Branched chain type silane coupling agent as well as preparation method and application thereof

Abstract

According to the branched chain type silane coupling agent as well as the preparation method and the application thereof, a plurality of organic functional groups for anchoring an organic matrix are introduced, and the structures, the number and the positions of the functional groups are optimized, so that the interface performance between an organic material and inorganic nanoparticles is greatly improved, the steric hindrance of a reaction is reduced, and the reaction time is shortened; the modification effect of the nano particles is improved. Taking titanium dioxide nano particle modification as an example, the transmittance of titanium dioxide dispersion liquid modified by the branched chain type silane coupling agent provided by the invention can reach 93%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of nanomaterials and optical materials, and particularly relates to a branched silane coupling agent, a preparation method and application thereof. BACKGROUND

[0002] As a kind of binder connecting organic materials and inorganic materials, silane coupling agent is widely used in glass fiber reinforced plastic, surface modification of inorganic materials, adhesion improvement of adhesive and performance optimization of coating and ink. The mechanism is that the two end groups of the molecular structure of silane coupling agent, which can be represented as Y-(CH2) n -Si-(OR)3, wherein Y is an organic functional group (such as amino, vinyl, mercapto, etc.), which can chemically react or physically entangle with organic materials (such as resin, rubber); OR is an alkoxy group (such as methoxy, ethoxy, etc.), which can be hydrolyzed to generate silicon hydroxyl (-Si-OH); (CH2) n is a carbon chain spacer group connecting the organic functional group and the silicon atom.

[0003] When the silane coupling agent is hydrolyzed, the following reaction occurs: Si-OR + H2O → Si-OH + R-OH. The silicon hydroxyl (-Si-OH) generated by hydrolysis can condense with the hydroxyl (-OH) on the surface of inorganic materials (such as glass, metal, filler) to form a covalent bond (-Si-O-M), M is inorganic material), while the organic functional group Y is combined with the organic matrix, thereby forming a "molecular bridge" between inorganic materials and organic materials, improving the interfacial compatibility.

[0004] However, the existing silane coupling agents on the market are all linear structures. If the Y group is referred to as an anchor group, in linear structure silane coupling agent, only one anchor group of a siloxane can be connected with organic materials, resulting in a lower upper limit of inorganic nanomaterial modification, which cannot meet the application requirements. Taking high refractive index titanium dioxide nanoparticles as an example, due to the limitations of existing technology, the light transmittance of high refractive index coating based on titanium dioxide nanoparticles is generally less than 92%.

[0005] Therefore, it is particularly important to explore and modify the structure of silane coupling agent for the modification of inorganic nanomaterials. SUMMARY

[0006] In view of the problems existing in the prior art, the present application provides a branched silane coupling agent, a preparation method and application thereof. The benzene ring, cyclohexyl group, carbon atom or nitrogen atom is used as the core of the branched chain, which carries multiple organic functional groups that can anchor organic materials, greatly improves the interfacial performance between inorganic materials and organic materials, fills the gap of only linear silane coupling agent on the market, greatly improves the compatibility of nanoparticles in organic components, and creates new possibilities for the application of nanomaterials in the field of optics.

[0007] In one aspect, the present application provides a branched silane coupling agent, having any one of the general structures shown in Formula 1-Formula 4:

[0008]

[0009] wherein A1 is methylene or ethylene, A2 is a carbon chain or oxacarbon chain of 1-10 carbons, R is any one of methyl, ethyl, propyl, and R1-R5 are any one or more of hydrogen atom, alkoxy, polyethoxy ether, acrylate group, and vinyl ether.

[0010] In recent years, the research on silane coupling agent modified nanoparticles has made remarkable progress in the fields of material science, energy, and biomedical science, and the core goal is to optimize the dispersibility, stability, and functional characteristics of nanoparticles through interface regulation. Existing linear silane coupling agents usually have a long alkyl chain, and only one organic functional group (such as amino, epoxy, and methacryloyloxy) at the end can react with organic materials, and the interaction between the silane coupling agent and the organic material is weak. In order to improve the upper limit requirement for the modification of inorganic nanomaterials, the present application innovatively introduces benzene ring, cyclohexyl, carbon atom or nitrogen atom as the branched core, changes the linear silane coupling agent into branched silane coupling agent, and designs a molecular structure with stronger interface force and larger spatial volume, so as to construct a more stable, more compatible, and more functional organic interface layer on the surface of nanoparticles.

