Colorless, water-clear carbon dioxide-based polycarbonate polyols and methods for their preparation

Abstract

This invention provides a colorless, water-permeable carbon dioxide-based polycarbonate polyol and its preparation method, relating to the fields of polyol synthesis and carbon dioxide resource utilization. Addressing the various light scattering centers formed by residual metal catalysts, cyclic carbonate byproducts, terminal hydroxyl aggregates, and chain entanglement agglomerates in existing carbon dioxide-based polycarbonate polyols, this invention employs a combined decatalyst removal and purification process: "mild acid hydrolysis and complexation – precise neutralization and chain stabilization – graded gradient adsorption – temperature-controlled vacuum dehydration – precision filtration for impurity removal." This process thoroughly removes various light scattering centers from the system without damaging the polycarbonate polyol's main chain structure. The prepared product is colorless and water-permeable, with a transmittance ≥98% in the entire visible light spectrum (300-800 nm) and a total metal ion residue ≤10 ppm. This provides a high-quality core raw material for the preparation of highly transparent waterborne polyurethane, suitable for large-scale industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyol synthesis and carbon dioxide resource utilization, and particularly relates to a colorless water-transparent carbon dioxide-based polycarbonate polyol and a preparation method thereof. BACKGROUND

[0002] With the capture and high-value utilization of greenhouse gas carbon dioxide having become a core research direction in the field of chemical and material science, carbon dioxide-based polycarbonate polyols (PPCD) are prepared by copolymerization of carbon dioxide and an epoxide compound, which is one of the most promising paths for high-value utilization of carbon dioxide at present. The main chain of PPCD contains carbonate bonds with high hydrolysis resistance and high oxidation resistance, and compared with traditional petroleum-based polyether polyols and polyester polyols, the waterborne polyurethane material prepared by PPCD has more excellent mechanical properties, weather resistance and biodegradability, and can be widely applied in the fields of environment-friendly coatings, adhesives, leather finishing agents, textile finishing agents and the like, and is an ideal green raw material for replacing petroleum-based polyols.

[0003] Currently, the industrialized PPCD is mainly prepared by copolymerization of carbon dioxide and propylene oxide through a double metal catalyst (DMC) catalytic system, which has the advantages of high catalytic activity and good selectivity, but also has the technical defects that cannot be avoided: after the copolymerization reaction is completed, the DMC metal catalyst and the unreacted monomers are left in the crude PPCD, and at the same time, the cyclic carbonate by-product is generated; in addition, the low molecular weight PPCD is easy to form local chain segment aggregation through hydrogen bonds due to the high concentration of terminal hydroxyl groups, and the high molecular weight PPCD is easy to form density fluctuations due to molecular chain entanglement, and the above substances and structural defects will form light scattering centers, which finally leads to low light transmittance, yellow appearance and poor optical uniformity of the PPCD product.

[0004] Existing purification technologies for PPCD mostly focus on the removal of metal catalysts, neglecting the complete elimination of light scattering centers, resulting in significant technical shortcomings: First, current decatalyst removal processes often employ high-temperature distillation, strong acid-base treatment, and organic solvent extraction. While these methods can remove some metal residues, they easily lead to the hydrolysis and degradation of carbonate bonds in the PPCD backbone, damaging the product's thermal stability and physicochemical properties. Simultaneously, the small molecule impurities generated during degradation can form new light scattering centers. Second, existing processes cannot simultaneously address multiple types of light scattering centers, such as cyclic carbonate byproducts, terminal hydroxyl aggregates, and chain entanglement agglomerates. They can only achieve limited transmittance improvements by controlling the PPCD molecular weight. For example, current research can only achieve a maximum transmittance of 92.8% in the visible light region for PPCD with a molecular weight of 2000, failing to achieve the optical effect of colorless, water-transparent light. The improvement effect on the optical properties of low molecular weight, high molecular weight, and branched PPCD is extremely poor. Third, the existing purification processes are mostly small-scale laboratory processes with strict parameter control, which cannot be adapted to industrial-scale production such as 900kg scale and above. After scale-up, the purification effect is prone to unevenness and low product qualification rate. Fourth, there are prominent technical difficulties in the core adsorption and filtration process: the existing adsorbents are mostly of a single type with unreasonable pore size distribution. They either cannot effectively adsorb nano-scale metal complexes and cyclic carbonate byproducts, or they are prone to agglomeration after adsorption, resulting in filter blockage and low filtration efficiency. In addition, some adsorbents will have weak interactions with PPCD, affecting the light transmittance and physicochemical properties of the product. At the same time, the filtration effect is poor, and the adsorbent residue cannot be completely removed. The remaining small solid particles will form light scattering centers again, which seriously affects the product quality.

