Preparation of bio-based polycarbonate polyol and bimetallic catalyst used in preparation of bio-based polycarbonate polyol

Abstract

The invention belongs to the technical field of high polymer material synthesis and catalysis, and relates to preparation of bio-based polycarbonate polyol and a bimetallic catalyst used in the bio-based polycarbonate polyol, the bimetallic catalyst is composed of a porous carrier and an active component loaded on the porous carrier, the active component is zinc-lithium bimetallic nanoparticles, and the molar ratio of zinc to lithium is (3-5): 1; the bio-based polycarbonate polyol is prepared by adopting the bimetallic catalyst, taking polyol A, carbonate B and polyol C as raw materials, and sequentially carrying out melt ester exchange and polycondensation. Wherein the polyol A is isosorbide, isohexitol or isomannitol, and the carbonate B is diphenyl carbonate or dimethyl carbonate; the temperature of melt ester exchange is 120-160 DEG C, and the temperature of polycondensation is 170-200 DEG C. The catalyst provided by the invention solves the technical problems of low molecular weight, wide distribution, dark color and poor performance of a product caused by high-temperature degradation of bio-based rigid cyclic diol in traditional ester exchange polymerization; the preparation method of the bio-based polycarbonate polyol is simple.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis and catalysis technology, and relates to the preparation of a bio-based polycarbonate polyol and the bimetallic catalyst used therein. Background Technology

[0002] Polycarbonate polyols are a class of polymers whose main chain contains carbonate groups (–O–C(O)–O–) and whose terminal groups are hydroxyl groups. Due to the abundance of polar carbonate units in their molecular structure, these polymers endow the materials with excellent mechanical strength, wear resistance, oil resistance, weather resistance, and a certain degree of hydrolysis resistance, and are widely used as key raw materials in outdoor powder coatings, elastomers, and adhesives.

[0003] Currently, the main synthetic routes for polycarbonate polyols include: phosgene method, transesterification method, ring-opening polymerization of cyclic carbonates, and copolymerization of carbon dioxide and epoxides. Among them, the transesterification method, which uses dimethyl carbonate (DMC) or diphenyl carbonate (DPC) and diols as raw materials, has advantages such as mature technology, high safety, and usually does not require solvents, and is one of the mainstream routes for current industrialization.

[0004] In recent years, to reduce dependence on petroleum resources and improve product sustainability, the synthesis of polycarbonate polyols using bio-based raw materials has become an important research direction. Among them, bio-based rigid cyclic diols derived from sugars, such as isosorbide and isohexide, are considered to be able to significantly increase the glass transition temperature (Tglass transition temperature) of polycarbonate due to their inherent rigid ring structure. g Ideal monomers for modulus and hardness.

[0005] However, successfully applying these bio-based rigid cyclic diols, especially isohexol with its more complex structure and greater steric hindrance, to the industrial production of transesterification faces unprecedented technical challenges that cannot be solved by existing technologies. The core of this challenge lies in the fundamental contradiction between the chemical instability of bio-based rigid cyclic diols and the high-temperature conditions required for transesterification reactions.

[0006] Patent applications CN1060299A and CN101024685A propose the preparation of aliphatic polycarbonate polyols by copolymerizing carbon dioxide and epoxides. The cost of producing the resin is much lower than that of similar resins reported internationally, and it contains more carbonate units with adjustable molecular weight and functionality. However, this method uses a polymer-supported DMC catalyst, which is difficult to separate from the product after polymerization, resulting in poor thermal stability of the product. The residual metal catalyst ions have a significant impact on the application of the resin. At the same time, a certain amount of by-products are also generated during the production process, which are difficult to separate from the product.

[0007] In existing research, Reference 1 (Synthesis of Polycarbonate Diols (PCDLs) via Two-step Process Using CH3COONa as an Effective Catalyst[J]. Chemical Research in Chinese Universities. 2018, 34, 578-583) reported a two-step method for preparing polycarbonate diols using sodium acetate as a catalyst, with DMC and 1,4-butanediol (BD), yielding a product with Mn≈2800 and PDI=1.33. The catalyst could be removed by washing with water. However, it was ineffective with rigid monomers such as isosorbide, and the resulting polymer had a glass transition temperature (Tg). g Its temperature is relatively low, and its heat resistance is limited.

[0008] Furthermore, Reference 2 (Limonene-derived Polycarbonates as Biobased UV-curable (powder) Coating Resins[J]. Progress in Organic Coatings. 2021, 151, 106073) utilized limonene oxide and CO2 copolymerization to prepare bio-based polycarbonates, followed by the introduction of long-chain diols via a transcarbonation reaction, thus achieving the construction of medium-molecular-weight resins. Although the raw materials are derived from natural terpenes, making them environmentally friendly, the uneven crosslinking and insufficient toughness of the product limit its application in high-durability coatings. Further improvements in polymer structure design and optimization of process conditions are important directions for future research.

[0009] In recent years, the development and utilization of bio-based raw materials has become an important research direction in the field of polyols. Isosorbide is a rigid cyclic diol prepared by catalytic hydrogenation of glucose. It is derived from renewable resources and has excellent rigid structure and chemical stability, making it very suitable as a basic monomer for functionalized polycarbonate polyols. This gives the products advantages such as being environmentally friendly, having good weather resistance, and good mechanical properties, and it is particularly suitable for the preparation of outdoor powder coatings.

