Branched polycarbonate and preparation method thereof

Abstract

The invention provides branched flame-retardant polycarbonate and a preparation method thereof. A branching agent used by the polycarbonate is synthesized from melamine and tetrachloroterephthalic acid. The preparation method of the polycarbonate comprises the following steps: reacting a bisphenol compound and a branching agent with an inert organic solvent containing phosgene in a reactor to obtain a polycarbonate oligomer solution, and carrying out condensation polymerization on the polycarbonate oligomer to obtain the polycarbonate, according to the method, the reaction rate can be increased under the condition that a catalyst is not used, the process risk and operation difficulty brought by the catalyst are solved, the conversion rate of the end-capping reagent is larger than 99.5%, the flame retardant property of the end-capping reagent reaches 1.0 mm V0 level due to introduction of the halogen-containing branching agent, and meanwhile, the product has better light stability and yellowing resistance.

Description

Technical Field

[0001] The invention relates to a branched flame-retardant and yellowing-resistant polycarbonate and a preparation method thereof, belonging to the technical field of polymer materials. Background Art

[0002] Polycarbonate (PC), as an important engineering plastic, has attracted much attention due to its excellent physical properties and wide range of applications. However, polycarbonate turns yellow when exposed to high temperatures and shear during extrusion and injection molding, and also degrades under light and heat conditions, reducing its use value. At the same time, polycarbonate products also require flame retardant properties. How to overcome the shortcomings of polycarbonate itself and make it more useful has become an important research direction.

[0003] As reported in the patents CN103059544A and CN105623231B, polycarbonate is usually blended with additives to achieve different properties of polycarbonate. However, during long-term use, the additives will precipitate from the inside of the polycarbonate to the surface, reducing the effect and causing surface defects of the product. Patent JPH09316187 introduces groups containing anti-ultraviolet function into the polycarbonate molecular chain through chemical bonds, so that the polycarbonate has anti-ultraviolet performance, but the branching agent containing terminal hydroxyl groups is easy to react with acyl chloride, reducing its effect.

[0004] Patent JP6357408B2 discloses the following method: using a polycarbonate oligomer introduced with a branching agent to react the polycarbonate oligomer with a dihydric phenol to produce a branched polycarbonate. The disadvantage of this method is that the resulting branched polycarbonate film has many crystal points, and triethylamine is added as a catalyst during the reaction, making the post-processing more complicated.

[0005] In the existing methods, various additives usually have only a single function and cannot achieve compatibility with multiple properties. The addition of multiple free additives further aggravates the migration of additives, causing problems such as crystal points on the surface of polycarbonate products and poor stability. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a branched flame retardant and yellowing resistant polycarbonate and a preparation method thereof. The present invention synthesizes a new branching agent, which not only increases the flame retardancy of the polycarbonate, but also makes the prepared branched polycarbonate have better light stability and yellowing resistance. To achieve this purpose of the invention, the present invention adopts the following technical scheme:

[0007] A branched flame-retardant polycarbonate, which uses a compound with the following structure as a branching agent:

[0008]

[0009] Wherein, x is a natural number from 1 to 4, preferably 4,

[0010] Preferably, the branching agent is prepared by reacting melamine with tetrachloroterephthalic acid.

[0011] Preferably, the reaction is carried out in a solvent, the solvent is a mixture of water and DMSO, wherein the mass ratio of water to DMSO is 3:1 to 6:1;

[0012] Preferably, the reaction temperature is 70-90°C;

[0013] Preferably, the mass ratio of melamine to tetrachloroterephthalic acid is 1:5-1:8;

[0014] Preferably, the mass ratio of water to DMSO is 4:1 to 6:1;

[0015] The present invention also provides a method for preparing the polycarbonate, comprising the following steps:

[0016] (1) firstly, a bisphenol compound and an alkali solution are mixed to obtain a mixed solution A, and a branching agent and a solvent are mixed to obtain a mixed solution B;

[0017] (2) adding the mixed solution A and the mixed solution B obtained in step (1) into a reactor respectively to carry out a phosgenation reaction with phosgene to obtain a polycarbonate oligomer solution;

[0018] (3) The polycarbonate oligomer solution obtained in step (2) is subjected to a polycondensation reaction to obtain polycarbonate.

