2-substituted imidazole alkali metal catalysts and methods of their catalytic preparation of polycarbonates

Abstract

The application discloses a 2-substituted imidazole alkali metal catalyst and a method for catalytically preparing polycarbonate, and belongs to the technical field of catalysts. The 2-substituted imidazole alkali metal catalyst is a 2-alkyl-substituted imidazole alkali metal salt, and the chemical structure general formula is 2-R-Im-M, wherein Im is an imidazole ring, R is one of an amino group, a halogen, a hydroxyl group, a nitro group, a linear alkyl group with a length of 0-6, and a branched alkyl group, and M is an alkali metal, which is one of potassium and sodium. In the 2-substituted imidazole alkali metal catalyst, a nitrogen atom on the imidazole ring forms a coordination bond with an alkali metal ion, and the coordination ratio of the nitrogen atom and the alkali metal ion is 1-2:1. Through the above mode, the efficiency of the process for catalytically preparing polycarbonate is high, and the prepared product is of excellent quality.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to 2-substituted imidazole alkali metal catalysts and methods for catalytically preparing polycarbonate. Background Technology

[0002] Polycarbonate is an engineering plastic with excellent comprehensive properties, including high light transmittance, strong impact resistance, and good heat resistance. It is widely used in optical devices, medical materials, automotive parts, and other fields. The melt transesterification process uses diphenyl carbonate (DPC) and bisphenol A (BPA) as raw materials. It does not require highly toxic phosgene and produces no solvent pollution, making it the mainstream industrial process for synthesizing polycarbonate. The core of this process lies in the research and application of highly efficient catalysts.

[0003] Catalysts used in the current melt transesterification method for synthesizing polycarbonate are mainly classified into metallic and non-metallic types. Metallic catalysts (such as alkali metal salts and rare earth metal complexes) exhibit high catalytic activity, but suffer from drawbacks such as difficulty in removing metal residues, susceptibility to side reactions (e.g., Fries rearrangement), and yellowing of the product, making it difficult to meet the quality requirements of high-end optical and medical-grade polycarbonate. Non-metallic catalysts (such as guanidines, amidines, and common imidazoles) can reduce metal residues, but they also suffer from insufficient catalytic activity, high reaction temperatures, and poor catalyst stability, limiting their industrial application.

[0004] In existing technologies, imidazole compounds are mostly used in combination with other metal salts as catalytic systems, or as the cationic portion of ionic liquids for polycarbonate synthesis. There are no reports of using 2-substituted imidazole alkali metal catalysts as the sole catalyst for the molten transesterification synthesis of polycarbonate from diphenyl carbonate and bisphenol A. For example, Chinese patent CN114085189B discloses a metal biimidazolium salt alkaline ionic liquid catalyst, using biimidazolium containing two imidazole rings as the anionic parent, reacting with alkali metal compounds (LiOH, NaOH, KOH) for dehydration and bonding, with the alkali metal providing the cation (Li... + Na + K + This constitutes an ionic liquid catalytic system, essentially an ionic liquid formed by biimidazole anions and alkali metal cations, without alkyl substitution at the 2-position. The catalyst matrix of the aforementioned patent is biimidazole (containing two interconnected imidazole rings), belonging to a bisimidazole structure; while the catalyst matrix of this invention is a single imidazole ring, and the key lies in the alkyl substitution modification at the 2-position (R is a C1~C6 straight / branched alkyl group, preferably methyl or butyl). Electron cloud density and steric hindrance are controlled through 2-position substitution. This structural design is completely unmentioned and undisclosed in the comparative patent, and suffers from high synthesis costs and limited catalytic efficiency in ionic liquids.

[0005] In addition, existing imidazole alkali metal salts often suffer from problems such as insufficient stability, poor solubility in molten reaction systems, and low catalytic selectivity. In particular, when the imidazole ring is not substituted at the 2-position, the electron cloud density distribution is uneven, the coordination stability is poor, and it is impossible to balance catalytic activity, product purity and process economy.

