JPH068350B2 - Method for preparing high molecular weight, optionally branched, polyarylene sulfides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for the preparation of high molecular weight, optionally branched, polyarylene sulfides from alkali sulfides and aromatic halide compounds, in which the reaction is carried out in a solvent containing 0.5 to 100 mole percent of a lactam, such as an N-alkyl lactam, based on the moles of aromatic dihalide.
It is carried out in a polar solvent.

Polyarylene sulfides and methods for their preparation are known (e.g., U.S. Pat. Nos. 2,513,188; 3,177,
No. 620; No. 3,354,129; No. 3,524,835; 3,7
No. 90,536; No. 3,839,301; No. 4,048,259;
No. 4,038,260; No. 4,038,261; No. 4,038,262
No. 4,056,515; 4,060,520; 4,064,1
14; 4,116,947 and 4,282,347, German Patent Publication Nos. 2,453,485 and 2,453,749,
and German Patent Publication Nos. 2,623,362; 2,623,3
No. 63; No. 2,623,333; No. 2,930,797; No. 2,93
See US Pat. Nos. 3,019,732 and 3,030,488.

Many of these documents describe the addition of inorganic or organic salts during the reaction process to decrease the melt flow of the resulting polyphenylene sulfide, i.e., to increase its melt viscosity. For example, injection molding parts,
Polyphenylene sulfide can be thermoplastically processed to produce films and fibers only if the melt viscosity is sufficiently high. Without the addition of the salts, the resulting polyphenylene sulfide can only attain the required low melt flow through a separate, additional post-condensation or curing step.

The salts used in the above documents are, for example, alkali metal carbonates (German Patent Publication No. 2,453,749),
Lithium halides or alkali metal carbonates (German Patent Publication No. 2,623,362), lithium chloride or lithium carbonate (German Patent Publication No. 2,623,363), alkali metal carbonates in combination with alkali metal carbonates (U.S. Pat. No. 4,038,259), lithium acetate (German Patent Publication No. 2,623,363), trialkali metal phosphates (German Patent Publication No. 2,930,710), trialkali metal phosphates (German Patent Publication No. 2,930,797), alkali metal fluorides (German Patent Publication No. 3,019,732), alkali metal sulfonates (U.S. Pat. No. 4,038,260
No. 4, 5, 6, 7, 8, 9, 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
030,518).

In addition, it is known from German Offenlegungsschrift 3,120,538 that polyarylene sulfides having high melt viscosities can be obtained by adding N,N-dialkylcarboxylic acid amides to the reaction mixture.

The use of polar solvents for the preparation of polyarylene sulfides is also known and is discussed in the literature above.

Lactams are also mentioned as solvents. However, when lactams, such as pyrrolidone and ε-caprolactam, are used as solvents, the p-polyphenylene sulfide obtained has unsatisfactory properties.
That is, they exhibit high melt flow and low melt viscosity and cannot be thermoplastically processed without curing.

Here, if a small amount of lactam is present in the reaction mixture, it can be directly, i.e., without the need for a separate heat treatment:
It has now been found possible to obtain polyarylene sulfides having high melt viscosities which can be thermoplastically processed.

When the reaction is carried out in a polar solvent, preferably an N-alkyl lactam, containing 0.5 to 100 mole % of lactam, based on the moles of aromatic dihalogen compound, according to the present invention, a product with a high melt viscosity can be obtained compared to the known method using pure N-alkyl lactam as solvent.
Less than mol % is ineffective, and more than 100 mol % interferes with the polymerization reaction.

It is known that the addition of aromatic polyhalogen compounds, especially aromatic trihalogen compounds, as branching agents increases the melt viscosity of polyarylene sulfides.

Using the method of the present invention, it is possible to obtain polyarylene sulfides having high melt viscosities without using aromatic polyhalogen compounds.

