CN114196002B - Preparation method of transparent flame-retardant novel polycarbonate, polycarbonate and application thereof - Google Patents

Abstract

The invention discloses a preparation method of transparent flame-retardant novel polycarbonate, the polycarbonate and application thereof, and the preparation method comprises the following steps: a) Carrying out photochemical reaction on a water phase formed by dissolving bisphenol A and triphenol in alkali liquor and an oil phase formed by dissolving phosgene in carbon tetrachloride to prepare a polycarbonate oligomer with hindered phenolic hydroxyl active groups, and then adding a catalyst and a capping reagent to react to obtain a high molecular weight linear polycarbonate solution; b) Reacting phosphorus oxychloride and bisphenol A under the action of a catalyst to produce an intermediate with a phosphoric acid acyl chloride end group; c) And (3) putting the products of the step A) and the step B) into a reaction kettle to react under certain conditions to generate the novel polycarbonate with the flame retardant short-side branched chain structure. The novel polycarbonate can realize the characteristics of transparency, high flame retardance, high flow, low internal stress and the like, has better heat resistance and impact property, and has intrinsic advantages in the application of transparent windows of electronics and electrics.

Description

Preparation method of transparent flame-retardant novel polycarbonate, polycarbonate and application thereof

Technical Field

The invention relates to the technical field of polycarbonate, in particular to a preparation method of transparent flame-retardant novel polycarbonate with flame retardant grafted with polycarbonate side groups polymerized, polycarbonate and application thereof.

Background

The Polycarbonate (PC) has outstanding performances of impact resistance, heat resistance, high light transmittance and the like, is second largest engineering plastic which is inferior to nylon worldwide, has wide application in national economy, and has entered into various fields of automobiles, electronics, electric appliances, buildings, office equipment, packaging, sports equipment, medical care, household appliances and the like. However, with the progress of society and the development of industry, such as the trend of thinning of electronic and electric appliances, higher requirements are put on flame retardance and flowability of polycarbonate materials, and in addition, transparent parts such as charging pile windows and the like require that the polycarbonate maintain flame retardance and high transparency, and meanwhile, internal stress cannot be too large, so that rainbow patterns are prevented from influencing perspective effects. The conventional polycarbonate has relatively poor flame retardant property and cannot meet the minimum flame retardant requirements of various industries, so that the conventional technical means is to carry out flame retardant modification on the polycarbonate, but most modification means bring various defects while the flame retardant property is improved, and the final requirement cannot be met.

For example, publication No. CN 101353473A discloses a method for improving flame retardance by adding brominated polycarbonate oligomer as a flame retardant to polycarbonate, wherein the flame retardance can be achieved in the film grade of 0.25mmV-0, but the brominated flame retardant generates a large amount of toxic and harmful substances when burned and is limited to be used by most countries, so that the method does not conform to the future social development trend and cannot be an effective solution. Patent CN 102844377B discloses a method for improving flame retardant performance by adding sulfonate flame retardant into polycarbonate, which can achieve flame retardant grade of 2.0mm v0 and haze of less than 2% at 3 mm; the method is the most commonly used method in the industry at present, but the sulfonate flame retardant cannot realize the flame retardant performance in the aspect of thin wall, V0 is a difficult problem which cannot be broken through at the present stage under the thickness of 0.8mm, 1.0mm, even 1.5mm and the like, and the flame retardant effect of the sulfonate is further reduced after the fluidity of the polycarbonate is improved, even the grade of 3.0mm V0 cannot be realized.

In patent CN110358276a, a method of adding an ionic liquid flame retardant is disclosed to improve the flame retardant property of polycarbonate, but in practical situations, the flame retardant efficiency of the ionic liquid is low, and an excellent flame retardant effect cannot be obtained, so that a mainstream flame retardant scheme is not formed.

Patent CN 109265950a discloses a method for preparing transparent polycarbonate material suitable for double-shot injection by adding liquid phosphorus flame retardant and powder flame retardant, but when the pure external phosphorus flame retardant or the powder flame retardant is hydroxide, the toughness of the material is greatly and negatively affected, so that the polycarbonate loses the advantage of high toughness.

Patent CN112538252a discloses that a phosphorus flame retardant and a silicon flame retardant are compounded and applied to siloxane copolycarbonates and arylated block copolycarbonates, and the product can realize higher flame retardant performance, but the substrate of the invention is not a conventional product, and cannot meet the requirements of large-scale popularization and low-price popularization in the aspects of market supply and product price.

Finally, most foreign copolymerized patents (such as sabicks, light emission and the like) focus on the preparation of silicon-based polycarbonate by silicon block copolymerization, and the copolymer has various advantages of low temperature resistance, flame retardance, solvent resistance and the like, but the flame retardance needs to be further improved.

In summary, transparent flame-retardant polycarbonates are currently experiencing increasing market demands, but the prior art approaches all have the difficult problems of respective technical bottlenecks.

Disclosure of Invention

The invention aims to overcome the defects of all the technologies and provide a preparation method of a transparent flame-retardant polycarbonate material with high flow and low internal stress. The invention forms polycarbonate with hindered phenol active groups by copolymerizing a ternary phenol component, wherein two phenolic hydroxyl groups in the ternary phenol react normally in the reaction process to form polycarbonate with a linear structure, and the other phenolic hydroxyl group generates a larger steric hindrance effect due to the existence of an adjacent group and cannot participate in the reaction under the same condition, so that the phenolic hydroxyl group exists as an active group; the intermediate with the dichloro end group of phosphoric acid and the hindered phenol hydroxyl are selected to react at high temperature, so that the phosphorus flame-retardant short side group in the molecular formula of the conventional linear polycarbonate can obtain a high-flow low-internal stress product and realize a higher flame-retardant effect.

It is still another object of the present invention to provide a novel transparent flame retardant polycarbonate prepared by the above-mentioned preparation method.

It is a further object of the present invention to provide the use of such novel polycarbonates which are transparent and flame retardant.

