An imidazole-complexed norbornene copolymer, its preparation method and application

Abstract

This invention discloses an imidazole-complexed norbornene copolymer, its preparation method, and its applications. The imidazole-complexed norbornene copolymer has the structure shown in Formula I; wherein x is selected from integers from 1 to 500. The nanofiber membrane prepared using this imidazole-complexed norbornene copolymer exhibits good oxygen removal performance.

Description

Technical Field

[0001] This invention relates to the field of oxygen removal materials technology. More specifically, it relates to an imidazole complexed norbornene copolymer, its preparation method, and its application. Background Technology

[0002] Oils and high-fat foods, such as edible vegetable oils, milk, and fresh meat, contain various unsaturated fatty acids, which are highly susceptible to oxidative rancidity during storage. Through auto-oxidation or enzymatic degradation of lipids, small unsaturated aldehydes and ketones such as malondialdehyde and methyl ketones are produced. This not only leads to deterioration of the food's sensory qualities (color, aroma, taste, etc.) and loss of various nutrients (essential fatty acids, fat-soluble vitamins, etc.), but may also pose potential health hazards. Recent studies have shown that excessive consumption of oil oxidation products poses potential health risks. For example, secondary byproducts of the oxidation of high-unsaturated fatty acid foods, such as 4-hydroxynonenal and malondialdehyde, exhibit toxicological effects at both animal and cellular levels and are considered potential carcinogens. Oxygen free radicals can cause low-density lipoprotein oxidation, forming oxidized low-density lipoprotein (OX-LDL), ultimately leading to various diseases such as atherosclerosis. Therefore, improving the oxidative stability of food lipids is not only related to food quality and nutrition but also to public health, and has become a research hotspot urgently needing solutions in the food industry.

[0003] Oxygen-absorbing materials play a crucial role in delaying food oxidation, extending shelf life, and maintaining the sensory quality and nutritional value of food, making them a major research focus in the food preservation field. The market for oxygen-absorbing packaging materials is projected to reach $2.67 billion by 2025, with a compound annual growth rate of 4.9% from 2017 to 2025, indicating a promising future. Currently, oxygen-absorbing technologies are mainly categorized as: vacuum or modified atmosphere packaging, chemical consumption of oxygen-absorbing agents, and active oxygen-absorbing packaging. Among these, 1) Modified atmosphere packaging, by altering the gas environment inside the packaging bag, prevents food from contacting oxygen and is widely used in food, beverage, pharmaceutical, and precision circuit packaging. However, due to the poor gas barrier properties of the materials, this technology cannot consume the oxygen that permeates through the packaging during storage. 0.5%–2% oxygen will still remain inside the packaging, accelerating lipid oxidation in high-fat foods; 2) Oxygen-absorbing agents react with molecular oxygen through redox reactions involving active substances or functional groups, causing irreversible binding of oxygen to the material or converting oxygen into other (neutral) substances. Traditional food oxygen scavengers, such as metal oxygen scavengers (e.g., iron, zinc, palladium), organic oxygen scavengers (e.g., gallic acid, ascorbic acid), inorganic oxygen scavengers (e.g., sulfites), and enzyme oxygen scavengers, are prone to accidental ingestion or potential leaching, causing secondary food contamination. Furthermore, they are sensitive to environmental conditions such as pH, water activity, and temperature, resulting in varying oxygen scavenging effects under different usage environments. Changes in properties after oxygen scavenging also lead to reduced oxygen scavenging efficiency. 3) Active oxygen scavenging packaging uses covalent bonds or surface coating adsorption to embed active ingredients in polymers, preparing traditional membrane materials through melt extrusion or casting. Currently reported active oxygen scavenging packaging mainly improves oxygen scavenging efficiency by embedding metal oxygen scavengers. However, in practical applications, the weak bonding ability between metal oxygen scavengers and materials in such active oxygen scavenging packaging also poses a risk of metal leaching, resulting in insufficient material safety. In addition, the inherent barrier properties of the film-forming substrate and its limited specific surface area make it difficult to achieve sufficient contact between the active ingredients and oxygen, leading to unsatisfactory oxygen scavenging effects. Improving the oxygen removal efficiency of food oxygen scavengers while overcoming the prominent contradiction between the sustainable application of oxygen scavenging materials and food safety has always been a technical challenge for research both domestically and internationally.

