An aromatic oxadiazole polymer modified membrane and a method for preparing the same

Abstract

The present application relates to a kind of aromatic oxadiazole polymer modified membrane and its preparation method.The preparation method of the modified membrane includes the following steps: step (1) with terephthalic dihydrazide as raw material, with polyphosphoric acid as solvent and dehydrating agent, polymerization is carried out to obtain prepolymer solution, wherein ternary acid and polyol are added during polymerization reaction;Step (2) the prepolymer solution obtained in step (1) is made into film, dried, to obtain modified membrane.The present application constructs the new network structure of aromatic oxadiazole polymer, and the modified membrane prepared has good film-forming property, is soft and transparent, has good mechanical property, has high thermal stability and chemical stability.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to an aromatic oxadiazole polymer modified film and its preparation method. Background Technology

[0002] In the field of membrane science, polymer membrane materials hold significant value. Over the past decade, polymer membranes have been widely applied in petrochemicals, battery component materials, fine chemicals, and biodegradation, achieving remarkable results. The preparation of functional membrane materials through chemical modification allows for continuous optimization of processes and the realization of commercialization.

[0003] Aromatic polyoxadiazoles (PODs) are aromatic heterocyclic polymers with good heat resistance, flame retardancy, and electrical insulation properties. Fibers and membrane materials made from this type of material have been developed for many years. However, because PODs are formed by the alternating conjugation of benzene and oxadiazole rings, the polymer molecules have a typical rigid rod-like molecular chain structure, resulting in highly rigid membrane materials that limit their applications. Furthermore, traditional low-temperature polymerization methods are cumbersome, produce products with limited composition and structure, low degree of polymerization, and high raw material costs, making them unsuitable for widespread production.

[0004]

[0005] Regarding the modification of POD, Chinese patent document CN109763351A discloses a modified polyarylene oxadiazole fiber containing a certain proportion of aliphatic diacid monomer shells, prepared by adding a certain proportion of aliphatic diacid monomer shells during the preparation of polyarylene oxadiazole. The modified polyarylene oxadiazole polymer exhibits a decrease in both thermal decomposition temperature and glass transition temperature, and a decrease in resistance to organic solvents, thus improving the dyeing difficulty of the fiber. However, overall, POD modification using this method alone is insufficient to improve the dyeing rate and color fastness of the fiber.

[0006] According to relevant reports, Hamciuc C., Hamciuc E., Ipate AM, et al. Copoly(1,3,4-oxadiazole-ether)s containing phthalide groups and thin films made therefrom[J].Polymer,2008,49(3):681-690.; Ongungal RM, Sivadas AP, Kumar NSS, et al. Self-assembly and mechanochromic luminescence switching of trifluoromethyl substituted 1,3,4-oxadiazole derivatives[J].Journal OfMaterials Chemistry C,2016,4(40), although the polymer chain structure can be adjusted by chemical modification, only by introducing flexible chemical groups into the main chain, the rigidity is reduced to a certain extent, but the modification ability is very limited under the strong conjugated structure of polymer molecules. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies and provide a modified aromatic oxadiazole polymer, its modified membrane, and a method for preparing the modified membrane. This invention aims to explore effective methods to modify the polymer structure, improve film-forming properties, and enhance the overall performance of the membrane, thereby promoting its potential applications.

[0008] In this invention, the modified aromatic oxadiazole polymer is referred to as "T-POD" and the membrane prepared from T-POD is referred to as "T-POD membrane".

[0009] One of the technical solutions of this invention provides a method for preparing an aromatic oxadiazole polymer-modified membrane, comprising the following steps:

[0010] Step (1) uses dihydrazide terephthalate as raw material, polyphosphoric acid as solvent and dehydrating agent, and carries out a polymerization reaction to obtain a prepolymer solution, wherein a tribasic acid and a polyol are added during the polymerization reaction;

[0011] Step (2) The prepolymer solution obtained in step (1) is used to form a film and dried to obtain the aromatic oxadiazole polymer modified film;

[0012] The structural formula of the tricarboxylic acid is R(COOH)3, and the structural formula of the polyol is... m, n, p, and q are each selected from 0 or 1, and m+n+p+q≥2; R is selected from C3-C6 alkyl, phenyl, or naphthyl; r is selected from C2-C6 alkyl or C2-C6 alkenyl; optionally, the aforementioned C3-C6 alkyl, phenyl, naphthyl, C2-C6 alkyl, or C3-C6 alkenyl groups are each independently substituted by 1-3 groups selected from the group consisting of: halogen, -OR a -CN, -NO2, C1-C6 alkyl or -NR a R b , where R a R b Each is independently selected from hydrogen or C1-C4 alkyl groups.

