Preparation method and application of ultrahigh-viscosity transesterification polycarbonate

Abstract

The invention relates to the technical field of polycarbonate preparation, and discloses a preparation method of ultrahigh-viscosity ester exchange polycarbonate, which comprises the following steps: step A, raw material pretreatment: diphenyl carbonate (DPC) and 2, 2-bis (p-hydroxyphenyl) propane (BPA) are respectively dried in a vacuum environment at 120-150 DEG C for 4-6 hours, moisture is removed, and hydrolysis side reaction is avoided; the dried diphenyl carbonate (DPC) and 2, 2-bis (p-hydroxyphenyl) propane (BPA) are added into a melting mixer according to a certain mass ratio, the temperature is increased to 180-200 DEG C under nitrogen protection, the stirring speed is 300-500 rpm, and finally the ultrahigh-viscosity, high-strength and natural anti-ultraviolet polycarbonate product based on the melt transesterification method is obtained. A chain extender needs to be additionally added to ultrahigh-viscosity polycarbonate prepared by a traditional phosgene method, and the ultrahigh-viscosity, high-strength and natural anti-ultraviolet polycarbonate can be prepared by a blending process without adding the chain extender, so that the type and application of polycarbonate prepared by a melt transesterification method are enriched.

Description

Technical Field

[0001] This invention relates to the field of polycarbonate preparation technology, specifically to a method for preparing ultra-high viscosity transesterification polycarbonate and its application. Background Technology

[0002] Polycarbonate (PC) is a general term for a class of high molecular weight polymers containing carbonate groups (-OROCO-) in their molecular chains. Depending on the type of R group, it can be classified into aliphatic, aromatic, and alicyclic types. As a high-performance colorless, transparent, amorphous thermoplastic engineering plastic, polycarbonate boasts superior impact resistance among transparent plastics, along with excellent impact resistance, creep resistance, dimensional stability, heat resistance, low water absorption, non-toxicity, and excellent dielectric properties.

[0003] Currently, there are two main types of methods for synthesizing polycarbonate in mass production: the phosgene method and the non-phosgene melt transesterification method. Among them, the phosgene method (including solution phosgene method and interfacial polycondensation method) is the traditional polycarbonate production process, while the non-phosgene melt transesterification method is a more environmentally friendly production process. It avoids the use of toxic phosgene and synthesizes polycarbonate through transesterification reaction.

[0004] In the production and application of polycarbonate, melt flow index is a crucial indicator for evaluating its processing performance. Ultra-high viscosity polycarbonate possesses unique processing characteristics and application value. The phosgene process for preparing ultra-high viscosity polycarbonate typically requires the addition of chain extenders to regulate its viscosity. These chain extenders enable the polymerization of PC from the conventional main chain to the branched chain, resulting in high molecular weight PC. However, the addition of chain extenders not only increases production costs but may also affect the purity and performance stability of the polycarbonate. Therefore, developing a method for directly producing ultra-high viscosity polycarbonate without the addition of chain extenders has significant technical and economic value. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing ultra-high viscosity transesterification polycarbonate and its applications.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing ultra-high viscosity transesterification polycarbonate, characterized by comprising the following steps:

[0007] Step A:

[0008] Raw material pretreatment: Diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were dried at 120-150℃ under vacuum for 4-6 hours to remove moisture and avoid hydrolysis side reactions;

[0009] Step B:

[0010] Melt blending and prepolymerization:

[0011] Dried diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were added to a melt mixer in a certain mass ratio. Under nitrogen protection, the temperature was raised to 180-200°C, the stirring speed was 300-500 rpm, and the mixture was melt-mixed for 30-60 min. Then, 0.2-1 ppm of catalyst was added, the temperature was raised to 200-260°C, the pressure was maintained at 30-50 kPa, and the prepolymerization reaction was carried out for 1-2 h to remove some phenol byproducts.

[0012] Step C:

[0013] Condensation reaction:

[0014] The prepolymer product is transferred to a polycondensation reactor, heated to 260-300℃, pressure reduced to 1-10 kPa, and stirring speed reduced to 50-100 rpm. The polycondensation reaction is carried out for 3-4 hours to further remove phenol until the system viscosity reaches the target value. When the melt viscosity reaches a certain level, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added.

[0015] Step D: Extrusion granulation:

[0016] The polycondensation product is fed into a twin-screw extruder. The melt is extruded through a die and then water-cooled and pelletized to obtain ultra-high viscosity polycarbonate particles.

