Method for preparing bio-based polyester-carbonate based on bio-based carbonic acid dicarboxylic acid

Abstract

The invention provides a method for preparing bio-based polyester-carbonate based on bio-based carbonic acid dicarboxylic acid, belongs to the technical field of high polymer materials, and aims to solve the problems that traditional aliphatic polyester is poor in thermal stability and insufficient in mechanical property, aromatic polyester is high in brittleness, synthesis depends on petrochemical raw materials and the like. Synthesizing homopolyester with dihydric alcohol through a melt polycondensation method; the performance optimization of the material is realized by regulating and controlling the flexibility and reaction conditions of the dihydric alcohol chain segment; the obtained homo-polyester has excellent thermal stability and mechanical properties and controllable molecular weight distribution; meanwhile, the aliphatic chain of the BDHC and the carbonic ester group have a synergistic effect, so that the degradation rate and the processing performance are balanced; the process is environment-friendly, does not need a high-activity condensing agent, is suitable for the fields of packaging materials, biomedicine, engineering plastics and the like, and provides an efficient solution for industrial production of the degradable polyester.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic carbonate. Background Art

[0002] In recent years, with the global emphasis on sustainable development and environmental protection, the research and development of biodegradable polymer materials has become a hot topic in the polymer field. Traditional aliphatic polyesters, such as polylactic acid (PLA), polycaprolactone (PCL), polyhydroxybutyrate (PHB), etc., have been widely used in packaging, agriculture, and biomedical fields due to their renewable and biodegradable properties. However, these materials have significant defects: poor thermal stability and insufficient mechanical properties. For example, the glass transition temperature of PLA is about 60°C, and the thermal decomposition temperature is usually lower than 200°C, making it prone to deformation or degradation during high-temperature processing or use; at the same time, it has high brittleness and low elongation at break, making it difficult to meet the application scenarios with high load or high toughness requirements.

[0003] To solve the above problems, researchers have tried to improve the properties of polyesters through chemical modification or copolymerization strategies. A common method is to introduce aromatic monomers to enhance the rigidity of the molecular chain. For example, polyesters incorporating aromatic monomers such as p-hydroxybenzoic acid (HBA) and vanillic acid (VA) significantly improve the thermal stability of the material. Or copolymerize glycolic acid with HBA to balance degradability and heat resistance by adjusting the segment ratio.

[0004] However, the molecular chains of such aromatic polyesters are too rigid, resulting in increased brittleness and decreased toughness of the material, and high-activity condensing agents (such as diphenyl chlorophosphate ester, etc.) need to be used during the synthesis process, increasing the cost and process complexity. In addition, some aromatic monomers are derived from petrochemical raw materials, which is contradictory to the goal of sustainable development.

[0005] Another improvement direction is to design new dicarboxylic acid monomers to optimize properties through molecular structure regulation. The carbonate group is regarded as a key group for improving the comprehensive properties of polyesters due to its high polarity and adjustable chain segment flexibility.

[0006] Traditional aromatic polyesters improve thermal stability through the rigidity of the benzene ring, but their aliphatic chains are short and the molecular chain packing is tight, resulting in limited processing performance and difficult-to-regulate degradation rate. In contrast, as a bio-based substance containing both aliphatic chains and carbonate groups, BDHC theoretically can balance the heat resistance, mechanical properties, and degradability of the material through the synergistic effect of the flexibility of the aliphatic chain and the polarity of the carbonate group.

[0007] However, existing research has paid insufficient attention to BDHC-based polyesters, and the related synthesis methods, structure-property relationships, and large-scale production potential have not been systematically explored.

[0008] In addition, traditional polyester synthesis processes (such as solution polycondensation) often face problems such as solvent residues, high energy consumption, and wide molecular weight distribution. Although the melt polycondensation method can avoid the use of solvents, it has extremely high requirements for monomer reactivity, catalyst efficiency, and process control. In the prior art, the melt polycondensation reaction rate of aliphatic polyesters is relatively slow, while for aromatic polyesters, the reaction is difficult to proceed completely due to the rigidity of the monomers, resulting in a relatively low molecular weight of the final product, which limits their practical applications.

[0009] In summary, the existing degradable polyester materials face the following core problems: traditional aliphatic polyesters have poor thermal stability, while aromatic polyesters have insufficient toughness; they have a high dependence on highly reactive monomers, complex processes, and it is difficult to increase the molecular weight; some raw materials are non-renewable, and the degradation rate does not match the usage requirements.

[0010] Based on this, it is necessary to provide a method for preparing bio-based polyesters with a simple process, which has the advantages of the toughness of traditional aliphatic polyesters and the thermal stability of aromatic polyesters, is easy to adjust the molecular chain properties, and is easy to degrade. Summary of the Invention

[0011] The object of the present invention is to provide a method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic carbonates to solve the problems of poor thermal stability and insufficient mechanical properties of traditional aliphatic polyesters, as well as high brittleness and synthesis dependence on petrochemical raw materials of aromatic polyesters.

