Isocyanate polymerization catalysts and methods for their preparation, methods for the preparation of polyisocyanates

Abstract

The application discloses an isocyanate polymerization catalyst and a preparation method thereof, and a preparation method of polyisocyanate, and a structural expression of the catalyst is as follows: the preparation method of the polyisocyanate is that, under an inert gas atmosphere, a polyisocyanate is used as a raw material to perform a self-polymerization reaction under the catalysis of the catalyst. The catalyst has a good catalysis effect, and the reaction temperature is stable, so that the catalyst is used for preparing an isocyanate trimer product with low viscosity and good storage stability.

Description

Technical Field

[0001] This invention relates to the field of isocyanate polymerization, and more particularly to an isocyanate polymerization catalyst and its preparation method, as well as a method for preparing polyisocyanates. Background Technology

[0002] Aliphatic diisocyanate polymers have irreplaceable advantages in polyurethane coatings and adhesives and are widely used. However, the volatility and high toxicity of monomeric aliphatic isocyanates in industry limit their application, thus prompting attempts to prepare them as polyisocyanates. Isocyanurates, due to their good rigidity, hydrolytic stability, and thermal stability, are widely used in industry, leading to extensive research on isocyanate trimerization catalysts. Currently, many types of trimerization catalysts exist, including composite catalysts (CN1074312), metal salt compounds (US4066628), phosphine compounds (US3702839), nitrogen heterocyclic compounds (US2013016865), tertiary amine compounds (US2013016865), and quaternary ammonium salts. However, these catalysts have several drawbacks, including difficult synthesis, large dosage requirements, need for high-temperature conditions or prone to temperature runaway and difficulty in temperature control, high color values, and poor product selectivity.

[0003] Therefore, there is a need to prepare a new type of catalyst. This type of catalyst has good catalytic effect, low catalyst dosage, stable reaction temperature, and produces isocyanate trimer products with low viscosity and good storage stability. Summary of the Invention

[0004] The purpose of this invention is to provide an isocyanate polymerization catalyst and its preparation method. This catalyst system is metal-free, exhibits high activity, a stable catalytic reaction process, and a simple and easy preparation method.

[0005] Another objective of this invention is to provide a method for preparing polyisocyanate, which has the advantages of using less catalyst, maintaining a stable reaction temperature, and producing polyisocyanate with low viscosity and low color number.

[0006] To achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0007] An isocyanate polymerization catalyst, the structural formula of which is as follows:

[0008] (I)

[0009] Where X is selected from halide ions, such as fluorine, chloride, bromine, and iodide ions;

[0010] R1 and R2 represent the same or different branched or branched aliphatic or alicyclic C1-C20 groups, preferably C1-C10 aliphatic or alicyclic substituents, and more preferably methyl, ethyl, isopropyl, cyclohexyl, or benzyl.

[0011] R3, R4, and R5 represent the same or different straight-chain or branched C1-C20 aliphatic, alicyclic, aromatic, or arylaliphatic groups; or R3, R4, and R5 combine with a nitrogen atom to form a cyclic structure; preferably C1-C10 alkyl, cyclopentyl, cyclohexyl, phenyl, and groups containing substituted phenyl or benzyl groups; further preferably methyl, ethyl, isopropyl, butyl, cyclohexyl, phenyl, adamantyl, or benzyl.

[0012] Specifically, the catalyst is prepared as follows:

[0013] The catalyst is obtained by mixing a dihalosilane with a tertiary amine in an inert solvent and stirring the mixture at 25-80°C.

[0014] It can be obtained by vacuum concentration or recrystallization using acetone and n-hexane as solvents.

[0015] Preferably, the structure of the dihalosilane is as follows:

[0016] Where X = F, Cl, Br, I; R1 and R2 are defined the same as above.

[0017] Preferably, the structural formula of the tertiary amine is:

[0018] The definitions of R3, R4, and R5 are the same as those above.

[0019] More preferably, the tertiary amine is one or more of triphenylamine, triisopropylamine, triethylamine, pyridine, triethylenediamine, N-methyl-N-ethylcycloamine, and N-benzyl-N-methyladamantaneamine.

[0020] Preferably, the molar ratio of the dihalosilane to the tertiary amine is 1:1 to 1:4, and more preferably 1:2 to 1:3.

