Whole bio-based copolymer based on citric acid bicyclic monomer, and preparation method and application thereof

Abstract

The invention discloses a full bio-based copolymer based on a citric acid bicyclic monomer, a preparation method and an application, and belongs to the technical field of material synthesis, citric acid-derived bicyclic OPD diol and OPBMC diester are synthesized through oxidation reduction and transesterification, and then 1, 4-butanediol is partially replaced with OPD or 2, 4-butanediol is partially replaced with OPBMC through melt phase polycondensation reaction. Two series of random copolyester PBxOyF copolymer and PBOmFn copolymer of the PBF are prepared by adding 2, 5-dimethyl furandicarboxylate into the PBF, and then adding the PBxOyF copolymer and the PBOmFn copolymer into the PBF. According to the full-bio-based copolymer based on the citric acid bicyclic monomer, the preparation method and the application, the citric acid bicyclic monomer obviously improves the glass transition temperature and shows good mechanical properties; therefore, the bicyclic monomer based on citric acid has huge potential in the aspect of synthesizing novel bio-based copolyester with expected thermodynamic properties, and is expected to further expand the application range of the 2.5 furandicarboxylic acid-based polyester.

Description

Technical Field

[0001] The present invention relates to the technical field of material synthesis, and particularly relates to a fully bio-based copolymer based on a citric acid bicyclic monomer, a preparation method and an application thereof. Background Art

[0002] The demand for bio-based polymers is increasing, mainly due to the growing concerns of the plastics industry about pollution and sustainability issues. In the past few decades, the academic and industrial communities have shown a significant increase in interest in polymers derived from renewable resources. A variety of polyesters, including polylactic acid (PLA), polyhydroxyalkanoates (PHA), and polybutylene succinate (PBS), have been successfully produced from renewable raw materials and brought to the market. However, compared with well-known engineering plastics such as polyethylene terephthalate (PET) and polycarbonate (PC), these bio-based polyesters still need to be improved in terms of mechanical and thermal properties. Their relatively weak properties are attributed to the lack of aromatic rings or rigid ring structures in their molecular configurations. Therefore, obtaining rigid monomers from sustainable sources is crucial for the development of new bio-based polymers.

[0003] 2,5-Furandicarboxylic acid is an important bio-based monomer that can be obtained by the oxidation and hydrolysis of cellulose or starch. Among the 12 value-added biomass chemicals recognized by the US Department of Energy, FDCA is the only rigid aromatic monomer. In recent years, significant progress has been made in the research on polyesters based on 2,5-furandicarboxylic acid, such as poly(ethylene 2,5-furandicarboxylate) (PEF), poly(propylene 2,5-furandicarboxylate) (PPF), and poly(butylene 2,5-furandicarboxylate) (PBF). Among them, PBF is synthesized from bio-based 2,5-furandicarboxylic acid and 1,4-butanediol (BDO), and its structure is very similar to that of the petroleum-based polyester poly(butylene terephthalate) (PBT). PBF has excellent flexibility, strength, and thermal stability, making it a promising material for food packaging and beverage bottle components. Nevertheless, PBF-based copolyesters with a higher glass transition temperature (T g ) will exhibit better thermal stability during processing and higher mechanical properties in practical applications, which may expand the application scope of PBF in current popular fields. Therefore, how to improve its T while maintaining the bio-based characteristics of PBF g is an urgent problem to be solved. Summary of the Invention

[0004] The object of the present invention is to provide a fully bio-based copolymer based on a citric acid bicyclic monomer, a preparation method and an application. The citric acid bicyclic monomer significantly increases the glass transition temperature and exhibits good mechanical properties, indicating that the bicyclic monomer based on citric acid has great potential in synthesizing novel bio-based copolyesters with expected thermodynamic properties, and is expected to further expand the application scope of 2,5-furandicarboxylic acid-based polyesters.

[0005] To achieve the above object, the present invention provides a fully bio-based copolymer based on a citric acid bicyclic monomer, and the fully bio-based copolymer includes PB x O y F copolymer and PBO m F n copolymer;

[0006] Among them, the molecular structural formula of the PB x O y F copolymer is:

[0007]

[0008] x is the molar percentage of 1,4-butanediol; y is the molar percentage of octahydro-2,5-pentadienediol, and the value range of y is 5-40 mol%, x + y = 100%;

[0009] The molecular structural formula of the PBO m F n copolymer is:

[0010]

[0011] m is the molar percentage of octahydro-2,5-pentadienediol dimethyl carbonate, n is the molar percentage of dimethyl 2,5-furandicarboxylate, the value range of m is 5-40 mol%, m + n = 100%.

[0012] Further, y is 5, 10, 20, 30, 40 mol%, and m is 5, 10, 20, 30, 40 mol%.

[0013] The present invention also provides a preparation method of the above-mentioned fully bio-based copolymer based on a citric acid bicyclic monomer, including the preparation method of the PB x O y F copolymer and the preparation method of the PBO x F y copolymer.

[0014] Preferably, the preparation method of the PB x O y F copolymer includes the following steps:

[0015] Step 1: Prepare octahydro-2,5-pentadienediol;

[0016] Step 2: Under a nitrogen atmosphere, place octahydro-2,5-pentadienediol, 1,4-butanediol, and dimethyl 2,5-furandicarboxylate in a three-necked round-bottom flask, add a transesterification catalyst, heat and stir to conduct a transesterification reaction;

[0017] Step 3: After the transesterification reaction is completed, add a polycondensation catalyst, continue to raise the temperature and reduce the pressure to conduct a melt polycondensation reaction, and finally obtain PB x O y F copolymer.

[0018] Preferably, in Step 2, the molar ratio of the mixture of octahydro-2,5-pentadienediol and 1,4-butanediol to dimethyl 2,5-furandicarboxylate is (1.1-2):1, the transesterification reaction temperature is 160-180 °C, and the reaction time is 2-7 h.

