Crystalline bifuran polyamide with high barrier property and strong ultraviolet absorptivity as well as preparation method and application of crystalline bifuran polyamide

Abstract

The invention relates to crystalline bifuran polyamide with high barrier property and strong ultraviolet absorptivity as well as a preparation method and application thereof, and belongs to the technical field of bio-based high polymer materials. The crystalline bifuran polyamide is obtained through an interfacial polymerization reaction of a bifuran acyl chloride monomer and an alicyclic diamine monomer. According to the crystalline bifuran polyamide provided by the invention, high crystallinity is realized by eliminating intramolecular hydrogen bonds, so that the bifuran polyamide material has excellent barrier property, strong ultraviolet absorption capacity and good mechanical property. The material has strong ultraviolet absorption capability, and can completely absorb ultraviolet light below 400nm; meanwhile, the polyamide film has excellent gas barrier property, the oxygen transmission rate is as low as 0.0139 barrer, the water vapor transmission rate is 0.94 * 10 <-4 > g.cm / cm.s.Pa, the polyamide film is in a leading level in the field of polyamide barrier materials, and the polyamide film has a wide application prospect in the fields of isolation packaging materials and ultraviolet shielding materials.

Description

Technical Field

[0001] This invention belongs to the field of bio-based polymer materials technology, and more specifically, relates to a crystalline bifuran polyamide with high barrier properties and strong ultraviolet absorption, its preparation method, and its application. Background Technology

[0002] Under the background of sustainable development strategy, the synthesis of bio-based polyamides using renewable biomass resources to replace petroleum-based products has become a research hotspot. 2,5-Furandicarboxylic acid (FDCA) is considered an ideal monomer to replace terephthalic acid due to its renewable, readily available, and environmentally friendly raw material source. Studies have shown that FDCA-based polymers can achieve or even outperform traditional petroleum-based aromatic polymers in terms of thermal, mechanical, and barrier properties.

[0003] 2,2'-Bifuran-5,5'-dicarboxylic acid (BFDCA) is an important derivative of FDCA, consisting of two coplanar furan rings linked by a 180° dihedral angle, forming an extended π-π conjugated structure. Compared to monofurans and biphenyls, bifurans exhibit stronger molecular rigidity due to their higher intercyclic rotational energy barrier, which helps improve the planarity, rigidity, mechanical properties, light absorption capacity, heat resistance, and gas barrier properties of furan-based polymers. Previous studies have shown that BFDCA-based polyesters have higher glass transition temperatures than PET and PEF, and exhibit higher modulus retention at high temperatures; their highly conjugated molecular structure also endows the materials with excellent UV absorption capabilities.

[0004] However, existing furan polyamides generally exhibit weak crystallinity. Studies have shown that the introduction of furan rings reduces hydrogen bonding between polyamide molecular chains while promoting intramolecular hydrogen bonding, thus hindering the orderly stacking of molecular chains and leading to a decrease in crystallinity. Since gas molecules have difficulty penetrating or diffusing through the crystalline regions of the polymer, the degree of crystallinity has a decisive influence on the gas barrier properties of the material. Therefore, how to eliminate intramolecular hydrogen bonds and improve the crystallinity of furan polyamides through molecular design, thereby synergistically enhancing their thermal properties, mechanical properties, UV absorption properties, and barrier properties, is a pressing technical problem that needs to be solved. Summary of the Invention

[0005] This invention overcomes the shortcomings of existing furan polyamides, such as low crystallinity, insufficient barrier properties, and inadequate UV absorption. It obtains crystalline furan polyamides through interfacial polymerization of a difuranyl chloride monomer and an alicyclic diamine monomer. The crystalline furan polyamide provided by this invention achieves high crystallinity by eliminating intramolecular hydrogen bonds, thus possessing excellent barrier properties, strong UV absorption capacity, and good mechanical properties.