[0005] In summary, existing technologies cannot completely eliminate various light scattering centers within the PPCD system without damaging its core structure. Consequently, it is impossible to prepare PPCD products that possess colorless, water-transparent optical effects, structural integrity, and stable performance. This severely limits the application of PPCD in high-end fields such as high-transparency waterborne polyurethane and optical-grade coatings. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this application provides a colorless, water-permeable carbon dioxide-based polycarbonate polyol and its preparation method. Targeting the various light scattering centers within existing industrial PPCD systems, a gentle and precise combined process completely eliminates these centers while fully preserving the PPCD polycarbonate backbone structure, achieving the core effect of colorless and water-permeable products. Simultaneously, it overcomes the industrialization challenges of the adsorption and filtration process, adapting to the needs of large-scale production.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a colorless, water-permeable carbon dioxide-based polycarbonate polyol includes the following steps: S1. Add the crude carbon dioxide-based polycarbonate polyol to the reactor and stir. S2. Heat to 70℃-90℃, add 4wt%-10wt% phosphoric acid aqueous solution, keep warm and stir for 5min-120min, then add alkaline solution, keep warm and stir for a period of time to adjust the pH of the system to 7.0-8.0; S3. Add magnesium silicate and continue stirring while keeping warm for 10-120 minutes. S4. Heat to 100℃-110℃, control the vacuum degree of the system to ≤-0.09MPa, and perform vacuum dehydration under heat and pressure. S5. Cool down to 80℃-90℃, add diatomaceous earth and stir for 10min-120min while keeping warm. S6. Filter the system and take samples for testing. When the total content of metal ions in the system is ≤10ppm, the colorless water-permeable carbon dioxide-based polycarbonate polyol can be obtained.

[0008] Furthermore, the crude carbon dioxide-based polycarbonate polyol is prepared by copolymerizing propylene oxide and carbon dioxide under the catalysis of a bimetallic catalyst using a polyether polyol as a starting agent.

[0009] Furthermore, the mass ratio of the crude carbon dioxide-based polycarbonate polyol to the aqueous phosphoric acid solution is 85-100:1-2.

[0010] Furthermore, the concentration of the alkaline solution is 1wt%-5wt%.

[0011] Furthermore, the stirring speed in the preparation method is 300 r / min-500 r / min.

[0012] Furthermore, the temperature in S2 is increased to 77℃-85℃.

[0013] Furthermore, the pH value described in S2 is 7.2-7.6.

[0014] Furthermore, the amount of magnesium silicate used is 0.2%-0.8% of the crude mass of carbon dioxide-based polycarbonate polyol.

[0015] Furthermore, the specific surface area of ​​the magnesium silicate is ≥300 m². 2 / g, with a pore size distribution of 200nm-300nm.

[0016] Furthermore, the stirring time in S3 is 10-60 minutes.

[0017] Furthermore, in step S4, the temperature is raised to 103℃-107℃; the vacuum degree is ≤-0.095MPa; and the vacuum dehydration time is 0.5h-2h.

[0018] Furthermore, the amount of diatomaceous earth used is 0.2%-0.8% of the crude mass of carbon dioxide-based polycarbonate polyol.

[0019] Furthermore, the diatomaceous earth has an average pore size of 500μm-550μm and a SiO2 mass fraction ≥85%; Furthermore, the holding and stirring time in S5 is 10-60 minutes.

[0020] Furthermore, the filtration accuracy in S6 is ≤5μm.

[0021] A colorless, water-permeable carbon dioxide-based polycarbonate polyol is prepared by the aforementioned preparation method. The number-average molecular weight of the carbon dioxide-based polycarbonate polyol is 1000 g / mol to 4000 g / mol, and the functionality is 2 to 3.

[0022] Furthermore, the colorless, water-permeable carbon dioxide-based polycarbonate polyol has a transmittance of ≥98% in the wavelength range of 300nm to 800nm.

[0023] Furthermore, compared with its crude product, the colorless water-permeable carbon dioxide-based polycarbonate polyol has a hydroxyl value deviation of ≤±2mg KOH / g and a rotational viscosity deviation of ≤±500mPa·s at 40℃.

[0024] Furthermore, the colorless, water-permeable carbon dioxide-based polycarbonate polyol can be used as a soft segment raw material to prepare highly transparent carbon dioxide-based waterborne polyurethane emulsions, waterborne coatings containing the emulsions, or waterborne adhesives.

[0025] Based on the limitations of existing PPCD optical performance and industrial production, the core technical points of this invention are as follows: (i) To address the solid light scattering centers formed by residual DMC metal catalyst, a mild phosphoric acid acid hydrolysis complexation method at 70℃-90℃ was adopted. This method not only achieved complete dissociation of the metal catalyst but also avoided the hydrolysis of polycarbonate bonds caused by high temperature and strong acid. By precisely neutralizing the system to a weakly alkaline state, the acid hydrolysis reaction was terminated, and degradation of the product during storage caused by acid residue was avoided. This eliminated the core light scattering center of residual metal catalyst from the root.

[0026] (II) Targeting the light scattering centers formed by cyclic carbonate byproducts and terminal hydroxyl polyagglomerates, and simultaneously addressing the core technical challenges of existing adsorption filtration methods, this invention innovatively employs a two-stage gradient adsorption scheme combining magnesium silicate and diatomaceous earth with precision filtration. Porous food-grade magnesium silicate with a specific surface area ≥300 m² / g and a pore size distribution of 200 nm-300 nm is selected as the primary adsorbent. Its porous structure can precisely adsorb small molecule byproducts such as polar metal complexes and cyclic carbonates, exhibiting high pore size matching, large adsorption capacity, and no interaction with PPCD. To avoid affecting product performance, filter-aid diatomaceous earth with an average pore size of 500μm-550μm and a SiO2 mass fraction of ≥85% is selected as the secondary adsorbent. It can not only deeply adsorb residual trace impurities, but also play a filter aid role, disperse adsorbent agglomerates, prevent filter blockage, and improve filtration efficiency. Finally, it is circulated and filtered through a precision filter press with a filter cloth precision of ≤5μm to completely remove the adsorbent and solid impurities. This fundamentally solves the technical difficulties of existing adsorption filtration such as "incomplete adsorption, low filtration efficiency, and residue residue", and simultaneously eliminates two types of light scattering centers.