[0012] The object of the present invention is achieved as follows:

[0013] A method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic carbonates, the specific steps are as follows:

[0014] Step 1: Weigh a certain amount of bio-based carboxylic acid in a beaker, gradually add deionized water until the solution is clear, and then add an excessive amount of methylimidazole; then transfer the beaker containing the mixture to a thermostatic magnetic stirring platform, keep the temperature at 25±2°C, start the magnetic stirrer and continuously stir until it is confirmed that the carboxyl groups are completely neutralized; after the reaction is complete, use a rotary evaporator to remove the solvent in the mixture under vacuum, and the obtained product is subjected to constant temperature dehydration treatment in an oven for 24 hours to obtain bio-based carboxylic acid-imidazolium salt;

[0015] Step 2: Weigh the bio-based carboxylic acid-imidazolium salt, the waste electrolyte, and the catalyst according to a molar ratio of 2-4:1-1.5:0.01, and add the above reactants to a dry mechanical star stirring device; introduce nitrogen into the stirring device for protection, and heat it to 180-200 °C, then continuously react for 3-5 h; after the reaction is terminated, let it cool naturally, dissolve the viscous product in dichloromethane, and adjust the pH to 2-3 by dropping 6M hydrochloric acid solution. Then, concentrate the acidified solution by rotary evaporation, wash it three times with a washing solvent in a gradient manner, transfer the washed product to a vacuum drying oven for constant temperature drying treatment to obtain the bio-based carboxylic acid ester monomer;

[0016] Step 3: Weigh the diol and the catalyst according to a molar ratio of 2-3:0.01, and add the above reactants to a rotating packed bed reactor. Then, stir and activate the above reactants at room temperature for 30 minutes; subsequently, weigh the bio-based carboxylic acid ester monomer according to a ratio of bio-based carboxylic acid ester monomer:diol = 1:2-3, add the bio-based carboxylic acid ester monomer to the activated rotating packed bed reactor, and install a water separator. Gradually heat the rotating packed bed reactor to 120-160 °C at a gradient heating rate, and introduce nitrogen into the rotating packed bed reactor for protection. Keep the temperature constant within the above temperature range and react for 3 hours; then switch the rotating packed bed reactor to a high vacuum mode and continue to react for 3-5 h until chain growth is completed; after the reaction is terminated, dissolve the molten polymer in dichloromethane to form a 10% concentration solution, slowly pour the above polymer into a vigorously stirred methanol precipitant for gradient precipitation, and collect the precipitated flocculent precipitate; after the collected flocculent precipitate is purified by secondary rotary evaporation, vacuum dry it for 48 h to obtain the target product, which is bio-based poly(ester-carbonate).

[0017] Further, the amount of methylimidazole added in Step 1 is to ensure that the carboxyl groups in the bio-based carboxylic acid are completely converted into carboxyl imidazoles and to ensure that the waste electrolyte in Step 2 fully reacts with the hydroxyl groups.

[0018] Further, the bio-based carboxylic acid is at least one of lactic acid (HL), citric acid (CA), and glycolic acid (GA).

[0019] Further, the waste electrolyte is first mixed with the imidazolium ionic liquid in a molar ratio of 1:1-3, and then the high-boiling carbonate obtained by vacuum distillation at 220 °C - 250 °C for 3 h in a short-path molecular evaporation reactor. The carbonate is a mixture of ethylene carbonate (EC), vinylene carbonate (VC), and propylene carbonate (PC), and the recovery rate of the mixture reaches 80-85%.

[0020] Further, the imidazolium ionic liquid is at least one of 1-methylimidazole chloride, N-methylimidazole bis(trifluoromethanesulfonyl)imide, 1-ethylimidazole p-toluenesulfonate, and 1-octylimidazole trifluoroacetate.

[0021] Further, the catalyst is an organic base, and the organic base is at least one of 1,3-ditolylguanidine, 1-(tolyl)biguanide, and diphenylguanidine.

[0022] Further, the diol is at least one of furan dimethanol (FDM), isosorbide (ISB), and 1,4-cyclohexanedimethanol (CHDM).

[0023] Further, the bio-based carboxylic acid-imidazolium salt (BHAI) is at least one of lactic acid imidazolium salt (HLI), citric acid imidazolium salt (CAI), and glycolic acid imidazolium salt (GAI).

[0024] Further, the bio-based carboxylic acid ester monomer (BDHC) is at least one of dilactic acid carbonate (BDLC), dicitric acid carbonate (BDCC), and dicitric acid carbonate (BDCC).

[0025] Further, the bio-based poly(ester-carbonate) is at least one of poly(dilactic acid-furan dimethanol carbonate) (PLFC), poly(dicitric acid-isosorbide carbonate) (PCIC), and poly(diglycolic acid-cyclohexanedimethanol carbonate) (PGCC).