Thus, the present invention provides a compound comprising: (a) 50 to 100 mol % of a compound of the following general formula: and 0 to 50 mol % of an aromatic dihalogen compound corresponding to
The following general formula: in which X represents a halogen atom, such as chlorine or bromine, in the meta- or para-position relative to one another; and R ¹ , which may be the same or different, is hydrogen, C _1
-C4 -alkyl, _C5 - _C10 cycloalkyl, _C6 -C
_and (b) ₀ to ₅ mol %, preferably _0.1 to _2.5 mol %, based on the total of the aromatic dihalogen compounds (I) and ( ^II ), of aromatic trihalogen or tetrahalogen compounds corresponding to the following general formula: ArXn (III), in which Ar represents an aromatic or heterocyclic group; X represents a halogen, such as chlorine or bromine; and n represents the number 3 or ⁴ ; and (c) 0 to 5 mol %, preferably 0.1 to 2.5 mol %, based on the total of the aromatic dihalogen compounds (I) and (II), of aromatic trihalogen or tetrahalogen compounds corresponding to the following general formula: ArXn (III), in which Ar represents an aromatic or heterocyclic group; X represents a halogen, such as chlorine or bromine; and n represents the number 3 or 4; and
Alkali metal sulfides, preferably sodium or potassium sulfides, or mixtures thereof, in the form of hydrates or hydrous mixtures, with alkali metal hydroxides, the molar ratio of (a+b):c being 0.75:1 to 1.2
(d) optionally present from known catalysts such as alkali metal carboxylates, alkali metal phosphates, alkali metal phosphonates, alkali metal fluorides, alkali metal alkylsulfonates or N,N-dialkylcarboxylic acid amides (German Patent Publication No. 3190538), in a ratio of 0.5:1, based on the number of moles of aromatic dihalogen compound;
The present invention relates to a process for preparing optionally branched polyarylene sulfides, characterized in that the reaction is carried out in a polar solvent containing 5 to 100 mole % of a lactam, preferably an N-alkyl lactam.

The reaction time can be as long as 24 hours, but is preferably 2 to 4 hours.
The reaction time is preferably 18 hours.

The reaction can be carried out in various ways: the alkali sulfide is preferably used in the form of a hydrate and a water-containing mixture or an aqueous solution. The dehydration can be partial or complete, for which purpose the alkali sulfide is first dehydrated together with an organic solvent and a lactam in a preliminary step carried out in the presence of an aromatic dihalogen and/or polyhalogen compound, optionally using an azeotrope-forming or water-entraining agent. It is also possible to dehydrate the entire reaction mixture using an aromatic dihalogen and/or polyhalogen compound as an azeotrope-forming agent.

If the dehydration is only partial, it must be carried out under pressure to reach the required reaction temperature.
The sulfide may be dried separately on its own by application of water and vacuum and then added to the reaction mixture. Depending on the initial nitrogen pressure, the pressure may be as high as 100 bar, but generally a pressure of 2 to 20 bar is used.

If the alkali sulfide is to be completely dehydrated, it is preferably carried out in the presence of all reactants and using aromatic dihalogen and polyhalogen compounds as water entrainers, and the reaction can be carried out in the absence of pressure or under pressure up to about 3 bar. High pressures up to 50 bar can also be applied to obtain reaction temperatures higher than the boiling point of the solvent or the mixture of the solvent and aromatic dihalogen and polyhalogen compounds.

Complete dehydration of all water-containing reactants is presumed for the process of the present invention.

The reactants can be added in a variety of ways.

Although it is possible to add all the reactants directly together, it is preferable to add one or more reactants sequentially, with dehydration, in this way it is possible to control the progress of the reaction and minimize residence time in the reaction mixture.

In comparison with the process according to, for example, German Patent Publication No. 3243185, which also removes water from the reaction, the process of the present invention results in lighter polyarylene sulfides which have greater impact strength, give off less gas when melted, and are therefore less corrosive.

The reaction mixture can be worked up and the polyarylene sulfide isolated by known methods.

The polyarylene sulfide can be isolated from the reaction solution by known methods, either directly or after the addition of, for example, water and/or dilute acid or an organic solvent in which the polyarylene sulfide is poorly soluble, for example, by filtration or centrifugation. Generally, the separation of the polyarylene sulfide is followed by washing with water. Washing or extraction with other washing solvents, which can be carried out in addition to or after the water wash, is also possible.

The polyarylene sulfide can also be recovered, for example, by distilling off the solvent and washing as described above.

Suitable alkali sulfides are, for example, sodium and potassium sulfide.Alkali sulfides can also be obtained from _H2S and alkali hydroxides or from hydrosulfides and alkali hydroxides.