[0021] Preferably, the reaction time is 1 to 6 hours, and more preferably 2 to 4 hours.

[0022] Preferably, the reaction temperature is 25~100℃, and more preferably 40~80℃.

[0023] The reaction solvent is an inert solvent, which can be benzene, acetone, xylene, toluene, tetrahydrofuran, etc.

[0024] The preparation method of the above catalyst can be represented by the following equation:

[0025]

[0026] Where X = F, Cl, Br, I.

[0027] The catalyst described in this invention can be used to prepare polyisocyanates.

[0028] A method for preparing polyisocyanate includes the following steps:

[0029] In an inert gas atmosphere, at least one polyisocyanate is subjected to a self-polymerization reaction catalyzed by at least one catalyst of Formula I to obtain an isocyanate trimer.

[0030] Preferably, the polyisocyanate can be one or more of all polyisocyanates known in the art. More preferably, one or more of pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), trimethyl-HDI (TMDI), 2-methylpentane-1,5-diisocyanate (MPDI), isophorone diisocyanate (IPDI), 1,3- and 1,4-bis(isocyanate-methyl)cyclohexane (H6XDI), bis(isocyanate-methyl)norbornene (NBDI), 3(4)-isocyanate-methyl-1-methyl-cyclohexyl isocyanate (IMCI), or 4,4'-bis(isocyanate-cyclohexyl)methane (H12MDI); more preferably, one or more of H6XDI, PDI, HDI, and IPDI.

[0031] Preferably, based on the mass of the isocyanate raw material, the amount of catalyst added is 10~800ppm, more preferably 100~500ppm, and even more preferably 150~400ppm.

[0032] The catalyst prepared in the method of this invention can be used in solution form or in a solvent-free manner. A suitable solvent, in principle, contains all solvents that can dissolve the catalyst without causing it to decompose or deteriorate, and that do not participate in the isocyanate reaction or participate in the reaction but only produce substances that are non-destructive to polyurethane chemistry. If the catalyst is used in solution form, the catalyst mass concentration is 10–70%, preferably 20–50%.

[0033] Furthermore, the self-polymerization reaction temperature is 20~200℃, preferably 40~150℃, and more preferably 50~100℃;

[0034] Furthermore, the reaction is terminated when the conversion rate of the polyisocyanate raw material reaches 10-70%, preferably 30-50%.

[0035] After the reaction is complete, an acid and / or an acid derivative may be added as a terminator to deactivate the catalyst. Alternatively, any other catalyst deactivation method known in the art may be used. The acid and / or acid derivative includes, but is not limited to, one or more of benzoyl chloride, phosphoric acid, benzyl sulfonate, phosphate ester, phosphite ester, and p-toluenesulfonic acid. The molar ratio of the terminator to the catalyst is 0.6 to 1.1.

[0036] After the catalyst is deactivated, the remaining trimerization solution is removed by conventional existing technologies such as thin-film evaporation, extraction, and distillation to obtain polyisocyanate products, in which the monomer content is less than 0.5 wt%.

[0037] The polyisocyanate prepared by the method of the present invention has a trimer content of more than 50 wt%, preferably 55 wt%-75 wt%, a low polymer content, generally below 8 wt%, and low viscosity, exhibiting excellent performance.

[0038] At room temperature, the obtained polyisocyanate product is in solid or liquid state and can be directly diluted with a solvent or used directly. The solvent is selected from one or more of butyl acetate, ethyl acetate, xylene, propylene glycol methyl ether acetate, etc., and the solid content of the diluted product can be 50-80 wt%.

[0039] The polyisocyanate prepared by this invention can be used to prepare paints, coating compositions, adhesives, and additives.

[0040] The polyisocyanate of the present invention can be used directly or in combination with other prior art isocyanate derivatives, such as biuret, urethane, carbamate, diuret, etc.

[0041] Compared with existing catalysts, the bis-silicon ammonium salt catalyst of the present invention has the advantages of stable reaction rate, controllable reaction temperature, low product viscosity, and good product storage stability. Detailed Implementation

[0042] The method provided by the present invention will be further illustrated by the following examples, but the present invention is not limited thereto.

[0043] Approximately 5 wt% (1H NMR) or approximately 50 wt% (13C NMR) of anhydrous deuterated solvent CDCl3 containing trace amounts of tetramethylsilane was measured on a Brucker DPX400 instrument at frequencies of 400 (1H NMR) or 100 (13C NMR), with a chemical shift of 0 ppm on 1H NMR.