In order to achieve the aim of the invention, the invention adopts the following technical scheme:

a method for preparing transparent flame-retardant novel polycarbonate, which comprises the following steps:

a) Carrying out photochemical reaction on a water phase formed by dissolving bisphenol A and triphenol in alkali liquor and an oil phase formed by dissolving phosgene in carbon tetrachloride to prepare a polycarbonate oligomer with hindered phenolic hydroxyl active groups, and then adding a catalyst and a capping reagent to react to obtain a high molecular weight linear polycarbonate solution;

b) Reacting phosphorus oxychloride and bisphenol A under the action of a catalyst at a certain temperature to generate an intermediate of the formula I, wherein n=1 and 2 until no hydrogen chloride is generated, and refluxing excessive phosphorus oxychloride to obtain a purified intermediate of the formula I;

c) Putting the intermediate of the formula I in the step b) into a reaction kettle containing the high molecular weight linear polycarbonate solution in the step a), performing interfacial polymerization under the actions of inert atmosphere, high temperature and high pressure and a catalyst, adding a blocking agent after a certain time, stopping the reaction after no hydrogen chloride is generated, and cooling, depressurizing and removing the solvent to obtain the transparent flame-retardant novel polycarbonate.

In a specific embodiment, the structural general formula of the triphenols in step a) is shown in formula II:

wherein R is ₁ 、R ₂ Each independently selected from a hydrocarbon group having 2 to 18 carbon atoms, or one or a combination of a benzene ring and a naphthalene ring, preferably methyl or ethyl; r is R ₃ Selected from hydrocarbon groups having 2 to 18 carbon atoms or branched structure groups thereof, preferably methyl groups.

In a specific embodiment, the concentration by mass of phenolate in the aqueous phenolate phase of step a) is between 10 and 15% and the proportion of triphenols in the total phenolate mass is between 0.1 and 5%; preferably, the lye is an aqueous solution of an alkali metal hydroxide, more preferably an aqueous solution of sodium hydroxide; the pH value of the phenolate water phase is controlled to be 11-11.8.

In a specific embodiment, the residence time of the reaction in step a) is from 5 to 50min, preferably from 5 to 40min, more preferably from 5 to 25min, and the total molar amount of phosgene in step a) is from 1.00 to 1.16 times, preferably from 1.02 to 1.10 times the sum of the molar amounts of triphenols and bisphenol A.

In a specific embodiment, the molar ratio of bisphenol a to phosphorus oxychloride in step b) is 1:2.5, the catalyst is selected from any one or a combination of calcium chloride and magnesium chloride, preferably calcium chloride, the addition amount of the catalyst is 0.1-0.4% of bisphenol A, preferably 0.15-0.3%, and the reaction temperature in the step b) is 100-120 ℃; the reaction residence time is 3.5-6h.

In a specific embodiment, the inert atmosphere in step c) is a nitrogen atmosphere, and the reaction temperature in the reaction vessel is 130-170 ℃, preferably 145-155 ℃; the reaction residence time is 4 to 6 hours, preferably 4.5 to 5.5 hours; the reaction pressure is 5 to 15atm, preferably 7 to 12atm, and more preferably 8 to 10atm.

In a specific embodiment, the catalyst in step c) is selected from any one or combination of calcium chloride and magnesium chloride, preferably calcium chloride, and the catalyst is added in an amount of 0.3-0.6% of the mass of the triphenol monomer in step a); preferably 0.4-0.55%; the end-capping agent is selected from phenol or p-tert-butylphenol, preferably phenol.

In a specific embodiment, the intermediate of formula I and the end-capping agent are added in step c) in a ratio of 1.01 to 1.30 based on moles of the trisphenol in the phenoxide of step a) for the moles of intermediate of formula I, moles of the trisphenol, moles of the end-capping agent: 1:4.04-5.20.

On the other hand, the novel transparent flame-retardant polycarbonate is prepared by the preparation method; preferably, the novel polycarbonate can realize flame retardant grade of 0.8-3.0mM V0/V1/V2, the melt index is 7-60g/10min, the light transmittance is more than 87%, and the impact performance reaches 500-900J/m.

In a further aspect, the use of the aforementioned transparent flame retardant novel polycarbonates in transparent windows, preferably in transparent windows in the electrical and electronic field.

Compared with the prior art, the invention has the following positive effects:

the triphenol component with the structure of formula II participates in the interfacial polymerization reaction of the polycarbonate, so that the hindered phenolic hydroxyl with activity is introduced into the molecular chain of the polycarbonate; reacting phosphorus oxychloride with bisphenol A under specific conditions to generate an intermediate I with a terminal band carrying a chlorine phosphate group; finally, the intermediate I reacts with phenolic hydroxyl groups with certain activity in the polycarbonate to produce the novel polycarbonate polymer with flame retardant side chains. The polymer is provided with the phosphorus flame-retardant groups, so that the molecular level dispersion of the flame-retardant groups is realized, the flame-retardant performance is greatly improved, and different flame-retardant grades of 0.8-3.0mm thickness V0-V2 can be realized according to the content difference; meanwhile, the existence of a short side chain leads to the increase of the molecular distance, the fluidity of the material is improved, and the internal stress after molding is greatly reduced; also, because the short side groups are very similar to the backbone results, the introduction of the side groups has no effect on the transparency of the material, maintaining the same transparency as conventional products.

The specific embodiment is as follows:

the following examples will further illustrate the method provided by the present invention for a better understanding of the technical solution of the present invention, but the present invention is not limited to the examples listed but should also include any other known modifications within the scope of the claims of the present invention.

A method for preparing transparent flame-retardant novel polycarbonate, which comprises the following steps:

a) Bisphenol A and triphenol are dissolved in alkali metal hydroxide water solution to form phenolate water phase, and phosgene is dissolved in carbon tetrachloride to form oil phase according to the concentration of 7%; carrying out photochemical reaction on the water phase and the oil phase to prepare a polycarbonate oligomer with hindered phenolic hydroxyl active groups; and adding a catalyst and a blocking agent to react to obtain the high molecular weight polycarbonate solution.

b) Under the action of a catalyst, phosphorus oxychloride and bisphenol A are raised to a certain temperature to react to generate an intermediate I (i.e. the intermediate of the formula I) until no hydrogen chloride is generated, and excessive phosphorus oxychloride is refluxed; where n=1 and 2, the intermediate i formed by the reaction is generally a mixture comprising n=1 and n=2.

c) Putting the intermediate generated in the step b) into an autoclave containing the high molecular weight linear polycarbonate carbon tetrachloride solution with the hindered phenolic hydroxyl active groups generated in the step a), raising the temperature to a certain temperature in a nitrogen atmosphere, performing interfacial polymerization reaction under the action of a catalyst, adding phenol for blocking after a certain time, stopping after no hydrogen chloride is generated, and performing devolatilization after cooling and depressurization to obtain the transparent flame-retardant polycarbonate.

