All-bio-based copolymers based on citric acid bicyclic monomers, preparation methods and applications

Abstract

This invention discloses a fully bio-based copolymer based on a citric acid bicyclic monomer, its preparation method, and its applications, belonging to the field of materials synthesis technology. The invention synthesizes bicyclic OPD diol and OPBMC diester derived from citric acid through redox and transesterification reactions. Subsequently, through melt polycondensation, 1,4-butanediol is partially replaced by OPD, or dimethyl 2,5-furandicarboxylate is replaced by OPBMC, to prepare two series of random copolyesters PBF. x OyF copolymer and PBO m F n Copolymer. This invention utilizes the above-mentioned fully bio-based copolymer based on citric acid bicyclic monomers, its preparation method, and its application. The citric acid bicyclic monomers significantly improve the glass transition temperature and exhibit good mechanical properties, indicating that citric acid-based bicyclic monomers have great potential in synthesizing novel bio-based copolyesters with expected thermodynamic properties, and are expected to further expand the application range of 2,5-furan dicarboxylic acid-based polyesters.

Description

Technical Field

[0001] This invention relates to the field of materials synthesis technology, and in particular to fully bio-based copolymers based on citric acid bicyclic monomers, their preparation methods, and applications. Background Technology

[0002] The demand for bio-based polymers is growing, primarily due to increasing concerns in the plastics industry regarding pollution and sustainability. Over the past few decades, academia and industry have shown a significant increase in interest in polymers derived from renewable resources. Several polyesters, including polylactic acid (PLA), polyhydroxyalkanoates (PHA), and polybutylene succinate (PBS), have been successfully produced from renewable feedstocks and brought to market. However, compared to established engineering plastics such as polyethylene terephthalate (PET) and polycarbonate (PC), these bio-based polyesters still require improvements in mechanical and thermal properties. Their relatively weaker properties are attributed to the lack of aromatic or rigid ring structures in their molecular configurations. Therefore, obtaining rigid monomers from sustainable sources is crucial for the development of novel bio-based polymers.

[0003] 2,5-Furandicarboxylic acid (FDCA) is an important bio-based monomer obtained through the oxidation and hydrolysis of cellulose or starch. Among the 12 value-added biomass chemicals approved by the U.S. Department of Energy, FDCA is the only rigid aromatic monomer. In recent years, significant progress has been made in the research of 2,5-furandicarboxylic acid-based polyesters, such as polyethylene (PEF), propylene (PPF), and butylene (PBF). PBF, synthesized from bio-based 2,5-furandicarboxylic acid and 1,4-butanediol (BDO), has a structure very similar to the petroleum-based polyester poly(butylene terephthalate) (PBT). PBF exhibits excellent flexibility, strength, and thermal stability, making it a promising material for food packaging and beverage bottle components. Nevertheless, it possesses a higher glass transition temperature (T0). g PBF-based copolyesters exhibit better thermal stability during processing and higher mechanical properties in practical applications, which may expand the application range of PBF in current popular fields. Therefore, how to improve the thermal stability of PBF while maintaining its bio-based properties is a key issue. g This is a problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a fully bio-based copolymer based on citric acid bicyclic monomers, its preparation method, and its application. Citric acid bicyclic monomers significantly improve the glass transition temperature and exhibit good mechanical properties, indicating that citric acid-based bicyclic monomers have great potential in synthesizing novel bio-based copolyesters with expected thermodynamic properties, and are expected to further expand the application range of 2,5-furandicarboxylic acid-based polyesters.

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

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

[0007]

[0008] x is the molar percentage of 1,4-butanediol; y is the molar percentage of octahydro-2,5-pentadienyldiol, and the value of y ranges from 5 to 40 mol%, x + y = 100%.

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

[0010]

[0011] m is the molar percentage of octahydro-2,5-pentadienyl diol dimethyl carbonate, n is the molar percentage of dimethyl 2,5-furandicarboxylate, and the value of m ranges from 5 to 40 mol%, with m+n=100%.

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

[0013] This invention also provides a method for preparing the above-mentioned fully bio-based copolymer based on citric acid bicyclic monomers, including PB. x O y Preparation method of F copolymer and PBO x F y Methods for preparing copolymers.