[0044] Mass spectrometry was performed using an Agilent 7890A-5975C.

[0045] Viscosity measurement method: Dynamic mechanical viscosity was measured using a Brookfield DV-IPrime viscometer with an S21 rotor at 25°C.

[0046] The color number of the product was determined using BYK's LCSIV colorimeter.

[0047] The NCO content was determined by titration using a Mettler 905 Titrando titration instrument according to DIN EN ISO 11909.

[0048] Gel chromatography was used to quantify the isocyanate monomers of the raw materials as a monitoring method to determine the reaction conversion rate (calculated based on the mass of the isocyanate monomers of the raw materials). The following chromatographic columns were used in series: LC-20AD / RID-10A, MZ-GelSDplus10E3A5um (8.0 x 300 mm), MZ-GelSDplus500A5um (8.0 x 300 mm), and MZ-Ge1SDp1us100A5um (8.0 x 300 mm). The mobile phase was Shimadzu; the flow rate was 1.0 mL / min; the analysis time was 40 min; and the column temperature was 35℃.

[0049] The content of trimer and polymer in this invention was characterized by molecular gel chromatography.

[0050] Unless otherwise specified, all reactions are carried out under a nitrogen atmosphere.

[0051] All isocyanate raw materials used are Wanhua H6XDI products;

[0052] 1-Benzyl-1-cyclohexyldichlorosilane was prepared by the polycondensation of 1-benzyldichlorosilane and chlorocyclohexane. The specific process is as follows: Under nitrogen atmosphere and ice bath conditions, 1 mol of 1-benzyldichlorosilane and 10 mL of tetrahydrofuran were added to a reaction flask, followed by the slow addition of sodium hydride (1.1 eq). After stirring for 30 min, chlorocyclohexane was slowly added dropwise to the reaction flask. After the addition was complete, the ice bath was removed, and the mixture was stirred at room temperature for 4 h to stop the reaction. 10 mL of 1M hydrochloric acid was added to the reaction flask, followed by extraction with 3 × 10 mL of tetrahydrofuran. The organic phase was then rotary evaporated under reduced pressure to obtain the target product, 1-benzyl-1-cyclohexyldichlorosilane. 1-Benzyldichlorosilane was purchased from Chongqing Chemhere Co., Ltd. (HONGKONGCHEMHERECO.LIMITED), and chlorocyclohexane and sodium hydride were purchased from Aladdin.

[0053] N-Methyl-N-ethylcyclohexylamine was prepared by reacting N-ethylmethylamine with chlorocyclohexane. The specific process is as follows: Under a nitrogen atmosphere and ice bath conditions, 1 mol of N-ethylmethylamine and 10 mL of tetrahydrofuran were added to a reaction flask, followed by the addition of triethylamine (1.1 eq) as a condensation agent. After stirring for 10 min, chlorocyclohexane was slowly added. After the addition was complete, the mixture was stirred for 4 h, and then the reaction was stopped. 10 mL of 1M hydrochloric acid was added to the reaction solution, followed by extraction with 3 × 10 mL of tetrahydrofuran. The mixture was filtered, and the filtrate was dried and rotary evaporated under reduced pressure to obtain the target product, N-methyl-N-ethylcyclohexylamine. N-ethylmethylamine and chlorocyclohexane were purchased from Aladdin.

[0054] N-Benzyl-N-methyladamantaneamine was prepared by reacting N-benzylmethylamine with 1-chloroadamantane, using the same method as that for N-methyl-N-ethylcyclohexylamine. N-Benzylmethylamine and 1-chloroadamantane were purchased from Aladdin.

[0055] Dimethyldichlorosilane was purchased from Aladdin;

[0056] Dimethyldifluorosilane was purchased from Shanghai Kaiyin Chemical Co., Ltd.

[0057] Dimethyldibromosilane was purchased by SAGECHEMLITIMED on a custom basis;

[0058] Dimethyldiiodosilane was purchased from Shenzhen Aituo Chemical Co., Ltd.;

[0059]

Example 1

[0060] Triethylamine (6 mmol, 606 g) was slowly added dropwise to an acetone (10 mL) solution containing dimethyldichlorosilane (3 mmol, 387 g). After stirring at room temperature for 3 h, the reaction solution was concentrated under vacuum to 5 mL, and then n-hexane (15 mL) was added to precipitate the product. The precipitate was then filtered and dried to obtain the target product, which was designated as catalyst #1.