[0006] Based on this, the present invention designs a 2-substituted imidazole alkali metal catalyst and a method for catalytically preparing polycarbonate to solve the above problems. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the prior art, the present invention provides a 2-substituted imidazole alkali metal catalyst and a method for catalytically preparing polycarbonate.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A 2-substituted imidazole alkali metal catalyst, wherein the 2-substituted imidazole alkali metal catalyst is a 2-alkyl-substituted imidazole alkali metal salt with the general chemical formula: 2-R-Im-M, wherein Im is an imidazole ring, R is one of amino, halogen, hydroxyl, nitro, C0~C6 straight-chain alkyl, branched alkyl, and M is an alkali metal, which is one of potassium and sodium; In the 2-substituted imidazole alkali metal catalyst, the nitrogen atom on the imidazole ring forms a coordination bond with the alkali metal ion, and the coordination ratio of the nitrogen atom to the alkali metal ion is 1~2:1.

[0009] To better achieve the objectives of this invention, this invention also provides a method for preparing polycarbonate using a 2-substituted imidazole alkali metal catalyst, the specific steps of which are as follows: Step (1) Feeding: Add bisphenol A, diphenyl carbonate and 2-substituted imidazole alkali metal catalyst to the reactor, wherein the amount of catalyst is 0.01~0.5wt% bisphenol A and the molar ratio of diphenyl carbonate to bisphenol A is 1.02~1.10:1; Step (2) Transesterification reaction: Heat the reaction system to 130~170℃ and react under reduced pressure for 30-60 min; Step (3) Polycondensation reaction: Heat the reaction system to 220~265℃, and gradually evacuate to 10℃. -3 ~10 -5 The reaction is carried out at MPa, and the temperature and vacuum are maintained for 1 to 3 hours. After the reaction is completed, polycarbonate is obtained.

[0010] Furthermore, in step (1) of feeding, the molar ratio of diphenyl carbonate to bisphenol A is 1.04~1.08:1.

[0011] Furthermore, in step (2) the transesterification reaction, the reaction system is heated to 140~160℃ and reacted under reduced pressure for 30~40 min.

[0012] Furthermore, in step (3) of the polycondensation reaction, the reaction system is heated to 230~240℃ and gradually evacuated to 5×10⁻⁶℃. -4 ~8×10 -5 MPa, maintain this temperature and vacuum for 1~2 hours.

[0013] To better achieve the objectives of this invention, this invention also provides a method for preparing a 2-substituted imidazole alkali metal catalyst, the specific steps of which are as follows: 2-R-methylimidazolium and an alkali metal source were added to a solvent at a molar ratio of 1 to 2:1. The mixture was stirred at 25 to 80 °C for 2 to 24 hours. After cooling to room temperature, unreacted impurities were removed by filtration. The solvent was removed under reduced pressure at 80 to 100 °C to obtain the target 2-substituted imidazolium alkali metal catalyst with a purity > 99%.

[0014] Furthermore, the alkali metal source is potassium hydroxide or sodium hydroxide, and the solvent is water, anhydrous methanol, or anhydrous ethanol.

[0015] To better achieve the objectives of this invention, this invention also provides a polycarbonate prepared by the above-described preparation method.

[0016] Compared with the prior art, the beneficial effects of this invention are as follows: 1. The 2-substituted imidazole alkali metal catalyst prepared by this invention has high catalytic efficiency in the catalytic preparation of polycarbonate, and the viscosity-average molecular weight of polycarbonate can reach up to 6.7 × 10⁻⁶. 4 The product obtained has a molecular weight distribution index of less than 2.2 and a g / mol concentration, indicating excellent quality. 2. The coordination structure of 2-substituted imidazole alkali metal catalysts enables bifunctional synergistic catalysis. The electronic effect of the 2-alkyl group can enhance catalytic activity. Among them, the activity of potassium catalysts is more than 40% higher than that of traditional imidazole catalysts and simple alkali metal salt catalysts, while sodium catalysts have slightly lower activity but lower cost, and can be flexibly adapted to different quality requirements. 3. The 2-substituted imidazole alkali metal catalyst prepared by this invention can be adapted to the high-temperature reaction conditions of molten transesterification, has no catalytic activity decay, has high solubility and uniform dispersion in molten systems, and has stable catalytic efficiency, without the need for complex stirring equipment. 4. The raw materials (2-alkylimidazolium and alkali metal source) for the preparation of the 2-substituted imidazole alkali metal catalyst in this invention are readily available, the synthesis steps are simple, no complex modification is required, the organic solvent can be recycled and reused, the preparation cost is lower than that of ionic liquids, rare earth metal complexes and other catalytic systems, and the polycarbonate preparation process does not require additional additives, the steps are simplified, the reaction energy consumption is low, and it is suitable for industrial continuous production, which has strong practicality and promotion value. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0018] Figure 1 The infrared detection results are those of the 2-methylimidazolium potassium catalyst prepared in Example 1 of this invention. Figure 2 The results show the thermal stability of the 2-methylimidazolium potassium catalyst prepared in Example 1 of this invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Example 1: Preparation of 2-methylimidazolium potassium catalyst 0.01 mol of 2-methylimidazole and 0.01 mol of potassium hydroxide were added to 50 mL of anhydrous ethanol and stirred at 25 °C for 8 h. The ethanol and a small amount of water were removed under vacuum at 90 °C and dried for 2 h to obtain the 2-methylimidazole potassium (2-Me-IM-K) catalyst.

