JPH08311202A - Purified polysulfone resin and method for purifying polysulfone resin - Google Patents

Abstract

PURPOSE: To obtain a purified polysulfone resin improved in stability and productivity in film formation without causing filter clogging due to the turbidness of the polymer solution by immersing a polysulfone resin in a liquid in which the resin can be swollen. CONSTITUTION: A polysulfone resin having a content of a cyclic dimer represented by formula II and obtained by copolymerizing a bisphenol A of formula I with dichlorodiphenyl sulfone of 50% or below is immersed in a liquid in which the resin can be swollen, and optionally irradiated with ultrasonic waves at 20kHz to 1MHz, and the liquid is evaporated to leave a purified polysulfone resin freed from the cyclic dimer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a purified polysulfone resin and a method for purifying a polysulfone resin which are excellent in stability of a polysulfone film-forming stock solution and in productivity in film formation.

[0002]

2. Description of the Related Art Fluid separation membranes made of polysulfone have excellent heat resistance and are used in many applications. In forming the film, polysulfone was added to dimethylacetamide (hereinafter,
A polymer solution dissolved in a specific organic solvent such as DMAC) or dimethylformamide (DMF) is extruded into a coagulation medium such as water to coagulate. By the way, it has been observed for a long time that this polysulfone film-forming stock solution shows a phenomenon that it becomes cloudy over time. However, its identity was not revealed. When the undiluted solution becomes cloudy, the filter for removing foreign matter in the film forming process is clogged, which lowers productivity.

In recent studies, it has been found that the white turbidity is due to the precipitation of cyclic dimers existing in the raw material polysulfone pellets. However, it is said that this cyclic dimer is generated at a probability that it is a polymerization step of a polymer, and it is impossible to prevent its formation and of course it is impossible to change the ratio. Further, there is no established technique for removing the cyclic dimer from the pellets, and therefore the white turbidity had to be left.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a purified polysulfone resin and a method for purifying a polysulfone resin, which are excellent in the stability of a stock solution and the productivity of film formation.

[0005]

[Means for Solving the Problems] The present inventors have removed a cyclic dimer, which is a causative substance that causes the polymer solution to become cloudy, and provide a stable solution capable of forming a stable film without clouding for a long period of time without causing filter clogging. As a result of earnest research for supplying the above, a method for selectively extracting cyclic dimers under specific conditions was found and the present invention was reached.

That is, the first aspect of the present invention is a purified polysulfone resin which is characterized by removing cyclic dimers. Although several kinds of polysulfone resins are known and recognized as a heat-resistant membrane material for super engineering plastics, in the present invention, the bisphenol A represented by the formula (1) and dichlorodiphenyl sulfone are Polymers, which are generally called polysulfones, are targeted.

[0007]

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Several low molecular weight polymers are formed during the polymerization of polysulfones. When polysulfone is dissolved in an organic solvent such as tetrahydrofuran (hereinafter referred to as THF) and its gel permeation chromatograph (hereinafter referred to as GPC) is measured, a plurality of peaks are obtained. It is a low molecular weight component called oligomer such as dimer, cyclic dimer (that is, cyclic dimer), trimer, cyclic trimer, tetramer and cyclic tetramer. Of these, cyclic multimers such as cyclic dimers are structurally difficult to dissolve in a solvent that dissolves the polymer and easily form crystals, but most of the crystals are cyclic dimers, and to eliminate cloudiness, use cyclic dimers. It turned out that it should be removed.

This cyclic dimer of polysulfone is represented by the formula (2).

[0010]

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The present invention can be applied to those in which a functional group such as a hydrophilic group is introduced in the polymerization process or those to which a functional group is added after the formation of the polymer, as long as the same cyclic dimer exists. In the present invention, the “removed” state means
It means that the residual ratio defined by the cyclic dimer content in the raw material after extraction with respect to the cyclic dimer content in the initial raw material is 50% or less. That is, it means a state in which the amount contained in the pellet is reduced to 50% or less.
It is more preferably 30% or less. If the water content is high or the temperature is high, it becomes cloudy.
The stock solution at 0 ° C does not become cloudy even if left for 1 week.

The cyclic dimer content is measured as follows. Approximately 20cc of T
Dissolve in HF and load column on TSKgel G2000Hx
A GPC chromatogram is obtained using HLP-8020 manufactured by Toyo Soda Co., Ltd. The content ratio is the cyclic dimer peak height with respect to the obtained polymer peak height.

The second aspect of the present invention is a method for purifying a polysulfone resin by removing the cyclic dimer. There are several possible methods for removing cyclic dimers. A method is known in which a stock solution is allowed to stand for a long period of time to become cloudy, and then settled, followed by filtration. However, it takes too much time until cloudy sedimentation occurs, which is unsuitable for industrial production. Further, since cyclic dimers are generally easily dissolved in a solvent that dissolves a polymer, if the undiluted stock solution that has precipitated and is in equilibrium is filtered once and left to stand, it becomes cloudy again. Unless this is repeated, the cyclic dimer content cannot decrease, so it is inappropriate in view of the productivity of industrial production.

As a result of intensive studies, the present inventors have found that the cyclic dimer can be removed by immersing it in a liquid that swells the polysulfone resin, and completed the present invention. This can be interpreted as an increase in the extraction speed as a result of the gap between the polymer chains of the polysulfone being open in the liquid that swells the polymer of the polysulfone and the mobility of the cyclic dimer trapped between the polymer chains increasing. . Further, when ultrasonic waves are irradiated in a liquid that swells the polysulfone resin, the movement is further promoted and the removal rate is improved. When the swollen polysulfone is rolled, the contact area is expanded and the removal rate is further accelerated. It is also useful to use the step of rolling in a liquid for swelling the polysulfone resin and the step of irradiating ultrasonic waves together. In this way, after extracting and separating the cyclic dimer, the swollen liquid is volatilized to obtain a purified polysulfone resin from which the cyclic dimer is removed.

