A method for preparing a controllable pbo polymer

Abstract

This invention belongs to the field of high-performance materials and discloses a method for preparing a controllable PBO polymer. The steps are as follows: phosphorus pentoxide is dissolved in polyphosphoric acid to obtain high-concentration polyphosphoric acid; in reactor A, DAR and small-particle-size TPA are subjected to initial prepolymerization in the high-concentration polyphosphoric acid; the above materials are transported to reactor B, and large-particle-size TPA is added for secondary prepolymerization; final polymerization is carried out in a twin-screw extruder, and by adding an appropriate amount of DAR, a PBO polymer with controllable degree of polymerization is obtained; the PBO polymer is precipitated in water and dried to obtain the PBO polymer. This method first adds phosphorus pentoxide to polyphosphoric acid to prepare high-concentration polyphosphoric acid, avoiding the problems of poor powder dispersion, exothermic dissolution, and excessively high temperature that occur when adding phosphorus pentoxide during the polymerization reaction. Furthermore, by adding DAR monomer in the extruder to control the degree of polymerization of PBO macromolecules, the degree of polymerization is controllable, which has high practical value.

Description

Technical Field

[0001] This invention belongs to the field of high-performance materials and discloses a method for preparing a controllable PBO polymer. Background Technology

[0002] Poly(p-phenylenebenzodioxazole) (PBO) fiber is one of the best-performing high-performance organic fibers currently available for industrial production. Its strength can reach 5.8 GPa, its modulus can reach 280 GPa, and its thermal decomposition temperature exceeds 650℃. It has excellent impact resistance, heat resistance, and chemical corrosion resistance, and has broad application prospects in both military and civilian fields.

[0003] The monomers for synthesizing PBO fibers are terephthalic acid (TPA) and 4,6-diaminoresorcinol hydrochloride (DAR), with polyphosphoric acid as the solvent and phosphorus pentoxide as a dehydrating agent. Currently, the preparation of PBO fibers is limited by polymer synthesis, making it difficult to effectively control the molecular weight of the PBO polymer. This results in significant differences in fiber properties within and between batches, hindering the improvement of product stability.

[0004] The synthesis of traditional PBO polymers involves two steps: The first step is prepolymerization in a reactor, which requires the addition of a large amount of powder. Phosphorus pentoxide powder is poorly dispersed during prepolymerization and stirring, and is prone to agglomeration. TPA monomer particles are usually processed to below 5 micrometers. They have good solubility in the early stages of the prepolymerization reaction, but the temperature is high in the later stages of prepolymerization. Small-particle-size TPA reacts too quickly, which can lead to local overheating and further accelerate the reaction, resulting in an excessively wide molecular weight distribution. The second step is to further polymerize the PBO prepolymer in a twin-screw extruder. The residence time of the PBO polymer in the twin-screw extruder is the polymerization time of the PBO polymer. However, the residence time of the PBO polymer in the extruder often fluctuates due to changes in the flow rate, resulting in inconsistent degrees of polymerization.

[0005] CN107761185A discloses a process control method for the production of PBO fibers. Using polyphosphoric acid, phosphorus pentoxide, 4,6-diaminoresorcinol hydrochloride, and terephthalic acid as raw materials, PBO fibers are produced through degassing, prepolymerization, postpolymerization, and spinning. Terephthalic acid is added in the three stages of raw material mixing, prepolymerization, and postpolymerization. The problem with this method is that although terephthalic acid is added in the three stages, small-particle-size TPA is used in all of them. At higher reaction temperatures in the later stages of polymerization, this can lead to excessively rapid reactions and uneven local polymerization, resulting in an excessively wide molecular weight distribution.