[0004] Unsaturated olefins, as a class of polymer-based oxygen scavengers containing highly reactive allyl hydrogen bonds, such as polybutadiene or norbornene (PN), contain highly reactive unsaturated hydrocarbons in their structure. At room temperature, the allyl hydrogen bonds (-CH=CH-) can combine with oxygen molecules to form peroxy (ROO·) and alkoxy (RO·) radicals. PN and its derivatives readily polymerize through ring-opening metathesis to form high molecular weight polymers containing multiple repeating units with multiple highly reactive allyl hydrogen bonds, thus possessing multiple active sites for oxygen reaction and improving oxygen removal. Therefore, copolymers formed from PN can serve as matrices and oxygen-consuming substrates for oxygen scavenging films, enabling the development of novel oxygen scavenging materials. In the research of oxygen scavenging membrane materials, the most reported polymers are currently 1,2-polybutadiene and 1,4-polybutadiene. Compared with these two polymers, PN and its derivatives, after polymerization, possess a higher content of active allyl hydrogen bond structures and exhibit higher catalytic activity, thus attracting widespread attention both domestically and internationally. However, the reaction has low activity at room temperature. Organometallic catalysts combine the easy processability of polymers with the functionality of metals. In the reaction of PN with oxygen, they have the characteristics of improving oxygen absorption rate and accelerating the removal rate. They catalyze the reaction of PN with oxygen to undergo catalytic and auto-oxidation reactions. By actively capturing and removing oxygen molecules, oxygen is ultimately removed. However, direct addition can easily leach out and cause secondary contamination of food. Summary of the Invention

[0005] Based on the above facts, in order to overcome the problems of low oxygen removal efficiency and secondary food contamination caused by catalyst leaching of traditional oxygen removal materials, and to break through the existing technological bottlenecks, the purpose of this invention is to provide an imidazole complexed norbornene copolymer, its preparation method, and its application. The nanofiber membrane prepared using this imidazole complexed norbornene copolymer exhibits good oxygen removal performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] On one hand, the present invention provides an imidazole complexed norbornene copolymer having the structure shown in Formula I:

[0008]

[0009] Wherein, x is selected from integers from 1 to 500.

[0010] In another aspect, the present invention provides a method for preparing an imidazole complexed norbornene copolymer, comprising the following steps:

[0011] An esterification reaction was carried out using 5-norbornene-2-carboxylic acid and 1-(2-hydroxyethyl)imidazolium as substrates to generate the compound shown in Formula II:

[0012]

[0013] The compound shown in Formula II was reacted with norbornene as a substrate to undergo a ring-opening metathesis polymerization reaction to obtain the compound shown in Formula III:

[0014]

[0015] The compound shown in Formula III was reacted with N,N'-bis(salicyl)ethylenediamine iron(II) to obtain the compound shown in Formula I;

[0016] The definition of x is as described above.

[0017] Furthermore, in the above preparation method, the reaction process for preparing the compound represented by Formula II via esterification is as follows:

[0018]

[0019] Furthermore, the esterification reaction is carried out in the presence of a catalyst; wherein the catalyst is selected from 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride.

[0020] Furthermore, the esterification reaction is carried out under the following conditions: stirring at room temperature for 5-8 hours.

[0021] Furthermore, the molar ratio of 5-norbornene-2-carboxylic acid to 1-(2-hydroxyethyl)imidazole is 1:1.4-1.5.

[0022] Furthermore, in the above preparation method, the reaction process for preparing the compound represented by Formula III via ring-opening metathesis polymerization is as follows:

[0023]

[0024] Furthermore, in the ring-opening metathesis polymerization reaction, the molar ratio of the compound represented by Formula II to norbornene is 1:8-1:12, preferably 1:10.