[0027] (III) Regarding the structured light scattering centers formed by the entanglement of high molecular weight PPCD chains, the present invention adopts a mild temperature control process throughout the process, and the vacuum dehydration temperature is strictly controlled at 100℃~110℃, which not only achieves the complete removal of moisture, but also avoids the irreversible entanglement and thermal oxidation degradation of molecular chains caused by high temperature, thus eliminating the structured light scattering centers formed by fluctuations in chain segment density.

[0028] (iv) No organic solvents are introduced in any process step of the present invention, no additional side reactions are generated, no new light scattering centers are formed, and it can be fully integrated with the existing PPCD industrial copolymerization production line without adding any complex equipment. It is suitable for industrial scale-up production of 900kg class and above.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention completely eliminates all types of light scattering centers within the PPCD system at its source, breaking through the performance bottleneck of existing technologies. It simultaneously solves the problems of multiple light scattering centers, including residual metal catalysts, cyclic carbonate byproducts, terminal hydroxyl aggregates, and chain entanglement agglomerates. The prepared PPCD products exhibit a transmittance of ≥98% across the entire visible light spectrum from 300nm to 800nm, far exceeding the highest transmittance level of 92.8% in existing technologies. The products also appear completely colorless and water-transparent, truly achieving an optical effect free of scattering centers. Furthermore, this invention overcomes the limitations of molecular weight and functionality, demonstrating excellent purification effects on all PPCDs with number average molecular weights from 1000g / mol to 4000g / mol and functionalities of 2 to 3, overcoming the limitation of existing technologies that can only optimize the transmittance of PPCDs with specific molecular weights.

[0030] 2. This invention achieves zero damage to the core structure of PPCD, fully preserving the product's excellent performance. The invention employs a mild acid-base system and temperature-controlled process, avoiding hydrolysis and thermal degradation of the polycarbonate backbone. Characterization shows that the carbonate bond characteristic peaks of the purified product are complete and clear, without peak shift or intensity attenuation, fully preserving the excellent thermal stability of PPCD. The product's core physicochemical properties, such as hydroxyl value and viscosity, perfectly match the design values, meeting the requirements for subsequent waterborne polyurethane preparation.

[0031] 3. This invention boasts strong process stability, making it suitable for large-scale industrial production, particularly overcoming the challenges of industrial scale-up in the adsorption and filtration process. The two-stage adsorbent combined with precision filtration effectively solves the problems of adsorbent agglomeration, filter clogging, and low filtration efficiency during industrial scale-up. In industrial-scale production (≥900kg), the filtration rate is stable with no clogging, adsorbent utilization is high, and continuous production is possible. Furthermore, the process steps are continuous, parameters are controllable, there are no high-risk operations, and no organic solvents are introduced. It can be directly integrated with existing PPCD industrial copolymerization production lines without the need for additional complex equipment. After scale-up, batch-to-batch performance deviation is ≤2%, metal ion residue is stable at ≤10ppm, transmittance is stable at ≥98%, and product qualification rate is 100%. This addresses the industry pain points of existing laboratory processes being unable to be industrially scaled up and exhibiting unstable adsorption and filtration effects.

[0032] 4. This invention expands the high-end application scenarios of PPCD, combining environmental friendliness and economic efficiency. The colorless, water-permeable PPCD prepared by this invention can be directly used to prepare highly transparent waterborne polyurethane emulsions, breaking through the limitations of existing PPCD applications, which are limited to ordinary coatings and adhesives. This extends its application to high-end fields such as optical-grade coatings, high-transparency leather finishing, and food-grade packaging adhesives. Simultaneously, this invention provides a mature industrialization path for the high-value utilization of carbon dioxide, further reducing the industrial production cost of PPCD and aligning with the strategic requirements of green and sustainable development. Attached Figure Description

[0033] Figure 1 Fourier transform infrared spectra of different PPCD products prepared in the embodiments of this application.

[0034] Figure 2 UV-Vis transmittance spectra of different PPCD systems prepared in the embodiments of this application.

[0035] Figure 3 Thermogravimetric curves of different PPCD products prepared in the embodiments of this application.

