A supported bifunctional catalyst for the synthesis of CO2-based polycarbonate polyols and its preparation method

Abstract

This invention discloses a supported bifunctional catalyst for the synthesis of CO2-based polycarbonate polyols and its preparation method. First, N-methylimidazolium tert-butylsalicylaldehyde is reacted with 3,4-diaminopyridine to obtain a Schiff base ligand, which is then coordinated with cobalt to obtain a Schiff base metal cobalt complex. Finally, this complex is reacted with chloromethyl polystyrene resin to generate a supported bifunctional Schiff base metal catalyst. When this catalyst is used for the thermocatalytic polymerization of CO2-based polycarbonate polyols, the reaction requires no co-catalyst, the polymerization reaction is relatively mild, carbon dioxide utilization is high, and the generated carbonate fragments reach over 94%; simultaneously, there is no catalyst residue, and the polymerization product is essentially colorless.

Description

Technical Field

[0001] This invention relates to a supported catalyst, specifically to a supported bifunctional catalyst for the synthesis of CO2-based polycarbonate polyols and its preparation method, belonging to the field of thermal catalysts. Background Technology

[0002] Synthesizing polycarbonate from CO2 and epoxides offers advantages such as high atom utilization, good process economy, and significant CO2 emission reduction, making it one of the CO2 chemical utilization technologies with potential for large-scale industrial application. CO2-based polycarbonate polyols prepared by reacting CO2 with propylene oxide are important raw materials for preparing polycarbonate-type polyurethanes. Compared with traditional polyether-type and polyester-type polyurethanes, polycarbonate-type polyurethanes exhibit superior hydrolysis resistance, mechanical properties, and biocompatibility. Furthermore, using polycarbonate polyols as raw materials for polyurethane preparation also helps reduce the generation of volatile organic compounds such as acetaldehyde. Currently, with the increasing demand for polyurethane, research on polycarbonate polyols has received significant attention within the industry. Therefore, polycarbonate polyols prepared based on CO2 and epoxides offer substantial economic, environmental, and social benefits.

[0003] However, catalysts currently available for the synthesis of CO2-based polycarbonate polyols still face a series of problems. Common homogeneous catalysts suffer from difficulties in catalyst extraction and metal ion color contamination. Double-metallic cyanide (DMC) is a commonly used heterogeneous catalyst, but its carbon dioxide utilization rate is low, and it is prone to high-temperature explosive polymerization, posing safety hazards. Summary of the Invention

[0004] One objective of this invention is to provide a supported bifunctional catalyst for the synthesis of CO2-based polycarbonate polyols. This catalyst eliminates the need for a co-catalyst, resulting in a milder polymerization reaction, high carbon dioxide utilization, and no catalyst residue, leading to a virtually colorless polymerization product.

[0005] The second objective of this invention is to provide a method for preparing the above-mentioned supported bifunctional catalyst, which has simple steps and high yield.

[0006] A third objective of this invention is to provide applications of the aforementioned supported bifunctional catalyst.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of this invention provides a supported bifunctional catalyst for the synthesis of CO2-based polycarbonate polyols, with the following molecular structure:

[0009]

[0010] The second aspect of this invention provides a method for preparing the above-mentioned supported bifunctional catalyst, which first synthesizes a Schiff base metal cobalt complex, and then loads it onto polystyrene resin through a chemical reaction to obtain a supported bifunctional Schiff base metal catalyst; the specific steps include:

[0011] (1) N-methylimidazolium tert-butylsalicylaldehyde and 3,4-diaminopyridine were refluxed in methanol for 6 h under an inert atmosphere. The product was purified and then treated to obtain Schiff base ligands. The molar ratio of N-methylimidazolium tert-butylsalicylaldehyde to 3,4-diaminopyridine was 2:1.

[0012] (2) The Schiff base ligand and cobalt acetate were refluxed in methanol under an inert atmosphere for 5 hours, and then the atmosphere was changed to oxygen. Lithium chloride was added to the system and the reaction was continued for 4 hours. After the reaction was completed, the oxygen was removed and the product was purified to obtain the Schiff base metal cobalt complex. The molar ratio of Schiff base ligand to cobalt acetate was 1.1:1 and the molar ratio of cobalt acetate to lithium chloride was 1:1.

