A method for synthesizing high performance polycarbonates based on novel bisphenol monomers

Abstract

This invention relates to the field of polymer synthesis technology, specifically a method for synthesizing high-performance polycarbonate based on novel bisphenol monomers. It aims to address the problems of low synthesis efficiency, poor polymerization controllability, material performance imbalance, and insufficient environmental sustainability in existing technologies for bisphenol monomers. This method is achieved through a combination of three core technologies: 1) a hafnium-based catalyst and lignin sulfonic acid synergistic catalytic system to directionally depolymerize lignin to generate diarylpropane-type bisphenol monomers, with a yield of 45.9~52.7wt%; 2) supercritical CO2 prepolymerization coupled with microchannel interfacial polymerization to synthesize polymers with Mw=48,800 g / mol and PDI=1.33 at 14 MPa and 120℃; 3) dimer fatty acid copolymerization and mesoporous SiO2 / hyperbranched imide-organosilicon composite modification, resulting in a material Tg=135℃, elongation at break ≥140%, and impact retention ≥70% after high-temperature cooking. Simultaneously, iron-based catalytic depolymerization and CO2 fixation technologies are integrated to construct a closed-loop recovery system, reducing the carbon footprint.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis technology, specifically a method for synthesizing high-performance polycarbonate based on novel bisphenol monomers. Background Technology

[0002] Polycarbonate (PC), as a high-performance engineering plastic, possesses characteristics such as high light transmittance, good mechanical strength, and excellent heat resistance, holding an irreplaceable position in fields such as electronics, transportation, and medical devices. Traditionally, polycarbonate is mainly synthesized using bisphenol A (BPA) as a monomer through the phosgene process or melt transesterification. However, BPA has endocrine-disrupting properties, raising serious concerns about its safety. Furthermore, the phosgene process involves the use of highly toxic raw materials and severe environmental pollution, while the melt transesterification method faces technical bottlenecks such as difficulties in phenol removal and a wide molecular weight distribution. To address the safety concerns surrounding bisphenol A (BPA), researchers have developed various novel bisphenol monomer substitutes, such as bio-based isosorbide, lignin-based bisphenols, and bisguaiacol F. However, the synthesis of these novel bisphenol monomers still suffers from several drawbacks: for example, the synthesis of lignin-based bisphenols often relies on strong acids or noble metal catalysts, resulting in insufficient reaction selectivity and yields of only 30-40 wt% in large-scale production. Furthermore, the complex separation and purification processes lead to high monomer costs. Bio-based monomers such as isosorbide have low reactivity, require high-temperature and high-pressure conditions for polymerization, significantly increasing energy consumption. Additionally, the glass transition temperature (Tg) of the synthesized polycarbonate is only around 100°C, which is insufficient for high-temperature applications. In terms of polymerization processes, existing technologies struggle to simultaneously control the molecular weight and molecular weight distribution of polycarbonates. In traditional melt transesterification, phenol removal as a byproduct is inefficient, limiting the formation of high molecular weight products; the resulting polymer typically has a distribution index (PDI) greater than 2.0. While supercritical CO2 polymerization can increase molecular weight to 48,800 g / mol, insufficient catalyst selectivity easily leads to side reactions such as crosslinking and branching, affecting the material's processing performance. Interfacial polymerization, despite its advantages of mild reaction conditions and high molecular weight, suffers from problems such as high organic solvent consumption and large mass transfer resistance, resulting in poor product purity and performance stability. In terms of material performance modification, existing technologies struggle to achieve synergistic improvements in heat resistance, hydrolysis resistance, mechanical properties, and optical properties. For example, while organosilicon modification can improve the hydrolysis resistance of polycarbonate, it leads to a decrease in light transmittance. In nanocomposite modification, nanoparticles tend to agglomerate, making uniform dispersion difficult and hindering their reinforcing effect. Bio-based polycarbonates typically suffer from insufficient rigidity and low elongation at break, limiting their application in high-end fields. Furthermore, existing polycarbonate synthesis processes lack environmental sustainability, with the phosgene method still dominating. The highly toxic raw materials and high energy consumption constrain green transformation, while chemical recycling technologies are not yet mature, with bisphenol monomer recovery rates only around 75%, and poor catalyst cycle stability making closed-loop recycling difficult. Therefore, developing a synthesis method that can simultaneously solve problems such as low synthesis efficiency of novel bisphenol monomers, poor polymerization controllability, material performance imbalance, and insufficient environmental sustainability is of great significance for promoting the green and high-performance development of polycarbonate materials. Summary of the Invention

[0003] To address the problems in existing technologies, this invention provides a method for synthesizing high-performance polycarbonate based on novel bisphenol monomers. Through synergistic catalysis, supercritical-interface polymerization coupling, multi-scale modification, and closed-loop recovery technologies, it achieves improved bisphenol monomer synthesis efficiency, precise control of the polymerization process, synergistic optimization of material properties, and improved environmental friendliness, providing technical support for the large-scale production and high-end applications of high-performance polycarbonate.

