Bio-based polymer material with gradient refractive index and preparation method of bio-based polymer material

Abstract

The invention discloses a preparation method of a bio-based polymer material with a gradient refractive index. The preparation method specifically comprises the following steps: step 1, preparing a nanocellulose dispersion liquid; step 2, synthesizing ethane-bridged ammonium iodide pyridine borate; step 3, synthesizing 2-butene bridged ammonium bromide pyridine borate; step 4, synthesizing 3-hexene bridged tetrafluoroboric acid pyridine borate; and 5, constructing the gradient refractive index high polymer material according to the products obtained in the steps 1-4. The invention further discloses the bio-based polymer material with the gradient refractive index. According to the invention, self-assembly of the organic nanocellulose and the organic ammonium pyridine borate is adopted, and the prepared gradient refractive index high polymer material has good stability and material reproducibility.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and relates to a bio-based polymer gradient refractive index polymer material. The present invention also relates to a preparation method of a bio-based polymer gradient refractive index polymer material. Background Art

[0002] Gradient refractive index optical materials are widely used in organic light-emitting diodes (OLEDs). In order to obtain gradient refractive index materials, people usually physically mix two or more different refractive index materials to construct different gradient refractive index materials. The refractive index of each layer is determined by the molar ratio of the two or more materials physically mixed. So far, in the preparation process of gradient refractive index materials, physical mixing mainly uses high-refractive-index inorganic materials (such as TiO2, SiO2) and low-refractive-index organic materials (such as polyethers, acrylic resins, etc.). Usually, inorganic-organic materials are compounded to prepare gradient refractive index materials. The inorganic materials need to be surface-modified before they can be dispersed in the organic materials. The dispersion ratio of inorganic materials and organic materials is related to the size of inorganic particles and the nature of surface modification, which increases the difficulty of preparing gradient refractive index materials. In addition, due to the poor compatibility and stability between inorganic materials and organic materials, it is difficult to control the refractive index of the prepared gradient refractive index materials. Moreover, for the gradient refractive index materials prepared by compounding inorganic materials and organic materials, the local refractive index of inorganic particles in the organic medium is uneven, which is prone to Rayleigh scattering, is not conducive to application in OLEDs, and results in a low light extraction efficiency. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method of a bio-based polymer gradient refractive index polymer material. This method uses the self-assembly of organic nanocellulose and organic ammonium borate pyridine to prepare a pure organic gradient refractive index polymer material with an adjustable refractive index range, and has a high light extraction rate when this material is used in OLEDs.

[0004] Another purpose of the present invention is to provide a bio-based polymer gradient refractive index polymer material.

[0005] The first technical solution adopted by the present invention is a preparation method of a bio-based polymer gradient refractive index polymer material, which specifically includes the following steps:

[0006] Step 1, prepare a nanocellulose dispersion;

[0007] Step 2, synthesize ethane-bridged ammonium iodide borate pyridine;

[0008] Step 3, synthesize 2-butene-bridged ammonium bromide borate pyridine;

[0009] Step 4, synthesize 3-hexene-bridged tetrafluoroborate borate pyridine;

[0010] Step 5. Construct a gradient refractive index polymer material based on the products obtained in Steps 1-4.

[0011] The characteristics of the first technical solution of the present invention also lie in:

[0012] The specific process of Step 1 is as follows:

[0013] Step 1.1. Take 5-10 g of cotton fiber pulp and immerse it in 200-400 mL of NaOH solution, stir at room temperature for 1-2 h; then take out the cotton fiber pulp and wash it with 500-800 mL of deionized water, repeat 3-5 times;

[0014] Step 1.2. Add the cotton fiber pulp treated in Step 1.1 to a homogenizer and homogenize it 30-40 times. Add the homogenized cotton fiber pulp to 1000-1500 mL of sulfuric acid solution with pH = 1-2, stir and react for 1-2 h. After the reaction, centrifuge the obtained solution at 5000-10000 r / min for half an hour, and dialyze the centrifuged liquid three times with a dialysis bag of 7000-12000 Da to obtain a light blue nanocellulose solution. Quantify the solid content of the nanocellulose to 2-3%, and then add fructose with a molecular weight of 1200-2000 to the nanocellulose solution and stir at 50-70 °C for 8-12 h to obtain a transparent nanocellulose dispersion.

[0015] In Step 1.2, the solid content of fructose is quantified to 0.5-1%.

[0016] The specific process of Step 2 is as follows:

[0017] Step 2.1. Take 12.3-24.6 g of 4-pyridineboronic acid and dissolve it in 20-30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0018] Step 2.2. Take 9.4-18.8 g of 1,2-dibromoethane and dissolve it in 20-30 mL of N,N-dimethylformamide solution to obtain a 1,2-dibromoethane solution;

[0019] Step 2.3: The 1,2-dibromoethane solution obtained in Step 2.2 was added dropwise to the 4-pyridineboronic acid solution obtained in Step 2.1. The resulting mixed solution was stirred at room temperature for 6 - 12 h. After the reaction was completed, the mixed solution was poured into 200 - 400 mL of deionized water. After stirring evenly, it was extracted with 200 - 300 mL of dichloromethane for 3 - 5 times. The final aqueous solution was collected and heated to 80 - 90 °C, and the volume of the aqueous solution was concentrated to 100 - 150 mL. After the temperature dropped to room temperature, it was left standing for 48 - 72 h, and white powder precipitated. Then, it was filtered, and the filter cake was collected and dried at 45 - 60 °C for 12 - 24 h to obtain the white product ethane-bridged ammonium iodide borate pyridine.

[0020] The specific process of Step 3 is as follows:

[0021] Step 3.1: Take 12.3 - 24.6 g of 4-pyridineboronic acid and dissolve it in 20 - 30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution.

[0022] Step 3.2: Dissolve 10.7 - 21.4 g of trans-1,4-dibromo-2-butene in 20 - 30 mL of N,N-dimethylformamide solution to obtain a trans-1,4-dibromo-2-butene solution.

[0023] Step 3.3: The trans-1,4-dibromo-2-butene solution obtained in Step 3.2 was added dropwise to the 4-pyridineboronic acid solution obtained in Step 3.1. The resulting mixed solution was stirred at room temperature for 6 - 12 h. After the reaction was completed, the mixed solution was poured into 200 - 400 mL of deionized water. After stirring evenly, it was extracted with 200 - 300 mL of dichloromethane for 3 - 5 times. The final aqueous solution was collected and heated to 80 - 90 °C, and the volume of the aqueous solution was concentrated to 100 - 150 mL. After the temperature dropped to room temperature, it was left standing for 48 - 72 h, and white powder precipitated. Then, it was filtered, and the filter cake was collected and dried at 45 - 60 °C for 12 - 24 h to obtain the white product 2-butene-bridged ammonium bromide borate pyridine.

[0024] The specific process of Step 4 is as follows:

[0025] Step 4.1: Take 12.3 - 24.6 g of 4-pyridineboronic acid and dissolve it in 20 - 30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution.

[0026] Step 4.2: Dissolve 12.1 - 24.2 g of trans-1,6-dibromo-3-hexene in 20 - 30 mL of N,N-dimethylformamide solution to obtain a trans-1,6-dibromo-3-hexene solution.

[0027] Step 4.3: The trans-1,6-dibromo-3-hexene solution obtained in Step 4.2 was dropped into the 4-pyridineboronic acid solution obtained in Step 4.1. The resulting mixed solution was stirred at room temperature for 6 - 12 h. Then, 55 - 110 g of sodium tetrafluoroborate and 100 - 200 mL of deionized water were added to the mixed solution, and stirring was continued for 2 - 4 h. After the reaction ended, the reaction solution was poured into 150 - 300 mL of deionized water. After stirring evenly, extraction was carried out with 250 - 500 mL of dichloromethane for 3 - 5 times. The final aqueous solution was collected and heated to 80 - 90 °C. The volume of the aqueous solution was concentrated to 100 - 150 mL. After the temperature dropped to room temperature, white powder precipitated out after standing for 48 - 72 h. Then, after filtration, the filter cake was collected and dried at 45 - 60 °C for 12 - 24 h to obtain the white product 3-hexene-bridged pyridine borate tetrafluoroborate.

[0028] The specific process of Step 5 is as follows:

[0029] Step 5.1: Weigh 10 - 20 mg of ethane-bridged ammonium iodide pyridine borate, 10 - 20 mg of 2-butene-bridged ammonium bromide pyridine borate, and 10 - 20 mg of 3-hexene-bridged pyridine borate tetrafluoroborate respectively.

[0030] Step 5.2: Take three portions of the nanocellulose dispersion prepared in Step 1, each with a volume of 5 - 10 mL, and add them to three beakers with a volume of 10 - 25 mL respectively. Then, place the three beakers in an ultrasonic device and ultrasonicate for 1 - 2 h.