[0019] Preferably, the transesterification catalyst in Step 2 is one or more of zinc acetate, magnesium acetate, manganese acetate, dibutyltin oxide, tetrabutyl titanate, and titanium isopropoxide.

[0020] Preferably, in Step 3, the pressure in the three-necked round-bottom flask is less than 100 Pa, the melt polycondensation reaction temperature is 180-200 °C, the reaction time is 4-6 h, and the polycondensation catalyst is one or more of antimony trioxide, tetrabutyl carbonate, potassium acetate, sodium acetate, and zinc acetate.

[0021] Further, the molar amount of the transesterification catalyst is 0.1%-0.6% of the molar amount of dimethyl 2,5-furandicarboxylate, and the molar amount of the polycondensation catalyst is 0.1%-0.8% of the molar amount of dimethyl 2,5-furandicarboxylate.

[0022] Preferably, the preparation method of the PBO m F n copolymer includes the following steps:

[0023] S1. Prepare octahydro-2,5-pentadienediol;

[0024] S2. Under a nitrogen atmosphere, place octahydro-2,5-pentadienediol dimethyl carbonate, 1,4-butanediol, and dimethyl 2,5-furandicarboxylate in a three-necked round-bottom flask, add a transesterification catalyst, heat and stir to conduct a transesterification reaction;

[0025] S3. After the transesterification reaction is completed, add a polycondensation catalyst and continue to raise the temperature and reduce the pressure to conduct a melt polycondensation reaction, and finally obtain PBO m F n copolymer.

[0026] Preferably, in S2, the molar ratio of the mixture of octahydro-2,5-pentadienediol dimethyl carbonate and 1,4-butanediol to dimethyl 2,5-furandicarboxylate is (1.1 - 2.5):1, the transesterification reaction temperature is 160 - 180 °C, and the reaction time is 3 - 4 h;

[0027] The transesterification catalyst is one or more of zinc acetate, dibutyltin oxide, tetrabutyl titanate, and titanium isopropoxide.

[0028] Further, the transesterification reaction temperature is 160 °C, 170 °C, or 180 °C, and the reaction time is 4 h or 5 h.

[0029] Preferably, in S3, the melt polycondensation reaction temperature is 180 - 200 °C, the reaction time is 2 - 7 h, and the polycondensation catalyst is one or more of titanium dioxide, antimony trioxide, tetrabutyl carbonate, potassium acetate, sodium acetate, and zinc acetate.

[0030] Further, the melt polycondensation reaction temperature is 180 °C, 190 °C, or 200 °C, and the reaction time is 4 h, 5 h, or 6 h.

[0031] Further, the molar amount of the transesterification catalyst is 0.1% - 0.6% of the total molar amount of dimethyl 2,5-furandicarboxylate and octahydro-2,5-pentadienediol dimethyl carbonate, and the molar amount of the polycondensation catalyst is 0.1% - 0.8% of the total molar amount of dimethyl 2,5-furandicarboxylate and octahydro-2,5-pentadienediol dimethyl carbonate.

[0032] The present invention also provides an application of the fully bio-based copolymer based on the citric acid bicyclic monomer, and applies the fully bio-based copolymer based on the citric acid bicyclic monomer described above to the preparation of high-performance environmentally friendly packaging materials.

[0033] Therefore, the present invention adopts the above-mentioned fully bio-based copolymer based on the citric acid bicyclic monomer, preparation method, and application, and has the following beneficial effects:

[0034] (1) Bicyclic diols derived from citric acid: octahydro-2,5-pentadienediol and bicyclic diesters: octahydro-2,5-pentadienediol dimethyl carbonate are synthesized through redox and transesterification reactions, and then PB x O y F copolymer and PBO m F n copolymer are prepared through melt polycondensation reaction, and its citric acid content is as high as 40 mol%;

[0035] (2) The introduction of citric acid bicyclic monomers significantly increases the glass transition temperature of PBF copolyesters and endows them with excellent mechanical properties. This indicates that citric acid-based bicyclic monomers have great potential in the synthesis of novel bio-based copolyesters with desired thermodynamic properties, and are expected to further expand the application scope of 2,5-furandicarboxylic acid-based polyesters.

[0036] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and examples. Description of the Drawings

[0037] Figure 1 is the synthesis route diagram of PBxOyF copolyesters and PBOmFn copolyesters of the present invention;

[0038] Figure 2 are the 1 H-NMR spectra and 13 13C-NMR spectra of octahydro-2,5-pentadienediol and 2,5-pentadienediol dimethyl carbonate prepared in the present invention, where (a) is the 1 H-NMR spectrum of octahydro-2,5-pentadienediol, (b) is the 1 H-NMR spectrum of octahydro-2,5-pentadienediol dimethyl carbonate, (c) is the 13C-NMR spectrum of octahydro-2,5-pentadienediol, and (d) is the 13 13C-NMR spectrum of octahydro-2,5-pentadienediol dimethyl carbonate;

[0039] Figure 3 are the 1 H-NMR spectra of Examples 1-10 and Comparative Example 1 of the present invention, where (a) is the 1 H-NMR spectrum of Examples 1-5 and Comparative Example 1, (b) is the 1 H-NMR spectrum of Examples 6-10 and Comparative Example 1;

[0040] Figure 4 are the 13 13C-NMR spectra of Examples 1-10 and Comparative Example 1 of the present invention, where (a) is the 13 13C-NMR spectrum of Examples 1-5 and Comparative Example 1, (b) is the 13 13C-NMR spectrum of Examples 6-10 and Comparative Example 1;

[0041] Figure 5 are the differential scanning calorimetry (DSC) curves of Examples 1-10 and Comparative Example 1 of the present invention, where (a) is the DSC curve of Examples 1-5 and Comparative Example 1, and (b) is the DSC curve of Examples 6-10 and Comparative Example 1;

[0042] Figure 6are the thermogravimetric (TGA) curves and their corresponding derivative thermogravimetric (DTG) curves of Examples 1-10 and Comparative Example 1 of the present invention. Among them, (a) are the TGA curves of Examples 1-5 and Comparative Example 1, (b) are the TGA curves of Examples 6-10 and Comparative Example 1, (c) are the DTG curves of Examples 1-5 and Comparative Example 1, and (d) are the DTG curves of Examples 6-10 and Comparative Example 1;