[0010] Reference 3 (Chemistry, Functionality, and Coating Performance of Biobased Copolycarbonates from 1,4:3,6-Dianhydrohexitols[J]. Journal of Applied Polymer. 2012, 121, 1450–1463) describes a reaction temperature as high as 245°C when using diphenyl carbonate to obtain high molecular weight. This precisely demonstrates that existing technologies cannot avoid the negative impacts of high temperatures, leading to numerous side reactions and impaired product performance. Therefore, although those skilled in the art are aware of the theoretical advantages of bio-based rigid diols, they are hindered in the practice of transesterification due to this irreconcilable contradiction, and cannot obtain high-quality products with intact structures and controllable molecular weights through simple combinations of known technologies.

[0011] Based on the above-mentioned technological status quo, existing technologies generally suffer from the following problems:

[0012] (1) The contradiction between reactivity and degradation risk: To overcome the huge steric hindrance of rigid cyclic diols and achieve effective transesterification, traditional processes must use high temperatures (usually >180℃, or even as high as 245℃). However, at such high temperatures, the secondary hydroxyl groups and their ether bonds in monomer molecules such as isohexol are extremely unstable, and severe intramolecular dehydration, cyclization, thermal oxidative degradation and other side reactions will occur. This directly leads to a deep yellow color of the product, a significantly broadened molecular weight distribution (PDI), the formation of gel particles, and the generation of cyclic byproducts that cannot participate in chain growth, resulting in the inability to effectively increase the molecular weight and the destruction of the end group structure.

[0013] (2) It is difficult to balance catalyst activity and recyclability: Traditional catalysts (such as sodium acetate, titanate, organotin) are effective for flexible chains, but have low catalytic efficiency for rigid monomers; while highly active catalysts (such as bimetallic cyanides) are mostly homogeneous systems, which are difficult to separate from solvent-free melt products, and residual metals affect the thermal stability of the product.

[0014] (3) High temperature is still required in the polycondensation stage: Even if transesterification is completed, the existing technology still requires 210~245℃ in the polycondensation stage to drive chain growth. This temperature is sufficient to cause further thermal aging of the formed oligomers, which is especially unfavorable to bio-based segments containing ether bonds.

[0015] Therefore, it is of great significance to study the preparation of a bio-based polycarbonate polyol and the bimetallic catalyst used therein in order to solve the problems existing in the prior art. Summary of the Invention

[0016] The purpose of this invention is to solve the above-mentioned problems existing in the prior art and to provide a preparation of bio-based polycarbonate polyols and the bimetallic catalyst used therein.

[0017] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0018] A bimetallic catalyst for preparing bio-based polycarbonate polyols comprises a porous support and an active component loaded thereon. The active component is zinc-lithium (Zn-Li) bimetallic nanoparticles, and the molar ratio of zinc to lithium is 3~5:1. This ratio window is not arbitrarily selected, but is a key feasible range determined for this reaction system (high steric hindrance + heat-sensitive monomer). Without this range, it is impossible to obtain bio-based polycarbonate polyols with intact structure, high Tg, and narrow PDI.

[0019] As a preferred technical solution:

[0020] The bimetallic catalyst for preparing bio-based polycarbonate polyols, as described above, uses MOFs as the porous support.

[0021] As described above, a bimetallic catalyst for preparing bio-based polycarbonate polyols uses ZIF-8 or MIL-101 MOFs. The MOFs of this invention play two main roles: first, stabilizing Zn-Li nanoclusters to prevent high-temperature sintering; and second, regulating the spatial orientation of large-volume rigid monomers through pore geometry constraints, thereby increasing the effective collision probability with bifunctional active sites. Studies have found that the pore structures of ZIF-8 (pore size ~3.4 Å) and MIL-101 (mesoporous ~29-34 Å) not only provide physical confinement, but more importantly—for isohexol molecules with a kinetic diameter greater than 6 Å, their rigid configuration prevents them from entering the pores of ZIF-8 or approaching the active site, forcing them to adopt an orientation that facilitates the approach of secondary hydroxyl groups to the Zn-Li bifunctional sites, thus effectively alleviating their inherent steric hindrance. This matching effect among the "support-substrate-active center" is something that traditional non-porous supports (such as SiO2, Al2O3) or homogeneous catalysts cannot achieve. Other MOF materials, such as UiO-66, typically have pore sizes of approximately 6–8 Å, which are larger than ZIF-8. However, their window size is close to the kinetic diameter of isohexol (>6 Å), which may result in a certain confinement effect. Besides MOF materials, common porous supports, such as molecular sieves HZSM-5, HY, and SAPO-34, have smaller pore sizes. Among them, only HY may allow isohexol to approach. Although the pore size of HY molecular sieve (~7.4 Å) can theoretically accommodate isohexol, its strong acidity easily catalyzes ether bond breakage or dehydration cyclization side reactions, leading to a darker product color and a wider molecular weight distribution. Therefore, it cannot play an orientation regulation role in this invention.

[0022] While supporting active components on porous supports is an existing technology, the Zn-Li bimetallic catalyst combination of this invention has unconventional features: ① Synergistic catalytic effect: The molar ratio of Zn to Li (3~5:1) optimizes electronic and geometric effects. Zn provides Lewis acidic sites to promote carbonyl activation, while Li provides basic sites to promote deprotonation. Together, they lower the energy barrier of transesterification, enabling the reaction to proceed efficiently at low temperatures (120~140℃). ② Support confinement effect: The nanopores of MOFs (such as ZIF-8 and MIL-101) not only improve dispersion but also alleviate the huge steric hindrance by spatially confining and regulating the orientation of rigid monomers. ③ Recyclability: The supported catalyst is easy to separate from the product, reducing metal residue. Although supported bimetallic materials (such as Zn-Mg and Li-Al) exist in the prior art, the low-temperature high-efficiency catalytic performance of the Zn-Li combination for bio-based rigid diols (especially isohexotol) has not been reported, and its ratio window is irreplaceable.