[0006] According to a first aspect of the present invention, a method for preparing crystalline synfuran polyamide is provided, comprising the following steps: (1) The bifuran dicarboxylic acid was reacted with excess thionyl chloride under reflux in the presence of a catalyst to obtain the bifuranyl chloride monomer; (2) Dissolve the bifuranyl chloride monomer obtained in step (1) in an organic solvent to obtain an organic phase, then add an alkaline aqueous solution to form a phase interface, then add an alicyclic diamine monomer dissolved in an alkaline aqueous solution to carry out an interfacial polymerization reaction to obtain crystalline bifuran polyamide.

[0007] Preferably, the alicyclic diamine monomer is piperazine or 4,4'-bipiperidine.

[0008] Preferably, in step (1), the catalyst is N,N-dimethylformamide, and the amount of N,N-dimethylformamide added is 0.5%-0.8% of the mass of bifurandicarboxylic acid.

[0009] Preferably, in step (1), the reflux reaction time is 3-8 hours.

[0010] Preferably, in step (2), the molar ratio of the alicyclic diamine monomer to the difuranyl chloride monomer is 1:1.

[0011] Preferably, in step (2), the alkaline aqueous solution is a KOH aqueous solution with a concentration of 0.5~2 mol / L.

[0012] Preferably, in step (2), the precipitate obtained after the interfacial polymerization reaction is filtered, washed with water and organic solvent in sequence, and then dried to obtain crystalline synfuran polyamide.

[0013] According to another aspect of the present invention, a crystalline synfuran polyamide is provided.

[0014] According to another aspect of the invention, the application of the crystalline synfuran polyamide in barrier packaging materials is provided.

[0015] According to another aspect of the present invention, the application of the crystalline synfuran polyamide in ultraviolet shielding materials is provided.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: (1) The crystalline bifuran polyamide prepared in this invention possesses excellent comprehensive properties: high crystallinity, excellent ultraviolet absorption performance, outstanding gas barrier properties, and good mechanical properties. Firstly, regarding ultraviolet absorption performance: the crystalline bifuran polyamide can completely absorb ultraviolet light below 400 nm, with a red shift of approximately 30 nm compared to monofuran polyamide. This is attributed to the synergistic enhancement effect of the bifuran extended π-π conjugated system and the crystalline ordered structure on light absorption. Secondly, regarding gas barrier properties: the oxygen transmittance of PABFPE is as low as 0.0139 barrer, and the water vapor transmittance is 0.94 × 10⁻⁶. -4 The performance is superior to most existing polyamide materials, exhibiting a high g·cm / cm²·s·Pa ratio. High crystallinity increases the volume fraction of impermeable crystalline regions, forcing gas molecules to diffuse along tortuous paths. Simultaneously, the anchoring effect of the crystalline regions on surrounding chain segments further reduces free volume. Finally, thermal stability: the glass transition temperature of bifuran polyamide reaches a maximum of 193℃, and the 5% thermal decomposition temperature reaches 393℃, significantly better than monofuran polyamide.

[0017] (2) The crystalline bifuran polyamide prepared by the present invention has high crystallinity, ranging from 55.0% to 78.6%. The PABFPE synthesized from piperazine and bifuranyl chloride has a crystallinity of 78.6%, and the PABFBPE synthesized from 4,4'-bipiperidine and bifuranyl chloride has a crystallinity of 55.0%.

[0018] (3) The crystalline bifuran polyamide prepared by the present invention has excellent ultraviolet absorption properties and can completely absorb ultraviolet light with wavelengths below 400nm, exhibiting excellent ultraviolet blocking ability and can be applied to ultraviolet shielding materials.

[0019] (4) The crystalline bifuran polyamide prepared in this invention has excellent gas barrier properties, with an oxygen permeability of 0.0139–0.0292 barrers and a water vapor permeability of 0.94 × 10⁻⁶. -4 ~2.81×10 -4 g·cm / cm²·s·Pa. PABFPE has an oxygen permeability as low as 0.0139 barrer and a water vapor permeability of 0.94 × 10⁻⁶. -4 g·cm / cm²·s·Pa, which is at the leading level in the field of polyamide barrier materials.

[0020] (5) The crystalline bifuran polyamide prepared by the present invention has good thermal stability, with a glass transition temperature of 143-193℃, a 5% thermal decomposition temperature of 393-409℃, and a maximum thermal decomposition temperature of 431-465℃.