[0017] Preferably, in step A, when removing moisture, the moisture content is controlled to be <50ppm to avoid hydrolysis side reactions, as moisture can cause hydrolysis side reactions and affect the molecular weight.

[0018] Preferably, in step B, the melting and initial reaction are as follows: under the protection of an inert gas, the material in the reactor is heated and melted, and the temperature is controlled at 180-200°C. At this temperature, the transesterification reaction is carried out under normal pressure or slightly negative pressure. The reaction will generate oligomers and produce phenol as a byproduct. The generated phenol is continuously discharged from the system by means of a distillation column, etc., to promote the forward reaction.

[0019] Preferably, in step C, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added at the end of the prepolymerization stage or just as the next stage begins. Adding them too early may cause side reactions with the catalyst or monomer, while adding them too late will result in uneven dispersion.

[0020] Preferably, the catalyst in step B is an alkali metal or alkaline earth metal compound, such as sodium hydroxide or lithium acetate.

[0021] Preferably, the mass ratio of DPC to BPA in step B is DPC:BPA = 4.5:5.

[0022] Preferably, the molar ratio of DPC to BPA in step B is DPC:BPA = 1.02 to 1.08:1.

[0023] Preferably, when the mass ratio of DPC:BPA is 4.5:5, the obtained product particles need to be washed and extracted. The particles are extracted with the solvent acetone to remove residual phenol and unreacted BPA monomers. Then, the particles are thoroughly dried until the moisture content is extremely low. The dried particles are then treated at 200-230°C for several to more than ten hours under nitrogen protection. This process allows the residual end groups (-OH and -OC6H5) to continue to react, further increasing the molecular weight, compensating for the initial DPC deficiency, and making the molecular weight distribution more uniform, ultimately obtaining a product with ultra-high viscosity and high strength.

[0024] An application of ultra-high viscosity transesterification polycarbonate, which is a polycarbonate with high viscosity, high strength, UV resistance and high purity, makes polycarbonate widely used in fields with extremely high material performance requirements.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention achieves ultra-high viscosity without the need for chain extenders:

[0027] Unlike the traditional phosgene method for preparing ultra-high viscosity polycarbonate, which requires the addition of chain extenders, this invention successfully prepares polycarbonate products with ultra-high viscosity (melt index as low as 1.5 g / 10 min) without the use of chain extenders by optimizing the raw material ratio (e.g., controlling the molar ratio of DPC to BPA to 1.02–1.08:1), precisely controlling process parameters (e.g., temperature, pressure, vacuum degree), and adding specific additives (e.g., tris[2,4-di-tert-butylphenyl]phosphite and pentaerythritol stearate) at the appropriate time. This simplifies the production process, reduces costs, and avoids the product purity and performance stability problems that may arise from the addition of chain extenders.

[0028] 2. The product of this invention possesses excellent overall performance:

[0029] The polycarbonate prepared by this invention not only has ultra-high viscosity, but also exhibits high strength and excellent mechanical properties, such as impact resistance, creep resistance, good heat resistance and natural UV resistance, which enables the product to meet higher requirements of application scenarios.

[0030] 3. The product of this invention has high purity and low residual monomer content:

[0031] By employing a high-vacuum polycondensation process, the byproduct phenol is effectively removed, reducing the residual phenol content in the final product. At the same time, through strict pretreatment of raw materials with moisture content controlled to <50ppm and optimized reaction conditions, side reactions such as hydrolysis are effectively avoided, ensuring the high purity and excellent compatibility of the product.

[0032] 4. The process is environmentally friendly and meets the requirements of green chemistry:

[0033] This invention uses a melt transesterification method instead of the phosgene method, which completely avoids the use of highly toxic phosgene (COCl2) as a raw material. The production process is more environmentally friendly and safe, and is in line with the current trend of green chemical industry and sustainable development.