[0023] The zinc-lithium bimetallic nanoparticles in the above-mentioned bimetallic catalyst for preparing bio-based polycarbonate polyols have an average particle size of 5~20 nm.

[0024] The present invention also provides a method for preparing bio-based polycarbonate polyol, which uses a bimetallic catalyst as described in any of the preceding claims, and uses polyol A, carbonate B and polyol C as raw materials to sequentially perform melt transesterification and polycondensation to obtain bio-based polycarbonate polyol.

[0025] Polyol A is isosorbide, isohexitol, or isomannitol; carbonate B is diphenyl carbonate or dimethyl carbonate; and polyol C is one or more of the following: ethylene glycol, 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, C5-C12 cycloalkane diols (e.g., 1,4-cyclohexanediol, 1,3-cyclohexanediol), furan ring-containing bio-based diols (e.g., 2,5-furandiol), trimethylolpropane, glycerol, and pentaerythritol.

[0026] The temperature for melt transesterification is 120~160℃, and the temperature for polycondensation is 170~200℃.

[0027] This invention uses a bio-based rigid cyclic diol (isosorbide, isohexol, or isomannitol) as the main monomer, derived from renewable resources (such as glucose). Its rigid ring, acting as a hard segment in the molecular chain, significantly restricts the movement of the molecular chain segments through steric hindrance and configurational locking effects, thereby significantly improving the material's thermal conductivity (T). gModulus, hardness, and dimensional stability. This structural design fundamentally overcomes the performance bottlenecks of traditional flexible chain aliphatic polycarbonate polyols, such as poor temperature resistance, easy creep, and insufficient strength, enabling them to meet the stringent requirements for heat resistance and mechanical strength in high-performance applications (such as outdoor powder coatings). Low-toxicity carbonates (such as diphenyl carbonate and dimethyl carbonate) are used as the carbonyl source, avoiding highly toxic reagents such as triphosgene. No organic solvents are required throughout the process, avoiding the use of highly toxic chemicals. Byproducts (phenol / methanol) can be recovered and reused through distillation, reducing environmental pollution. Compared with the phosgene method and carbon dioxide copolymerization method, the process is simplified and energy consumption is significantly reduced.

[0028] This invention employs a gradient process of "low-temperature transesterification-lower-temperature polycondensation": ① Transesterification stage: carried out at 120-160℃, far below the degradation threshold (typically >180℃), using the high activity of the Zn-Li bimetallic catalyst to suppress side reactions. ② Polycondensation stage: carried out at 170-200℃ under vacuum conditions, removing byproducts and shifting the reaction equilibrium towards the product side, promoting chain growth. Compared to traditional technologies requiring polycondensation temperatures of 200-245℃, this invention significantly lowers the polycondensation temperature to 170-200℃, further suppressing the thermal degradation of bio-based rigid cyclic diols. This temperature separation ensures a match between reaction kinetics and thermodynamics, guaranteeing reaction efficiency while maximizing the suppression of side reactions.

[0029] As a preferred technical solution:

[0030] In the preparation method of the bio-based polycarbonate polyol described above, the melt transesterification time is 2-4 hours; the polycondensation is carried out under vacuum conditions for 0.5-1 hours.

[0031] The method for preparing a bio-based polycarbonate polyol as described above involves a molar ratio of polyol A to carbonate B of 1.05–1.4:1, a molar ratio of polyol A to polyol C of 1–9:1, and an addition amount of a bimetallic catalyst of 0.03–0.05 mol% of carbonate B. The polyol undergoes transesterification and melt polycondensation reactions with the carbonate, achieving hydroxyl end-capping and a medium molecular weight through excess alcohol.

[0032] The method for preparing a bio-based polycarbonate polyol as described above, wherein the number-average molecular weight (M) of the bio-based polycarbonate polyol is... n The value is 2000~3500 (polycarbonate polyols, as resins for powder coatings, typically require M...). n The temperature should not be too high, as this will lead to high melt viscosity, difficult processing, and poor film formation. The molecular weight distribution index (PDI) should be <1.4, and the glass transition temperature (T0) should also be... g ≥60℃.

[0033] Invention principle:

[0034] Traditional thinking holds that high temperature is a necessary condition for promoting transesterification and polycondensation, but the degradation problem of bio-based rigid cyclic diols in high-temperature transesterification polymerization has not yet been effectively solved by existing technologies.

[0035] This invention employs a specially designed Zn-Li bimetallic catalyst, which can significantly reduce the reaction temperature of both the transesterification and polycondensation stages, enabling the reaction to proceed efficiently at low temperatures. This successfully solves the technical bottleneck of easy degradation of bio-based rigid cyclic diols (especially isohexol) in traditional high-temperature polymerization.