[0013] In a preferred embodiment of the present invention, the temperature of the polymerization reaction in step (1) is 100-140°C, the tribasic acid and polyol are added during the first 1-5 hours of the polymerization reaction, and the polymerization reaction continues for 3-9 hours after the addition of the tribasic acid and polyol.

[0014] In a preferred embodiment of the present invention, the tricarboxylic acid is selected from tricornioic acid, citric acid, methanetriacetic acid, 1,2,3-benzenedric acid, 1,3,5-benzenedric acid, or 1,2,4-benzenedric acid.

[0015] In a preferred embodiment of the present invention, This indicates a polyol comprising diols, triols, and tetraols, preferably selected from ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-cyclohexanediol, glycerol, trimethylolethane, pentaerythritol, 1,2,4,5-cyclohexanetetrol, 2-hydroxymethyl-1,3-butanediol, or 2,3-dihydroxymethane-1,3-butanediol.

[0016] In a preferred embodiment of the present invention, the mass ratio of polyphosphoric acid to dihydrazide terephthalate is 3:1-10:1, preferably 5:1-8:1.

[0017] In a preferred embodiment of the present invention, the molar ratio of the tricarboxylic acid to terephthalic acid dihydrazide is 0.01:1-0.15:1, preferably 0.02:1-0.1:1.

[0018] In a preferred embodiment of the present invention, the molar ratio of polyol to dihydrazide terephthalate is 0.01:1-0.3:1, preferably 0.02:1-0.15:1.

[0019] In a preferred embodiment of the present invention, step (1) involves a self-polymerization reaction of the raw materials before adding the tribasic acid and polyol to form the main chain structure of the polymer, followed by the addition of the tribasic acid and polyol for chemical modification of the structure. The tribasic acid and polyol can be added simultaneously, or the tribasic acid can be added first, followed by the polyol.

[0020] In a preferred embodiment of the present invention, in step (2), the membrane formation method is selected from phase inversion, solution casting, or direct membrane formation, with phase inversion being preferred. Phase inversion involves immersing a polymer solution in a non-solvent bath, where the polymer rapidly precipitates at the interface, forming an extremely thin, dense layer. Below this dense layer, a porous layer is formed; this interface, dense on the outside and porous on the inside, constitutes the basic structure of the membrane. The coating process employs spin coating, using a 100-micron coating rod.

[0021] In a preferred embodiment of the present invention, the drying temperature in step (2) is 150-200°C and the drying time is 3-8 hours.

[0022] The raw material terephthalic acid dihydrazide in the T-POD membrane preparation method of the present invention can be commercially available or prepared using synthetic methods known in the art, preferably by reacting dimethyl terephthalate with hydrazine hydrate. The dimethyl terephthalate can be commercially available or prepared using synthetic methods known in the art, preferably by reacting terephthalic acid with methanol.

[0023] The alkyl groups described in this invention include chain alkyl groups and cycloalkyl groups, and the alkenyl groups include chain alkenyl groups and cycloalkenyl groups; specifically, for example, C1-C6 alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, 2-hydroxypropyl, n-butyl, isobutyl, tert-butyl, n-pentane, isopentane, neopentane, cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl, and C2-C6 alkenyl groups include, but are not limited to, vinyl, propenyl, butenyl, allyl, allyl, and cyclohexenyl.

[0024] "Substitution" means that at least one hydrogen atom is replaced by a non-hydrogen group, provided that the normal valence is maintained and the substitution yields a stable compound. Unless otherwise stated, the definitions of substituents in this invention are independent and not related to each other.

[0025] "Halogen" or "halogen" includes fluorine, chlorine, bromine, and iodine. "Halogenated alkyl" includes a branched or straight-chain saturated aliphatic hydrocarbon group having a specified number of carbon atoms and being substituted with one or more halogens. One or more halogens may be independently selected from fluorine, chlorine, bromine, and iodine. Examples of halogenated alkyl groups include, but are not limited to, fluoromethyl, difluoromethyl, trichloromethyl, pentafluoroethyl, pentachloroethyl, 2,2,2-trifluoroethyl, heptafluoropropyl, and heptachloropropyl.

