High-refractive-index light-cured resin and preparation method thereof

Abstract

The invention provides high-refractive-index light-cured resin and a preparation method thereof. An intramolecular structure of the light-cured resin comprises a flexible block, a rigid block and an active block. The flexible block is realized by introducing a high-refractive-index dithioether derivative, the rigid block is realized by introducing an arylethene derivative, and the active block introduces a photocuring active group through a hydroxyl derivative. The light-cured resin provided by the invention is prepared through two-step reaction, the refractive index can reach 1.7 or above, and the light-cured resin has relatively high mechanical strength and good flexibility, and can be used for manufacturing products such as high-refractive-index optical cement, high-refractive-index nanoimprint adhesive, high-refractive-index adhesive, high-refractive-index lens, high-refractive-index ink and the like.

Description

Technical Field

[0001] The invention belongs to the field of optical technology and light-curing glue, and particularly relates to a high-refractive-index light-curing resin and a preparation method thereof. Background Art

[0002] In the fields of optoelectronic display and precision optical manufacturing, high-refractive-index photocurable materials serve as key media for packaging, nanoimprinting, and lens bonding, and their performance directly determines the optical quality and reliability of devices. In advanced display technologies, new display devices such as Mini-LED and Micro-LED have increasingly stringent requirements for the refractive index of packaging materials. High-refractive-index packaging materials can effectively reduce light reflection losses at interfaces, improving light extraction efficiency and display contrast. Nanoimprinting technology is a core process for preparing micro-nano optical structures. The performance of high-refractive-index nanoimprint adhesives directly affects the optical performance of micro-nano structures, and is related to the manufacturing level of precision optical devices such as diffractive optical elements and microlens arrays. In the assembly of precision optical lenses, high-refractive-index lens adhesives must not only ensure a secure connection between optical components, but also maintain the stability of light transmission and reduce aberrations and light loss caused by refractive index mismatch.

[0003] In the field of photocurable adhesives, there are three approaches to increasing the refractive index: introducing high-refractive-index monomers, introducing high-refractive-index photocurable resins, and introducing high-refractive-index inorganic nanomaterials. While introducing high-refractive-index inorganic nanomaterials can significantly increase the refractive index, it also significantly increases the cost of the adhesive. Furthermore, due to the self-condensation of inorganic nanoparticles, the shelf life of the adhesive is shorter than that of purely organic systems, limiting its application. Introducing high-refractive-index monomers can also increase the refractive index of the adhesive, but most commercially available high-refractive-index monomers are monofunctional. From the perspective of adhesive formulation design, a high proportion of monofunctional monomers in the formulation will lead to a low cure rate and insufficient mechanical strength. This is because the greater the weight proportion of active groups in the molecule, the greater the loss in refractive index. Therefore, a certain amount of photocurable resin is essential in the formulation. Photocurable resins can adjust the viscosity and cure shrinkage of the formulation, as well as ensure a high crosslink density during the curing process, thereby maintaining a high level of mechanical strength. However, existing photocurable resins generally suffer from low refractive index, poor flexibility, and poor strength, limiting their practical application.

[0004] Therefore, improving the refractive index, flexibility and mechanical strength of photocurable resins is of great significance to promoting the application of high-refractive-index photocurable resins in the fields of optical technology and photocurable adhesives. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a high-refractive index photocurable resin and a preparation method thereof. The high-refractive index photocurable resin uses aromatic vinyl compounds and vinyl sulfide as main raw materials. First, the flexibility, strength, refractive index and functional number of the target photocurable resin are controlled by free radical polymerization reaction to obtain an oligomer with hydroxyl functional groups. Secondly, the oligomer is given photocuring activity through an acyl chloride reaction to obtain a photocurable resin with a refractive index higher than 1.7. At the same time, the flexibility and mechanical strength of the photocurable resin are also improved.

[0006] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0007] In one aspect, the present invention provides a high refractive index photocurable resin having a general structural formula as shown in Formula 1:

[0008] Wherein R1 is an aromatic group, R2 is a sulfur-containing alkyl group, R3 is an aromatic group or an alkyl group, and R4 is a photocurable active functional group.