[0004] The technical solution adopted by this invention to solve its technical problem is: a method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer, comprising the following steps: (1) Synthesis of novel bisphenol monomer: Using lignin as raw material, under near-neutral high temperature of 180~220℃, a synergistic catalytic system of hafnium-based catalyst and lignin sulfonic acid (mass ratio 1:2~1:4) was adopted, combined with the free radical capture mechanism of phenol, to carry out a directional Cγ condensation reaction to generate diarylpropane type bisphenol monomer (Bisphenol P3), with a monomer yield of 45.9~52.7wt% (based on lignin mass); (2) Polymerization process: The bisphenol monomer obtained in step (1) is mixed with diphenyl carbonate at a molar ratio of 1:1.05~1:1.15. The mixture is first prepolymerized in a supercritical CO2 atmosphere under the conditions of pressure 12~16MPa and temperature 110~130℃ for 2~3h to obtain a prepolymer with Mw=5,000~6,000g / mol. Then, the prepolymer and triphosgene are added to a microchannel reactor at a mass ratio of 10:1~10:1.2. A 5~8% NaOH aqueous solution is introduced as the aqueous phase and dichloromethane is introduced as the organic phase. The mixture is subjected to interfacial polycondensation under ultrasonic dispersion (power 180~220W) for 1~1.5h. After separation and purification, a polycarbonate intermediate is obtained. (3) Multi-scale modification: Add 5-8% of dimer fatty acid, 3-5% of mesoporous SiO2 (particle size 20-30nm) and 2-4% of hyperbranched imide-organosilicon copolymer (HBP-Si) to the polycarbonate intermediate in step (2) and melt blend in a twin-screw extruder at an extrusion temperature of 230-250℃ and a rotation speed of 300-350r / min to obtain high-performance polycarbonate; (4) Closed-loop recycling: The polycarbonate waste generated after polymerization or use is depolymerized at 130~150℃ using the Fe(OTf)2 / HBpin catalytic system. The bisphenol monomer recovery rate is ≥85%. The CO2 generated by depolymerization is copolymerized with propylene oxide to generate propylene carbonate, which is recycled for polymerization reaction.

[0005] Specifically, the hafnium-based catalyst in step (1) is HfCl4 or Hf(OTf)4, and the degree of sulfonation of lignin sulfonic acid is 2.5~3.0 mmol / g.

[0006] Specifically, in step (2), the inner diameter of the microchannel reactor is 40~60μm, the volume ratio of the organic phase to the aqueous phase is 1:2~1:3, and the drop acceleration rate of triphosgene is 0.5~1mL / min.

[0007] Specifically, in step (3), the acid value of the dimer fatty acid is 190~210 mgKOH / g, and the degree of branching of the hyperbranched imide-organosilicon copolymer is 0.6~0.8.

[0008] Specifically, in step (4), the molar ratio of Fe(OTf)2 to HBpin is 1:5 to 1:8, and the depolymerization reaction time is 3 to 4 hours.

[0009] Specifically, in step (2), the phenol removal rate of the prepolymerization process is ≥90%, and the polycarbonate intermediate after interfacial polycondensation has Mw=45,000~50,000g / mol and PDI=1.3~1.4.

[0010] Specifically, the polycarbonate obtained after melt blending in step (3) has a tensile strength ≥60MPa, a light transmittance ≥90%, and an impact strength retention rate ≥70% after resisting damp heat aging (121℃, 2atm, 24h).

[0011] Specifically, in step (1), the lignin is alkali lignin or enzymatically hydrolyzed lignin with a purity ≥90% and a particle size of 100~200 mesh.

[0012] Specifically, in step (2), the purity of the supercritical CO2 is ≥99.9%, and the stirring rate of the prepolymerization process is 500~800 r / min.

[0013] Specifically, in step (3), the specific surface area of ​​the mesopore SiO2 is 800~1000 m². 2 / g, with a pore size of 5~10nm.

[0014] The beneficial effects of this invention are: This invention employs a synergistic catalytic system of hafnium-based catalyst and lignin sulfonic acid, combined with directional Cγ condensation reaction and phenol radical capture mechanism. This avoids the extensive use of strong acids or precious metals in traditional processes, significantly improving the synthesis efficiency and selectivity of lignin-based bisphenol monomers, simplifying the separation and purification process, and reducing monomer production costs, thus laying the foundation for the large-scale application of novel bisphenol monomers. Furthermore, the use of bio-based lignin as a raw material reduces dependence on fossil resources and enhances the sustainability of the process.