[0036] PCCD1-PCCD5 correspond to the PCCD products prepared in Examples 1-5, respectively; PCCD2-A to PCCD2-E correspond to the PCCD products prepared in Examples 2-6, respectively. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] A method for preparing a colorless, water-permeable carbon dioxide-based polycarbonate polyol includes the following steps: S1. Add the crude carbon dioxide-based polycarbonate polyol to the reactor and stir. S2. Heat to 70℃-90℃, add 4wt%-10wt% phosphoric acid aqueous solution, keep warm and stir for 5min-120min, then add alkaline solution, keep warm and stir for a period of time to adjust the pH of the system to 7.0-8.0; S3. Add magnesium silicate and continue stirring while keeping warm for 10-120 minutes. S4. Heat to 100℃-110℃, control the vacuum degree of the system to ≤-0.09MPa, and perform vacuum dehydration under heat and pressure. S5. Cool down to 80℃-90℃, add diatomaceous earth and stir for 10min-120min while keeping warm. S6. Filter the system and take samples for testing. When the total content of metal ions in the system is ≤10ppm, the colorless water-permeable carbon dioxide-based polycarbonate polyol can be obtained.

[0039] In some embodiments, the crude carbon dioxide-based polycarbonate polyol is prepared by copolymerizing propylene oxide and carbon dioxide under the catalysis of a bimetallic catalyst using a polyether polyol as a starting agent.

[0040] In some embodiments, the mass ratio of the crude carbon dioxide-based polycarbonate polyol to the aqueous phosphoric acid solution is 85-100:1-2; example, but not limiting, mass ratios of the crude carbon dioxide-based polycarbonate polyol to the aqueous phosphoric acid solution are 85:1-1.2, 87:1-1.2, 89:1-1.2, 90:1-1.2, 92:1-1.2, 93:1.3-1.5, 94:1.3-1.5, 95:1.3-1.5, 96:1.3-1.5, 98:1.3-1.5, 100:1.3-1.5, etc.; a preferred mass ratio is 87-92:1-1.2, and more preferably 89-90:1-1.1. This ratio provides just the right amount of phosphate, with a slight excess, to completely complex and dissociate the residual DMC metal catalyst under mild conditions of 70-90℃, while maintaining the acidity of the system at an extremely low level to prevent hydrolysis and degradation of the carbonate backbone. If the amount of phosphate is too small, the metal ions will not dissociate completely, and the light scattering centers generated by the metal catalyst cannot be completely eliminated, resulting in a decrease in product transmittance. If the amount of phosphate is too large, the strong acid environment will cause the polycarbonate bonds to hydrolyze and break, resulting in a decrease in molecular weight, deterioration of thermal stability, and the generation of new impurity light scattering centers. At the same time, it will significantly increase the burden of neutralization and desalination, making it impossible for the product to meet the technical requirements of being colorless, water-transparent, and structurally intact.

[0041] In some embodiments, the concentration of the phosphoric acid aqueous solution is 6.8wt%-8.5wt%.

[0042] In some embodiments, the concentration of the alkaline solution is 1wt%-5wt%; example, but not limiting, the concentration of the alkaline solution is 1.5wt%, 2.0wt%, 2.3wt%, 2.5wt%, 2.8wt%, 3.0wt%, 3.2wt%, 3.3wt%, 3.5wt%, 3.7wt%, 4.0wt%, 4.2wt%, 4.4wt%, 4.6wt%, 4.8wt%, 5.0wt%, etc.

[0043] In some embodiments, the stirring speed in the preparation method is 300 r / min-500 r / min; optional speeds include 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, etc.; more preferably, it is 300 r / min-400 r / min. The above-specified rotational speed range is specified for several reasons. First, during acid dissociation and alkali neutralization, this speed ensures that the acid and alkali solutions are rapidly and uniformly dispersed into the crude PPCD product. If the speed is too low, the local acid and alkali concentrations in the crude product may be too high, leading to hydrolysis or saponification of the PPCD main chain. Second, during the treatment of magnesium silicate and diatomaceous earth, this speed ensures effective powder suspension while avoiding excessive shear force that could break the powder into fine particles, affecting the smoothness of subsequent precision filtration. Third, this speed matches the characteristics of industrial scale-up, enabling uniform macroscopic mixing throughout the reactor without causing liquid splashing, shaft power overload, or air entrapment, ensuring stable reproducibility of the process from laboratory pilot-scale testing to industrial production.

[0044] In some embodiments, the temperature in S2 is raised to 77°C-85°C; more preferably, to 80°C-82°C. This temperature range provides the activation energy required for the complexation reaction between phosphate and the residual DMC catalyst, allowing the phosphate to completely dissociate the metal ions in a relatively short time. Furthermore, this temperature, combined with a phosphoric acid solution of a specified concentration, creates a milder dissociation environment, preventing the breaking of carbonate bonds that could lead to a decrease in molecular weight, deviation of hydroxyl value, and a reduction in thermal decomposition temperature, while also preventing the formation of new light scattering centers.

[0045] In some embodiments, the stirring time after adding the phosphoric acid aqueous solution is 20-50 minutes.

[0046] In some embodiments, the pH value in S2 is 7.2-7.6; the alkali includes, but is not limited to, at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0047] In some embodiments, the amount of magnesium silicate used is 0.2%-0.8% of the crude mass of carbon dioxide-based polycarbonate polyol. Examples, but not limited to, are 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, and 0.8% of the crude mass of carbon dioxide-based polycarbonate polyol; preferably 0.3%-0.6%, more preferably 0.4%-0.5%. The range of magnesium silicate usage matches the total amount of metal ions and polar byproducts generated by the slight excess acidolysis and precise neutralization of phosphoric acid in step S2. Under specific surface area and pore size, it can fully capture dissociated metal ions, phosphate complexes, and cyclic carbonate nanoscale scattering centers, while avoiding self-aggregation or occupying too much filter cake volume due to excess, which would lead to a decrease in the filtration aid effect of subsequent diatomaceous earth secondary adsorption or filter cloth clogging during precision filtration.