[0043] Figure 7 are the wide-angle X-ray diffraction (WAXD) spectra of Examples 1-10 and Comparative Example 1 of the present invention. Among them, (a) are the WAXD spectra of Examples 1-5 and Comparative Example 1, and (b) are the WAXD spectra of Examples 6-10 and Comparative Example 1;

[0044] Figure 8 are the stress-strain curves of Examples 1-10 and Comparative Example 1;

[0045] Figure 9 is the DSC chart of Example 2 and Comparative Example 1;

[0046] Figure 10 is the DSC chart of Example 5 and Comparative Example 1;

[0047] Figure 11 is the DSC chart of Example 6 and Comparative Example 1;

[0048] Figure 12 is the mechanical property chart of Example 6 and Comparative Example 1;

[0049] Figure 13 is the DSC chart of Example 7 and Comparative Example 1;

[0050] Figure 14 is the mechanical property chart of Example 7 and Comparative Example 1. Detailed implementation manners

[0051] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and examples.

[0052] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0053] The present invention provides a fully bio-based copolymer based on a citric acid bicyclic monomer. The preparation method of the fully bio-based copolymer is as Figure 1 shown. The fully bio-based copolymer includes PB x O y F copolymer and PBO m F n copolymer, as Figure 1 shown.

[0054] Among them, PB x O y The molecular structural formula of the F copolymer is:

[0055]

[0056] x is the molar percentage of 1,4-butanediol; y is the molar percentage of octahydro-2,5-pentadienediol, and the value range of y is 5 - 40 mol%, x + y = 100%;

[0057] PBO m F n The molecular structural formula of the copolymer is:

[0058]

[0059] m is the molar percentage of octahydro-2,5-pentadienediol dimethyl carbonate, n is the molar percentage of dimethyl 2,5-furandicarboxylate, the value range of m is 5 - 40 mol%, m + n = 100%.

[0060] The synthesis of octahydro-2,5-pentadienediol includes the following steps:

[0061] Add 250 mL of anhydrous methanol into a three-necked flask equipped with a magnetic stirrer. Slowly add 14.08 g of sodium hydroxide (352 mmol) at 0 °C to obtain a milky white solution. Subsequently, slowly drip 60 g of dimethyl 1,3-acetonedicarboxylate (344 mmol) within 1.5 h. After the addition, a pale yellow precipitate is observed. The obtained slurry is refluxed and stirred at 65 °C for 3 h until the precipitate is completely dissolved. Remove the oil bath, and slowly add 11.4 g of 40% aqueous glyoxal solution (197 mmol) under rapid stirring, maintaining the internal temperature at 65 - 70 °C. The obtained orange-yellow slurry is stirred overnight at 25 °C, filtered by vacuum filtration, and washed with 50 mL of methanol to obtain a pale yellow disodium salt (46.4 g, yield 65%).

[0062] Dissolve 46.4 g of the above disodium salt in a mixed solution of 275 mL of 1 M hydrochloric acid and 46.4 mL of glacial acetic acid, and reflux at 120 °C for 3 h. After cooling to room temperature, extract with dichloromethane. Wash the organic phase with saturated sodium bicarbonate, dry with anhydrous sodium sulfate, filter, and concentrate under reduced pressure to obtain an orange-yellow solid octahydro-2,5-pentadienedione (yield about 80%).

[0063] Dissolve 9.8 g of octahydro-2,5-pentadienedione in 118 mL of methanol. Slowly add 6.9 g of sodium borohydride at 0 °C, and a large number of bubbles will be generated immediately. After stirring at room temperature for 12 h, add 196 mL of 2 mol / L hydrochloric acid and 392 mL of 4 mol / L sodium hydroxide solution successively under an ice bath. The mixture is extracted with dichloromethane, and the combined organic phases are dried over anhydrous magnesium sulfate, filtered, and then rotary evaporated to obtain white solid octahydro-2,5-pentadienediol (yield about 78%).

[0064] The structural formula of octahydro-2,5-pentadienediol is as follows:

[0065]

[0066] Synthesis operation of octahydro-2,5-pentadienediol dimethyl carbonate:

[0067] Dissolve 7.4 g of octahydro-2,5-pentadienediol in 117 mL of dimethyl carbonate, add 1 mL of tetrabutyl titanate as a catalyst, and reflux at 85 °C for 36 h for the esterification reaction. After the reaction is completed, filter the milky white slurry with an organic phase filter membrane, and concentrate the colorless filtrate under reduced pressure. The residue is recrystallized from methanol to obtain colorless crystal product octahydro-2,5-pentadienediol dimethyl carbonate (yield about 50%).

[0068] The structural formula of octahydro-2,5-pentadienediol dimethyl carbonate is as follows:

[0069]

[0070] For octahydro-2,5-pentadienediol 1 The 1H-NMR spectrum is as shown in (a) of Figure 2 , and the 13C-NMR spectrum of octahydro-2,5-pentadienediol is as shown in (b) of 13 . For octahydro-2,5-pentadienediol dimethyl carbonate, the 1H-NMR spectrum is as shown in (c) of Figure 2 , and the 13C-NMR spectrum of octahydro-2,5-pentadienediol dimethyl carbonate is as shown in (d) of 1 Figure 2 . 13 Figure 2 The 13C-NMR spectrum is as shown in (d) of Figure 2 .

[0071] Example 1

[0072] PB 95Synthesis of O5F: Dimethyl 2,5-furandicarboxylate (DMFD, 80 mmol, 14.73 g), 1,4-butanediol (93.6 mmol, 8.435 g), octahydro-2,5-pentadienediol (10.4 mmol, 1.48 g) and the transesterification catalyst titanium isopropoxide (0.2 mol% of DMFD, 0.040 g) were added to the reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 160 °C and maintained for 4 h until all by-products were distilled out to complete the transesterification reaction; during the polycondensation reaction, the polycondensation catalyst tetrabutyl titanate (0.2 mol% of DMFD, 0.054 g) was added, the pressure of the system was reduced to below 100 Pa, the reaction temperature was raised to 180 °C and maintained for 3 h until the Weissenberg effect appeared to obtain the product PB 95 O5F.