[0031] Step 5.3: Add the ethane-bridged ammonium iodide pyridine borate, 2-butene-bridged ammonium bromide pyridine borate, and 3-hexene-bridged pyridine borate tetrafluoroborate weighed in Step 5.1 to the three beakers containing the nanocellulose dispersion in Step 5.2 respectively.

[0032] Step 5.4: Place the three beakers in Step 5.3 in an ultrasonic device and ultrasonicate for 1 - 2 h. Take out the beaker containing the ethane-bridged ammonium iodide pyridine borate. Pour the nanocellulose dispersion containing the ethane-bridged ammonium iodide pyridine borate in this beaker into a petri dish with a diameter of 5 - 10 cm, and then let it stand in a constant temperature and humidity chamber for 48 - 72 h to form the first layer of gel-like liquid crystal.

[0033] Step 5.5: Use a syringe to spread the nanocellulose dispersion containing 2-butene-bridged ammonium bromide pyridine borate onto the surface of the first layer of gel-like liquid crystal formed in Step 5.4 by injection, and then let it stand in a constant temperature and humidity chamber for 48 - 72 h to form the second layer of gel-like liquid crystal.

[0034] Step 5.6, use a syringe to spread the nanocellulose dispersion containing 3-hexene-bridged pyridinium borate tetrafluoroborate onto the surface of the second-layer gel-like liquid crystal formed in Step 5.5 by injection, and then leave it to stand in a constant temperature and humidity chamber for 72 h to form the third-layer gel-like liquid crystal;

[0035] Step 5.7, leave the three-layer gel-like liquid crystal material obtained in Steps 5.4 to 5.6 to stand in a constant temperature and humidity chamber, and continue to dry for 48 - 72 h to obtain the final gradient refractive index material.

[0036] In Steps 5.4 to 5.6, the humidity in the constant temperature and humidity chamber is 30 - 40% RH, and the temperature is 35 - 40 °C.

[0037] In Step 5.7, the humidity in the constant temperature and humidity chamber is 20 - 30% RH, and the temperature is 45 - 50 °C.

[0038] The second technical solution adopted by the present invention is a bio-based polymer gradient refractive index polymer material prepared by using the preparation method of the above-mentioned bio-based polymer gradient refractive index polymer material.

[0039] The beneficial effects of the present invention are as follows:

[0040] 1) The present invention constructs three types of ammonium pyridinium borates, and sequentially self-assembles them with nanocellulose to obtain a flexible and transparent nanocellulose liquid crystal film with a three-layer gradient refractive index. The regulation of the film refractive index is mainly determined by the molecular length of the ammonium pyridinium borate, and at the same time, counter anions such as iodine, bromine, and tetrafluoroboric acid are introduced into the three-layer gradient refractive index structure respectively, increasing the refractive index difference between the layers of the gradient refractive index, and improving the light extraction performance of the light-emitting device through the gradient refractive index.

[0041] 2) The present invention uses green, environmentally friendly, and renewable cellulose as a raw material to construct a liquid crystal film material with a gradient refractive index structure. The refractive index regulation adopts the self-assembly of organic nanocellulose - organic ammonium pyridinium borate, which can avoid the deficiencies such as poor compatibility, stability, and material reproducibility caused by organic-inorganic hybridization. The gradient refractive index of the present invention is jointly regulated by the molecular length of the organic ammonium pyridinium borate and the counter anion. The obtained film has excellent flexibility and transparency, and improves the light extraction performance of the light-emitting device through the gradient refractive index. Description of the Drawings

[0042] Figure 1 It is the ultraviolet absorption spectrum of the three-layer gel-like liquid crystal material in Example 1 of the preparation method of a bio-based polymer gradient refractive index polymer material of the present invention;

[0043] Figure 2It is a schematic diagram of the structure of a light-emitting device fabricated using the gradient refractive index polymer materials prepared in Example 1 and Comparative Examples 1-4 of the preparation method of a bio-based polymer gradient refractive index polymer material of the present invention as the substrate;

[0044] Figure 3 is Figure 2 The light extraction efficiency diagram of the light-emitting device fabricated therein. Detailed implementation manners

[0045] The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0046] The preparation method of a bio-based polymer gradient refractive index polymer material of the present invention specifically includes the following steps:

[0047] Step 1, preparation of a nanocellulose dispersion, specifically:

[0048] Take 5-10 g of cotton fiber pulp, immerse it in 200-400 mL of NaOH (pH = 10-11) solution, and stir at room temperature for 1-2 h. Take out the cotton fiber pulp, wash it with 500-800 mL of deionized water, and repeat 3-5 times. Further, add the cotton fiber pulp into a high-pressure (40-60 MPa) homogenizer and homogenize it 30-40 times. After homogenization, add the cotton fiber pulp into 1000-1500 mL of sulfuric acid solution with pH = 1-2, and stir and react for 1-2 h. After the reaction, the obtained solution is centrifuged at 5000-10000 r / min for half an hour to remove large particles or easily sedimentable cellulose. The centrifuged liquid is dialyzed three times using a dialysis bag with a molecular weight cut-off of 7000-12000 Da. A light blue nanocellulose solution is obtained, and the solid content of the nanocellulose is quantified to 2-3%. Then, fructose with a molecular weight of 1200-2000 is added to the nanocellulose solution, and stirred at 50-70 °C for 8-12 h to obtain a transparent dispersion, where the solid content of fructose is quantified to 0.5-1%.

[0049] Step 2, synthesis of ethane-bridged ammonium iodide borate pyridine, specifically:

[0050] First, take 12.3-24.6 g of 4-pyridineboronic acid and dissolve it in 20-30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0051] Secondly, dissolve 9.4-18.8 g of 1,2-dibromoethane in 20-30 mL of N,N-dimethylformamide solution to obtain a 1,2-dibromoethane solution;

[0052] Finally, slowly add the 1,2-dibromoethane solution dropwise to the 4-pyridineboronic acid solution (the dropping time is 30 - 60 min), and stir the resulting mixed solution at room temperature for 6 - 12 h. After the reaction is completed, pour the mixed solution into 200 - 400 mL of deionized water, stir evenly, extract with 200 - 300 mL of dichloromethane, and repeat 3 - 5 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and 1,2-dibromoethane). Collect the final aqueous solution and heat it to 80 - 90 °C, concentrate the volume of the aqueous solution to 100 - 150 mL, cool the temperature to room temperature, let it stand for 48 - 72 h to precipitate white powder, further filter, collect the filter cake and dry it at 45 - 60 °C for 12 - 24 h to obtain the white product ethane-bridged ammonium iodide pyridine borate.

[0053] Step 3, Synthesis of 2-butene-bridged ammonium bromide pyridine borate, specifically:

[0054] First, take 12.3 - 24.6 g of 4-pyridineboronic acid and dissolve it in 20 - 30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0055] Secondly, dissolve 10.7 - 21.4 g of trans-1,4-dibromo-2-butene in 20 - 30 mL of N,N-dimethylformamide solution to obtain a trans-1,4-dibromo-2-butene solution;

[0056] Finally, slowly add the trans-1,4-dibromo-2-butene solution dropwise to the 4-pyridineboronic acid solution (the dropping time is 30 - 60 min), and stir the resulting mixed solution at room temperature for 6 - 12 h. After the reaction is completed, pour the mixed solution into 200 - 400 mL of deionized water, stir evenly, extract with 200 - 300 mL of dichloromethane, and repeat 3 - 5 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,4-dibromo-2-butene). Collect the final aqueous solution and heat it to 80 - 90 °C, concentrate the volume of the aqueous solution to 100 - 150 mL, cool the temperature to room temperature, let it stand for 48 - 72 h to precipitate white powder, further filter, collect the filter cake and dry it at 45 - 60 °C for 12 - 24 h to obtain the white product 2-butene-bridged ammonium bromide pyridine borate.

[0057] Step 4, Synthesis of 3-hexene-bridged tetrafluoroborate pyridine borate, specifically:

[0058] First, take 12.3 - 24.6 g of 4-pyridineboronic acid and dissolve it in 20 - 30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0059] Secondly, dissolve 12.1 - 24.2 g of trans - 1,6 - dibromo - 3 - hexene in 20 - 30 mL of N,N - dimethylformamide solution to obtain a trans - 1,6 - dibromo - 3 - hexene solution;

[0060] Finally, slowly drip the trans - 1,6 - dibromo - 3 - hexene solution into the 4 - pyridineboronic acid solution (the dripping time is 30 - 60 min), and stir the obtained mixed solution at room temperature for 6 - 12 h. Further add 55 - 110 g of excessive sodium tetrafluoroborate and 100 - 200 mL of deionized water to the mixed solution, and continue to stir for 2 - 4 h. After the reaction is completed, pour the reaction solution into 150 - 300 mL of deionized water, stir evenly, extract with 250 - 500 mL of dichloromethane for 3 - 5 times (to remove the N,N - dimethylformamide solvent and the unreacted raw materials of 4 - pyridineboronic acid and trans - 1,6 - dibromo - 3 - hexene). Collect the final aqueous solution and heat it to 80 - 90 °C, concentrate the volume of the aqueous solution to 100 - 150 mL, cool the temperature to room temperature, and let it stand for 48 - 72 h to precipitate white powder. Further, filter it, collect the filter cake and dry it at 45 - 60 °C for 12 - 24 h to obtain the white product 3 - hexene - bridged pyridine borate tetrafluoroborate.