[0013] (3) Take chloromethyl polystyrene resin (Merrifield Resin), keep the molar ratio of resin reaction sites to Schiff base metal cobalt complex at 1:1.5, swell in anhydrous N,N-dimethylformamide (DMF) environment for 24 h, and stir for 3 days to obtain a supported bifunctional Schiff base metal catalyst.

[0014] Preferably, the purification and post-treatment methods described in steps (1) and (2) are both recrystallization using petroleum ether.

[0015] Preferably, the stirring speed in step (3) is 350-450 rpm / min.

[0016] A third aspect of the present invention provides the above-mentioned supported bifunctional catalyst for catalyzing the copolymerization of carbon dioxide and propylene oxide to produce CO2-based polycarbonate polyols.

[0017] This invention involves the thermal polymerization of carbon dioxide and propylene oxide under the action of the aforementioned supported bifunctional catalyst to obtain CO2-based polycarbonate polyols. The polymerization reaction is relatively mild, with a reaction temperature ≤65℃ and a reaction pressure ≤2.5MPa. The carbon dioxide utilization rate is high, and the carbonate fragmentation reaches over 94%. At the same time, there is no catalyst residue, resulting in a virtually colorless polymerization product. The molecular weight of the polymerization product is between 700-900 g / mol, and the hydroxyl value is between 110-130 mgKOH / g, making it a superior polyurethane raw material.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The supported bifunctional Schiff base metal catalyst provided by this invention provides a mild reaction condition, requiring no high temperature and pressure, no co-catalyst, and high safety when used for the thermocatalytic polymerization of CO2-based polycarbonate polyols.

[0020] 2. When the supported bifunctional Schiff base metal catalyst provided by this invention is used for the thermocatalytic polymerization of CO2-based polycarbonate polyols, the catalyst can be recovered without residue, and a basically colorless polymerization product is obtained.

[0021] 3. The supported bifunctional Schiff base metal catalyst provided by this invention has a high carbon dioxide utilization rate and the carbonate fragmentation rate reaches more than 94% when used for the thermocatalytic polymerization of CO2-based polycarbonate polyols.

[0022] 4. When the supported bifunctional Schiff base metal catalyst provided by this invention is used for the thermocatalytic polymerization of CO2-based polycarbonate polyols, by adjusting parameters such as catalyst dosage, reaction temperature, pressure, and time, polymer products with molecular weights between 700-900 g / mol and hydroxyl values ​​between 110-130 mg KOH / g can be obtained. Attached Figure Description

[0023] Figure 1 This is a synthetic route for supported bifunctional Schiff base metal catalysts.

[0024] Figure 2 Infrared spectra of chloromethyl polystyrene resin, supported bifunctional Schiff base metal catalyst, and Schiff base cobalt complex.

[0025] Figure 3 A color comparison image of the polymerization product after the catalyst has been filtered out.

[0026] Figure 4 The image shows the 1H NMR spectrum of CO2-based polycarbonate polyols. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments, but are not limited thereto.

[0028] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available products with a purity of analytical grade or higher.

[0029] Example 1: Synthesis of a supported bifunctional Schiff base metal catalyst

[0030] N-methylimidazolium tert-butylsalicylaldehyde (1.2 g, 4.2 mmol) and 3,4-diaminopyridine (0.23 g, 2.1 mmol) were dissolved in methanol and refluxed at 70 °C for 6 h under nitrogen atmosphere. After rotary evaporation, the mixture was dried in a vacuum oven and recrystallized from petroleum ether to obtain the Schiff base ligand.

[0031] Schiff base ligand (1.43 g, 2.1 mmol) and cobalt acetate (0.338 g, 1.91 mmol) were refluxed in methanol for 5 h under nitrogen atmosphere. The nitrogen atmosphere was then removed, replaced with oxygen, and lithium chloride (0.081 g, 1.91 mmol) was added, followed by reflux for another 4 h. After removing the oxygen, the mixture was rotary evaporated, dried, and recrystallized from petroleum ether to obtain the cobalt Schiff base complex.

[0032] 0.5 g of chloromethyl polystyrene resin (Merrifield Resin, 0.5 mmol reaction sites) was swollen in anhydrous N,N-dimethylformamide (DMF) for 24 h. Then, 0.587 g of a cobalt Schiff base complex (0.75 mmol) was added, and the mixture was stirred at 400 rpm / min for 3 days to obtain a supported bifunctional Schiff base metal catalyst with a yield of 83.7%. The reaction route is as follows. Figure 1 As shown.