[0073] Example 2

[0074] PB 90 O 10 Synthesis of O5F: Dimethyl 2,5-furandicarboxylate (DMFD, 80 mmol, 14.73 g), 1,4-butanediol (108 mmol, 9.73 g), octahydro-2,5-pentadienediol (12 mmol, 1.71 g) and the transesterification catalyst titanium isopropoxide (0.3 mol% of DMFD, 0.061 g) were added to the reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 170 °C and maintained for 4 h until all by-products were distilled out to complete the transesterification reaction; during the polycondensation reaction, the polycondensation catalyst tetrabutyl titanate (0.2 mol% of DMFD, 0.054 g) was added, the pressure of the system was reduced to below 100 Pa, the reaction temperature was raised to 180 °C and maintained for 4 h until the Weissenberg effect appeared to obtain the product PB 90 O 10 F.

[0075] Example 3

[0076] PB 80 O 20Synthesis of PB-F: Dimethyl 2,5-furandicarboxylate (DMFD, 80 mmol, 14.73 g), 1,4-butanediol (128 mmol, 11.53 g), octahydro-2,5-norbornanediol (32 mmol, 4.55 g) and the transesterification catalyst zinc acetate (0.6 mol% of DMFD, 0.088 g) were added to a reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 170 °C and maintained for 5 h until all by-products were distilled off to complete the transesterification reaction; during the polycondensation reaction, the polycondensation catalyst titanium isopropoxide (0.4 mol% of DMFD, 0.081 g) was added, the pressure of the system was reduced to below 100 Pa, the reaction temperature was raised to 190 °C and maintained for 5 h until the Weissenberg effect appeared to obtain the product PB-F. 80 O 20 F.

[0077] Example 4

[0078] PB 70 O 30 Synthesis of PB-F: Dimethyl 2,5-furandicarboxylate (DMFD, 80 mmol, 14.73 g), 1,4-butanediol (100.8 mmol, 9.09 g), octahydro-2,5-norbornanediol (43.2 mmol, 6.15 g) and the transesterification catalyst dibutyltin oxide (0.6 mol% of DMFD, 0.119 g) were added to a reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 170 °C and maintained for 6 h until all by-products were distilled off to complete the transesterification reaction; during the polycondensation reaction, the polycondensation catalyst antimony trioxide (0.8 mol% of DMFD, 0.187 g) was added, the pressure of the system was reduced to below 100 Pa, the reaction temperature was raised to 200 °C and maintained for 4 h until the Weissenberg effect appeared to obtain the product PB-F. 70 O 30 F.

[0079] Example 5

[0080] PB 60 O 40Synthesis of F: Dimethyl 2,5-furandicarboxylate (DMFD, 80 mmol, 14.73 g), 1,4-butanediol (67.2 mmol, 6.05 g), octahydro-2,5-pentadienediol (44.8 mmol, 6.38 g), and the transesterification catalysts titanium isopropoxide (0.2 mol% of DMFD, 0.04 g) and tetrabutyl titanate (0.15 mol% of diester, 0.041 g) were added to a reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 180 °C and maintained for 7 h until all by-products were distilled off, completing the transesterification reaction; during the polycondensation reaction, titanium isopropoxide (0.4 mol% of DMFD, 0.08 g) as the polycondensation catalyst was added, the pressure of the system was reduced to below 100 Pa, the reaction temperature was raised to 200 °C and maintained for 6 h until the Weissenberg effect occurred, obtaining the product PB 60 O 40 F.

[0081] Example 6

[0082] PBO5F 95 Synthesis of PBO5F: Dimethyl 2,5-furandicarboxylate (DMFD, 76 mmol, 13.99 g), octahydro-2,5-pentadienediol bismethyl carbonate (OPBMC, 4 mmol, 1.03 g), 1,4-butanediol (128 mmol, 11.54 g), and the transesterification catalyst titanium isopropoxide (0.3 mol% (DMFD + OPBMC)), 0.061 g) were added to a reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 160 °C and maintained for 3.5 h until all by-products were distilled off, obtaining a low-molecular-weight oligomer and completing the transesterification reaction; during the polycondensation reaction, tetrabutyl titanate (0.1 mol% (DMFD + OPBMC)), 0.04 g) as the polycondensation catalyst was added, the pressure of the system was gradually reduced to below 100 Pa, the reaction temperature was raised to 180 °C and maintained for 4 h until the Weissenberg effect occurred, obtaining the product PBO5F 95 .

[0083] Example 7

[0084] PBO 10 F 90Synthesis of PBO: Dimethyl 2,5-furandicarboxylate (DMFD, 72 mmol, 13.26 g), octahydro-2,5-pentadienediol dimethyl carbonate (OPBMC, 8 mmol, 2.06 g), 1,4-butanediol (160 mmol, 14.42 g) and the transesterification catalyst titanium isopropoxide (0.2 mol% (DMFD + OPBMC)), 0.04 g) were added to a reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 160 °C and maintained for 4 h until all by-products were distilled off to obtain a low molecular weight oligomer, completing the transesterification reaction; during the polycondensation reaction, the polycondensation catalyst titanium isopropoxide (0.2 mol% (DMFD + OPBMC)), 0.04 g) was added, and the pressure of the system was gradually reduced to below 100 Pa, the reaction temperature was raised to 180 °C and maintained for 5 h until the Weissenberg effect appeared, obtaining the product PBO 10 F 90 .