[0006] CN1513899A discloses a method for preparing poly(p-phenylenebenzodioxazole) and the stirrer used therein, comprising adding 4,6-diaminoresorcinol hydrochloride, polyphosphoric acid, and terephthalic acid with a particle size of less than 10 micrometers to a cylindrical reactor equipped with a stirrer; maintaining the mixture at 50-65°C for about 2 hours; then reacting at 110-120°C under an inert gas pressure of 0.2-1.0 MPa for 5-7 hours; then removing the pressure, raising the temperature to 140-150°C, and evacuating to a vacuum of 20-100 Pa for 6-7 hours; and finally reacting at 180-190°C under normal pressure for 12-15 hours. The problem with this method is that the polymerization reaction is carried out entirely in the reactor, resulting in a long reaction time, low efficiency, and unsuitability for continuous production. Furthermore, the stirring paddle has poor stirring effect on high-viscosity materials, especially in the later stages of polymerization when the viscosity is very high, making it difficult for the paddle to effectively disperse and renew the interface, easily leading to uneven polymerization degree and a wide molecular weight distribution.

[0007] In summary, existing technologies have various technical problems in both PBO prepolymerization and polymerization, which seriously affect the consistency of polymerization. Therefore, it is necessary to design new synthesis methods to solve these problems. Summary of the Invention

[0008] This invention addresses the shortcomings of existing technologies by providing a method for preparing a controllable PBO polymer, comprising the following steps: (1) dissolving phosphorus pentoxide in polyphosphoric acid to obtain high-concentration polyphosphoric acid; (2) performing initial prepolymerization of DAR and small-particle-size TPA in the high-concentration polyphosphoric acid in reactor A; (3) transferring the above materials to reactor B and adding large-particle-size TPA for secondary prepolymerization; (4) performing final polymerization in a twin-screw extruder, and obtaining a PBO polymer with controllable degree of polymerization by automatically adding an appropriate amount of DAR; (5) precipitating the PBO polymer in water and drying it to obtain the PBO polymer. This invention first adds phosphorus pentoxide to polyphosphoric acid to prepare a high-concentration PBO polymer. Polyphosphoric acid avoids the problem of poor powder dispersion caused by adding phosphorus pentoxide during the polymerization reaction. Furthermore, this method can release the heat of solution beforehand, avoiding the exothermic reaction and excessively high temperature problems caused by adding phosphorus pentoxide during polymerization. Secondly, this invention uses two different particle sizes of TPA for prepolymerization. The initial prepolymerization uses small-particle-size TPA, which has strong solubility in polyphosphoric acid and good reaction uniformity. The secondary prepolymerization uses large-particle-size TPA, which has a slower reaction rate, avoiding the problems of explosive polymerization and wide molecular weight distribution caused by excessively high temperature. This patent can continuously prepare PBO polymer powder with controllable degree of polymerization by automatically adding an appropriate amount of DAR for end-capping. After subsequent dissolution and slurry preparation, this powder can be further processed and shaped, demonstrating high practical value.

[0009] The main principle of this invention is as follows: the existing technologies in the background all use small-particle-size TPA, while in the PBO preparation process of this application, a two-stage prepolymerization method is adopted. The first prepolymerization adds small-particle-size TPA, which has strong solubility in polyphosphoric acid and good reaction uniformity. The second prepolymerization uses large-particle-size TPA, which has a slow reaction rate and avoids the problems of explosive polymerization and wide molecular weight distribution caused by excessively high temperature.

[0010] Guided by the above concept, the specific technical solution of the present invention is as follows: A method for preparing a controllable PBO polymer includes the following steps: (1) Add polyphosphoric acid to a nitrogen-filled reactor, heat to 80-100℃, add phosphorus pentoxide, stir for 1-2 hours, heat to 100-120℃, stir for 3-5 hours, and cool to 50-60℃ to obtain high-concentration polyphosphoric acid.

[0011] (2) High-concentration polyphosphoric acid is transported to reactor A, the temperature is controlled at 50-60℃, antioxidant is added, and the mixture is stirred for 10-20 min. 4,6-diaminoresorcinol hydrochloride is added and stirred for 5-10 min. Small-particle-size TPA is added and stirred for 10-20 min. The temperature is raised to 80℃ and stirred for 3-5 h. The temperature is raised to 100℃ and stirred for 4-6 h.