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

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

[0016] Step 2: Under a nitrogen atmosphere, octahydro-2,5-pentadienyldiol, 1,4-butanediol and dimethyl 2,5-furandicarboxylate are placed in a three-necked round-bottom flask, and an ester exchange catalyst is added. The mixture is heated and stirred to carry out the ester exchange reaction.

[0017] Step 3: After the transesterification reaction is completed, a polycondensation catalyst is added, and the temperature is increased and the pressure is reduced to carry out a melt polycondensation reaction, finally yielding PB. x O y F copolymer.

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

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

[0020] Preferably, in step three, the pressure in the three-necked round-bottom flask is less than 100 Pa, the melt polycondensation reaction temperature is 180-200℃, 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] Furthermore, 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 transesterification catalyst is 0.1%-0.8% of the molar amount of dimethyl 2,5-furandicarboxylate.

[0022] Preferred, PBO m F n The method for preparing the copolymer includes the following steps:

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

[0024] S2. Under a nitrogen atmosphere, octahydro-2,5-pentadienyl diol dimethyl carbonate, 1,4-butanediol and dimethyl 2,5-furandicarboxylate were placed in a three-necked round-bottom flask, and an ester exchange catalyst was added. The mixture was heated and stirred to carry out the ester exchange reaction.

[0025] S3. After the transesterification reaction is completed, a polycondensation catalyst is added, and the temperature is raised and the pressure is reduced to carry out a melt polycondensation reaction, finally yielding PBO. m F n Copolymer.

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

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

[0028] Furthermore, the transesterification reaction temperature is 160℃, 170℃ or 180℃, and the reaction time is 4h or 5h.

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

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

[0031] Furthermore, 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-pentadienyldiol 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-pentadienyldiol dimethyl carbonate.

[0032] The present invention also provides the application of the fully bio-based copolymer based on citric acid bicyclic monomers, applying the above-mentioned fully bio-based copolymer based on citric acid bicyclic monomers to the preparation of high-performance environmentally friendly packaging materials.

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

[0034] (1) Bicyclic diols derived from citric acid, namely octahydro-2,5-pentadienyl diol and octahydro-2,5-pentadienyl diol dimethyl carbonate, were synthesized by redox and transesterification reactions. PB was then prepared by melt polycondensation. x O y F copolymer and PBO m F n The copolymer has a citric acid content as high as 40 mol%.

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

[0036] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0037] Figure 1 This is a synthetic route diagram of the PBxOyF copolyester and PBOmFn copolyester of the present invention;

[0038] Figure 2 It is the octahydro-2,5-pentadienyldiol and 2,5-pentadienyldiol dimethyl carbonate prepared in this invention. 1 H-NMR spectrum and 13 C10-NMR spectra, where (a) represents octahydro-2,5-pentadienyldiol. 1 H-NMR spectrum, (b) is octahydro-2,5-pentadienyldiol dimethyl carbonate. 1 13C-NMR spectra, (c) is the 13C-NMR spectrum of octahydro-2,5-pentadienyldiol, and (d) is the 13C-NMR spectrum of octahydro-2,5-pentadienyldiol dimethyl carbonate. 13 C-NMR spectrum;

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

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

[0041] Figure 5 These are the differential scanning calorimetry (DSC) curves of Examples 1-10 and Comparative Example 1 of the present invention, wherein (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 6These are the thermogravimetric (TGA) curves of Examples 1-10 and Comparative Example 1 of the present invention and their corresponding differential thermogravimetric (DTG) curves, wherein (a) is the TGA curve of Examples 1-5 and Comparative Example 1, (b) is the TGA curve of Examples 6-10 and Comparative Example 1, (c) is the DTG curve of Examples 1-5 and Comparative Example 1, and (d) is the DTG curve of Examples 6-10 and Comparative Example 1.

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

[0044] Figure 8 The stress-strain curves for Examples 1-10 and Comparative Example 1 are shown.