[0085] Example 8

[0086] PBO 20 F 80 Synthesis of PBO: Dimethyl 2,5-furandicarboxylate (DMFD, 64 mmol, 11.78 g), octahydro-2,5-pentadienediol dimethyl carbonate (OPBMC, 16 mmol, 4.12 g), 1,4-butanediol (200 mmol, 18.02 g) and the transesterification catalyst titanium isopropoxide (0.2 mol% (DMFD + OPBMC)), 0.04 g) were added to a reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 170 °C and maintained for 4 h until all by-products were distilled off to obtain a low molecular weight oligomer, completing the transesterification reaction; during the polycondensation reaction, the polycondensation catalyst antimony trioxide (0.6 mol% (DMFD + OPBMC)), 0.14 g) was added, and the pressure of the system was gradually reduced to below 100 Pa, the reaction temperature was raised to 190 °C and maintained for 4.5 h until the Weissenberg effect appeared, obtaining the product PBO 20 F 80 .

[0087] Example 9

[0088] PBO 30 F 70Synthesis of 30 F 70 : Dimethyl 2,5-furandicarboxylate (DMFD, 56 mmol, 10.31 g), octahydro-2,5-pentadienediol dimethyl carbonate (OPBMC, 24 mmol, 6.18 g), 1,4-butanediol (128 mmol, 11.53 g) and the transesterification catalyst dibutyltin oxide (0.6 mol% (DMFD + OPBMC)), 0.11 g) were added to the reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 170 °C and maintained for 4 h until all by-products were distilled off to obtain a low molecular weight oligomer, completing the transesterification reaction; during the polycondensation reaction, the polycondensation catalyst titanium isopropoxide (0.4 mol% (DMFD + OPBMC)), 0.08 g) was added, the pressure of the system was gradually reduced to below 100 Pa, the reaction temperature was raised to 190 °C and maintained for 6 h until the Weissenberg effect appeared to obtain the product PBO

[0089] Example 10

[0090] PBO 40 F 60 Synthesis of 40 F 60 : Dimethyl 2,5-furandicarboxylate (DMFD, 48 mmol, 8.84 g), octahydro-2,5-pentadienediol dimethyl carbonate (OPBMC, 32 mmol, 8.24 g), 1,4-butanediol (104 mmol, 9.37 g) and the transesterification catalyst zinc acetate (0.6 mol% (DMFD + OPBMC)), 0.088 g) were added to the reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 180 °C and maintained for 4 h until all by-products were distilled off to obtain a low molecular weight oligomer, completing the transesterification reaction; during the polycondensation reaction, the polycondensation catalyst tetrabutyl titanate (0.4 mol% (DMFD + OPBMC)), 0.108 g) was added, the pressure of the system was gradually reduced to below 100 Pa, the reaction temperature was raised to 200 °C and maintained for 5 h until the Weissenberg effect appeared to obtain the product PBO

[0091] Comparative Example 1

[0092] Preparation of PBF: Dimethyl 2,5-furandicarboxylate (DMFD, 80 mmol, 14.73 g), 1,4-butanediol (128 mmol, 11.53 g), and the transesterification catalyst titanium isopropoxide (0.2 mol% of DMFD, 0.04 g) were added to a reaction flask. Nitrogen was introduced into the reaction system, the temperature was raised to 170 °C and maintained for 4 h until all by-products were distilled off to complete the transesterification reaction; during the polycondensation reaction, the polycondensation catalyst titanium isopropoxide (0.1 mol% of DMFD, 0.02 g) was added, the pressure of the system was reduced to below 100 Pa, the reaction temperature was raised to 180 °C and maintained for 4 h until the Weissenberg effect appeared to obtain the product PBF.

[0093] Perform property characterization on the products obtained in Examples 1-10 and Comparative Example 1.

[0094] I. Viscosity test:

[0095] The intrinsic viscosity [η] of the copolyester was measured using an Ubbelohde viscometer (model B-013205, capillary inner diameter 0.7 - 0.8 mm). Using a 1,1,2,2-tetrachloroethane / phenol mixed solvent (mass ratio 2:3) as the test medium, the test was carried out under the constant temperature condition of 25 °C. The specific viscosity logarithm and viscosity-average molecular weight of the copolyester were calculated through the following formula:

[0096]

[0097] where t0 is the solvent outflow time, t1 is the solution outflow time, and c is the solution concentration (5 g / L). K and α are characteristic constants of the test system (K = 2.11×10 -5 , α = 1.02).

[0098] Table 1 shows that the intrinsic viscosity [η] of Examples 1-10 and Comparative Example 1 ranges from 0.72 to 1.25 dL / g, and the viscosity-average molecular weight (M η ) fluctuates between 27.7 and 47.6 kg / mol. The yields of all copolymers are between 80% and 89%.

[0099] Table 1 Yields, intrinsic viscosities, and viscosity-average molecular weights (M η ) of Examples 1-10 and Comparative Example 1

[0100]

[0101] II. Structure characterization

[0102] Use a Bruker AVANCE NEO type nuclear magnetic resonance spectrometer to measure the 1 H-NMR and 1313C-NMR spectrum, with the solvent being a mixed solution of deuterated chloroform / trifluoroacetic acid (volume ratio 1:2). The results are as Figure 3 and Figure 4 shown.

[0103] As can be seen from (a) in Figure 3 , the methylene protons -OCH2- (10) and -CH2- (11) of the 1,4-butanediol unit appear at 4.40 ppm and 1.84 ppm respectively. The characteristic peak of -CH- (9 and 9') in the furan ring appears at 7.45 ppm. For Examples 1-5 (PB x O y F copolymer), the proton signal at 5.43 ppm belongs to the hydrogen atoms at positions 3 / c and 7 / g, and the signal at 2.66 ppm corresponds to the hydrogen atoms at positions 1 / a and 5 / e. The signals at 2.34 ppm come from the outer ring protons (2 / 4 / 6 / 8 / b / d / f / h) and inner ring protons (2' / 4' / 6' / 8' / b' / d' / f' / h') of the octahydro-2,5-pentadienediol unit respectively. As can be seen from (b) in Figure 3 , except for the proton signals (11, 12, 13) of Comparative Example 1 (PBF), the protons at 5.43, 2.66, 2.34, 4.22 and 1.82 ppm in the octahydro-2,5-pentadienediol dimethyl carbonate unit correspond to the hydrogen atoms at positions 3 / 7, 1 / 5 and the outer ring (2 / 4 / 6 / 8) protons respectively. The signals at 4.23 ppm and 1.82 ppm originate from the protons at positions 9 and 10 of the BDO unit respectively.