[0009] In order to solve the problems of low refractive index and insufficient mechanical strength of existing photocurable resins, the present invention provides a high-refractive-index photocurable resin, whose molecular structure contains a flexible block (R2), a rigid block (R1) and an active block (R3). High-refractive-index ethylene disulfide derivatives are introduced into the flexible block, aromatic vinyl derivatives are introduced into the rigid block, and photocurable active groups (R4) are introduced into the active block via hydroxyl derivatives. This can achieve the adjustment of the flexibility, strength and refractive index of the photocurable resin. The obtained photocurable resin has both rigidity and flexibility, and the refractive index can reach above 1.7.

[0010] Furthermore, the R1 is selected from any one or more of the following formulas 2 to 6:

[0011]

[0012] Furthermore, the R2 is selected from any one or more of the following formulas 7 to 9:

[0013]

[0014] Furthermore, the R4 is selected from any one or more of the following formulas 10 to 11:

[0015]

[0016] Furthermore, the R4 is selected from any one or more of the following formulas 12 to 14:

[0017]

[0018] The introduction of high-refractive-index monomers can increase the refractive index of photocurable glue, but most of the high-refractive-index monomers on the market are monofunctional monomers. Since the greater the weight proportion of the active groups in the molecule, the greater the loss of refractive index, therefore, if the proportion of monofunctional monomers in the glue formula is too high, it will lead to a lower curing rate and insufficient mechanical strength. Therefore, it is necessary to introduce a certain amount of photocurable resin into the formula. Photocurable resin can not only adjust the viscosity of the formula and the curing shrinkage rate, but also ensure a higher cross-linking density during the curing process of the glue, thereby maintaining a higher level of mechanical strength. In some embodiments, the present invention compares the performance of photocurable resins with different molecular structures, as well as the comprehensive performance of photocurable glues prepared from the resins, including aspects such as refractive index, elongation, and mechanical strength. The results show that the specific structures of R1, R2, and R3 contained in the structure of the photocurable resin have a significant impact on the performance of the resin and glue. It is preferred that the photocurable resin and glue are prepared with a rigid monomer containing a structure of formula 5, a flexible monomer containing a structure of formula 7, and an active monomer containing a structure of formula 10 as raw materials. Photocurable resins with a refractive index greater than 1.7 and photocurable glues with a refractive index of 1.69 can be prepared, and mechanical strength and flexibility can be balanced.

[0019] In addition, because the key to the preparation of high-refractive index resins lies in the introduction of high-polarizability groups, the introduction of advanced polarizability groups such as aromatic groups and sulfur atoms can greatly improve the refractive index of the resin. The greater the weight ratio of the advanced polarizability groups, the more effective the improvement of the refractive index. However, the rigid monomers containing aromatic groups mainly provide mechanical strength for the resin, and the flexible monomers with sulfur-containing groups mainly provide flexibility for the resin. If the proportion of rigid monomers is too high, the prepared resin may be too rigid and prone to brittle cracking; if the proportion of flexible monomers is too large, the refractive index and mechanical strength of the prepared resin cannot meet the requirements. Therefore, it is necessary to balance the proportion of rigid monomers and active monomers in the raw materials. The present invention has proved through experimental exploration that when the ratio of the amount of rigid monomers, flexible monomers, and active monomers in the raw materials is controlled at 10:5:1, that is, when m:n:l=10:5:1 in the chemical formula, the obtained resin has the best comprehensive performance and the highest refractive index.

[0020] In some embodiments, m, n, and l are integers, preferably, m:n:l=10:5:1.

[0021] Experimental results show that the performance of the high-refractive-index photocurable resin of Formula 1 is only affected by the specific structure and proportion of R1, R2, and R3, and will not change due to changes in the order of R1, R2, and R3.

[0022] Furthermore, the structural formula of the high refractive index photocurable resin is shown in any one or more of Formula 15 to Formula 16:

[0023]

[0024] The high-refractive-index photocurable resin provided by the present invention has a refractive index of 1.65 or above, and its application scenarios include but are not limited to optical adhesives, nanoimprint adhesives, lens adhesives, light-emitting device packaging adhesives, brightness enhancement films, lenses, diffraction light waveguides, microlens production, etc.