[0025] Furthermore, the catalyst used in the ring-opening metathesis polymerization reaction is a Grubbs 2nd generation catalyst. The molar ratio of the compound represented by Formula II, norbornene, and the Grubbs 2nd generation catalyst is 1:10:0.01-0.3.

[0026] Furthermore, the conditions for the ring-opening metathesis polymerization reaction are: stirring for 5-10 hours at room temperature under nitrogen purging.

[0027] Furthermore, in the above preparation method, the reaction formula for preparing the compound of formula I by reacting the compound represented by formula III with N,N'-bis(salicyl)ethylenediamine iron(II) is as follows:

[0028]

[0029] ; where x is defined as described above.

[0030] Furthermore, the molar ratio of the compound represented by Formula III to N,N'-bis(salicyl)ethylenediamine iron (II) is 3:1.

[0031] Furthermore, the reaction conditions of the compound represented by Formula III with N,N'-bis(salicyl)ethylenediamine iron (II) are as follows: dissolve the compound represented by Formula III in CHCl2 for 4 hours to prepare a 1-8 wt% solution, add N,N'-bis(salicyl)ethylenediamine iron Fe(II)salen, and continue the reaction under stirring at room temperature. The preferred reaction time is 3 hours.

[0032] In another aspect, the present invention provides an oxygen-removing nanofiber membrane, which is prepared by electrospinning from raw materials comprising the imidazole complexed norbornene copolymer or the imidazole complexed polybutadiene polymer as described above.

[0033] The present invention has found that, compared with other film formation methods (such as casting film formation), the oxygen removal effect of the oxygen removal nanofiber membrane prepared by electrospinning is significantly better.

[0034] Furthermore, the oxygen-removing nanofiber membrane is a porous micro / nanofiber membrane.

[0035] Furthermore, the diameter of the fibers in the oxygen-removing nanofiber membrane is 100-200 nm.

[0036] Furthermore, the thickness of the oxygen-removing nanofiber membrane is 0.05-0.2 mm, preferably 0.1 mm.

[0037] Furthermore, the conditions for electrospinning include: a voltage of 12-25kV, a spinning distance of 10-15cm, and a spinning flow rate of 0.05-1.5mL / h.

[0038] Furthermore, the preparation of the imidazole complexed polybutadiene polymer includes the following steps:

[0039] An 8 wt% solution was prepared by adding 1,2-PB to a THF solution using THF as the solvent.

[0040] Stir with a magnetic stirrer for 24 hours in a nitrogen atmosphere at room temperature.

[0041] Fe(II)salen-bim and ML were added, and the mixture was stirred for 3 hours under nitrogen atmosphere to obtain the imidazole complexed polybutadiene polymer.

[0042] Furthermore, the preparation of the Fe(II)salen-bim includes the following steps:

[0043] Fe(II)salen and 1-benzylimidazole (bim) in a molar ratio of 1:1 were shaken and mixed in dimethylformamide (DMF) solvent to obtain Fe(II)salen-bim.

[0044] Furthermore, the molar ratio of 1,2-PB, Fe(II)salen and 1-benzylimidazole is 1850:3.6:3.6.

[0045] The beneficial effects of this invention are as follows:

[0046] The nanofiber membrane prepared by the imidazole complexed norbornene copolymer provided by this invention forms a micro-nano-scale porous fibrous structure with PN copolymer as the backbone. It fully utilizes the porous characteristics of nanofibers, which can reduce the mass transfer resistance at the oxygen-reaction substrate interface. At the same time, the extremely high specific surface area of ​​the nanofibers endows the catalytic reaction with high reactivity. Compared with membrane materials prepared by traditional processes, it is expected to achieve high oxygen removal rate with low cost and low dosage, and provides an innovative path to overcome the shortcomings of traditional oxygen removal materials and construct new food oxygen removal materials.