[0026] In this disclosure, the designation Cx-Cy is used when referring to substituent groups, indicating that the number of carbon atoms in the substituent group can be x to y. For example, C3-C6 indicates that the group contains 3, 4, 5, or 6 carbon atoms.

[0027] "Polyols" refers to a large class of alcohols containing two or more hydroxyl groups in their molecules, specifically including diols, triols, tetraols, pentaols, and hexaols. More specifically, examples include propylene glycol, glycerol, trimethylolethane, pentaerythritol, 1,2,4,5-cyclohexanetetrol, 2,3-dihydroxymethane-1,3-butanediol, xylitol, and sorbitol.

[0028] The second technical solution of the present invention is to provide an aromatic oxadiazole polymer modified membrane (T-POD membrane), which is prepared by the aforementioned preparation method according to the present invention.

[0029] The resulting aromatic oxadiazole polymer-modified film has a thickness of 350-450 μm, and is soft and transparent.

[0030] The aromatic oxadiazole polymer-modified film obtained contains the structural unit shown in formula (I).

[0031]

[0032] The definitions of R, r, m, n, p, and q are the same as those in the previous definitions in the specification.

[0033] This invention investigates the chemical modification of POD. Based on an innovative approach, a novel T-POD polymer network structure is constructed by adding a tribasic acid as a modifier and a polyol as a chain extender during the POD polymerization reaction, and the reaction mechanism is explored. The chemical reaction formula for this mechanism is as follows, where the tribasic acid R(COOH)3 is used as the modifier, and the polyol... As chain extenders, TPH represents dihydrazide terephthalate, PPA represents polyphosphoric acid, and POD and T-POD represent polymers.

[0034]

[0035] The chemical reaction formula shows that during the POD polymerization reaction, the polymer chain structure is adjusted by adding tribasic acid as a modifier to graft polymers, and polyol is added to introduce into the polymer cyclic structure as a chain extender to form hydrogen bonds, thus constructing a supramolecular network structure. During the further heating and cyclization dehydration process, the electron-withdrawing property of the N-N bond is further enhanced, and the hydrogen bonding effect of the polymer network structure is also further enhanced.

[0036] This invention provides an aromatic oxadiazole polymer-modified membrane, T-POD, which constructs a novel polymer network structure. The T-POD membrane is prepared using a blending modification method. During the polymerization reaction, a tribasic acid is introduced as a modifier to increase the chain length of the aromatic oxadiazole molecules, and a polyol is used as a chain extender to construct intermolecular hydrogen bonds in the aromatic oxadiazole. Through the synergistic effect of the modifier and chain extender, and by selecting suitable reaction components, component ratios, and process conditions, the rigidity of the polymer molecules is reduced, thereby improving the overall performance of the membrane. Compared with POD membranes, the T-POD membrane of this invention exhibits superior film-forming properties, is soft and transparent, displays excellent mechanical properties, and possesses high thermal and chemical stability, showing broad application prospects. Attached Figure Description

[0037] Figure 1 The TGA graph was used to test the thermal stability of the second membrane, where the horizontal axis represents temperature (°C) and the vertical axis represents weight percentage (%).

[0038] Figure 2 The fluorescence emission spectra of the three films were tested, where the horizontal axis represents wavelength (nm) and the vertical axis represents fluorescence intensity (au).

[0039] Figure 3(a) shows the X-ray diffraction patterns of the four membranes tested, where the horizontal axis is the 2θ angle (°) and the vertical axis is the intensity.

[0040] Figure 3(b) shows the X-ray diffraction peak intensity trend of the four films tested, where the horizontal axis is the 2θ angle (°) and the vertical axis is the intensity.

[0041] Figure 4 The scanning electron microscope images of five films are used for testing. In the images, (A), (B), (C) and (D) represent the surface at high magnification, (A)1, (B)1, (C)1 and (D)1 represent the surface at low magnification, (a), (b), (c) and (d) represent the cross-section at low magnification, and (a)1, (b)1, (c)1 and (d)1 represent the cross-section at high magnification.

[0042] Figure 5 To test the water absorption rate curves and oxidative stability curves of the six membranes, the left vertical axis represents the water absorption rate (wt%), and the right vertical axis represents the oxidative weight loss (wt%).

[0043] Figure 6 To test the ATR-FTIR spectra of seven films, the horizontal axis represents wavelength (cm). -1 The vertical axis represents transmittance (%). Detailed Implementation

[0044] The technical solution of the present invention is not limited to the embodiments listed below, but also includes any combination of the specific embodiments.