[0012] (3) The above materials are transported to reactor B, large-particle-size TPA is added, and the mixture is stirred for 20-30 min; the temperature is raised to 120℃ and stirred for 3-5 h; the temperature is raised to 140℃ and stirred for 2-4 h; the temperature is raised to 150℃ and stirred for 5-6 h to obtain PBO prepolymer. The above two steps, through stepwise stirring and heating, can achieve a steady and controllable prepolymerization in a stepwise manner.

[0013] (4) The above PBO prepolymer is transported to a twin-screw extruder. The molecular weight is further increased by the high-temperature shearing action of the extruder. The twin-screw extruder is an upper and lower stage extruder. A small amount of DAR monomer is continuously added to the feed port of the upper stage extruder to end-cap the PBO polymer in the extruder, and the molecular weight is precisely controlled to obtain a PBO polymer with controllable degree of polymerization.

[0014] (5) Dilute the above PBO polymer with polyphosphoric acid and add it to water under high-speed stirring. The PBO polymer precipitates out and is filtered and dried to obtain the PBO polymer.

[0015] Preferably, in step (1), the amount of phosphorus pentoxide added is 22%-26% of the mass of polyphosphoric acid.

[0016] In step (2), the antioxidant is stannous chloride; the amount of stannous chloride added is 0.1%-0.2% of the mass of polyphosphoric acid, the amount of 4,6-diaminoresorcinol hydrochloride added is 16%-19% of the mass of polyphosphoric acid, the D90 particle size range of small-particle terephthalic acid is 2-4μm, and its added amount is 60%-80% of the molar amount of 4,6-diaminoresorcinol hydrochloride; the above-mentioned small-particle terephthalic acid dissolves quickly in polyphosphoric acid in the early stage of the reaction, has good reaction uniformity, and can quickly generate oligomers with good uniformity.

[0017] In step (3), the D90 particle size range of the large-particle-size terephthalic acid is 10-12 μm, and its addition amount is 20%-40% of the molar amount of 4,6-diaminoresorcinol hydrochloride. The reaction rate of the above-mentioned large-particle-size terephthalic acid is relatively slow, which can achieve stable polymerization and synthesize a narrow molecular weight, which is beneficial to subsequent spinning.

[0018] In step (4), the twin-screw extruder is a two-stage extruder with an upper and lower stage. The upper stage temperature range is 150℃-180℃, and the lower stage temperature range is 190-210℃. The rotation speed is 10rpm-20rpm, and the residence time of the PBO material in the extruder is 1-2 hours. An online viscometer is installed at the die head of the twin-screw extruder. By dynamically adding trace amounts of 4,6-diaminoresorcinol hydrochloride monomer at the feed inlet of the upper stage of the twin-screw extruder, when 4,6-diaminoresorcinol hydrochloride... When the amount of salt monomer exceeds that of terephthalic acid monomer, the excess 4,6-diaminoresorcinol hydrochloride monomer can act as an end-capping agent. By end-capping the PBO polymer with excess monomer, the viscosity of the online viscometer can be controlled, maintaining it between 10,000 P and 15,000 P, thus achieving dynamic control of the polymer viscosity. The corresponding mass of 4,6-diaminoresorcinol hydrochloride monomer added is 0.1-0.4 wt% of the twin-screw extruder outlet flow rate, dynamically adjusted according to the target viscosity value. Furthermore, the twin-screw extruder used in this application can complete the reaction in just 1-2 hours, offering high efficiency suitable for continuous production. The twin-screw extruder also possesses extremely strong shearing and kneading capabilities, far exceeding those of the agitator in CN1513899A, thus being highly beneficial for the dispersion and interfacial renewal of high-viscosity materials, resulting in excellent polymer uniformity.

[0019] In step (5), after the PBO polymer is diluted, the solid content of the PBO polymer in the solution is 3%-5%, the stirring speed during the stirring and precipitation process is 1000rpm-2000rpm, the drying temperature is 120-150℃, and the drying time is 3-5h.