[0034] 5. Wide range of applications and high product added value:

[0035] The ultra-high viscosity, high-performance polycarbonate prepared by this method greatly enriches the product types of polycarbonate produced by melt transesterification. Its excellent combination of properties (high viscosity, high strength, UV resistance, and high purity) makes it widely applicable in fields with extremely high material performance requirements, such as high-end engineering plastics, electronics and electrical appliances, automotive industry, medical devices, food packaging (such as mineral water barrels and baby bottles), and optical devices, thus expanding the application range of materials and increasing product added value. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0037] Example 1:

[0038] A method for preparing ultra-high viscosity transesterification polycarbonate includes the following steps:

[0039] Step A:

[0040] Raw material pretreatment: Diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were dried at 120-150℃ under vacuum for 4-6 hours to remove moisture and avoid hydrolysis side reactions;

[0041] Diphenyl carbonate (DPC): One of the reactants, it undergoes transesterification with BPA, providing carbonate groups (-O-(C=O)-O-);

[0042] 2,2-Bis(p-hydroxyphenyl)propane (BPA): Another reactive monomer, it is the backbone structural unit of polycarbonate, which determines its mechanical strength and heat resistance;

[0043] Step B:

[0044] Melt blending and prepolymerization:

[0045] Dried diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were added to a melt mixer in a certain mass ratio. Under nitrogen protection, the temperature was raised to 180-200°C, the stirring speed was 300-500 rpm, and the mixture was melt-mixed for 30-60 min. Then, 0.2 ppm of catalyst was added, the temperature was raised to 200-260°C, the pressure was maintained at 30-50 kPa, and the prepolymerization reaction was carried out for 1-2 h to remove some phenol byproducts.

[0046] Step C:

[0047] Condensation reaction:

[0048] The prepolymer product is transferred to a polycondensation reactor, heated to 260-300℃, pressure reduced to 1-10 kPa, and stirring speed reduced to 50-100 rpm. The polycondensation reaction is carried out for 3-4 hours to further remove phenol until the system viscosity reaches the target value. When the melt viscosity reaches a certain level, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added.

[0049] Tris[2,4-di-tert-butylphenyl]phosphite is an auxiliary antioxidant and hydrolysis stabilizer. During high-temperature processing, it can effectively decompose hydrogen peroxide, prevent the oxidative degradation of polymer chains (maintaining strength and color), and capture trace amounts of moisture and acid, inhibiting the hydrolytic breakage of ester bonds, thereby maintaining high molecular weight (ultra-high viscosity).

[0050] Pentaerythritol stearate is a lubricant and release agent. In the later high-temperature and high-viscosity stage, it can reduce the melt viscosity, improve fluidity, facilitate the removal of air bubbles and the transport of melt, and at the same time help the final product to detach from the reactor wall, preventing local overheating and degradation caused by sticking to the wall.

[0051] Step D: Extrusion granulation:

[0052] The polycondensation product is fed into a twin-screw extruder. The melt is extruded through a die and then water-cooled and pelletized to obtain ultra-high viscosity polycarbonate particles.

[0053] As a further technical solution of the present invention, when removing water in step A, the water content is controlled to be <50ppm to avoid hydrolysis side reactions, because water can cause hydrolysis side reactions and affect molecular weight.

[0054] As a further technical solution of the present invention, in step B, the melting and initial reaction are as follows: under the protection of an inert gas, the material in the reactor is heated and melted, and the temperature is controlled at 180-200°C. At this temperature, the transesterification reaction is carried out under normal pressure or slightly negative pressure. The reaction will generate oligomers and produce phenol as a byproduct. The generated phenol is continuously discharged from the system by means of a distillation column, etc., to promote the forward reaction.

[0055] As a further technical solution of the present invention, in step C, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added at the end of the prepolymerization stage or just when transitioning to the next stage. Adding them too early may cause side reactions with the catalyst or monomer, while adding them too late will result in uneven dispersion.

[0056] As a further technical solution of the present invention, the catalyst in step B is an alkali metal or alkaline earth metal compound, such as sodium hydroxide, lithium acetate, etc.

[0057] As a further technical solution of the present invention, the mass ratio of DPC and BPA in step B is DPC:BPA = 4.5:5;

[0058] BPA molecular weight: 228.29 g / mol;

[0059] DPC molecular weight: 214.19 g / mol;

[0060] Calculate the molar ratio:

[0061] Assuming the mass of BPA is 5g, its molar number is: 5 / 228.29≈0.0219mol;

[0062] The mass of DPC is 4.5g, and its molar number is: 4.5 / 214.19≈0.0210mol;

[0063] Therefore, the molar ratio of DPC:BPA is approximately 0.0210:0.0219 ≈ 0.96:1;

[0064] This mass ratio corresponds to a molar ratio of <1:1;

[0065] Due to the relative deficiency of DPC in the formulation, the product may contain unreacted BPA end groups, affecting thermal stability. The obtained product particles need to be washed and extracted with acetone to remove residual phenol and unreacted BPA monomers. Then, the particles are thoroughly dried until the moisture content is extremely low. The dried particles are then treated at 200-230℃ for several to more than ten hours under nitrogen protection. This process allows the residual end groups (-OH and -OC6H5) to continue to react, further increasing the molecular weight, compensating for the initial deficiency of DPC, and making the molecular weight distribution more uniform, ultimately obtaining a product with ultra-high viscosity and high strength.