[0045] Example 1: Preparation of dimethyl terephthalate

[0046] To a 200 mL round-bottom flask containing terephthalic acid (8.0 g, 48.2 mmol), add 80 mL of anhydrous methanol and 0.5 mL of concentrated sulfuric acid (catalyst). Maintain the reaction mixture under reflux for 12 hours, then cool to room temperature. Add sodium bicarbonate solution (0.5 M) to adjust the pH to 7, then filter. Wash the collected solid with deionized water (10.0 mL × 3), then dry to give dimethyl terephthalate (8.7 g, 44.8 mmol), in 92.9% yield.

[0047] 1H NMR spectrum (400 MHz, CDCl3) δ / ppm 8.12 (s, 4H), 3.97 (s, 6H).

[0048] Example 2: Preparation of diphenyl terephthalate dihydrazide

[0049] The dimethyl terephthalate (8.7 g, 44.0 mmol) obtained in Example 1 was placed in methanol containing 4 mol of 80% hydrazine hydrate and stirred at 90 °C for 8 h. The reaction mixture was cooled to room temperature, and a pale yellow solid precipitated. The precipitate was filtered and washed three times with deionized water (10.0 mL × 3). The solid was dissolved in deionized water and recrystallized, then filtered and dried. Dihydrazide terephthalate (7.5 g, 39.0 mmol) was obtained in 88.6% yield.

[0050] The 1H NMR spectra (400 MHz, dimethyl sulfoxide-d6) δ / ppm were 8.61 (d, 2H), 6.95 (s, 4H), and 4.06 (s, 4H), respectively.

[0051] In the following Examples 3-7, T-POD is used. X The T-POD membranes prepared in these examples represent the molar percentage of the tricarboxylic acid and diterephthalic acid dihydrazide, which is then multiplied by 100. For example, T-POD2 indicates that 2 equivalents of the polycarboxylic acid and 100 equivalents of diterephthalic acid dihydrazide were used in the reaction.

[0052] Example 3: Preparation of T-POD2 membrane

[0053] a. Under magnetic stirring, add 20.0 g of polyphosphoric acid (PPA, CAS No. 8017-16-1, content 85%) to a 50 mL round-bottom flask and heat at 140 °C until PPA melts. Add 3 g (15.5 mmol) of terephthalic acid dihydrazide and stir at 140 °C for 1 h. Then, add 0.065 g (0.31 mmol) of 1,2,3-benzenetricarboxylic acid and 0.042 g (0.31 mmol) of pentaerythritol and continue stirring at 140 °C for 3 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0054] b. Spin-coat the prepolymer solution using the phase inversion method, then dry it in a vacuum oven at 170°C for 8 hours, and remove it to remove the film.

[0055] The T-POD2 membrane is 380μm thick, soft, and transparent.

[0056] Example 4: Preparation of T-POD4 membrane

[0057] a. Under magnetic stirring, add 20.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 130 °C until PPA melts. Add 3 g of terephthalic acid dihydrazide and stir at 130 °C for 1.5 h. Then, add 0.13 g of 1,2,3-benzenetricarboxylic acid and 0.084 g of pentaerythritol and continue stirring at 130 °C for 3 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0058] b. Spin-coat the prepolymer solution using the phase inversion method, then dry it in a vacuum oven at 180°C for 6 hours, and remove it to remove the film.

[0059] The T-POD4 membrane is 400μm thick, soft, and transparent.

[0060] Example 5: Preparation of T-POD6 membrane

[0061] a. Under magnetic stirring, add 20.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 120 °C until PPA melts. Add 3 g of terephthalic acid dihydrazide and stir at 120 °C for 2 h. Then, add 0.195 g of 1,2,3-benzenetricarboxylic acid and 0.126 g of pentaerythritol and continue stirring at 120 °C for 4 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0062] b. Spin-coat the prepolymer solution using the phase inversion method, then dry it in a vacuum oven at 180°C for 6 hours, and remove it to remove the film.

[0063] The T-POD6 membrane is 410μm thick, soft, and transparent.

[0064] Example 6: Preparation of T-POD8 membrane

[0065] a. Under magnetic stirring, add 20.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 120 °C until PPA melts. Add 3 g of terephthalic acid dihydrazide and stir at 120 °C for 3 h. Then, add 0.26 g of 1,2,3-benzenetricarboxylic acid and 0.168 g of pentaerythritol and continue stirring at 120 °C for 6 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0066] b. Spin-coating the prepolymer solution using the phase inversion method, then drying it in a vacuum oven at 190°C for 4 hours, and finally removing it from the mold.