[0011] Compared with existing linear silane coupling agents, when benzene ring is used as the branched core, on the one hand, the rigid benzene ring and the branched chain connected thereto increase the spatial volume of the coupling agent molecules on the surface of the nanoparticles, physically hindering the particles from approaching, and on the other hand, due to the relatively active hydrogen atoms on the benzene ring, further chemical modification (such as nitration, halogenation, and sulfonation) is easy to be carried out, thereby introducing multiple specific functional groups, multiple terminal functional groups or branched chains increase the interaction sites with the polymer matrix, which provides great flexibility for designing nanoparticles with multiple functions (such as strengthening, toughening, electrically conductive, thermally conductive, antibacterial, fluorescent, etc.). In addition, by designing the length and flexibility of the branched chain, the performance of the interface layer can be optimized. Compared with other ways of providing branched chains, such as cyclohexyl, carbon atom or nitrogen atom, the branched silane coupling agent prepared by using benzene ring as the branched core can achieve excellent nanoparticle modification effect, and at the same time, the preparation process is simpler and the cost is lower.

[0012] Further, R1 and R5 are hydrogen atoms, and R2, R3, and R4 are any one or more of alkoxy, polyethoxy ether, acrylate group, and vinyl ether.

[0013] In some embodiments, the present application connects siloxane to the 1 position of the benzene ring through alkyl A1, and the 2-6 positions of the benzene ring are substituted by R1-R5 organic functional groups or hydrogen atoms. The polarity of the silane coupling agent is determined by the polarity of R1-R5, among which the polarity of the alkyl group is the smallest, followed by the hydrogen atom, followed by the alkoxy group, followed by the polyethoxy ether, the vinyl ether, and the acrylate group. The hydrogen atom can reduce the steric hindrance of the silane coupling agent, which is beneficial to better reaction in subsequent application; the flexible long chain can provide better wrapping effect. In order to reduce the reaction hindrance of the modification reaction, and enhance the compatibility and interaction between the nanoparticles and the organic matrix, the present application compares and explores the number, position and type of functional groups of R1-R5 substituent groups. The results show that compared with vinyl ether, acrylate group, and polyethoxy ether, the longer chain of polyethoxy ether makes the physical entanglement between nanoparticles and materials stronger, and improves the interfacial compatibility. However, when the polyethoxy ether is designed at the 2 and 5 positions of the benzene ring, the flexible long chain will form a physical barrier on both sides of the benzene ring plane, wrapping the siloxane group at the 1 position, increasing the steric hindrance, thereby increasing the difficulty of the hydroxyl group on the surface of the nanoparticles to approach the silanol group, resulting in a decrease in condensation efficiency. In addition, the number of polyethoxy ethers on the benzene ring is not the more the better, when the number reaches 4, since one of the polyethoxy ethers will also be located at the 2 or 5 position, the same problem of increased steric hindrance occurs. Therefore, the number of polyethoxy ethers on the benzene ring is designed to be 3, and the position is located at the 3, 4, and 5 positions (i.e. R2-R4), which is the best for nanoparticle modification.

[0014] Preferably, the branched silane coupling agent has a general structure formula as shown in formula 1:

[0015]

[0016] The R1 and R5 are hydrogen atoms, and the R2, R3, and R4 are polyethoxy ethers.

[0017] Further, the polyethoxy ether has a general structure formula as shown in formula 5, the acrylate group has a general structure formula as shown in formula 6, and the vinyl ether has a general structure formula as shown in formula 7:

[0018]

[0019] wherein N is an integer greater than 0, and A3 is a methyl group or a hydrogen atom.

[0020] Further, the branched silane coupling agent has a structure formula as shown in formula 8 or formula 9:

[0021]

[0022]

[0023] In another aspect, the present application provides a preparation method of branched silane coupling agent, which is prepared by a chemical general formula shown in formula 10 or formula 11:

[0024]

[0025] In some embodiments, when the A group is methylene, the synthesis of the silane coupling agent introduces siloxane through Grignard reaction, i.e. the reaction formula of formula 10; when the A group is ethylene, the synthesis of the silane coupling agent introduces siloxane through platinum-catalyzed addition, i.e. the reaction formula of formula 11.