[0020] The PBO polymer obtained through the above method achieves controllable molecular weight and a narrow molecular weight distribution. A two-step prepolymerization method, with the phased addition of small- and large-particle TPA, achieves stable prepolymerization and effectively reduces the molecular weight distribution. During the twin-screw extruder polymerization stage, the degree of PBO macromolecular polymerization within the extruder is dynamically supplemented by DAR monomer, thus controlling the molecular weight. The controllable PBO polymer prepared by this invention has a narrow molecular weight distribution, resulting in better uniformity of the condensed structure of the spun fiber, fewer weak bonds, and ultimately, superior mechanical properties compared to conventional techniques. Furthermore, the PBO polymer prepared by this invention can be adjusted according to the target fiber properties; for example, the molecular weight can be increased to achieve high performance, while it can be decreased to achieve high spinnability and low hairiness, achieving adjustable and controllable molecular weight with good repeatability.

[0021] Compared with existing technologies, the technical solution provided by this invention dissolves phosphorus pentoxide in polyphosphoric acid first, and uses the high-concentration polyphosphoric acid after dissolving phosphorus pentoxide as a solvent. This avoids the need to add phosphorus pentoxide in subsequent reactions, where phosphorus pentoxide needs to be added simultaneously with DAR and TPA, and excessive powder can easily cause agglomeration. This invention uses a two-stage prepolymerization method. The first prepolymerization adds small-particle-size TPA, which has strong solubility in polyphosphoric acid and good reaction uniformity. The second prepolymerization uses large-particle-size TPA, which has a slow reaction rate and avoids problems such as explosive polymerization and wide molecular weight distribution caused by excessive temperature. In the final polymerization of this invention, a trace amount of DAR monomer is added at the feed inlet of a twin-screw extruder, and the viscosity of the extruder head is dynamically controlled to achieve stable polymerization of PBO polymer by controlling the viscosity. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation method of this application. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, which will enable those skilled in the art to have a more comprehensive understanding of the invention, but will not limit the invention in any way. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] Example 1 A method for preparing a controllable PBO polymer, comprising the following steps: (1) In a nitrogen-filled reactor, add 10 kg of polyphosphoric acid, heat to 80-100℃, add 2.2 kg of phosphorus pentoxide, stir for 1 h, heat to 100℃, stir for 3 h, and cool to 50℃ to obtain high-concentration polyphosphoric acid. (2) High-concentration polyphosphoric acid is transported to reactor A, the temperature is controlled at 50℃, 0.01 kg of antioxidant stannous chloride is added, and the mixture is stirred for 10 min. 1.6 kg of 4,6-diaminoresorcinol hydrochloride (DAR) is added, and the mixture is stirred for 5 min. 0.74 kg of TPA with a particle size of 2 μm is added, and the mixture is stirred for 10 min. The temperature is raised to 80℃ and stirred for 3 h. The temperature is raised to 100℃ and stirred for 4 h. (3) The above PBO material is transported to reactor B, 0.50 kg of TPA with a particle size of 10 μm is added, stirred for 20 min, heated to 120 °C, stirred for 3 h, heated to 140 °C, stirred for 2 h, heated to 150 °C, stirred for 5 h, and PBO prepolymer is obtained. (4) The PBO prepolymer is fed to the upper and lower twin-screw extruders, where the temperature of the upper extruder is 150℃ and the temperature of the lower extruder is 210℃, the speed is 10rpm, and the residence time of the PBO material in the extruder is 1h. An online viscometer is installed at the die head of the twin-screw extruder. A small amount of DAR monomer is continuously added to the feed port of the upper extruder. The amount of DAR added is dynamically adjusted according to the fluctuation of the value of the viscometer at the die head. The mass of the added DAR monomer is 0.100-0.106wt% of the outlet flow rate of the twin-screw extruder. The viscosity value of the online viscometer is controlled to be maintained at around 10000P, so as to achieve dynamic control of the polymer viscosity and obtain a PBO polymer with controllable viscosity.