[0104] From the 13C-NMR spectra of Examples 1-5 and Comparative Example 1 13 ([(a) in Figure 4 ), the carbon signals of the furan ring appear at 122 ppm (9 / 9'), 146 ppm (10 / 10') and 160 ppm (11 / 11') respectively. The characteristic peaks corresponding to the octahydro-2,5-pentadienediol unit are located at 22 ppm (13), 40 ppm (1 / 5 / 2 / 4 / 6 / 8), 66 ppm (12) and 80 ppm (3 / 7). For Examples 6-10 and Comparative Example 1 ([(b) in Figure 4 ), the signals at 22 ppm (13 / 15), 68 ppm (14) and 158 ppm (16 / 17) belong to the octahydro-2,5-pentadienediol dimethyl carbonate segment. All the observed peaks are consistent with the theoretical chemical shift values, confirming the successful synthesis of the products of Examples 1-10 and Comparative Example 1.

[0105] III. Thermal Property Characterization

[0106] Differential Scanning Calorimetry

[0107] The DSC-25 differential scanning calorimeter from TA Instruments was used to study the thermal properties of the copolymer under a nitrogen atmosphere. The specific procedure was as follows: Weigh 5-10 mg of the sample and place it in an aluminum crucible. Heat it at a rate of 10 °C / min to 200 °C and hold for 3 min to eliminate the thermal history. Then cool it to 0 °C at a rate of 10 °C / min and maintain for 3 min. Finally, heat it to 200 °C again at the same rate.

[0108] Figure 5 are the differential scanning calorimetry (DSC) curves of Examples 1-10 of the present invention and Comparative Example 1, and the corresponding data are listed in Table 2. By comparing Examples 1-5 ( Figure 5 (a) in) and Examples 6-10 ( Figure 5 (b) in) with the melting point and melting enthalpy (ΔH m ) of the homopolymer obtained in Comparative Example 1, it can be found that after introducing octahydro-2,5-pentanediol or octahydro-2,5-pentanediol dimethyl carbonate, the T m and ΔH m of Examples 1-10 are significantly reduced. This indicates that due to the increased rigidity of the bicyclic citric acid unit, the regularity of the polymer chain is severely disrupted, resulting in the formation of imperfect crystals with a lower melting point. All copolymers exhibit a single T g , indicating that there is no microphase separation in the amorphous regions of Examples 1-10. Different from the melting behavior, the T g of Examples 1-10 increases with the introduction of the bicyclic citric acid unit because the citric acid structure imparts higher rigidity to the copolymer chain, thereby reducing the free volume. Among them, the increase in T g of Examples 1-5 is more significant because the flexible 1,4-butanediol chain segment in Examples 1-5 is replaced by a more rigid octahydro-2,5-pentanediol unit.

[0109] Table 2 Thermal property data of Examples 1-10 and Comparative Example 1

[0110]

[0111] Thermogravimetric analysis

[0112] The TGA-Q50 thermogravimetric analyzer was used to evaluate the thermal stability under a nitrogen atmosphere (flow rate 40 mL / min). Take 5-10 mg of Examples 1-10 and Comparative Example 1 respectively, and perform thermogravimetric analysis by heating from room temperature to 500 °C at a rate of 20 °C / min.

[0113] Thermal stability is an important performance index in the application and processing of polymers. Figure 6 are the thermogravimetric (TGA) curves and the corresponding derivative thermogravimetric (DTG) curves of Examples 1-10 of the present invention and Comparative Example 1, and the relevant statistical data are shown in Table 3.

[0114] The thermal decomposition of Comparative Example 1 is a single-step process, and the initial 5% weight loss temperature (T d , 5%) is 359 °C, and the temperature at the maximum decomposition rate (T d,max1 ) is 390 °C. In contrast, Examples 1-5 ( Figure 6 in (a) and Figure 6 in (b)) and Examples 6-10 ( Figure 6 in (c) and Figure 6 in (d)) show a significant reduction in thermal stability, and their thermal decomposition process is more complex, showing two distinct decomposition stages (T d,max1 and T d,max2 ) in a nitrogen atmosphere. The additional thermal decomposition phenomenon observed at 312 - 332 °C is attributed to the decomposition of the citric acid unit. However, these copolyesters can still maintain their basic structure unchanged at a high temperature of 300 °C, indicating their suitability for high-efficiency thermal processing processes.

[0115] Table 3 Thermal stability performance parameters of Examples 1-10 and Comparative Example 1

[0116] Sample <![CDATA[T d,5％ (℃)]]> <![CDATA[T d,max1 (℃)]]> <![CDATA[T d,max2 (℃)]]> PBF 359 390 — <![CDATA[PB 95 O5F]]> 343 320 394 <![CDATA[PB 90 O 10 F]]> 326 325 382 <![CDATA[PB 80 O 20 F]]> 308 323 378 <![CDATA[PB 70 O 30 F]]> 302 320 364 <![CDATA[PB 60 O 40 F]]> 300 312 350 <![CDATA[PBO5F 95 > 328 332 395 <![CDATA[PBO 10 F 90 > 315 318 390 <![CDATA[PBO 20 F 80 > 308 328 396 <![CDATA[PBO 30 F 70 > 302 316 382 <![CDATA[PBO 40 F 60 > 302 325 399

[0117] IV. Crystallization performance characterization

[0118] Crystallization performance test: The crystal structure of the copolyester was analyzed by wide-angle X-ray diffraction (WAXD) using copper target Kα radiation (λ = 0.154 nm). The test conditions were: voltage 40 kV, current 200 mA, scanning rate 2° / min, and scanning angle range 5° to 60°. The samples were prepared by hot pressing, and the thickness was controlled at 1 mm.