[0021] like Figure 1 As shown, the 2-Me-IM-K catalyst prepared in Example 1 was characterized by infrared spectroscopy. It was observed that 2-methylimidazolium potassium showed an infrared signature at 2925 cm⁻¹. -1 (-CH3 asymmetric stretching) and 2867 cm -1 A strong absorption peak appears at (-CH3 symmetric stretching), with a sharp peak shape and good separation, which is a typical characteristic of the 2-methyl group. (1610 cm⁻¹) -1 The nearby C=N stretching peak is the most characteristic absorption peak of the imidazole ring. After 2-methyl substitution, due to the electron-donating effect of the methyl group, this peak is more pronounced than that of free 2-methylimidazolium (~1600 cm⁻¹). -1 Slightly shifted towards higher wavenumbers, ~10 cm -1 1439 cm -1 The C=C stretching peak is of medium intensity and symmetrical, which is a direct reflection of the imidazole ring conjugated system. If the peak disappears or splits, it indicates that the imidazole ring structure is destroyed. The infrared results show that the target product catalyst was successfully synthesized.

[0022] Thermogravimetric analysis was performed on the thermal stability of the catalyst. Figure 2 It can be seen that the catalyst has a decomposition temperature >380℃, excellent thermal stability, and will not be deactivated due to high-temperature polymerization during the reaction process.

[0023] Example 2: Preparation of 2-methylimidazolium sodium catalyst 0.02 mol of 2-methylimidazole and 0.01 mol of sodium hydroxide were added to 50 mL of anhydrous ethanol and stirred at 25 °C for 4 h. The ethanol, unreacted imidazole and a small amount of water were removed under vacuum at 90 °C and dried for 2 h to obtain sodium 2-methylimidazole (2-Me-IM-Na) catalyst.

[0024] Infrared spectroscopy showed that the target product catalyst was successfully synthesized, and thermogravimetric analysis showed that the catalyst decomposition temperature was >375℃.

[0025] Example 3: Preparation of 2-Aminoimidazolium potassium 0.015 mol of 2-aminoimidazole and 0.01 mol of potassium hydroxide were added to 50 mL of deionized water and stirred at 25 °C for 12 h. Water and a small amount of residual solvent were removed under vacuum at 90 °C and dried for 3 h to obtain potassium 2-aminoimidazole (2-NH2-IM-K) catalyst.

[0026] Infrared spectroscopy showed that the target product catalyst was successfully synthesized, and thermogravimetric analysis showed that the catalyst decomposition temperature was >375℃.

[0027] Example 4: Preparation of 2-chloroimidazolium potassium 0.01 mol of 2-chloroimidazole and 0.01 mol of potassium hydroxide were added to 50 mL of anhydrous ethanol and stirred at 80 °C for 6 h. After cooling to room temperature, the mixture was filtered to remove unreacted impurities. Ethanol was removed under vacuum at 85 °C and dried for 2 h to obtain potassium 2-chloroimidazole (2-Cl-IM-K) catalyst.

[0028] Infrared spectroscopy showed that the target product catalyst was successfully synthesized, and thermogravimetric analysis showed that the catalyst decomposition temperature was >385℃.

[0029] Example 5: Preparation of 2-hydroxyimidazolium potassium 0.01 mol of 2-hydroxyimidazole and 0.01 mol of potassium hydroxide were added to 50 mL of methanol and stirred at 40 °C for 24 h. The methanol and a small amount of water were removed under vacuum at 90 °C and dried for 2 h to obtain potassium 2-hydroxyimidazole (2-OH-IM-K) catalyst.

[0030] Infrared spectroscopy showed that the target product catalyst was successfully synthesized, and thermogravimetric analysis showed that the catalyst decomposition temperature was >380℃.