[0061] Step 5, self - assemble to construct a gradient refractive index material, specifically:

[0062] Weigh 10 - 20 mg of ethane - bridged ammonium iodide - type pyridine borate, 10 - 20 mg of 2 - butene - bridged ammonium bromide - type pyridine borate, and 10 - 20 mg of 3 - hexene - bridged tetrafluoroborate - type pyridine borate respectively. Take three portions of 5 - 10 mL of nanocellulose dispersion and add them into three 10 - 25 mL beakers respectively. Place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 - 2 h. Then, add ethane - bridged ammonium iodide - type pyridine borate, 2 - butene - bridged ammonium bromide - type pyridine borate, and 3 - hexene - bridged tetrafluoroborate - type pyridine borate into the three beakers containing nanocellulose dispersion respectively, and further place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 - 2 h. Take out the beaker containing ethane - bridged ammonium iodide - type pyridine borate (put the other two beakers in the refrigerator at 5 - 10 °C for standby). Pour the dispersion in it into a petri dish with a diameter of 5 - 10 cm, and then let it stand in a constant - temperature and constant - humidity chamber (humidity is 30 - 40% RH, temperature is 35 - 40 °C) for 48 - 72 h to form the first - layer gel - like liquid crystal. Further, use a syringe to slowly spread the dispersion containing 2 - butene - bridged ammonium bromide - type pyridine borate onto the surface of the first - layer gel - like liquid crystal, and then let it stand in a constant - temperature and constant - humidity chamber (humidity is 30 - 40% RH, temperature is 35 - 40 °C) for 48 - 72 h to form the second - layer gel - like liquid crystal. Further, use a syringe to slowly spread the dispersion containing 3 - hexene - bridged tetrafluoroborate - type pyridine borate onto the surface of the second - layer gel - like liquid crystal, and then let it stand in a constant - temperature and constant - humidity chamber (humidity is 30 - 40% RH, temperature is 35 - 40 °C) for 72 h to form the third - layer gel - like liquid crystal. Let the obtained three - layer gel - like liquid crystal material stand in a constant - temperature and constant - humidity chamber (humidity is 20 - 30% RH, temperature is 45 - 50 °C) and continue to dry for 48 - 72 h to obtain the final gradient - refractive - index polymer material.

[0063] The refractive index of each layer in the gradient - refractive - index material is measured from the corresponding layer dispersion and then determined. In order to measure the refractive index of the three - layer gel - like liquid crystal material prepared in step 5, three single - refractive - index materials need to be prepared separately, as follows:

[0064] The specific steps are as follows: Weigh 10 - 20 mg of ethane - bridged ammonium iodide - type pyridine borate, 10 - 20 mg of 2 - butene - bridged ammonium bromide - type pyridine borate, and 10 - 20 mg of 3 - hexene - bridged tetrafluoroborate - type pyridine borate respectively. Take three portions of 5 - 10 mL of nanocellulose dispersion and add them into three 10 - 25 mL beakers respectively. Place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 - 2 h. Then, add ethane - bridged ammonium iodide - type pyridine borate, 2 - butene - bridged ammonium bromide - type pyridine borate, and 3 - hexene - bridged tetrafluoroborate - type pyridine borate into the three beakers containing nanocellulose dispersion respectively, and further place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 - 2 h. Pour the dispersions in the three beakers into petri dishes with a diameter of 5 - 10 cm respectively, and then let them stand in a constant - temperature and constant - humidity chamber (humidity is 30 - 40% RH, temperature is 35 - 40 °C) for 48 - 72 h to form three gel - like liquid crystals. Let the three obtained gel - like liquid crystal materials stand in a constant - temperature and constant - humidity chamber (humidity is 20 - 30% RH, temperature is 45 - 50 °C) and continue to dry for 48 - 72 h to obtain three single - refractive - index materials containing ethane - bridged ammonium iodide - type pyridine borate, 2 - butene - bridged ammonium bromide - type pyridine borate, and 3 - hexene - bridged tetrafluoroborate - type pyridine borate respectively.

[0065] Example 1

[0066] Step 1: Preparation of nanocellulose dispersion. Specifically, take 5 g of cotton fiber pulp and immerse it in 200 mL of NaOH (pH = 10) solution, and stir at room temperature for 1 h. Take out the cotton fiber pulp and wash it with 500 mL of deionized water for 3 times. Further, add the cotton fiber pulp into a high - pressure (40 MPa) homogenizer and homogenize it 30 times. After homogenization, add the cotton fiber pulp into 1000 mL of sulfuric acid solution with pH = 1 and stir for 1 h. After the reaction, the obtained solution is centrifuged at 5000 r / min for half an hour using a centrifuge to remove large particles or easily sedimented cellulose. The centrifuged liquid is dialyzed three times using a 7000 Da dialysis bag. A light - blue nanocellulose solution is obtained. Quantify the solid content of nanocellulose to 2%, and then add fructose with a molecular weight of 1200 into the nanocellulose solution and stir at 50 °C for 8 h to obtain a transparent dispersion, where the solid content of fructose is quantified to 0.5%.

[0067] Step 2, Synthesis of ethane-bridged ammonium iodide borate pyridine, specifically: Take 12.3 g of 4-pyridineboronic acid and dissolve it in 20 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution; then dissolve 9.4 g of 1,2-dibromoethane in 20 mL of N,N-dimethylformamide solution to obtain a 1,2-dibromoethane solution; finally, slowly add the 1,2-dibromoethane solution dropwise to the 4-pyridineboronic acid solution (the dropping time is 30 min), and stir the resulting mixed solution at room temperature for 6 h. After the reaction, pour the mixed solution into 200 mL of deionized water, stir evenly, extract with 200 mL of dichloromethane, and repeat 3 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and 1,2-dibromoethane). Collect the final aqueous solution and heat it to 80 °C, concentrate the volume of the aqueous solution to 100 mL, cool the temperature to room temperature, and let it stand for 48 h to precipitate white powder. Further filter it, collect the filter cake and dry it at 45 °C for 12 h to obtain the white product ethane-bridged ammonium iodide borate pyridine.

[0068] Step 3, Synthesis of 2-butene-bridged ammonium bromide borate pyridine, specifically:

[0069] Take 12.3 g of 4-pyridineboronic acid and dissolve it in 20 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution; then dissolve 10.7 g of trans-1,4-dibromo-2-butene in 20 mL of N,N-dimethylformamide solution to obtain a trans-1,4-dibromo-2-butene solution; finally, slowly add the trans-1,4-dibromo-2-butene solution dropwise to the 4-pyridineboronic acid solution (the dropping time is 30 min), and stir the resulting mixed solution at room temperature for 6 h. After the reaction, pour the mixed solution into 200 mL of deionized water, stir evenly, extract with 200 mL of dichloromethane, and repeat 3 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,4-dibromo-2-butene). Collect the final aqueous solution and heat it to 80 °C, concentrate the volume of the aqueous solution to 100 mL, cool the temperature to room temperature, and let it stand for 48 h to precipitate white powder. Further filter it, collect the filter cake and dry it at 45 °C for 12 h to obtain the white product 2-butene-bridged ammonium bromide borate pyridine.

[0070] Step 4, synthesis of 3-hexene-bridged pyridine borate tetrafluoroborate, specifically: Take 12.3 g of 4-pyridineboronic acid and dissolve it in 20 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution; then dissolve 12.1 g of trans-1,6-dibromo-3-hexene in 20 mL of N,N-dimethylformamide solution to obtain a trans-1,6-dibromo-3-hexene solution; finally, slowly add the trans-1,6-dibromo-3-hexene solution dropwise to the 4-pyridineboronic acid solution (the dropping time is 30 min), and stir the obtained mixed solution at room temperature for 6 h. Further add 55 g of excessive sodium tetrafluoroborate and 100 mL of deionized water to the mixed solution, and continue stirring for 2 h. After the reaction is completed, pour the reaction solution into 150 mL of deionized water, stir evenly, and extract with 250 mL of dichloromethane for 3 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,6-dibromo-3-hexene). Collect the final aqueous solution and heat it to 80 °C, concentrate the volume of the aqueous solution to 100 mL, cool the temperature to room temperature, and let it stand for 48 h to precipitate white powder. Further, filter it, collect the filter cake and dry it at 45 °C for 12 h to obtain the white product 3-hexene-bridged pyridine borate tetrafluoroborate.