[0119] Figure 7 are the wide-angle X-ray diffraction (WAXD) spectra of Examples 1-10 and Comparative Example 1 of the present invention. From Figure 7 in (a) and Figure 7 in (b), it can be seen that Comparative Example 1 is a semi-crystalline polymer, and characteristic diffraction peaks appear at 2θ = 17.88°, 22.34°, and 24.77°. The diffraction peak positions of Examples 1, 2, and 6 are the same as those of Comparative Example 1, indicating that they have the same crystal form structure. No obvious diffraction peaks appear in the remaining examples, indicating an amorphous state. As the content of the citric acid unit increases, the crystallinity of the copolyester gradually decreases, and the inhibitory effect of the introduction of the octahydro-2,5-pentadienediol dimethyl carbonate unit on the crystallinity is more significant than that of the octahydro-2,5-pentadienediol unit. This phenomenon is consistent with the trend of the melting enthalpy measured by DSC, which may be due to the steric hindrance effect of the octahydro-2,5-pentadienediol dimethyl carbonate unit, resulting in difficulty in molecular chain packing and a decrease in the chain segment movement ability.

[0120] V. Mechanical Property Characterization

[0121] Tensile property test: According to ASTM D638 standard, the test was carried out at 25 °C using a universal testing machine (CMT6104, MTS Industrial Systems (China) Co., Ltd.). The crosshead speed was 5 mm / min. Dumbbell-shaped specimens (width 2 mm, thickness 5 mm) were prepared by a micro-injection molding machine (SZS-15, Wuhan Ruiming Experimental Instrument Co., Ltd.).

[0122] Figure 8 Figure 7 shows the stress-strain curves of Examples 1-10 and Comparative Example 1, and the corresponding data are shown in Table 4. The presence of the bicyclic citric acid unit has a significant effect on the tensile properties of the copolymer. In Examples 6-10, the tensile strength and Young's modulus first increase and then decrease with the increase in the content of octahydro-2,5-pentadienediol dimethyl carbonate. When its content exceeds 28 mol%, the performance begins to decline. This behavior may be due to the decrease in molecular weight and crystallinity of Examples 8 and 9. Although the crystallinity decreases with the increase in the content of octahydro-2,5-pentadienediol dimethyl carbonate, the tensile strengths of Examples 6 and 7 are significantly higher than that of Comparative Example 1, ranging between 35-45 MPa. This improvement can be attributed to the competitive effect between the increase in chain rigidity and the decrease in crystallinity. In addition, Examples 1-2 exhibit brittle fracture characteristics, and with the increase in the content of octahydro-2,5-pentadienediol, the tensile strength and elongation at break decrease significantly.

[0123] Table 4 Mechanical property parameters of Examples 1-2, Examples 6-10 and Comparative Example 1

[0124]

[0125] In summary, Figure 9 Figure 8 is the DSC diagram of Example 2 and Comparative Example 1. As can be seen from the figure, the glass transition temperature (T g ) of Example 2 increases from 36.4 °C in Comparative Example 1 to 43.1 °C.

[0126] Figure 10 Figure 9 is the DSC diagram of Example 5 and Comparative Example 1. As can be seen from the figure, the glass transition temperature (T g ) of Example 5 increases from 36.4 °C in Comparative Example 1 to 63.1 °C.

[0127] Figure 11 Figure 10 is the DSC diagram of Example 6 and Comparative Example 1. As can be seen from the figure, the glass transition temperature (T g ) of Example 6 increases from 36.4 °C in Comparative Example 1 to 63.1 °C.

[0128] Figure 12 Figure 11 is the mechanical property diagram of Example 6 and Comparative Example 1. FromFigure 12 It can be seen that the tensile strength and Young's modulus of Example 6 are increased from 33 MPa and 897 MPa of Comparative Example 1 to 35 MPa and 1015 MPa respectively.

[0129] Figure 13 This is the DSC chart of Example 7 and Comparative Example 1. It can be seen from the chart that the glass transition temperature (T g ) of Example 7 is increased from 36.4 °C in Comparative Example 1 to 39.7 °C.

[0130] Figure 14 This is the mechanical property chart of Example 7 and Comparative Example 1. It can be seen from the chart that the tensile strength, Young's modulus and elongation at break of Example 7 are increased from 33 MPa, 897 MPa and 450% of Comparative Example 1 to 45 MPa, 1230 MPa and 600% respectively.

[0131] The fully biodegradable copolymer prepared through Example 7, which has excellent flexibility, mechanical strength and thermal stability, shows good application prospects in fields such as high-performance environmental protection packaging materials (food packaging materials and soft drink bottle components, such as bottle bodies and bottle cap assemblies).

[0132] Table 5 Performance comparison of Example 7, Comparative Example 1 and currently commercially available plastics PBT, PBAT and PBS

[0133]

[0134] Compared with Comparative Example 1 and currently commercial plastics such as petroleum-based polybutylene terephthalate (PBT, C. Lavilla, A. Martínez de Ilarduya, A. Alla, M. G. García-Martín, J. A. Galbis, S. Munoz-Guerra, Bio-Based Aromatic Polyesters from a Novel Bicyclic Diol Derived from D-Mannitol. Macromolecules 2012, 45, 8257) and biodegradable poly(butylene adipate-co-terephthalate) (PBAT, Qingyang Luan, Han Hu, Xingyu Ouyang, Xiaoyu Jiang, Chen Lin, Hanxu Zhu, Ting Shi, Yi Lei Zhao, Jinggang Wang, Jin Zhu. New modifications of PBAT by a small amount of oxalic acid: Fast crystallization and enhanced degradation in all natural environments, Journal of Hazardous Materials 2024, 465, 133475.), poly(butylene succinate) (PBS, Liuchun Zheng, Xuedong Lv, Yongjun Zhang, Yi Liu. Biodegradable poly(butylene succinate) copolyesters modified by rigid 2,2,4,4-Tetramethyl-1,3-Cyclobutanediol, Polymer 2024, 313, 127672) (as shown in Table 5), Example 7 exhibits more excellent performance in many key performance indicators, such as the glass transition temperature (T g ), mechanical properties (tensile strength, elongation at break and Young's modulus), and the temperature at 5% weight loss determined by thermogravimetric analysis (TGA) (T d,5％ ), etc.: its T g is increased to 35.9 °C, and the elongation at break is as high as 600%. The rigid ring structure of the citric acid unit enhances the tensile strength of the material to 45 MPa, and the modulus reaches 1230 MPa. From the perspective of environmental friendliness and sustainable development, the development of a novel all-bio-based copolyester based on a citric acid bicyclic monomer will further expand the application of bio-based 2,5-furandicarboxylic acid-based polyesters in the field of high-performance environmental protection packaging materials.