[0036] Existing bimetallic systems (such as Zn-Mg, Sn-Zn, and Ti-Al) cannot achieve efficient synergistic catalysis at 120–160 °C due to acid-base mismatch or lack of effective electronic or steric synergy. The Zn-Li bimetallic catalyst of this invention provides Lewis acidic sites to promote carbonyl activation, while Li provides basic sites to promote the deprotonation of secondary hydroxyl groups in rigid diols. Both are co-loaded on a porous support in a specific molar ratio of 3–5:1, synergistically lowering the energy barrier of the transesterification reaction and enabling the reaction to proceed efficiently at low temperatures (120–160 °C). However, in catalyzing the transesterification reaction of bio-based rigid cyclic diols (such as isohexotol) with carbonates, neither Zn nor Li alone can achieve efficient low-temperature polymerization: Zn alone lacks sufficient deprotonation capacity, making it difficult to activate sterically hindered secondary hydroxyl groups; Li alone is too basic, easily initiating ether bond cleavage or intramolecular dehydration side reactions. Not any Zn-Li combination can achieve efficient low-temperature polymerization. Through extensive experimental research, this invention has found that when the molar ratio of Zn to Li is controlled within the range of 3:1 to 5:1, the following conditions can be met simultaneously: (1) the Zn site density is sufficient to effectively activate the carbonyl group of carbonate; (2) the Li site density is sufficient to promote the deprotonation of the secondary hydroxyl group of rigid diol, while avoiding excessively strong overall alkalinity of the system; (3) the two metals form a highly dispersed, stable, and tightly contacted structure on the surface of the support (possibly an electronically coupled bimetallic nanocluster), effectively suppressing phase separation. If Zn:Li < 3:1 (Li excess), the product color is significantly darker (yellow to brown), there are more byproducts, and the GPC spectrum shows shoulder peaks or high molecular weight tails; if Zn:Li > 5:1 (Zn excess), the transesterification conversion rate is less than 60%, the molecular weight is low, it cannot continue to increase, and the molecular weight distribution is wide. Therefore, this ratio window is not arbitrarily selected, but is the only feasible range determined for this reaction system (high steric hindrance + heat-sensitive monomer). Beyond this range, it is impossible to obtain polycarbonate polyols with complete structure, high Tg, and narrow PDI. Therefore, only by strictly controlling the molar ratio of Zn to Li within the window range of 3:1 to 5:1 can spatially proximate Lewis acid-base bifunctional active sites be constructed at the nanoscale. Combined with the confinement effect of porous supports, the simultaneous synergistic activation of carbonate carbonyl groups and deprotonation of glycol hydroxyl groups can be achieved, thus balancing high catalytic activity and high reaction selectivity. Once this ratio window is deviated from, side reactions will dominate, leading to a sharp deterioration in product performance.

[0037] Beneficial effects:

[0038] (1) A bimetallic catalyst for preparing bio-based polycarbonate polyols according to the present invention, Zn-Li bifunctional catalysis reduces the activation energy of transesterification and polycondensation reactions, enabling the reaction to proceed rapidly at a lower temperature and avoiding degradation side reactions (such as dehydration and cyclization) caused by high temperature.

[0039] (2) The present invention provides a bimetallic catalyst for preparing bio-based polycarbonate polyols, which solves the technical problem that bio-based rigid cyclic diols (especially isohexol) are prone to degradation at high temperatures in traditional transesterification polymerization, resulting in products with low molecular weight, wide distribution, dark color and poor performance.

[0040] (3) The present invention provides a method for preparing a bio-based polycarbonate polyol. By combining the synergistic catalytic effect of the Zn-Li bimetallic catalyst with the gradient process of "low-temperature transesterification-lower-temperature polycondensation", the technical bottleneck of easy degradation of bio-based rigid cyclic diols (especially isohexol) in traditional high-temperature polymerization is successfully solved, and highly selective synthesis is achieved. The product has a complete structure, light color, and narrow molecular weight distribution (PDI < 1.4).

[0041] (4) A method for preparing a bio-based polycarbonate polyol according to the present invention, wherein the obtained polycarbonate polyol has a high glass transition temperature (T). g With a temperature of ≥ 60℃, high hardness, and regular end-group structure, it is particularly suitable for high-performance powder coatings.

[0042] (5) The present invention provides a method for preparing a bio-based polycarbonate polyol. The preparation process is simple, the production process avoids the use of organic solvents and highly toxic chemicals, and the by-products phenol or methanol can be recovered and reused through simple distillation, thereby reducing the environmental impact.

[0043] (6) The preparation method of a bio-based polycarbonate polyol of the present invention further reduces energy consumption and thermal degradation risk by lowering the polycondensation temperature to 170~200℃; the catalyst has high efficiency, low dosage and is easy to recycle; the by-products can be recycled and reused, the whole process is environmentally friendly and easy to scale up production. Attached Figure Description

[0044] Figure 1 The NMR spectra are for polycarbonate polyols; where PI0CDL represents IS / DPC=1.05:1 (IS is isosorbide), PI1CDL represents IS / DPC=1.1:1, PI2CDL represents IS / DPC=1.2:1, and PI3CDL represents IS / DPC=1.3:1.

[0045] Figure 2 The GPC spectrum for Comparative Example 1 was obtained using a Waters ACQUITY gel permeation chromatograph.