In the step a), the structural general formula of the triphenol is shown as formula II:

wherein R is ₁ 、R ₂ Is a hydrocarbyl group of 2 to 18 carbon atoms or one or a combination of large molecular weight groups such as benzene rings, naphthalene rings, etc., for example ethyl, propyl, butyl, pentyl, hexyl, heptyl, octane, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl long chain alkyl groups or branched structures thereof or benzene rings, naphthalene rings, preferably methyl or ethyl; r is R ₃ Long-chain alkyl groups selected from the group consisting of hydrocarbon groups having 2 to 18 carbon atoms such as ethyl, propyl, butyl, pentyl, hexyl, heptyl, octane, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, or branched structures thereof, preferably methyl.

In a preferred embodiment, the trisphenol compound is(formula a),(formula b) or->(formula c). The method for producing such a trisphenol compound is not particularly limited, and for example, reference may be made to a method similar to that described in Xie Song (J.1, 1-tris (4-hydroxyphenyl) ethane synthesis and purification, university of Tianjin science and technology, journal, 27 (2): 30-33).

In said step a), the mass concentration of phenolate in the aqueous phase of phenolate comprising bisphenol a and the triphenols of specific structure is 10-15%, including for example but not limited to 10%, 11%, 12%, 13%, 14%, 15%; wherein the specific structure of the triphenols comprises 0.1-5% of the total mass of the phenoxide, such as but not limited to 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%; at this feed ratio, the mole ratio of the triphenols in the phenoxide is about 0.08% to 4%. Alkali metal hydroxide, including but not limited to sodium hydroxide, potassium hydroxide, etc., is also added to the phenolate-containing aqueous phase, and sodium hydroxide is commonly used in the art to adjust the pH of the aqueous phase to promote ionization of phenol, with the pH being controlled to 11-11.8, including but not limited to 11, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8; too low a pH will result in the inability of the particular triphenols and bisphenol components to ionize, affecting the polymerization conversion, while too high a pH will result in an increase in the rate of phosgene alkaline hydrolysis.

This is because: in the preparation process of the polycarbonate, the chloroformate group and the phenol oxygen anion mainly perform polycondensation reaction at an oil-water interface, and the phenolic hydroxyl group can participate in the reaction only after ionization. The two-stage ionization constants of BPA are 9.6 and 10.2 respectively, the ionization degree is insufficient when the pH is too low, and 6 water compound is separated out when the pH is too high, for example, more than 98 percent of BPA is ionized in a divalent state when the pH of a 16.5wt% BPA/NaOH aqueous solution at 25 ℃ is pH=12.5, and Na appears when the pH reaches 13 ₂ BPA·6H ₂ And O crystals are precipitated. In the pH range of the invention, three phenolic hydroxyl groups exist in the specific triphenol component in the step a), two phenolic hydroxyl groups at two sides are completely ionized to participate in interfacial polymerization, but the third phenolic hydroxyl group is most difficult to ionize and cannot participate in reaction, and active groups exist in a molecular chain. By the design, the hindered phenolic hydroxyl subsequently reacts with the intermediate with the phosphoric acid dichloro end group and the formula I, so that the conventional linear polycarbonate has phosphorus flame-retardant short side groups in molecular formula, and a high-flow low-internal stress product is obtained, and meanwhile, a high flame-retardant effect is realized.

In step a), the oil phase is typically phosgene dissolved in carbon tetrachloride solvent, and phosgene is typically dissolved in carbon tetrachloride to a concentration of 7% in the art to form an oil phase, but is not limited to this concentration. Further, in the step a), the total molar amount of phosgene is 1.00 to 1.16 times, including, but not limited to, 1, 1.01 times, 1.02 times, 1.03 times, 1.04 times, 1.05 times, 1.06 times, 1.07 times, 1.08 times, 1.09 times, 1.1 times, 1.11 times, 1.12 times, 1.13 times, 1.14 times, 1.15 times, preferably 1.02 to 1.10 times, the sum of the molar amounts of the triphenols of the specific structures and the bisphenol A.

In the step a), the water phase and the oil phase are mixed and initially reacted to generate a polycarbonate low molecular weight oligomer with hindered phenolic hydroxyl active groups, the polycarbonate low molecular weight oligomer is further subjected to chain extension and polymerization reaction after a catalyst is added to obtain a high molecular weight linear polycarbonate, a blocking agent is added to terminate the polymerization reaction after blocking, and the upper water phase is removed to obtain a high molecular weight linear polycarbonate solution.

Wherein the catalyst may be selected from tertiary amines, quaternary amine salts such as triethylamine or a combination of such ammonium salts with one or more phase transfer catalysts. The end-capping agent may be added at any stage prior to or in synchronization with the catalyst addition; the capping agent may be phenol, p-tert-butylphenol, cumylphenol, octylphenol or other monophenols, preferably phenol.

Wherein the total residence time of the reaction in the step a) is 5-50min, including, but not limited to, 5min, 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, preferably 5-40min, further preferably 5-25min, and the longer residence time of the reaction can lead to higher polymerization degree of the oligomer and influence the molecular weight control of the final product, the number average molecular weight of the finished product is controlled to 19000-25000g/mol, and the molecular weight distribution width is controlled to be 0.5-2.5.

The reactor of step a) may be a reactor commonly used in the art for photochemical reactions, for example a reactor comprising at least one tubular mixing reactor, or at least one continuous stirred tank reactor, or a combination thereof

In the step b), the mole ratio of bisphenol A to phosphorus oxychloride is 1:2.5, including for example but not limited to 2.1, 2.2, 2.3, 2.4, 2.5; the catalyst is one or a combination of calcium chloride, magnesium chloride and magnesium chloride, preferably calcium chloride, and the content of the catalyst is 0.1-0.4% of the mass of bisphenol A, more preferably 0.15-0.3%, for example, including but not limited to 0.15%, 0.2%, 0.25%, 0.3%, preferably 0.22%; the catalyst can be removed along with the water phase after the reaction is completed, so that the subsequent influence on polycarbonate is avoided. The reaction temperature of this step is 100-120 ℃, including, for example, but not limited to, 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃; the reaction residence time is 3.5 to 6 hours, including for example but not limited to 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours; if the reaction temperature is too low, the reaction speed is too slow, and if the temperature is too high, byproducts are increased; if the time is too short, the reaction is incomplete. The reaction pressure in this step is not particularly limited, and is usually carried out at atmospheric pressure. The reaction in the step is carried out until no bubble is generated (hydrogen chloride gas) to prove that the reaction is finished, and excessive unreacted phosphorus oxychloride is separated through reflux after the reaction is finished, so that a purer intermediate of the formula I is obtained;