[0067] The T-POD8 membrane is 400μm thick, soft, and transparent.

[0068] Example 7 T-POD 10 Membrane preparation

[0069] a. Under magnetic stirring, add 20.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 110 °C until PPA melts. Add 3 g of terephthalic acid dihydrazide and stir at 110 °C for 4 h. Then, add 0.325 g of 1,2,3-benzenetricarboxylic acid and 0.21 g of pentaerythritol and continue stirring at 110 °C for 8 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0070] b. Spin-coat the prepolymer solution using the phase inversion method, then dry it in a vacuum oven at 200°C for 3 hours, and remove it to remove the film.

[0071] The T-POD10 membrane is 420μm thick, soft, and transparent.

[0072] Example 8 T-POD a Membrane preparation

[0073] a. Under magnetic stirring, add 30.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 140 °C until PPA melts. Add 3.0 g of terephthalic acid dihydrazide and stir at 140 °C for 2 h. Then, add 0.261 g (1.24 mmol) of 1,3,5-benzenetricarboxylic acid and 0.144 g (1.24 mmol) of 1,4-cyclohexanediol and continue stirring at 140 °C for 6 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0074] b. Spin-coating the prepolymer solution using a phase inversion method, then drying it in a vacuum oven at 200℃ for 5 hours, and finally removing and demolding it. The T-film is 400μm thick, soft, and transparent.

[0075] Example 9T-POD b Membrane preparation

[0076] a. Under magnetic stirring, add 12.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 100 °C until PPA melts. Add 4.0 g (20.6 mmol) of terephthalic acid dihydrazide and stir at 100 °C for 2 h. Then add 0.52 g (2.47 mmol) of 1,2,4-benzenetricarboxylic acid. After another 0.5 h, add 0.341 g (4.12 mmol) of glycerol and continue stirring at 100 °C for 8 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0077] b. Spin-coat the prepolymer solution using the phase inversion method, then dry it in a vacuum oven at 180°C for 8 hours, and remove it to remove the film.

[0078] The film is 430μm thick, soft, and transparent.

[0079] Example 10T-POD c Membrane preparation

[0080] a. Under magnetic stirring, add 24.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 120 °C until PPA melts. Add 3.0 g of terephthalic acid dihydrazide and stir at 120 °C for 2 h. Then add 0.027 g (0.154 mmol) of trimalic acid. After another 0.9 h, add 0.04 g of pentaerythritol and continue stirring at 120 °C for 9 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0081] b. Spin-coat the prepolymer solution using the phase inversion method, then dry it in a vacuum oven at 160°C for 7 hours, and remove it to remove the film.

[0082] The film is 390μm thick, soft, and transparent.

[0083] Example 11 T-POD d Membrane preparation

[0084] a. Under magnetic stirring, add 15.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 120 °C until PPA melts. Add 3.0 g of terephthalic acid dihydrazide and stir at 120 °C for 2 h. Then add 0.30 g (1.55 mmol) of citric acid. After another h, add 0.35 g (4.6 mmol) of 1,2-propanediol and continue stirring at 120 °C for 5 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0085] b. Spin-coat the prepolymer solution using the phase inversion method, then dry it in a vacuum oven at 180°C for 6 hours, and remove it to remove the film.

[0086] The film is 400μm thick, soft, and transparent.

[0087] Example 12T-POD e Membrane preparation

[0088] a. Under magnetic stirring, add 20.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 120 °C until PPA melts. Add 3.0 g of terephthalic acid dihydrazide and stir at 120 °C for 3 h. Then add 0.49 g (2.34 mmol) of 1,2,3-benzenetricarboxylic acid. After another 0.5 h, add 0.556 g (4.63 mmol) of trimethylolpropane and continue stirring at 120 °C for 6 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0089] b. Spin-coating the prepolymer solution using the phase inversion method, then drying it in a vacuum oven at 190°C for 4 hours, and finally removing it from the mold.

[0090] The film is 430μm thick, soft, and transparent.

[0091] Example 13 T-POD f Membrane preparation

[0092] a. Under magnetic stirring, add 20.0 g of polyphosphoric acid (PPA) to a 50 mL round-bottom flask and heat at 110 °C until PPA melts. Add 5.0 g (25.7 mmol) of terephthalic acid dihydrazide and stir at 110 °C for 4 h. Then add 0.81 g (3.85 mmol) of 1,2,5-benzenetricarboxylic acid. After another h, add 0.93 g (7.73 mmol) of 2-hydroxymethyl-1,3-butanediol and continue stirring at 110 °C for 8 h to form a homogeneous viscous liquid, which is the prepolymer solution.