[0025] (5) The above PBO polymer was diluted with polyphosphoric acid to a solid content of 3%, and added to water with a stirring speed of 1000 rpm. The PBO polymer precipitated. The precipitate was dried at 120°C for 3 hours to obtain the PBO polymer. The intrinsic viscosity of this PBO polymer was 20±1 dL / g and the molecular weight was 2.32±0.06 million.

[0026] Example 2 A method for preparing a controllable PBO polymer, comprising the following steps: (1) In a nitrogen-purified reactor, add 10 kg of polyphosphoric acid, heat to 100°C, add 2.6 kg of phosphorus pentoxide, stir for 2 h, heat to 120°C, stir for 5 h, and cool to 60°C to obtain high-concentration polyphosphoric acid. (2) High-concentration polyphosphoric acid is transported to reactor A, the temperature is controlled at 60℃, 0.02 kg of antioxidant stannous chloride is added, and the mixture is stirred for 20 min. 1.90 kg of 4,6-diaminoresorcinol hydrochloride (DAR) is added, and the mixture is stirred for 10 min. 1.18 kg of TPA with a particle size of 4 μm is added, and the mixture is stirred for 20 min. The temperature is raised to 80℃ and stirred for 5 h. The temperature is raised to 100℃ and stirred for 6 h. (3) The above PBO material is transported to reactor B, 0.29 kg of TPA with a particle size of 12 μm is added, stirred for 30 min, heated to 120 °C, stirred for 5 h, heated to 140 °C, stirred for 4 h, heated to 150 °C, stirred for 6 h, and PBO prepolymer is obtained. (4) The PBO prepolymer is fed to the upper and lower twin-screw extruders. The temperature of the upper extruder is 180℃ and the temperature of the lower extruder is 190℃. The speed is 20rpm and the residence time of the PBO material in the extruder is 2h. An online viscometer is installed at the die head of the twin-screw extruder. A small amount of DAR monomer is continuously added to the feed port of the upper extruder. The amount of DAR added is dynamically adjusted according to the fluctuation of the value of the viscometer at the die head. The mass of the added DAR monomer is 0.400-0.406wt% of the outlet flow rate of the twin-screw extruder. The viscosity value of the online viscometer is controlled to be maintained at about 15000P, so as to achieve dynamic control of the polymer viscosity and obtain a PBO polymer with controllable viscosity.

[0027] (5) The above PBO polymer was diluted with polyphosphoric acid to a solid content of 5%, and added to water with a stirring speed of 2000 rpm. The PBO polymer precipitated. The precipitate was dried at 150°C for 5 hours to obtain the PBO polymer. The intrinsic viscosity of this PBO polymer was 30±1 dL / g and the molecular weight was 2.91±0.05 million.

[0028] Example 3 A method for preparing a controllable PBO polymer, comprising the following steps: (1) In a nitrogen-filled reactor, add 10 kg of polyphosphoric acid, heat to 90°C, add 2.5 kg of phosphorus pentoxide, stir for 1.5 h, heat to 110°C, stir for 4 h, and cool to 55°C to obtain high-concentration polyphosphoric acid. (2) High-concentration polyphosphoric acid is transported to reactor A, the temperature is controlled at 55℃, 0.015 kg of antioxidant stannous chloride is added, and the mixture is stirred for 15 min. 1.70 kg of 4,6-diaminoresorcinol hydrochloride (DAR) is added, and the mixture is stirred for 8 min. 0.92 kg of TPA with a particle size of 3 μm is added, and the mixture is stirred for 15 min. The temperature is raised to 80℃ and stirred for 4 h. The temperature is raised to 100℃ and stirred for 5 h. (3) The above PBO material is transported to reactor B, 0.40 kg of TPA with a particle size of 11 μm is added, stirred for 25 min, heated to 120°C, stirred for 4 h, heated to 140°C, stirred for 3 h, heated to 150°C, stirred for 5.5 h, and PBO prepolymer is obtained. (4) The PBO prepolymer is fed to the upper and lower twin-screw extruders. The temperature of the upper extruder is 160℃ and the temperature of the lower extruder is 205℃. The speed is 17rpm and the residence time of the PBO material in the extruder is 1.6h. An online viscometer is installed at the die head of the twin-screw extruder. A small amount of DAR monomer is continuously added to the feed port of the upper extruder. The amount of DAR added is dynamically adjusted according to the fluctuation of the value of the viscometer at the die head. The mass of the added DAR monomer is 0.300-0.306wt% of the outlet flow rate of the twin-screw extruder. The viscosity value of the online viscometer is controlled to be maintained at about 13000P, so as to achieve dynamic control of the polymer viscosity and obtain a PBO polymer with controllable viscosity.