[0048] In some embodiments, the specific surface area of ​​the magnesium silicate is ≥300 m². 2 / g, with a pore size distribution of 200nm-300nm. Porous magnesium silicate with the above specific surface area and pore size distribution was selected as the primary adsorbent. Its porous structure can accurately adsorb small molecule byproducts such as polar metal complexes and cyclic carbonates. It exhibits high pore size matching, large adsorption capacity, and does not interact with PPCD, thus avoiding any impact on product performance.

[0049] In some embodiments, the heat preservation and stirring time in S3 is 10 min to 60 min; preferably 20 min to 50 min.

[0050] In some embodiments, the temperature in step S4 is raised to 103°C-107°C; the vacuum degree is ≤-0.095MPa; and the vacuum dehydration time is 0.5h-2h.

[0051] In some embodiments, the amount of diatomaceous earth used is 0.2%-0.8% of the crude weight of carbon dioxide-based polycarbonate polyol. Examples, but not limited to, are 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, and 0.8% of the crude weight of carbon dioxide-based polycarbonate polyol; preferably 0.3%-0.6%, more preferably 0.4%-0.5%. If the amount used is too low, the adsorption capacity is insufficient, and the metal ions and polar impurities remaining after the first-stage adsorption cannot be completely removed. If the amount used is too high, it will not only increase the cost, but also exacerbate the filtration resistance due to the enhanced interaction force between adsorbent particles, disrupting the synergistic balance of "high-efficiency adsorption of magnesium silicate + diatomaceous earth filtration aid", making it difficult to achieve stable and smooth filtration operation in 900kg-scale production.

[0052] In some embodiments, the diatomaceous earth has an average pore size of 500μm-550μm and a SiO2 mass fraction of ≥85%. Using filter-aid diatomaceous earth with the above average pore size and SiO2 mass fraction as a secondary adsorbent can not only synergistically adsorb residual trace impurities with magnesium silicate, but also play a filter aid role, disperse adsorbent agglomerates, prevent filter blockage, and improve filtration efficiency.

[0053] In some embodiments, the heat preservation and stirring time in S5 is 10 min to 60 min, preferably 20 min to 50 min.

[0054] In some embodiments, the filtration accuracy in S6 is ≤5μm; preferably 3μm.

[0055] In some implementations, inductively coupled plasma optical emission spectrometry (ICP-OES) is used to detect the total metal ion content.

[0056] A colorless, water-permeable carbon dioxide-based polycarbonate polyol is prepared by the aforementioned preparation method. The number-average molecular weight of the carbon dioxide-based polycarbonate polyol is 1000 g / mol to 4000 g / mol, and the functionality is 2 to 3.

[0057] In some embodiments, the colorless, water-permeable carbon dioxide-based polycarbonate polyol has a transmittance of ≥98% in the wavelength range of 300nm to 800nm.

[0058] In some embodiments, compared with its crude product, the colorless water-permeable carbon dioxide-based polycarbonate polyol has a hydroxyl value deviation of ≤±2mg KOH / g, a rotational viscosity deviation of ≤±500mPa·s at 40°C, and an initial thermal decomposition temperature of ≥250°C under a nitrogen atmosphere.

[0059] In all the following examples and comparative examples, the crude PPCD used was prepared by copolymerization from the same batch, and the characterization and testing methods used all adopted conventional testing standards in the art to ensure the consistency and comparability of the data; the codes and specifications of different carbon dioxide-based polycarbonate polyols are defined as follows: PPCD1: A carbon dioxide-based polycarbonate polyol with a number-average molecular weight of 1000 g / mol and a functionality of 2.

[0060] PPCD2: A carbon dioxide-based polycarbonate polyol with a number-average molecular weight of 2000 g / mol and a functionality of 2.

[0061] PPCD3: A carbon dioxide-based polycarbonate polyol with a number-average molecular weight of 3000 g / mol and a functionality of 2.

[0062] PPCD4: A carbon dioxide-based polycarbonate polyol with a number-average molecular weight of 4000 g / mol and a functionality of 2.

[0063] PPCD5: A carbon dioxide-based polycarbonate polyol with a number-average molecular weight of 2000 g / mol and a functionality of 3.