[0015] By coupling supercritical CO2 prepolymerization with microchannel interfacial polymerization, the high diffusion characteristics of supercritical CO2 are utilized to efficiently remove polymerization byproducts, solving the chain termination problem caused by byproduct residues in traditional polymerization processes. The narrow channel structure of the microchannel reactor, combined with ultrasonic dispersion technology, effectively reduces interphase mass transfer resistance, resulting in a more uniform polymerization reaction, significantly optimizing the molecular weight and molecular weight distribution of the polymer, and improving the processing stability and consistency of the material. Furthermore, supercritical CO2 and organic solvents can be efficiently recycled and reused, reducing environmental pollution and lowering the environmental impact of the process.

[0016] A multi-scale modification strategy employing dimer fatty acid copolymerization and mesoporous SiO2 / hyperbranched imide-organosilicon copolymer composites achieved a synergistic improvement in the material's mechanical properties, heat resistance, hydrolysis resistance, and optical properties. The introduction of dimer fatty acids improved the flexibility of the polymer backbone. The core-shell structure formed by the mesoporous SiO2 and hyperbranched imide-organosilicon copolymer not only leveraged the reinforcing effect of nanoparticles but also avoided their aggregation problem, thereby enhancing the material's resistance to damp heat aging. This approach overcomes the bottleneck of mutually restrictive performance in traditional modification techniques and expands the material's application scenarios.

[0017] By integrating Fe(OTf)2 / HBpin catalytic depolymerization and CO2 fixation technologies, a closed-loop industrial chain of synthesis-use-recycling-resynthesis has been constructed. The catalytic depolymerization process achieves efficient recovery of bisphenol monomers from polycarbonate waste, with high-purity recovered monomers that can be directly used for secondary polymerization. The CO2 generated during depolymerization is captured and copolymerized with propylene oxide to generate polymerization raw materials, realizing the recycling of carbon resources, significantly reducing the carbon footprint of the process, improving the environmental friendliness of the entire industrial chain, and conforming to the development trend of green chemical industry.

[0018] The entire process design of this invention is scientific and reasonable, with each step working in synergy. It not only solves several core problems in the existing polycarbonate synthesis, such as low monomer synthesis efficiency, poor polymerization controllability, material performance imbalance, and insufficient environmental sustainability, but also has advantages such as mild process conditions, strong operational controllability, and easy large-scale scaling. It provides a brand-new technical solution for the green and high-performance production of high-performance polycarbonate, and has important industrial application value and market prospects. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Figure 1 The flowchart illustrates a method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer, as provided by this invention. Detailed Implementation

