High molecular weight aliphatic polycarbonate and preparation method thereof

Abstract

The invention belongs to the technical field of carbon dioxide conversion and polymer synthesis, and particularly relates to high-molecular-weight aliphatic polycarbonate and a preparation method thereof. According to the invention, carbon dioxide and aliphatic dihydric alcohol are subjected to dehydration polycondensation to prepare low-polycarbonate, and the low-polycarbonate is connected in series with a melt polycondensation process to prepare high-molecular-weight aliphatic polycarbonate. The method does not need to use an epoxy raw material monomer, and has the advantages of simple preparation process, low cost, controllable molecular weight of the product, designable structure and excellent industrial prospect. Meanwhile, the carbon resource carbon dioxide is effectively converted in the synthesis of the polymer, and the method has important promotion significance for reducing the emission of carbon dioxide and coping with global climate change.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon dioxide conversion and polymer synthesis, and particularly relates to a class of high molecular weight aliphatic polycarbonates and a preparation method thereof. Background Art

[0002] With the continuous advancement of human science and technology, our dependence on fossil energy has gradually increased, resulting in increasing carbon emissions year by year. The resulting greenhouse effect and other climate impacts have reached a point where they cannot be ignored. Currently, carbon dioxide conversion has become one of the hottest topics. Progress has been made in converting carbon dioxide into various chemicals at various levels, but research on converting carbon dioxide into polymers is still not extensive or sufficient. Polymers are high-value-added products, and breakthroughs in converting carbon dioxide into polymers would have significant significance both in terms of environmental protection and economic value.

[0003] Carbon dioxide-based polymers are primarily polycarbonate (PC) materials, which can be divided into indirect carbon dioxide-based polycarbonate (PC) and direct carbon dioxide-based polycarbonate (PC) based on the source of the monomer. Indirect carbon dioxide-based polycarbonate (PC) refers to polycarbonate (PC) produced by converting carbon dioxide into dimethyl carbonate (DMC) and diphenyl carbonate (DPC, a further conversion product of DMC) as carbonate-based monomers, which are then further melt-polycondensed with other dihydroxy monomers. This preparation method is simple and easy to scale up, but the process is relatively long in terms of the conversion of the initial carbon source. Direct carbon dioxide-based polycarbonate (PC), on the other hand, directly uses carbon dioxide as a monomer and polymerizes it with other monomers to obtain polycarbonate. This route has a short process flow, but the process is relatively complex and costly, making it difficult to achieve industrial production.

[0004] Patent application publication number CN117024728A discloses a hyperbranched CO2-based polycarbonate ether polyol, produced from CO2, a polyol initiator, and an epoxide under catalyst catalysis. This polyol can improve the stability of varnish applications and reduce costs. Patent application publication number CN116640295A discloses a water-soluble polycarbonate material and synthesis method. Using polycarbonate prepared by alternating copolymerization of alkylene oxide and CO2 as a raw material, the carboxyl protecting groups on the side chains are removed, carboxyl functional groups are introduced, and a polymer containing carboxylate functional groups is further prepared. This polycarbonate can be used in drug delivery, cancer treatment, genetic diagnosis, antibacterial materials, and other applications. However, these direct CO2-based polycarbonates (PCs) are mostly obtained by copolymerizing CO2 with epoxides, which have harsh reaction conditions and high catalyst costs. Furthermore, some epoxides are flammable and explosive. In addition, carbon dioxide and diols can be dehydrated and condensed to obtain polycarbonate under certain conditions. This method is green and environmentally friendly, has low raw material costs, and is easy to produce on a large scale. However, due to the reaction inertness of carbon dioxide and the reverse effect of the reaction equilibrium of small molecular by-products, it is difficult to obtain high molecular weight polycarbonate (PC).

[0005] Therefore, how to develop a high molecular weight polycarbonate directly polymerized by carbon dioxide and without the participation of epoxy monomers and a preparation method thereof is a technical problem that needs to be solved urgently. Summary of the Invention

[0006] To address the technical challenges of existing carbon dioxide polymerization conversion technologies, such as reliance on epoxy raw material monomers, high catalyst costs, harsh reaction conditions, and difficulty in scalable production, the present invention provides a class of high-molecular-weight aliphatic polycarbonates based on carbon dioxide polycondensation and a method for preparing the same. This method utilizes a dehydration polycondensation of carbon dioxide and an aliphatic diol to prepare polycarbonate oligomers, followed by a subsequent melt polycondensation process to produce the high-molecular-weight aliphatic polycarbonate. This method eliminates the need for epoxy raw material monomers, is simple to manufacture, is cost-effective, and offers controllable product molecular weight and designable structure, demonstrating promising prospects for industrialization.