[0093] b. Spin-coat the prepolymer solution using the phase inversion method, then dry it in a vacuum oven at 200°C for 3 hours, and remove it to remove the film.

[0094] The film is 410μm thick, soft, and transparent.

[0095] Comparative Example 1: Preparation of POD membrane

[0096] Under magnetic stirring, polyphosphoric acid (PPA, 20.0 g) was added to a 50 mL round-bottom flask and heated at 120 °C until PPA melted. Then, 3 g of terephthalic acid dihydrazide was added and the mixture was stirred at 120 °C for 4 h to form a uniform viscous liquid, which is the film-forming solution.

[0097] The film-forming solution was spin-coated using a phase inversion method, placed in a vacuum oven at 180°C for 6 hours, and then removed and demolded.

[0098] The POD film is 400μm thick, has poor film-forming properties, is relatively hard, and has low transparency.

[0099] Test 1: Mechanical Properties of the Membrane

[0100] The T-POD membranes of Examples 3-13 and the POD membrane of Comparative Example 1 were used to test tensile stress and tensile strain rate.

[0101] Using a single-arm tensile testing machine, the samples were cut into dumbbell-shaped strips measuring 60×4×0.4mm. Before testing, the instrument parameters were set with a clamping distance of 20mm and a tensile speed of 1mm / min. Each filter membrane was tested three times.

[0102] Strain rate: Where L(o) is the original length and L(t) is the membrane elongation at time t.

[0103] The test results are shown in Table 1.

[0104] Table 1 Mechanical properties of the membrane

[0105]

[0106]

[0107] The mechanical properties of the membrane can be characterized by tensile stress and tensile strain rate. Table 1 shows that compared with the POD membrane, the T-POD membrane has significantly higher tensile stress and lower tensile strain rate, indicating that the T-POD membrane has good mechanical properties. In particular, the tensile stress of the T-POD6 membrane reaches 167 MPa.

[0108] Test 2: Thermal stability of the membrane (TGA)

[0109] Thermogravimetric analysis (TGA) was performed on the T-POD membranes from Examples 3-7 and the POD membrane from Comparative Example 1.

[0110] The thermogravimetric analyzer gradually heats the instrument from 30°C to 800°C at a rate of 5°C / minute in a nitrogen atmosphere.

[0111] The test results are attached. Figure 1 .

[0112] Figure 1 The results showed that, compared with POD membranes, T-POD... 2 / 4 / 6 The membrane exhibits high thermal stability, T-POD 8 / 10 The thermal decomposition stability of the membrane decreased slightly.

[0113] Test 3: Fluorescence emission spectrum of the membrane

[0114] The T-POD films of Examples 3-7 and the POD film of Comparative Example 1 were used to test the fluorescence emission spectra.

[0115] In a spectrophotometer, when irradiated with excitation light, the sample absorbs light energy and emits blue fluorescence at wavelengths of approximately 415 nm and 475 nm.

[0116] The test results are attached. Figure 2 .

[0117] Figure 2 The results showed that the fluorescence intensity of the T-POD film changed compared to the POD film. This phenomenon can be attributed to the alternating conjugated rigid planar molecular structure of the aromatic oxadiazole ring. The highly conjugated, rigid, and low-vibrational molecular structure greatly enhances the fluorescence quantum efficiency and fluorescence intensity of the POD molecule. T-POD modified with tricarboxylic acids and polyols exhibited a gradual transition from a linear planar molecular structure to a network structure. The polycarboxylic acid modifier has a benzene ring structure; its introduction into the polymer increases the rigidity of the structure, thus increasing the fluorescence intensity. As the content of the polyol gradually increases, flexible groups are introduced into the polymer structure, thereby weakening its conjugation and rigidity, and thus reducing the fluorescence performance.

[0118] Test 4: X-ray diffraction of the membrane

[0119] The T-POD films from Examples 3-7 and the POD film from Comparative Example 1 were tested for X-ray diffraction.

[0120] X-ray diffractometer, 2θ = 24°.

[0121] Test results: See Figure 3(a) for the X-ray diffraction pattern of the film; see Figure 3(b) for the X-ray diffraction peak intensity trend of the film.

