JP2729257B2 - Method for producing low molecular weight styrenic polymer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a low molecular weight styrene-based polymer.

(Prior art and its problems) Many studies have been made on a method for obtaining polystyrene by cationic polymerization of styrene.
For example, PHPlesch's book, The Chemistly of Cationi
c Polymerization ”(1963).
In this, polymerization of styrene using a Lewis acid as a catalyst is mainly studied at −20 to 30 ° C. In addition to a catalyst, a cocatalyst is required. The reaction rate is said to be the fastest when the reaction rate is about twice as high. Further, "Trans Faraday Soc.", 54, 894 in (1958) is to the dichloroethane solvent, the analyzed styrene polymerization reaction of tin tetrachloride as a catalyst at 25 ° C., the amount of water as a co-catalyst a catalyst It has been reported that a little more than twice the molar amount is optimal. In any case,
In order to efficiently produce polystyrene by cationic polymerization, a trace amount of water control in the order of tens of ppm is indispensable.

Also, Joseph P. Kennedy's book `` Cationic Polymeriz
ation of Olefns (A Critical Inventry, 1975) concluded that cationic polymerization would be unattractive as an industrial process due to the poor physical properties of polystyrene obtained by cationic polymerization. I have.

As described above, the industrial production method of polystyrene by cationic polymerization has not received much attention.

Japanese Patent Publication No. Sho 62-46561 proposes an industrial method for producing low molecular weight polystyrene using a Lewis acid, particularly boron trifluoride as a catalyst at a high temperature. However, even in this method, the amount of water used as a cocatalyst is as small as 0.13 to 2.68 times the molar amount of the catalyst, and the allowable amount of water in the polymerization reaction system is small. The molecular weight distribution of the produced polystyrene is represented by the ratio of the weight average molecular weight to the number average molecular weight and is 2.9 or more, and polystyrene having a narrow molecular weight distribution cannot be produced. In addition, the low-molecular-weight polystyrene produced by cationic polymerization generally contains a large amount of dimers and trimers. Therefore, when a sulfonation reaction is performed, the viscosity increases due to the sulfonated products of these dimers and trimers. Therefore, there is a problem that it is difficult to efficiently perform the sulfonation.

Furthermore, Japanese Patent Application Laid-Open No. 63-277205 proposes a method for producing low molecular weight polystyrene using polystyrene sulfonic acid as a catalyst. In this case, the polystyrene sulfonic acid used as a catalyst is expected to have a wide molecular weight distribution of the generated polystyrene unless the purity is high,
It is difficult to produce a high-purity product by an ordinary method, and it is not suitable for industrial production of polystyrene having a narrow molecular weight distribution.

As described above, there has been no industrially advantageous method for producing low molecular weight polystyrene having a narrow molecular weight distribution using a cationic polymerization method.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems encountered in the production of polystyrene-based polymers having a low molecular weight, and provides a method capable of producing a low-molecular-weight polymer excellent in color tone with a narrow molecular weight distribution at a high conversion. Is the task.

(Means for Solving the Problems) The present inventors have conducted intensive studies to solve the above problems, and as a result, have completed the present invention.

That is, according to the present invention, for a halogenated hydrocarbon solvent containing a metal halide as a catalyst and water as a cocatalyst, the amount of the catalyst is 0.
The polymerization reaction is carried out while dropping the styrene monomer under the conditions of 01 to 0.5% by weight, the molar ratio of the cocatalyst to the catalyst is 5 or more, and the polymerization temperature is 30 to 150 ° C. After completion of the dropwise addition, a catalyst comprising a metal halide is added so as to be at least twice the weight of the catalyst present in the solvent and the total amount of the catalyst is 0.15 to 1.5% by weight of the total styrene monomer. The present invention further provides a method for producing a low-molecular-weight styrene-based polymer, characterized in that the polymerization reaction is further continued under the condition that the molar ratio of the cocatalyst to all catalysts is 5 or more and the polymerization temperature is 30 to 150 ° C.

As the styrene monomer used in the present invention, a commercially available styrene monomer can be used, and it may contain about several hundred ppm of water. The styrene-based monomer generally contains a polymerization inhibitor, but may contain such a polymerization inhibitor. The styrene-based monomer includes, in addition to styrene, a nuclear-substituted styrene having a substituent such as chlorine or a methyl group.

In the polymerization reaction of the present invention, a metal halide is used as a catalyst and water is used as a cocatalyst, and a halogenated hydrocarbon is used as a reaction solvent. As the metal halide used as a catalyst, use of a metal chloride is particularly preferred. Such materials include, for example, tin dichloride, tin tetrachloride, aluminum chloride, titanium tetrachloride and the like. Examples of the halogenated hydrocarbon used as a reaction solvent include, for example, dichloromethane, chloroform, carbon tetrachloride, dichloroethane, tetrachloroethane, tetrachloroethylene and the like.