[0019] Preferably, optional alkali solution and blocking agent are added in step (3).

[0020] Preferably, in the step (3), the polycarbonate oligomer is dispersed in a disperser to obtain an emulsion and then subjected to a polycondensation reaction.

[0021] Preferably, a bisphenol compound is also added to the polycondensation reaction in step (3).

[0022] In step (1), in order to make the bisphenol compound and the branching agent dissolve better, they may be heated appropriately, and the heating temperature is 30-40°C.

[0023] Mixed liquid A and mixed liquid B react with phosgene reactor to obtain polycarbonate oligomers; wherein, the molecular chain of polycarbonate oligomers can be ionized in the reaction liquid to obtain polymer chains containing phenol oxygen anions, so it can act as a surfactant at the water-oil interface to stabilize the emulsion; then, alkali solution and end-capping agent are added to the polycarbonate oligomers obtained above, and then the emulsion is obtained through a disperser, and then transported to a polycondensation kettle, and polycarbonate is obtained after reacting with bisphenol A compound, wherein the polycondensation kettle can be a single kettle, or two kettles or three kettles. From the above, it can be seen that this invention improves the synthesis rate of polycarbonate without adding a catalyst, eliminates the process risks and operating difficulties brought by the catalyst, improves the conversion efficiency of the end-capping agent, and successfully prepares branched polycarbonate with an end-capping agent conversion rate of >99.5%.

[0024] The bisphenol compound in step (1) is one or more of 2,2-bis(4-hydroxyphenyl)propane (i.e., bisphenol A), bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, bis(4-hydroxyphenyl)sulfide, 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)octane, bis(4-hydroxyphenyl)phenylmethane, bis(4-hydroxyphenyl)diphenylmethane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, bis(4-hydroxyphenyl)oxide and bis(4-hydroxyphenyl)sulfone, preferably bisphenol A;

[0025] The molar ratio of the bisphenol compound to the branching agent in step (1) is 45-65:1.

[0026] Preferably, the pH of the mixed solution A in step (1) is 11-14.

[0027] Preferably, the alkali solution is selected from an aqueous solution of an alkali metal hydroxide or an aqueous solution of an alkali metal carbonate, preferably an aqueous solution of sodium hydroxide or potassium hydroxide.

[0028] Preferably, the molar amount of phosgene is 1.08-1.25 times the sum of the molar amounts of the branching agent and the bisphenol, and more preferably 1.12-1.21 times.

[0029] Preferably, the phosgene is dissolved in an inert solvent.

[0030] As a preferred embodiment, the reaction temperature in step (2) is 20-35°C, and the residence time is 5-15 min.

[0031] As a preferred embodiment, the amount of the bisphenol compound added in step (3) is 0.0001 to 0.11 times the mass of the bisphenol compound in step (1);

[0032] Preferably, the end-capping agent is a monophenol, which may be one or more of phenol, p-tert-butylphenol, cumylphenol, and isooctylphenol;

[0033] Preferably, the amount of the end-capping agent added is 3.0% to 8.0% of the total molar amount of the bisphenol compound and the branching agent added in step (2) and step (3);

[0034] Preferably, the disperser is a dynamic disperser, and the rotation speed can reach 3000-20000 rpm.

[0035] As a preferred embodiment, the operating temperature of the disperser is 20-30°C.

[0036] Preferably, the average particle size of the latex particles in the emulsion is 5.0 to 11.0 μm.

[0037] As a preferred embodiment, the reaction conditions in step (3) are:

[0038] Preferably, the amount of alkali solution added in step (3) is 0.05% to 5% of the total mass of the mixed solution A in step (2).