[0071] Step 5, self-assemble to construct a gradient refractive index material, specifically: Weigh 10 mg of ethane-bridged ammonium iodide borate pyridine, 10 mg of 2-butene-bridged ammonium bromide borate pyridine, and 10 mg of 3-hexene-bridged tetrafluoroborate borate pyridine respectively. Take three 5 mL nano-cellulose dispersions and add them into three 10 mL beakers respectively. Place the three beakers in an ultrasonic cleaner (with a power of 150 W) and ultrasonicate for 1 h. Then, add ethane-bridged ammonium iodide borate pyridine, 2-butene-bridged ammonium bromide borate pyridine, and 3-hexene-bridged tetrafluoroborate borate pyridine into the three beakers containing nano-cellulose dispersions respectively, and further place the three beakers in an ultrasonic cleaner (with a power of 150 W) and ultrasonicate for 1 h. Take out the beaker containing ethane-bridged ammonium iodide borate pyridine (put the other two beakers in the refrigerator and store them at 5 °C for later use). Pour the dispersion in it into a petri dish with a diameter of 5 cm, and then let it stand in a constant temperature and humidity chamber (humidity is 30% RH, temperature is 35 °C) for 48 h to form the first layer of gel-like liquid crystal. Further, slowly spread the dispersion containing 2-butene-bridged ammonium bromide borate pyridine on the surface of the first layer of gel-like liquid crystal with a syringe, and then let it stand in a constant temperature and humidity chamber (humidity is 30% RH, temperature is 35 °C) for 48 h to form the second layer of gel-like liquid crystal. Further, slowly spread the dispersion containing 3-hexene-bridged tetrafluoroborate borate pyridine on the surface of the second layer of gel-like liquid crystal with a syringe, and then let it stand in a constant temperature and humidity chamber (humidity is 30% RH, temperature is 35 °C) for 72 h to form the third layer of gel-like liquid crystal. Let the obtained three-layer gel-like liquid crystal material stand in a constant temperature and humidity chamber (humidity is 20% RH, temperature is 45 °C) and continue to dry for 48 h to obtain the final gradient refractive index material.

[0072] In order to measure the refractive index of the three-layer gel-like liquid crystal material prepared in Step 5, three single refractive index materials need to be prepared separately, specifically as follows:

[0073] Weigh 10 mg of ethane-bridged ammonium iodide-based pyridine borate, 10 mg of 2-butene-bridged ammonium bromide-based pyridine borate, and 10 mg of 3-hexene-bridged tetrafluoroborate-based pyridine borate respectively. Take three 5-mL nano-cellulose dispersions and add them into three 10-mL beakers respectively. Place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 h. Then, add ethane-bridged ammonium iodide-based pyridine borate, 2-butene-bridged ammonium bromide-based pyridine borate, and 3-hexene-bridged tetrafluoroborate-based pyridine borate into the three beakers containing nano-cellulose dispersions respectively, and further place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 h. Pour the dispersions in the three beakers into petri dishes with a diameter of 5 cm, and then let them stand in a constant temperature and humidity chamber (humidity is 30% RH, temperature is 35 °C) for 48 h to form three gel-like liquid crystals. Let the three obtained gel-like liquid crystal materials stand in a constant temperature and humidity chamber (humidity is 20% RH, temperature is 45 °C) and continue to dry for 48 h to obtain three single refractive index materials containing ethane-bridged ammonium iodide-based pyridine borate, 2-butene-bridged ammonium bromide-based pyridine borate, and 3-hexene-bridged tetrafluoroborate-based pyridine borate respectively.

[0074] Comparative Example 1 (No fructose is added to the nano-cellulose dispersion, and the remaining steps are the same as those in Example 1. The gradient refractive index material has a low curl rate and the overall gradient refractive index decreases)

[0075] Step 1, preparation of nano-cellulose dispersion, specifically:

[0076] Take 5 g of cotton fiber pulp and immerse it in 200 mL of NaOH (pH = 10) solution, and stir at room temperature for 1 h. Take out the cotton fiber pulp, wash it with 500 mL of deionized water, and repeat 3 times. Further, add the cotton fiber pulp into a high-pressure (40 MPa) homogenizer and homogenize 30 times. After homogenization, add the cotton fiber pulp into 1000 mL of sulfuric acid solution with pH = 1 and stir and react for 1 h. After the reaction, the obtained solution is centrifuged at 5000 r / min for half an hour by a centrifuge to remove large particles or easily sedimented cellulose, and the centrifuged liquid is dialyzed three times with a 7000 Da dialysis bag. A light blue nano-cellulose solution is obtained, and the solid content of nano-cellulose is quantified to be 2%.

[0077] Steps 2 to 5 are the same as those in Example 1; in order to measure the refractive index of the three-layer gel-like liquid crystal material prepared in Step 5, three single refractive index materials need to be prepared separately, and the preparation process is the same as that in Example 1.

[0078] Comparative Example 2 (During the synthesis of 3-hexene-bridged tetrafluoroborate-based pyridine borate, sodium tetrafluoroborate is not added to replace bromide ions, and the remaining steps are the same as those in Example 1. For the obtained gradient refractive index material, due to the increase in the refractive index of the third layer, the gradient difference between the second layer and the third layer decreases)

[0079] Step 1 is the same as in Example 1; Step 2 is the same as in Example 1; Step 3 is the same as in Example 1;

[0080] Step 4, Synthesis of 3-hexene bridged ammonium bromide pyridine borate, specifically:

[0081] Take 12.3 g of 4-pyridineboronic acid and dissolve it in 20 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0082] Then dissolve 12.1 g of trans-1,6-dibromo-3-hexene in 20 mL of N,N-dimethylformamide solution to obtain a trans-1,6-dibromo-3-hexene solution;

[0083] Finally, slowly add the trans-1,6-dibromo-3-hexene solution dropwise to the 4-pyridineboronic acid solution (the dropping time is 30 min), and stir the obtained mixed solution at room temperature for 6 h. After the reaction is completed, pour the reaction solution into 150 mL of deionized water, stir evenly, extract with 250 mL of dichloromethane for 3 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,6-dibromo-3-hexene). Collect the final aqueous solution and heat it to 80 °C, concentrate the volume of the aqueous solution to 100 mL, cool the temperature to room temperature, and let it stand for 48 h to precipitate white powder. Further filter it, collect the filter cake and dry it at 45 °C for 12 h to obtain the white product 3-hexene bridged ammonium bromide pyridine borate.

[0084] Step 5 is the same as in Example 1;

[0085] In order to measure the refractive index of the three-layer gel-like liquid crystal material prepared in Step 5, three single refractive index materials need to be prepared separately, and the preparation process is the same as in Example 1.

[0086] Comparative Example 3 (Sodium tetrafluoroborate is added to replace bromide ions during the synthesis of 2-butene bridged ammonium bromide pyridine borate, while sodium tetrafluoroborate is not added to replace bromide ions during the synthesis of 3-hexene bridged tetrafluoroboric acid pyridine borate, and the refractive index sizes of the two layers are reversed, destroying the gradient refractive index)

[0087] Step 1 is the same as in Example 1; Step 2 is the same as in Example 1;

[0088] Step 3, Synthesis of 2-butene bridged ammonium bromide borate pyridine, specifically: Take 12.3 g of 4-pyridineboronic acid and dissolve it in 20 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution; then dissolve 10.7 g of trans-1,4-dibromo-2-butene in 20 mL of N,N-dimethylformamide solution to obtain a trans-1,4-dibromo-2-butene solution; finally, slowly add the trans-1,4-dibromo-2-butene solution dropwise to the 4-pyridineboronic acid solution (the dropping time is 30 min), and stir the resulting mixed solution at room temperature for 6 h. Further add 55 g of excessive sodium tetrafluoroborate and 100 mL of deionized water to the mixed solution, and continue stirring for 2 h. After the reaction is completed, pour the mixed solution into 200 mL of deionized water, stir evenly, extract with 200 mL of dichloromethane for 3 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,4-dibromo-2-butene). Collect the final aqueous solution and heat it to 80 °C, concentrate the volume of the aqueous solution to 100 mL, cool the temperature to room temperature, and let it stand for 48 h to precipitate white powder. Further filter it, collect the filter cake and dry it at 45 °C for 12 h to obtain the white product 2-butene bridged ammonium tetrafluoroborate borate pyridine.