[0064] Example 1 This embodiment provides a method for preparing colorless, water-permeable carbon dioxide-based polycarbonate polyols, the specific steps of which are as follows: Step S1, Raw material input: Add 900 kg of crude PPCD1 to a 1000 L stainless steel reactor, start stirring, control the speed at 350 r / min, and keep it stable throughout the process; Step S2, Acid-Compound Complexation and Neutralization: The reactor was heated to 80°C, and a pre-prepared aqueous solution of phosphoric acid (938g of 85% industrial-grade phosphoric acid completely dissolved in 10kg of deionized water) was added to the system at a uniform rate. After the addition was complete, the mixture was kept at 80°C and stirred at 350r / min for 30min to complete the complexation and dissociation of the residual metal catalyst in the crude product. Subsequently, a pre-prepared aqueous solution of sodium hydroxide (576g of analytical grade sodium hydroxide completely dissolved in 20kg of deionized water) was added to the system at a uniform rate. After the addition was complete, the mixture was kept at 80°C and stirred at 350r / min for 30min. The pH of the system was measured to be 7.4, indicating that it was weakly alkaline. Step S3, Primary Adsorption Purification: Maintain the system temperature at 80℃ and the rotation speed at 350 r / min, and add a specific surface area of ​​350 m² to the system. 2 / g, 4kg of food-grade magnesium silicate with a pore size distribution of 250nm, were heated and stirred for 30min to fully adsorb and dissociate metal ions, phosphate complexes and cyclic carbonate byproducts. Step S4, Vacuum Dehydration: Heat the reactor to 105℃, turn on the vacuum system, control the system vacuum degree ≤-0.095MPa, maintain the temperature and pressure for vacuum dehydration for 1 hour, and completely remove free water and trace low boiling point impurities from the system. Step S5, Secondary Adsorption Filtration: Cool the system to 85℃, maintain the rotation speed at 350r / min, add 4kg of filter aid diatomaceous earth with an average pore size of 8μm to the system, keep it warm and stir for 30min to deeply adsorb residual impurities and improve the filtration performance of the system at the same time. Step S6, Precision Filtration and Finished Product Testing: The system is circulated and filtered through a precision filter press with a filter cloth precision of 3μm to remove magnesium silicate, diatomaceous earth and adsorbed solid impurities, resulting in a clear and transparent liquid; 100g of sample is taken and the metal ion content is detected by ICP-OES. The total metal ion content is measured to be 7.5ppm, which meets the qualified standard of ≤10ppm. Finally, the colorless water-permeable carbon dioxide-based polycarbonate polyol product (i.e., PCCD1 product) is obtained.

[0065] Example 2 This embodiment provides a colorless, water-permeable carbon dioxide-based polycarbonate polyol and its preparation method, which is basically the same as that in Example 1. The difference is that only the crude PPCD1 in step S1 is replaced with crude PPCD2. The final PCCD2 product has a total metal ion content of 6.2 ppm, which meets the qualified standard of ≤10 ppm.

[0066] Example 3 This embodiment provides a colorless, water-permeable carbon dioxide-based polycarbonate polyol and its preparation method, which is basically the same as that in Example 1. The difference is that only the crude PPCD1 in step S1 is replaced with crude PPCD3. The final PCCD3 product has a total metal ion content of 6.9 ppm, which meets the qualified standard of ≤10 ppm.

[0067] Example 4 This embodiment provides a colorless, water-permeable carbon dioxide-based polycarbonate polyol and its preparation method, which is basically the same as that in Example 1. The difference is that only the crude PPCD1 in step S1 is replaced with crude PPCD4. The final PCCD4 product has a total metal ion content of 7.8 ppm, which meets the qualified standard of ≤10 ppm.

[0068] Example 5 This embodiment provides a colorless, water-permeable carbon dioxide-based polycarbonate polyol and its preparation method, which is basically the same as that in Example 1. The difference is that only the crude PPCD1 in step S1 is replaced with crude PPCD5. The final PCCD5 product has a total metal ion content of 8.1 ppm, which meets the qualified standard of ≤10 ppm.

[0069] Comparative Example 1 This comparative example provides a crude product of carbon dioxide-based polycarbonate polyol PPCD2.

[0070] Comparative Example 2 This comparative example describes a conventional high-temperature decatalyst removal process for existing carbon dioxide-based polycarbonate polyols. It uses the same batch of crude PPCD2 as in Example 2. The specific steps are as follows: 900 kg of crude PPCD2 is added to a reactor, heated to 140°C, and subjected to high-vacuum distillation for 2 hours to remove low-boiling-point impurities. The temperature is then lowered to 80°C, 4 kg of magnesium silicate is added, and the mixture is stirred for 30 minutes. The mixture is then filtered to obtain the final PCCD2-A product. All other test conditions are identical to those in Example 2.

[0071] Comparative Example 3 This comparative example is basically the same as Example 2, except that in step S2, the reactor is heated to 80°C, and a pre-prepared phosphoric acid aqueous solution (938g of 85% industrial-grade phosphoric acid completely dissolved in 10kg of deionized water) is added to the system at a uniform rate. After the addition is complete, the mixture is kept at 80°C and stirred at 350r / min for 60min, without adding sodium hydroxide aqueous solution for neutralization. This comparative example yields the PCCD2-B product. The remaining test conditions are completely consistent with those of Example 2.

[0072] Comparative Example 4 This comparative example is basically the same as Example 2, except for the following steps: In step S2, the reactor is heated to 60°C, and a pre-prepared aqueous solution of phosphoric acid (938g of 85% industrial-grade phosphoric acid completely dissolved in 10kg of deionized water) is added to the system at a uniform rate. After the addition is complete, the mixture is kept at 60°C and stirred at 350r / min for 30min. Subsequently, a pre-prepared aqueous solution of sodium hydroxide (576g of analytical grade sodium hydroxide completely dissolved in 20kg of deionized water) is added to the system at a uniform rate. After the addition is complete, the mixture is kept at 60°C and stirred at 350r / min for another 30min. This comparative example yields the PCCD2-C product. The remaining test conditions are completely consistent with those of Example 2.