[0039] Preferably, the reaction equipment is a single kettle or two kettles in series or three kettles in series;

[0040] Preferably, the reaction residence time is 0.4 to 4 h, and the reaction temperature is 30 to 35 ° C;

[0041] The polycarbonate reaction liquid obtained in step (3) is subjected to demulsification, separation, purification and drying to obtain a polycarbonate product.

[0042] As a preferred embodiment, the carbonate polymer prepared in step (3) has a weight average molecular weight of 18000-45000 g / mol;

[0043] As a preferred embodiment, the conversion rate of the capping agent is >99.5%.

[0044] As a preferred embodiment, the flame retardant performance of the prepared polycarbonate reaches 1.0mm V0 level, and the product has better light stability and yellowing resistance.

[0045] Compared with the prior art, the advantages of the present invention are:

[0046] (1) By adding BPA in the polycondensation stage, the polycondensation time is shortened without adding a catalyst, the degree of hydrolysis of the acyl chloride during the polycondensation process is reduced, the end-capping efficiency of the end-capping agent is improved, the conversion rate of the end-capping agent is high, and the process risks and operational difficulties caused by the catalyst are solved.

[0047] (2) The prepared branching agent contains halogen, so that the flame retardant performance reaches 1.0 mmV0 level without adding flame retardant.

[0048] (3) The branching agent has an ultraviolet absorption structure, which can avoid the problem of late additive precipitation and improve the long-term light stability and yellowing resistance of polycarbonate. DETAILED DESCRIPTION

[0049] The present invention is illustrated by the following examples, but the scope of the present invention is not limited to these examples.

[0050] The main raw materials used in the examples or comparative examples of the present invention are:

[0051] BPA: bisphenol A, industrial grade, purchased from Lihua Yiweiyuan Chemical Co., Ltd.;

[0052] THPE: 1,1,1-tris(4-hydroxyphenyl)ethane, technical grade, purchased from Honshu Chemical Industry Co., Ltd.;

[0053] PTBP: p-tert-butylphenol, technical grade, purchased from Tongcheng Chemical Co., Ltd.;

[0054] Melamine: analytical grade, purchased from Sigma-Adrich;

[0055] Tetrachloroterephthalic acid: 97%, purchased from Maclean;

[0056] DMSO: analytical grade, purchased from Sigma-Adrich;

[0057] Sodium hydroxide: analytical grade, purchased from Tianjin Kemeiou Chemical Reagent Co., Ltd.;

[0058] Phosgene: industrial grade, Wanhua Chemical;

[0059] Dichloromethane: analytical grade, purchased from Tianjin Kemeiou Chemical Reagent Co., Ltd.;

[0060] Other raw materials and reagents were purchased from commercial sources unless otherwise specified.

[0061] The performance evaluation method is as follows:

[0062] (1) The weight average molecular weight was determined by gel permeation chromatography. Equipment manufacturer: Agilent Technologies, equipment model: 1260 InfinityⅡ.

[0063] (2) The content of the end-capping agent in the aqueous phase was determined by high performance liquid chromatography, equipment manufacturer: Agilent Technologies, equipment model: 1260 InfinityⅡ.

[0064] (3) Index for judging the degree of branching of the product: Index for judging the degree of branching of the product: Melt index R value, melt index instrument equipment manufacturer: Goettfert, equipment model: MI40. The specific method is as follows: Test the melt index a of the final product at 300℃ / 1.2kg and the melt index b at 300℃ / 10kg respectively, then the melt index R value = (log(a)-log(b)) / (log(10)-log(1.2))(Ⅰ)

[0065] The melt index R value of linear PC is less than 1.10, and the higher the degree of branching, the higher the melt index R value.

[0066] (4) Flame retardant properties: The flammability test was conducted according to the "Flammability Test for Plastic Materials, UL94" regulations. The flame retardant rating was determined based on the burning rate, extinguishing time, resistance to falling, and whether the falling was burning. The sample used for the test was 125 mm in length and 13 mm in width. The thickness of the present invention was selected as 1.0 mm during the test. According to the UL94 regulations, the flame retardant rating of the material can be classified as (UL94-HB): V0, V1, V2, 5VA and / or 5VB.