When a polymerization reaction is carried out according to the present invention, a polymerization reaction (first polymerization reaction) is carried out while dropping a styrene-based monomer (hereinafter also referred to as a monomer) into a reaction solvent containing a catalyst and a cocatalyst. After completion of the dropping of the monomer, a polymerization reaction (second polymerization reaction) is performed by adding a catalyst, thereby completing the polymerization reaction.

The amount of the catalyst used in the first polymerization reaction is from 0.01 to 0.5% by weight based on the total amount of the monomers. If the amount is less than this, the polymerization rate becomes extremely slow, which is not preferable. It is not preferable because the amount of trimer produced increases. The catalyst may be added to the reaction system all at once or in portions. Also,
Upon addition of the catalyst, the catalyst may be diluted with the same solvent as used in the present invention or another solvent inert to the reaction. The amount of the cocatalyst (water) used in the first polymerization reaction is 5 or more in molar ratio to the catalyst, and is equal to or less than the saturated water content of the solvent. If the use amount of the cocatalyst is too small, the reaction rate becomes slow, which is not preferable.On the other hand, if the amount of the saturated solvent exceeds the saturated water content, the reaction system becomes heterogeneous,
This is not preferable because the reaction rate is significantly reduced. The amount of the cocatalyst to be used is usually in the range of 5 to 25 in molar ratio to the catalyst. The ratio between the halogenated hydrocarbon solvent and the styrene monomer used in the polymerization reaction of the present invention is not particularly limited. However, considering the control of the reaction system and the post-treatment step, the weight ratio of the solvent and the styrene-based monomer is preferably 10/90 to 90 /
It is better to set to 10, more preferably 20/80 to 80/20.

It is preferable that the monomer is dropped in the first polymerization reaction by performing the polymerization while controlling the dropping speed to keep the concentration of the monomer in the reaction system substantially constant. The monomer concentration in the system during the reaction is preferably maintained within ± 3% of the set value. The set monomer concentration is preferably 1 to 40% by weight, more preferably 1 to 30% by weight.

Regarding the polymerization temperature in the first polymerization reaction, usually 30
A range of ~ 150 ° C is suitable, but preferably 40 ~ 150 ° C,
More preferably, the range of 50 to 150 ° C is appropriate. When the polymerization temperature is lower than 30 ° C., the reaction rate is low, so that it is not industrially suitable. On the other hand, if the temperature is higher than 150 ° C, dimer or 3
It is not appropriate because the monomer easily forms. There is no problem if the polymerization is carried out at a temperature higher than the boiling point of the solvent, but in this case, it is necessary to make the reaction vessel pressure-resistant. The polymerization is preferably carried out at the boiling point of the reaction solvent, whereby effects such as easy control of the polymerization temperature can be obtained. The polymerization time varies depending on the polymerization temperature, the amount of the catalyst, the method of adding the catalyst and the like, and cannot be uniquely defined, but is usually 3 to 12 hours.

In the present invention, after completion of the dropping of the monomer, a new catalyst is added, and a second polymerization reaction is further performed. In the second polymerization reaction, the amount of the catalyst to be added is at least twice the weight of the catalyst used in the first polymerization reaction, and the total amount of the catalyst is 0.15 to 1.5% by weight of the total monomers. Amount. If the amount of the catalyst added in the second polymerization reaction is too large, the amount of dimers and trimers formed increases, and the color tone of the polymer deteriorates. On the other hand, if the amount is too small, the polymer absorption rate (reaction rate) decreases. It is not preferable because it lowers. As the polymerization temperature in the second polymerization reaction, the same temperature as the polymerization temperature in the first polymerization reaction is employed. Further, the usage ratio of the cocatalyst is 5 or more and not more than the saturated water content of the solvent in a molar ratio to the total amount of the catalyst (the total of the amount of the catalyst in the first polymerization reaction and the amount of the catalyst in the second polymerization reaction). In the second polymerization reaction, a cocatalyst is added as necessary so that the ratio of the cocatalyst to the total amount of the catalyst is within the above range according to the amount of the catalyst added.
The time of the second polymerization reaction varies depending on the polymerization temperature, the amount of the catalyst, the method of adding the catalyst, and the like. Although it is difficult to determine a unique droplet, it is usually 1 to 8 hours.

In this method, since the allowable amount of water is large, when the reaction solvent is recycled and used, the halogenated hydrocarbon purified by simple distillation can be directly used as the polymerization solvent. It is known that in cationic polymerization, since a counter ion is always present at the growth terminal of the polymer, the influence of the solvent on the polymerization reaction is large. When the reaction is performed at a temperature higher than room temperature as in the present invention, it is considered that the halogenated hydrocarbon and water contribute to the improvement of the reaction rate as a mixed solvent.

The metal halide catalyst remaining after the completion of the reaction can be easily removed by filtering or washing with water the resulting precipitate after neutralization with ammonia or the like according to a conventional method. It is also possible to remove by filtration after having been adsorbed by the adsorbent.