[0046] Figure 3 The GPC spectrum for Comparative Example 2 was obtained using an Agilent Technologies 1260 Infinity II gel permeation chromatograph. Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0048] The test methods involved in the performance indicators in the embodiments and comparative examples of this invention are as follows:

[0049] Number-average molecular weight and molecular weight distribution index (PDI): The number-average molecular weight and molecular weight distribution index of polycarbonate diols were determined using GPC (mobile phase: DMF). Sample preparation: A certain amount of bio-based polycarbonate polyol sample was fully dissolved in DMF solvent and filtered to prepare a sample with a concentration of 2-3 mg / mL. Polystyrene was used as a standard, DMF was used as the eluent, and the flow rate was set to 1.0 mL / min, the injection volume to 100 μL, the column temperature to 40°C, and the RI detector cell temperature to 40°C.

[0050] Glass transition temperature (T) g The glass transition temperature of the synthesized bio-based polycarbonate polyol was determined by DSC under N2 flow rate of 50 mL / min. Sample mass was 5–10 mg. The test procedure was a heating-cooling-heating sequence with the following parameters: initial temperature 40℃ and held for 1 min; then heating to 200℃ at a rate of 10℃ / min and held for 1 min; then cooling to 0℃ at a rate of 10℃ / min and held for 1 min; finally heating back to 200℃ at a rate of 10℃ / min. The sample was vacuum-dried for 12 h before testing. All thermal performance data were obtained from the second DSC heating.

[0051] Hydroxyl value: The hydroxyl value of bio-based polycarbonate polyols was determined by potentiometric titration using the acetic anhydride-pyridine method according to HG / T 2709-2022 standard. A specified amount of the test sample (m) was weighed into a 150ml beaker. 25mL of a DMF solution (12g / L) of 4-dimethylaminopyridine catalyst was added to the beaker containing the sample. The mixture was stirred continuously on a magnetic stirrer until the sample was completely dissolved. 5mL of acetylation reagent (DMF solution of acetic anhydride with a concentration of 180g / L) was added, and the mixture was stirred for 15min for acetylation. 10mL of water was added, and the reaction was stirred for 5min. 60mL of acetone was added. Subsequently, potentiometric titration was performed using a potassium hydroxide-methanol standard solution (0.5mol / L). The point of maximum potential change was taken as the titration endpoint, and the volume V1 consumed at the titration endpoint was recorded. The recorded value was substituted into formula (1) to calculate the hydroxyl value (-OH%).

[0052] (1).

[0053] Table 1 Experimental Reagents and Materials

[0054] Reagent Name Specification Manufacturer Isohexetol ≥99.8% Rogate diphenyl carbonate ≥99% Aladdin Ethylene glycol 99% Sinopharm Reagent Butylene glycol 99% Titan Hexanediol 99% Titan Octanediol 99% Titan 1,4-Cyclohexanediethanol ≥99.5% Sinopharm Reagent Furandiethanol ≥99% Sinopharm Reagent

[0055] Table 2 Experimental Instruments and Equipment

[0056] Equipment Name model Manufacturer Automatic potentiometric titrator ZDJ-4B Shanghai Instrument & Electronic Science Co., Ltd. Differential Scanning Calorimeter (DSC) Q20 TA Company, USA Nuclear magnetic resonance (NMR) spectrometer Avance III HD 600MHz Swiss Bruker company Gel permeation chromatography (GPC) ACQUITY Waters Company, USA Gel permeation chromatography (GPC) Agilent 1260 Infinity II Agilent Technologies, Inc.

[0057] Example 1

[0058] A method for preparing a bio-based polycarbonate polyol, the specific steps of which are as follows:

[0059] (1) Preparation of raw materials:

[0060] Bimetallic catalyst: It consists of ZIF-8 and the active component supported on it. The active component is zinc-lithium bimetallic nanoparticles with an average particle size of 5 nm and a molar ratio of zinc to lithium of 3:1.

[0061] Polyol A: Isosorbide;

[0062] Carbonate B: Diphenyl carbonate;

[0063] Polyol C: Ethylene glycol;

[0064] (2) In the presence of a bimetallic catalyst, polyol A, carbonate B and polyol C are used as raw materials to undergo melt transesterification and polycondensation in sequence to obtain bio-based polycarbonate polyol.

[0065] The molar ratio of polyol A to carbonate B is 1.05:1, the molar ratio of polyol A to polyol C is 9:1, and the amount of bimetallic catalyst added is 0.03 mol% of carbonate B; the temperature of melt transesterification is 130℃, and the time of melt transesterification is 3 h; polycondensation is carried out under vacuum conditions (pressure <150 Pa), the temperature of polycondensation is 200℃, and the time of polycondensation is 0.5 h.

[0066] The transesterification conversion rate was 85%; the yield of the final bio-based polycarbonate polyol was 83%, the number average molecular weight was 2468, the molecular weight distribution index (PDI) was 1.27, the glass transition temperature (Tg) was 65.4℃, and the hydroxyl value was 52.3 mgKOH / g.

[0067] like Figure 1As shown, when the molar ratio of isosorbide to diphenyl carbonate (IS / DPC) is 1.05:1, 1.1:1, 1.2:1, and 1.3:1, respectively, it can be found that the polymer synthesized using diphenyl carbonate (DPC) exhibits benzoic acid ester end groups, which usually show aromatic proton signals in the range of 7-8 ppm. However, no aromatic proton signals are found in the NMR spectrum, indicating that hydroxyl end capping has been achieved.

[0068] Comparative Example 1

[0069] A method for preparing a bio-based polycarbonate polyol is basically the same as in Example 1, except that the molar ratio of zinc to lithium in the bimetallic catalyst is 2:1.