[0067] (5) Light stability performance: Tested in accordance with the test standard SAEJ1960, the test conditions are irradiance 0.55W / (m 2 *nm)@340nm, blackboard temperature is (70±2)℃, box temperature is (50±2)℃, relative humidity is (50±10)%RH, cumulative duration is 168.

[0068] (6) Yellowing resistance: At an injection molding machine barrel temperature of 300°C, the sample was directly injection molded into a sheet, and then the sample was retained in the barrel for 20 minutes before injection molding. The change in the yellowness index YI of the injection molded sheet before and after the test was performed. The YI test refers to the ASTM E313 standard.

[0069] (7) Element content analysis: X-ray photoelectron spectroscopy (XPS) was performed using an ESCALAB 250 XPS with an emission source of AlKαX. The binding energy of the test element was calibrated using C1s of 284.8 eV.

[0070] (8) Infrared analysis: An INVENIO S Fourier transform infrared spectrometer was used in ATR mode with a wave number range of 4000 cm -1 ~400cm -1 , the resolution is 4cm -1 .

[0071] Example 1

[0072] Preparation of branching agent:

[0073] The branching agent is prepared by adding melamine and tetrachloroterephthalic acid in a mass ratio of 1:7.2 into a solvent in which the mass ratio of water and DMSO is 4:1, reacting at 80°C, and drying the reaction solution by rotary evaporation at 90°C.

[0074] Elemental analysis results: theoretical value, C: 31.6%, O: 18.7%, N: 8.2%, Cl: 41.5%; actual value, C: 31.4%, O: 19.2%, N: 7.6%, Cl: 41.8%.

[0075] In the infrared spectrum, the branching agent is at 1647 cm -1 and 1541cm -1 The C=O stretching vibration peak appeared at 1531 cm -1 The CN and NH stretching vibration peaks were enhanced, proving the synthesis of branching agent.

[0076] Preparation of polycarbonate:

[0077] Step (1): preparing an alkaline solution of BPA (mixed solution A) and a dichloromethane solution of a branching agent (mixed solution B) in a batching tank, wherein the concentration of BPA in the mixed solution A is 15.1 wt %, the concentration of sodium hydroxide is 6.1 wt %, and the concentration of the branching agent in the mixed solution B is 7.0 wt %. Nitrogen is purged and stirring is started; the obtained BPA alkaline solution is kept warm at 35° C.; and simultaneously preparing a PTBP / dichloromethane solution with a concentration of 11 wt % and placing them in a capping agent tank.

[0078] Step (2): injecting an alkaline solution of BPA and a dichloromethane solution of a branching agent into a reactor at flow rates of 142.0 g / min and 25.4 g / min, respectively, simultaneously adding 11.4 g / min of phosgene and 148 g / min of dichloromethane, controlling the reactor outlet temperature at 32-35° C., and the residence time at 12 min, to carry out a phosgenation reaction to obtain a polycarbonate oligomer mixed solution.

[0079] Step (3): Add PTBP in dichloromethane solution and 32 wt% sodium hydroxide aqueous solution to the polycarbonate oligomer obtained in step (2) at 6.69 g / min and 4.50 g / min, respectively, then transport the mixed solution to a disperser, the speed of the disperser is set to 8000 rpm, to obtain an emulsion, and add mixed solution A to the emulsion at a flow rate of 1.41 g / min, react in the first polycondensation kettle for 40 minutes, and then transport to the second polycondensation kettle, the reaction in the second polycondensation kettle is completed, and polycarbonate is obtained after demulsification, separation, purification and drying. Test data are shown in Table 1 below.

[0080] Example 2

[0081] Preparation of branching agent:

[0082] Same as Example 1.

[0083] Preparation of polycarbonate:

[0084] Step (1) is the same as in Example 1.