[0045] Figure 9 These are the DSC diagrams of Example 2 and Comparative Example 1;

[0046] Figure 10 These are the DSC diagrams of Example 5 and Comparative Example 1;

[0047] Figure 11 These are the DSC diagrams of Example 6 and Comparative Example 1;

[0048] Figure 12 These are mechanical property diagrams of Example 6 and Comparative Example 1;

[0049] Figure 13 These are the DSC diagrams of Example 7 and Comparative Example 1;

[0050] Figure 14 These are mechanical property diagrams of Example 7 and Comparative Example 1. Detailed Implementation

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

[0052] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0053] This invention provides a fully bio-based copolymer based on a citric acid bicyclic monomer, and the preparation method of the fully bio-based copolymer is as follows: Figure 1 As shown, the fully bio-based copolymer includes PB x O y F copolymer and PBO m F n copolymers, such as Figure 1 As 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-pentadienyldiol, and the value of y ranges from 5 to 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-pentadienyl diol dimethyl carbonate, n is the molar percentage of dimethyl 2,5-furandicarboxylate, and the value of m ranges from 5 to 40 mol%, with m+n=100%.

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

[0061] 250 mL of anhydrous methanol was added to a three-necked flask equipped with a magnetic stirrer. 14.08 g of sodium hydroxide (352 mmol) was slowly added at 0 °C, yielding a milky white solution. Subsequently, 60 g of dimethyl 1,3-propanone dicarboxylate (344 mmol) was slowly added dropwise over 1.5 h, resulting in a pale yellow precipitate. The resulting slurry was refluxed at 65 °C with stirring for 3 h until the precipitate was completely dissolved. The oil bath was removed, and 11.4 g of 40% glyoxal aqueous solution (197 mmol) was slowly added with rapid stirring, maintaining an internal temperature of 65-70 °C. The resulting orange-yellow slurry was stirred overnight at 25 °C, filtered under vacuum, and washed with 50 mL of methanol to obtain a pale yellow disodium salt (46.4 g, yield 65%).

[0062] The above 46.4 g disodium salt was dissolved in a mixed solution of 275 mL 1 M hydrochloric acid and 46.4 mL glacial acetic acid, and refluxed at 120 °C for 3 h. After cooling to room temperature, it was extracted with dichloromethane. The organic phase was washed with saturated sodium bicarbonate, dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to give an orange-yellow solid octahydro-2,5-pentadienedione (yield approximately 80%).

[0063] 9.8 g of octahydro-2,5-pentadienedione was dissolved in 118 mL of methanol. 6.9 g of sodium borohydride was slowly added at 0 °C, immediately producing a large number of bubbles. After stirring at room temperature for 12 h, 196 mL of 2 mol / L hydrochloric acid and 392 mL of 4 mol / L sodium hydroxide solution were added sequentially in an ice bath. The mixture was extracted with dichloromethane, and the combined organic phases were dried over anhydrous magnesium sulfate. After filtration, rotary evaporation yielded octahydro-2,5-pentadienedione as a white solid (yield approximately 78%).

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

[0065]

[0066] Synthesis of octahydro-2,5-pentadienyl diol dimethyl carbonate:

[0067] 7.4 g of octahydro-2,5-pentadienyldiol was dissolved in 117 mL of dimethyl carbonate, and 1 mL of tetrabutyl titanate was added as a catalyst. The mixture was refluxed at 85 °C for 36 h to carry out the esterification reaction. After the reaction was completed, the milky white slurry was filtered through an organic phase filter membrane, and the colorless filtrate was concentrated under reduced pressure. The residue was recrystallized from methanol to give the colorless crystalline product octahydro-2,5-pentadienyldiol dimethyl carbonate (yield approximately 50%).

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

[0069]

[0070] Octahydro-2,5-pentadienyldiol 1 H-NMR spectrum as shown Figure 2 As shown in (a), octahydro-2,5-pentadienyldiol 13 C-NMR spectrum as shown Figure 2 As shown in (b), octahydro-2,5-pentadienyl diol dimethyl carbonate 1 H-NMR spectrum as shown Figure 2 As shown in (c), octahydro-2,5-pentadienyl diol dimethyl carbonate 13 C-NMR spectrum as shown Figure 2 As shown in (d) in the figure.

[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-pentadienyl glycol (10.4 mmol, 1.48 g), and the transesterification catalyst titanium isopropoxide (0.2 mol% DMFD, 0.040 g) were added to a reaction flask. Nitrogen gas was introduced into the reaction system, the temperature was raised to 160 °C, and maintained for 4 h, until all byproducts were distilled off, completing the transesterification reaction. During the polycondensation reaction, tetrabutyl titanate (0.2 mol% DMFD, 0.054 g) was added as a polycondensation catalyst, the system pressure was reduced to below 100 Pa, the reaction temperature was raised to 180 °C, and maintained for 3 h, until the Weissenberg effect occurred, yielding product PB. 95 O5F.