[0070] The transesterification conversion rate was 68%; the yield of the final bio-based polycarbonate polyol was 65%, the number average molecular weight was 2850, the molecular weight distribution index (PDI) was 2.35, the glass transition temperature (Tg) was 63.8℃, and the hydroxyl value was 39.5 mgKOH / g.

[0071] like Figure 2 As shown, comparing Comparative Example 1 and Example 1, it can be found that the product obtained in Comparative Example 1 is dark yellow in color, has a significantly reduced yield, and a wider molecular weight distribution (PDI = 2.35). This is because the excess Li (Zn:Li = 2:1) leads to an excessively strong alkalinity in the system, which catalyzes side reactions such as the breaking of ether bonds and intramolecular dehydration cyclization in isosorbide molecules, generating a large number of irregularly structured byproducts and disrupting the regularity of the polymer chain.

[0072] In summary, if Zn:Li < 3:1 (Li in excess), the product color is significantly darker (yellow to brown), there are more byproducts, and the molecular weight distribution in the GPC spectrum is wider.

[0073] Comparative Example 2

[0074] A method for preparing a bio-based polycarbonate polyol is basically the same as in Example 1, except that the molar ratio of zinc to lithium in the bimetallic catalyst is 6:1.

[0075] The transesterification conversion rate was 53%; the yield of the final bio-based polycarbonate polyol was 58%, the number average molecular weight was 881, the molecular weight distribution index (PDI) was 2.67, the glass transition temperature (Tg) was 52.3℃, and the hydroxyl value was 127.4 mgKOH / g.

[0076] Comparing Comparative Example 2 with Example 1, it can be found that the transesterification conversion rate and yield of Comparative Example 2 are low, the number average molecular weight of the final product is much lower than 2000, and the molecular weight distribution index (PDI) is 2.67. This is because the excess Zn (Zn:Li=6:1) results in insufficient basic sites (Li) in the system, which cannot effectively activate the sterically hindered secondary hydroxyl groups of the rigid cyclic diol, leading to incomplete transesterification and hindered chain growth, resulting in low molecular weight oligomers with wide distribution.

[0077] like Figure 3 As shown, if Zn:Li > 5:1 (Zn in excess): the transesterification conversion rate is less than 60%, the molecular weight is low and cannot continue to increase, and the molecular weight distribution is wide.

[0078] Example 2

[0079] A method for preparing a bio-based polycarbonate polyol, the specific steps of which are as follows:

[0080] (1) Preparation of raw materials:

[0081] Bimetallic catalyst: It consists of MIL-101 and the active component supported thereon. The active component is zinc-lithium bimetallic nanoparticles with an average particle size of 8 nm and a molar ratio of zinc to lithium of 4:1.

[0082] Polyol A: Isohexetol;

[0083] Carbonate B: Dimethyl carbonate;

[0084] Polyol C: 1,4-Butanediol;

[0085] (2) In the presence of a bimetallic catalyst, polyol A, carbonate B and polyol C are used as raw materials to undergo melt transesterification and polycondensation in sequence to obtain bio-based polycarbonate polyol.

[0086] The molar ratio of polyol A to carbonate B is 1.1:1, the molar ratio of polyol A to polyol C is 7:1, and the amount of bimetallic catalyst added is 0.04 mol% of carbonate B; the temperature of melt transesterification is 120℃, and the time of melt transesterification is 4 h; polycondensation is carried out under vacuum conditions (pressure <150 Pa), the temperature of polycondensation is 190℃, and the time of polycondensation is 0.75 h.

[0087] The transesterification conversion rate was 81%; the yield of the final bio-based polycarbonate polyol was 82%, the number average molecular weight was 2470, the molecular weight distribution index (PDI) was 1.27, the glass transition temperature (Tg) was 68.3℃, and the hydroxyl value was 52.4 mgKOH / g.

[0088] Example 3

[0089] A method for preparing a bio-based polycarbonate polyol, the specific steps of which are as follows:

[0090] (1) Preparation of raw materials:

[0091] Bimetallic catalyst: It consists of ZIF-8 and the active component supported thereon. The active component is zinc-lithium bimetallic nanoparticles with an average particle size of 12 nm and the molar ratio of zinc to lithium is 5:1.

[0092] Polyol A: Isomannitol;

[0093] Carbonate B: Diphenyl carbonate;

[0094] Polyol C: 1,4-cyclohexanediethanol;

[0095] (2) In the presence of a bimetallic catalyst, polyol A, carbonate B and polyol C are used as raw materials to undergo melt transesterification and polycondensation in sequence to obtain bio-based polycarbonate polyol.

[0096] The molar ratio of polyol A to carbonate B is 1.2:1, the molar ratio of polyol A to polyol C is 5:1, and the amount of bimetallic catalyst added is 0.05 mol% of carbonate B; the temperature of melt transesterification is 140℃, and the time of melt transesterification is 2 h; polycondensation is carried out under vacuum conditions (pressure <150 Pa), the temperature of polycondensation is 180℃, and the time of polycondensation is 0.75 h.

[0097] The transesterification conversion rate was 84%; the yield of the final bio-based polycarbonate polyol was 84%, the number average molecular weight was 3466, the molecular weight distribution index (PDI) was 1.28, the glass transition temperature (Tg) was 64.6℃, and the hydroxyl value was 32.7 mgKOH / g.

[0098] Example 4

[0099] A method for preparing a bio-based polycarbonate polyol, the specific steps of which are as follows:

[0100] (1) Preparation of raw materials:

[0101] Bimetallic catalyst: It consists of MIL-101 and the active component supported thereon. The active component is zinc-lithium bimetallic nanoparticles with an average particle size of 15 nm and a molar ratio of zinc to lithium of 3.5:1.