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The technical solution of the present invention uses BDHC to replace the petroleum-based dibasic acid used in the traditional process and different aromatic dibasic alcohols to synthesize bio-based poly(ester-carbonate) on the basis of the original polyester synthesis process. Moreover, when BDHC is used as a comonomer, the synthesized bio-based poly(ester-carbonate) can improve the thermal stability and toughness of the homopolyester, and the performance of the homopolyester can be adjusted by adjusting different diol segments. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 It is the infrared spectrum of BDHC-based homopolyester;

[0030] Figure 2 In FIG. a is the 1H NMR spectrum of BDHC-based homopolyester; FIG. b is the 13C NMR spectrum of BDHC-based homopolyester;

[0031] Figure 3GPC spectrum of BDHC-based homopolyester;

[0032] Figure 4 DSC spectrum of BDHC-based homopolyester;

[0033] Figure 5 In the figure, a is the TGA graph of BDHC-based homopolyester; b is the DTG graph of the homopolyester;

[0034] Figure 6 In the figure, a is the stress-strain curve graph of BDHC-based homopolyester; b is the graph of tensile strength and elongation at break. Specific implementation mode

[0035] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. If not specifically specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0036] The main method proposed by the present invention to solve the above problems is to use a bio-based carboxylic acid ester monomer (BDHC) as a raw material to react with a diol to prepare a BDHC-based homopolyester. This method can improve the thermal stability and toughness of the homopolyester, and can adjust the performance of the homopolyester by adjusting different diol segments.

[0037] The present invention provides a method for preparing a bio-based polyester-carbonate based on a bio-based dicarboxylic carbonate, and the specific steps are as follows:

[0038] Step 1: Weigh a quantitative bio-based carboxylic acid in a beaker, gradually add deionized water until the solution is clear, and then add an excessive amount of methylimidazole; then transfer the beaker containing the mixture to a thermostatic magnetic stirring platform, keep the temperature at 25±2°C, and start the magnetic stirrer to continuously stir; during the reaction, regularly use pH test paper to detect the change of the pH value of the mixture until it is confirmed that the carboxyl group is completely neutralized; after the reaction is complete, use a rotary evaporator to remove the solvent in the mixture under vacuum, obtain the product, and transfer the product to a vacuum drying oven, maintain the temperature of the drying oven at 40°C, and perform constant temperature dehydration treatment on the product for 24h to obtain a bio-based carboxylic acid-imidazolium salt (BHAI);

[0039] Step 2: Weigh the bio-based carboxylic acid-imidazolium salt (BHAI), the waste electrolyte, and the catalyst according to a molar ratio of 2-4:1-1.5:0.01, and add the above reactants to a dry mechanical star-shaped stirring device; introduce nitrogen into the stirring device for protection, and after heating to 180-200 °C, continuously react for 3-5 h; after the reaction terminates, naturally cool to 25 °C, dissolve the viscous product in dichloromethane, and adjust the pH to 2-3 by dropping 6M hydrochloric acid solution. Then, after concentrating the acidified solution by rotary evaporation, use ethyl acetate as the washing solvent and perform three-gradient washing. Transfer the washed product to a vacuum drying oven and perform constant-temperature drying at 40 °C to obtain the bio-based carboxylic acid ester monomer (BDHC).

[0040] Step 3: Weigh the diol and the catalyst according to a molar ratio of 2-3:0.01, and add the above reactants to a rotating packed bed reactor. Then, stir and activate the above reactants at room temperature for 30 minutes; subsequently, weigh the bio-based carboxylic acid ester monomer (BDHC) according to a ratio of bio-based carboxylic acid ester monomer (BDHC):diol = 1:2-3. Add the bio-based carboxylic acid ester monomer (BDHC) to the activated rotating packed bed reactor, install a water separator, and gradually heat the rotating packed bed reactor to 120-160 °C at a heating rate of 5 °C / min. Introduce nitrogen into the rotating packed bed reactor for protection and maintain a constant reaction at the above temperature range for 3 hours; then switch the rotating packed bed reactor to a high-vacuum mode and continue to react for 3-5 h until chain growth is completed; after the reaction terminates, dissolve the molten polymer in dichloromethane to form a 10% concentration solution, slowly pour the above polymer into a vigorously stirred methanol precipitant for gradient precipitation, and collect the precipitated flocculent precipitate; after the collected flocculent precipitate is purified by secondary rotary evaporation, vacuum dry it at 50 °C for 48 h to obtain the target product, which is a bio-based polyester-carbonate.

[0041] Optionally, the amount of methylimidazole added in Step 1 is to ensure that the carboxyl groups in the bio-based carboxylic acid are completely converted into carboxyl imidazoles and to ensure that the waste electrolyte in Step 2 fully reacts with the hydroxyl groups.