[0021] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0022] like Figure 1 As shown, the present invention provides a method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer, comprising the following steps: Step 1: Synthesis of novel bisphenol monomer: Using lignin (alkali lignin or enzymatically hydrolyzed lignin, purity ≥90%, particle size 100~200 mesh) as raw material, add it to a reaction vessel. Phenol is added as a free radical scavenger at a lignin-to-phenol mass ratio of 1:3~1:5. Then, a synergistic catalytic system of hafnium-based catalyst (HfCl4 or Hf(OTf)4) and lignin sulfonate is added, wherein the mass ratio of hafnium-based catalyst to lignin sulfonate is 1:2~1:4, and the degree of sulfonation of lignin sulfonate is 2.5~3.0 mmol / g. The reaction vessel is heated to 180~220℃ and kept at near-neutral conditions for 4~6 hours to carry out a directional Cγ condensation reaction, generating a diarylpropane-type bisphenol monomer (Bisphenol P3). After the reaction was completed, unreacted phenol was separated by vacuum distillation (pressure 5~10 kPa, temperature 180~200℃), and then purified by silica gel column chromatography (eluent: petroleum ether / ethyl acetate = 5:1, volume ratio) to obtain bisphenol monomer with a purity ≥99% and a yield of 45.9~52.7 wt% (based on lignin mass). Step 2, Polymerization process: The bisphenol monomer obtained in Step 1 is mixed with diphenyl carbonate at a molar ratio of 1:1.05~1:1.15 and added to a supercritical reactor. CO2 with a purity ≥99.9% is introduced, the temperature is raised to 110~130℃, the pressure is increased to 12~16MPa, the stirring rate is 500~800r / min, and the prepolymerization reaction is carried out for 2~3h to remove some phenol, and a prepolymer with Mw=5,000~6,000g / mol is obtained, with a phenol removal rate ≥90%. The prepolymer was then dissolved in dichloromethane to prepare an organic phase with a mass fraction of 10-15%. Triphosgene was dissolved in dichloromethane at a mass ratio of prepolymer to triphosgene of 10:1 to 10:1.2 as an acylating agent. Simultaneously, a NaOH aqueous solution with a mass fraction of 5-8% was prepared as the aqueous phase. The organic phase, aqueous phase, and acylating agent were separately introduced into a microchannel reactor (inner diameter 40-60 μm), with a volume ratio of organic phase to aqueous phase of 1:2 to 1:3. The triphosgene drop rate was 0.5-1 mL / min. The interfacial polycondensation reaction was carried out under ultrasonic dispersion (power 180-220 W) for 1-1.5 h. After the reaction, the product was filtered, washed until neutral, and vacuum dried (temperature 80-100℃, time 12-16 h) to obtain a polycarbonate intermediate with Mw = 45,000-50,000 g / mol and PDI = 1.3-1.4. Step 3, Multi-scale Modification: Add 5-8% by weight of dimer fatty acid (acid value 190-210 mg KOH / g) and 3-5% by weight of mesoporous SiO2 (particle size 20-30 nm, specific surface area 800-1000 m²) to the polycarbonate intermediate from Step 2. 2The mixture contains 2-4% of a hyperbranched imide-organosilicon copolymer (HBP-Si, branching degree 0.6-0.8) with a pore size of 5-10 nm and a density of 0.6-0.8. The mixture is added to a twin-screw extruder, with the extrusion temperature set at 230-250℃ (zone 1: 230℃, zone 2: 240℃, zone 3: 250℃, die head: 245℃), and the screw speed at 300-350 r / min. The mixture is melt-blended and extruded, then water-cooled and pelletized to obtain high-performance polycarbonate granules. Step 4, Closed-Loop Recycling: Waste generated during polymerization or recycled polycarbonate products are pulverized to a particle size of 5-10 mm and added to a reactor. Fe(OTf)2 catalyst is added at a mass ratio of polycarbonate to Fe(OTf)2 of 100:1-100:2, followed by HBpin at a molar ratio of Fe(OTf)2 to HBpin of 1:5-1:8. The temperature is raised to 130-150℃ and maintained for 3-4 hours for catalytic depolymerization. The bisphenol monomer recovery rate is ≥85%, and the purity is ≥98%. CO2 generated during depolymerization is recovered through a gas collection device and added to the reactor with propylene oxide at a molar ratio of 1:1.2-1:1.5. Under the action of a zinc salt catalyst, copolymerization is performed at 80-100℃ and a pressure of 2-3 MPa to produce propylene carbonate. Propylene carbonate can be further reacted with bisphenol monomers for polycarbonate synthesis, achieving carbon recycling.

[0023] Example 1: Preparation of high-performance polycarbonate based on alkali lignin Synthesis of novel bisphenol monomers The raw materials selected were alkali lignin (purity 92%, particle size 150 mesh), phenol (analytical grade, purity 99.5%), hafnium-based catalyst HfCl4 (analytical grade, purity 99.9%), and lignin sulfonic acid (sulfonation degree 2.8 mmol / g). Add 50g of alkali lignin and 200g of phenol (lignin to phenol mass ratio 1:4) to a 500mL high-pressure reactor, then add 2g of HfCl4 and 6g of lignin sulfonic acid (mass ratio 1:3). After sealing the reactor, purge with nitrogen three times (0.5MPa each time), raise the temperature to 200℃ (heating rate 5℃ / min), and maintain the temperature for 5h (stirring rate 400r / min) to carry out the directional Cγ condensation reaction. After the reaction was completed, the temperature was lowered to 120℃, and vacuum distillation was started (pressure 8 kPa). The fraction (unreacted phenol, recovery rate ≥90%) was collected. The remaining product was dissolved in 100 mL of dichloromethane, and the insoluble matter (unreacted lignin, mass approximately 8.5 g) was removed by filtration. The filtrate was purified by silica gel column chromatography (silica gel particle size 100~200 mesh, eluent: petroleum ether / ethyl acetate = 5:1, volume ratio, flow rate 2 mL / min). The target fraction was collected and rotary evaporated (60℃, vacuum degree -0.095 MPa) to obtain 24.25 g of white solid bisphenol monomer (Bisphenol P3), yield 48.5 wt% (based on lignin mass). The purity was 99.2% as determined by HPLC, and the melting point was 158~160℃. Polymerization process 20g of the above-mentioned bisphenol monomer and 22.8g of diphenyl carbonate (molar ratio 1:1.1, diphenyl carbonate purity 99.8%) were added to a 200mL supercritical reactor. 99.99% pure CO2 was introduced, the temperature was raised to 120℃, and the pressure was increased to 14MPa (pressure increase rate 0.5MPa / min). The stirring rate was 600r / min, and the prepolymerization reaction was carried out for 2.5h. The molecular weight of the prepolymer was measured by GPC (gel permeation chromatography, mobile phase tetrahydrofuran, standard polystyrene). The prepolymer Mw was 5500g / mol, and the phenol removal rate was 92% (phenol content in the reactor tail gas was detected by gas chromatography).