[0021] (6) This invention is the first to successfully eliminate the hydrogen bonding effect within the molecular chain of furan polyamide by introducing alicyclic diamines (piperazine, 4,4'-bipiperidine). Traditional furan polyamides have obvious intramolecular hydrogen bonds, which restrict the regular arrangement of chain segments; while this invention shields the intramolecular hydrogen bonds through molecular design, enabling the molecular chains to achieve close packing, thereby obtaining high crystallinity.

[0022] (7) The preparation process of the present invention is green and environmentally friendly. The present invention adopts interfacial polymerization method, which has mild reaction conditions and simple operation. The synthesized polymer is white in color and has a high molecular weight, which is in line with the concept of green and sustainable development. Attached Figure Description

[0023] Figure 1 The TGA and DSC curves of the polymers prepared in Examples 2-3 and Comparative Examples 1-8 are as follows: (a) DSC curve of the monofuran polymer after the second heating; (b) DSC curve of the bifuran polymer after the second heating; (c) TGA curve of the monofuran polymer; (d) TGA curve of the bifuran polymer.

[0024] Figure 2 The XRD curves of the polymers prepared in Examples 2-3 and Comparative Examples 1-8 are as follows: (a) XRD curves of monofuran polyamides PAF6, PAF8, and PAF10; (b) XRD curves of monofuran polyimide PAFPE; (c) XRD curves of monofuran polyimide PAFBPE; (d) XRD curves of difuran polyamides PABF6, PABF8, and PABF10; (e) XRD curves of difuran polyimide PABFPE; (f) XRD curves of difuran polyimide PABFBPE.

[0025] Figure 3 The ultraviolet-visible absorption spectra of the polymer films prepared in Examples 2-3 and Comparative Examples 1-8 are as follows: (a) Ultraviolet absorption spectrum of monofuran polymer; (b) Ultraviolet absorption spectrum of bifuran polymer. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0027] This invention provides a method for preparing a crystalline bifuran polyamide with high barrier properties and strong ultraviolet absorption, comprising the following steps: (1) Synthesis of bifuranyl chloride monomer: Under reflux condensation conditions, bifuran dicarboxylic acid was added to the reaction vessel, placed in an ice-water bath, excess thionyl chloride was added, and a catalyst was added. The temperature was raised to the oil bath temperature under stirring, and the reaction was refluxed for 4-6 hours. After the reaction was completed, excess thionyl chloride was removed by rotary evaporation to obtain bifuranyl chloride monomer.

[0028] (2) Interfacial polymerization reaction: The bifuranyl chloride monomer obtained in step (1) is dissolved in an organic solvent to obtain an organic phase; an alkaline aqueous solution is slowly added to the obtained solution to form a phase interface; then the alicyclic diamine monomer dissolved in the alkaline aqueous solution is slowly added along the wall of the container, wherein the molar ratio of the alicyclic diamine monomer to the bifuranyl chloride monomer is 1:1; the obtained mixture is vigorously stirred for 20 to 30 hours to carry out the interfacial polymerization reaction.

[0029] (3) Post-treatment: After the reaction is completed, the precipitate in the reaction system is filtered, and the residue is washed with water and organic solvent in sequence, and dried to obtain bifuran polyamide.

[0030] In some embodiments, the catalyst in step (1) is DMF, and the amount added is 0.5%-0.8% of the mass of difurandicarboxylic acid; the reflux reaction time is 3-8 hours.

[0031] In some embodiments, the organic solvent in step (2) is dichloromethane; the alkaline aqueous solution is KOH aqueous solution with a concentration of 0.5~2 mol / L, more preferably 1 mol / L.

[0032] In some embodiments, the alicyclic diamine monomer in step (2) is piperazine or 4,4'-bipiperidine. By introducing an alicyclic diamine, the hydrogen bonding within the polyamide molecular chain is successfully eliminated, enabling the molecular chain to achieve regular stacking and thus obtaining high crystallinity.

[0033] In some embodiments, the organic solvent used for washing in step (3) includes methanol and dichloromethane.

[0034] The following are specific examples.