[0047] In the preparation method of the imidazole complexed norbornene copolymer of the present invention, norbornene is used as the deoxygenation functional substrate, and diethylenediamine benzylimidazolium iron complex is used as the catalyst. Through ring-opening metathesis polymerization and imidazole iron complexation, an iron-based catalyst grafted integrated deoxygenation polymer is synthesized. Using this as a substrate, a stable molding process for high specific surface area porous deoxygenation materials is established, and a novel polynorbornene (PN)-based deoxygenation nanofiber membrane material and its preparation method are developed. This method pioneers a comprehensive technical breakthrough in the molding mechanism, process control, and effect evaluation of novel deoxygenation materials. The nanofiber membrane prepared by the method of the present invention has a fiber diameter of 100-200 nm. The nanofiber membrane ensures food safety from material selection to preparation process and exhibits extremely high deoxygenation capacity unaffected by humidity. The deoxygenation efficiency can still reach more than 324.75 mL oxygen / g (film) after 30 days. Attached Figure Description

[0048] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0049] Figure 1 The Fourier transform infrared spectra of 5-norbornene-2-carboxylic acid, 1-(2-hydroxyethyl)imidazolium and N-im are shown in Example 1.

[0050] Figure 2The Fourier transform infrared spectra of N-im, norbornene (PN), and grafted imidazole norbornene copolymer (PN-im) in Example 1 are shown.

[0051] Figure 3 The 1H NMR spectrum of the grafted imidazole norbornene copolymer obtained in Example 1 is shown.

[0052] Figure 4 The Fourier transform infrared spectrum of the iron-based catalyst imidazole complexed norbornene copolymer obtained in Example 1 is shown.

[0053] Figure 5 A scanning electron microscope image of the polynorbornene nanofiber membrane prepared in Example 1 is shown.

[0054] Figure 6 The diagram shows the oxygen removal efficiency of commercially available iron powder and the polynorbornene nanofiber membranes in Examples 1-3. Detailed Implementation

[0055] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] A method for preparing an imidazole-complexed norbornene copolymer includes the following steps:

[0058] 1) Synthesis of grafted imidazolyl norbornene:

[0059] Using 0.075 mol of 5-norbornene-2-carboxylic acid and 0.11 mol of 1-(2-hydroxyethyl)imidazolium as substrates, and in 500 mL of THF with 4-(4,6-dimethoxytriazine)-4-methylmorpholinium chloride (DMT-MM) as catalyst, an esterification reaction was carried out (stirred at room temperature for 5-8 hours) to form a carbonyl bond between the -COOH group of 5-norbornene-2-carboxylic acid and the -OH group of 1-(2-hydroxyethyl)imidazolium. The resulting product was then purified by silica gel column chromatography to obtain a yellow oily substance, 5-norbornene-2-yl-carboxyethyl-1-imidazolium (N-im), which is grafted imidazolyl norbornene (N-im).

[0060]

[0061] The Fourier transform infrared spectra of the above-mentioned 5-norbornene-2-carboxylic acid, 1-(2-hydroxyethyl)imidazolium and N-im are as follows: Figure 1 As shown in the figure. From the figure, we can see that 1702cm -1 The wavelength peak is the carbonyl bond formed by the esterification of -COOH in 5-norbornene-2-carboxylic acid and -OH in 1-(2-hydroxyethyl)imidazolium.

[0062] 2) Synthesis of grafted imidazole-based norbornene copolymer:

[0063] 50 mmol of norbornene (PN) and 0.5 mmol of 5-norbornene-2-ylcarboxyethyl-1-imidazolium (N-im) were dissolved in THF as solvent. Then, 10–300 μmol of Grubbs II catalyst was added to induce a ring-opening metathesis polymerization of the cyclic olefin. In the presence of the Grubbs II metal catalyst, the carbon-carbon double bonds in the cyclic olefin break, and the molecules recombine through chain initiation, chain propagation, and chain termination to form new molecules, yielding a grafted imidazolium-based norbornene copolymer (PN-im). This polymer retains unsaturated double bonds and exhibits characteristics of living polymerization. The mixture was stirred at room temperature under nitrogen purging for 10 hours. The reaction mixture was repeatedly precipitated with 500 mL of methanol, and the resulting precipitate was freeze-dried under vacuum.