[0024] The prepolymer was then dissolved in 150 mL of dichloromethane to prepare an organic phase with a mass fraction of 12%; 2.2 g of triphosgene (prepolymer to triphosgene mass ratio 10:1.1, triphosgene purity 99%) was dissolved in 30 mL of dichloromethane as an acylating agent; 225 mL of a 6% NaOH aqueous solution was prepared (organic phase to aqueous phase volume ratio 1:2.5).

[0025] The organic and aqueous phases were separately introduced into a microchannel reactor (50 μm inner diameter, 316L stainless steel) using a metering pump (5 mL / min flow rate). Simultaneously, an acylation agent was added dropwise to the reactor at a rate of 0.8 mL / min using another metering pump. An ultrasonic generator (200 W power, 20 kHz frequency) was activated, and the reactor temperature was controlled at 25 °C for 1.2 h. The reaction product was filtered under reduced pressure (0.22 μm pore size), washed with deionized water until the filtrate pH reached 7, then washed three times with anhydrous ethanol, and vacuum dried at 90 °C for 14 h to obtain 28.5 g of white polycarbonate intermediate powder. GPC analysis showed that the intermediate had a Mw of 47000 g / mol and a PDI of 1.35; DSC (differential scanning calorimetry, heating rate 10 °C / min, N2 atmosphere) analysis showed a Tg of 128 °C. Multiscale modification Take 25g of polycarbonate intermediate, add 1.5g of dimer fatty acid (acid value 200mgKOH / g) and 1.0g of mesoporous SiO2 (particle size 25nm, specific surface area 900m²). 2 0.75 g of hyperbranched imide-organosilicon copolymer (HBP-Si, branching degree 0.7, self-made: prepared by reacting pyromellitic dianhydride with aminopropyltriethoxysilane and then by hyperbranching polymerization) was mixed in a high-speed mixer for 10 min (2000 r / min) to obtain a mixture. The mixture was added to a twin-screw extruder (model SHJ-20, screw length-to-diameter ratio 36:1), and the extrusion temperature was set as follows: zone 1 235℃, zone 2 245℃, zone 3 250℃, die head 245℃, screw speed 320r / min, and feed rate 2kg / h. After extrusion, the mixture was cooled by water (water temperature 25℃) and pelletized to obtain high-performance polycarbonate granules. Performance testing: Tensile properties were tested according to GB / T1040.3-2006, with a tensile strength of 62 MPa and an elongation at break of 145%; light transmittance (400~800 nm) was tested according to GB / T2410-2008, with an average value of 91%; impact strength (simply supported beam, notched type) was tested according to GB / T1843-2008, with an initial impact strength of 8.5 kJ / m. 2 After the sample was placed in a high-pressure autoclave at 121℃ and 2 atm for 24 hours of wet heat aging, the impact strength retention rate was 72%; the 5% thermal weight loss temperature (T5%) was 385℃ as determined by TGA (thermogravimetric analysis, heating rate 10℃ / min, air atmosphere). Closed-loop recycling Take 10g of the above polycarbonate particles (crushed to a particle size of 5-8mm), add them to a 100mL three-necked flask, add 0.1g Fe(OTf)2 (purity 98%) and 0.42g HBpin (pinacol borane, purity 98%, Fe(OTf)2 to HBpin molar ratio 1:6), purge with nitrogen three times, heat to 140℃, and reflux for 3.5h. After the reaction is complete, add 50mL of dichloromethane to dissolve the product, filter to remove catalyst residue, and distill the filtrate under reduced pressure (80℃, 5kPa), collecting the fraction at 150-160℃ to obtain 8.6g of bisphenol monomer, with a recovery rate of 86% and a purity of 98.5% (HPLC detection). The CO2 generated during the depolymerization process is recovered through a gas collection device (with a drying tube), with a collection volume of approximately 1.2 L (under standard conditions). This collected CO2 is then added to a 50 mL high-pressure reactor along with 1.8 g of propylene oxide (molar ratio 1:1.3) and 0.05 g of Zn(OAc)2 (catalyst). The reactor is heated to 90 °C and pressurized to 2.5 MPa, and reacted for 4 h to obtain 2.3 g of propylene carbonate (purity 99%, GC detection), which can be used for subsequent polymerization reactions. Example 2: Preparation of high-performance polycarbonate based on enzymatic hydrolysis of lignin Synthesis of novel bisphenol monomers The raw materials selected were enzymatically hydrolyzed lignin (95% purity, 120 mesh particle size), phenol (analytical grade), hafnium-based catalyst Hf(OTf)4 (99.9% purity), and lignin sulfonic acid (sulfonation degree 2.6 mmol / g).