[0026] Further, when prepared by the chemical general formula shown in formula 10, the method comprises the following steps:

[0027] S1: the benzyl chloride derivative is mixed with magnesium powder and diethyl ether, and iodine is added under nitrogen protection for sufficient reaction;

[0028] S2: after the reaction, cooling to-5-10℃, adding chlorosiloxane for reaction;

[0029] S3: filtering out impurities, distillation under reduced pressure, and separation and purification to obtain the target product.

[0030] In some embodiments, when prepared by the chemical general formula shown in formula 10, the method comprises the following steps:

[0031] The benzyl chloride derivative is mixed with magnesium powder and diethyl ether, and a small amount of iodine is added under nitrogen protection, followed by heating and refluxing for 0.5-2 hours, and then cooling to-5-10℃, and then adding chlorosiloxane for reaction for 5-20 hours. Then, the solid impurities are filtered out, and the obtained crude product is separated and purified by distillation under reduced pressure to obtain the target product.

[0032] Further, when prepared by the chemical general formula shown in formula 11, the method comprises the following steps:

[0033] S1: the styrene derivative, trialkoxysilane, and catalyst are stirred and reacted in a solvent under nitrogen condition;

[0034] S2: filtering out impurities, distillation under reduced pressure, and separation and purification to obtain the target product.

[0035] In some embodiments, when prepared by the chemical general formula shown in formula 11, the method comprises the following steps:

[0036] The styrene derivative and trialkoxysilane, a catalyst preferably chloroplatinic acid (H2PtCl6), and a solvent preferably diethyl ether or tetrahydrofuran are stirred at room temperature under nitrogen atmosphere for 5-10 hours, preferably 8 hours, and then the solid impurities are filtered out, and the obtained crude product is separated and purified by distillation under reduced pressure to obtain the target product.

[0037] In another aspect, the present invention provides an application of a branched silane coupling agent for surface modification of nanoparticles or surface treatment of inorganic materials, wherein the branched silane coupling agent has any one of the general structural formulas shown in Formulas 1 to 4:

[0038]

[0039] Among them, A1 is methylene or ethylene, A2 is a carbon chain or oxygen-carbon chain of 1-10 carbon atoms, R is any one of methyl, ethyl, and propyl, and R1-R5 are any one or more of hydrogen atom, alkoxy, polyethoxy ether, acrylate, and vinyl ether.

[0040] The application fields of the branched silane coupling agent provided by the present invention include high-refractive-index nanoimprint adhesives, high-refractive-index photocurable adhesives, low-refractive-index nanoimprint adhesives, low-refractive-index photocurable adhesives, anti-reflection films, anti-reflection films, etc.

[0041] Furthermore, when the branched silane coupling agent is used for surface modification of nanoparticles, R is a methyl group; when the branched silane coupling agent is used for surface treatment of inorganic materials, R is an ethyl group.

[0042] Furthermore, R1 and R5 are hydrogen atoms, and R2, R3, and R4 are any one or more of alkoxy, polyethoxy ether, acrylate, and vinyl ether.

[0043] Preferably, the branched silane coupling agent has a general structural formula as shown in Formula 1:

[0044]

[0045] The R1 and R5 are hydrogen atoms, and the R2, R3, and R4 are polyethoxy ethers.

[0046] The present invention has the following beneficial effects:

[0047] 1. The benzene ring is used as the core of the branched chain, and multiple functional groups capable of anchoring the organic matrix are introduced at its end, which significantly improves the interfacial compatibility between the organic matrix and the nanoparticles, improves the modification effect of the nanoparticles, and makes the transmittance of the modified titanium dioxide dispersion reach 93%.

[0048] 2. The functional group structure introduced at the end of the benzene ring is preferably a long flexible chain polyethoxy ether, which has similar polarity to the organic solvent (taking propylene glycol methyl ether acetate, propylene glycol methyl ether, and butanone as examples) and the diluent monomer (taking benzyl acrylate, acryloylmorpholine, and o-phenyl methacrylate as examples). According to the principle of like dissolves like, the long flexible chain polyethoxy ether can promote the compatibility between the organic matrix and the nanoparticles. Experiments have shown that the introduction of such groups can improve the storage stability of the nanoparticles.

[0049] 3. The number and position of organic functional groups on the benzene ring are optimized, preferably 3 polyethoxy ether groups are sequentially located at the 3, 4 and 5 positions of the benzene ring, which reduces the steric hindrance and improves the modification reaction effect. DETAILED DESCRIPTION

[0050] The application will be further described in detail below in conjunction with examples. It should be noted that the following examples are intended to facilitate the understanding of the application and do not limit the application in any way.