[0122] 3(a) X-ray diffraction patterns were used to study the crystallization behavior of the film. The POD film exhibited a strong and broad diffraction peak at 2θ = 24°, indicating that POD has high crystallinity due to its rigid molecular structure. The position of the diffraction peak remained almost unchanged with the addition of modifiers and chain extenders, but its intensity changed accordingly.

[0123] 3(b) The X-ray diffraction peak intensity trend diagram shows that with the increase of tricarboxylic acid concentration, the polymer network structure gradually forms, leading to an increase in diffraction peak intensity and further amplification of polyol crosslinking intensity. The diffraction peak intensity reaches its maximum at T-POD6. However, with the continued increase of tricarboxylic acid concentration, the polymer network structure changes from a relatively ordered state to a disordered state, resulting in a decrease in crystallinity. At 2θ=24°, T-POD... 10 The lowest diffraction peak intensity indicates that appropriate amounts of tricarboxylic acids and polyols improve the molecular arrangement of the polymer and promote further growth of the membrane molecular chains.

[0124] Test 5: Scanning electron microscope images of the membrane

[0125] The T-POD films from Examples 3-7 and the POD film from Comparative Example 1 were subjected to scanning electron microscopy tests.

[0126] The test results are attached. Figure 4 .

[0127] Figure 4 Displays (A), (A)1 and (a), (a)1 depict scanning electron microscopy (SEM) images of pure POD films, revealing that the surface and cross-section of the film are relatively rough, superficial, and loose. However, after trace POD modification, T-POD... X The roughness and looseness of the membrane decreased or disappeared, as shown in Figures (B), (B)1 and (b), (b)1. Increasing the tricarboxylic acid content to 6%, as shown in Figures (C), (C)1 and (c), (c)1, resulted in a smoother and more compact surface and cross-section of the T-POD6 membrane, with almost no observable defects. We speculate that the addition of the polyol further enhanced the intermolecular hydrogen bonds between the POD membrane layers, leading to higher integrity and significantly improved toughness under a microscope. However, excessive tricarboxylic acid can cause localized defects in the modified membrane. Photos (D), (D)1 and (d), (d)1 show that the T-POD8 membrane has a smooth surface and cross-section, but with noticeable cracks. We speculate that excessive tricarboxylic acid increases the crosslinking density, making the membrane brittle and leading to crack formation during processing. It is reasonable that membrane materials with better shape can be obtained when the polymer has a moderate crosslinking density and relatively few bonded molecular chains.

[0128] Test 6: Water absorption rate and oxidative stability of the membrane

[0129] Take the T-POD membranes from Examples 3-7 and the POD membrane from Comparative Example 1, and use the solution impregnation method. The water absorption rate test is performed by impregnation with deionized water, and the oxidation stability test is performed by impregnation with ferric chloride hexahydrate solution. The weight change is analyzed by weighing with a balance, and the water absorption rate and oxidation weight loss rate are calculated.

[0130] The test results are attached. Figure 5 .

[0131] Figure 5 The water absorption curves show that the abundance of hydrophobic tertiary amine groups in the polymer increases with increasing polymer modification concentration. Therefore, the water absorption rate of the membrane initially decreases, reaching a minimum of 13.3% when the tricarboxylic acid content is 6 mol%. However, with further increases in the tricarboxylic acid content, the water absorption rate gradually increases. This can be attributed to the increased intermolecular crosslinking of the compound and the dense network membrane structure formed due to the crosslinking of the polyol, which restricts the diffusion of water molecules. Furthermore, defects in the polymer under highly crosslinked structures also contribute to the increased water absorption rate.

[0132] Figure 5 The oxidation stability curves show that the oxidation stability of the T-POD membrane is significantly improved compared with that of the POD membrane, and the oxidation stability of the T-POD membrane also increases with the increase of the amount of tricarboxylic acid added.

[0133] Test 7: ATR-FTIR spectrum of the membrane

[0134] The T-POD films from Examples 3-7 and the POD film from Comparative Example 1 were used to test Fourier transform infrared spectra.

[0135] Fourier transform infrared spectrometer was used.

[0136] The test results are attached. Figure 6 .