Depending on the amount of alkali metal hydrosulfide present in the reaction solution as an impurity in the alkali metal sulfide, an appropriate amount of alkali metal hydroxide may be additionally introduced. Instead of alkali metal hydroxide, a compound which separates or generates alkali metal hydroxide under reaction conditions may also be added.

According to the present invention, aromatic meta- and para-dihalogen compounds corresponding to the general formulae (I) and (II) can be used. The ratio of aromatic meta-dihalogen compounds to para-compounds can be up to 30:70.

In order to obtain thermoplastically processable polyarylene sulfides, it is particularly preferred to use aromatic p-dihalogen compounds.

If the preparation of branched polyarylene sulfides is intended, at least 0.005 mole % of aromatic trihalogen or tetrahalogen compound (III) should be used.

Examples of aromatic dihalogen compounds corresponding to general formula (I) that can be used according to the invention are p-dichlorobenzene, p-dibromobenzene, 1-chloro-bromobenzene, 1,3-dichlorobenzene, 1,3-dibromobenzene and 1-chloro-3-bromobenzene, which can be used alone or in mixtures with one another.
4-Bromobenzene is particularly preferred.

Examples of aromatic dihalogen compounds corresponding to formula (II) which can be used according to the invention are 2,5-dichlorotoluene, 2,5-dichloroxylene, 1-ethyl-2,
5-dichlorobenzene, 1-ethyl-2,5-dibromobenzene, 1-ethyl-2-bromo-5-chlorobenzene, 1,2,4,5-tetramethyl-3,5-dichlorobenzene, 1-cyclohexyl-2,5-dichlorobenzene, 1-phenyl-2,5-dichlorobenzene, 1-
Benzyl-2,5-dichlorobenzene, 1-phenyl-
2,5-Dibromobenzene, 1-p-tolyl-2,5-
Dichlorobenzene, 1-p-tolyl-2,5-dibromobenzene, 1-hexyl-2,5-dichlorobenzene,
2,4-dichlorotoluene, 2,4-dichloroxylene, 2,4-dibromocumene and 1-cyclohexyl-
3,5-dichlorobenzene. These can be used either alone or in mixtures with one another.

Examples of aromatic trihalogen and tetrahalogen compounds corresponding to formula (III) suitable for use in the present invention are: 1,
2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4-tribromobenzene, 1,3,
5-trichloro-2,4,5-trimethylbenzene,
1,2,3-trichloronaphthalene, 1,2,4-trichloronaphthalene, 1,2,6-trichloronaphthalene, 2,3,4-trichlorotoluene, 2,3,6-trichlorotoluene, 1,2,3,4-tetrachloronaphthalene, 1,2,4,5-tetrachlorobenzene, 2,
2',4,4'-tetrachlorobiphenyl and 1,3,
It is 5-trichlorotriazine.

Generally, any polar solvent can be used for the reaction, which ensures adequate solubility of the organic and possibly inorganic reactants under the reaction conditions. However, the solvent used is preferably a cyclic urea, and more preferably an N-alkyl lactam.

N-alkyl lactams are optionally chain-substituted C ₃ -C 4 -N-alkyl lactams which are inert under the reaction conditions.
It is a lactam of a _C11 amino acid.

The N-alkyl lactam used may be, for example, N-
Methyl-caprolactam, N-ethyl-caprolactam, N-isopropyl-caprolactam, N-isobutyl-caprolactam, N-propyl-caprolactam,
N-butyl-caprolactam, N-cyclohexyl-caprolactam, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-isopropyl-2-pyrrolidone, N-isobutyl-2-pyrrolidone, N-propyl-
2-pyrrolidone, N-butyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, N-methyl-3-methyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, N-methyl-3-methyl-2-pyrrolidone, N-
Methyl-3,4,5-trimethyl-2-pyrrolidone, N
N-methyl-2-piperidone, N-ethyl-2-piperidone, N-isopropyl-2-piperidone, N-isobutyl-2-piperidone, N-methyl-6-methyl-2-piperidone, N-methyl-3-ethyl-2-piperidone.

Mixtures of the above solvents may also be used.