[0042] Specifically, an excessive amount of methylimidazole is added in Step 1 to ensure that the carboxyl groups in the bio-based carboxylic acid are completely converted into carboxyl imidazoles, reduce the influence of carboxyl groups on the hydroxyl group transesterification in the original substance, improve the activity of the hydroxyl groups in the original substance, and ensure that the waste electrolyte in Step 2 fully reacts with the hydroxyl groups to improve its conversion rate.

[0043] Optionally, the bio-based carboxylic acid is at least one of lactic acid (HL), citric acid (CA), and glycolic acid (GA).

[0044] Optionally, the waste electrolyte is first mixed with an imidazole ionic liquid at a molar ratio of 1:1 to 3, and then the high-boiling carbonate obtained by subjecting it to vacuum distillation for 3 h at 220°C to 250°C in a short-path molecular evaporation reactor, and the carbonate is a mixture of ethylene carbonate (EC), vinylene carbonate (VC), and propylene carbonate (PC), and the recovery rate of the mixture reaches 80 to 85%.

[0045] Optionally, the imidazole ionic liquid is at least one of 1-methylimidazole chloride, N-methylimidazole bis(trifluoromethanesulfonyl)imide, 1-ethylimidazole p-toluenesulfonate, and 1-octylimidazole trifluoroacetate.

[0046] Optionally, the catalyst is an organic base, and the organic base is at least one of 1,3-di-o-tolylguanidine, 1-(o-tolyl)biguanide, and diphenylguanidine.

[0047] Optionally, the diol is at least one of furan dimethanol (FDM), isosorbide (ISB), and 1,4-cyclohexanedimethanol (CHDM).

[0048] Optionally, the bio-based carboxylic acid-imidazole ionic salt (BHAI) is at least one of lactate imidazolium salt (HLI), citrate imidazolium salt (CAI), and glycolate imidazolium salt (GAI).

[0049] Optionally, the bio-based carboxylic acid ester monomer (BDHC) is at least one of dilactate carbonate (BDLC), dicitrate carbonate (BDCC), and dicitrate carbonate (BDCC).

[0050] Optionally, the bio-based polyester-carbonate is at least one of poly(dilactate-furan dimethanol) carbonate (PLFC), poly(dicitrate-isosorbide) carbonate (PCIC), and poly(diglycolate-cyclohexanedimethanol) carbonate (PGCC).

[0051] The following is a detailed introduction to the specific embodiments of the present invention:

[0052] Example 1

[0053] The waste electrolyte is mixed with 1-methylimidazole chloride at a molar ratio of 1:1, and then the high-boiling carbonate obtained by subjecting it to vacuum distillation for 3 h at 220°C in a short-path molecular evaporation reactor, and the carbonate is a mixture of ethylene carbonate (EC), vinylene carbonate (VC), and propylene carbonate (PC), and the recovery rate of the mixture reaches 80%.

[0054] Example 2

[0055] The high-boiling carbonate obtained by mixing waste electrolyte with N-methylimidazole bis(trifluoromethanesulfonyl)imide salt at a molar ratio of 1:1.5 and then performing vacuum distillation at 230°C for 3 h through a short-path molecular evaporation reactor, and the carbonate is a mixture of ethylene carbonate (EC), vinylene carbonate (VC), and propylene carbonate (PC), with the mixture recovery rate reaching 82.3%.

[0056] Example 3

[0057] The high-boiling carbonate obtained by mixing waste electrolyte with 1-ethylimidazole p-toluenesulfonate at a molar ratio of 1:2 and then performing vacuum distillation at 240°C for 3 h through a short-path molecular evaporation reactor, and the carbonate is a mixture of ethylene carbonate (EC), vinylene carbonate (VC), and propylene carbonate (PC), with the mixture recovery rate reaching 84.6%.

[0058] Example 4

[0059] The high-boiling carbonate obtained by mixing waste electrolyte with 1-octylimidazole trifluoroacetate at a molar ratio of 1:3 and then performing vacuum distillation at 250°C for 3 h through a short-path molecular evaporation reactor, and the carbonate is a mixture of ethylene carbonate (EC), vinylene carbonate (VC), and propylene carbonate (PC), with the mixture recovery rate reaching 85%.

[0060] Example 5

[0061] The oven was adjusted to 110°C, and all glassware used in the experiment was dried for more than 24 h; a quantitative amount of lactic acid (HL) was taken in a beaker, and deionized water was gradually added until the solution was clear, and then an excessive amount of methylimidazole was added; the beaker containing the compound was transferred to a thermostatic magnetic stirring platform, and the temperature was maintained at 25 ± 2°C. The magnetic stirrer was started and continuously stirred. The pH value of the mixture was regularly detected using pH test paper until it was confirmed that the carboxyl group was completely neutralized; after the reaction was complete, the solvent in the system was removed under vacuum using a rotary evaporator to obtain the product, and the product was transferred to a vacuum drying oven. The temperature of the drying oven was maintained at 40°C, and the product was subjected to constant-temperature dehydration treatment for 24 h to obtain lactic acid imidazolium salt (HLI).