[0007] In a first aspect, the present invention provides a method for preparing a type of high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation, wherein carbon dioxide and aliphatic diol are used as raw materials, and in the presence of an organic base catalyst and a condensation agent, the carbon dioxide and the aliphatic diol are dehydrated and polycondensed to obtain a low molecular weight polycarbonate; then, in the presence of a polycondensation catalyst, the low molecular weight polycarbonate is melt polycondensed in series to obtain the high molecular weight aliphatic polycarbonate; the low molecular weight polycarbonate is an alcohol hydroxyl terminated oligomer with a degree of polymerization of 1-10.

[0008] The organic base catalyst is at least one of N,N,N',N'-tetramethylethylenediamine (TMEDA), 4-dimethylaminopyridine (DMAP), 4-pyrrolidinylpyridine (PPY), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD), 1,1,3,3-tetramethylguanidine (TMG), and 2-tert-butyl-1,1,3,3-tetramethylguanidine (t-Bu-TMG), preferably DBU, MTBD, and t-Bu-TMG.

[0009] The condensing agent is at least one of dicyclohexylcarbodiimide and diisopropylcarbodiimide, preferably diisopropylcarbodiimide.

[0010] Furthermore, the polycondensation catalyst is at least one of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, lithium acetylacetonate, zirconium acetylacetonate, and cesium carbonate, preferably lithium acetylacetonate.

[0011] Furthermore, the structural formula of the aliphatic diol is:

[0012] Among them, n=2, 3, 4, 5.

[0013] Furthermore, the molar ratio of the aliphatic diol, the organic base catalyst and the condensation agent is: 1: (0.005-0.5): (0.5-0.9).

[0014] Furthermore, the carbon dioxide polycondensation reaction pressure is 1 MPa.

[0015] Furthermore, the mass ratio of the oligocarbonate to the polycondensation catalyst is 1:(0.001-0.005).

[0016] Furthermore, the preparation method of high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation specifically comprises the following steps: R1, dehydration polycondensation of carbon dioxide and aliphatic diol: aliphatic diol, organic base catalyst, and condensation agent are placed in a pressure-resistant autoclave, heated to 130°C in a carbon dioxide atmosphere at 1 MPa for dehydration polycondensation, reacted for 6-24 hours, and then post-treated to obtain oligocarbonate; R2, melt polycondensation of oligocarbonate: placing the oligocarbonate prepared in step R1 and a polycondensation catalyst in a reactor, heating and reacting under an inert gas atmosphere and mechanical stirring to obtain the high molecular weight aliphatic polycarbonate; Furthermore, in step R2, the mixture is first heated to 120-160° C. under an inert gas atmosphere and mechanical stirring for 1-2 hours, and then slowly heated to 220-280° C. and depressurized to 10-50 Pa for melt polycondensation, and the reaction is continued for 4-8 hours.

[0017] Furthermore, the R1 post-treatment process is as follows: after the reaction is completed, an appropriate amount of solvent is added to fully dissolve the oligomer at -20-0°C, filtered, and the filtrate is acid-washed, dried, rotary evaporated and vacuum dried to obtain the low molecular weight prepolymer, i.e., oligocarbonate.

[0018] In a second aspect, the present invention provides a high molecular weight aliphatic polycarbonate based on carbon dioxide condensation obtained by the above-mentioned preparation method, the structural formula of which is:

[0019] Among them, x=4, 6, 8, 10.

[0020] Furthermore, the high molecular weight aliphatic polycarbonate has a number average molecular weight of 40,000-80,000 g / mol.

[0021] Beneficial effects: The present invention provides a high-molecular-weight aliphatic polycarbonate based on carbon dioxide polycondensation and a polycondensation method thereof. The monomers used are carbon dioxide and aliphatic diols, rather than the epoxy compounds used in conventional methods. Furthermore, the process employs a dehydration polycondensation of carbon dioxide and diols to prepare a prepolymer, followed by a subsequent melt polycondensation of the prepolymer. This ensures a sufficiently high molecular weight product while being adaptable to existing production equipment and technology, making it easily scalable and of great significance in terms of both environmental protection and economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The synthetic route for high molecular weight polybutylene carbonate is shown in FIG. Figure 2 The high molecular weight aliphatic polycarbonate in Example 2 1 H-NMR spectrum; Figure 3 This is the gel permeation chromatography (GPC) curve of the high molecular weight aliphatic polycarbonate in Example 2. DETAILED DESCRIPTION

[0023] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0024] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] The preferred embodiments of the present invention will be described in detail below with reference to the examples. It should be understood that the following examples are provided for illustrative purposes only and are not intended to limit the scope of the present invention. Those skilled in the art may make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0026] Test instrument model: The nuclear magnetic resonance spectrometer used was Vaian DLG400 (Varian, USA), and the gel permeation chromatograph used was 1515 (Waters, USA).