[0035] Example 1: Synthesis of bifuranyl chloride monomer (BFDCl) 300 mg of bifurandicarboxylic acid was added to a 500 ml round-bottom flask equipped with a magnetic stirrer. The flask was placed in an ice-water bath, and excess thionyl chloride was added while stirring. 0.5% (by weight of) DMF catalyst (1.5 mg) of bifurandicarboxylic acid was added using a pipette. The ice-water bath was removed, and the mixture was refluxed in an oil bath for 5 h. After the reaction was complete, excess thionyl chloride was removed by rotary evaporation to obtain 325 mg of bifuranyl chloride monomer (BFDCl), with a yield of 93.0%.

[0036] Example 2: Synthesis of Crystalline Allylfuran Polyamide PABFPE 300 mg of the bifuranyl chloride (1.16 mmol) prepared in Example 1 was dissolved in 3 ml of dichloromethane in a 50 ml round-bottom flask equipped with a magnetic flask. A 1 M aqueous solution of KOH (0.9 ml) was slowly added along the wall of the flask to induce phase separation. 100.0 mg (1.16 mmol) of the diamine monomer piperazine was dissolved in 1 mol / L KOH (2.7 ml) and then slowly added along the wall of the flask to the above system. The resulting mixture was stirred vigorously for 24 hours. After the reaction was complete, the precipitate was filtered off, and the residue was washed successively with water, methanol, and dichloromethane, and dried to obtain poly(piperazine-1,4-diyl-2,2'-bifuran-5,5'-dicarbonyl) (PABFPE). XRD characterization showed that the polymer was highly crystalline with a crystallinity of 78.6%.

[0037] Example 3: Synthesis of crystalline bifuran polyamide PABFBPE The diamine monomer piperazine was replaced with 4,4'-bipiperidine (1.16 mmol), and the remaining procedures were the same as in Example 2, to synthesize poly(4,4'-bipiperidine-1,1'-diyl-2,2'-bifuran-5,5'-dicarbonyl) (PABFBPE). XRD characterization showed that the polymer was crystalline with a crystallinity of 55.0%.

[0038] Comparative Example 1: Synthesis of Amorphous Furan Polyamide PABF6 300 mg of bifuranyl chloride (1.16 mmol) prepared in Example 1 was dissolved in 3 ml of dichloromethane in a 50 ml round-bottom flask equipped with a magnetic flask. A 1 M aqueous solution of KOH (0.9 ml) was slowly added along the wall of the flask to induce phase separation. 134.8 mg (1.16 mmol) of the aliphatic diamine monomer 1,6-hexanediamine was dissolved in 1 mol / L KOH (2.7 ml) and then slowly added along the wall of the flask to the above system. The resulting mixture was stirred vigorously for 24 hours. After the reaction was complete, the precipitate was filtered off, and the residue was washed successively with water, methanol, and dichloromethane, and dried to obtain poly(hexamethylene bifuranamide) (PABF6). XRD characterization showed that the polymer was amorphous.

[0039] Comparative Example 2: Synthesis of Amorphous Furan Polyamide PABF8 The aliphatic diamine monomer was replaced with 1,8-octanediamine (1.16 mmol), and the remaining procedures were the same as in Comparative Example 1, to synthesize poly(octamethylene difuranamide) (PABF8). XRD characterization showed that the polymer was amorphous.

[0040] Comparative Example 3: Synthesis of Amorphous Furan Polyamide PABF10 The aliphatic diamine monomer was replaced with 1,10-decanediamine (1.16 mmol), and the remaining procedures were the same as in Comparative Example 1, to synthesize poly(decamethylene bifuranamide) (PABF10). XRD characterization showed that the polymer was amorphous.

[0041] Comparative Example 4 300 mg of monofurandicarboxylic acid was added to a 500 ml flask equipped with a magnetic stirrer. The flask was placed in an ice-water bath, and excess thionyl chloride was added while stirring. 0.5% (by weight of the difurandicarboxylic acid) of DMF catalyst (1.5 mg) was added using a pipette. The mixture was refluxed in an oil bath for 5 h. Excess thionyl chloride was removed by rotary evaporation to obtain monofuranyl chloride (FDCl) (346 mg, 93.4% yield).