[0061] The catalyst structure characterization data are as follows:

[0062] 1HNMR(400M,TMS): δ3.28(12H,q),1.56(18H,t),0.14(6H,s).

[0063] 13CNMR(100M,TMS): δ-11.1,9.4,47.3.

[0064] [M+H]+331.21(ESI)

[0065]

Example 2

[0066] Triphenylamine (6 mmol, 1472 g) was slowly added dropwise to an acetone (10 mL) solution containing dimethyldichlorosilane (3 mmol, 387 g). After stirring at 50 °C for 4 h, the reaction solution was concentrated under vacuum to 5 mL, and then n-hexane (15 mL) was added to precipitate the product. The precipitate was then filtered and dried to obtain the target product, which was designated as catalyst #2.

[0067] The catalyst structure characterization data are as follows:

[0068] 1HNMR (400M, TMS): δ7.48~7.52(18H,m), 7.38~7.44(12H,m), 0.12(6H,s).

[0069] 13CNMR (100M, TMS): δ-12.3, 128.7, 130.5.

[0070] [M+H]+619.21(ESI)

[0071]

Example 3

[0072] Pyridine (6 mmol, 474.6 g) was slowly added dropwise to an acetone (15 mL) solution containing dimethyldibromosilane (3 mmol, 654 g). After stirring at 60 °C for 5 h, the reaction solution was concentrated under vacuum to 5 mL, and then n-hexane (15 mL) was added to precipitate the product. The precipitate was then filtered and dried to obtain the target product, which was designated as catalyst #3.

[0073] The catalyst structure characterization data are as follows:

[0074] 1HNMR(400M,TMS): δ8.74~8.86(6H,m),8.22(4H,m),0.18(6H,s).

[0075] 13CNMR (100M, TMS): δ-6.3, 128.4, 142.5, 146.1.

[0076] [M+H]+376.95(ESI)

[0077]

Example 4

[0078] Triethylenediamine (6 mmol, 673.08 g) was slowly added dropwise to a toluene (10 mL) solution containing dimethyldiiodosilane (3 mmol, 936 g). After stirring at 70 °C for 4 h, the reaction solution was concentrated under vacuum to 5 mL, and then n-hexane (15 mL) was added to precipitate the product. The precipitate was then filtered and dried to obtain the target product, designated as catalyst #4.

[0079] The catalyst structure characterization data are as follows:

[0080] 1HNMR(400M,TMS): δ3.34(12H,m),2.80(12H,t),0.20(6H,s).

[0081] 13CNMR (100M, TMS): δ-8.2, 53.9, 58.1.

[0082] [M+H]+536.03(ESI)

[0083]

Example 5

[0084] N-methyl-N-ethylcyclohexylamine (6 mmol, 847.6 g) was slowly added dropwise to a toluene (10 mL) solution containing dimethyldichlorosilane (3 mmol, 387 g). After stirring at 60 °C for 5 h, the reaction solution was concentrated under vacuum to 5 mL, and then n-hexane (15 mL) was added to precipitate the product. The precipitate was then filtered and dried to obtain the target product, designated as catalyst #5.

[0085] The catalyst structure characterization data are as follows:

[0086] 1HNMR(400M,TMS): δ3.52(2H,dt),3.28(4H,q),2.90(6H,s),1.72~1.97(8H,m),1.56(6H,t),1.42~1.48(12H,m),0.14(6H,s).

[0087] 13CNMR (100M, TMS): δ-11.11,9.4,24.0,25.7,29.2,36.3,47.9,62.7.

[0088] [M+H]+411.27(ESI)

[0089]

Example 6

[0090] N-Benzyl-N-methyladamantaneamine (6 mmol, 1532.4 g) was slowly added dropwise to a toluene (10 mL) solution containing dimethyldichlorosilane (3 mmol, 387 g). After stirring at 75 °C for 6 h, the reaction solution was concentrated under vacuum to 5 mL, and then n-hexane (15 mL) was added to precipitate the product. The precipitate was then filtered and dried to obtain the target product, designated as catalyst #6.