[0085] Step (2): injecting an alkaline solution of BPA and a dichloromethane solution of a branching agent into a reactor at flow rates of 142.0 g / min and 26.3 g / min, respectively, simultaneously adding 11.8 g / min of phosgene and 115 g / min of dichloromethane, controlling the reactor outlet temperature at 32-35° C., and the residence time at 12 min, to carry out a phosgenation reaction to obtain a polycarbonate oligomer mixed solution.

[0086] Step (3): Add PTBP in dichloromethane solution and 32 wt% sodium hydroxide aqueous solution to the polycarbonate oligomer obtained in step (2) at 6.69 g / min and 4.32 g / min, respectively, then transport the mixed solution to a disperser, the speed of the disperser is set to 12000 rpm, to obtain an emulsion, and add mixed solution A to the emulsion at a flow rate of 1.15 g / min, react in the first polycondensation kettle for 40 minutes, and then transport to the second polycondensation kettle, the reaction in the second polycondensation kettle is completed, and polycarbonate is obtained after demulsification, separation, purification and drying. Test data are shown in Table 1 below.

[0087] Example 3

[0088] Preparation of branching agent:

[0089] Same as Example 1.

[0090] Preparation of polycarbonate:

[0091] Step (1) is the same as in Example 1.

[0092] Step (2): injecting an alkaline solution of BPA and a dichloromethane solution of a branching agent into a reactor at flow rates of 142.0 g / min and 25.4 g / min, respectively, simultaneously adding 11.0 g / min of phosgene and 117 g / min of dichloromethane, controlling the reactor outlet temperature at 32-35° C., and the residence time at 12 min, to carry out a phosgenation reaction to obtain a polycarbonate oligomer mixed solution.

[0093] Step (3): Add PTBP in dichloromethane solution and 32 wt% sodium hydroxide aqueous solution to the polycarbonate oligomer obtained in step (2) at 6.18 g / min and 4.41 g / min, respectively, then transport the mixed solution to a disperser, the speed of the disperser is set to 9000 rpm, to obtain an emulsion, and add mixed solution A to the emulsion at a flow rate of 1.62 g / min, react in the first polycondensation kettle for 40 minutes, and then transport to the second polycondensation kettle, the reaction in the second polycondensation kettle is completed, and polycarbonate is obtained after demulsification, separation, purification and drying. Test data are shown in Table 1 below.

[0094] Example 4

[0095] Preparation of branching agent:

[0096] Same as Example 1.

[0097] Preparation of polycarbonate:

[0098] Step (1) is the same as in Example 1.

[0099] Step (2): injecting an alkaline solution of BPA and a dichloromethane solution of a branching agent into a reactor at flow rates of 142.0 g / min and 24.1 g / min, respectively, simultaneously adding 11.3 g / min of phosgene and 135 g / min of dichloromethane, controlling the reactor outlet temperature at 32-35° C., and the residence time at 12 min, to carry out a phosgenation reaction to obtain a polycarbonate oligomer mixed solution.

[0100] Step (3): Add PTBP in dichloromethane solution and 32 wt% sodium hydroxide aqueous solution to the polycarbonate oligomer obtained in step (2) at 6.30 g / min and 4.45 g / min, respectively, then transport the mixed solution to a disperser, the speed of the disperser is set to 10000 rpm, to obtain an emulsion, and add mixed solution A to the emulsion at a flow rate of 1.32 g / min, react in the first polycondensation kettle for 40 minutes, then transport to the second polycondensation kettle, the reaction in the second polycondensation kettle is completed, and polycarbonate is obtained after demulsification, separation, purification and drying. Test data are shown in Table 1 below.

[0101] Comparative Example 1

[0102] Step (1): Step (1): Prepare an alkaline solution of BPA (mixed solution A) and a dichloromethane solution of THPE (mixed solution B) in a batching tank, respectively. The concentration of BPA in mixed solution A is 15.1 wt%, and the concentration of sodium hydroxide is 6.1 wt%. In mixed solution B, the concentration of THPE is 7.0 wt%. Nitrogen is purged and stirring is started. 11 wt% PTBP / dichloromethane solution is placed in a capping agent tank.