[0042] Comparative Example 5 In a 50 ml round-bottom flask equipped with a magnetic flask, 300 mg of the monofuranyl chloride (1.16 mmol) prepared in Comparative Example 4 was dissolved in 3 ml of dichloromethane. A 1 M aqueous solution of KOH (0.9 ml) was slowly added along the flask wall to induce phase separation. 134.8 mg (1.16 mmol) of the aliphatic diamine monomer 1,6-hexanediamine was dissolved in 1 mol / L KOH (2.7 ml) and then slowly added along the wall to the above system. The resulting mixture was stirred vigorously for 24 hours. After the reaction was complete, the precipitate was filtered off, and the residue was washed successively with water, methanol, and dichloromethane, and dried to obtain poly(hexamethylene furanamide) (PAF6). XRD characterization showed that the polymer was amorphous.

[0043] Comparative Example 6 The aliphatic diamine monomer was replaced with 1,8-octanediamine (1.16 mmol), and the remaining procedures were the same as in Comparative Example 5, to synthesize poly(octamethylenefuranamide) (PAF8). XRD characterization showed that the polymer was amorphous.

[0044] Comparative Example 7 The aliphatic diamine monomer was replaced with 1,10-decanediamine (1.16 mmol), and the remaining procedures were the same as in Comparative Example 5, to synthesize poly(decamethylene furanamide) (PAF10). XRD characterization showed that the polymer was amorphous.

[0045] Comparative Example 8 The aliphatic diamine monomer was replaced with piperazine (1.16 mmol), and the remaining procedures were the same as in Comparative Example 5, to synthesize poly(piperazine-1,4-diyl-2,5-furandicarbonyl) (PAFPE). XRD characterization showed that the polymer was crystalline.

[0046] Comparative Example 9 The aliphatic diamine monomer was replaced with 4,4'-dipiperidine (1.16 mmol), and the remaining procedures were the same as in Comparative Example 5, to synthesize poly(4,4'-bipiperidine-1,1'-diyl-2,5-furandicarbonyl) (PAFBPE). XRD characterization showed that the polymer was crystalline.

[0047] Performance Test Example 1: Thermal Performance Test The polymers prepared in Examples 2-3, Comparative Examples 1-3, and 5-9 were subjected to TGA and DSC tests, and the results are shown in the figure. Figure 1 And Table 1 (Table 1 shows the glass transition temperature T of the polymer) g 5% weight loss temperature T d-5% (°C) and maximum weight loss temperature T d-max (°C) The 5% thermal decomposition temperatures (Td-5%) of the bifuran polymers PABF6, PABF8, PABF10, PABFPE, and PABFBPE are 409°C, 407°C, 407°C, 393°C, and 403°C, respectively, and their maximum thermal decomposition temperatures (Tmax) are 445°C, 463°C, 465°C, 431°C, and 443°C, respectively, exhibiting excellent thermal stability. The 5% thermal decomposition temperatures (Td-5%) of the monofuran polymers PAF6, PAF8, PAF10, PAFPE, and PAFBPE are 395°C, 405°C, 390°C, 399°C, and 389°C, respectively, and their maximum thermal decomposition temperatures (Tmax) are 445°C, 459°C, 440°C, 431°C, and 418°C, respectively. Regarding the glass transition temperature (Tg), the Tg of PABF6, PABF8, and PABF10 are 149℃, 137℃, and 125℃, respectively, while the Tg of PABFPE and PABFBPE are as high as 193℃ and 143℃, respectively. The Tg of PAF6, PAF8, and PAF10 are 121℃, 113℃, and 72℃, respectively, while the Tg of PABFPE and PABFBPE are as high as 124℃ and 120℃, respectively. The results indicate that the introduction of the bifuran group significantly increases both the thermal decomposition temperature (Td) and the glass transition temperature (Tg) of the materials. This is mainly attributed to the increased rigidity of the molecular structure and the amplification of the conjugation effect. Compared to monofuran polymers, the bicyclic structure of bifurans extends the conjugation length, making the main chain chemical bonds more stable, thereby improving thermal stability. Simultaneously, bifurans increase the internal rotational steric hindrance of the main chain, restricting chain segment movement and leading to a significant increase in the glass transition temperature.