[0064]

[0065] The Fourier transform infrared spectra of the above-mentioned N-im, norbornene (PN), and grafted imidazole norbornene copolymer (PN-im) are shown below. Figure 2 As shown in the figure. The wavelength position is 1658 cm. -1 The peak at 1445 cm⁻¹ is a characteristic peak derived from the allyl bond of norbornene. -1 and 1264cm -1 The peak at this point is a characteristic peak of the imidazole group.

[0066] The above-mentioned grafted imidazole-based norbornene copolymer was detected by proton nuclear magnetic resonance spectroscopy at 500 MHz using deuterated chloroform as a solvent. Figure 3As shown, the NMR peaks at 7.46-6.96 ppm correspond to imidazole groups, and those at 5.35-5.20 ppm correspond to allyl bonds. This result corresponds to the FTIR results, and together they confirm the synthesis of the copolymer. ¹H-NMR (500MHz, CDCl₃) δppm: from PN: 5.35(s,¹H), 5.20(s,¹H), 2.77(s,¹H), 2.43(s,¹H), 1.89-1.75(br,³H), 1.33(s,²H), 1.00(m,¹H); from N-im: 7.46(s,¹H), 7.00(s,¹H), 6.96(s,¹H), 6.15-6.09(m,¹H), 5.82(m,¹H), 4.28-4.20(m,⁴H), 3.17-3.03(s,¹H), 3.02-2.88(m,²H), 2.27(m,¹H), 1.87(m,¹H), 1.37(m,³H).

[0067] 3) Synthesis of iron-based catalyst imidazole complexed norbornene copolymer

[0068] A 1-8 wt% solution was prepared by dissolving PN-im (molar mass of the repeating PN-im unit) in CHCl2 for 4 h. Then, N,N'-bis(salicyl)ethylenediamine iron Fe(II)salen was added at a molar ratio of PN:N,N'-bis(salicyl)ethylenediamine iron:3:1 and the reaction was continued for 3 h under the original conditions to obtain the imidazole complexed norbornene copolymer.

[0069]

[0070] Figure 4 The image shows the Fourier transform infrared spectrum of the prepared iron-based catalyst imidazole-complexed norbornene copolymer. The spectrum indicates that the iron-based catalyst imidazole-complexed norbornene copolymer contains 1445 cm⁻¹... -1 and 1265cm -1 The peak at 970 cm⁻¹ is a characteristic peak of the imidazole group. -1 The characteristic peak at this point indicates the presence of Fe-N coordination bonds, confirming the successful combination of the iron-based catalyst and the grafted imidazole-based norbornene copolymer.

[0071] Preparation of a novel polynorbornene (PN)-based oxygen-removing nanofiber membrane:

[0072] Electrospinning equipment was used to prepare polynorbornene-based deoxygenating nanofiber membranes. This equipment has a built-in push-pump automatic control sample injection system to precisely control the sample flow rate. After studying the effects of process parameters such as spinning solution concentration, spinning voltage, spinning distance, spinning flow rate, and solution characteristics on the microstructure of the spun fibers, the final electrospinning process conditions for the novel polynorbornene (PN)-based deoxygenating nanofiber membrane were determined as follows: the iron-based catalyst imidazole complexed norbornene copolymer spinning solution prepared above was injected into a syringe with a metal needle. Spinning was carried out under the following conditions: temperature 30℃, voltage 12-25kV, flow rate 0.05-1.5mL / h, and spinning distance 10-15cm. The fibers aggregated on the collector surface, ultimately forming a porous membrane material with micro-nano scale diameter – the PN-im / Fe(Ⅱ)salen deoxygenating nanofiber membrane.