[0073] Example 2

[0074] PB 90 O 10 Synthesis of F: Dimethyl 2,5-furandicarboxylate (DMFD, 80 mmol, 14.73 g), 1,4-butanediol (108 mmol, 9.73 g), octahydro-2,5-pentadienyldiol (12 mmol, 1.71 g), and the transesterification catalyst titanium isopropoxide (0.3 mol / L DMFD, 0.061 g) were added to a reaction flask. Nitrogen gas was introduced into the reaction system, the temperature was raised to 170 °C, and maintained for 4 h, until all byproducts were distilled off, completing the transesterification reaction. During the polycondensation reaction, tetrabutyl titanate (0.2 mol% DMFD, 0.054 g) was added as a polycondensation catalyst, the system pressure was reduced to below 100 Pa, the reaction temperature was raised to 180 °C, and maintained for 4 h, until the Weissenberg effect occurred, yielding product PB. 90 O 10 F.

[0075] Example 3

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

[0077] Example 4

[0078] PB 70 O 30 Synthesis of F: Dimethyl 2,5-furandicarboxylate (DMFD, 80 mmol, 14.73 g), 1,4-butanediol (100.8 mmol, 9.09 g), octahydro-2,5-pentadienyl glycol (43.2 mmol, 6.15 g), and the transesterification catalyst dibutyltin oxide (0.6 mol% DMFD, 0.119 g) were added to a reaction flask. Nitrogen gas was introduced into the reaction system, the temperature was raised to 170 °C, and maintained for 6 h, until all byproducts were distilled off, completing the transesterification reaction. During the polycondensation reaction, antimony trioxide (0.8 mol% DMFD, 0.187 g) was added as a polycondensation catalyst, the system pressure was reduced to below 100 Pa, the reaction temperature was raised to 200 °C, and maintained for 4 h, until the Weissenberg effect occurred, yielding product PB. 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-pentadienyl diol (44.8 mmol, 6.38 g), and transesterification catalysts titanium isopropoxide (0.2 mol% DMFD, 0.04 g) and tetrabutyl titanate (0.15 mol% diester, 0.041 g) were added to a reaction flask. Nitrogen gas was introduced into the reaction system, the temperature was raised to 180 °C and maintained for 7 h, and the reaction was continued until all byproducts were distilled off, completing the transesterification reaction. During the polycondensation reaction, titanium isopropoxide (0.4 mol% DMFD, 0.08 g) was added as a polycondensation catalyst, the system pressure was reduced to below 100 Pa, the reaction temperature was raised to 200 °C and maintained for 6 h, until the Weissenberg effect occurred, yielding product PB. 60 O 40 F.

[0081] Example 6

[0082] PBO5F 95 Synthesis: Dimethyl 2,5-furandicarboxylate (DMFD, 76 mmol, 13.99 g), octahydro-2,5-pentadienyl diol dimethyl 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 gas was introduced into the reaction system, the temperature was raised to 160℃ and maintained for 3.5 h, and the reaction continued until all byproducts were distilled off, yielding low molecular weight oligomers, thus completing the transesterification reaction. During the polycondensation reaction, tetrabutyl titanate (0.1 mol% (DMFD+OPBMC)), a polycondensation catalyst (0.04 g), was added. The pressure of the system was gradually reduced to below 100 Pa, the reaction temperature was raised to 180℃ and maintained for 4 h, until the Weissenberg effect occurred, yielding the product PBO5F. 95 .

[0083] Example 7

[0084] PBO 10 F 90Synthesis: Dimethyl 2,5-furandicarboxylate (DMFD, 72 mmol, 13.26 g), octahydro-2,5-pentadienyl diol 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 gas was introduced into the reaction system, the temperature was raised to 160 °C and maintained for 4 h, and the reaction continued until all byproducts were distilled off, yielding low molecular weight oligomers, thus completing the transesterification reaction. During the polycondensation reaction, 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 occurred, yielding the product PBO. 10 F 90 .