[0025] In another aspect, the present invention provides a method for preparing a high refractive index photocurable resin, which is prepared by the following general chemical formula:

[0026]

[0027] Among them, R1 is an aromatic group, R2 is a sulfur-containing alkyl group, R3 is an aromatic group or an alkyl group, and R4 is a photocurable active functional group.

[0028] Furthermore, the Cl-R4 is one of acryloyl chloride, methacryloyl chloride, and epichlorohydrin.

[0029] Furthermore, the

[0030] It is prepared by the following chemical formula:

[0031]

[0032] Furthermore, the free radical initiator includes any one of cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl hydroperoxide, azobisisobutyronitrile, and azobisisoheptanenitrile.

[0033] In some embodiments, the present invention demonstrates through comparative experiments that preferably using azobisisobutyronitrile as a free radical initiator can effectively control the progress of the polymerization reaction, so that the molecular weight of the photocurable resin is maintained in a suitable range of 1000-3000.

[0034] Furthermore, the method comprises the following steps:

[0035] S1: dissolving the aromatic vinyl compound and vinyl sulfide raw materials in dimethylformamide, and adding azobisisobutyronitrile as a free radical initiator to fully react;

[0036] S2: After the reaction is terminated, the solvent is removed, eluted, and impurities are removed to obtain oligomers;

[0037] S3: dissolving the oligomer in dichloromethane, adding triethylamine dropwise, and then adding acryloyl chloride or methacryloyl chloride or epichlorohydrin dropwise and stirring. After the reaction is terminated, extracting, drying, and evaporating to remove the solvent to obtain a high refractive index photocurable resin.

[0038] In some embodiments, the method comprises:

[0039] The first step of the reaction is to dissolve the starting raw materials (weighed according to the ratio of rigid monomer: flexible monomer: active monomer of 10:5:1) in dimethylformamide to prepare a 10% mass fraction solution; then add a free radical initiator, the mass of which is 5% of the total mass of the monomers; the preferred reaction temperature is 70 degrees, the preferred reaction time is 2 hours, and a small amount of benzenethiophenol methanol solution is added to terminate the reaction.

[0040] The first step of post-reaction treatment process: After the reaction is terminated, all solvents are removed under reduced pressure, the crude product is sealed in a semipermeable membrane, and methanol and ethyl acetate are used to elute the crude product in sequence to remove small molecular weight impurities, such as unreacted monomers, initiators and chain terminators, to obtain a high refractive index oligomer M1 with a hydroxyl group.

[0041] The second step is to impart photocuring activity to the oligomer through a hydroxyl reaction: first, oligomer M1 is completely dissolved in dichloromethane, and then triethylamine is added dropwise, controlling the molar amount of triethylamine to be 1.5 times the molar amount of 4-methylstyrene. The reaction system is then cooled in an ice bath and stirred at 300 rpm. Acryloyl chloride is slowly added dropwise, controlling the molar amount of acryloyl chloride to be 1.1 times the molar amount of 4-methylstyrene. After the addition is completed, the reaction system is naturally warmed to room temperature and stirred for 5 hours. After the reaction is completed, a small amount of water is first added to terminate the reaction. The reaction solution is then extracted with saline, and all organic phases are collected and dried over anhydrous sodium sulfate. After drying, the sodium sulfate is first removed by filtration, and then all solvents are removed using a rotary evaporator to obtain the target photocurable resin.

[0042] In another aspect, the present invention provides a high-refractive index photocurable glue, which is prepared from raw materials including a high-refractive index photocurable resin, wherein the high-refractive index photocurable resin is as shown above, or is prepared using the method as described above.

[0043] Furthermore, the raw materials also include an initiator, a diluent and a cross-linking agent.

[0044] In some embodiments, the initiator is selected from any one of IGM-TPO, IGM-184, and IGM-1173.

[0045] In some embodiments, the diluent is selected from any one of OPPEA, PHEA, IBOMA, ACMO, THMA, and DCPA.

[0046] In some embodiments, the crosslinking agent is selected from any one of trimethylolpropane triacrylate (SR-351NS), pentaerythritol triacrylate (SR-444NS), dipropylene glycol diacrylate (SR 508NS), and dipropylene glycol diacrylate (SR508NS).

[0047] In some embodiments, the raw material includes, by percentage, 80% high refractive index photocurable resin, 1% initiator, 10% diluent and 9% crosslinking agent.