[0031] Example 6: Preparation of 2-nitroimidazole sodium 0.01 mol of 2-nitroimidazole and 0.01 mol of sodium hydroxide were added to 50 mL of anhydrous ethanol and stirred at 60 °C for 2 h. The ethanol was removed under vacuum at 90 °C and dried for 2 h to obtain sodium 2-nitroimidazole (2-NO2-IM-Na) catalyst.

[0032] Infrared spectroscopy showed that the target product catalyst was successfully synthesized, and thermogravimetric analysis showed that the catalyst decomposition temperature was >370℃.

[0033] Example 7: Preparation of 2-Isopropylimidazolium Potassium 0.01 mol of 2-isopropylimidazolium and 0.01 mol of potassium hydroxide were added to 50 mL of anhydrous methanol and stirred at 60 °C for 2 h. The methanol was removed under vacuum at 90 °C and dried for 2 h to obtain potassium 2-isopropylimidazolium (2-iPr-IM-K) catalyst.

[0034] Infrared spectroscopy showed that the target product catalyst was successfully synthesized, and thermogravimetric analysis showed that the catalyst decomposition temperature was >370℃.

[0035] Example 8: Potassium 2-methylimidazolium-catalyzed synthesis of polycarbonate 22.83 g (0.1 mol) of bisphenol A and 22.71 g (0.106 mol) of diphenyl carbonate were added to the reactor. The molar ratio of diphenyl carbonate to bisphenol A was 1.06:1, i.e., n(DPC):n(BPA) = 1.06:1. The 2-methylimidazolium potassium catalyst prepared in Example 1 was added in an amount of 0.5% wt BPA.

[0036] The temperature was raised to 140℃, and a reduced pressure reaction was carried out for 40 min to obtain a low molecular weight prepolymer. The reaction system was then heated to 220℃, and gradually evacuated to a pressure reduction level using a water pump (10...). -3 (MPa), maintain this temperature and vacuum for 1.5 h, and after the reaction is complete, polycarbonate is obtained.

[0037] The prepared polycarbonate was subjected to relevant performance tests, and the viscosity-average molecular weight (Mw) of the polycarbonate was found to be 4.0 × 10⁻⁶. 4 g / mol, molecular weight distribution index PDI=2.12.

[0038] Example 9: Potassium 2-methylimidazolium-catalyzed synthesis of polycarbonate 22.83 g (0.1 mol) of bisphenol A and 23.14 g (0.108 mol) of diphenyl carbonate were added to the reactor, i.e., n(DPC):n(BPA) = 1.08:1. The 2-methylimidazolium potassium catalyst prepared in Example 1 was added at an amount of 0.4% wt BPA. The temperature was raised to 140 °C, and the reaction was carried out under reduced pressure for 40 min to obtain a low molecular weight prepolymer. The reaction system was then heated to 240 °C and gradually evacuated to a vacuum of 5 × 10⁻⁶. -4 The reaction was carried out at MPa, maintained at this temperature and vacuum for 2 h, and polycarbonate was obtained after the reaction was completed.

[0039] Product performance testing: Mw = 6.7 × 10 4 g / mol, PDI=2.15.

[0040] Example 10: Synthesis of polycarbonate catalyzed by sodium 2-methylimidazolium 22.83 g (0.1 mol) of bisphenol A and 23.14 g (0.108 mol) of diphenyl carbonate were added to the reactor, i.e., n(DPC):n(BPA) = 1.08:1. The sodium 2-methylimidazolium catalyst prepared in Example 2 was added at an amount of 0.5% wt BPA. The temperature was raised to 140 °C, and the reaction was carried out under reduced pressure for 40 min to obtain a low molecular weight prepolymer. The reaction system was then heated to 240 °C and gradually evacuated to a vacuum of 5 × 10⁻⁶. -4 The reaction was carried out at MPa, maintained at this temperature and vacuum for 2 h, and polycarbonate was obtained after the reaction was completed.

[0041] Product performance testing: Mw = 3.1 × 10 4 g / mol, PDI=1.90.

[0042] Example 11: Potassium 2-aminoimidazolium-catalyzed synthesis of polycarbonate 22.83 g (0.1 mol) of bisphenol A and 22.28 g (0.104 mol) of diphenyl carbonate were added to the reactor, i.e., n(DPC):n(BPA) = 1.04:1. The 2-aminoimidazolium potassium catalyst prepared in Example 3 was added at an amount of 0.2% wt BPA. The temperature was raised to 140 °C, and the reaction was carried out under reduced pressure for 30 min to obtain a low molecular weight prepolymer. The reaction system was then heated to 230 °C and gradually evacuated to a vacuum of 5 × 10⁻⁶. -4 The reaction was carried out at MPa, maintained at this temperature and vacuum for 1 h, and polycarbonate was obtained after the reaction was completed.