[0085] Example 8

[0086] PBO 20 F 80 Synthesis: Dimethyl 2,5-furandicarboxylate (DMFD, 64 mmol, 11.78 g), octahydro-2,5-pentadienyl diol dimethyl carbonate (OPBMC, 16 mmol, 4.12 g), 1,4-butanediol (200 mmol, 18.02 g), and titanium isopropoxide (0.2 mol% (DMFD+OPBMC)), 0.04 g), an esterification catalyst, were added to a reaction flask. Nitrogen gas was introduced into the reaction system, the temperature was raised to 170 °C and maintained for 4 h, and the reaction continued until all byproducts were distilled off, yielding low molecular weight oligomers, thus completing the esterification reaction. During the polycondensation reaction, antimony trioxide (0.6 mol% (DMFD+OPBMC)), 0.14 g), a polycondensation catalyst, was added. The system pressure 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 occurred, yielding the product PBO. 20 F 80 .

[0087] Example 9

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

[0089] Example 10

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

[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 titanium isopropoxide (0.2 mol% DMFD, 0.04 g), a transesterification catalyst, were added to a reaction flask. Nitrogen gas was introduced into the reaction system, the temperature was raised to 170 °C, and maintained for 4 h until all byproducts were distilled off, completing the transesterification reaction. During the polycondensation reaction, titanium isopropoxide (0.1 mol% DMFD, 0.02 g), a polycondensation catalyst, was added, the system pressure was reduced to below 100 Pa, the reaction temperature was raised to 180 °C, and maintained for 4 h until the Weissenberg effect occurred, yielding the product PBF.

[0093] The products obtained in Examples 1-10 and Comparative Example 1 were characterized in terms of performance.

[0094] I. Viscosity Test:

[0095] The intrinsic viscosity [η] of the copolyester was determined using an Ubbelohde viscometer (model B-013205, capillary inner diameter 0.7-0.8 mm). The test medium was a 1,1,2,2-tetrachloroethane / phenol mixed solvent (mass ratio 2:3), and the test was conducted at a constant temperature of 25℃. The specific concentration logarithmic viscosity and viscosity-average molecular weight of the copolyester were calculated using the following formulas:

[0096]

[0097] Where t0 is the solvent effluent time, t1 is the solution effluent time, and c is the solution concentration (5 g / L). K and α are the characteristic constants of the test system (K = 2.11 × 10⁻⁶). -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) is... η The concentrations fluctuated between 27.7 and 47.6 kg / mol. The yields of all copolymers ranged from 80% to 89%.

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

[0100]

[0101] II. Structural Characterization

[0102] The nuclear magnetic resonance spectrometer used to measure the nuclear magnetic resonance spectrometers of Examples 1-10 and Comparative Example 1 was used. 1 H-NMR and 13C-NMR spectra, with a mixed solution of deuterated chloroform / trifluoroacetic acid (volume ratio 1:2) as the solvent, results are as follows: Figure 3 and Figure 4 As shown.

[0103] Depend on Figure 3 As shown in (a), 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 peaks of -CH-(9 and 9′) in the furan ring appear at 7.45 ppm. For Examples 1-5 (PB) x O y For the F copolymer, the proton signal at 5.43 ppm is attributed to hydrogen atoms at positions 3 / c and 7 / g, and the signal at 2.66 ppm corresponds to hydrogen atoms at positions 1 / a and 5 / e. The signal at 2.34 ppm originates 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-pentadienyldiol unit. Figure 3 As shown in (b), apart from 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-pentadienyldiol dimethyl carbonate unit correspond to 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] Examples 1-5 and Comparative Example 1 13 C-NMR spectrum ( Figure 4 As shown in (a)), the carbon atom 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-pentadienyldiol 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 ( Figure 4 The signals at (b)), 22 ppm (13 / 15), 68 ppm (14), and 158 ppm (16 / 17) are attributed to the octahydro-2,5-pentadienyl diol dimethyl carbonate segment. All 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 Performance Characterization

[0106] Differential scanning calorimetry

[0107] The thermal properties of the copolymer were studied using a TA Instruments DSC-25 differential scanning calorimeter under a nitrogen atmosphere. The specific procedure was as follows: 5-10 mg of sample was weighed and placed in an aluminum crucible, heated to 200 °C at 10 °C / min and held at that temperature for 3 min to eliminate thermal history; the temperature was then lowered to 0 °C at 10 °C / min and held for 3 min; the temperature was then raised to 200 °C again at the same rate.