[0026] 50g of enzymatically hydrolyzed lignin and 187.5g of phenol (mass ratio 1:3.75) were added to a 500mL high-pressure reactor. 1.8g of Hf(OTf)4 and 4.5g of lignin sulfonic acid (mass ratio 1:2.5) were also added. After nitrogen purging, the mixture was heated to 190℃ (heating rate 4℃ / min) and maintained at this temperature for 4.5h (stirring rate 350r / min). After the reaction, phenol was recovered by vacuum distillation at 110℃ and 6kPa (recovery rate 91%). The remaining product was dissolved in 90mL of dichloromethane, and unreacted lignin (approximately 6.2g) was removed by filtration. The filtrate was purified by silica gel column chromatography (eluent as in Example 1, flow rate 1.8mL / min). Rotary evaporation yielded 25.85g of white bisphenol monomer, with a yield of 51.7wt% (based on lignin mass). HPLC analysis showed a purity of 99.4% and a melting point of 159–161℃. Polymerization process 20g of the bisphenol monomer and 22.1g of diphenyl carbonate (molar ratio 1:1.07) were added to a 200mL supercritical reactor, 99.99% CO2 was introduced, the temperature was raised to 115℃, the pressure was increased to 13MPa, the stirring rate was 550r / min, and prepolymerization was carried out for 2.2h. GPC analysis showed that the prepolymer Mw = 5200g / mol, and the phenol removal rate was 93%. The prepolymer was dissolved in 140 mL of dichloromethane (12.5% ​​by mass), and 2.1 g of triphosgene (mass ratio 10:1.05) was dissolved in 28 mL of dichloromethane to prepare 210 mL of 5.5% NaOH aqueous solution (organic phase: aqueous phase = 1:2.6). The phases were introduced into a microchannel reactor (45 μm inner diameter) using a metering pump. The acylating agent was dropped at a rate of 0.7 mL / min, the ultrasonic power was 190 W, and the reaction was carried out at 25 °C for 1.1 h. After washing and drying, 27.8 g of polycarbonate intermediate was obtained. GPC analysis showed Mw = 46200 g / mol and PDI = 1.33; DSC analysis showed Tg = 130 °C. Multiscale modification Take 25g of the intermediate, add 1.4g of dimer fatty acid (acid value 195mgKOH / g) and 0.9g of mesoporous SiO2 (particle size 22nm, specific surface area 950m²). 20.7g HBP-Si (branching degree 0.68) and 0.7g HBP-Si were mixed at high speed for 10min and then extruded and pelletized through a twin-screw extruder (temperature: zone 1 230℃, zone 2 240℃, zone 3 248℃, die head 242℃, speed 310r / min).

[0027] Performance testing: Tensile strength 63.5 MPa, elongation at break 148%; light transmittance 91.5%; initial impact strength 8.7 kJ / m². 2 The retention rate after damp heat aging was 73.5%; T5% = 388℃. Closed-loop recycling 10g of the polycarbonate granules were taken and mixed with 0.09g of Fe(OTf)₂ and 0.39g of HBpin (molar ratio 1:5.8), and refluxed at 135℃ for 3.3h. After depolymerization, 8.7g of bisphenol monomer was obtained, with a recovery rate of 87% and a purity of 98.6%. Approximately 1.22L of CO₂ was recovered and copolymerized with 1.75g ​​of propylene oxide to obtain 2.25g of propylene carbonate (purity 99.1%). Example 3: Preparation of polycarbonate based on highly sulfonated lignin sulfonic acid Synthesis of novel bisphenol monomers The raw materials were alkali lignin (90% purity, 180 mesh particle size), phenol, HfCl4, and lignin sulfonic acid (sulfonation degree 3.0 mmol / g). 50 g of lignin and 225 g of phenol (mass ratio 1:4.5) were added to a 500 mL reactor, along with 2.1 g of HfCl4 and 8.4 g of lignin sulfonic acid (mass ratio 1:4). After nitrogen purging, the mixture was heated to 210 °C and held at this temperature for 5.5 h (stirring rate 420 r / min).

[0028] Phenol was recovered by vacuum distillation (recovery rate 89%). After filtration to remove impurities, the filtrate was purified to obtain 23.45 g of bisphenol monomer, with a yield of 46.9 wt%, a purity of 99.1%, and a melting point of 157~159℃. Polymerization process 20g of bisphenol monomer and 23.2g of diphenyl carbonate (molar ratio 1:1.12) were mixed and prepolymerized under supercritical conditions of 125℃, 15MPa, and stirring at 650r / min for 2.8h. The prepolymer had a molecular weight (Mw) of 5800g / mol and a phenol removal rate of 89%. Subsequent interfacial polymerization: The prepolymer was dissolved in 160 mL of dichloromethane (11.5%), 2.3 g of triphosgene (10:1.15), and 240 mL of 6.5% NaOH aqueous solution (1:2.4). A microchannel reactor with an inner diameter of 55 μm was used, the acylating agent was dropped at a rate of 0.9 mL / min, and the reaction was conducted under ultrasonic waves at 210 W for 1.3 h. 29.1 g of intermediate was obtained, with Mw = 48500 g / mol, PDI = 1.36, and Tg = 127 °C.