[0033] Infrared spectra of Schiff base cobalt complexes, supported bifunctional Schiff base metal catalysts, and chloromethyl polystyrene resin are shown below. Figure 2 As shown, the infrared spectrum of the Schiff base cobalt complex at 1640 cm⁻¹ -1 The peak corresponds to the characteristic absorption peak of the C=N group, proving the successful synthesis of the complex. The 905 cm⁻¹ peak in the infrared spectrum after the reaction of chloromethyl polystyrene resin with the Schiff base cobalt complex is... -1 835cm -1 740cm -1 The disappearance of the three corresponding C-Cl peaks indicates that the Schiff base cobalt complex has been successfully chemically loaded onto chloromethyl polystyrene resin, resulting in a supported bifunctional Schiff base metal catalyst.

[0034] Example 2: Application of supported bifunctional Schiff base metal catalysts

[0035] After the reactor is thoroughly dried, 10g of propylene oxide is placed in a reactor equipped with a rotor, and 0.16-0.2g of catalyst is added (no co-catalyst is needed). Carbon dioxide is introduced to 1.5-2.5 MPa, and the reaction is carried out at 55-65℃ for 28-30 hours. After the polymerization reaction is complete, the unreacted propylene oxide is distilled off at 40℃ to constant weight, and the catalyst is filtered out to obtain a nearly colorless purified polymerization product. Figure 3Table 1 shows the data of different CO2-based polycarbonate polyol products obtained under different reaction conditions. The molecular weights of the polymerized products were measured to be 700-900 g / mol, and the hydroxyl values ​​were between 110-130 mgKOH / g. The 1H NMR spectrum of product 1 is shown in the figure. Figure 4 As shown, this proves that the structure of CO2-based polycarbonate polyol is correct.

[0036] The proton NMR data are as follows: 1 ¹H NMR (600MHz, Chloroform-d) δ 4.86 (s, ¹H), 4.53 (s, ¹H), 4.01 (s, ¹H), 2.99 (s, ¹H), 2.75 (s, ¹H), 2.42 (s, ¹H), 1.48 (s, ³H), 1.30 (s, ²H). Based on integrated area calculations, the polycarbonate content in the polymer is 94.5%.

[0037] Table 1: Product Data

[0038]

[0039] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A supported bifunctional catalyst for the synthesis of CO2-based polycarbonate polyols, with the following molecular structure: 。 2. A method for preparing the supported bifunctional catalyst for the synthesis of CO2-based polycarbonate polyols as described in claim 1, characterized in that, Includes the following steps: (1) N-methylimidazolium tert-butylsalicylaldehyde and 3,4-diaminopyridine were refluxed in methanol for 6 h under an inert atmosphere. The product was purified and then treated to obtain Schiff base ligands. The molar ratio of N-methylimidazolium tert-butylsalicylaldehyde to 3,4-diaminopyridine was 2:

1. (2) The Schiff base ligand and cobalt acetate were refluxed in methanol under an inert atmosphere for 5 hours, and then the atmosphere was changed to oxygen. Lithium chloride was added to the system and the reaction was continued for 4 hours. After the reaction was completed, the oxygen was removed and the product was purified to obtain the Schiff base metal cobalt complex. The molar ratio of Schiff base ligand to cobalt acetate was 1.1:1 and the molar ratio of cobalt acetate to lithium chloride was 1:

1. (3) Take chloromethyl polystyrene resin, keep the molar ratio of the resin reaction site to the Schiff base metal cobalt complex at 1:1.5, swell in anhydrous N,N-dimethylformamide for 24 h, and stir for 3 days to obtain a supported bifunctional Schiff base metal catalyst.

3. The method for preparing the supported bifunctional catalyst for the synthesis of CO2-based polycarbonate polyols according to claim 2, characterized in that, The purification and post-treatment methods described in steps (1) and (2) are both recrystallization using petroleum ether.

4. The method for preparing the supported bifunctional catalyst for the synthesis of CO2-based polycarbonate polyols according to claim 2, characterized in that, The stirring speed in step (3) is 350-450 rpm / min.

5. The supported bifunctional catalyst of claim 1 is used to catalyze the copolymerization of carbon dioxide and propylene oxide to produce CO2-based polycarbonate polyols.

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