wherein n is 1 and 2;

in the step c), the high molecular weight linear polycarbonate and carbon tetrachloride solution in the step a) and the intermediate in the formula I in the step b) are subjected to interfacial polymerization reaction, wherein the reaction is usually carried out in an inert gas protection atmosphere such as nitrogen, wherein the catalyst is one or a combination of calcium chloride, magnesium chloride and magnesium chloride, preferably calcium chloride, and the addition amount of the catalyst is 0.3-0.6% of the mass of the triphenol monomer, more preferably 0.4-0.55%, and for example, the reaction comprises but is not limited to 0.4%, 0.45%, 0.5% and 0.55%; the reaction temperature in the autoclave is 130-170 ℃, including for example but not limited to 130 ℃, 135 ℃, 140 ℃, 145 ℃, 150 ℃, 155 ℃, 160 ℃, 165 ℃, 170 ℃, preferably 145-155 ℃; the reaction residence time is from 4 to 6 hours, including for example but not limited to 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, preferably from 4.5 to 5.5 hours; the reaction pressure is 5 to 15atm, preferably 7 to 12atm, further preferably 8 to 10atm, including, for example, but not limited to, 8atm, 9atm, 10atm; if the reaction temperature is too low, the reaction speed is too slow, and if the temperature is too high, byproducts are increased, and the color turns yellow; if the time is too short, the reaction is incomplete, and the yield of the target product is lowered.

In the step, a reaction kettle contains the high molecular weight linear polycarbonate solution obtained in the step a), the intermediate of the formula I and the end capping agent are added into the reaction kettle, the addition amount of the intermediate of the formula I and the end capping agent is calculated by the mole number of the triphenols in the phenolate in the step a), and the ratio of the mole number of the intermediate of the formula I to the mole number of the triphenols to the mole number of the end capping agent is 1.01-1.30:1:4.04-5.20. After the reaction is stopped, the temperature is reduced to normal temperature and normal pressure, and the transparent flame-retardant novel polycarbonate is finally obtained through removing volatile solvents such as carbon tetrachloride and the like. Specifically, after the reaction is finished, separating and removing an upper water phase, and respectively adopting dilute sodium hydroxide, dilute hydrochloric acid and desalted water to carry out multi-step washing and separation on the polymer oil phase solution, and removing impurities such as residual monomers, catalysts, inorganic salts and the like in the solution to obtain a pure polymer solution. Further adopting a multi-step flash evaporation process to increase the concentration of the polymer in the solution, finally adopting a double screw extruder to remove the residual solvent under a certain vacuum degree and granulating to obtain the transparent flame-retardant novel polycarbonate resin.

The reaction kettle in the step c) is a continuous stirring kettle type reactor, can be a reactor for interfacial polymerization reaction commonly used in the field, for example, can be a tubular mixing reactor, or a combination of the two.

The transparent flame-retardant novel polycarbonate of the invention can also be blended and processed into polycarbonate molded parts according to the requirements, for example, any antioxidant, plasticizer, leveling agent, flow aid, heat stabilizer, hydrolysis stabilizer, UV absorber, antistatic agent, pigment and the like are added according to the processing requirements.

The transparent flame-retardant novel polycarbonate prepared by the invention can realize different flame-retardant grades of 0.8-3.0mm V0/V1/V2, namely can realize the flame-retardant grades of V0, V1 and V2 under the condition of 0.8mm, and can realize the flame-retardant grades of V0, V1 and V2 under the condition of 3.0mm thickness, which is greatly improved compared with the prior art for the application of ultra-thin transparent windows of electronics and electrics. This is mainly because the novel polycarbonate of the invention realizes the molecular level dispersion of phosphorus elements in the polycarbonate, and greatly improves the flame retardant property of the final material. In addition, the novel polycarbonate has good flow processability, high flow of 7-60g/10min is realized in terms of melt index, the processability is greatly improved, compared with the prior art, the light transmittance of the polycarbonate is not reduced, the light transmittance is still kept above 87%, and the transparent flame-retardant polycarbonate is very suitable for being used as a transparent window in different fields.

The invention is further illustrated, but not limited, by the following more specific examples.

The main raw materials used in the following examples were respectively:

bisphenol A, commercial grade, purchased from vinca chemical industry;

sodium hydroxide: analytically pure, purchased from the company Miou chemical reagent, inc. of Tianjin, city;

phosgene: industrial grade, homemade;

carbon tetrachloride: analytically pure, purchased from the company Miou chemical reagent, inc. of Tianjin, city;

phenol: analytically pure, purchased from Shandong province chemical institute;

triethylamine: analytically pure, purchased from the company Miou chemical reagent, inc. of Tianjin, city;

hydrochloric acid: analytically pure, purchased from the economic technology development area refinement plant in the Shandong Laiyang city;

p-tert-butylphenol: analytically pure, purchased from japan ink chemical industries, inc;

phosphorus oxychloride: industrial grade, jiangsu Tianyuan chemical industry;

and (3) drying the final product in a 120 ℃ oven for 4 hours, and performing injection molding in an injection molding machine at 270 ℃ to obtain sample bars with different standard sizes, so as to perform the tests of transmittance, flame retardant property, impact property and the like.

Melt index was measured using ASTM D1238 under conditions of 300 ℃/1.2kg;

impact properties were tested using ASTM D256 standard at 23 ℃;

the transmittance was tested using ASTM D1003, test thickness 2mm;

flame retardant properties were tested using UL94 standards.

Preparation example 1: preparation of the trisphenol Compound of formula a

The specific triphenolic compound was synthesized as follows:

1534g phenol, 4.08mol dimethylphenol (or diethylphenol) and 40g mercaptopropionic acid are added into a 50L reaction kettle with stirring paddles, 260ml acetylacetone is added dropwise during stirring for 20min, the temperature is raised to 50 ℃, 50ml98% concentrated sulfuric acid is added dropwise during 13min, the system temperature is maintained within the range of 50-53 ℃ for reaction for 30h, then the temperature is reduced to 25 ℃, carbon tetrachloride is added for stirring for 1h, filtering is carried out, and devolatilization is carried out at 78 ℃ to obtain a crude compound mixture.