[0029] (5) The above PBO polymer was diluted with polyphosphoric acid to a solid content of 4%, and added to water with a stirring speed of 1500 rpm. The PBO polymer precipitated. The precipitate was dried at 130°C for 4 hours to obtain the PBO polymer. The intrinsic viscosity of this PBO polymer was 26±0.8 dL / g and the molecular weight was 2.68±0.04 million.

[0030] Comparative Example 1: The preparation steps of conventional PBO polymer are as follows: (1) Add 10 kg of polyphosphoric acid and 0.015 kg of antioxidant stannous chloride to a nitrogen-purified reactor, stir for 20 min, add 1.70 kg of 4,6-diaminoresorcinol hydrochloride, stir for 120 min, add 2.10 kg of phosphorus pentoxide, stir for 60 min, add 1.32 kg of terephthalic acid with a particle size of 5 μm, stir for 30 min, heat to 90 °C, stir for 5 h, heat to 120 °C, stir for 6 h, add 0.4 kg of phosphorus pentoxide, heat to 150 °C, stir for 3 h to obtain PBO prepolymer solution; (2) The PBO prepolymer is fed to the upper and lower twin-screw extruders. The temperature of the upper extruder is 160°C and the temperature of the lower extruder is 205°C. The speed is 17 rpm. The residence time of the PBO material in the extruder is 1.6 h to obtain the PBO polymer.

[0031] (3) The above PBO polymer was diluted with polyphosphoric acid to a solid content of 4%, and added to water with a stirring speed of 1500 rpm. The PBO polymer precipitated and was then dried at 130°C for 4 hours to obtain the PBO polymer. The intrinsic viscosity of this PBO polymer was 22±3 dL / g and the molecular weight was 245±0.17 million.

[0032] Comparison shows that the intrinsic viscosity and molecular weight fluctuation range of the PBO polymer obtained in Comparative Example 1 are much higher than those in Examples 1-3. This is because the examples pre-add phosphorus pentoxide to polyphosphoric acid, using high-concentration polyphosphoric acid with good uniformity as a solvent, avoiding uneven dispersion and particulate impurities caused by subsequent phosphorus pentoxide addition. Secondly, the examples use two different particle sizes of TPA for prepolymerization. The first prepolymerization uses small-particle-size TPA, which has strong solubility and good reaction uniformity, while the second prepolymerization uses large-particle-size TPA, which has a slower reaction rate, avoiding problems such as explosive polymerization and wide molecular weight distribution caused by excessively high temperatures. Furthermore, the examples use a method of adding a trace amount of monomer DAR in a twin-screw extruder. By dynamically controlling the amount of DAR added, the online viscosity of the material at the extruder head is controlled, thus ensuring the stability of the polymer's intrinsic viscosity and molecular weight. Therefore, the PBO polymer prepared by this invention has significantly better stability and less fluctuation than the comparative examples. Simultaneously, the uniformity of the condensed structure of the fiber after spinning is better, with fewer weak bonds, and the final mechanical properties of the fiber are superior to those of conventional techniques. Furthermore, the PBO polymer prepared by this invention has good controllability of molecular weight, and different molecular weights can be selected according to different fiber application scenarios, thus having a wider range of applications.