[0108] Figure 5 The differential scanning calorimetry (DSC) curves of Examples 1-10 and Comparative Example 1 are shown in Table 2, and the corresponding data are listed in Table 2. By comparing Examples 1-5 ( Figure 5 (a) and Examples 6-10 Figure 5 The melting point and enthalpy of fusion (ΔH) of the homopolymer obtained in (b) and ratio 1 m It can be observed that after introducing octahydro-2,5-pentadienyldiol or octahydro-2,5-pentadienyldiol dimethyl carbonate, the T in Examples 1-10... m and ΔH m All showed a significant decrease. This indicates that the regularity of the polymer chains was severely disrupted due to the increased rigidity of the bicyclic citric acid units, resulting in the formation of imperfect crystals with lower melting points. All copolymers exhibited a single T... g This indicates that there is no microphase separation in the amorphous regions of Examples 1-10. Unlike the melting behavior, the T0 of Examples 1-10... g The increase is due to the introduction of citric acid bicyclic units, as the citric acid structure imparts higher rigidity to the copolymer chains, thereby reducing free volume. Specifically, T in Examples 1-5... g The improvement is more significant because the flexible 1,4-butanediol segment in Examples 1-5 is replaced by the more rigid octahydro-2,5-pentadienyldiol unit.

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

[0110]

[0111] Thermogravimetric analysis

[0112] Thermal stability was evaluated using a TGA-Q50 thermogravimetric analyzer under a nitrogen atmosphere (flow rate 40 mL / min). 5-10 mg of Examples 1-10 and Comparative Example 1 were taken and thermogravimetric analysis was performed by increasing the temperature from room temperature to 500 °C at a programmed rate of 20 °C / min.

[0113] Thermal stability is an important performance indicator for polymer applications and processing. Figure 6 The thermogravimetric (TGA) curves of Examples 1-10 and Comparative Example 1 of this invention and their corresponding differential thermogravimetric (DTG) curves are shown in Table 3. Relevant statistical data are shown in Table 3.

[0114] The thermal decomposition of Comparative Example 1 is a single-step process, with an initial 5% weight loss temperature (T). d The temperature at which the maximum decomposition rate (T5%) is 359℃ is also the temperature at which the maximum decomposition rate (T5%) is reached. d,max1 The temperature was 390°C. In contrast, Examples 1-5 ( Figure 6 (a) and Figure 6 (b) in Examples 6-10 Figure 6 (c) and Figure 6 The thermal stability of (d) is significantly reduced, and its thermal decomposition process is more complex, exhibiting two distinct decomposition stages (T) under a nitrogen atmosphere. d,max1 and T d,max2 The additional thermal decomposition observed at 312–332 °C is attributed to the decomposition of citric acid units. However, these copolyesters retain a largely unchanged structure even at 300 °C, indicating their suitability for efficient thermal processing.

[0115] Table 3 Thermal stability 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. Characterization of Crystallization Properties

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

[0119] Figure 7 These are the wide-angle X-ray diffraction (WAXD) spectra of Embodiments 1-10 and Comparative Example 1 of the present invention, obtained by... Figure 7 (a) and Figure 7 As shown in (b), Comparative Example 1 is a semi-crystalline polymer, exhibiting characteristic diffraction peaks at 2θ = 17.88°, 22.34°, and 24.77°. The diffraction peak positions of Examples 1, 2, and 6 are consistent with Comparative Example 1, indicating that they have the same crystalline structure. The remaining examples did not show obvious diffraction peaks, indicating that they exhibit amorphous characteristics. With the increase of citric acid unit content, the crystallinity of the copolyester gradually decreased, and the introduction of octahydro-2,5-pentadienyldiol dimethyl carbonate units had a more significant inhibitory effect on crystallinity than octahydro-2,5-pentadienyldiol units. This phenomenon is consistent with the trend of melting enthalpy change measured by DSC, which may be due to the steric hindrance effect of octahydro-2,5-pentadienyldiol dimethyl carbonate units, leading to difficulties in molecular chain stacking and a decrease in chain segment mobility.