[0073] Figure 5 The image shows scanning electron microscope (SEM) images of the novel norbornene (PN)-based oxygen-removing nanofiber membranes prepared (from left to right, different magnifications: 500x, 2000x, 5000x). The images show that the prepared oxygen-removing nanofiber membranes exhibit good fiber uniformity, small diameter (100-200 nm), and high specific surface area and porosity.

[0074] Example 2

[0075] Preparation and evaluation of oxygen removal effect of polybutadiene deoxygenating nanofiber membrane

[0076] 1. Synthesis of 1,2-PB / Fe(II)salen

[0077] 1,2-Polybutadiene (1,2-PB) was dissolved in tetrahydrofuran, and then precipitated again with anhydrous methanol. This precipitation-dissolution step was repeated three times. The final purified 1,2-PB was obtained by vacuum drying and stored in a glove box. An 8 wt% solution was prepared by adding the purified 1,2-PB to a THF solution using THF as the solvent. The solution was stirred with a magnetic stirrer for 24 h at room temperature under nitrogen atmosphere.

[0078] Add Fe(II)salen-bim (Fe(II)salen and 1-benzylimidazole (bim) in a molar ratio of 1:1 are shaken and mixed in dimethylformamide (DMF) solvent to obtain Fe(II)salen-bim) and continue stirring for 3 hours.

[0079] The molar ratio of 1,2-PB, Fe(II)salen, and bim is 1850 / 3.6 / 3.6.

[0080] 2. Preparation of oxygen-removing nanofiber membranes

[0081] In Example 2, except that the iron-based catalyst imidazole complexed norbornene copolymer was replaced by the synthesized 1,2-PB / Fe(Ⅱ)salen complex as described above as the main body for oxygen removal, the thin film was prepared in the same manner as in Experimental Example 1, and the oxygen removal activity was measured and evaluated.

[0082] Example 3

[0083] Preparation and evaluation of oxygen removal effect of pure polynorbornene deoxygenation nanofiber membrane

[0084] 1. Synthesis of norbornene copolymer

[0085] Norbornene (4.7 g, 50 mmol) in 400 mL THF and Grubbs 2nd catalyst (42.5 mg, 50 μmol) in 50 mL THF were mixed and stirred for 5 hours at room temperature under nitrogen purging. The reaction mixture was repeatedly precipitated with 500 mL methanol, and the resulting precipitate was freeze-dried under vacuum. An 8 wt% solution of PN was prepared by adding a certain amount of PN to the CHCl2 solution using CHCl2 as a solvent, and stirred with a magnetic stirrer for 4 hours at room temperature under nitrogen purging.

[0086] 2. Preparation of pure polynorbornene deoxygenating nanofiber membrane

[0087] In Experiment 3, except that the above-mentioned polymerized norbornene copolymer was used to replace the iron-based catalyst imidazole complexed norbornene copolymer as the main body for oxygen removal, the thin film was prepared in the same manner as in Experiment 1, and the oxygen removal activity was measured and evaluated.

[0088] The above Examples 1-3 and the deoxygenation activation methods of commercially available iron powder (black) electrospun film are as follows:

[0089] Deoxygenation efficiency measurement:

[0090] The deoxygenation efficiency of the electrospun film at room temperature was determined using a gas analyzer. Measurements were taken every 24 hours, repeated three times, and continuously until the oxygen content no longer decreased.

[0091] The formula for calculating deoxygenation efficiency is as follows:

[0092]

[0093] Wherein, R is the oxygen removal rate of the material, expressed as the number of oxygen molecules absorbed per gram of material per day (mL / g.day), V is the volume of the container, %O1 is the initial oxygen content in the glass bottle, i.e., 20.9%, %O2 is the final oxygen content in the glass bottle at time (t), m is the mass of the oxygen removal material (g), and t is the time in days.

[0094] Specifically:

[0095] Add 0.1000g of electrospun film (uniform size and thickness) to a 250mL glass bottle and store at room temperature. Measure the oxygen content (%) in the glass bottle using a gas analyzer every 24 hours, repeating the measurement three times until the oxygen content no longer decreases. Calculate the deoxygenation efficiency according to equation (1).