Adding 600g of crude product into 3L of 38% methanol water solution for purification, stirring at room temperature for 40min, and filtering to obtain yellow product; purifying 300g of the yellow product again in 1.16L of methanol, dropwise adding 10% KBH4 aqueous solution after stirring, dropwise adding the mixture until no yellow precipitate is generated, and drying the mixture in vacuum at 70 ℃ to obtain the specific triphenolic compound with the purity of 99.9%.

Preparation example 2: preparation of the trisphenol Compound of formula c

The specific triphenolic compound was synthesized as follows:

1534g phenol, 4.08mol diethylphenol and 40g mercaptopropionic acid are added into a 50L reaction kettle with stirring paddles, 260ml acetylacetone is added dropwise in the course of stirring for 20min, the temperature is raised to 50 ℃, 50ml98% concentrated sulfuric acid is added dropwise in the course of 13min, the system temperature is maintained to react for 30h in the range of 50-53 ℃, then the temperature is reduced to 25 ℃, carbon tetrachloride is added, stirring is carried out for 1h, filtering is carried out, and devolatilization is carried out at 78 ℃ to obtain a crude compound mixture.

Adding 600g of crude product into 3L of 38% methanol water solution for purification, stirring at room temperature for 40min, and filtering to obtain yellow product; purifying 300g of the yellow product again in 1.16L of methanol, dropwise adding 10% KBH4 aqueous solution after stirring, dropwise adding the mixture until no yellow precipitate is generated, and drying the mixture in vacuum at 70 ℃ to obtain the specific triphenolic compound with the purity of 99.9%.

Preparation example 3: preparation of the trisphenol Compound of formula b

The specific triphenolic compound was synthesized as follows:

1534g of phenol, 4.08mol of 2-ethyl-6-methylphenol and 40g of mercaptopropionic acid are added into a 50L reaction kettle with stirring paddles, 260ml of acetylacetone is dropwise added in the stirring period of 20min, the temperature is raised to 50 ℃, 50ml of 98% concentrated sulfuric acid is dropwise added in the stirring period of 13min, the system temperature is maintained in the range of 50-53 ℃ for reaction for 30h, then the temperature is reduced to 25 ℃, carbon tetrachloride is added for stirring for 1h, filtering is carried out, and devolatilization is carried out at 78 ℃ to obtain a crude compound mixture.

Adding 600g of crude product into 3L of 38% methanol water solution for purification, stirring at room temperature for 40min, and filtering to obtain yellow product; purifying 300g of the yellow product again in 1.16L of methanol, dropwise adding 10% KBH4 aqueous solution after stirring, dropwise adding the mixture until no yellow precipitate is generated, and drying the mixture in vacuum at 70 ℃ to obtain the specific triphenolic compound with the purity of 99.9%.

Preparation example 4: preparation of intermediates of formula I

The synthesis of intermediate I formed in step b) proceeds as follows:

adding 0.5g of calcium chloride catalyst and 383.3g of phosphorus oxychloride into a 100L autoclave reactor with stirring, starting heating and stirring, gradually adding 4566g of bisphenol A solution (concentration 5%) in the reaction process, and filling nitrogen protection gas into the autoclave; slowly heating to 110 ℃, and ending the reaction after the reaction lasts for 5 hours; and (3) distilling the reactant when the temperature of the reactant is reduced to 60 ℃, and removing excessive phosphorus oxychloride to obtain a tetrachloro biphosphate-bisphenol A aqueous solution of the intermediate I for later use.

Devolatilization operation:

the later devolatilization process of the embodiment of the invention comprises the following steps: the oil-water two phases after the reaction are separated by an inclined plate separator to obtain an upper water phase and a lower oil phase, the lower oil phase is washed by 0.25wt% of NaOH, 0.4wt% of HCl and desalted water with the conductivity less than 0.2us/cm in sequence, the flow rate of the washing liquid is 100kg/hr, the concentration of the polymer is further increased to more than 80% by adopting two-stage flash evaporation, and the operation conditions of the first-stage flash evaporation are as follows: inlet pressure 2MPa (G), temperature 160 ℃, flash tank pressure 0.4MPa (G) and temperature 95 ℃; the secondary flash evaporation operation conditions are as follows: inlet pressure 7MPa (G), temperature 280 ℃, flash tank pressure 1MPa (G), temperature 240 ℃. Finally, the high-temperature solution directly enters a Keplong ZSK35 type double-screw extruder to remove residual methylene dichloride under the vacuum degree of l00mbar, and the branched polycarbonate resin product is obtained by extrusion and granulation.

Example 1

Mixing and dissolving the triphenol of formula a, bisphenol a, sodium hydroxide and water to form a sodium phenolate aqueous solution, namely an aqueous phase, wherein the total concentration of phenolate is 10wt%, and the specific triphenol component accounts for 0.5% of the total phenolate, and the pH=11.0; phosgene was dissolved in carbon tetrachloride to form an oil phase, wherein the phosgene concentration was 7%. The aqueous phase, phosgene and carbon tetrachloride were fed into a photochemical reactor comprising a series of static mixers at a flow rate of 600kg/h, 28.1kg/h and 402kg/h, respectively, with an internal diameter of 54mm, a length of 650mm, a reaction residence time of about 5min, and a reaction outlet temperature of 34 ℃. Immediately after the photochemical reaction, the mixture enters a stirred tank reactor with two tanks connected in series, and 5wt% of a capping agent p-tert-butylphenol/carbon tetrachloride solution, 30wt% of a sodium hydroxide solution and 1.5wt% of a catalyst triethylamine/carbon tetrachloride solution and carbon tetrachloride are respectively added into a first reaction tank at the flow rates of 42.0kg/h, 17.0kg/h, 9.5kg/h and 150kg/h, the effective volumes of the reaction tanks are respectively 100L and 600L, and the reaction temperature is 35 ℃ and the residence time is 10min. After the reaction is finished, roughly separating a lower oil phase (with the concentration of 15%, the feeding mass of 396.385 kg) and the intermediate aqueous solution (with the concentration of 10.8%, the feeding mass of 3.35 kg) produced in the step b), respectively entering a plurality of parallel kettle reactors with stirring, wherein the adding amount of catalyst calcium chloride is 1.04g, raising the temperature to 145 ℃ under nitrogen atmosphere, reacting for 3 hours, adding phenol (with the feeding mass of 0.26 kg), continuing to react for 1.4 hours, and ending the reaction, wherein the reaction pressure is 8atm; and then preparing the flame-retardant polycarbonate through a later devolatilization operation.