[0062] Example 6

[0063] The oven was adjusted to 110 °C, and all glassware used in the experiment was dried for more than 24 h; a certain amount of citric acid (CA) was taken in a beaker, and deionized water was gradually added until the solution was clear, and then an excessive amount of methylimidazole was added; the beaker containing the compound was transferred to a thermostatic magnetic stirring platform, and the magnetic stirrer was started to continuously stir under the condition of maintaining the temperature at 25 ± 2 °C. The pH value of the mixture was regularly detected using pH test paper until it was confirmed that the carboxyl group was completely neutralized; after the reaction was complete, the solvent in the system was removed under vacuum using a rotary evaporator to obtain the product, and the product was transferred to a vacuum drying oven. The temperature of the drying oven was maintained at 40 °C, and the product was subjected to constant-temperature dehydration treatment for 24 h to obtain citric acid imidazolium salt (CAI).

[0064] Example 7

[0065] The oven was adjusted to 110 °C, and all glassware used in the experiment was dried for more than 24 h; a certain amount of glycolic acid (GA) was taken in a beaker, and deionized water was gradually added until the solution was clear, and then an excessive amount of methylimidazole was added; the beaker containing the compound was transferred to a thermostatic magnetic stirring platform, and the magnetic stirrer was started to continuously stir under the condition of maintaining the temperature at 25 ± 2 °C. The pH value of the mixture was regularly detected using pH test paper until it was confirmed that the carboxyl group was completely neutralized; after the reaction was complete, the solvent in the system was removed under vacuum using a rotary evaporator to obtain the product, and the product was transferred to a vacuum drying oven. The temperature of the drying oven was maintained at 40 °C, and the product was subjected to constant-temperature dehydration treatment for 24 h to obtain glycolic acid imidazolium salt (GAI).

[0066] Example 8

[0067] The oven was adjusted to 110 °C, and all glassware used in the experiment was dried for more than 24 h; lactate imidazolium salt (HLI), waste electrolyte, and catalyst were weighed according to a molar ratio of 2:1:0.01, and the above reactants were added to a dry mechanical star-shaped stirring device. Nitrogen was introduced into the stirring device for protection, and after heating to 180 °C, the reaction was continued for 3 h; after the reaction was terminated, it was naturally cooled to 25 °C, the viscous product was dissolved in dichloromethane, and 6M hydrochloric acid solution was added dropwise to adjust the pH to 2 - 3; then the acidified solution was concentrated by rotary evaporation, and ethyl acetate was used as the washing solvent for three gradient washings (the amount of solvent used each time was 3 times the volume of the product), and finally it was dried in a vacuum environment at 40 °C to obtain bis(lactate) carbonate (BDLC);

[0068] Example 9

[0069] The oven was adjusted to 110 °C, and all glassware used in the experiment was dried for more than 24 h; citric acid imidazolium salt (CAI), waste electrolyte and catalyst were weighed according to the molar ratio of 3:1.2:0.01, and the above reactants were added to a dry mechanical star-shaped stirring device. Nitrogen was introduced into the stirring device for protection, and the temperature was raised to 190 °C and the reaction was continued for 3 h; after the reaction was terminated, the temperature was naturally cooled to 25 °C, the viscous product was dissolved in dichloromethane, and 6 M hydrochloric acid solution was added dropwise to adjust the pH to 2-3; then the acidified solution was concentrated by rotary evaporation, ethyl acetate was used as the washing solvent, and three gradient washings were carried out (the solvent dosage for each time was 3 times the volume of the product), and finally dried in a vacuum environment at 40 °C to obtain bis(citric acid) carbonate (BDCC);

[0070] Example 10

[0071] The oven was adjusted to 110 °C, and all glassware used in the experiment was dried for more than 24 h; glycolic acid imidazolium salt (GAI), waste electrolyte and catalyst were weighed according to the molar ratio of 4:1.5:0.01, and the above reactants were added to a dry mechanical star-shaped stirring device. Nitrogen was introduced into the stirring device for protection, and the temperature was raised to 200 °C and the reaction was continued for 3 h; after the reaction was terminated, the temperature was naturally cooled to 25 °C, the viscous product was dissolved in dichloromethane, and 6 M hydrochloric acid solution was added dropwise to adjust the pH to 2-3; then the acidified solution was concentrated by rotary evaporation, ethyl acetate was used as the washing solvent, and three gradient washings were carried out (the solvent dosage for each time was 3 times the volume of the product), and finally dried in a vacuum environment at 40 °C to obtain bis(glycolic acid) carbonate (BDGC);