[0137] Figure 6 This is the infrared spectrum of the T-POD film material. Specifically, at 2956 cm⁻¹... -1 and 2919cm -1 The modifier, corresponding to the saturated hydrocarbon in the polymer, introduces a partially flexible chain into the oxadiazole molecular chain, increasing the chain's flexibility and thus enhancing the vibrations of the carboxylic acid group and the benzene ring. At 853 cm⁻¹ -1 The location is a disubstituted benzene ring group in the polymer, at 975 cm⁻¹ -1 and 1091cm -1 This corresponds to the -COC- group in the oxadiazole ring of the polymer, at 1347 cm⁻¹. -1 The presence of the -C=NN=C- group in the corresponding oxadiazole ring at the corresponding position demonstrates that the hydrazide group in the polymer was successfully converted into a five-membered oxadiazole ring under certain conditions, resulting in the successful synthesis of the polyoxadiazole polymer. With increasing tricarboxylic acid content, the peak value may shift or change in intensity at different wavenumbers, which is due to the influence of tricarboxylic acid modification on the molecular structure and vibrational modes. The stretching vibration peak of C=O on the oxadiazole ring is located at 1720-1700 cm⁻¹. -1 Between, at 1274cm -1 There is an absorption peak at 3243 cm⁻¹, corresponding to the -CN- group in the polymer. -1 and 1651cm -1 The position corresponds to the -NH bond in the unreacted hydrazide group in the polymer. The position of the oxadiazole ring stretching vibration peak changes with the increase of the content of the tricarboxylic acid modifier, which may be due to the aggregation of molecular chains caused by the flexible chains in the aromatic oxadiazole molecular chain. The changes in the curves in the spectrum can prove the synthesis of T-POD polymer.

Claims

1. A method for preparing an aromatic oxadiazole polymer-modified membrane, characterized in that, Includes the following steps: Step (1) Using dihydrazide terephthalate as raw material and polyphosphoric acid as solvent and dehydrating agent, a polymerization reaction is carried out to obtain a prepolymer solution, wherein a tribasic acid and a polyol are added during the polymerization reaction; Step (2) The prepolymer solution obtained in step (1) is used to form a film and dried to obtain the aromatic oxadiazole polymer modified film; The structural formula of the tricarboxylic acid is R(COOH)3, and the structural formula of the polyol is... m, n, p, and q are each selected from 0 or 1, and m + n + p + q ≥ 2; R is selected from C3-C6 alkyl, phenyl, or naphthyl; r is selected from C2-C6 alkyl or C2-C6 alkenyl; optionally, the aforementioned C3-C6 alkyl, phenyl, naphthyl, C2-C6 alkyl, or C2-C6 alkenyl groups are each independently substituted by 1 to 3 groups selected from the group consisting of: halogen, -OR a -CN, -NO2, C1-C6 alkyl or -NR a R b , where R a R b Each is independently selected from hydrogen or C1-C4 alkyl groups.

2. The preparation method according to claim 1, wherein, The polymerization reaction in step (1) is carried out at a temperature of 100-140℃. Tribasic acid and polyol are added during the first 1-5 hours of the polymerization reaction. After the addition of tribasic acid and polyol, the polymerization reaction continues for 3-9 hours.

3. The preparation method according to claim 1, characterized in that, The tricarboxylic acid is selected from triglyceride, citric acid, methanetriacetic acid, 1,2,3-benzenedric acid, 1,3,5-benzenedric acid, or 1,2,4-benzenedric acid.

4. The preparation method according to claim 1, characterized in that, The polyol is selected from ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-cyclohexanediol, glycerol, trimethylolethane, pentaerythritol, 1,2,4,5-cyclohexanetetrol, 2-hydroxymethyl-1,3-butanediol, or 2,3-dihydroxymethane-1,3-butanediol.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the polyphosphoric acid to dihydrazide terephthalate is 3:1-10:

1.

6. The preparation method according to claim 1, characterized in that, The molar ratio of the tricarboxylic acid to terephthalic acid dihydrazide is 0.01:1 to 0.15:

1.

7. The preparation method according to claim 1, characterized in that, The molar ratio of the polyol to terephthalic acid dihydrazide is 0.01:1 to 0.3:

1.

8. The preparation method according to claim 1, characterized in that, The film-forming method in step (2) is selected from phase inversion method, solution casting method or direct film formation method. The drying temperature is 150-200℃ and the drying time is 3-8 hours.

9. An aromatic oxadiazole polymer-modified membrane, characterized in that, It is prepared by the method according to any one of claims 1 to 8.

10. The aromatic oxadiazole polymer-modified membrane according to claim 9, characterized in that, Contains the structural unit shown in equation (I) Formula (I) The definitions of R, r, m, n, p, and q are the same as those in claim 1.

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