[0096] Specific results are as follows Figure 6 As shown. From Figure 6 It can be seen that commercially available iron powder has an oxygen removal rate of only 25 mL oxygen / g (membrane), and it reaches saturation by the second day, unable to continue removing oxygen. The oxygen removal efficiencies of polynorbornene nanofiber membranes and polybutadiene nanofiber membranes are far higher than those of commercially available iron powder. The oxygen removal efficiency of the polynorbornene nanofiber membrane reaches as high as 181.25 mL oxygen / g (membrane) by the seventh day, and shows a continuous upward trend, stabilizing at 324.75 mL oxygen / g (membrane) by the 30th day. The polybutadiene nanofiber membrane stabilizes at 284.25 mL oxygen / g (membrane). Compared with the polynorbornene nanofiber membrane with added Fe(II)salen, the pure polynorbornene nanofiber membrane has a low oxygen removal efficiency, with a maximum oxygen removal efficiency of only 4.75 mL oxygen / g (membrane).

[0097] Comparative Example 1

[0098] A cast film was prepared as follows: The mixed solution of iron-based catalyst imidazole complexed norbornene copolymer obtained in Example 1 was poured into a Teflon petri dish and allowed to stand under nitrogen for one day to allow the solvent to completely evaporate, thus obtaining a PN-im / Fe(Ⅱ)salen cast film. The oxygen removal efficiency of the cast film was determined using the method described above, and the maximum oxygen removal efficiency of the cast film was 236.75 ml oxygen / g film.

[0099] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. An oxygen-removing nanofiber membrane, characterized by, It is prepared by electrospinning from a raw material containing an imidazole complexed norbornene copolymer, wherein the imidazole complexed norbornene copolymer has the structure shown in Formula I: I； The preparation method of the imidazole complexed norbornene copolymer includes the following steps: 5-norbornene-2-carboxylic acid and 1-(2-hydroxyethyl)imidazole were used as substrates for esterification to produce a compound represented by Formula II, wherein the molar ratio of 5-norbornene-2-carboxylic acid to 1-(2-hydroxyethyl)imidazole was 1:1.4-1.5, and the esterification reaction was carried out under the following conditions: stirring at room temperature for 5-8 hours. II; The compound shown in Formula II was reacted with norbornene as a substrate to undergo a ring-opening metathesis polymerization reaction to obtain the compound shown in Formula III, wherein the molar ratio of the compound shown in Formula II to norbornene was 1:8-1:12, and the conditions for the ring-opening metathesis polymerization reaction were: stirring for 5-10 hours at room temperature under nitrogen purging. III; The compound shown in Formula III was reacted with N,N'-bis(salicyl)ethylenediamine iron(II) in a molar ratio of 3:1, and the reaction method was as follows: The compound shown in Formula III was dissolved in CHCl2 for 4 h to prepare a 1-8 wt% solution. N,N'-bis(salicyl)ethylenediamine iron Fe(II)salen was added and the reaction was continued for 3 h under stirring at room temperature. The compound described in Formula I is obtained; The oxygen-removing nanofiber membrane is a porous nanofiber membrane; The thickness of the oxygen-removing nanofiber membrane is 0.05-0.2 mm; The conditions for electrospinning include: voltage of 12-25kV, spinning distance of 10-15cm, and spinning flow rate of 0.05-1.5mL / h.

2. The oxygen removing nanofiber membrane according to claim 1, characterized in that, The esterification reaction is carried out in the presence of a catalyst; wherein the catalyst is selected from 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride.

3. The oxygen removing nanofiber membrane according to claim 1, wherein, The catalyst used in the ring-opening metathesis polymerization reaction is a Grubbs second-generation catalyst; and / or The conditions for the ring-opening metathesis polymerization reaction are: stirring for 5-10 hours at room temperature under nitrogen purging.

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