[0072] Example 11

[0073] The oven was adjusted to 110 °C, and all glassware used in the experiment was dried for more than 24 h; Furan dimethanol (FDM) and the catalyst were weighed according to a molar ratio of 2:0.01 in a high-gravity reactor, and then the above reactants were stirred and activated at room temperature for 30 minutes; Subsequently, bis (lactic acid carbonate) (BDLC) was weighed according to a molar ratio of bis (lactic acid carbonate) (BDLC): furan dimethanol (FDM) = 1:2, and bis (lactic acid carbonate) (BDLC) was added to the activated high-gravity reactor, and a water separator was installed. The high-gravity reactor was heated to 120 °C at a heating rate of 5 °C / min, and nitrogen was introduced into the high-gravity reactor for protection. The reaction was kept at a constant temperature within the above temperature range for 3 h; Then, the high-gravity reactor was switched to a high-vacuum mode and continued to react for 3 h to complete chain growth; After the reaction was terminated, the molten polymer was dissolved in dichloromethane to form a 10% concentration solution, and the above solution was slowly poured into a vigorously stirred methanol precipitant (solvent / precipitant volume ratio 1:10) for gradient precipitation; And the precipitated flocculent precipitate was collected. After the collected flocculent precipitate was purified by secondary rotary evaporation, it was vacuum dried at 50 °C for 48 h to obtain the target product, named poly (lactic acid carbonate-furan dimethanol ester) (PLFC).

[0074] Example 12

[0075] The oven was adjusted to 110 °C, and all glassware used in the experiment was dried for more than 24 h; Isosorbide (ISB) and the catalyst were weighed according to a molar ratio of 2.5:0.01 in a high-gravity reactor, and then the above reactants were stirred and activated at room temperature for 30 minutes; Subsequently, bis (citric acid carbonate) (BDCC) was weighed according to a molar ratio of bis (citric acid carbonate) (BDCC): isosorbide (ISB) = 1:2.5, and bis (lactic acid carbonate) (BDLC) was added to the activated high-gravity reactor, and a water separator was installed. The high-gravity reactor was heated to 140 °C at a heating rate of 5 °C / min, and nitrogen was introduced into the high-gravity reactor for protection. The reaction was kept at a constant temperature within the above temperature range for 3 h; Then, the high-gravity reactor was switched to a high-vacuum mode and continued to react for 4 h to complete chain growth; After the reaction was terminated, the molten polymer was dissolved in dichloromethane to form a 10% concentration solution, and the above solution was slowly poured into a vigorously stirred methanol precipitant (solvent / precipitant volume ratio 1:10) for gradient precipitation; And the precipitated flocculent precipitate was collected. After the collected flocculent precipitate was purified by secondary rotary evaporation, it was vacuum dried at 50 °C for 48 h to obtain the target product, named poly (citric acid carbonate-isosorbide ester) (PCIC).

[0076] Example 13

[0077] The oven was adjusted to 110 °C, and all glass instruments used in the drying experiment were dried for more than 24 h; 1,4-cyclohexanedimethanol (CHDM) and the catalyst were weighed at a molar ratio of 3:0.01 in a rotating packed bed reactor, and then the above reactants were stirred and activated at room temperature for 30 minutes; Subsequently, bis(2-hydroxyethyl) carbonate (BDGC) was weighed at a molar ratio of bis(2-hydroxyethyl) carbonate (BDGC):1,4-cyclohexanedimethanol (CHDM) = 1:3, and bis(2-lactate) carbonate (BDLC) was added to the activated rotating packed bed reactor, and a water separator was installed. The temperature of the rotating packed bed reactor was raised to 160 °C at a heating rate of 5 °C / min, and nitrogen was introduced into the rotating packed bed reactor for protection. The reaction was kept at a constant temperature within the above temperature range for 3 h; Then, the rotating packed bed reactor was switched to a high vacuum mode and continued to react for 5 h to complete chain growth; After the reaction was terminated, the molten polymer was dissolved in dichloromethane to form a 10% concentration solution, and the above solution was slowly poured into a vigorously stirred methanol precipitant (solvent / precipitant volume ratio 1:10) for gradient precipitation; And the precipitated flocculent precipitate was collected. After the collected flocculent precipitate was purified by secondary rotary evaporation, it was vacuum dried at 50 °C for 48 h to obtain the target product, named poly(glycolic acid-co-cyclohexanedimethylene carbonate) (PGCC).

[0078] It can be seen from Figure 1 that in the above reaction product, the hydroxyl group is at 3400 cm-1, the stretching vibration peak of the ester group is at 1750 cm-1, and the symmetric stretching absorption peak of the methylene group in the chain is at 2910 cm-1. The above test results indicate that the product is the target product.