[0051] In the following examples, the experimental methods used are conventional methods unless otherwise specified.

[0052] In the following examples, the materials, reagents, etc. used are commercially available unless otherwise specified.

[0053] Example 1: Preparation of branched silane coupling agent (Formula 12).

[0054] The synthesis reaction formula of the branched silane coupling agent (Formula 12) is as follows:

[0055]

[0056] The specific preparation method is as follows:

[0057] The silane coupling agent (Formula 12) is prepared from Formula 12-N1 (3, 4, 5-trihydroxybenzaldehyde, purchased from Shanghai Aldrin) and Formula 12-N2 (diethylene glycol-2-bromoethyl methyl ether, purchased from Shanghai Aldrin) as starting materials, through three-step reactions, namely reaction iii, reaction iv and reaction i, to obtain the target product. Reaction iii is prepared according to the method in the reference (Langmuir (2016), 32(10), 2338-2347), and reaction iv is prepared according to the method in the reference (Journal of Molecular Structure (2024), 1311, 138420).

[0058] The specific synthesis process of Formula 12-B (reaction iii) is as follows:

[0059] Formula 12-N1 (15.41 g, 0.1 mol) and potassium carbonate (34.55 g, 0.25 mol) were added to a flask, the air in the flask was replaced with nitrogen by displacement, then 200 ml of dimethylformamide (DMF) solvent was injected, and stirring was started at room temperature, then the reactant Formula 12-N2 (79.49 g, 0.35 mol) previously dissolved in 200 ml of DMF was injected, and stirring was started at 65 degrees for 12 hours. After the reaction was completed, a small amount of water was added to quench the reaction, and then all the solvent was removed by reduced pressure distillation. The obtained crude product and inorganic salt impurities were first dissolved in dichloromethane, then extracted with an aqueous solution three times to remove inorganic impurities, and finally purified by silica gel column chromatography to obtain the product (Formula 12-B) 54.12 g, with a yield of 85%.

[0060] The specific synthesis process of Formula 12-C (reaction iv) is as follows:

[0061] First, the raw material Formula 12-B (31.83 g, 50 mmol) was dissolved in 50 ml of methanol, cooled to 0 degrees, and then sodium borohydride (5.67 g, 150 mmol) was added. Stirring was started at 0 degrees for 30 minutes, then the temperature was returned to room temperature and stirring was started for 30 minutes. Then the reaction liquid was poured into an aqueous ammonium chloride solution, and the intermediate product was extracted three times with dichloromethane. The collected product was dried and then dissolved in 70 ml of super dry tetrahydrofuran. Diisopropylamine (7.59, 75 mmol) was first added to the system, then the mixture was cooled to 0 degrees, and then dichlorosulfoxide (7.14 g, 60 mmol) was added. The temperature was then returned to room temperature and heated to reflux for 2 hours. After the reaction was completed, the reaction liquid was poured into 200 ml of water, then extracted with dichloromethane, and then washed with 2M HCl and sodium bicarbonate solution respectively. The collected organic phase was dried, filtered and distilled to obtain the benzyl chloride product (Formula 12-C) 29.57 g, with a yield of 90%.

[0062] The specific synthesis process of Formula 12 (reaction i) is as follows:

[0063] First, the raw material Formula 12-C (13.14 g, 0.02 mol) was mixed with magnesium powder (5.76 g, 0.24 mol) and ether, and then a small amount of iodine was added under nitrogen protection. Then heating was started to reflux for 1 hour, then the temperature was cooled to 0 degrees, and then chlorosiloxane (2.81 g, 0.02 mol) was added. The reaction was carried out for 10 hours. Then the solid impurities were removed by filtration, and the obtained crude product was purified by reduced pressure distillation to obtain the target product Formula 12 (12.63 g), with a yield of 85%.

[0064] Example 2: Preparation of branched silane coupling agent (Formula 13).

[0065] The synthesis reaction formula of the branched silane coupling agent (Formula 13) is as follows:

[0066]

[0067] The specific preparation method is:

[0068] The starting material is formula 13-N (3,4,5-trihydroxystyrene, purchased from Hong Kong Chemhere Co., Ltd.), which is prepared by two-step reactions of reaction iii and reaction ii to obtain the target silane coupling agent formula 13.