[0048] Crystallinity primarily affects the glass transition temperature (Tg), while its influence on the thermal decomposition temperature (Td) is relatively small. The crystalline regions of crystalline polymers act as physical cross-linking points, restricting the movement of chain segments in the amorphous regions. Therefore, their Tg is typically higher than that of chemically similar but completely amorphous polymers; for example, crystalline PABFPE (Tg = 193℃) is much higher than amorphous PABF6 (149℃). The thermal decomposition temperature, on the other hand, depends mainly on the chemical bond energy of the molecular chains and the intrinsic stability of the conjugated structure, and is less affected by the aggregated structure. Therefore, regardless of crystallinity, as long as the main chain structure is similar (e.g., PABFPE and amorphous PABF8), their Td values ​​remain at a high level with little difference.

[0049] Table 1

[0050] Performance Test Example 2: Crystallization Performance Test XRD tests were performed on the polymers prepared in Examples 2-3, Comparative Examples 1-3, and 5-9, and the results are as follows: Figure 2 As shown, the XRD curves of PAF6, PAF8, PAF10, PABF6, PABF8, and PABF10 show only a broad peak at 2θ≈22°, indicating that they are amorphous polymers. In contrast, PAFPE, PAFBPE, PABFPE, and PABFBPE all exhibit sharp crystallization peaks, with crystallinities as high as 68.8%, 38.2%, 78.6%, and 55.0%, respectively. The reason alicyclic monomers lead to crystallinity is that they suppress intramolecular hydrogen bonds, which are detrimental to crystallization, and promote the formation of intermolecular hydrogen bonds. Simultaneously, their rigidity forces the molecular chains to extend, which is beneficial for orderly stacking. The reason bifurans increase crystallinity is that bifurans have better geometric symmetry, structural elongation, and π-π stacking ability than monofurans. This allows the molecular chains to be arranged more regularly and densely in the crystal lattice, thereby improving the degree of crystallization (i.e., crystallinity). Performance Test Example 3: Ultraviolet Absorption Performance Test UV-Vis spectroscopy was performed on the polymer films prepared in Examples 2-3, Comparative Examples 1-3, and 5-9, and the results are as follows: Figure 3 As shown, the bifuran polymers PABF6, PABF8, PABF10, PABFPE, and PABFBPE exhibit better UV absorption performance than the monofuran polymers PAF6, PAF8, PAF10, PAFPE, and PAFBPE. Among them, the crystalline bifuran polyimides PABFPE and PABFBPE demonstrate excellent UV blocking ability in the UV range below 400 nm, completely absorbing UV light in this band, with an absorption boundary red-shifted by approximately 30 nm compared to monofuran polyamides. This is attributed to the synergistic enhancement effect of the bifuran-extended conjugated system and the crystalline ordered structure.