In the context of the present invention, lactams are lactams of _C3 to _C15 amino acids, optionally substituted on the carbon chain, which are inert under the reaction conditions.

Aliphatic lactams, which may contain aromatic groups, are suitable. For example, the following lactams can be used, optionally in mixtures: 2-pyrrolidone, (γ-butyrolactam), 5-methyl-2-pyrrolidone, 5-ethyl-2-pyrrolidone, 2-piperidone,
(δ-valerolactam), 6-methyl-2-piperidone, 6-cyclohexyl-2-piperidone, ε-caprolactam, ω-amino-enanthic lactam, ω-aminocaprylic lactam, ω-aminolauric lactam, ω-amino-hexadecanoic lactam, 1-methyl-5-homopiperazinone, 5-ethoxy-2-pyrrolidone, 5-benzyl-2-pyrrolidone, 5,5-dimethyl-6-methoxy-2-piperidone.

The polyarylene sulfide according to the present invention can be mixed with other polymers and fillers such as pigments, for example, graphite, metal powder, glass powder, quartz powder, glass fiber or carbon fiber, and additives commonly used for polyarylene sulfides, such as stabilizers and mold release agents, can also be added.

Generally, the melt flow rate of polyarylene sulfide is
The index is 31 in accordance with ASTM 1238-70.
It is measured at 6°C using a 5 kg weight and expressed in g/10 min.

However, at high melt flow indices, this measurement method encounters difficulties due to the high flow rate of the polymer melt.

Therefore, the melt viscosity η _m of the polymer melt is measured at 306° C. as a function of the shear force τ (in Pa) using an Instron rotational viscometer.

This method allows the measurement of melt viscosity over a very wide range, from ^10-1 to ^10-7 Pa s. In an Instron rheometer, the polymer is melted between a fixed plate and a rotating cone, and the torque of the cone is measured. From this torque, angular velocity, and instrument data, the relationship between melt viscosity and shear stress can be calculated. An Instron Model 3250 rheometer with a cone and plate having a diameter of 2 cm was used.

The melt viscosity reported is the melt viscosity measured at a shear force τ of 10 ² Pa.

It is also possible to analyze polyarylene sulfides using chromatographic methods to obtain information about their molecular weight distribution. Typical examples of such methods are, for example, high pressure liquid chromatography (HPLC) and gel permeation chromatography (GPC).

The stationary phase may be a commercially available support material, such as Li-chloride.
Prep (Chroprep), Rover (Lobá
r), Li-closorb (Chrosorb), Li
- Chrospher, Perisorb
(Perisorb), Hibar (Hiber),
Lactogel (Fractogel), Fructosyl
(Fractosil), Ultrastyragel (Ul
trastyragel), Microstyragel (Mic
rostyragel), Zobax (Zorba
x), Bondagel (Bondagel) and Chaude
Shodex can be used.

As the solvent and eluent, conventional solvents and diluents can be used. These solvents and diluents must be capable of dissolving the polymer sufficiently. Examples include 1-chloronaphthalene, diphenyl, N-methyl-pyrrolidone, N-
Cyclohexyl-pyrrolidone, N-methyl-piperidine, N-methylcaprolactam, N-methyl-laurinlactam, sulfone, N,N-dimethyl-imidazolidone, N,N'-dimethylproperazinone, hexamethyl-
Mention may be made of phosphoric triamide (NMP), 1-methyl-1-oxaphospholane and mixtures thereof.

It is possible to calibrate the analytical method by means of absolute or relative standards. Reference materials for relative calibration include common polymers such as polystyrene, polyethylene, polyethylene-terephthalate, polybutylene-terephthalate, polyesters such as aromatic polyesters, polycarbonates such as PA6,
Polyamides such as PA66, PA11, polysulfones and polyethersulfones can be used.

Chromatography for analytical determination of molecular weight and molecular weight distribution can be carried out at various pressures from about 1 to 10 bar.

The chromatography can be carried out over a wide temperature range from about 20 to 250°C.

Furthermore, for purposes of improvement, it is also possible to add substances such as alkali halides, alkaline earth halides, phosphonium or ammonium compounds to the sample to be analyzed.

The weight average molecular weight Mw can be determined by analyzing the analytical results thus obtained.