[0089] Step 4, Synthesis of 3-hexene bridged ammonium bromide borate pyridine, specifically: Take 12.3 g of 4-pyridineboronic acid and dissolve it in 20 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution; then dissolve 12.1 g of trans-1,6-dibromo-3-hexene in 20 mL of N,N-dimethylformamide solution to obtain a trans-1,6-dibromo-3-hexene solution; finally, slowly add the trans-1,6-dibromo-3-hexene solution dropwise to the 4-pyridineboronic acid solution (the dropping time is 30 min), and stir the resulting mixed solution at room temperature for 6 h. After the reaction is completed, pour the reaction solution into 150 mL of deionized water, stir evenly, extract with 250 mL of dichloromethane for 3 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,6-dibromo-3-hexene). Collect the final aqueous solution and heat it to 80 °C, concentrate the volume of the aqueous solution to 100 mL, cool the temperature to room temperature, and let it stand for 48 h to precipitate white powder. Further filter it, collect the filter cake and dry it at 45 °C for 12 h to obtain the white product 3-hexene bridged ammonium bromide borate pyridine.

[0090] Step 5, same as Example 1; In order to measure the refractive index of the three-layer gel-like liquid crystal material prepared in Step 5, three single refractive index materials need to be prepared separately, and the specific preparation process is the same as Example 1.

[0091] Comparative Example 4 (During the preparation of the gradient refractive index material, instead of self-assembly, high-temperature rapid drying was used, and the refractive index gradient difference between layers became smaller)

[0092] Steps 1 to 4 are the same as those in Example 1.

[0093] Step 5, rapid drying was used to construct the gradient refractive index material, specifically as follows:

[0094] Weigh 10 mg of ethane-bridged ammonium iodide borate pyridine, 10 mg of 2-butene-bridged ammonium bromide borate pyridine, and 10 mg of 3-hexene-bridged tetrafluoroborate borate pyridine respectively. Take three 5-mL nanocellulose dispersions and add them to 3 separate 10-mL beakers. Place the 3 beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 h. Then, add ethane-bridged ammonium iodide borate pyridine, 2-butene-bridged ammonium bromide borate pyridine, and 3-hexene-bridged tetrafluoroborate borate pyridine to the 3 beakers containing nanocellulose dispersions respectively, and further place the 3 beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 h. Take out the beaker containing ethane-bridged ammonium iodide borate pyridine (put the other two beakers in the refrigerator and refrigerate at 5 °C for later use). Pour the nanocellulose dispersion containing ethane-bridged ammonium iodide borate pyridine into a petri dish with a diameter of 5 cm, and then let it stand in a constant temperature and humidity chamber (humidity is 30% RH, temperature is 80 °C) for rapid drying. A first-layer film is formed in 8 h. Further, slowly spread the dispersion containing 2-butene-bridged ammonium bromide borate pyridine on the surface of the first-layer film with a syringe, and then let it stand in an incubator (humidity is 30% RH, temperature is 80 °C) for 8 h to form a second-layer film. Further, slowly spread the dispersion containing 3-hexene-bridged tetrafluoroborate borate pyridine on the surface of the second-layer film with a syringe, and then let it stand in a constant temperature and humidity chamber (humidity is 30% RH, temperature is 80 °C) and continue drying for 8 h to form a third-layer film, thus achieving the construction of the gradient refractive index material by rapid drying.

[0095] In order to measure the refractive index of the three-layer gel-like liquid crystal material prepared in Step 5, three single refractive index materials need to be prepared separately, specifically as follows:

[0096] Weigh 10 mg of ethane - bridged ammonium iodide - based pyridine borate, 10 mg of 2 - butene - bridged ammonium bromide - based pyridine borate, and 10 mg of 3 - hexene - bridged tetrafluoroborate - based pyridine borate respectively. Take three 5 - mL nano - cellulose dispersions and add them into three 10 - mL beakers respectively. Place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 h. Then, add ethane - bridged ammonium iodide - based pyridine borate, 2 - butene - bridged ammonium bromide - based pyridine borate, and 3 - hexene - bridged tetrafluoroborate - based pyridine borate into the three beakers containing nano - cellulose dispersions respectively, and further place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1 h. Pour the dispersions in the three beakers into petri dishes with a diameter of 5 cm, and then let them stand in a constant - temperature and constant - humidity chamber (humidity is 30% RH, temperature is 80 °C) for 8 h to form three kinds of films. Let the three obtained film materials stand in a constant - temperature and constant - humidity chamber (humidity is 20% RH, temperature is 45 °C) and continue to dry for 8 h to obtain three single - refractive - index film materials containing ethane - bridged ammonium iodide - based pyridine borate, 2 - butene - bridged ammonium bromide - based pyridine borate, and 3 - hexene - bridged tetrafluoroborate - based pyridine borate respectively.

[0097] As shown in Table 1 below, the curlability and refractive indices of each layer of the gradient refractive index materials in Example 1 and Comparative Examples 1 - 4 are as follows:

[0098] Table 1

[0099] Curling performance δ Refractive index of the first layer Refractive index of the second layer Refractive index of the third layer Example 1 1 1.62 1.51 1.36 Comparative Example 1 0.2 1.60 1.49 1.34 Comparative Example 2 1 1.62 1.51 1.47 Comparative Example 3 1 1.62 1.43 1.47 Comparative Example 4 0.6 1.58 1.53 1.50

[0100] The curlability can be measured by curling the material with a cylinder of a certain radius. After curling, the material can fully recover without deformation or damage. The curlability can be represented by δ: δ = 1 / λ, where λ is the diameter of the cylinder (unit: cm). The smaller δ is, the better the curlability.

[0101] The curlability of Comparative Example 1 is relatively poor, only 0.2. The main reason is the lack of fructose component. Fructose molecules can form hydrogen bonds with the hydroxyl groups on the surface of nano - cellulose due to the large number of hydroxyl groups, playing a plasticizing role, effectively avoiding the interaction between nano - cellulose and nano - cellulose particles, and enhancing the curlability of the material.

[0102] At the same time, the curlability of Comparative Example 4 is relatively low, mainly for the following reasons. In this gradient refractive index material prepared by the rapid drying method, a chiral liquid crystal structure is not formed in the material, and at the same time, the surface tension of the rapidly dried material cannot be effectively released.

[0103] The gradient refractive index performance of Example 1 and Comparative Example 1 is the best, that is, the refractive index difference between the first layer and the second layer, and between the second layer and the third layer is relatively large. However, the values of the first, second, and third layers in Comparative Example 1 are relatively small compared to the corresponding layers in Example 1 because the fructose component is missing. It should be noted that the refractive index of the first layer in Example 1 is the highest, mainly because the ethane-bridged ammonium iodide-based pyridine borate molecules added to the first layer have the smallest molecular size, reducing the liquid crystal pitch. And the molecule contains the halogen iodine element that increases the refractive index. The refractive index of the third layer is the lowest, mainly because the 3-hexene-bridged tetrafluoroborate-based pyridine borate itself has the largest molecular size, increasing the liquid crystal pitch. And tetrafluoroboric acid has a relatively large volume and contains the halogen fluorine element that reduces the refractive index.

[0104] During the synthesis of 3-hexene-bridged tetrafluoroborate-based pyridine borate in Comparative Example 2, sodium tetrafluoroborate was not added to replace bromide ions. As a result, the refractive index of the third layer of the obtained gradient refractive index material increased, leading to a decrease in the gradient difference between the second layer and the third layer.

[0105] During the synthesis of 2-butene-bridged ammonium bromide-based pyridine borate in Comparative Example 3, sodium tetrafluoroborate was added to replace bromide ions, while sodium tetrafluoroborate was not added to replace bromide ions during the synthesis of 3-hexene-bridged tetrafluoroborate-based pyridine borate. The refractive index sizes of the two layers were reversed, destroying the gradient refractive index.

[0106] In Comparative Example 4 (during the preparation of the gradient refractive index material, instead of self-assembly, a high-temperature rapid drying method was used. Since no liquid crystal structure was formed, the refractive index of each layer approached the refractive index of nanocellulose, and the refractive index gradient difference between the layers became smaller.

[0107] As Figure 1 shown, the reflection peak positions of the three-layer refractive index materials in Example 1 are at 557 nm, 578 nm, and 620 nm respectively. The reflection peak wavelengths gradually increase from the first layer to the third layer, which is mainly caused by the birefringence of the liquid crystal optical properties. The size of its reflection wavelength is related to the liquid crystal pitch. It can be seen from this that the liquid crystal pitch of the first layer is the smallest, the third layer is the largest, and the second layer is in the middle. The different pitches are mainly caused by the different molecular size lengths of ethane-bridged ammonium iodide-based pyridine borate, 2-butene-bridged ammonium bromide-based pyridine borate, and 3-hexene-bridged tetrafluoroborate-based pyridine borate.