[0029] Multiscale modification Take 25g of intermediate, add 1.6g of dimer fatty acid (acid value 205mgKOH / g) and 1.1g of mesoporous SiO2 (particle size 28nm, specific surface area 850m²). 2 / g) and 0.8g HBP-Si (branching degree 0.72), extrusion temperature: zone 1 238℃, zone 2 246℃, zone 3 252℃, die head 246℃, speed 330r / min. Performance testing: Tensile strength 61 MPa, elongation at break 142%; light transmittance 90.5%; initial impact strength 8.3 kJ / m². 2 The retention rate after damp heat aging is 71%; T5% = 382℃. Closed-loop recycling 10g of granules were depolymerized (0.11g Fe(OTf)2, 0.45g HBpin, reaction at 145℃ for 3.8h) to obtain 8.5g of bisphenol monomer (recovery rate 85%, purity 98.4%), and 2.35g of propylene carbonate was prepared by recovering CO2. Comparative Example (Comparison with Existing Technology) Comparative Example 1: Synthesis of polycarbonate via conventional bisphenol A-phosgene method Process: Bisphenol A was used as the monomer, dichloromethane was used as the solvent, and phosgene was subjected to interfacial polymerization in NaOH aqueous solution. The reaction temperature was 25℃, the stirring rate was 300 r / min, and the reaction time was 2 h. After washing and drying, the product was directly injection molded (unmodified). Performance: Mw=38000g / mol, PDI=1.85; tensile strength 65MPa, elongation at break 95%; light transmittance 90%; impact retention after damp heat aging 45%; T5%=370℃. Disadvantages: Uses highly toxic phosgene, consumes a large amount of organic solvents (800 kg of dichloromethane per ton of product); lacks a recycling process, bisphenol A poses a safety risk; low elongation at break and poor hydrolysis resistance. Comparative Example 2: Synthesis of existing lignin-based bisphenol monomers (strong acid catalysis) Process: Using sulfuric acid (98% concentration) as a catalyst, lignin and phenol are reacted at 120°C for 6 hours, and subsequent purification is the same as in this invention. Results: The bisphenol monomer yield was 32.5 wt%, and the purity was 97.8% (including residual sulfuric acid); the polycarbonate after polymerization had a Mw of 35000 g / mol and a PDI of 1.92; due to the low monomer purity, the light transmittance of the material was only 82%. Disadvantages: Strong acid corrodes equipment, resulting in high wastewater treatment costs; low monomer yield and insufficient purity lead to polymer performance degradation. Compare with Example 3: Single supercritical CO2 polymerization (interface-free polymerization) Process: Bisphenol monomer and diphenyl carbonate are directly polymerized in supercritical CO2 (under the same conditions as the prepolymerization in Example 1), and the reaction is carried out for 4 hours without subsequent interfacial polycondensation. Properties: Polymer Mw = 28000 g / mol, PDI = 1.78; tensile strength 52 MPa, elongation at break 110%; due to low molecular weight, impact strength is only 6.2 kJ / m. 2 . Defects: Supercritical processes alone are insufficient to remove residual phenol, resulting in inadequate chain growth and insufficient molecular weight and mechanical properties.

[0030] Comparative Example 4: Traditional nano-SiO2 modification (without HBP-Si) Process: Polycarbonate intermediate is directly melt-blended with 1.0g of mesoporous SiO2 (same as in Example 1), without HBP-Si.

[0031] Performance: SiO2 agglomerate particle size ≥200nm; light transmittance 78%; tensile strength 58MPa; elongation at break 125%; impact retention rate after damp heat aging 55%. Defects: The nanoparticles are severely aggregated, resulting in a significant decrease in light transmittance and limited improvement in hydrolysis resistance, making it impossible to achieve a balance in performance.

[0032] Comparative Example 5: Conventional Chemical Recovery (High-Temperature Pyrolysis) Process: Polycarbonate waste is pyrolyzed at 400℃ in a nitrogen atmosphere, and the bisphenol monomer is recovered by distillation of the product. Results: Bisphenol monomer recovery rate was 68%, purity was 95% (including pyrolysis byproducts); energy consumption was 2.1 times that of the recovery process in Example 1; no CO2 was recovered. Disadvantages: High energy consumption, low recovery rate, insufficient monomer purity for direct reuse, no carbon cycle design, and poor environmental benefits.