[0033] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a controllable PBO polymer, characterized in that, Includes the following steps: (1) Add polyphosphoric acid to a nitrogen-purified reactor, heat to 80-100℃, add phosphorus pentoxide, stir for 1-2 hours, heat to 100-120℃, stir for 3-5 hours, and cool to 50-60℃ to obtain high-concentration polyphosphoric acid. (2) High-concentration polyphosphoric acid is transported to reactor A, the temperature is controlled at 50-60℃, antioxidant is added, and the mixture is stirred for 10-20 min. Then, 4,6-diaminoresorcinol hydrochloride is added and stirred for 5-10 min. Finally, small-particle-size TPA is added and stirred for 10-20 min. Heat to 80℃ and stir for 3-5 hours; heat to 100℃ and stir for 4-6 hours. (3) The above materials are transported to reactor B, large-particle-size TPA is added, and the mixture is stirred for 20-30 min; the temperature is raised to 120℃ and stirred for 3-5 h; the temperature is raised to 140℃ and stirred for 2-4 h; the temperature is raised to 150℃ and stirred for 5-6 h to obtain PBO prepolymer. (4) The above PBO prepolymer is fed to a twin-screw extruder. The molecular weight is further increased by the high-temperature shearing action of the extruder. The twin-screw extruder is an upper and lower stage extruder. A small amount of DAR monomer is continuously added to the feed port of the upper stage extruder to end-cap the PBO polymer in the extruder, and the molecular weight is precisely controlled to obtain a PBO polymer with controllable degree of polymerization. (5) Dilute the above PBO polymer with polyphosphoric acid and add it to water under high-speed stirring. The PBO polymer precipitates out and is filtered and dried to obtain the PBO polymer.

2. The method for preparing the controllable PBO polymer according to claim 1, characterized in that: In step (1), the amount of phosphorus pentoxide added is 22%-26% of the mass of polyphosphoric acid.

3. The method for preparing the controllable PBO polymer according to claim 1, characterized in that: In step (2), the antioxidant is stannous chloride; the amount of stannous chloride added is 0.1%-0.2% of the mass of polyphosphoric acid, the amount of 4,6-diaminoresorcinol hydrochloride added is 16%-19% of the mass of polyphosphoric acid, and the D90 particle size range of small-particle terephthalic acid is 2-4μm, and its added amount is 60%-80% of the molar amount of 4,6-diaminoresorcinol hydrochloride.

4. The method for preparing the controllable PBO polymer according to claim 1 or 3, characterized in that: In step (3), the D90 particle size range of the large-particle terephthalic acid is 10-12 μm, and its addition amount is 20%-40% of the molar amount of 4,6-diaminoresorcinol hydrochloride.

5. The method for preparing the controllable PBO polymer according to claim 1, characterized in that: In step (4), the upper stage temperature range of the twin-screw extruder is 150℃-180℃, the lower stage temperature range is 190-210℃, the rotation speed is 10rpm-20rpm, and the residence time of PBO material in the extruder is 1-2h. By dynamically adding a trace amount of 4,6-diaminoresorcinol hydrochloride monomer at the feed inlet of the upper stage of the twin-screw extruder, its viscosity is kept between 10000P-15000P, thereby achieving dynamic control of polymer viscosity.

6. The method for preparing the controllable PBO polymer according to claim 5, characterized in that: The mass of the added 4,6-diaminoresorcinol hydrochloride monomer is 0.1-0.4 wt% of the twin-screw extruder outlet flow rate.

7. The method for preparing the controllable PBO polymer according to claim 1, characterized in that: In step (5), after the PBO polymer is diluted, the solid content of the PBO polymer in the solution is 3%-5%, the stirring speed during the stirring and precipitation process is 1000rpm-2000rpm, the drying temperature is 120-150℃, and the drying time is 3-5h.

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