[0069] The specific synthesis process of formula 13-B (reaction iii) is as follows:

[0070] First, formula 13-N (15.21 g, 0.1 mol) and potassium carbonate (34.55 g, 0.25 mol) are added to a two-necked flask, the air in the two-necked flask is replaced with nitrogen by degassing, then 200 ml of dimethylformamide (DMF) solvent is injected, stirring is started at room temperature, then the reactant formula 12-N2 (79.49 g, 0.35 mol) is dissolved in 200 ml of DMF and injected, and stirring is carried out at 65 degrees for 12 hours. After the reaction is completed, a small amount of water is added to quench the reaction, and then all the solvents are removed by reduced pressure distillation. The obtained crude product and inorganic salt impurities are first dissolved in dichloromethane, then extracted with an aqueous solution three times to remove inorganic impurities, and finally purified by silica gel column chromatography to obtain the product (formula 13-B) 52.69 g, with a yield of 83%.

[0071] The specific synthesis process of formula 13 (reaction ii) is as follows:

[0072] First, the starting material formula 13-B (31.74 g, 0.05 mol) is mixed with trialkoxysilane (7.33 g, 0.06 mol), a catalyst chloroplatinic acid (H2PtCl6), a solvent ether, and nitrogen atmosphere, and stirred at room temperature for 5-10 hours, preferably 8 hours. Then, the solid impurities are removed by filtration, and the obtained crude product is purified by reduced pressure distillation to obtain the target product (formula 13) 35.96 g, with a yield of 95%.

[0073] Example 3: Preparation of branched silane coupling agent (formula 14).

[0074] The synthesis reaction formula of the branched silane coupling agent (formula 14) is as follows:

[0075]

[0076] The specific preparation method is:

[0077] The starting material is formula 12-N1, which is prepared by three-step reactions of reaction v, reaction iv and reaction i

[0078] wherein reaction v comprises the following steps:

[0079] S1 : First, 12-N1 is blended with triethylamine in dichloromethane;

[0080] S2: Acryloyl chloride is added dropwise;

[0081] S3: Normal temperature reaction for 5 hours

[0082] S4: After extraction, drying, distillation and purification, 14-B is obtained.

[0083] wherein 14-C is prepared by reaction iv of Reference Example 1, and 14 is prepared by reaction i of Reference Example 1.

[0084] Example 4: Preparation of branched silane coupling agent (Formula 15).

[0085] The synthesis reaction formula of branched silane coupling agent (Formula 15) is as follows:

[0086]

[0087] The specific preparation method is as follows:

[0088] Starting from 12-N1, through three-step reactions, i.e. reaction vi, reaction iv, and reaction i, silane coupling agent 15 is prepared.

[0089] wherein reaction vi is prepared by the method of reference (Russian Journal of Organic Chemistry (2015), 51(2), 188-194) through the following steps:

[0090] S1 : First, 12-N1 is blended with triethylamine in dichloromethane;

[0091] S2: Acryloyl chloride is added dropwise;

[0092] S3: Normal temperature reaction for 5 hours

[0093] wherein 15-C is prepared by reaction iv of Reference Example 1, and 15 is prepared by reaction i of Reference Example 1.

[0094] Example 5: Preparation of branched silane coupling agent (Formula 16)

[0095] The synthesis reaction formula of branched silane coupling agent (Formula 16) is as follows:

[0096]

[0097] The specific preparation method is similar to that of formula 12. With p-hydroxybenzaldehyde (formula 16-N, purchased from Shanghai Aldrin) as a starting material, formula 16 is prepared through three-step reactions, i.e., reaction iii, reaction iv, and reaction i.

[0098] Formula 16-B is prepared by referring to the process of reaction iii in Embodiment 1, formula 16-C is prepared by referring to the process of reaction iv in Embodiment 1, and formula 16 is prepared by referring to the process of reaction i in Embodiment 1.

[0099] Embodiment 6: Preparation of branched silane coupling agent (formula 17).

[0100] The synthesis reaction formula of the branched silane coupling agent (formula 17) is as follows:

[0101]

[0102] The specific preparation method is similar to that of formula 12. With p-hydroxybenzaldehyde (formula 16-N, purchased from Shanghai Aldrin) as a starting material, formula 16 is prepared through three-step reactions, i.e., reaction iii, reaction iv, and reaction i.

[0103] Formula 17-B is prepared by referring to the process of reaction iii in Embodiment 1, formula 17-C is prepared by referring to the process of reaction iv in Embodiment 1, and formula 17 is prepared by referring to the process of reaction i in Embodiment 1.