[0091] The catalyst structure characterization data are as follows:

[0092] 1HNMR (400M, TMS): δ7.16~7.25(10H,m), 4.51(4H,s), 2.90(6H,s), 1.3~2.02(30H,m), 0.16(6H,s).

[0093] 13CNMR(100M,TMS): δ-11.0,26.4,29,36.6,37,49.0,54.6,58.4,59.0,61,125.7,128.6,129.0,132.6.

[0094] [M+H]+639.37(ESI)

[0095]

Example 7

[0096] Triphenylamine (6 mmol, 1472 g) was slowly added dropwise to 10 mL of acetone solution containing 3 mmol, 429 g of 1-methyl-1-ethyldichlorosilane. After stirring at 50 °C for 4 h, the reaction solution was concentrated under vacuum to 5 mL, and then 15 mL of n-hexane was added to precipitate the product. The precipitate was then filtered and dried to obtain the target product, designated as catalyst #7.

[0097] The catalyst structure characterization data are as follows:

[0098] 1HNMR(400M,TMS): δ7.04~7.35(30H,m),1.45(1H,m),0.97(6H,d),0.94(3H,s),0.67(2H,q).

[0099] 13CNMR (100M, TMS): δ-9.4, 2.2, 5.0, 17.9, 121.2, 128.7, 130.5, 138.0.

[0100] [M+H]+661.26(ESI)

[0101]

Example 8

[0102] Triphenylamine (6 mmol, 1472 g) was slowly added dropwise to a toluene (10 mL) solution containing 1-benzyl-1-cyclohexyldichlorosilane (3 mmol, 819.81 g). After stirring at 60 °C for 4 h, the reaction solution was concentrated under vacuum to 5 mL, and then n-hexane (15 mL) was added to precipitate the product. The precipitate was then filtered and dried to obtain the target product, designated as catalyst #8.

[0103] 1HNMR (400M, TMS): δ7.00~7.35(35H,m), 1.89(2H,s), 1.19~1.53(11H,m).

[0104] 13CNMR(100M,TMS): δ3.9,5.9,25.7,26.7,27.0,121.2,128.6,128.7,129.0,130.5,138,140.5

[0105] [M+H]+763.30(ESI)

[0106] The anionic and cationic structural expressions of the catalysts prepared in Examples 1-8 are shown in Table 1:

[0107] Table 1 Catalyst Structure

[0108]

[0109] [Example 9] Catalyst Performance Testing

[0110] Under anhydrous and oxygen-free conditions, 1000g of H6XDI was placed in a round-bottom flask equipped with a stirrer, thermometer, and nitrogen inlet. The flask was heated to 70℃ in a water bath, and catalysts #1-#8 were added with continuous stirring. The proportion of catalyst added to the total mass of H6XDI in the performance tests of different catalysts is shown in Table 2. The temperature rise during the reaction was observed, and the reaction process was judged by monitoring the monomer content of the reaction solution. When the NCO content of the reaction solution was between 22 and 24 wt%, diisooctyl phosphate was added in an equimolar amount to terminate the reaction.

[0111] The monomer in the reaction solution was removed by evaporation using a thin-film evaporator under conditions of preheating temperature 100℃, separation temperature 140℃, and absolute pressure below 200Pa, so that the monomer content was below 0.5wt%, yielding the polyisocyanate product. The obtained product was diluted with ethyl acetate to a solid content of 75%. The reaction results are shown in Table 2.

[0112] Comparative Example 1

[0113] The catalyst used in Comparative Example 1 was tetramethylammonium hydroxide, and the rest of the methods were the same as in Example 6. The reaction results are shown in Table 2.

[0114] Comparative Example 2

[0115] Comparative Example 2 used ammonium tributylbenzylethylhexanoate as the catalyst, and the rest of the methods were the same as in Example 6. The reaction results are shown in Table 2.

[0116] Table 2 Results of Examples and Comparative Examples

[0117]

[0118] To obtain H6XDI trimer products, silicon salt is used as a catalyst, resulting in a small maximum temperature rise, a stable reaction process, slightly lower polymer content, high trimer content, low product viscosity, and good storage stability.