[0033] This invention innovates the entire process of synergistic catalytic synthesis of bisphenol monomers—supercritical polymerization—interfacial coupling polymerization—multi-scale modification—closed-loop recovery, solving problems such as low monomer yield, poor polymerization controllability, material performance imbalance, and environmental unfriendliness in existing technologies. Compared with the control example, the bisphenol monomer yield of this invention is increased by more than 40%, the polymer PDI is reduced to 1.3~1.4, and the comprehensive material properties (tensile strength ≥60MPa, elongation at break ≥140%, light transmittance ≥90%, and wet heat aging retention ≥70%) are significantly better than those of existing technologies. At the same time, it achieves a 40% reduction in carbon footprint and a 60% reduction in solvent consumption, providing a feasible solution for the green and large-scale production of high-performance polycarbonate.

[0034] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer, characterized in that, Includes the following steps: (1) Synthesis of novel bisphenol monomers: Using lignin as raw material, under near-neutral high temperature conditions of 180~220℃, a synergistic catalytic system of hafnium-based catalyst and lignin sulfonic acid with a mass ratio of 1:2~1:4 was adopted, combined with the free radical capture mechanism of phenol, to carry out a directional Cγ condensation reaction to generate diarylpropane-type bisphenol monomers. The monomer yield based on lignin quality was 45.9~52.7wt%. (2) Polymerization process: The bisphenol monomer obtained in step (1) is mixed with diphenyl carbonate at a molar ratio of 1:1.05~1:1.

15. The mixture is first prepolymerized in a supercritical CO2 atmosphere under the conditions of pressure 12~16MPa and temperature 110~130℃ for 2~3h to obtain a prepolymer with Mw=5,000~6,000g / mol. Then, the prepolymer and triphosgene are added to a microchannel reactor at a mass ratio of 10:1~10:1.

2. A 5~8% NaOH aqueous solution is introduced as the aqueous phase and dichloromethane is introduced as the organic phase. The mixture is subjected to interfacial polycondensation under ultrasonic dispersion conditions for 1~1.5h. After separation and purification, a polycarbonate intermediate is obtained. (3) Multi-scale modification: Add 5-8% of dimer fatty acid, 3-5% of mesoporous SiO2 with a particle size of 20-30nm and 2-4% of hyperbranched imide-organosilicon copolymer to the polycarbonate intermediate in step (2), melt blend in a twin-screw extruder, extrusion temperature of 230-250℃ and speed of 300-350r / min to obtain high-performance polycarbonate; (4) Closed-loop recycling: The polycarbonate waste generated after polymerization or use is depolymerized at 130~150℃ using the Fe(OTf)2 / HBpin catalytic system. The bisphenol monomer recovery rate is ≥85%. The CO2 generated by depolymerization is copolymerized with propylene oxide to generate propylene carbonate, which is recycled for polymerization reaction.

2. The method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer according to claim 1, characterized in that: The hafnium-based catalyst mentioned in step (1) is HfCl4 or Hf(OTf)4, and the degree of sulfonation of lignin sulfonic acid is 2.5~3.0 mmol / g.

3. The method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer according to claim 1, characterized in that: In step (2), the inner diameter of the microchannel reactor is 40~60μm, the volume ratio of the organic phase to the aqueous phase is 1:2~1:3, and the drop acceleration rate of triphosgene is 0.5~1mL / min.

4. The method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer according to claim 1, characterized in that: In step (3), the acid value of the dimer fatty acid is 190~210 mgKOH / g, and the degree of branching of the hyperbranched imide-organosilicon copolymer is 0.6~0.

8.

5. The method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer according to claim 1, characterized in that: In step (4), the molar ratio of Fe(OTf)2 to HBpin is 1:5 to 1:8, and the depolymerization reaction time is 3 to 4 hours.

6. The method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer according to claim 1, characterized in that: In step (2), the phenol removal rate of the prepolymerization process is ≥90%, and the polycarbonate intermediate after interfacial polycondensation has Mw=45,000~50,000g / mol and PDI=1.3~1.

4.

7. The method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer according to claim 1, characterized in that: The polycarbonate obtained after melt blending in step (3) has a tensile strength ≥60MPa, a light transmittance ≥90%, and an impact strength retention rate ≥70% after damp heat aging.

8. The method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer according to claim 1, characterized in that: In step (1), the lignin is alkali lignin or enzymatically hydrolyzed lignin with a purity ≥90% and a particle size of 100~200 mesh.

9. The method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer according to claim 1, characterized in that: In step (2), the purity of supercritical CO2 is ≥99.9%, and the stirring rate of the prepolymerization process is 500~800 r / min.

10. The method for synthesizing high-performance polycarbonate based on a novel bisphenol monomer according to claim 1, characterized in that: Step (3) The specific surface area of ​​the mesopore SiO2 is 800~1000m². 2 / g, with a pore size of 5~10nm.

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