The weight average molecular weight Mw is 25,000 to 500,000, preferably 25,000 to 380,000, and more preferably 2
5,000 to 300,000, most preferably 25,000
It ranges from 0 to 150,000.

The method of the present invention provides a 20 to 500,000 P copolymer having a relationship of 1gηm = 3.48 · 1gMw(rel) - 14.25 ± 0.1 between the melt viscosity ηm and the weight average relative molecular weight Mw.
Polyarylene sulfides are obtained having melt viscosities of as and relative molecular weights of 25,000 to 500,000.

The polyarylene sulfide is characterized in that there is a relationship between ηm and Mw, preferably lgηm=3.48·lgMw(rel)−14.25±0.05.

The polyarylene sulfide according to the present invention, preferably p-polyarylene sulfide, generally has a viscosity of 0.3×10 ³ to 5×10 ⁶ Pa·s immediately after isolation from the reaction mixture.
They have a melt viscosity of 1.5×10 3 to 10 ⁴ Pa·s, preferably 1.5×10 ³ to 10 4 Pa·s, and good color properties.
It can be directly processed into films, molded parts or fibers by extrusion blowing, injection molding or other conventional processing methods. The obtained products are suitable for various applications, such as automotive parts, accessories, electrical parts such as switches, electronic boards, pumps, etc.
They can be used in chemical and weather resistant parts and devices such as housings and pump flywheels, etching baths, sealing rings, parts for office and communication equipment, household appliances, valves, and ball bearing parts.

Example 1 This example describes the preparation of polyphenylene sulfide in accordance with US Pat. No. 3,354,129 for comparative purposes.

129 g of sodium sulfide trihydrate (corresponding to 1 mole of _Na2S ) and 300 g of N-methyl-2-pyrrolidone were placed in a stirred autoclave. The mixture was flushed with nitrogen and gradually heated to 202°C. 19 ml of water was distilled off during this process. The mixture was then cooled to approximately 160°C, and 147 g of dichlorobenzene (=1 mole) in approximately 50 g of N-methyl-2-pyrrolidone was added. The reaction mixture was heated to 245°C under an initial pressure of 2.5 bar for 30 minutes, during which time the pressure rose to 10 bar, and the temperature was maintained at this level for 3 hours. After cooling to room temperature, the gray solid was isolated and carefully washed with water to remove inorganic impurities.

After drying under reduced pressure at 80°C, 100.3 g (93%) of poly-p-phenylene sulfide was obtained with the following characteristics: melt viscosity = 4.5 Pa·s (at τ = ¹⁰² Pa); thermoplastic processing was not possible without hardening.

Example 2 1110 g N-methyl caprolactam, 323.5 g
Sodium sulfide hydrate ( 2.45 mol), 28.0 g of 50% sodium hydroxide, 3
41.1 g of 1,4-dichlorobenzene ( 2.32 moles), 4.21 g of 1,2,4-trichlorobenzene (1 mole % based on dichlorobenzene), 30.2
g of N,N-dimethyl acetamide (15 mol %, based on Na ₂ S) and 4.44 g (0.035 mol) of ε
- Caprolactam is introduced under nitrogen into a 2 liter three-necked flask equipped with a thermometer, a stirrer and a distillation column with a distillate separator. The reaction mixture is gradually heated to boiling point. Water is separated from the distilling azeotrope of water and p-dichlorobenzene, and the p-dichlorobenzene is returned to the reactor. After 2 hours, water can no longer be detected in either the distillate or the residue. After a further 9 hours of heating under reflux, precipitation in water, acidification,
After washing with water to remove the electrolyte and drying, the product is isolated as white fibers and characterized by its melt viscosity ηm.

ηm=6.2×10 ³ Pa·s (for τ=10 ² Pa).

Example 3 As in Example 2, except that 1.68 g of 1,2,4-trichlorobenzene (0.4 mole % based on dichlorobenzene) was used as branching agent.

ηm=1.45×10 ³ Pa·s (for τ=10 ² Pa).

Example 4 In this example, the branching agent, 1,2,4-trichlorobenzene, was not used.

ηm=3.2×10 ² Pa·s (for τ=10 ² Pa).