[0043] Product performance testing: Mw = 3.8 × 10 4 g / mol, PDI=2.08.

[0044] Example 12: Potassium 2-chloroimidazolium-catalyzed synthesis of polycarbonate 22.83 g (0.1 mol) of bisphenol A and 22.71 g (0.106 mol) of diphenyl carbonate were added to the reactor, i.e., n(DPC):n(BPA) = 1.06:1. The 2-chloroimidazolium potassium catalyst prepared in Example 4 was added at an amount of 0.35% wt BPA. The temperature was raised to 160 °C, and the reaction was carried out under reduced pressure for 35 min to obtain a low molecular weight prepolymer. The reaction system was then heated to 235 °C and gradually evacuated to a vacuum of 8 × 10⁻⁸ °C. -5 The reaction was carried out at MPa, maintained at this temperature and vacuum for 1.5 h, and polycarbonate was obtained after the reaction was completed.

[0045] Product performance testing: Mw = 5.3 × 10 4 g / mol, PDI=2.10.

[0046] Example 13: Potassium 2-hydroxyimidazolium-catalyzed synthesis of polycarbonate 22.83 g (0.1 mol) of bisphenol A and 23.14 g (0.108 mol) of diphenyl carbonate were added to the reactor, i.e., n(DPC):n(BPA) = 1.08:1. The 2-hydroxyimidazolium potassium catalyst prepared in Example 5 was added at an amount of 0.45% wt BPA. The temperature was raised to 150 °C, and the reaction was carried out under reduced pressure for 38 min to obtain a low molecular weight prepolymer. The reaction system was then heated to 235 °C and gradually evacuated to a vacuum of 3 × 10⁻⁶. -4 The reaction was carried out at MPa, maintained at this temperature and vacuum for 1.8 h, and polycarbonate was obtained after the reaction was completed.

[0047] Product performance testing: Mw = 5.6 × 10 4 g / mol, PDI=2.12.

[0048] Example 14: Synthesis of polycarbonate catalyzed by sodium 2-nitroimidazolium 22.83 g (0.1 mol) of bisphenol A and 22.28 g (0.104 mol) of diphenyl carbonate were added to the reactor, i.e., n(DPC):n(BPA) = 1.04:1. The sodium 2-nitroimidazole catalyst prepared in Example 6 was added at an amount of 0.3% wt BPA. The temperature was raised to 150 °C, and the reaction was carried out under reduced pressure for 33 min to obtain a low molecular weight prepolymer. The reaction system was then heated to 235 °C and gradually evacuated to a vacuum of 5 × 10⁻⁶. -4 The reaction was carried out at MPa, maintained at this temperature and vacuum for 1.5 h, and polycarbonate was obtained after the reaction was completed.

[0049] Product performance testing: Mw = 3.1 × 10 4 g / mol, PDI=1.95.

[0050] Example 15: 2-Isopropylimidazolium potassium-catalyzed synthesis of polycarbonate 22.83 g (0.1 mol) of bisphenol A and 22.28 g (0.104 mol) of diphenyl carbonate were added to the reactor, i.e., n(DPC):n(BPA) = 1.04:1. The 2-isopropylimidazolium potassium catalyst prepared in Example 7 was added at an amount of 0.3% wt BPA. The temperature was raised to 150 °C, and the reaction was carried out under reduced pressure for 33 min to obtain a low molecular weight prepolymer. The reaction system was then heated to 235 °C and gradually evacuated to a vacuum of 5 × 10⁻⁶. -4 The reaction was carried out at MPa, maintained at this temperature and vacuum for 1.5 h, and polycarbonate was obtained after the reaction was completed.

[0051] Product performance testing: Mw = 2.7 × 10 4 g / mol, PDI=2.0.

[0052] The properties of the polycarbonate products prepared in Examples 8-15 are summarized in Table 1.

[0053] Table 1 Summary of the properties of the polycarbonate products prepared in Examples 7-13 Compared with existing technologies, the traditional catalysts used in existing technologies require a long transesterification reaction of about 2 hours and a polymerization reaction of about 1.5 hours to prepare polycarbonate products. However, the preparation method of the present invention reduces the total reaction time to about 2 hours, increasing the reaction rate by 40%.