[0079] It can be seen from Figure 2 that the molecular formulas on the left from top to bottom are: PLFC, PCIC, and PGCC; With the spatial structure and electronic effect of the dibasic acid, the -CH2 in isosorbide in Figure a gradually moves to the low-frequency region from 5.42 ppm; In Figure b, the characteristic peak of -CH2 on BDHC changes little, but gradually moves to the high-frequency region with the increase of the rigidity of the diol chain segment.

[0080] It can be seen from Figure 3 that the number-average molecular weight of the above reaction product is 25 - 71 kg / mol, indicating that the molecular weight distribution index of the product is 1.70 - 2.45.

[0081] It can be seen from Figure 4 that the Tg of the above reaction product is 55.4 - 76.3 °C, and the Tm is 242.2 - 253.4 °C; This is because the introduction of the carbonate group further increases the intermolecular force and improves the rigidity of the molecular chain. The existence of the carbonate group structure restricts the regular arrangement of the polymer molecular chain and cannot present a regular crystal form under the action of temperature.

[0082] It can be seen from Figure 5 a that at 600 °C, the residual mass percentage (Rw) of the above reaction product is in the range of 10.2-17.8%, and from Figure 5 b, it can be seen that the first inflection point of the curve is the initial decomposition temperature (Td,5%) of 248.5-260.3 °C, and the peak of the curve is the highest decomposition temperature (Td,max) of 310.0-357.3 °C; as the flexibility of the bio-based carbonate diol polyester segment increases, its Young's modulus ranges from 2037 MPa to 2435 MPa, and the fracture strength ranges from 22 MPa to 45 MPa.

[0083] It can be seen from Figure 6 a that there are obvious yield points in the stress-strain curves of BDHC-based homopolyesters, which is the same as that of typical thermoplastics; from Figure 6 b, it can also be found that BDHC-based homopolyesters have good elastic behavior and high tensile strength.

[0084] Combining the data in the figure, the performance of three common bio-based homopolyesters on the market is compared as shown in Table 1:

[0085] Table 1 Comparison of the properties of BDHC-based high-performance homopolyesters and commercially available polyesters

[0086]

[0087] As can be seen from Table 1, the initial decomposition temperature (Td,5%) of the BDHC-based homopolyester obtained by weighing BDGC, 1,4-cyclohexanedimethanol CHDM and the catalyst in a molar ratio of 1:3:0.01 is as high as 260.3 °C, which is higher than that of polylactic acid (PLA) and polycaprolactone (PCL). It is suitable for high-temperature processing (such as injection molding and blow molding) and high-temperature use environments (such as electronic packaging materials), while maintaining biodegradable characteristics. Moreover, different material properties can be achieved by adjusting the type of diol (for example, the breaking strength of the BDHC-based homopolyester obtained by weighing BDLC, FDM and the catalyst in a molar ratio of 1:2:0.01 reaches 45 MPa), which can adapt to different application scenarios; the melting point of the BDHC-based homopolyester is much higher than that of PLA and PCL (for example, PCIC obtained by weighing BDCC, ISB and the catalyst in a molar ratio of 1:2.5:0.01), which is suitable for high-temperature applications (such as automotive parts); and the synthesis process of the BDHC-based homopolyester uses melt polycondensation method, without solvents, low energy consumption and no residue, and its environmental protection is better than the traditional solution polycondensation method; if BDHC is from a bio-based source, it can also reduce the dependence on petroleum resources, meeting the sustainable development goals. In terms of applications, due to the combination of heat resistance and degradability of the BDHC-based homopolyester, it can replace polylactic acid (PLA) for hot-fill food containers, and it is superior to polycaprolactone (PCL) in terms of strength and controllability of degradation rate, making it suitable for orthopedic fixation materials or drug sustained-release carriers.

[0088] In summary, as the diol in the homopolyester changes from furan dimethanol (FDM) to 1,4-cyclohexanedimethanol (CHDM), the tensile strength of the polyester increases significantly; on the one hand, this change is due to the restricted rotation of the furan ring in the polyester chain segment. Since the cyclohexyl group offsets the limitation of the non-rotatable structure in the structure, the addition of diol improves the entanglement between the flexibility and molecular weight of the polyester, thus significantly enhancing the polymer strength; this phenomenon is consistent with the trend of mechanical property changes caused by introducing other diols into the polyester; therefore, it can be concluded that dicarbonate diacid as a comonomer can introduce carbonate groups into the polyester without damaging the mechanical and thermal properties, so as to achieve the purpose of optimizing the polyester properties.

[0089] The present invention relates to a method for preparing bio-based polyester-carbonate based on bio-based dicarbonic acid; the present invention solves the problems of poor thermal stability of traditional aliphatic polyesters, insufficient toughness of aromatic polyesters, low degradation rate and high dependence on highly active monomers, complex processes and difficulty in increasing the molecular weight, and can be used for the industrial production of new biodegradable polyesters.

[0090] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claimed rights.