[0073] Comparative Example 5 This comparative example is basically the same as Example 2, except that in step S2, the reactor is heated to 80°C, and a pre-prepared phosphoric acid aqueous solution (2143g of 85% industrial-grade phosphoric acid completely dissolved in 10kg of deionized water) is added to the system at a uniform rate. After the addition is complete, the mixture is kept at 80°C and stirred at 350r / min for 30min. Subsequently, a pre-prepared sodium hydroxide aqueous solution (576g of analytical grade sodium hydroxide completely dissolved in 20kg of deionized water) is added to the system at a uniform rate. After the addition is complete, the mixture is kept at 80°C and stirred at 350r / min for another 30min. This comparative example yields the PCCD2-D product. The remaining test conditions are completely consistent with those of Example 2.

[0074] Comparative Example 6 This comparative example is basically the same as Example 2, except that in step S3, the system temperature is maintained at 80°C and the rotation speed is 350 r / min, and a specific surface area of ​​250 m² is added to the system. 2 4 kg of food-grade magnesium silicate with a pore size distribution of 150 nm was added and stirred at a controlled temperature for 30 min to fully adsorb and dissociate metal ions, phosphate complexes, and cyclic carbonate byproducts. This comparative example yielded the PCCD2-E product. All other test conditions were identical to those in Example 2.

[0075] Performance testing methods and results: The samples of the above embodiments and comparative examples were subjected to performance testing and characterization in accordance with conventional characterization and testing methods in the art.

[0076] I. Optical Performance Testing The transmittance of all PCCD products prepared in the examples and comparative examples within the wavelength range of 300–800 nm was tested using a conventional Shimadzu UV-2600 UV-Vis spectrometer. The test results are shown in Table 1 below. The full-band transmittance spectra of the different PCCD products prepared in this invention are shown in [reference needed]. Figure 2 .

[0077] Table 1. Optical performance and appearance test results of the PPCDs prepared in the examples and comparative examples.

[0078] Test results show that the entire series of PPCD1-PCCD5 products prepared by this invention have a transmittance of ≥98% across the entire wavelength range of 300~800nm, and exhibit a colorless, water-clear appearance, which is far superior to the comparative sample. Comparative Example 2, due to high-temperature treatment causing molecular chain entanglement, showed no significant improvement in transmittance compared to its crude product, PCCD2-A. Comparative Example 3, lacking a neutralization step, experienced significant transmittance reduction due to impurities generated by polycarbonate main chain hydrolysis, resulting in a cloudy, yellowish appearance. This fully demonstrates that strict control of the pH after neutralization is necessary to solve the technical problems in the process of this invention. In Comparative Example 4, the acid hydrolysis and complexation temperature was lowered from 80℃ to 60℃. The slow reaction kinetics led to incomplete removal of metal ions, resulting in a slightly yellowish, transparent appearance for PCCD2-C. This indicates that excessively low temperatures affect the acid hydrolysis and complexation efficiency, failing to achieve the colorless, water-clear standard. In Comparative Example 5, the amount of phosphoric acid was increased from 938g to 2143g, and the concentration of the phosphoric acid aqueous solution was increased from approximately 7.3wt% to approximately 15wt%. Excess phosphoric acid introduced a large number of phosphate ions, which, after neutralization, produced excess phosphate exceeding the adsorbent's processing capacity. The transmittance of the finished product PCCD2-D at 800nm ​​and 360nm decreased to 91.8% and 87.5%, respectively, and its appearance was slightly turbid and yellowish. This indicates that excessive phosphoric acid usage actually led to impurity residue and decreased transmittance. In Comparative Example 6, magnesium silicate with a specific surface area of ​​250m² / g and a pore size of 150nm was used instead of the food-grade magnesium silicate with a specific surface area of ​​350m² / g and a pore size of 250nm used in Example 2. The adsorption capacity and selectivity decreased significantly, and the finished product PCCD2-E was slightly yellow and transparent. This indicates that the specific surface area and pore size distribution of magnesium silicate are crucial to the adsorption and purification effect; selecting appropriate specifications is essential for achieving deep impurity removal.

[0079] II. Results of Chemical Structure Characterization The PPCD1-PPCD5 products from Examples 1-5 were tested using a conventional Bruker Tensor II Fourier transform infrared spectrometer. The test curves are shown in the appendix. Figure 1 The results showed that in the FT-IR spectra of all samples, the 1740 cm⁻¹... -1 Characteristic peak of C=O carbonate bond at 1234 cm⁻¹ -1 With 1065cm -1 The COC characteristic peaks are all clear and complete, with no peak position shift or peak intensity attenuation, which fully proves that the preparation process of the present invention does not damage the core chemical structure of PPCD itself.