[0027] Example 1 (Prepolymerization: Dehydration Polycondensation of Carbon Dioxide and 1,4-Butanediol) 4.506 g of 1,4-butanediol (50 mmol), 0.0761 g of DBU (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were placed in a pressure autoclave. High-purity carbon dioxide was introduced to 1 MPa, followed by release to atmospheric pressure, and this process was repeated three times. Carbon dioxide was then added to 1 MPa, and the reaction was heated to 130°C for 24 h. After cooling to room temperature, the pressure was released, and 15 mL of dichloromethane was added. The mixture was filtered, and the filtrate was washed with 10 mL of 1.0 M hydrochloric acid and 10 mL of deionized water, respectively. The mixture was then dried over anhydrous magnesium sulfate, filtered, rotary evaporated, and vacuum dried at 50°C for 12 h to yield a low molecular weight prepolymer.

[0028] Example 2 (Melt Polycondensation: Synthesis of Polybutylene Carbonate) 12 g of low molecular weight prepolymer and 0.012 g of lithium acetylacetonate were placed in a three-necked flask, the inert gas was replaced three times, and then heated to 160°C and reacted under mechanical stirring for 1 hour. The system pressure was slowly reduced to about 30 Pa, and then slowly heated to 230°C and reacted for 4 hours to obtain high molecular weight polybutylene carbonate.

[0029] The product was characterized by H NMR spectrum and GPC, and the results were shown in Figure 2 、 Figure 3 .

[0030] Example 3 (Prepolymerization: Dehydration Polycondensation of Carbon Dioxide and 1,6-Hexanediol) 5.9085 g of 1,6-hexanediol (50 mmol), 0.0856 g of t-Bu-TMG (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were placed in a pressure autoclave. High-purity carbon dioxide was introduced to 1 MPa, followed by release to atmospheric pressure, and this process was repeated three times. Carbon dioxide was then added to 1 MPa, and the reaction was heated to 130°C for 24 hours. After cooling to room temperature, the pressure was released, and 15 mL of dichloromethane was added. The filtrate was filtered, washed with 10 mL of 1.0 M hydrochloric acid, and then 10 mL of deionized water. The filtrate was then dried over anhydrous magnesium sulfate, filtered, rotary evaporated, and dried under vacuum at 50°C for 12 hours to obtain a low molecular weight prepolymer.

[0031] Example 4 (Melt Polycondensation: Synthesis of Poly(hexanediol Carbonate)) 12 g of low molecular weight prepolymer and 0.012 g of lithium acetylacetonate were placed in a three-necked flask, the inert gas was replaced three times, and then heated to 160°C and reacted under mechanical stirring for 1 hour. The system pressure was slowly reduced to about 30 Pa, and then slowly heated to 240°C and reacted for 4 hours to obtain high molecular weight poly(hexane carbonate).

[0032] Example 5 (Prepolymerization: Dehydration Polycondensation of Carbon Dioxide and 1,8-Octanediol) 7.3115 g of 1,8-octanediol (50 mmol), 0.0856 g of t-Bu-TMG (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were placed in a pressure autoclave. High-purity carbon dioxide was introduced to 1 MPa, followed by release to atmospheric pressure, and this process was repeated three times. Carbon dioxide was then added to 1 MPa, and the reaction was heated to 130°C for 24 hours. After cooling to room temperature, the pressure was released, and 15 mL of dichloromethane was added. The filtrate was filtered, washed with 10 mL of 1.0 M hydrochloric acid, and then 10 mL of deionized water. The filtrate was then dried over anhydrous magnesium sulfate, filtered, rotary evaporated, and vacuum dried at 50°C for 12 hours to obtain a low molecular weight prepolymer.

[0033] Example 6 (Melt Polycondensation: Synthesis of Polyoctane Carbonate) 12 g of low molecular weight prepolymer and 0.012 g of lithium acetylacetonate were placed in a three-necked flask, the inert gas was replaced three times, and then heated to 160°C and reacted for 2 h under mechanical stirring. The system pressure was slowly reduced to about 30 Pa, and then slowly heated to 260°C and reacted for 5 h to obtain high molecular weight polyoctane carbonate.