[0135] Therefore, the present invention adopts the above-mentioned all-bio-based copolymer based on citric acid bicyclic monomer, preparation method and application. The citric acid bicyclic monomer significantly increases the glass transition temperature and exhibits good mechanical properties, indicating that the bicyclic monomer based on citric acid has great potential in synthesizing novel bio-based copolyesters with expected thermodynamic properties and is expected to further expand the application scope of 2,5-furandicarboxylic acid-based polyesters.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A fully biobased copolymer based on a citric acid bicyclic monomer, characterized in that: The all-bio-based copolymer includes PB x O y F copolymer and PBO m F n copolymer; Among them, PB x O y The molecular structural formula of the F copolymer is: x is the molar percentage of 1,4 - butanediol; y is the molar percentage of octahydro - 2,5 - pentadienediol, and the value range of y is 5 - 40 mol%, and x + y = 100 mol%. PBO m F n The molecular structural formula of the copolymer is as follows: m is the molar percentage of dimethyl octahydro - 2,5 - pentadienediol dicarbonate, n is the molar percentage of dimethyl 2,5 - furandicarboxylate, the value range of m is 5 - 40 mol%, and m + n = 100 mol%.

2. The preparation method of the all-bio-based copolymer based on the citric acid bicyclic monomer according to claim 1, characterized in that: Including PB x O y Preparation methods of OBF copolymers and PBO x F y Preparation method of F copolymer.

3. The preparation method of the all-bio-based copolymer based on the citric acid bicyclic monomer according to claim 2, wherein: PB x O y The preparation method of the O-F copolymer comprises the following steps: Step 1: Prepare octahydro - 2,5 - pentadienediol; Step 2: Under a nitrogen atmosphere, place octahydro - 2,5 - pentadienediol, 1,4 - butanediol and dimethyl 2,5 - furandicarboxylate in a three - necked round - bottom flask, add a transesterification catalyst, heat and stir to carry out the transesterification reaction; Step 3: After the transesterification reaction, a polycondensation catalyst is added, and the temperature is further increased and the pressure is reduced to carry out a melt polycondensation reaction to finally obtain a PB x O y F copolymer.

4. The preparation method of the all-bio-based copolymer based on the citric acid bicyclic monomer according to claim 3, wherein: In Step 2, the molar ratio of the mixture of octahydro - 2,5 - pentadienediol and 1,4 - butanediol to dimethyl 2,5 - furandicarboxylate is (1.1 - 2):1, the transesterification reaction temperature is 160 - 180 °C, and the reaction time is 2 - 7 h.

5. The preparation method of the all-bio-based copolymer based on the citric acid bicyclic monomer according to claim 3, characterized in that: The transesterification catalyst in Step 2 is one or more of zinc acetate, magnesium acetate, manganese acetate, dibutyltin oxide, tetrabutyl titanate and titanium isopropoxide.

6. The preparation method of the all-bio-based copolymer based on the citric acid bicyclic monomer according to claim 3, characterized in that: In Step 3, the pressure in the three - necked round - bottom flask is less than 100 Pa, the melt polycondensation reaction temperature is 180 - 200 °C, the reaction time is 4 - 6 h, and the polycondensation catalyst is one or more of antimony trioxide, tetrabutyl carbonate, potassium acetate, sodium acetate, zinc acetate.

7. The preparation method of the all-bio-based copolymer based on a bicyclic monomer of citric acid according to claim 2, characterized in that: PBO m F n The preparation method of the copolymer comprises the following steps: S1: Prepare octahydro - 2,5 - pentadienediol; S2: Under a nitrogen atmosphere, place dimethyl octahydro - 2,5 - pentadienediol dicarbonate, 1,4 - butanediol and dimethyl 2,5 - furandicarboxylate in a three - necked round - bottom flask, add a transesterification catalyst, heat and stir to carry out the transesterification reaction; S3. After the transesterification reaction, a polycondensation catalyst is added, and the temperature is further increased while reducing the pressure to carry out a melt polycondensation reaction, and finally PBO is obtained. m F n Copolymer.

8. The preparation method of the all-bio-based copolymer based on the citric acid bicyclic monomer according to claim 7, characterized in that: In S2, the molar ratio of the mixture of dimethyl octahydro - 2,5 - pentadienediol dicarbonate and 1,4 - butanediol to dimethyl 2,5 - furandicarboxylate is (1.1 - 2.5):1, the transesterification reaction temperature is 160 - 180 °C, and the reaction time is 3 - 4 h; The transesterification catalyst is one or more of zinc acetate, dibutyltin oxide, tetrabutyl titanate and titanium isopropoxide.

9. The preparation method of the all-bio-based copolymer based on the citric acid bicyclic monomer according to claim 7, wherein: In S3, the melt polycondensation reaction temperature is 180 - 200 °C, the reaction time is 2 - 7 h, and the polycondensation catalyst is one or more of antimony trioxide, tetrabutyl titanate, titanium isopropoxide.

10. Application of a fully biobased copolymer based on a citric acid bicyclic monomer, characterized in that: Apply the all - biobased copolymer based on the citric acid bicyclic monomer described in Claim 1 to the preparation of high - performance environmentally friendly packaging materials.

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