[0066] An application of ultra-high viscosity transesterification polycarbonate: This polycarbonate, characterized by high viscosity, high strength, UV resistance, and high purity, is widely used in fields with extremely high material performance requirements, such as high-end engineering plastics, electronics and electrical engineering, automotive industry, medical devices, food packaging (e.g., mineral water barrels, baby bottles), and optical devices, thus expanding the application range of the material and increasing the added value of products.

[0067] Example 2:

[0068] A method for preparing ultra-high viscosity transesterification polycarbonate includes the following steps:

[0069] Step A:

[0070] Raw material pretreatment: Diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were dried at 120-150℃ under vacuum for 4-6 hours to remove moisture and avoid hydrolysis side reactions;

[0071] Diphenyl carbonate (DPC): One of the reactants, it undergoes transesterification with BPA, providing carbonate groups (-O-(C=O)-O-);

[0072] 2,2-Bis(p-hydroxyphenyl)propane (BPA): Another reactive monomer, it is the backbone structural unit of polycarbonate, which determines its mechanical strength and heat resistance;

[0073] Step B:

[0074] Melt blending and prepolymerization:

[0075] Dried diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were added to a melt mixer in a certain mass ratio. Under nitrogen protection, the temperature was raised to 180-200°C, the stirring speed was 300-500 rpm, and the mixture was melt-mixed for 30-60 min. Then, 1 ppm of catalyst was added, the temperature was raised to 200-260°C, the pressure was maintained at 30-50 kPa, and the prepolymerization reaction was carried out for 1-2 h to remove some phenol byproducts.

[0076] Step C:

[0077] Condensation reaction:

[0078] The prepolymer product is transferred to a polycondensation reactor, heated to 260-300℃, pressure reduced to 1-10 kPa, and stirring speed reduced to 50-100 rpm. The polycondensation reaction is carried out for 3-4 hours to further remove phenol until the system viscosity reaches the target value. When the melt viscosity reaches a certain level, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added.

[0079] Tris[2,4-di-tert-butylphenyl]phosphite is an auxiliary antioxidant and hydrolysis stabilizer. During high-temperature processing, it can effectively decompose hydrogen peroxide, prevent the oxidative degradation of polymer chains (maintaining strength and color), and capture trace amounts of moisture and acid, inhibiting the hydrolytic breakage of ester bonds, thereby maintaining high molecular weight (ultra-high viscosity).

[0080] Pentaerythritol stearate is a lubricant and release agent. In the later high-temperature and high-viscosity stage, it can reduce the melt viscosity, improve fluidity, facilitate the removal of air bubbles and the transport of melt, and at the same time help the final product to detach from the reactor wall, preventing local overheating and degradation caused by sticking to the wall.

[0081] Step D: Extrusion granulation:

[0082] The polycondensation product is fed into a twin-screw extruder. The melt is extruded through a die and then water-cooled and pelletized to obtain ultra-high viscosity polycarbonate particles.

[0083] As a further technical solution of the present invention, when removing water in step A, the water content is controlled to be <50ppm to avoid hydrolysis side reactions, because water can cause hydrolysis side reactions and affect molecular weight.

[0084] As a further technical solution of the present invention, in step B, the melting and initial reaction are as follows: under the protection of an inert gas, the material in the reactor is heated and melted, and the temperature is controlled at 180-200°C. At this temperature, the transesterification reaction is carried out under normal pressure or slightly negative pressure. The reaction will generate oligomers and produce phenol as a byproduct. The generated phenol is continuously discharged from the system by means of a distillation column, etc., to promote the forward reaction.

[0085] As a further technical solution of the present invention, in step C, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added at the end of the prepolymerization stage or just when transitioning to the next stage. Adding them too early may cause side reactions with the catalyst or monomer, while adding them too late will result in uneven dispersion.

[0086] As a further technical solution of the present invention, the catalyst in step B is an alkali metal or alkaline earth metal compound, such as sodium hydroxide, lithium acetate, etc.