Claims

1. A method for preparing polyisocyanate, characterized in that, Includes the following steps: Under an inert gas atmosphere, a self-polymerization reaction is carried out under the catalysis of at least one polyisocyanate as a raw material catalyst to obtain an isocyanate trimer; The catalyst has the following structural formula: （I） Where X is selected from halide ions; R1 and R2 represent the same or different groups, selected from methyl, ethyl, isopropyl, cyclohexyl, and benzyl. R3, R4, and R5 represent the same or different groups; selected from C1 to C10 alkyl, cyclohexyl, phenyl, adamantyl, and benzyl groups.

2. The preparation method according to claim 1, characterized in that, X is selected from fluorine, chloride, bromide, and iodide ions, and R3, R4, and R5 are selected from methyl, ethyl, isopropyl, butyl, cyclohexyl, phenyl, adamantyl, and benzyl.

3. The preparation method according to claim 1, characterized in that, The catalyst is prepared by the following method: The catalyst is obtained by mixing a dihalosilane with a tertiary amine in an inert solvent and stirring the mixture at 25-80°C.

4. The preparation method according to claim 3, characterized in that, The structure of the dihalosilane is as follows: Where X = F, Cl, Br, I; R1 and R2 are defined the same as above.

5. The preparation method according to claim 3, characterized in that, The structural formula of the tertiary amine is: The definitions of R3, R4, and R5 are the same as those above.

6. The preparation method according to claim 3, characterized in that, The tertiary amine is one or more of triphenylamine, triisopropylamine, triethylamine, pyridine, triethylenediamine, N-methyl-N-ethylcycloamine, and N-benzyl-N-methyladamantaneamine.

7. The preparation method according to claim 3, characterized in that, The molar ratio of the dihalosilane to the tertiary amine is 1:1 to 1:

4.

8. The preparation method according to claim 7, characterized in that, The molar ratio of the dihalosilane to the tertiary amine is 1:2 to 1:

3.

9. The preparation method according to claim 3, characterized in that, The reaction time is 1 to 6 hours.

10. The preparation method according to claim 9, characterized in that, The reaction time is 2-4 hours.

11. The preparation method according to claim 3, characterized in that, The reaction temperature is 25~100℃.

12. The preparation method according to claim 11, characterized in that, The reaction temperature is 40~80℃.

13. The preparation method according to claim 3, characterized in that, The inert solvent is selected from one or more of benzene, acetone, xylene, toluene, or tetrahydrofuran.

14. The preparation method according to claim 1, characterized in that, The polyisocyanate is selected from one or more of pentamethylene diisocyanate, hexamethylene diisocyanate, trimethyl-HDI, 2-methylpentane 1,5-diisocyanate, isophorone diisocyanate, 1,3- and 1,4-bis(isocyanate methyl)cyclohexane, bis(isocyanate methyl)norbornene, 3(4)-isocyanate methyl-1-methyl-cyclohexyl isocyanate or 4,4'-bis(isocyanate cyclohexyl)methane.

15. The preparation method according to claim 1, characterized in that, Based on the mass of the isocyanate raw material, the amount of catalyst added is 10~800ppm.

16. The preparation method according to claim 15, characterized in that, Based on the mass of the isocyanate raw material, the amount of catalyst added is 100~500ppm.

17. The preparation method according to claim 16, characterized in that, Based on the mass of the isocyanate raw material, the amount of catalyst added is 150~400ppm.

18. The preparation method according to claim 1, characterized in that, The self-polymerization reaction temperature is 20~200℃.

19. The preparation method according to claim 18, characterized in that, The self-polymerization reaction temperature is 40~150℃.

20. The preparation method according to claim 19, characterized in that, The self-polymerization reaction temperature is 50~100℃.

21. The preparation method according to claim 1, characterized in that, The reaction is terminated when the conversion rate of the polyisocyanate raw material reaches 10-70%.

22. The preparation method according to claim 21, characterized in that, The reaction is terminated after the conversion rate of the polyisocyanate raw material reaches 30-50%.

23. According to the preparation method of claim 1, after the reaction is completed, an acid and / or an acid derivative is optionally added as a terminator to deactivate the catalyst, wherein the acid and / or acid derivative includes one or more of benzoyl chloride, phosphoric acid, benzyl sulfonate, phosphate ester, phosphite ester and p-toluenesulfonic acid, and the molar ratio of the amount of terminator added to the catalyst is 0.6 to 1.1.

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