[0048] In some embodiments, the light-curing adhesive is obtained by light curing under the following conditions: LED 365nm light source, 100mW / cm 2 , 15s.

[0049] In another aspect, the present invention provides a use of a high-refractive index photocurable resin for preparing an agent for improving the refractive index, mechanical strength, and flexibility of a high-refractive index photocurable glue, wherein the high-refractive index photocurable resin has a general structural formula as shown in Formula 1:

[0050] Wherein R1 is an aromatic group, R2 is a sulfur-containing alkyl group, R3 is an aromatic group or an alkyl group, and R4 is a photocurable active functional group.

[0051] The present invention has the following beneficial effects:

[0052] 1. The present invention uses high-refractive-index ethylene disulfide derivatives and vinyl aromatic compounds as the main starting materials, and simultaneously introduces active monomers and photocurable active functional groups to prepare a high-refractive-index photocurable resin with a refractive index of more than 1.7, while also achieving a balance between the mechanical strength and flexibility of the photocurable resin.

[0053] 2. By optimizing the proportions of rigid monomers, flexible monomers, and active monomers, the preferred molar ratio of rigid monomers, flexible monomers, and active monomers is 10:5:1. The resulting photocurable resin has high refractive index and mechanical strength, good flexibility, and significantly improved overall performance of the photocurable resin.

[0054] 3. By optimizing the monomer concentration, free radical initiator concentration, reaction time and temperature in the raw materials, the molecular weight of the photocurable resin reaches an appropriate range (1000-3000) and has a narrow molecular weight distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is the refractive index test result of the photocurable resin P1.

[0056] Figure 2 The refractive index test results of the photocurable glue prepared from the photocurable resin P1.

[0057] Figure 3 This is a scanning electron microscope image of the imprinted nanoscale ruler grating of the photocurable glue prepared from the photocurable resin P1. DETAILED DESCRIPTION

[0058] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be noted that the following examples are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0059] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0060] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0061] Example 1: Preparation of high refractive index photocurable resin (Formula 15)

[0062] The synthesis reaction formula of the high refractive index photocurable resin (Formula 15) is as follows:

[0063]

[0064] The specific preparation method is:

[0065] (1) First step reaction: The starting raw materials 2-vinylanthracene (purchased from Alfa), bis(2-(vinylthio)ethyl)sulfane, and 4-methylstyrene (purchased from Alfa) were dissolved in dimethylformamide at a molar ratio of 10:5:1 to prepare a 10% mass fraction solution; then a free radical initiator azobisisobutyronitrile (purchased from Alfa) was added, the mass of which was 5% of the total mass of the raw materials, the reaction temperature was 70°C, the reaction time was 2 h, and a small amount of benzenethiophenol methanol solution was added to terminate the reaction.

[0066] The synthesis method of bis(2-(vinylthio)ethyl)sulfane is as follows:

[0067] Bis(2-(vinylthio)ethyl)sulfide (purchased from Anaiji, 1 equ.) was dissolved in a 20% by mass solution of sodium ethoxide (1 equ.) in ethanol. The system was then cooled to 0°C. 1-bromoethylene (purchased from Alfa, 2.1 equ.) was added dropwise under this condition. The temperature was then returned to room temperature, and a solution of sodium ethoxide (5 equ.) in ethanol was added. The temperature was raised to 70°C and the reaction was allowed to proceed for 16 hours. The reaction was then quenched with aqueous sodium bicarbonate solution, extracted with dichloromethane and saturated brine, and the organic phase was collected, dried over anhydrous sodium sulfate, filtered, and the solvent removed. The main fraction, bis(2-(vinylthio)ethyl)sulfane, was collected by distillation under reduced pressure in an 85% yield.

[0068] (2) Post-reaction treatment process of the first step: After the reaction is terminated, all solvents are removed under reduced pressure, and the crude product is sealed in a semipermeable membrane. Methanol and ethyl acetate are used to elute the crude product in sequence to remove small molecular weight impurities, such as unreacted monomers, initiators and chain terminators, to obtain a high refractive index oligomer M1 with a hydroxyl group.