[0102] Polyol A: Isosorbide;

[0103] Carbonate B: Dimethyl carbonate;

[0104] Polyol C: 2,5-furandiethanol;

[0105] (2) In the presence of a bimetallic catalyst, polyol A, carbonate B and polyol C are used as raw materials to undergo melt transesterification and polycondensation in sequence to obtain bio-based polycarbonate polyol.

[0106] The molar ratio of polyol A to carbonate B is 1.3:1, the molar ratio of polyol A to polyol C is 3:1, and the amount of bimetallic catalyst added is 0.03 mol% of carbonate B; the temperature of melt transesterification is 125℃, and the time of melt transesterification is 3.5 h; polycondensation is carried out under vacuum conditions (pressure <150 Pa), the temperature of polycondensation is 175℃, and the time of polycondensation is 1 h.

[0107] The transesterification conversion rate was 85%; the yield of the final bio-based polycarbonate polyol was 87%, the number average molecular weight was 3291, the molecular weight distribution index (PDI) was 1.28, the glass transition temperature (Tg) was 77.3℃, and the hydroxyl value was 34.1 mgKOH / g.

[0108] Example 5

[0109] A method for preparing a bio-based polycarbonate polyol, the specific steps of which are as follows:

[0110] (1) Preparation of raw materials:

[0111] Bimetallic catalyst: It consists of ZIF-8 and the active component supported thereon. The active component is zinc-lithium bimetallic nanoparticles with an average particle size of 18 nm and a molar ratio of zinc to lithium of 4.5:1.

[0112] Polyol A: Isohexetol;

[0113] Carbonate B: Diphenyl carbonate;

[0114] Polyol C: 1,6-hexanediol and 1,8-octanediol in a volume ratio of 1:1;

[0115] (2) In the presence of a bimetallic catalyst, polyol A, carbonate B and polyol C are used as raw materials to undergo melt transesterification and polycondensation in sequence to obtain bio-based polycarbonate polyol.

[0116] The molar ratio of polyol A to carbonate B is 1.4:1, the molar ratio of polyol A to polyol C is 1:1, and the amount of bimetallic catalyst added is 0.05 mol% of carbonate B; the temperature of melt transesterification is 135℃, and the time of melt transesterification is 2.5 h; polycondensation is carried out under vacuum conditions (pressure <150 Pa), the temperature of polycondensation is 170℃, and the time of polycondensation is 1 h.

[0117] The transesterification conversion rate was 87%; the yield of the final bio-based polycarbonate polyol was 89%, the number average molecular weight was 2328, the molecular weight distribution index (PDI) was 1.28, the glass transition temperature (Tg) was 72.4℃, and the hydroxyl value was 53.7 mgKOH / g.

[0118] Example 6

[0119] A method for preparing a bio-based polycarbonate polyol, the specific steps of which are as follows:

[0120] (1) Preparation of raw materials:

[0121] Bimetallic catalyst: It consists of MIL-101 and the active component supported thereon. The active component is zinc-lithium bimetallic nanoparticles with an average particle size of 20 nm and a molar ratio of zinc to lithium of 3:1.

[0122] Polyol A: Isomannitol;

[0123] Carbonate B: Dimethyl carbonate;

[0124] Polyol C: 1,6-Hexanediol;

[0125] (2) In the presence of a bimetallic catalyst, polyol A, carbonate B and polyol C are used as raw materials to undergo melt transesterification and polycondensation in sequence to obtain bio-based polycarbonate polyol.

[0126] The molar ratio of polyol A to carbonate B is 1.3:1, the molar ratio of polyol A to polyol C is 4:1, and the amount of bimetallic catalyst added is 0.03 mol% of carbonate B; the temperature of melt transesterification is 120℃, and the time of melt transesterification is 4 h; polycondensation is carried out under vacuum conditions (pressure <150 Pa), the temperature of polycondensation is 180℃, and the time of polycondensation is 0.75 h.

[0127] The transesterification conversion rate was 85%; the yield of the final bio-based polycarbonate polyol was 87%, the number average molecular weight was 3016, the molecular weight distribution index (PDI) was 1.29, the glass transition temperature (Tg) was 75.6℃, and the hydroxyl value was 37.2 mgKOH / g.

[0128] Example 7

[0129] A method for preparing a bio-based polycarbonate polyol, the specific steps of which are as follows:

[0130] (1) Preparation of raw materials:

[0131] Bimetallic catalyst: It consists of ZIF-8 and the active component supported thereon. The active component is zinc-lithium bimetallic nanoparticles with an average particle size of 10 nm and the molar ratio of zinc to lithium is 5:1.

[0132] Polyol A: Isosorbide;

[0133] Carbonate B: Diphenyl carbonate;

[0134] Polyol C: 1,8-Octanediol;

[0135] (2) In the presence of a bimetallic catalyst, polyol A, carbonate B and polyol C are used as raw materials to undergo melt transesterification and polycondensation in sequence to obtain bio-based polycarbonate polyol.

[0136] The molar ratio of polyol A to carbonate B is 1.2:1, the molar ratio of polyol A to polyol C is 2:1, and the amount of bimetallic catalyst added is 0.04 mol% of carbonate B; the temperature of melt transesterification is 130℃, and the time of melt transesterification is 3 h; polycondensation is carried out under vacuum conditions (pressure <150 Pa), the temperature of polycondensation is 190℃, and the time of polycondensation is 0.75 h.