(Effect of the Invention) According to the present invention, the weight average molecular weight is in the range of 1,000 to 50,000, preferably 1,000 to 20,000, and the ratio (w / n) between the weight average molecular weight (w) and the number average molecular weight (n). But
1.5 to 3.0, advantageously in the range 1.5 to 2.5, dimer and 3
A low-molecular-weight styrene-based polymer having a narrow molecular weight distribution with a total content of monomers of 0.01 to 2% by weight can be obtained at a high conversion. Moreover, the polymer obtained in the present invention is excellent in color tone.

In the method of the present invention, since the water tolerance is large,
Disadvantages of conventional cationic polymerization are that there is no need to control a very small amount of water in the reaction system.In addition, when the reaction solvent is recycled and used, there is no need to remove water with a rectification device or the like. Is advantageous in that the reaction time can be shortened, and the method of the present invention is excellent as an industrial method.

The low-molecular-weight styrene-based polymer obtained in the present invention has a narrow molecular weight distribution and a high reaction rate, so if the catalyst and the solvent are removed, it is suitable as a plasticizer for resin molding, a binder for a toner and a pigment, and an insulating agent. Things.

In the method of the present invention, since a halogenated hydrocarbon inert to a sulfonating reagent is used as a reaction solvent, there is no need to replace the solvent when sulfonating the resulting styrene-based polymer. Can be directly sulfonated, which is industrially very advantageous. In particular, when sulfonating a styrene-based polymer having a small content of a dimer or trimer, a large increase in viscosity does not occur, and therefore, sulfonation can be achieved easily and efficiently. The thus obtained sulfonated styrene-based polymer in a small amount exhibits an excellent action as a dispersant, and is suitable as a dispersant for coal / water slurry, a cement dispersant, and the like.

(Example) Next, the present invention will be described in more detail with reference to examples.

Example 1 A 500 ml four-necked flask was equipped with a stirrer, a thermometer, a dropping funnel and a condenser. This reaction vessel is charged with 200 g of ethylene dichloride, and 0.01 g of tin tetrachloride as a catalyst and 0.007 g of pure water as a cocatalyst are added. The temperature was raised to 84 ° C., which is the boiling point of ethylene dichloride, while stirring the inside of the reaction system, and 100 g of styrene was added dropwise using a dropping funnel over 8 hours to carry out the first polymerization reaction. After dropping, 0.15 g of tin tetrachloride and 0.35 g of pure water were added, and 84
Stirring was further continued at 2 ° C. for 2 hours to carry out a second polymerization reaction to obtain polystyrene. The obtained polystyrene was analyzed using gel permeation chromatography (hereinafter abbreviated as GPC), and as a result, the conversion was 99.2%. (W / n ratio, the same applies hereinafter)
The color tone was 2.6 and the color tone was 20.

The GPC analysis was carried out using columns G4000H and G1000H manufactured by Tosoh Corporation and based on a calibration curve prepared similarly using standard polystyrene manufactured by Tosoh Corporation. The color tone is measured by the APHA color method.

Example 2 An experiment was performed in the same manner as in Example 1, except that the reaction conditions shown in Table 1 were used.

The obtained polystyrene was analyzed using GPC, and the reaction rate, molecular weight, molecular weight distribution and color tone were determined. The results are summarized in Table 1.

As can be seen from the results shown in Table 1, the polymers obtained according to the present invention (Experiments No. 1 to No. 3) have a high polymer yield (reaction rate), a narrow molecular weight distribution, and Excellent in color tone of polymer.

In contrast, in an experiment showing a comparative example, H ₂ O / SnCl ₄
Is more than 25 (Experiment No. 4), the polymer yield is low, while the amount of catalyst (SnCl ₄ ) is 1.5% by weight of the monomer.
(Experiment No. 5), the color tone of the polymer becomes significantly impaired. On the other hand, if the amount of catalyst added is too small (Experiment No. 6), the polymer yield will decrease.

Claims (3)

(57) [Claims] (1) a halogenated hydrocarbon solvent containing a metal halide as a catalyst and water as a cocatalyst, the amount of the catalyst is 0.01 to 0.5% by weight based on all styrene monomers;
The molar ratio of the cocatalyst to the catalyst is 5 or more and the polymerization temperature is
The polymerization reaction is carried out while dropping the styrenic monomer under the conditions of 30 to 150 ° C., and after the dropping of all the styrenic monomers, the catalyst comprising the metal halide is added to the weight of the catalyst present in the solvent. And the total catalyst amount is 0.15 to 1.5% by weight of the total styrenic monomer. The molar ratio of the cocatalyst to the total catalyst is 5 or more and the polymerization temperature is 30 to 150 ° C. A process for producing a low-molecular-weight styrene-based polymer, characterized by further continuing the polymerization reaction under the conditions of (1). 2. The method of claim 1 wherein said polymerization temperature is the boiling point of the solvent. 3. The weight average molecular weight is in the range of 1,000 to 50,000, and the ratio of the weight average molecular weight to the number average molecular weight is 1.5 to
3. The method according to claim 1, wherein a low molecular weight styrenic polymer in the range of 3.0 is obtained.