[0108] To further evaluate the optophysical properties of the gradient refractive index materials, a series of optoelectronic devices were constructed using the gradient refractive index materials prepared in Example 1 and Comparative Examples 1-4 as the substrates. The device structure is as Figure 2As shown. All optical devices are fabricated using the same preparation method and process parameters. The solution spin-coating method is used to perform spin-coating on the substrate surface in sequence: the anode PEDOT:PSS-1000 is spin-coated at a speed of 1200 rpm for 30 s; the hole transport layer PEDOT:PSS-800 is spin-coated at a speed of 3000 rpm for 20 s; the light-emitting layer Super Yellow is spin-coated at a speed of 1200 rpm for 30 s; the electron transport layer ethoxylated polyethyleneimine is spin-coated at a speed of 1200 rpm for 30 s; the cathode indium gallium eutectic alloy is spin-coated at a speed of 1200 rpm for 30 s. An annealing process is carried out for each function, with an annealing temperature of 85 °C and an annealing time of 30 min. Note that (the first layer of the gradient refractive index polymer material (i.e., Figure 2 the gradient refractive index substrate therein) faces upward, that is, the first layer is in contact with the anode. Since the refractive index of the anode is 1.8 and the refractive index of air is 1, the gradient refractive index requires a higher refractive index near the anode and as low a refractive index as possible near the air.

[0109] As Figure 3 shown, using the same device preparation process and device structure, the performance of the optoelectronic device constructed in Figure 2 is tested. Under the same test conditions (6 V voltage), the light extraction efficiency of the device shows differences. As is well known, for bottom-emitting devices, the refractive index of the substrate affects the light extraction efficiency of the device. The gradient refractive index is beneficial to the extraction of light by the device and improves the light extraction efficiency. It can be seen that Example 1 and Comparative Example 1 have a relatively high light extraction efficiency of 33 - 34%. Due to the destruction of the refractive index gradient of the material in Comparative Example 4, the light extraction efficiency is only 15%.

[0110] Example 2

[0111] A preparation method of a bio-based polymer gradient refractive index polymer material according to the present invention specifically includes the following steps:

[0112] Step 1, preparation of a nano-cellulose dispersion liquid, specifically:

[0113] Take 10 g of cotton fiber pulp and immerse it in 400 mL of NaOH (pH = 11) solution, and stir at room temperature for 2 h. Take out the cotton fiber pulp, wash it with 800 mL of deionized water, and repeat 5 times. Further, add the cotton fiber pulp to a high-pressure (60 MPa) homogenizer and homogenize it 40 times. After homogenization, add the cotton fiber pulp to 1500 mL of sulfuric acid solution with pH = 2, and stir and react for 2 h. After the reaction, the obtained solution is centrifuged at 10000 r / min for half an hour to remove large particles or easily sedimented cellulose, and the centrifuged liquid is dialyzed three times with a 12000 Da dialysis bag. A light blue nanocellulose solution is obtained. Quantify the solid content of the nanocellulose as 3%, and then add fructose with a molecular weight of 2000 to the nanocellulose solution, and stir at 70 °C for 12 h to obtain a transparent dispersion, in which the solid content of fructose is quantified as 1%.

[0114] Step 2, Synthesis of ethane-bridged ammonium iodide borate pyridine, specifically:

[0115] Take 24.6 g of 4-pyridineboronic acid and dissolve it in 30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0116] Then dissolve 18.8 g of 1,2-dibromoethane in 30 mL of N,N-dimethylformamide solution to obtain a 1,2-dibromoethane solution;

[0117] Finally, slowly drop the 1,2-dibromoethane solution into the 4-pyridineboronic acid solution (the dropping time is 60 min), and stir the obtained mixed solution at room temperature for 12 h. After the reaction, pour the mixed solution into 400 mL of deionized water, stir evenly, extract with 300 mL of dichloromethane, and repeat 5 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and 1,2-dibromoethane). Collect the final aqueous solution and heat it to 90 °C, concentrate the volume of the aqueous solution to 150 mL, cool the temperature to room temperature, and let it stand for 72 h to precipitate white powder. Further, filter it, collect the filter cake and dry it at 60 °C for 24 h to obtain the white product ethane-bridged ammonium iodide borate pyridine.

[0118] Step 3, Synthesis of 2-butene-bridged ammonium bromide borate pyridine, specifically:

[0119] Take 24.6 g of 4-pyridineboronic acid and dissolve it in 30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0120] Then dissolve 21.4 g of trans-1,4-dibromo-2-butene in 30 mL of N,N-dimethylformamide solution to obtain a trans-1,4-dibromo-2-butene solution;

[0121] Finally, the trans-1,4-dibromo-2-butene solution was slowly added dropwise to the 4-pyridineboronic acid solution (the dropping time was 60 min), and the resulting mixed solution was stirred at room temperature for 12 h. After the reaction was completed, the mixed solution was poured into 400 mL of deionized water. After stirring evenly, it was extracted with 300 mL of dichloromethane 5 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,4-dibromo-2-butene). The final aqueous solution was collected and heated to 90 °C, and the volume of the aqueous solution was concentrated to 150 mL. After the temperature was lowered to room temperature and allowed to stand for 72 h, a white powder precipitated. Further, after filtration, the filter cake was collected and dried at 60 °C for 24 h to obtain the white product 2-butene-bridged ammonium bromide borate pyridine.

[0122] Step 4, Synthesis of 3-hexene-bridged tetrafluoroborate borate pyridine, specifically:

[0123] Take 24.6 g of 4-pyridineboronic acid and dissolve it in 30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0124] Then, 24.2 g of trans-1,6-dibromo-3-hexene was dissolved in 30 mL of N,N-dimethylformamide solution to obtain a trans-1,6-dibromo-3-hexene solution;

[0125] Finally, the trans-1,6-dibromo-3-hexene solution was slowly added dropwise to the 4-pyridineboronic acid solution (the dropping time was 60 min), and the resulting mixed solution was stirred at room temperature for 12 h. Further, 110 g of excessive sodium tetrafluoroborate and 200 mL of deionized water were added to the mixed solution, and stirring was continued for 4 h. After the reaction was completed, the reaction solution was poured into 300 mL of deionized water. After stirring evenly, it was extracted with 500 mL of dichloromethane 5 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,6-dibromo-3-hexene). The final aqueous solution was collected and heated to 90 °C, and the volume of the aqueous solution was concentrated to 150 mL. After the temperature was lowered to room temperature and allowed to stand for 72 h, a white powder precipitated. Further, after filtration, the filter cake was collected and dried at 60 °C for 24 h to obtain the white product 3-hexene-bridged tetrafluoroborate borate pyridine.

[0126] Step 5, Self-assembly to construct a gradient refractive index material, specifically:

[0127] Weigh 20 mg of ethane-bridged ammonium iodide-based pyridine borate, 20 mg of 2-butene-bridged ammonium bromide-based pyridine borate, and 20 mg of 3-hexene-bridged tetrafluoroborate-based pyridine borate respectively. Take three 10-mL nano-cellulose dispersions and add them into three 25-mL beakers respectively. Place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 2 h. Then, add ethane-bridged ammonium iodide-based pyridine borate, 2-butene-bridged ammonium bromide-based pyridine borate, and 3-hexene-bridged tetrafluoroborate-based pyridine borate into the three beakers containing nano-cellulose dispersions respectively, and further place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 2 h. Take out the beaker containing ethane-bridged ammonium iodide-based pyridine borate (put the other two beakers in the refrigerator and store them at 10 °C for later use). Pour the dispersion in it into a petri dish with a diameter of 10 cm, and then let it stand in a constant temperature and humidity chamber (humidity is 40% RH, temperature is 40 °C) for 72 h to form the first layer of gel-like liquid crystal. Further, slowly spread the dispersion containing 2-butene-bridged ammonium bromide-based pyridine borate on the surface of the first layer of gel-like liquid crystal with a syringe, and then let it stand in a constant temperature and humidity chamber (humidity is 40% RH, temperature is 40 °C) for 72 h to form the second layer of gel-like liquid crystal. Further, slowly spread the dispersion containing 3-hexene-bridged tetrafluoroborate-based pyridine borate on the surface of the second layer of gel-like liquid crystal with a syringe, and then let it stand in a constant temperature and humidity chamber (humidity is 40% RH, temperature is 40 °C) for 72 h to form the third layer of gel-like liquid crystal. Let the obtained three-layer gel-like liquid crystal material stand in a constant temperature and humidity chamber (humidity is 30% RH, temperature is 50 °C) and continue to dry for 72 h to obtain the final gradient refractive index material.

[0128] To measure the refractive index of the three-layer gel-like liquid crystal material prepared in step 5, three single refractive index materials need to be prepared separately, as follows:

[0129] Weigh 20 mg of ethane-bridged ammonium iodide-based pyridine borate, 20 mg of 2-butene-bridged ammonium bromide-based pyridine borate, and 20 mg of 3-hexene-bridged tetrafluoroborate-based pyridine borate separately. Take three 10-mL nano-cellulose dispersions and add them into three 25-mL beakers respectively. Place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 2 h. Then, add ethane-bridged ammonium iodide-based pyridine borate, 2-butene-bridged ammonium bromide-based pyridine borate, and 3-hexene-bridged tetrafluoroborate-based pyridine borate into the three beakers containing nano-cellulose dispersions respectively, and further place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 2 h. Pour the dispersions in the three beakers into petri dishes with a diameter of 10 cm, and then let them stand in a constant temperature and humidity chamber (humidity is 40% RH, temperature is 40 °C) for 72 h to form three gel-like liquid crystals. Let the three obtained gel-like liquid crystal materials stand in a constant temperature and humidity chamber (humidity is 30% RH, temperature is 50 °C) and continue to dry for 72 h to obtain three single refractive index materials containing ethane-bridged ammonium iodide-based pyridine borate, 2-butene-bridged ammonium bromide-based pyridine borate, and 3-hexene-bridged tetrafluoroborate-based pyridine borate respectively.