At this time, oligomers other than cyclic dimers may be removed, but this does not hinder the purpose of the present invention. Examples of the liquid for swelling the polysulfone resin used in the present invention include dimethyl sulfoxide (hereinafter referred to as DMSO) and ketones. In addition to the swelling ability, considering that the pellet is dried again after extracting the oligomer, it is volatile. Most preferred are ketones represented by acetone.

The wave number and output of the ultrasonic waves to be irradiated vary depending on the scale of equipment and required capacity, but are from 20 kHz to 1 MHz.
About 40 to 100 kHz is preferably used. The output is determined by the size of the device, but in the laboratory, several hundred W is sufficient. Further, the lower the bath ratio of the polymer and the extraction swelling agent, the better the extraction becomes possible, but it can be appropriately determined in consideration of the productivity and the achievement level.

As a rolling method, conventionally known techniques such as a screw and a roller can be applied. It is also possible to stir and raise the temperature in order to carry out extraction efficiently. The swelling agent is preferably contacted and updated in a batch manner. Repeating the update has a high effect of reducing the remaining rate. The swelling agent extracted at the end can be removed by a method such as volatilization to obtain a polysulfone resin from which cyclic dimers have been removed.

On the other hand, it is also possible to prepare the polymer solution while leaving the extraction solvent without volatilizing. For example, DMSO is a swelling agent that is well miscible with DMAC, which is a good solvent for polysulfone, and is effective for performance control, so there may be no problem even if it is left as it is.

[0019]

EXAMPLES The present invention will now be described in more detail by way of examples.

[0020]

Example 1 A collection vial containing about 0.1 g of polysulfone pellets (UDEL P-3500 manufactured by Teijin Amoco Co., Ltd.) and 100 ml of reagent grade acetone made by Wako Pure Chemical Industries, Ltd. was ultrasonically cleaned by Yamato Scientific Co., Ltd. BLANSONIC 221 (45kHz, 60W)
And sonicated for 8 hours. The cyclic dimer residual rate after 8 hours was 55%.

When the acetone was renewed three times and the operation was carried out for a total of 32 hours, the residual rate was 17%. 20 g of the polysulfone solid matter having a residual rate of 17% thus purified was dissolved in 80 g of DMAC (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) to obtain a polymer solution. This solution did not become cloudy at all even when left at 20 ° C. for 10 days or longer. This stock solution was subjected to constant volume filtration with a candle filter having a nominal pore size of 0.5 micron manufactured by Nippon Pole Co., Ltd. No increase in filtration pressure was observed.

[0022]

Example 2 As in Example 1, ultrasonic treatment was carried out for 3 hours. One hour and two hours later, the pellets were taken out and rolled with a glass rod. The cyclic dimer residual rate after 3 hours was 42%. Residual rate 4 thus purified
20 g of a 2% polysulfone solid was dissolved in 80 g of DMAC to obtain a polymer solution. This solution did not become cloudy at all even when left at 20 ° C. for 10 days or longer. This stock solution was subjected to constant volume filtration with a candle filter having a nominal pore size of 0.5 micron manufactured by Nippon Pole Co., Ltd. No increase in filtration pressure was observed.

[0023]

Comparative Example 1 The same treatment as in Example 1 was carried out except that ethanol was used instead of acetone. The residual rate after 3 hours was 98%. Ethanol causes the polysulfone porous membrane to swell, but the pellet does not. Such liquids are difficult to remove from pellets. 20 g of the polysulfone pellet having a residual rate of 98% treated in this manner was dissolved in 80 g of DMAC to obtain a polymer solution. This solution became cloudy immediately after standing at 20 ° C. for several days. When this stock solution was filtered with a constant volume of the same candle filter having a nominal pore diameter of 0.5 μm as that used in Example 1, an increase in filtration pressure was observed.

[0024]

Industrial Applicability According to the present invention, polysulfone from which the cyclic dimer, which is the causative agent of white turbidity, is removed can be obtained, so that it is possible to prepare a stable stock solution for forming a film that does not cause white turbidity and improve the productivity of film formation. To do.

Claims (6)

[Claims] 1. A purified polysulfone resin having a cyclic dimer removed. 2. A method for purifying a polysulfone resin for removing a cyclic dimer from the polysulfone resin, which comprises immersing the polysulfone resin in a liquid for swelling the polysulfone resin. 3. A method for purifying a polysulfone resin for removing cyclic dimers from the polysulfone resin, which comprises the step of irradiating ultrasonic waves in a liquid for swelling the polysulfone resin. 4. A polysulfone resin for removing cyclic dimers from a polysulfone resin, which comprises a step of rolling in a liquid for swelling the polysulfone resin, a step of irradiating ultrasonic waves, and a step of volatilizing the swollen liquid. Purification method 5. The method for purifying a polysulfone resin for removing cyclic dimer from the polysulfone resin according to claim 2, wherein the liquid for swelling the polysulfone resin is a ketone. 6. The method for purifying a polysulfone resin for removing a cyclic dimer from the polysulfone resin according to claim 2, wherein the liquid for swelling the polysulfone resin is acetone.