[0137] The transesterification conversion rate was 88%; the yield of the final bio-based polycarbonate polyol was 93%, the number average molecular weight was 2054, the molecular weight distribution index (PDI) was 1.29, the glass transition temperature (Tg) was 125.4℃, and the hydroxyl value was 55 mgKOH / g.

[0138] Example 8

[0139] A method for preparing a bio-based polycarbonate polyol is basically the same as in Example 1, except that the MOFs in Example 1 are replaced with UiO-66.

[0140] The transesterification conversion rate was 83%; the yield of the final bio-based polycarbonate polyol was 72%, the number average molecular weight was 1850, the molecular weight distribution index (PDI) was 1.45, the glass transition temperature (Tg) was 62.1℃, and the hydroxyl value was 60.5 mgKOH / g.

[0141] Example 9

[0142] A method for preparing a bio-based polycarbonate polyol is basically the same as in Example 1, except that the MOFs in Example 1 are replaced with molecular sieves HY.

[0143] The transesterification conversion rate was 82%, and the yield of the final bio-based polycarbonate polyol was 68%, with a number-average molecular weight of 2100, a molecular weight distribution index (PDI) of 1.85, a glass transition temperature (Tg) of 68.7℃, and a hydroxyl value of 53.2 mgKOH / g.

[0144] Example 10

[0145] A method for preparing a bio-based polycarbonate polyol, the specific steps of which are as follows:

[0146] (1) Preparation of raw materials:

[0147] Bimetallic catalyst: It consists of ZIF-8 and the active component supported on it. The active component is zinc-lithium bimetallic nanoparticles with an average particle size of 10 nm and the molar ratio of zinc to lithium is 4:1.

[0148] Polyol A: Isosorbide;

[0149] Carbonate B: Diphenyl carbonate;

[0150] Polyol C: Trimethylolpropane;

[0151] (2) In the presence of a bimetallic catalyst, polyol A, carbonate B and polyol C are used as raw materials to undergo melt transesterification and polycondensation in sequence to obtain bio-based polycarbonate polyol.

[0152] The molar ratio of polyol A to carbonate B was 1.25:1, the molar ratio of polyol A to polyol C was 9:1, and the amount of bimetallic catalyst added was 0.04 mol% of carbonate B; the temperature of melt transesterification was 135℃, and the time of melt transesterification was 3.5 h; polycondensation was carried out under vacuum conditions (pressure <150 Pa), the temperature of polycondensation was 185℃, and the time of polycondensation was 50 min.

[0153] The transesterification conversion rate was 87%; the yield of the final bio-based polycarbonate polyol was 88%, the number average molecular weight was 2800, the molecular weight distribution index (PDI) was 1.32, the glass transition temperature (Tg) was 61.8℃, and the hydroxyl value was 112 mgKOH / g.

[0154] This embodiment successfully introduced trimethylolpropane as a branching unit, and using the catalyst and low-temperature process of this invention, prepared a bio-based polycarbonate triol with a narrow molecular weight distribution and excellent overall performance. The product maintains a light-colored appearance and a high glass transition temperature, while its branched structure provides moderate viscosity, facilitating subsequent processing and applications.

Claims

1. A bimetallic catalyst for the preparation of a bio-based polycarbonate polyol, characterized by: The porous carrier and the active component loaded thereon, the active component being zinc-lithium bimetallic nanoparticles, and the molar ratio of zinc to lithium being 3-5:

1.

2. The bimetallic catalyst for producing a bio-based polycarbonate polyol according to claim 1, characterized in that, The porous carrier is MOFs.

3. The bimetallic catalyst for producing a bio-based polycarbonate polyol according to claim 2, characterized in that, The MOFs are ZIF-8 or MIL-101.

4. The bimetallic catalyst for producing a bio-based polycarbonate polyol according to claim 1, characterized in that, The average particle size of the zinc-lithium bimetallic nanoparticles is 5-20 nm.

5. A process for the preparation of a bio-based polycarbonate polyol using the bimetallic catalyst according to any one of claims 1 to 4, characterized in that, A bio-based polycarbonate polyol is prepared by sequentially performing melt ester exchange and polycondensation using polyol A, carbonate B and polyol C as raw materials; The polyol A is isosorbide, isohexide or isomannite, the carbonate B is diphenyl carbonate or dimethyl carbonate, and the polyol C is one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, C5-C12 cycloalkanediol, bio-based dihydric alcohol containing furan ring, trimethylolpropane, glycerol and pentaerythritol. The temperature for melt ester exchange is 120-160℃, and the temperature for polycondensation is 170-200℃.

6. The method of making a bio-based polycarbonate polyol according to claim 5, wherein, The time for melt ester exchange is 2-4h, and the time for polycondensation is 0.5-1h under vacuum.

7. The method of making a bio-based polycarbonate polyol according to claim 5, wherein, The molar ratio of polyol A to carbonate B is 1.05-1.4:1, the molar ratio of polyol A to polyol C is 1-9:1, and the addition amount of bimetallic catalyst is 0.03-0.05mol% of carbonate B.

8. The method of making a bio-based polycarbonate polyol of claim 5, wherein, The bio-based polycarbonate polyol has a number average molecular weight of 2000-5000, a molecular weight distribution index of <1.4, and a glass transition temperature of ≥60℃.

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