[0130] Example 3

[0131] A preparation method of a bio-based polymer gradient refractive index polymer material of the present invention specifically includes the following steps:

[0132] Step 1, preparation of nano-cellulose dispersion, specifically:

[0133] Take 8 g of cotton fiber pulp and immerse it in 300 mL of NaOH (pH = 11) solution, and stir at room temperature for 1.5 h. Take out the cotton fiber pulp, wash it with 600 mL of deionized water, and repeat 4 times. Further add the cotton fiber pulp into a high-pressure (50 MPa) homogenizer and homogenize 38 times. After homogenization, add the cotton fiber pulp into 1200 mL of sulfuric acid solution with pH = 2 and stir and react for 1.5 h. After the reaction, the obtained solution is centrifuged at 8000 r / min for half an hour to remove large particles or easily sedimentable cellulose, and the centrifuged liquid is dialyzed three times with an 8000 Da dialysis bag. A light blue nano-cellulose solution is obtained, the solid content of nano-cellulose is quantified to 2.5%, and then fructose with a molecular weight of 1800 is added into the nano-cellulose solution and stirred at 60 °C for 10 h to obtain a transparent dispersion, where the solid content of fructose is quantified to 0.8%.

[0134] Step 2, synthesis of ethane-bridged ammonium iodide-based pyridine borate, specifically:

[0135] Take 18.6 g of 4-pyridine borate and dissolve it in 25 mL of N,N-dimethylformamide solution to obtain a 4-pyridine borate solution;

[0136] Then, 12.8 g of 1,2-dibromoethane was dissolved in 25 mL of N,N-dimethylformamide solution to obtain a 1,2-dibromoethane solution;

[0137] Finally, the 1,2-dibromoethane solution was slowly added dropwise to the 4-pyridineboronic acid solution (the dropping time was 40 min), and the resulting mixed solution was stirred at room temperature for 8 h. After the reaction was completed, the mixed solution was poured into 300 mL of deionized water. After stirring evenly, it was extracted with 280 mL of dichloromethane 4 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and 1,2-dibromoethane). The final aqueous solution was collected and heated to 85 °C, the volume of the aqueous solution was concentrated to 120 mL, the temperature was lowered to room temperature, and white powder precipitated after standing for 56 h. Further, it was filtered, the filter cake was collected and dried at 55 °C for 18 h to obtain the white product ethane-bridged ammonium iodide borate pyridine.

[0138] Step 3, Synthesis of 2-butene-bridged ammonium bromide borate pyridine, specifically:

[0139] 18.8 g of 4-pyridineboronic acid was dissolved in 25 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0140] Then, 16.8 g of trans-1,4-dibromo-2-butene was dissolved in 25 mL of N,N-dimethylformamide solution to obtain a trans-1,4-dibromo-2-butene solution;

[0141] Finally, the trans-1,4-dibromo-2-butene solution was slowly added dropwise to the 4-pyridineboronic acid solution (the dropping time was 40 min), and the resulting mixed solution was stirred at room temperature for 8 h. After the reaction was completed, the mixed solution was poured into 300 mL of deionized water. After stirring evenly, it was extracted with 280 mL of dichloromethane 4 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,4-dibromo-2-butene). The final aqueous solution was collected and heated to 85 °C, the volume of the aqueous solution was concentrated to 120 mL, the temperature was lowered to room temperature, and white powder precipitated after standing for 56 h. Further, it was filtered, the filter cake was collected and dried at 55 °C for 18 h to obtain the white product 2-butene-bridged ammonium bromide borate pyridine.

[0142] Step 4, Synthesis of 3-hexene-bridged tetrafluoroborate borate pyridine, specifically:

[0143] 18.8 g of 4-pyridineboronic acid was dissolved in 25 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution;

[0144] Then, 16.8 g of trans-1,6-dibromo-3-hexene was dissolved in 25 mL of N,N-dimethylformamide solution to obtain a trans-1,6-dibromo-3-hexene solution;

[0145] Finally, the trans-1,6-dibromo-3-hexene solution was slowly added dropwise to the 4-pyridineboronic acid solution (the dropping time was 40 min), and the resulting mixed solution was stirred at room temperature for 8 h. Further, 88 g of excessive sodium tetrafluoroborate and 150 mL of deionized water were added to the mixed solution, and stirring was continued for 3 h. After the reaction was completed, the reaction solution was poured into 200 mL of deionized water. After stirring evenly, extraction was performed with 400 mL of dichloromethane for 4 times (to remove the N,N-dimethylformamide solvent and the unreacted raw materials of 4-pyridineboronic acid and trans-1,6-dibromo-3-hexene). The final aqueous solution was collected and heated to 85 °C, and the volume of the aqueous solution was concentrated to 120 mL. After the temperature was lowered to room temperature and allowed to stand for 56 h, white powder precipitated. Further, after filtration, the filter cake was collected and dried at 55 °C for 18 h to obtain the white product 3-hexene-bridged pyridine borate tetrafluoroborate.

[0146] Step 5, self-assembling to construct a gradient refractive index material, specifically:

[0147] Weigh 15 mg of ethane-bridged ammonium iodide-based pyridine borate, 15 mg of 2-butene-bridged ammonium bromide-based pyridine borate, and 15 mg of 3-hexene-bridged tetrafluoroborate-based pyridine borate separately. Take three 8-mL nanocellulose dispersions and add them to three 20-mL beakers respectively. Place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1.5 h. Then, add ethane-bridged ammonium iodide-based pyridine borate, 2-butene-bridged ammonium bromide-based pyridine borate, and 3-hexene-bridged tetrafluoroborate-based pyridine borate to the three beakers containing nanocellulose dispersions respectively, and further place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1.5 h. Take out the beaker containing ethane-bridged ammonium iodide-based pyridine borate (put the other two beakers in the refrigerator and store them at 8 °C for later use). Pour the dispersion in it into a petri dish with a diameter of 8 cm, and then let it stand in a constant temperature and humidity chamber (humidity is 35% RH, temperature is 38 °C) for 56 h to form the first layer of gel-like liquid crystal. Further, slowly spread the dispersion containing 2-butene-bridged ammonium bromide-based pyridine borate on the surface of the first layer of gel-like liquid crystal with a syringe, and then let it stand in a constant temperature and humidity chamber (humidity is 35% RH, temperature is 38 °C) for 56 h to form the second layer of gel-like liquid crystal. Further, slowly spread the dispersion containing 3-hexene-bridged tetrafluoroborate-based pyridine borate on the surface of the second layer of gel-like liquid crystal with a syringe, and then let it stand in a constant temperature and humidity chamber (humidity is 35% RH, temperature is 38 °C) for 72 h to form the third layer of gel-like liquid crystal. Let the obtained three-layer gel-like liquid crystal material stand in a constant temperature and humidity chamber (humidity is 25% RH, temperature is 48 °C) and continue to dry for 56 h to obtain the final gradient refractive index material.

[0148] In order to measure the refractive index of the three-layer gel-like liquid crystal material prepared in step 5, three single refractive index materials need to be prepared separately, as follows:

[0149] Weigh 15 mg of ethane-bridged ammonium iodide-based pyridine borate, 15 mg of 2-butene-bridged ammonium bromide-based pyridine borate, and 15 mg of 3-hexene-bridged tetrafluoroborate-based pyridine borate respectively. Take three 8 mL nano-cellulose dispersions and add them into three 20 mL beakers respectively. Place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1.5 h. Then, add ethane-bridged ammonium iodide-based pyridine borate, 2-butene-bridged ammonium bromide-based pyridine borate, and 3-hexene-bridged tetrafluoroborate-based pyridine borate into the three beakers containing nano-cellulose dispersions respectively, and further place the three beakers in an ultrasonic device (with a power of 150 W) and ultrasonicate for 1.5 h. Pour the dispersions in the three beakers into petri dishes with a diameter of 8 cm respectively, and then leave them standing in a constant temperature and humidity chamber (humidity is 35% RH, temperature is 38 °C) for 56 h to form three gel-like liquid crystals. Leave the three obtained gel-like liquid crystal materials standing in a constant temperature and humidity chamber (humidity is 25% RH, temperature is 48 °C), and continue to dry for 72 h to obtain three single refractive index materials containing ethane-bridged ammonium iodide-based pyridine borate, 2-butene-bridged ammonium bromide-based pyridine borate, and 3-hexene-bridged tetrafluoroborate-based pyridine borate respectively.