[0087] As a further technical solution of the present invention, the molar ratio of DPC and BPA in step B is DPC:BPA = 1.02:1. A slight excess of DPC helps to complete the reaction and control the end groups.

[0088] An application of ultra-high viscosity transesterification polycarbonate: This polycarbonate, characterized by high viscosity, high strength, UV resistance, and high purity, is widely used in fields with extremely high material performance requirements, such as high-end engineering plastics, electronics and electrical engineering, automotive industry, medical devices, food packaging (e.g., mineral water barrels, baby bottles), and optical devices, thus expanding the application range of the material and increasing the added value of products.

[0089] Example 3:

[0090] A method for preparing ultra-high viscosity transesterification polycarbonate includes the following steps:

[0091] Step A:

[0092] Raw material pretreatment: Diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were dried at 120-150℃ under vacuum for 4-6 hours to remove moisture and avoid hydrolysis side reactions;

[0093] Diphenyl carbonate (DPC): One of the reactants, it undergoes transesterification with BPA, providing carbonate groups (-O-(C=O)-O-);

[0094] 2,2-Bis(p-hydroxyphenyl)propane (BPA): Another reactive monomer, it is the backbone structural unit of polycarbonate, which determines its mechanical strength and heat resistance;

[0095] Step B:

[0096] Melt blending and prepolymerization:

[0097] Dried diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were added to a melt mixer in a certain mass ratio. Under nitrogen protection, the temperature was raised to 180-200°C, the stirring speed was 300-500 rpm, and the mixture was melt-mixed for 30-60 min. Then, 0.6 ppm of catalyst was added, the temperature was raised to 200-260°C, the pressure was maintained at 30-50 kPa, and the prepolymerization reaction was carried out for 1-2 h to remove some phenol byproducts.

[0098] Step C:

[0099] Condensation reaction:

[0100] The prepolymer product is transferred to a polycondensation reactor, heated to 260-300℃, pressure reduced to 1-10 kPa, and stirring speed reduced to 50-100 rpm. The polycondensation reaction is carried out for 3-4 hours to further remove phenol until the system viscosity reaches the target value. When the melt viscosity reaches a certain level, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added.

[0101] Tris[2,4-di-tert-butylphenyl]phosphite is an auxiliary antioxidant and hydrolysis stabilizer. During high-temperature processing, it can effectively decompose hydrogen peroxide, prevent the oxidative degradation of polymer chains (maintaining strength and color), and capture trace amounts of moisture and acid, inhibiting the hydrolytic breakage of ester bonds, thereby maintaining high molecular weight (ultra-high viscosity).

[0102] Pentaerythritol stearate is a lubricant and release agent. In the later high-temperature and high-viscosity stage, it can reduce the melt viscosity, improve fluidity, facilitate the removal of air bubbles and the transport of melt, and at the same time help the final product to detach from the reactor wall, preventing local overheating and degradation caused by sticking to the wall.

[0103] Step D: Extrusion granulation:

[0104] The polycondensation product is fed into a twin-screw extruder. The melt is extruded through a die and then water-cooled and pelletized to obtain ultra-high viscosity polycarbonate particles.

[0105] As a further technical solution of the present invention, when removing water in step A, the water content is controlled to be <50ppm to avoid hydrolysis side reactions, because water can cause hydrolysis side reactions and affect molecular weight.

[0106] As a further technical solution of the present invention, in step B, the melting and initial reaction are as follows: under the protection of an inert gas, the material in the reactor is heated and melted, and the temperature is controlled at 180-200°C. At this temperature, the transesterification reaction is carried out under normal pressure or slightly negative pressure. The reaction will generate oligomers and produce phenol as a byproduct. The generated phenol is continuously discharged from the system by means of a distillation column, etc., to promote the forward reaction.

[0107] As a further technical solution of the present invention, in step C, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added at the end of the prepolymerization stage or just when transitioning to the next stage. Adding them too early may cause side reactions with the catalyst or monomer, while adding them too late will result in uneven dispersion.

[0108] As a further technical solution of the present invention, the catalyst in step B is an alkali metal or alkaline earth metal compound, such as sodium hydroxide, lithium acetate, etc.

[0109] As a further technical solution of the present invention, the molar ratio of DPC and BPA in step B is DPC:BPA = 1.08:1. A slight excess of DPC helps to complete the reaction and control the end groups.