Example 2

Mixing and dissolving the triphenol of formula a, bisphenol a, sodium hydroxide and water to form a sodium phenolate aqueous solution, namely an aqueous phase, wherein the total phenolate concentration is 15wt%, and the specific triphenol component accounts for 3% of the total phenolate concentration, and the pH=11.5; phosgene was dissolved in carbon tetrachloride to form an oil phase, wherein the phosgene concentration was 7%. The aqueous phase, phosgene and carbon tetrachloride were fed into a photochemical reactor comprising a series of static mixers at a flow rate of 600kg/h, 41.0kg/h and 586kg/h, respectively, with an internal diameter of 54mm, a length of 650mm and a reaction residence time of about 10min, and the reaction outlet temperature was controlled at 34 ℃. Immediately after the photochemical reaction is finished, the mixture enters a stirred tank reactor with two tanks connected in series, and 5wt% of capping agent p-tert-butylphenol/carbon tetrachloride solution, 30wt% of sodium hydroxide solution and 1.5wt% of catalyst triethylamine/carbon tetrachloride solution and carbon tetrachloride are respectively added into a first reaction tank at the flow rates of 42.0kg/h, 17.0kg/h, 9.5kg/h and 231kg/h, the effective volumes of the reaction tanks are respectively 100L and 600L, the reaction residence time is 12min, and the reaction temperature is 35 ℃. After the reaction is finished, roughly separating a lower oil phase (the feeding mass is 380.96kg, the concentration is 15%) and an intermediate I aqueous solution (the feeding amount is 17.67kg, the concentration is 10.8%) produced in the step b), respectively entering a plurality of parallel kettle reactors with stirring, wherein the adding amount of catalyst calcium chloride is 4.8g, raising the temperature to 150 ℃ under nitrogen atmosphere, reacting for 3.5h, adding phenol (the feeding amount is 1.37 kg), continuing to react for 2h, and finishing the reaction, wherein the reaction pressure is 10atm; and then preparing the flame-retardant polycarbonate through a later devolatilization operation.

Example 3

Mixing and dissolving the triphenol of formula a, bisphenol a, sodium hydroxide and water to form a sodium phenolate aqueous solution, namely an aqueous phase, wherein the total phenolate concentration is 12wt%, and the specific triphenol component accounts for 5% of the total phenolate mass, and the pH=11.8; phosgene was dissolved in carbon tetrachloride to form an oil phase, wherein the phosgene concentration was 7%. The aqueous phase, phosgene and carbon tetrachloride were fed into a photochemical reactor comprising a series of static mixers at a flow rate of 600kg/h, 32.1kg/h and 459kg/h, respectively, with an internal diameter of 54mm, a length of 650mm and a reaction residence time of about 20min, and the reaction outlet temperature was controlled at 34 ℃. Immediately after the photochemical reaction, the mixture enters a stirred tank reactor with two tanks connected in series, and 5wt% of capping agent p-tert-butylphenol/carbon tetrachloride solution, 30wt% of sodium hydroxide solution and 1.5wt% of catalyst triethylamine/carbon tetrachloride solution and carbon tetrachloride are respectively added into a first reaction tank at the flow rates of 42.0kg/h, 17.0kg/h, 9.5kg/h and 185.1kg/h, the effective volumes of the reaction tanks are respectively 100L and 600L, the reaction time is 15min, and the reaction temperature is 35 ℃. Coarsely separating a lower oil phase (with the concentration of 15 percent and the feeding mass of 369.02 kg) after the reaction is finished, respectively feeding the lower oil phase and the intermediate aqueous solution (with the concentration of 10.8 percent and the feeding mass of 28.75 kg) produced in the step b) into a plurality of parallel kettle reactors with stirring, adding 8.73g of catalyst calcium chloride, raising the temperature to 155 ℃ under the nitrogen atmosphere, reacting for 4 hours, adding 2.23kg of phenol, continuing to react for 1.5 hours, and finishing the reaction, wherein the reaction pressure is 15atm; and then preparing the flame-retardant polycarbonate through a later devolatilization operation.

Example 4

Mixing and dissolving the triphenol of formula c, bisphenol a, sodium hydroxide and water to form a sodium phenolate aqueous solution, namely an aqueous phase, wherein the total concentration of phenolate is 12wt%, and the specific triphenol component accounts for 1.2% of the total amount of phenolate, and the pH=11.8; phosgene was dissolved in carbon tetrachloride to form an oil phase, wherein the phosgene concentration was 7%. The aqueous phase, phosgene and carbon tetrachloride were fed into a photochemical reactor comprising a series of static mixers at a flow rate of 600kg/h, 33.5kg/h and 477kg/h, respectively, with an internal diameter of 54mm, a length of 650mm and a reaction residence time of about 7min, and the reaction outlet temperature was controlled at 34 ℃. Immediately after the photochemical reaction, the mixture enters a stirred tank reactor with two tanks connected in series, and 5wt% of a capping agent p-tert-butylphenol/carbon tetrachloride solution, 30wt% of a sodium hydroxide solution and 1.5wt% of a catalyst triethylamine/carbon tetrachloride solution and carbon tetrachloride are respectively added into a first reaction tank at the flow rates of 42.0kg/h, 17.0kg/h, 9.5kg/h and 177.1kg/h, the effective volumes of the reaction tanks are respectively 100L and 600L, and the reaction temperature is 35 ℃ and the residence time is 16min. After the reaction is finished, roughly separating a lower oil phase (the feeding mass is 392.54kg, the concentration is 15%) and the intermediate I aqueous solution produced in the step b) (the feeding mass is 6.93kg, the concentration is 10.8%) respectively enter a plurality of parallel kettle reactors with stirring, the adding amount of catalyst calcium chloride is 2.72g, the temperature is increased to 170 ℃ under the nitrogen atmosphere, phenol with the mass of 0.54kg is added after the reaction is carried out for 4 hours, the reaction is finished after the continuous reaction is carried out for 1.5 hours, and the reaction pressure is 15atm; and then preparing the flame-retardant polycarbonate through a later devolatilization operation.