[0103] Step (2): injecting a BPA sodium hydroxide mixed solution and a branching agent dichloromethane solution into a reactor at flow rates of 142.0 g / min and 21.4 g / min, respectively, simultaneously adding 11.3 g / min of phosgene and 135 g / min of dichloromethane, controlling the reactor outlet temperature at 32-35° C., and the residence time at 12 min, to carry out a phosgenation reaction to obtain a polycarbonate oligomer mixed solution.

[0104] Step (3): 6.18 g / min and 4.42 g / min of PTBP in dichloromethane and 32 wt% of sodium hydroxide aqueous solution were added to the polycarbonate oligomer mixed solution obtained in step (2), and then the mixed solution was transported to a disperser, the speed of the disperser was set to 10000 rpm, and an emulsion was obtained. The emulsion was reacted in a first polycondensation kettle for 40 minutes, and then transported to a second polycondensation kettle. After the reaction in the second polycondensation kettle was completed, polycarbonate was obtained after demulsification, separation, purification and drying. The test data is shown in Table 1 below.

[0105] Comparative Example 2

[0106] Step (1): Step (1): Mix liquid A and liquid B in a batching tank and a branching agent tank, respectively, wherein the concentration of BPA in liquid A is 15.1 wt%, and the concentration of sodium hydroxide is 6.1 wt%, and the concentration of THPE in liquid B is 7.0 wt%, and the concentration of alkali solution is 5.6 wt%, and nitrogen is purged and stirring is started; 11 wt% PTBP / dichloromethane solution is placed in a capping agent tank.

[0107] Step (2): injecting alkaline solutions of BPA and THPE into the reactor at flow rates of 142.0 g / min and 6.7 g / min, respectively, simultaneously adding 11.4 g / min of phosgene and 148 g / min of dichloromethane, controlling the reactor outlet temperature at 32-35° C., the residence time at 12 min, continuously adding alkaline solution so that the pH of the aqueous phase of the reaction solution is 12-13, and performing phosgenation reaction to obtain a polycarbonate oligomer mixed solution.

[0108] Step (2): injecting alkaline solutions of BPA and THPE into reactor 3 at flow rates of 142.0 g / min and 8.22 g / min, respectively, simultaneously adding 11.4 g / min of phosgene and 148 g / min of dichloromethane, controlling the reactor outlet temperature at 32-35° C., and the residence time at 12 min, to carry out phosgenation reaction to obtain a polycarbonate oligomer mixed solution.

[0109] Step (3): Add PTBP in dichloromethane and 32 wt% sodium hydroxide aqueous solution to the polycarbonate oligomer mixture obtained in step (2) at 2.34 g / min and 4.51 g / min, respectively, and then transfer the mixture to a disperser with the speed of the disperser set to 8000 rpm to obtain an emulsion, react in a first polycondensation kettle for 40 min, and then transfer to a second polycondensation kettle. After the reaction in the second polycondensation kettle is completed, the polycarbonate is obtained after demulsification, separation, purification and drying. The test data is shown in Table 1 below.

[0110] Table 1. Experimental test data

[0111]

[0112] From the above data comparison, it can be seen that this invention, by using a branching agent containing triazine, increases the synthesis rate of polycarbonate without adding a catalyst, eliminates the process risk and operation difficulty brought by the catalyst, increases the conversion efficiency of the end-capping agent, and successfully prepares a branched polycarbonate with an end-capping agent conversion rate of > 99.5%, and the flame retardant performance reaches the 1mm V0 level, while improving the light stability and yellowing resistance of the polycarbonate. The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, without departing from the method of the present invention, several improvements and supplements can be made, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A branched flame retardant polycarbonate, characterized in that: It uses the following compound as a branching agent: Here, x is a natural number from 1 to 4, and preferably 4.