Example 5 The procedure was the same as in Example 2, except that 3.77 g of pyrrolidone was used instead of 4.44 g of ε-caprolactam.
After precipitation, a white p-polyphenylene sulfide was obtained having the following melt viscosity: ηm=5.8×10 ³ Pa·s (for τ=10 ² Pa).

Example 6 The procedure of Example 2 was repeated except that 8.74 g of lauric lactam was used instead of 4.44 g of ε-caprolactam.
m is ηm=4.2×10 ³ Pa·s (for τ=10 ² Pa).

It was.

Example 7 1110 g N-methyl-caprolactam, 323.5 g
Sodium sulfide hydrate ( 2.45 mol), 2.4 g of 50% sodium hydroxide, 34
1.1 g of 1,4-dichlorobenzene ( 2.32 moles), 38.05 g of sodium acetate (Na ₂ S
Based on The procedure of Example 4 was repeated except that 4.44 g (0.025 mole) of ε-caprolactam and 2.00 g (0.20 mole%) of ε-caprolactam were used.
233.4 g of white polyphenylene sulfide was obtained, having a melt viscosity ηm of 3.0×10 ² Pa·s (for τ=10 ² Pa).

Example 8 The procedure of Example 7 was repeated, except that 29.4 g of ε-caprolactam was used and the solution of N-methyl-caprolactam and dichlorobenzene, and also sodium sulfide hydrate, ε-caprolactam, and sodium acetate were simultaneously mixed and dehydrated. Melt viscosity ηm = 3.5 × 10 ²
Pa·s (for τ=10 ² Pa).

p-Polyphenylene sulfide prepared according to Example 2 of German Patent Publication No. 3243189 (removal of free water from the reaction, no lactam added) was used in Examples 7 and 8.
than the p-polyphenylene sulfide prepared according to the present invention, both before and after melting.
It exhibited a darker color and released corrosive gaseous components to a greater extent upon melting. Melting was carried out at 320°C.
The acidic gas was passed through a gas washing bottle containing 1N sodium hydroxide solution together with nitrogen as an accompanying gas, and the amount of sodium hydroxide used and neutralized was determined by titration.

Claims (9)

[Claims] Claim 1: a) 50 to 100 mol % of an aromatic dihalogen compound corresponding to the following general formula (I): and 0 to 50 mol % of an aromatic dihalogen compound corresponding to the following general formula (II): in these formulae, X represents a halogen atom in the meta- or para-position relative to one another, ^R1 may be the same or different and represent hydrogen, alkyl, cycloalkyl, aryl, alkylaryl, arylalkyl, and in addition, two ^R1 groups in the ortho-position relative to one another may combine to form an aromatic or heterocyclic ring, and one of the ^R1 groups is always different from hydrogen; and b) from 0 to 5 mole %, based on the sum of components (a) and (b), of aromatic trihalogen or tetrahalogen compounds ArXn (III) corresponding to the following general formula (III): in which Ar represents an aromatic or heterocyclic group; X represents a halogen; and n is the number 3 or 4; and c) alkali metal sulfides, the molar ratio of (a+b):c being from 0.85:1 to 1.15:1, based on the number of moles of aromatic dihalogen compounds,
A method for producing a high molecular weight polyarylene sulfide, which comprises reacting in a polar solvent containing 5 to 100 mol % of a lactam. 2. The method according to claim 1, wherein an aliphatic lactam is used. 3. The method according to claim 1, wherein ε-caprolactam is used. 4. The process according to claim 1, wherein the water-containing reactants are completely dehydrated and the reaction is carried out in the absence of pressure or under low pressure. 5. Based on the number of moles of alkali sulfide,
1 to 100 mol %, preferably 1 to 25 mol % of N,N
2. The process according to claim 1, characterized in that a dialkylcarboxylic acid amide is additionally used. 6. The process of claim 1, wherein the reaction is carried out batchwise or continuously. 7. The method according to claim 1, wherein the reactants and the polar solvent are mixed and reacted, individually or in the form of a mixture or solution, at a temperature of 200° C. with dehydration. 8. The method according to claim 1, wherein N-methyl-ε-caprolactam is used as the polar organic solvent. 9. The method according to claim 1, wherein 1,2,4-trichlorobenzene is used as the aromatic polyhalogen compound of formula (III).