[0069] (3) Second step reaction: The oligomer M1 is completely dissolved in dichloromethane, and then triethylamine is added dropwise, with the molar amount of triethylamine controlled to be 1.5 times the molar amount of 4-methylstyrene. The reaction system is then cooled in an ice bath and stirred at 300 rpm. Acryloyl chloride is slowly added dropwise, with the molar amount of acryloyl chloride controlled to be 1.1 times the molar amount of 4-methylstyrene. After the addition is completed, the reaction system is naturally warmed to room temperature and stirred for 5 hours. After the reaction is completed, a small amount of water is first added to terminate the reaction. The reaction solution is then extracted with saline, and all organic phases are collected and dried over anhydrous sodium sulfate. After drying, the sodium sulfate is first removed by filtration, and then all solvents are removed using a rotary evaporator to obtain the target photocurable resin P1, whose structural formula is shown in Formula 15.

[0070]

[0071] Example 2: Preparation of high refractive index photocurable resin (Formula 16)

[0072] The synthesis reaction formula of the high refractive index photocurable resin (Formula 16) is as follows:

[0073]

[0074] The specific preparation method is:

[0075] (1) First step reaction: The starting raw materials N-vinylcarbazole (purchased from Alfa), bis(2-(vinylthio)ethyl)sulfane (synthesized in the same manner as in Example 1), and 4-methylstyrene were dissolved in dimethylformamide at a molar ratio of 10:5:1 to prepare a 10% mass fraction solution; then, a free radical initiator azobisisobutyronitrile was added at a mass ratio of 5% of the total mass of the raw materials, the reaction temperature was 70°C, the reaction time was 2 h, and a small amount of benzenethiophenol methanol solution was added to terminate the reaction.

[0076] (2) The post-treatment process of the first step reaction and the second step reaction are the same as those in Example 1. After removing all the solvents, the target photocurable resin P2 can be obtained, and its structural formula is shown in Formula 16.

[0077]

[0078] Example 3: Preparation of high refractive index photocurable resin (Formula 17)

[0079] The synthesis reaction formula of the high refractive index photocurable resin (Formula 17) is as follows:

[0080]

[0081] The specific preparation method is:

[0082] (1) First step reaction: The starting raw materials 4-vinylbiphenyl (purchased from Alfa), bis(2-(vinylthio)ethyl)sulfane (synthesized in the same manner as in Example 1), and 4-methylstyrene were dissolved in dimethylformamide at a molar ratio of 10:5:1 to prepare a 10% mass fraction solution; then, a free radical initiator azobisisobutyronitrile was added at a mass ratio of 5% of the total mass of the raw materials, the reaction temperature was 70°C, the reaction time was 2 h, and a small amount of benzenethiophenol methanol solution was added to terminate the reaction.

[0083] (2) The post-treatment process of the first step reaction and the second step reaction are the same as those in Example 1. After removing all the solvents, the target photocurable resin P3 can be obtained, and its structural formula is shown in Formula 17.

[0084]

[0085] Example 4: Preparation of high refractive index photocurable resin (Formula 18)

[0086] The synthesis reaction formula of the high refractive index photocurable resin (Formula 18) is as follows:

[0087]

[0088] The specific preparation method is:

[0089] (1) First step reaction: The starting raw materials N-vinylcarbazole, 1,2-bis(vinylthio)ethane, and 4-methylstyrene were dissolved in dimethylformamide at a molar ratio of 10:5:1 to prepare a 10% mass fraction solution; then, a free radical initiator azobisisobutyronitrile was added, the mass of which was 5% of the total mass of the raw materials. The reaction temperature was 70°C, the reaction time was 2 h, and a small amount of benzenethiophenol methanol solution was added to terminate the reaction.

[0090] The synthesis method of 1,2-bis(vinylthio)ethane is as follows:

[0091] Ethanedithiol (purchased from Anaiji, 1 equ.) was dissolved in a 20% mass fraction of sodium ethoxide (1 equ.) in ethanol. The system was then cooled to 0 degrees. Under this condition, 1-bromoethylene (purchased from Alfa, 2.1 equ.) was added dropwise. After returning to room temperature, an ethanol solution of sodium ethoxide (5 equ) was added. The temperature was raised to 70 degrees and the reaction was completed after 16 hours. The reaction was then quenched with sodium bicarbonate aqueous solution, extracted with dichloromethane and saturated brine, and all organic phases were collected, dried over anhydrous sodium sulfate, filtered and the solvent removed, and the main fraction was collected by vacuum distillation, which was the target product 1,2-bis(vinylthio)ethane with a yield of 90%.