Claims

1. A preparation method of a bio-based polymer gradient refractive index polymer material, characterized in that: Specifically, it includes the following steps: Step 1, prepare a nano-cellulose dispersion; Step 2, synthesize ethane-bridged ammonium iodide borate pyridine; Step 3, synthesize 2-butene-bridged ammonium bromide borate pyridine; Step 4, synthesize 3-hexene-bridged tetrafluoroborate borate pyridine; Step 5, construct a gradient refractive index polymer material according to the products obtained in Steps 1-4.

2. The preparation method of a bio-based polymer gradient refractive index polymer material according to claim 1, characterized in that: The specific process of Step 1 is as follows: Step 1.1, take 5-10 g of cotton fiber pulp and immerse it in 200-400 mL of NaOH solution, stir at room temperature for 1-2 h; then take out the cotton fiber pulp and wash it with 500-800 mL of deionized water, repeat 3-5 times; Step 1.2, add the cotton fiber pulp treated in Step 1.1 to a homogenizer and homogenize it 30-40 times. Add the homogenized cotton fiber pulp to 1000-1500 mL of sulfuric acid solution with pH = 1-2, stir and react for 1-2 h. After the reaction, centrifuge the obtained solution at 5000-10000 r / min for half an hour. Dialyze the centrifuged liquid three times with a 7000-12000 Da dialysis bag to obtain a light blue nano-cellulose solution. Quantify the nano-cellulose solid content to 2-3%, and then add fructose with a molecular weight of 1200-2000 to the nano-cellulose solution, stir at 50-70 °C for 8-12 h to obtain a transparent nano-cellulose dispersion.

3. The preparation method of a bio-based polymer gradient refractive index polymer material according to claim 2, characterized in that: In Step 1.2, the fructose solid content is quantified to 0.5-1%.

4. The preparation method of a bio-based polymer gradient refractive index polymer material according to claim 1, characterized in that: The specific process of Step 2 is as follows: Step 2.1, take 12.3-24.6 g of 4-pyridineboronic acid and dissolve it in 20-30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution; Step 2.2, dissolve 9.4-18.8 g of 1,2-dibromoethane in 20-30 mL of N,N-dimethylformamide solution to obtain a 1,2-dibromoethane solution; Step 2.3, drop the 1,2-dibromoethane solution obtained in Step 2.2 into the 4-pyridineboronic acid solution obtained in Step 2.

1. Stir the obtained mixed solution at room temperature for 6-12 h. After the reaction, pour the mixed solution into 200-400 mL of deionized water, stir evenly, and extract with 200-300 mL of dichloromethane, repeat 3-5 times; collect the final aqueous solution and heat it to 80-90 °C, concentrate the volume of the aqueous solution to 100-150 mL, cool the temperature to room temperature, and let it stand for 48-72 h to precipitate white powder. Then filter it, collect the filter cake and dry it at 45-60 °C for 12-24 h to obtain a white product, ethane-bridged ammonium iodide borate pyridine.

5. The preparation method of a bio-based polymer gradient refractive index polymer material according to claim 1, wherein: The specific process of Step 3 is as follows: Step 3.1, take 12.3-24.6 g of 4-pyridineboronic acid and dissolve it in 20-30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution; Step 3.2, dissolve 10.7-21.4 g of trans-1,4-dibromo-2-butene in 20-30 mL of N,N-dimethylformamide solution to obtain a trans-1,4-dibromo-2-butene solution; Step 3.3: Drop the trans-1,4-dibromo-2-butene solution obtained in Step 3.2 into the 4-pyridineboronic acid solution obtained in Step 3.

1. Stir the resulting mixed solution at room temperature for 6 - 12 h. After the reaction, pour the mixed solution into 200 - 400 mL of deionized water, stir evenly, extract with 200 - 300 mL of dichloromethane, and repeat 3 - 5 times. Collect the final aqueous solution and heat it to 80 - 90 °C. Concentrate the volume of the aqueous solution to 100 - 150 mL, cool to room temperature, and let it stand for 48 - 72 h to precipitate white powder. Then, filter it, collect the filter cake, and dry it at 45 - 60 °C for 12 - 24 h to obtain the white product 2-butene-bridged ammonium bromide borate pyridine.

6. The preparation method of a bio-based polymer gradient refractive index polymer material according to claim 1, characterized in that: The specific process of Step 4 is as follows: Step 4.1: Dissolve 12.3 - 24.6 g of 4-pyridineboronic acid in 20 - 30 mL of N,N-dimethylformamide solution to obtain a 4-pyridineboronic acid solution. Step 4.2: Dissolve 12.1 - 24.2 g of trans-1,6-dibromo-3-hexene in 20 - 30 mL of N,N-dimethylformamide solution to obtain a trans-1,6-dibromo-3-hexene solution. Step 4.3: Drop the trans-1,6-dibromo-3-hexene solution obtained in Step 4.2 into the 4-pyridineboronic acid solution obtained in Step 4.

1. Stir the resulting mixed solution at room temperature for 6 - 12 h. Add 55 - 110 g of sodium tetrafluoroborate and 100 - 200 mL of deionized water to the mixed solution, and continue to stir for 2 - 4 h. After the reaction, pour the reaction solution into 150 - 300 mL of deionized water, stir evenly, extract with 250 - 500 mL of dichloromethane, and repeat 3 - 5 times. Collect the final aqueous solution and heat it to 80 - 90 °C. Concentrate the volume of the aqueous solution to 100 - 150 mL, cool to room temperature, and let it stand for 48 - 72 h to precipitate white powder. Then, filter it, collect the filter cake, and dry it at 45 - 60 °C for 12 - 24 h to obtain the white product 3-hexene-bridged tetrafluoroborate borate pyridine.

7. The preparation method of a bio-based polymer gradient refractive index polymer material according to claim 1, characterized in that: The specific process of Step 5 is as follows: Step 5.1: Weigh 10 - 20 mg of ethane-bridged ammonium iodide borate pyridine, 10 - 20 mg of 2-butene-bridged ammonium bromide borate pyridine, and 10 - 20 mg of 3-hexene-bridged tetrafluoroborate borate pyridine respectively. Step 5.2: Take three portions of 5 - 10 mL of the nanocellulose dispersion prepared in Step 1, and add them to three 10 - 25 mL beakers respectively. Place the three beakers in an ultrasonic cleaner and ultrasonicate for 1 - 2 h. Step 5.3: Add the ethane-bridged ammonium iodide borate pyridine, 2-butene-bridged ammonium bromide borate pyridine, and 3-hexene-bridged tetrafluoroborate borate pyridine weighed in Step 5.1 to the three beakers of nanocellulose dispersion in Step 5.2 respectively. Step 5.4: Place the three beakers in Step 5.3 into an ultrasonic device and ultrasonicate for 1 - 2 h. Take out the beaker containing ethane - bridged ammonium iodide - based pyridine borate, pour the nano - cellulose dispersion containing ethane - bridged ammonium iodide - based pyridine borate in this beaker into a petri dish with a diameter of 5 - 10 cm, and then let it stand in a constant temperature and humidity chamber for 48 - 72 h to form the first - layer gel - like liquid crystal. Step 5.5: Use a syringe to spread the nano - cellulose dispersion containing 2 - butene - bridged ammonium bromide - based pyridine borate onto the surface of the first - layer gel - like liquid crystal formed in Step 5.4 by injection, and then let it stand in a constant temperature and humidity chamber for 48 - 72 h to form the second - layer gel - like liquid crystal. Step 5.6: Use a syringe to spread the nano - cellulose dispersion containing 3 - hexene - bridged tetrafluoroborate - based pyridine borate onto the surface of the second - layer gel - like liquid crystal formed in Step 5.5 by injection, and then let it stand in a constant temperature and humidity chamber for 72 h to form the third - layer gel - like liquid crystal. Step 5.7: Let the three - layer gel - like liquid crystal material obtained in Steps 5.4 - 5.6 stand in a constant temperature and humidity chamber and continue to dry for 48 - 72 h to obtain the final gradient refractive index material.

8. The preparation method of a bio-based polymer gradient refractive index polymer material according to claim 7, characterized in that: In Steps 5.4 - 5.6, the humidity in the constant temperature and humidity chamber is 30 - 40% RH, and the temperature is 35 - 40 °C.

9. The preparation method of a bio-based polymer gradient refractive index polymer material according to claim 7, characterized in that: In Step 5.7, the humidity in the constant temperature and humidity chamber is 20 - 30% RH, and the temperature is 45 - 50 °C.

10. A bio - based polymer gradient refractive index polymer material is prepared by using the preparation method of a bio - based polymer gradient refractive index polymer material according to any one of claims 1 - 9.

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