Example 5

Mixing and dissolving the triphenol of formula b, bisphenol a, sodium hydroxide and water to form a sodium phenolate aqueous solution, namely an aqueous phase, wherein the total phenolate concentration is 15wt%, and the specific triphenol component accounts for 3.5% of the total phenolate concentration, and the pH=11.8; phosgene was dissolved in carbon tetrachloride to form an oil phase, wherein the phosgene concentration was 7%. The aqueous phase, phosgene and carbon tetrachloride were fed into a photochemical reactor comprising a series of static mixers at a flow rate of 600kg/h, 42.2kg/h and 603kg/h, respectively, with an internal diameter of 54mm, a length of 650mm, a reaction residence time of about 13min, and a reaction outlet temperature of 34 ℃. Immediately after the photochemical reaction is finished, the mixture enters a stirred tank reactor with two tanks connected in series, and 5wt% of capping agent p-tert-butylphenol/carbon tetrachloride solution, 30wt% of sodium hydroxide solution and 1.5wt% of catalyst triethylamine/carbon tetrachloride solution and carbon tetrachloride are respectively added into a first reaction tank at the flow rates of 42.0kg/h, 17.0kg/h, 9.5kg/h and 229.1kg/h, the effective volumes of the reaction tanks are respectively 100L and 600L, the reaction time is 12min, and the reaction temperature is 35 ℃. After the reaction is finished, roughly separating a lower oil phase (the feeding mass is 378.09kg, the concentration is 15%) and the intermediate aqueous solution produced in the step b) (the feeding mass is 20.33kg, the concentration is 10.8%) respectively enter a plurality of parallel kettle reactors with stirring, the adding amount of catalyst calcium chloride is 4.87g, the temperature is increased to 140 ℃ under the nitrogen atmosphere for 3.5 hours, phenol with the mass of 1.58kg is added, the reaction is continued for 1.5 hours, and the reaction pressure is 7atm; and then preparing the flame-retardant polycarbonate through a later devolatilization operation.

Example 6

Mixing and dissolving the triphenol of formula a, bisphenol a, sodium hydroxide and water to form a sodium phenolate aqueous solution, namely an aqueous phase, wherein the total concentration of phenolate is 13wt%, and the specific triphenol component accounts for 0.1% of the total amount of phenolate, and the pH=11.8; phosgene was dissolved in carbon tetrachloride to form an oil phase, wherein the phosgene concentration was 7%. The aqueous phase, phosgene and carbon tetrachloride were fed into a photochemical reactor consisting of a series of static mixers at a flow rate of 600kg/h, 38.9kg/h and 555.8kg/h, respectively, with an internal diameter of 54mm, a length of 650mm and a reaction residence time of about 5min, and the reaction outlet temperature was controlled at 34 ℃. Immediately after the photochemical reaction, the mixture enters a stirred tank reactor with two tanks connected in series, and 5wt% of a capping agent p-tert-butylphenol/carbon tetrachloride solution, 30wt% of a sodium hydroxide solution and 1.5wt% of a catalyst triethylamine/carbon tetrachloride solution and carbon tetrachloride are respectively added into a first reaction tank at the flow rates of 42.0kg/h, 17.0kg/h, 9.5kg/h and 174.3kg/h, the effective volumes of the reaction tanks are respectively 100L and 600L, and the reaction temperature is 35 ℃ and the residence time is 10min. After the reaction is finished, roughly separating a lower oil phase (the feeding mass is 399.16kg, the concentration is 15%) and the intermediate aqueous solution produced in the step b) (the feeding mass is 0.78kg, the concentration is 10.8%) respectively into a plurality of parallel kettle reactors with stirring, adding a catalyst, namely 0.25g of calcium chloride, raising the temperature to 130 ℃ under nitrogen atmosphere, reacting for 3 hours, adding phenol with the mass of 0.06kg, continuing to react for 1 hour, and ending the reaction, wherein the reaction pressure is 5atm; and then preparing the flame-retardant polycarbonate through a later devolatilization operation.

Comparative example 1

PC with mi=10 and 5% phosphorus flame retardant BDP were co-extruded and pelletized in an extruder, and then physical properties were tested.

Comparative example 2

PC with mi=20 and 0.2% sulfonate flame retardant PFBS were co-extruded in an extruder to pellet, and then subjected to physical property test.

Comparative example 3

PC with mi=10 and 3% phosphorus flame retardant BDP were co-extruded and pelletized in an extruder, and then physical properties were tested.

Comparative example 4

The specific triphenols were increased from 3.5% to 5.5% compared to example 5, the other feed ratios remaining unchanged, as follows:

mixing and dissolving the triphenols of formula b, bisphenol a, sodium hydroxide and water to form a sodium phenolate aqueous solution, namely an aqueous phase, wherein the total concentration of phenolates is 15wt%, the specific triphenolic component accounts for 5.5% of the total amount of phenolates, and the ph=11.8 dissolves phosgene in carbon tetrachloride to form an oil phase, wherein the phosgene concentration is 7%. The aqueous phase, phosgene and carbon tetrachloride are respectively introduced into an photochemical reactor consisting of a group of static mixers at the flow rates of 600kg/h, 41kg/h and 586kg/h, the internal diameter of the reactor is 54mm, the length is 650mm, the reaction residence time is about 13min, and the reaction outlet temperature is controlled to be 34 ℃. Immediately after the photochemical reaction, the mixture enters a stirred tank reactor with two tanks connected in series, and 5wt% of capping agent p-tert-butylphenol/carbon tetrachloride solution, 30wt% of sodium hydroxide solution and 1.5wt% of catalyst triethylamine/carbon tetrachloride solution and carbon tetrachloride are respectively added into a first reaction tank at the flow rates of 42.0kg/h, 17.0kg/h, 9.5kg/h and 238.1kg/h, the effective volumes of the reaction tanks are respectively 100L and 600L, the reaction time is 12min, and the reaction temperature is 35 ℃. After the reaction is finished, roughly separating a lower oil phase (with the concentration of 15 percent and the feeding mass of 366.62 kg) and the intermediate aqueous solution produced in the step b) (with the concentration of 10.8 percent and the mass of 30.98 kg) respectively into a plurality of parallel kettle reactors with stirring, adding a catalyst with the calcium chloride content of 116.7g, raising the temperature to 140 ℃ under nitrogen atmosphere, reacting for 3.5 hours, adding 2.4kg of phenol, continuing to react for 1.5 hours, and ending the reaction, wherein the reaction pressure is 7atm; and then preparing the flame-retardant polycarbonate through a later devolatilization operation.