[0104] Embodiment 7: Synthesis and modification of titanium dioxide

[0105] The present application takes the modification of titanium dioxide nanoparticles by silane coupling agent as the starting point, adopts the single variable principle, and evaluates the appearance, stability, and transmittance of the nanoparticle dispersion liquid modified by the silane coupling agents prepared in Embodiments 1-6 and commercially available straight-chain silane coupling agent (purchased from Shin-Etsu Group, model number HWG32260, structural formula as shown in formula 18) to judge the interface modification effect of the silane coupling agent.

[0106]

[0107] The specific experimental method is as follows:

[0108] According to the molar ratio of n-hexanoic acid to butyl titanate of 0.2-1 (preferably 0.5), a certain amount of butyl titanate and n-hexanoic acid are weighed and sequentially placed in a beaker, and are magnetically stirred for 1-10 min (preferably 5 min) to mix them uniformly. Then, the same mass of deionized water is slowly added, and the precursor mixture is magnetically stirred for 1-20 min (preferably 10 min) to mix uniformly to form a transparent sol.

[0109] The sol was transferred to a hydrothermal reactor with a Teflon inner liner. After sealing the reactor, it was placed in an electrically heated air oven and heated at 240°C for 3 hours to complete the solvothermal reaction. After the reactor was allowed to cool to room temperature, the suspension was removed and the precipitate was separated from the suspension using a centrifuge. The white precipitate was the nano-TiO2, which was washed three times with absolute ethanol to obtain a nano-TiO2 wet solid. The nano-TiO2 wet solid was diluted in ethanol at a concentration of 1 mg / ml to obtain an average particle size D50 of 23 nm. The nano-TiO2 wet solid was dissolved in propylene glycol methyl ether (PGME) to obtain a white suspension, which was transferred to a three-necked flask. The silane coupling agent prepared in Examples 1-6 and a commercially available silane coupling agent were added to the suspension in combination with KBM503 at 10% and 2%, respectively. The mixture was stirred in a constant temperature water bath at 70°C for 1 hour to obtain modified TiO2 dispersions in seven groups. The contents of the modified TiO2 dispersions in each group were as follows:

[0110] Group 1: The branched silane coupling agent (Formula 12) of Example 1 was selected, and the amount added was 10% of the weight of the TiO2 wet solid. The amount of KBM503 added was 2% of the weight of the TiO2 wet solid. Modified titanium dioxide dispersion I was obtained, and the solid content was 30%.

[0111] Group 2: The branched silane coupling agent (Formula 13) of Example 2 was selected, and the amount added was 10% of the weight of the TiO2 wet solid. The amount of KBM503 added was 2% of the weight of the TiO2 wet solid. Modified titanium dioxide dispersion II was obtained, and the solid content was 30%.

[0112] Group 3: The branched silane coupling agent (Formula 14) of Example 3 was selected, and the amount added was 10% of the weight of the TiO2 wet solid. The amount of KBM503 added was 2% of the weight of the TiO2 wet solid. Modified titanium dioxide dispersion III was obtained, and the solid content was 30%.

[0113] Group 4: The branched silane coupling agent (Formula 15) of Example 4 was selected, and the amount added was 10% of the weight of the TiO2 wet solid. The amount of KBM503 added was 2% of the weight of the TiO2 wet solid. Modified titanium dioxide dispersion IV was obtained, and the solid content was 30%.

[0114] Group 5: The branched silane coupling agent (Formula 16) of Example 5 was selected, and the amount added was 10% of the weight of the TiO2 wet solid. The amount of KBM503 added was 2% of the weight of the TiO2 wet solid. Modified titanium dioxide dispersion V was obtained, and the solid content was 30%.

[0115] Group 6: branched silane coupling agent (Formula 17) of Example 6 was selected, and the addition amount was 10% of the TiO2wet solid weight, and the addition amount of KBM503 was 2% of the TiO2wet solid weight, to obtain modified titanium dioxide dispersion VI with a solid content of 30%.

[0116] Group 7: a commercially available branched silane coupling agent (Formula 18) was selected, and the addition amount was 10% of the TiO2wet solid weight, and the addition amount of KBM503 was 2% of the TiO2wet solid weight, to obtain modified titanium dioxide dispersion VII with a solid content of 30%.