[0120] V. Characterization of Mechanical Properties

[0121] Tensile property testing: Tests were conducted at 25°C using a universal testing machine (CMT6104, MITES Industrial Systems (China) Co., Ltd.) according to ASTM D638 standard. The crosshead speed was 5 mm / min. Dumbbell-shaped specimens (2 mm wide, 5 mm thick) were prepared using a miniature injection molding machine (SZS-15, Wuhan Ruiming Experimental Instrument Co., Ltd.).

[0122] Figure 8 The stress-strain curves for Examples 1-10 and Comparative Example 1 are shown in Table 4. The presence of bicyclic citric acid units significantly affects the tensile properties of the copolymers. In Examples 6-10, tensile strength and Young's modulus initially increased and then decreased with increasing octahydro-2,5-pentadienyl diol dimethyl carbonate content, with properties beginning to decline when its content exceeded 28 mol%. This behavior is likely due to the decreased molecular weight and crystallinity in Examples 8 and 9. Although crystallinity decreased with increasing octahydro-2,5-pentadienyl diol dimethyl carbonate content, the tensile strength of Examples 6 and 7 was significantly higher than that of Comparative Example 1, ranging from 35 to 45 MPa. This improvement can be attributed to the competing effect between increased chain rigidity and decreased crystallinity. Furthermore, Examples 1-2 exhibited brittle fracture characteristics, with tensile strength and elongation at break significantly decreasing with increasing octahydro-2,5-pentadienyl diol content.

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

[0124]

[0125] In summary, Figure 9 These are the DSC charts of Example 2 and Comparative Example 1. As can be seen from the charts, the glass transition temperature (T) of Example 2 is... g The temperature increased from 36.4℃ in Comparative Example 1 to 43.1℃.

[0126] Figure 10 These are the DSC charts of Example 5 and Comparative Example 1. As can be seen from the charts, the glass transition temperature (T) of Example 5 is... g The temperature increased from 36.4℃ in Comparative Example 1 to 63.1℃.

[0127] Figure 11 These are the DSC charts of Example 6 and Comparative Example 1. As can be seen from the charts, the glass transition temperature (T) of Example 6 is... g The temperature increased from 36.4℃ in Comparative Example 1 to 63.1℃.

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

[0129] Figure 13 These are the DSC charts of Example 7 and Comparative Example 1. As can be seen from the charts, the glass transition temperature (T) of Example 7 is... g The temperature was increased from 36.4℃ in Comparative Example 1 to 39.7℃.

[0130] Figure 14 The graph shows the mechanical properties of Example 7 and Comparative Example 1. As can be seen from the graph, the tensile strength, Young's modulus and elongation at break of Example 7 increased from 33 MPa, 897 MPa and 450% of Comparative Example 1 to 45 MPa, 1230 MPa and 600%, respectively.

[0131] The fully bio-based copolymer prepared in Example 7, with its excellent flexibility, mechanical strength, and thermal stability, shows promising application prospects in high-performance environmentally friendly packaging materials (food packaging materials and soft drink bottle components, such as bottle bodies and caps).

[0132] Table 5 compares the performance of Example 7 with Comparative Example 1 and currently commercially available plastics PBT, PBAT, and PBS.

[0133]

[0134] Compared with Comparative Example 1 and currently commercially available 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 polybutylene adipate 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.), compared with polybutylene 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 showed better performance in several key performance indicators, such as glass transition temperature (T). g Mechanical properties (tensile strength, elongation at break, and Young's modulus), and the temperature at which 5% weight loss occurs, as determined by thermogravimetric analysis (TGA) (T... d,5％ It exhibits superior performance in aspects such as T g The elongation at break reaches 600% at a temperature increased to 35.9℃. The rigid ring structure of the citric acid unit enhances the tensile strength to 45MPa and the modulus to 1230MPa. From an environmentally friendly and sustainable development perspective, the development of novel fully bio-based copolyesters based on citric acid bicyclic monomers will further expand the application of bio-based 2,5-furan dicarboxylic acid polyesters in the field of high-performance environmentally friendly packaging materials.