[0080] III. Test Results of Thermal and Physicochemical Properties The PCCD1-PCCD5 products from the examples were tested using a standard NETZSCH TG 209 F3 thermogravimetric analyzer and a Brookfield DV2T rotational viscometer. The thermogravimetric curves are shown below. Figure 3 The results showed that the initial thermal decomposition temperatures of the finished products in Examples 1-5 were all ≥250℃, completely consistent with the crude raw materials. The hydroxyl values ​​and viscosities of all samples deviated from the design values ​​by ≤±2%, indicating stable core physicochemical properties. In Comparative Example 3, the initial thermal decomposition temperature of the PCCD2-B product decreased to 262℃, and the hydroxyl value deviation reached ±8mg KOH / g, proving that the failure to neutralize the strong acid led to severe damage to the product's structure and performance.

[0081] IV. Downstream Application Validation Results Using the PPCD samples from Example 2 and Comparative Example 1, waterborne polyurethane emulsions were prepared according to conventional processes in the art. The results showed that the WPU emulsion prepared using the colorless, water-permeable PPCD from Example 2 had a transmittance of 82.3% at 800 nm and appeared as a highly transparent light blue color; while the WPU emulsion prepared using the PPCD from Comparative Example 1 had a transmittance of only 68.7% at 800 nm and appeared as a semi-transparent color.

[0082] The above results fully demonstrate that the PPCD product prepared by this invention can significantly improve the transparency of downstream waterborne polyurethane, and is fully compatible with the application requirements of high transparency coatings.

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0084] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a colorless, water-permeable carbon dioxide-based polycarbonate polyol, characterized in that, Includes the following steps: S1. Add the crude carbon dioxide-based polycarbonate polyol to the reactor and stir. S2. Heat to 70℃-90℃, add 4wt%-10wt% phosphoric acid aqueous solution, keep warm and stir for 5min-120min, then add alkaline solution, keep warm and stir for a period of time to adjust the pH of the system to 7.0-8.0; S3. Add magnesium silicate and continue stirring while keeping warm for 10-120 minutes. S4. Heat to 100℃-110℃, control the vacuum degree of the system to ≤-0.09MPa, and perform vacuum dehydration under heat and pressure. S5. Cool down to 80℃-90℃, add diatomaceous earth and stir for 10min-120min while keeping warm. S6. Filter the system and take samples for testing. When the total content of metal ions in the system is ≤10ppm, the colorless water-permeable carbon dioxide-based polycarbonate polyol can be obtained.

2. The method for preparing colorless, water-permeable carbon dioxide-based polycarbonate polyol according to claim 1, characterized in that, The preparation of the crude carbon dioxide-based polycarbonate polyol is as follows: using polyether polyol as a starting agent, propylene oxide and carbon dioxide are copolymerized under the catalysis of a bimetallic catalyst. And / or, the mass ratio of the crude carbon dioxide-based polycarbonate polyol to the aqueous phosphoric acid solution is 85-100:1-2; And / or, the concentration of the alkaline solution is 1wt%-5wt%.

3. The method for preparing colorless, water-permeable carbon dioxide-based polycarbonate polyol according to claim 1, characterized in that, The stirring speed in the preparation method is 300 r / min-500 r / min; And / or, the temperature in S2 is raised to 77℃-85℃; And / or, the pH value described in S2 is 7.2-7.

6.

4. The method for preparing colorless, water-permeable carbon dioxide-based polycarbonate polyol according to claim 1, characterized in that, The amount of magnesium silicate used is 0.2%-0.8% of the crude mass of carbon dioxide-based polycarbonate polyol; And / or, the specific surface area of ​​the magnesium silicate is ≥300 m². 2 / g, with a pore size distribution of 200nm-300nm; And / or, the stirring time in S3 is 10min-60min.

5. The method for preparing colorless, water-permeable carbon dioxide-based polycarbonate polyol according to claim 1, characterized in that, The temperature in S4 is raised to 103℃-107℃; And / or, vacuum degree ≤ -0.095MPa; And / or, the vacuum dehydration time is 0.5h-2h.

6. The method for preparing colorless, water-permeable carbon dioxide-based polycarbonate polyol according to claim 1, characterized in that, The amount of diatomaceous earth used is 0.2%-0.8% of the crude mass of carbon dioxide-based polycarbonate polyol; And / or, the diatomaceous earth has an average pore size of 500μm-550μm and a SiO2 mass fraction ≥85%; And / or, the stirring time in S5 is 10min-60min.

7. The method for preparing colorless, water-permeable carbon dioxide-based polycarbonate polyol according to claim 1, characterized in that, The filtration accuracy of the filter in S6 is ≤5μm.

8. A colorless, water-permeable carbon dioxide-based polycarbonate polyol, prepared by the preparation method according to any one of claims 1-7, characterized in that, The carbon dioxide-based polycarbonate polyol has a number-average molecular weight of 1000 g / mol to 4000 g / mol and a functionality of 2 to 3.

9. The colorless, water-permeable carbon dioxide-based polycarbonate polyol according to claim 8, characterized in that, The colorless, water-permeable carbon dioxide-based polycarbonate polyol has a transmittance of ≥98% in the wavelength range of 300nm to 800nm.

10. The colorless, water-permeable carbon dioxide-based polycarbonate polyol according to claim 8, characterized in that, Compared with its crude product, the colorless water-permeable carbon dioxide-based polycarbonate polyol has a hydroxyl value deviation of ≤±2mg KOH / g and a rotational viscosity deviation of ≤±500mPa·s at 40℃.

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