Comparative example 5

Compared with example 2, the flame-retardant polycarbonate was prepared without adding only the triphenols under exactly the same conditions.

The data of the physical property test of the polycarbonate bars of the examples and comparative examples are compared as follows:

name of the name	Impact Property	Flame retardant Properties	Melt index	Transmittance of light
					Example 1	800	3.0V2	9	88
Implementation of the embodimentsExample 2	600	1.2V0	20	87
					Example 3	510	0.8V0	45	88
Example 4	750	2.0V1	15	89
					Example 5	570	1.0V1	27	87
Example 6	820	3.0V2	7	88
					Comparative example 1	200	1.2V0	18	88
Comparative example 2	750	3.0V1	20	87
					Comparative example 3	450	1.5V1	15	87
Comparative example 4	310	0.8V0	62	85
					Comparative example 5	830	3.0HB	6.5	89

While the present invention has been described in detail through the foregoing description of the preferred embodiment, it should be understood that the foregoing description is not to be considered as limiting the invention. Those skilled in the art will appreciate that certain modifications and adaptations of the invention are possible and can be made under the teaching of the present specification. Such modifications and adaptations are intended to be within the scope of the present invention as defined in the appended claims.

Claims (24)

1. A method for preparing transparent flame-retardant polycarbonate, which is characterized by comprising the following steps:

a) Carrying out photochemical reaction on a phenolate water phase formed by dissolving bisphenol A and triphenol in alkali liquor and an oil phase formed by dissolving phosgene in carbon tetrachloride to prepare a polycarbonate oligomer with hindered phenolic hydroxyl active groups, and then adding a catalyst and a capping reagent to react to obtain a high molecular weight linear polycarbonate solution;

b) Reacting phosphorus oxychloride and bisphenol A under the action of a catalyst at a certain temperature to generate an intermediate of the formula I, wherein n=1 and 2 until no hydrogen chloride is generated, and refluxing excessive phosphorus oxychloride to obtain a purified intermediate of the formula I;

i

c) Putting the intermediate of the formula I in the step b) into a reaction kettle containing the high molecular weight linear polycarbonate solution in the step a), performing interfacial polymerization under the actions of inert atmosphere, high temperature and high pressure conditions and a catalyst, adding a blocking agent after a certain time, stopping the reaction after no hydrogen chloride is generated, and cooling, depressurizing and removing the solvent to obtain transparent flame-retardant polycarbonate;

the structural general formula of the triphenol in the step a) is shown as a formula II:

II (II)

Wherein R is ₁ 、R ₂ Each independently selected from one or a combination of methyl, hydrocarbon group with 2-18 carbon atoms, benzene ring and naphthalene ring; r is R ₃ Selected from methyl groups or hydrocarbon groups having 2 to 18 carbon atoms.

2. The process according to claim 1, wherein R ₁ 、R ₂ Each independently selected from methyl or ethyl; r is R ₃ Is methyl.

3. The preparation method according to claim 1, wherein the mass concentration of the phenoxide in the phenoxide aqueous phase of step a) is 10-15%, and the content of the triphenols in the total mass of the phenoxide is 0.1-5%.

4. A process according to claim 3, wherein the lye is an aqueous solution of an alkali metal hydroxide.

5. The method according to claim 4, wherein the alkaline solution is an aqueous sodium hydroxide solution.

6. A process according to claim 3, wherein the pH of the phenolate aqueous phase is controlled to be 11-11.8.

7. The method according to any one of claims 1 to 6, wherein the residence time of the reaction in step a) is 5 to 50min.

8. The process according to claim 7, wherein the residence time of the reaction in step a) is from 5 to 40min.

9. The process according to claim 8, wherein the residence time of the reaction in step a) is from 5 to 25min.

10. The process according to claim 7, wherein the total molar amount of phosgene in step a) is from 1.00 to 1.16 times the sum of the molar amounts of triphenols and bisphenol-A.

11. The process according to claim 10, wherein the total molar amount of phosgene in step a) is 1.02-1.10 times the sum of the molar amounts of triphenols and bisphenol-A.

12. The process according to claim 1 or 2, wherein the molar ratio of bisphenol a to phosphorus oxychloride in step b) is 1:2.5, the catalyst is selected from any one or a combination of calcium chloride and magnesium chloride, and the addition amount of the catalyst is 0.1-0.4% of the mass of bisphenol A.

13. The preparation method according to claim 12, wherein the catalyst is calcium chloride, and the catalyst is added in an amount of 0.15-0.3% by mass of bisphenol a.

14. The method of claim 12, wherein the reaction temperature in step b) is 100-120 ℃; the reaction residence time is 3.5-6h.

15. The preparation method according to claim 1 or 2, wherein the inert atmosphere in the step c) is a nitrogen atmosphere, and the reaction temperature in the reaction kettle is 130-170 ℃; the reaction residence time is 4-6h; the reaction pressure is 5-15atm.

16. The method of claim 15, wherein the reaction temperature in the reaction vessel is 145-155 ℃; the reaction residence time is 4.5-5.5h; the reaction pressure is 7-12atm.

17. The method of claim 16, wherein the reaction pressure is 8-10atm.

18. The preparation method according to claim 15, wherein the catalyst in the step c) is selected from any one of calcium chloride and magnesium chloride or a combination thereof, and the addition amount of the catalyst is 0.3-0.6% of the mass of the triphenol monomer in the step a); the end-capping agent is selected from p-tert-butylphenol or phenol.

19. The preparation method according to claim 18, wherein the catalyst in the step c) is calcium chloride, and the catalyst is added in an amount of 0.4 to 0.55% by mass of the triphenol monomer in the step a); the end capping agent is phenol.

20. The process according to claim 18, wherein the intermediate of formula i and the capping agent are added in step c) in a ratio of 1.01 to 1.3 based on moles of the triphenols in the phenoxide of step a): 1:4.04-5.20.

21. A transparent flame retardant polycarbonate prepared by the preparation method of any one of claims 1 to 20.

22. The transparent flame retardant polycarbonate of claim 21, wherein the polycarbonate achieves a flame retardant rating of 0.8-3.0mm V0/V1/V2, a melt index of 7-60g/10min, a light transmittance of 87% or more, and an impact performance of 500-900J/m.

23. Use of a polycarbonate prepared by the method of any one of claims 1 to 20 or a polycarbonate of any one of claims 21 to 22 in a transparent window.

24. The use according to claim 23, in transparent windows in the electrical and electronic field.