[0135] Therefore, the present invention employs the above-mentioned fully bio-based copolymer based on citric acid bicyclic monomers, preparation method and application. Citric acid bicyclic monomers significantly improve the glass transition temperature and exhibit good mechanical properties. This indicates that citric acid-based bicyclic monomers have great potential in synthesizing novel bio-based copolyesters with expected thermodynamic properties, and are expected to further expand the application range of 2,5-furan dicarboxylic 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 not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A fully bio-based copolymer based on a citric acid bicyclic monomer, characterized in that: All-bio-based copolymers include 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-pentadienyldiol, and the value of y ranges from 5 to 40 mol%, x + y = 100 mol%. PBO m F n The molecular structural formula of the copolymer is: m is the molar percentage of octahydro-2,5-pentadienyl diol dimethyl carbonate, n is the molar percentage of dimethyl 2,5-furandicarboxylate, and the value of m ranges from 5 to 40 mol%, with m+n=100 mol%.

2. The method for preparing the fully bio-based copolymer based on citric acid bicyclic monomers as described in claim 1, characterized in that: Including PB x O y Preparation method of F copolymer and PBO x F y Methods for preparing copolymers.

3. The method for preparing the fully bio-based copolymer based on citric acid bicyclic monomers according to claim 2, characterized in that: PB x O y The preparation method of F copolymer includes the following steps: Step 1: Preparation of octahydro-2,5-pentadienediol; Step 2: Under a nitrogen atmosphere, octahydro-2,5-pentadienyldiol, 1,4-butanediol and dimethyl 2,5-furandicarboxylate are placed in a three-necked round-bottom flask, and an ester exchange catalyst is added. The mixture is heated and stirred to carry out the ester exchange reaction. Step 3: After the transesterification reaction is completed, a polycondensation catalyst is added, and the temperature is increased and the pressure is reduced to carry out a melt polycondensation reaction, finally yielding PB. x O y F copolymer.

4. The method for preparing the fully bio-based copolymer based on citric acid bicyclic monomers according to claim 3, characterized in that: In step two, the molar ratio of the mixture of octahydro-2,5-pentadienyldiol and 1,4-butanediol to dimethyl 2,5-furandicarboxylate is (1.1-2):1, the transesterification reaction temperature is 160-180℃, and the reaction time is 2-7h.

5. The method for preparing the fully bio-based copolymer based on citric acid bicyclic monomers according to claim 3, characterized in that: The transesterification catalyst in step two is one or more of zinc acetate, magnesium acetate, manganese acetate, dibutyltin oxide, tetrabutyl titanate, and titanium isopropoxide.

6. The method for preparing the fully bio-based copolymer based on citric acid bicyclic monomers according to claim 3, characterized in that: In step three, the pressure in the three-necked round-bottom flask is less than 100 Pa, the melt polycondensation reaction temperature is 180-200℃, 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.

7. The method for preparing the fully bio-based copolymer based on citric acid bicyclic monomers according to claim 2, characterized in that: PBO m F n The method for preparing the copolymer includes the following steps: S1. Preparation of octahydro-2,5-pentadienediol; S2. Under a nitrogen atmosphere, octahydro-2,5-pentadienyl diol dimethyl carbonate, 1,4-butanediol and dimethyl 2,5-furandicarboxylate were placed in a three-necked round-bottom flask, and an ester exchange catalyst was added. The mixture was heated and stirred to carry out the ester exchange reaction. S3. After the transesterification reaction is completed, a polycondensation catalyst is added, and the temperature is raised and the pressure is reduced to carry out a melt polycondensation reaction, finally yielding PBO. m F n Copolymer.

8. The method for preparing the fully bio-based copolymer based on citric acid bicyclic monomers according to claim 7, characterized in that: In S2, the molar ratio of the mixture of octahydro-2,5-pentadienyl diol dimethyl carbonate and 1,4-butanediol to dimethyl 2,5-furandicarboxylate is (1.1-2.5):1, the transesterification reaction temperature is 160-180℃, and the reaction time is 3-4h. The transesterification catalyst is one or more of zinc acetate, dibutyltin oxide, tetrabutyl titanate, and titanium isopropoxide.

9. The method for preparing the fully bio-based copolymer based on citric acid bicyclic monomers according to claim 7, characterized in that: In S3, the melt polycondensation reaction temperature is 180-200℃, the reaction time is 2-7h, and the polycondensation catalyst is one or more of antimony trioxide, tetrabutyl titanate, and titanium isopropoxide.

10. The application of a fully bio-based copolymer based on a citric acid bicyclic monomer, characterized in that: The fully bio-based copolymer based on citric acid bicyclic monomers as described in claim 1 is applied to the preparation of high-performance environmentally friendly packaging materials.

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