[0110] An application of ultra-high viscosity transesterification polycarbonate: This polycarbonate, characterized by high viscosity, high strength, UV resistance, and high purity, is widely used in fields with extremely high material performance requirements, such as high-end engineering plastics, electronics and electrical engineering, automotive industry, medical devices, food packaging (e.g., mineral water barrels, baby bottles), and optical devices, thus expanding the application range of the material and increasing the added value of products.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will readily make equivalent substitutions for its features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ultra-high viscosity transesterification polycarbonate, characterized in that, Includes the following steps: Step A: Raw material pretreatment: Diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were dried at 120-150℃ under vacuum for 4-6 hours to remove moisture and avoid hydrolysis side reactions; Step B: Melt blending and prepolymerization: Dried diphenyl carbonate (DPC) and 2,2-bis(p-hydroxyphenyl)propane (BPA) were added to a melt mixer in a certain mass ratio. Under nitrogen protection, the temperature was raised to 180-200°C, the stirring speed was 300-500 rpm, and the mixture was melt-mixed for 30-60 min. Then, 0.2-1 ppm of catalyst was added, the temperature was raised to 200-260°C, the pressure was maintained at 30-50 kPa, and the prepolymerization reaction was carried out for 1-2 h to remove some phenol byproducts. Step C: Condensation reaction: The prepolymer product is transferred to a polycondensation reactor, heated to 260-300℃, pressure reduced to 1-10 kPa, and stirring speed reduced to 50-100 rpm. The polycondensation reaction is carried out for 3-4 hours to further remove phenol until the system viscosity reaches the target value. When the melt viscosity reaches a certain level, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added. Step D: Extrusion granulation: The polycondensation product is fed into a twin-screw extruder. The melt is extruded through a die and then water-cooled and pelletized to obtain ultra-high viscosity polycarbonate particles.

2. In the method for preparing ultra-high viscosity transesterification polycarbonate according to claim 1, when removing water in step A, the water content is controlled to be <50ppm to avoid hydrolysis side reactions, because water can cause hydrolysis side reactions and affect the molecular weight.

3. The method for preparing ultra-high viscosity transesterification polycarbonate according to claim 1, wherein in step B, melting and initial reaction are as follows: under inert gas protection, the material in the reactor is heated and melted, and the temperature is controlled at 180-200℃. At this temperature, the transesterification reaction is carried out under normal pressure or slightly negative pressure. The reaction will generate oligomers and produce phenol as a byproduct. The generated phenol is continuously discharged from the system by means of fractionation column, etc., to promote the forward reaction.

4. In the method for preparing ultra-high viscosity transesterification polycarbonate according to claim 1, in step C, powdered tris[2,4-di-tert-butylphenyl] phosphite and pentaerythritol stearate are added at the end of the prepolymerization stage or just as the process transitions to the next stage. Adding them too early may cause side reactions with the catalyst or monomer, while adding them too late will result in uneven dispersion.

5. The method for preparing ultra-high viscosity transesterification polycarbonate according to claim 1, wherein the catalyst in step B is an alkali metal or alkaline earth metal compound, such as sodium hydroxide, lithium acetate, etc.

6. In the method for preparing ultra-high viscosity transesterification polycarbonate according to claim 1, the mass ratio of DPC and BPA in step B is DPC:BPA = 4.5:

5.

7. In the method for preparing ultra-high viscosity transesterification polycarbonate according to claim 1, the molar ratio of DPC and BPA in step B is DPC:BPA = 1.02 to 1.08:

1.

8. In the preparation method of ultra-high viscosity transesterification polycarbonate according to claim 6, when the mass ratio of DPC:BPA = 4.5:5, the obtained product particles need to be washed and extracted. The particles are extracted with acetone solvent to remove residual phenol and unreacted BPA monomers. Then, the particles are thoroughly dried until the moisture content is extremely low. The dried particles are treated at 200-230℃ for several hours to more than ten hours under nitrogen protection. This process allows the residual end groups (-OH and -OC6H5) to continue to react, further increasing the molecular weight, making up for the initial DPC deficiency, and making the molecular weight distribution more uniform, ultimately obtaining an ultra-high viscosity, high strength product.

9. An application of ultra-high viscosity transesterification polycarbonate, characterized in that, With its high viscosity, high strength, UV resistance, and high purity, polycarbonate is widely used in fields with extremely high material performance requirements.