[0034] Example 7 (Prepolymerization: Dehydration Polycondensation of Carbon Dioxide and 1,10-Decanediol) 8.714 g of 1,10-decanediol (50 mmol), 0.0856 g of t-Bu-TMG (0.5 mmol), and 5.679 g of diisopropylcarbodiimide (45 mmol) were placed in a pressure autoclave. High-purity carbon dioxide was introduced to 1 MPa, followed by release to atmospheric pressure, and this process was repeated three times. Carbon dioxide was then added to 1 MPa, and the reaction was heated to 130°C for 24 hours. After cooling to room temperature, the pressure was released, and 15 mL of dichloromethane was added. The filtrate was filtered, washed with 10 mL of 1.0 M hydrochloric acid, and then 10 mL of deionized water. The filtrate was then dried over anhydrous magnesium sulfate, filtered, rotary evaporated, and vacuum dried at 50°C for 12 hours to obtain a low molecular weight prepolymer.

[0035] Example 8 (Melt Polycondensation: Synthesis of Decanediol Polycarbonate) 12 g of low molecular weight prepolymer and 0.012 g of lithium acetylacetonate were placed in a three-necked flask, the inert gas was replaced three times, and then heated to 160°C and reacted for 2 h under mechanical stirring. The system pressure was slowly reduced to about 30 Pa, and then slowly heated to 280°C and reacted for 5 h to obtain high molecular weight polydecanediol carbonate.

[0036] The above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent structure or equivalent process transformation made using the description of the present invention, or directly or indirectly applied in other related technical fields, are also included in the scope of protection of the present invention.

Claims

1. A method for preparing a high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation, characterized in that: Using carbon dioxide and aliphatic diol as raw materials, under the action of an organic base catalyst and a condensation agent, carbon dioxide and aliphatic diol are dehydrated and polycondensed to obtain a low-molecular-weight polycarbonate; then, under the condition of a polycondensation catalyst, the low-molecular-weight polycarbonate is melt-polycondensed in series to obtain the high-molecular-weight aliphatic polycarbonate; the low-molecular-weight polycarbonate is an alcohol hydroxyl-terminated oligomer with a polymerization degree of 1-10; The organic base catalyst is at least one of N,N,N',N'-tetramethylethylenediamine, 4-dimethylaminopyridine, 4-pyrrolidinylpyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5,7-triazabicyclo[4.4.0]decene-5-ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,1,3,3-tetramethylguanidine and 2-tert-butyl-1,1,3,3-tetramethylguanidine; The condensing agent is at least one of dicyclohexylcarbodiimide and diisopropylcarbodiimide.

2. The method for preparing a high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation according to claim 1, characterized in that: The structural formula of the aliphatic diol is: Among them, n=2, 3, 4, 5.

3. The method for preparing a high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation according to claim 2, characterized in that: The molar ratio of the aliphatic diol, the organic base catalyst and the condensation agent is: 1: (0.005-0.5): (0.5-0.9).

4. The method for preparing a high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation according to claim 3, characterized in that: The polycondensation catalyst is at least one of sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, lithium acetylacetonate, zirconium acetylacetonate and cesium carbonate.

5. The method for preparing a high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation according to claim 4, characterized in that: The mass ratio of the oligomeric carbonate to the polycondensation catalyst is 1:(0.001-0.005).

6. The method for preparing a high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation according to any one of claims 4 to 5, characterized in that: The specific steps include: R1. Dehydration polycondensation of carbon dioxide and aliphatic diol: aliphatic diol, organic base catalyst and condensation agent are placed in a pressure-resistant autoclave, heated to 130° C. in a carbon dioxide atmosphere at 1 MPa for dehydration polycondensation, reacted for 6-24 hours, and then post-treated to obtain oligocarbonate; R2. Melt polycondensation of oligocarbonate: The oligocarbonate prepared in step R1 and a polycondensation catalyst are placed in a reactor, and heated to react under an inert gas atmosphere and mechanical stirring to obtain the high molecular weight aliphatic polycarbonate.

7. The method for preparing a high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation according to claim 6, characterized in that: In the step R2, the mixture is first heated to 120-160° C. in an inert gas atmosphere and mechanically stirred for 1-2 hours, and then slowly heated to 220-280° C. and depressurized to 10-50 Pa for melt polycondensation, and the reaction is continued for 4-8 hours.

8. The method for preparing a high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation according to claim 6, characterized in that: The R1 post-treatment process is as follows: after the reaction is completed, a proper amount of solvent is added to fully dissolve the oligomer at -20-0°C, filtered, and the filtrate is acid-washed, dried, rotary evaporated and vacuum dried to obtain the oligocarbonate.

9. A high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation obtained by the preparation method according to any one of claims 1 to 5, 7 to 8, characterized in that: The structural formula of the high molecular weight aliphatic polycarbonate is: Among them, x=4, 6, 8, 10.

10. The high molecular weight aliphatic polycarbonate based on carbon dioxide polycondensation according to claim 9, characterized in that: The number average molecular weight of the high molecular weight aliphatic polycarbonate is 40000-80000 g / mol.

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