[0051] Performance Test Example 4: Gas Barrier Performance Test Gas barrier properties of the polymer films prepared in Examples 2-3, Comparative Examples 1-3, and 5-9 were tested, and the results are shown in Table 2. Table 2 shows the oxygen permeability (OP) and water vapor permeability (WVP) of the polymer films in Examples 2 and Comparative Examples 1-8. The oxygen permeability (OP) of the bifuran polyamides PABF6, PABF8, and PABF10 were 0.0180 barrer, 0.0275 barrer, and 0.0292 barrer, respectively, all of which were superior to the corresponding monofuran polyamides PAF6, PAF8, and PAF10, which had oxygen permeability (OP) of 0.0566 barrer, 0.0753 barrer, and 0.0938 barrer, respectively. The water vapor permeability (WVP) of the bifuran polyamides PABF6, PABF8, and PABF10 was 2.81 × 10⁻⁶, respectively. -4 g·cm / cm²·s·Pa, 2.26×10 -4 g·cm / cm²·s·Pa and 1.50×10 -4 The g·cm / cm²·s·Pa values ​​are all superior to the water vapor permeability (WVP) of the corresponding monofuran polyamides PAF6, PAF8, and PAF10, which are 4.25×10 g·cm / cm²·s·Pa respectively. -4 g·cm / cm²·s·Pa, 3.75×10 -4 g·cm / cm²·s·Pa and 3.22×10 -4 The oxygen permeability of crystalline monofuran polyamide PAFPE is 0.0442 barrer, and its water vapor transmission rate (WVP) is 2.82 × 10⁻⁶ g·cm / cm²·s·Pa. -4 g·cm / cm²·s·Pa. Crystalline bifuran polyamide PABFPE exhibits the best barrier properties, with an OP as low as 0.0139 barrer and a water vapor transmission rate (WVP) of 0.94 × 10⁻⁶ g·cm / cm²·s·Pa. -4The g·cm / cm²·s·Pa value is among the leading levels in the field of polyamide barrier materials. Introducing bifuran groups and increasing crystallinity both significantly improve the barrier properties of the material. These two mechanisms work synergistically at different scales to jointly inhibit the permeation of gas or water vapor molecules. On the one hand, the bicyclic rigid structure of bifurans increases the internal rotational steric hindrance of the molecular chain compared to monofurans, reducing the intrinsic free volume of the polymer. Simultaneously, its conjugated planarity facilitates close packing between chains, making small molecule diffusion more difficult. Therefore, amorphous bifuran polymers (such as PABF6) are comprehensively superior to their corresponding monofuran polymers (such as PAF6) in both oxygen permeability and moisture permeability. On the other hand, increased crystallinity introduces impermeable crystalline regions at the supramolecular scale as a physical barrier, forcing permeating molecules to bypass the amorphous regions, greatly extending the diffusion path. At the same time, the crystalline regions also restrict the chain segment movement in the amorphous regions, further reducing permeability. When the rigid chain structure of bifuran is combined with high crystallinity (such as PABFPE with a crystallinity of up to 78.6%), the material achieves optimized barrier performance, with an oxygen permeability as low as 0.0139 barrer and a water vapor permeability as low as 0.94 × 10⁻⁶. -4 g·cm / cm²·s·Pa, making it the best barrier material among all samples.

[0052] Table 2

[0053] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing crystalline bifuran polyamide, characterized in that, Includes the following steps: (1) The bifuran dicarboxylic acid was reacted with excess thionyl chloride under reflux in the presence of a catalyst to obtain the bifuranyl chloride monomer; (2) Dissolve the bifuranyl chloride monomer obtained in step (1) in an organic solvent to obtain an organic phase, then add an alkaline aqueous solution to form a phase interface, then add an alicyclic diamine monomer dissolved in an alkaline aqueous solution to carry out an interfacial polymerization reaction to obtain crystalline bifuran polyamide.

2. The method for preparing crystalline bifuran polyamide as described in claim 1, characterized in that, The alicyclic diamine monomer is piperazine or 4,4'-bipiperidine.

3. The method for preparing crystalline syn-furan polyamide as described in claim 1 or 2, characterized in that, In step (1), the catalyst is N,N-dimethylformamide, and the amount of N,N-dimethylformamide added is 0.5%-0.8% of the mass of bifurandicarboxylic acid.

4. The method for preparing crystalline syn-furan polyamide as described in claim 1 or 2, characterized in that, In step (1), the reflux reaction takes 3-8 hours.

5. The method for preparing crystalline syn-furan polyamide as described in claim 1 or 2, characterized in that, In step (2), the molar ratio of the alicyclic diamine monomer to the difuranyl chloride monomer is 1:

1.

6. The method for preparing crystalline syn-furan polyamide as described in claim 1 or 2, characterized in that, In step (2), the alkaline aqueous solution is a KOH aqueous solution with a concentration of 0.5~2 mol / L.

7. The method for preparing crystalline syn-furan polyamide as described in claim 1 or 2, characterized in that, In step (2), the precipitate obtained after the interfacial polymerization reaction is filtered, washed with water and organic solvent in sequence, and then dried to obtain crystalline polyfuran polyamide.

8. The crystalline bifuran polyamide prepared by any one of claims 1-7.

9. The application of the crystalline synfuran polyamide as described in claim 8 in barrier packaging materials.

10. The application of the crystalline tandem furan polyamide as described in claim 8 in ultraviolet shielding materials.

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