2. The branched flame retardant polycarbonate according to claim 1, characterized in that The branching agent is prepared by reacting melamine with tetrachloroterephthalic acid; Preferably, the reaction is carried out in a solvent, the solvent is a mixture of water and DMSO, wherein the mass ratio of water to DMSO is 3:1 to 6:1, more preferably 4:1 to 6:1; Preferably, the reaction temperature is 70-90°C; Preferably, the mass ratio of melamine to tetrachloroterephthalic acid is 1:5-1:

8.

3. The method for preparing the polycarbonate according to claim 1 or 2, characterized in that: The following steps are involved: (1) firstly, a bisphenol compound and an alkali solution are mixed to obtain a mixed solution A, and a branching agent and a solvent are mixed to obtain a mixed solution B; (2) adding the mixed solution A and the mixed solution B obtained in step (1) into a reactor respectively to carry out a phosgenation reaction with phosgene to obtain a polycarbonate oligomer solution; (3) The polycarbonate oligomer solution obtained in step (2) is subjected to a polycondensation reaction to obtain polycarbonate.

4. The preparation method according to claim 3, characterized in that: In step (3), an optional alkali solution and a capping agent are added; Preferably, in the step (3), the polycarbonate oligomer is dispersed in a disperser to obtain an emulsion and then subjected to polycondensation reaction; Preferably, a bisphenol compound is also added to the polycondensation reaction in step (3).

5. The preparation method according to claim 3 or 4, characterized in that: The bisphenol compound in step (1) is one or more of 2,2-bis(4-hydroxyphenyl)propane (i.e., bisphenol A), bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, bis(4-hydroxyphenyl)sulfide, 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)octane, bis(4-hydroxyphenyl)phenylmethane, bis(4-hydroxyphenyl)diphenylmethane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, bis(4-hydroxyphenyl)oxide and bis(4-hydroxyphenyl)sulfone, preferably bisphenol A; Preferably, the molar ratio of the bisphenol to the branching agent in step (1) is 45 to 65:1; Preferably, the pH of the mixed solution A in step (1) is 11 to 14; Preferably, the alkali solution is selected from an aqueous solution of an alkali metal hydroxide or an aqueous solution of an alkali metal carbonate, preferably an aqueous solution of sodium hydroxide or potassium hydroxide.

6. The preparation method according to any one of claims 3 to 5, characterized in that: The molar amount of phosgene is 1.08-1.25 times the sum of the molar amounts of the branching agent and the bisphenol compound, and more preferably 1.12-1.21 times; Preferably, the phosgene is dissolved in an inert solvent; Preferably, the reaction temperature in step (2) is 20-35° C., and the residence time is 5-15 min.

7. The preparation method according to any one of claims 3 to 6, characterized in that: The amount of the bisphenol compound added in step (3) is 0.0001 to 0.11 times the mass of the bisphenol compound in step (1); Preferably, the end-capping agent is a monophenol, which may be one or more of phenol, p-tert-butylphenol, cumylphenol, and isooctylphenol; Preferably, the amount of the end-capping agent added is 3.0% to 8.0% of the total molar amount of the bisphenol compound and the branching agent added in step (2) and step (3); Preferably, the amount of alkali solution added in step (3) is 0.05% to 5% of the total mass of the mixed solution A in step (2).

8. The preparation method according to any one of claims 3 to 7, characterized in that: The disperser is preferably a dynamic disperser, and the rotation speed can reach 3000-20000rpm; Preferably, the disperser operating temperature is 20-30°C; Preferably, the average particle size of the latex particles in the emulsion is 5.0 to 11.0 μm; Preferably, the reaction equipment is a single kettle or two kettles in series or three kettles in series; Preferably, the reaction residence time is 0.4 to 4 h, and the reaction temperature is 30 to 35 °C.

9. The preparation method according to any one of claims 3 to 8, characterized in that: The weight average molecular weight of the carbonate polymer prepared in step (3) is 18000-45000 g / mol.

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