[0054] As shown in Examples 1-13 and Table 1, when the 2-substituted imidazole alkali metal catalyst prepared in this invention is used in the catalytic preparation of polycarbonate, the resulting polycarbonate product has a viscosity-average molecular weight of up to 6.7 × 10⁻⁶. 4 The molecular weight distribution index is less than 2.2, indicating that the 2-substituted imidazole alkali metal catalyst has high catalytic activity and the product obtained is of excellent quality. Meanwhile, the catalysts prepared in each embodiment all have a decomposition temperature >370℃, which is fully adapted to the high-temperature reaction conditions of molten transesterification and there is no catalytic activity decay phenomenon. Comparing Examples 8 and 9, under the same R-group (methyl) and process conditions, the potassium-based catalyst exhibits significantly higher activity than the sodium-based catalyst. However, the sodium-based catalyst has a narrower molecular weight distribution. This indicates that the type of alkali metal can be flexibly selected according to product quality requirements: potassium-based catalysts are suitable for high molecular weight products, while sodium-based catalysts are suitable for applications with high requirements for molecular weight distribution.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A 2-substituted imidazole alkali metal catalyst, characterized in that, The 2-substituted imidazole alkali metal catalyst is a 2-alkyl-substituted imidazole alkali metal salt with the general chemical formula: 2-R-Im-M, where Im is an imidazole ring, R is one of amino, halogen, hydroxyl, nitro, C0~C6 straight-chain alkyl, branched alkyl, and M is an alkali metal, which is one of potassium and sodium. In the 2-substituted imidazole alkali metal catalyst, the nitrogen atom on the imidazole ring forms a coordination bond with the alkali metal ion, and the coordination ratio of the nitrogen atom to the alkali metal ion is 1~2:

1.

2. A method for preparing polycarbonate using a 2-substituted imidazole alkali metal catalyst according to claim 1, characterized in that, The specific steps are as follows: Step (1) Feeding: Add bisphenol A, diphenyl carbonate and 2-substituted imidazole alkali metal catalyst to the reactor, wherein the amount of catalyst is 0.01~0.5wt% bisphenol A and the molar ratio of diphenyl carbonate to bisphenol A is 1.02~1.10:1; Step (2) Transesterification reaction: Heat the reaction system to 130~170℃ and react under reduced pressure for 30-60 min; Step (3) Polycondensation reaction: Heat the reaction system to 220~265℃, and gradually evacuate to 10℃. -3 ~10 -5 The reaction is carried out at MPa, and the temperature and vacuum are maintained for 1 to 3 hours. After the reaction is completed, polycarbonate is obtained.

3. The method for preparing polycarbonate using a 2-substituted imidazole alkali metal catalyst according to claim 2, characterized in that, In step (1), the molar ratio of diphenyl carbonate to bisphenol A is 1.04~1.08:

1.

4. The method for preparing polycarbonate using a 2-substituted imidazole alkali metal catalyst according to claim 2, characterized in that, In step (2) the transesterification reaction, the reaction system is heated to 140~160℃ and reacted under reduced pressure for 30~40 min.

5. The method for preparing polycarbonate using a 2-substituted imidazole alkali metal catalyst according to claim 2, characterized in that, In step (3) of the polycondensation reaction, the reaction system is heated to 230~240℃ and gradually evacuated to 5×10⁻⁶℃. -4 ~8×10 -5 MPa, maintain this temperature and vacuum for 1~2 hours.

6. A method for preparing a 2-substituted imidazole alkali metal catalyst according to claim 1, characterized in that, The specific steps are as follows: 2-R-methylimidazolium and an alkali metal source were added to a solvent at a molar ratio of 1 to 2:

1. The mixture was stirred at 25 to 80 °C for 2 to 24 hours. After cooling to room temperature, unreacted impurities were removed by filtration. The solvent was removed under reduced pressure at 80 to 100 °C to obtain the target 2-substituted imidazolium alkali metal catalyst with a purity > 99%.

7. A method for preparing a 2-substituted imidazole alkali metal catalyst according to claim 6, characterized in that, The alkali metal source is potassium hydroxide or sodium hydroxide, and the solvent is water, anhydrous methanol or anhydrous ethanol.

8. A polycarbonate prepared by any one of the preparation methods according to claims 2 to 5.

Images