[0117] The optical performance verification method of the titanium dioxide dispersion is as follows: the titanium dioxide dispersion of Group 7 is combined with a photocuring resin (Sartomer SR351NS), a photoinitiator (IGM 184) and a stabilizer (IGM Omnistab IN 515) are added, and a high refractive index photocuring adhesive is prepared. Among them, the addition ratio of the titanium dioxide dispersion, the photocuring resin, the photoinitiator and the stabilizer is 8 parts, 10 parts, 1 part and 0.02 parts respectively by weight, a film is prepared by spin coating the adhesive on a clean glass, the film is cured by an LED lamp 365 nm light source, the refractive index of the film is tested by an ellipsometer, and the transmittance of the film is tested by an ultraviolet spectrophotometer. In addition, the titanium dioxide dispersion of Group 7 is placed for 1 week, and the particle size distribution is analyzed by dynamic light scattering, and the difference in particle size change before and after 1 week is counted to evaluate the stability of the modified nanomaterial. The performance test results of the high refractive index adhesives of the 7 groups are shown in Table 1.

[0118] Table 1 Performance test results of the high refractive index adhesives of the 7 groups

[0119]

[0120]

[0121] As shown in the results of Table 1, after the TiO2was modified by silane coupling agents with different structures, the refractive index and film thickness of the obtained TiO2dispersion had little difference, being 1.91 and 500 nm respectively. This indicates that the silane coupling agent has little effect on the refractive index and thickness of the nanoparticles, but has a greater effect on the transmittance. It can be seen that, compared with the existing straight-chain silane coupling agent modification effect (Group 7), the branched silane coupling agent can obtain the same or even better modification effect of the nanoparticles. Among them, the modified TiO2dispersion obtained by using the silane coupling agents prepared in Examples 1 and 2 has the highest transmittance of 93%, indicating that the silane coupling agents of Examples 1 and 2 have the best effect when used for nanoparticle modification. At the same time, by comparing the average particle size change value of the TiO2dispersion of Group 7 after 1 week, it can be seen that the nanoparticles in the dispersions of Groups 3 to 7 obviously agglomerate and settle, indicating that the TiO2nanoparticle dispersion modified by the silane coupling agents of Formula 12 and Formula 13 has better stability and better effect.

[0122] Comparing the film permeability of the first, third, and fourth groups, it can be found that the permeability of the TiO2 dispersion liquid modified by the silane coupling agent prepared in Examples 3 and 4 is significantly lower than that of Example 1, both lower than 90%, which cannot meet the use requirements. At the same time, comparing the particle size change values of the four groups of TiO2 dispersion liquids after one week, it can be found that the particle size of the TiO2 dispersion liquids of the third and fourth groups increases significantly, and the stability is poor. By analyzing the structural differences of the silane coupling agents of the four groups, it is speculated that the reason for the significant difference in the dispersibility of the TiO2 dispersion liquid is that in the molecular structure of the silane coupling agent of Example 1, the long flexible chain polyethoxy ether is used as the anchor group on the benzene ring of R2-R4, which is different from the acrylate group used in Example 3 and the vinyl ether used in Example 4. The three long flexible chain polyethoxy ethers provided by Example 1 can better wrap the modified TiO2 nanoparticles, so that the modified TiO2 nanoparticles are combined with the organic polymer matrix through the polyethoxy ether, and a better dispersion effect is achieved. In contrast, the structure chain of the acrylate group and the vinyl ether is shorter, so it cannot effectively wrap the nanoparticles, resulting in poor interfacial compatibility between the nanoparticles and the organic matrix, and poor dispersibility. Therefore, the polyethoxy ether is preferred for the organic functional groups on the benzene ring of R2-R4 in the silane coupling agent.

[0123] Comparing the permeability test results of the first, fifth and sixth groups, it can be seen that the number and position of the organic functional groups on the benzene ring of the silane coupling agent significantly affect the dispersibility and stability of the modified TiO2 dispersion liquid. When the substituent on the benzene ring only contains one polyethoxy ether (Example 5), the permeability of the modified TiO2 dispersion liquid is only slightly higher than that of the commercially available linear silane coupling agent, which is 82%, which does not meet the use requirements (≥90%); when the substituent on the benzene ring occupies positions 2 and 5 (Example 6), the prepared silane coupling agent is used to modify TiO2 nanoparticles, and the obtained dispersion liquid has a permeability of only 70%, which is not as good as Example 1. The reason is that the number of organic functional groups on the benzene ring determines the similarity between the organic matrix, theoretically, the more the number of organic functional groups, the better the similarity between the nanoparticles and the organic matrix, and according to the principle of similarity, the better the compatibility, but when the polyethoxy ether on the benzene ring is close to the siloxane substituent, the steric hindrance formed by the long chain will hinder the condensation reaction between the surface hydroxyl group of the nanoparticle and the silanol group, thereby reducing the modification effect, and the permeability is even less than that of the single-substituted silane coupling agent. Therefore, the number of polyethoxy ethers on the benzene ring is preferably three, and the position is preferably 3, 4, and 5 (i.e., R2-R4).