Claims

1. A method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate, characterized in that: The specific steps are as follows: Step 1: weigh a quantitative amount of bio-based carboxylic acid in a beaker, gradually add deionized water until the solution is clear, and then add an excess of methylimidazole; then transfer the beaker containing the mixture to a constant temperature magnetic stirring platform, maintain the temperature at 25±2°C, start the magnetic stirrer and continue stirring until it is confirmed that the carboxyl group is completely neutralized; after the reaction is complete, use a rotary evaporator to vacuum remove the solvent in the mixture, and then perform a constant temperature dehydration treatment for 24 hours in a drying oven to obtain a bio-based carboxylic acid-imidazole ion salt; Step 2: weighing bio-based carboxylic acid-imidazole ion salt, waste electrolyte and catalyst according to a molar ratio of 2-4:1-1.5:0.01, and adding the above reactants into a dry mechanical star-shaped stirring device; introducing nitrogen into the stirring device for protection, and heating to 180-200°C, and continuing the reaction for 3-5 hours; after the reaction is terminated, the temperature is naturally lowered, the viscous product is dissolved in dichloromethane, and a 6M hydrochloric acid solution is added dropwise to adjust the pH to 2-3, and then the acidified solution is concentrated by rotary evaporation, and washed three times with a washing solvent in a gradient manner, and the washed product is transferred to a vacuum drying oven for constant temperature drying treatment to obtain a bio-based carboxylic acid ester monomer; Step 3: weigh diol and catalyst according to a molar ratio of 2 to 3:0.01, and add the above reactants to the supergravity reactor, and then stir and activate the above reactants at room temperature for 30 minutes; then weigh the bio-based carboxylate monomer according to the molar ratio of bio-based carboxylate monomer: diol = 1:2 to 3, add the bio-based carboxylate monomer to the activated supergravity reactor, install a water separator, gradually heat the supergravity reactor to 120 to 160°C at a gradient heating rate, and introduce nitrogen protection into the supergravity reactor, and maintain a constant temperature reaction within the above temperature range for 3 hours; then switch the supergravity reactor to a high vacuum mode and continue the reaction for 3 to 5 hours until the chain growth is completed; after terminating the reaction, dissolve the molten polymer in dichloromethane to form a 10% concentration solution, slowly pour the above polymer into a vigorously stirred methanol precipitant to implement gradient precipitation, and collect the precipitated flocculent precipitate; the collected flocculent precipitate is purified by secondary rotary evaporation and vacuum dried for 48 hours to obtain the target product, which is bio-based polyester-carbonate.

2. The method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate according to claim 1, characterized in that: The amount of methylimidazole added in step 1 is to ensure that the carboxyl groups in the bio-based carboxylic acid are completely converted into carboxyimidazole and to ensure that the waste electrolyte in step 2 fully reacts with the hydroxyl groups.

3. The method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate according to claim 1, characterized in that: The bio-based carboxylic acid is at least one of lactic acid, citric acid, and glycolic acid.

4. The method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate according to claim 1, characterized in that: The waste electrolyte is first mixed with an imidazolium ionic liquid in a molar ratio of 1:1 to 3, and then subjected to reduced pressure distillation at 220°C to 250°C for 3 hours in a short-range molecular evaporation reactor to obtain a high-boiling point carbonate, and the carbonate is a mixture of ethylene carbonate, vinylene carbonate, and propylene carbonate, and the recovery rate of the mixture reaches 80 to 85%.

5. The method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate according to claim 4, characterized in that: The imidazolium ionic liquid is at least one of 1-methyl imidazolium chloride, N-methyl imidazolium bis(trifluoromethanesulfonyl) imide, 1-ethyl imidazolium p-toluenesulfonate, and 1-octylimidazole trifluoroacetate.

6. The method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate according to claim 1, characterized in that: The catalyst is an organic base, and the organic base is at least one of 1,3-di-o-tolylguanidine, 1-(o-tolyl)biguanidine and diphenylguanidine.

7. The method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate according to claim 1, characterized in that: The diol is at least one of furandimethanol, isosorbide and 1,4-cyclohexanedimethanol.

8. The method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate according to claim 1, characterized in that: The bio-based carboxylic acid-imidazole ion salt is at least one of lactic acid imidazolate, citric acid imidazolate, and glycolic acid imidazolate.

9. The method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate according to claim 1, characterized in that: The bio-based carboxylate monomer is at least one of dilactate carbonate, dicitrate carbonate, and dicitrate carbonate.

10. The method for preparing bio-based polyester-carbonate based on bio-based dicarboxylic acid carbonate according to claim 1, characterized in that: The bio-based polyester-carbonate is at least one of poly(dilactic acid)-furan dimethanol carbonate, poly(dicilic acid)-isosorbide carbonate, and poly(dihydroxyacetic acid)-cyclohexanedimethanol carbonate.

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