrocarbon solvent phase and to transfer the sulfonated polymer or a salt thereof to the water phase; distilling the separated solvent phase after adjusting the pH of the phase to a level of 4 to 10 to thus recover the halogenated hydrocarbon solvent; and supplying the solvent thus recovered to the step for recycling.

2. The method of claim 1 wherein the halogenated hydrocarbon solvent is dichloroethane.

3. The method of claim 1 wherein the polymerizable monomer is an aromatic vinyl monomer having 8 to 12 carbon atoms.

4. The method of claim 3 wherein the polymerizable monomer is styrene.

The method of claim 1 wherein the polymerization of the monomer in the step is cationic polymerization in which a Lewis acid is used as a catalyst; the content of water present in the halogenated hydrocarbon solvent used in the step ranges from 50 to 1000 ppm; and the content of water in the solvent recovered in the step is lower than that present in the halogenated hydrocarbon solvent used in the step

6. The method of claim 5 wherein the amount c the catalyst ranges from 0.01 to 1 part by weight per 100 parts by weight of the polymerizable monomer and the catalyst is added to the polymerization system in advance or it is gradually added to the system.

7. The method of claim 1 wherein the polymerization of the monomer is carried out at a ratio of the polymerizable monomer to the halogenated hydrocarbon solvent ranging from 1/99 to 80/20 and the concentration of the polymerizable monomer ranging from 1 to 80% by weight.

8. The method of claim 1 wherein in the sulfonation, the sulfonating agent is added to the polymer solution having a polymer concentration ranging from 5 to 20% by weight in an amount 0.5 to moles per mole of the monomer unit constituting the polymer.

9. The method of claim 1 wherein the sulfonating agent is sulfuric acid anhydride or a gas containing sulfuric acid anhydride. A method of preparing a water soluble sulfonated polymer substantially as hereinbefore described with reference to S Examples numbers 1, 2 and 3. C Dated this 7th day of November 1995 LION CORPORATION By their Patent Attorneys COLLISON CO (2 I- 1~11 Abstract of the Disclosure A coherent method for preparing a water-soluble sulfonated polymer comprises the steps of polymerizing a polymerizable monomer in a halogenated hydrocarbon solvent to form a polymer and then preparing a solution of the polymer with or without separation of solid matter present in the polymerization system; bringing the resulting polymer solution into contact with a sulfonating agent to thus sulfonate the polymer in the solution; allowing the resulting sulfonated polymer solution to stand while adding water with or without neutralization of the solution to thus separate into the aqueous phase and the halogenated hydrocarbon solvent phase and to transfer the sulfonated polymer or a salt thereof to the water phase; distilling the separated solvent phase after adjusting the pH of the phase to a level of 4 to 10 to thus recover the halogenated .L .hydrocarbon solvent; and supplying the solvent thus recovered to the step for recycling. The method has various industrial advantages such as high operating efficiency. Moreover, the method C S permits the effective reuse of the halogenated hydrocarbon solvent and the production of a highly pure water-soluble sulfonated polymer 20 showing uniform quality in a high yield. I,