[0124] In addition, the branched silane coupling agent prepared by taking carbon atom, nitrogen atom and cyclohexyl as the branched core respectively is compared with the branched silane coupling agent of Example 1 in terms of the effect on TiO2 nanoparticle modification. It is found that the nanoparticle modified by the branched silane coupling agent provided in Example 1 has better dispersion stability. In addition, it is also found that the method for preparing the branched silane coupling agent by using benzene ring is more simple, time-saving and cost-saving, and has higher efficiency. In summary, the nanoparticle material modified by the branched silane coupling agent provided in Example 1 has excellent light transmittance, and is expected to be applied to the optical field such as diffraction optical waveguide and high refractive index lens preparation.

[0125] Although the present application is disclosed as above, the present application is not limited to this. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application, and the protection scope of the present application is limited by the scope defined by the claims.

Claims

1. A branched silane coupling agent, characterized in that: It has any one of the general structural formulas shown in Formula 1 to Formula 4: Among them, A1 is methylene or ethylene, A2 is a carbon chain or oxygen-carbon chain of 1-10 carbon atoms, R is any one of methyl, ethyl, and propyl, and R1-R5 are any one or more of hydrogen atom, alkoxy, polyethoxy ether, acrylate, and vinyl ether.

2. The branched silane coupling agent according to claim 1, wherein The R1 and R5 are hydrogen atoms, and the R2, R3, and R4 are any one or more of alkoxy, polyethoxy ether, acrylate, and vinyl ether.

3. The branched silane coupling agent according to claim 2, wherein The polyethoxy ether has a general structural formula as shown in Formula 5, the acrylate group has a general structural formula as shown in Formula 6, and the vinyl ether has a general structural formula as shown in Formula 7: Wherein N is an integer greater than 0, and A3 is a methyl group or a hydrogen atom.

4. The branched silane coupling agent according to claim 3, wherein It has a structural formula as shown in Formula 8 or Formula 9:

5. A method for preparing a branched silane coupling agent, characterized in that: Prepared by the chemical formula shown in Formula 10 or Formula 11:

6. The preparation method according to claim 5, wherein When the general chemical formula shown in Formula 10 is used for preparation, the following steps are included: S1: Mix the benzyl chloride derivative with magnesium powder and ether, and add iodine under nitrogen protection to fully react; S2: After the reaction, cool to -5-10°C and add chlorosiloxane for reaction; S3: Filter to remove impurities, perform vacuum distillation, and separate and purify to obtain the target product.

7. The preparation method according to claim 5, wherein When prepared using the general chemical formula shown in Formula 11, The following steps are involved: S1: Stirring the styrene derivative, trialkoxysilane, catalyst and solvent under nitrogen; S2: Filter to remove impurities, perform vacuum distillation, and separate and purify to obtain the target product.

8. Use of a branched silane coupling agent for surface modification of nanoparticles or surface treatment of inorganic materials, characterized in that: The branched silane coupling agent has any one of the general structural formulas shown in Formula 1 to Formula 4: Among them, A1 is methylene or ethylene, A2 is a carbon chain or oxygen-carbon chain of 1-10 carbon atoms, R is any one of methyl, ethyl, and propyl, and R1-R5 are any one or more of hydrogen atom, alkoxy, polyethoxy ether, acrylate, and vinyl ether.

9. The use according to claim 8, characterized in that When the branched silane coupling agent is used for surface modification of nanoparticles, R is a methyl group; when the branched silane coupling agent is used for surface treatment of inorganic materials, R is an ethyl group.

10. The use according to claim 9, characterized in that The R1 and R5 are hydrogen atoms, and the R2, R3, and R4 are any one or more of alkoxy, polyethoxy ether, acrylate, and vinyl ether.

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