[0092] (2) The post-treatment process of the first step reaction and the second step reaction are the same as those in Example 1. After removing all the solvents, the target photocurable resin P4 can be obtained, and its structural formula is shown in Formula 18.

[0093]

[0094] Example 5: Preparation of high refractive index photocurable resin (Formula 19)

[0095] The synthesis reaction formula of the high refractive index photocurable resin (Formula 19) is as follows:

[0096]

[0097] The specific preparation method is:

[0098] (1) First step reaction: First, the starting raw materials 2-vinylanthracene, 1,2-bis(vinylthio)ethane (synthesized in the same manner as in Example 4), and 4-methylstyrene were dissolved in dimethylformamide at a molar ratio of 10:5:1 to prepare a 10% mass fraction solution; then, a free radical initiator azobisisobutyronitrile was added, the mass of which was 5% of the total mass of the raw materials, the reaction temperature was 70°C, the reaction time was 2 h, and a small amount of benzenethiophenol methanol solution was added to terminate the reaction.

[0099] (2) The post-treatment process of the first step reaction and the second step reaction are the same as those in Example 1. After removing all the solvents, the target photocurable resin P5 can be obtained, and its structural formula is shown in Formula 19.

[0100]

[0101] Example 6: Preparation of high refractive index photocurable resin (Formula 20)

[0102] The synthesis reaction formula of the high refractive index photocurable resin (Formula 20) is as follows:

[0103]

[0104] The specific preparation method is:

[0105] (1) First step reaction: First, the starting raw materials 2-vinylanthracene, bis(2-(vinylthio)ethyl)sulfane (synthesized in the same manner as in Example 1), and 4-hydroxystyrene (purchased from Alfa) were dissolved in dimethylformamide at a molar ratio of 10:5:1 to prepare a 10% mass fraction solution; then, a free radical initiator azobisisobutyronitrile was added, the mass of which was 5% of the total mass of the raw materials, the reaction temperature was 70°C, the reaction time was 2 h, and a small amount of benzenethiophenol methanol solution was added to terminate the reaction.

[0106] (2) The post-treatment process of the first step reaction and the second step reaction are the same as those in Example 1. After removing all the solvents, the target photocurable resin P6 can be obtained, and its structural formula is shown in Formula 20.

[0107]

[0108] Example 7: Preparation of high refractive index photocurable resin (Formula 21)

[0109] The synthesis method of the high refractive index photocurable resin (Formula 21) is basically the same as that of Example 1, except that in the first step, the starting raw materials 2-vinylanthracene, bis(2-(vinylthio)ethyl)sulfane, and 4-methylstyrene are dissolved in dimethylformamide in a molar ratio of 15:5:1 to form a 10% mass fraction solution; then, a free radical initiator azobisisobutyronitrile is added, the mass of which is 5% of the total mass of the raw materials, the reaction temperature is 70°C, the reaction time is 2 h, and a small amount of benzenethiophenol methanol solution is added to terminate the reaction.

[0110] The post-treatment process of the first step reaction and the second step reaction are the same as those in Example 1. After removing all the solvents, the target photocurable resin P7 can be obtained, and its structural formula is shown in Formula 21.

[0111]

[0112] Example 8: Preparation of high refractive index photocurable resin (Formula 22)

[0113] The synthesis method of the high refractive index photocurable resin (Formula 22) is basically the same as that of Example 1, except that in the first step, the starting raw materials 2-vinylanthracene, bis(2-(vinylthio)ethyl)sulfane, and 4-methylstyrene are dissolved in dimethylformamide in a molar ratio of 20:4:1 to prepare a 10% mass fraction solution; then, a free radical initiator azobisisobutyronitrile is added, the mass of which is 5% of the total mass of the raw materials, the reaction temperature is 70°C, the reaction time is 2 h, and a small amount of benzenethiophenol methanol solution is added to terminate the reaction.

[0114] The post-treatment process of the first step reaction and the second step reaction are the same as those in Example 1. After removing all the solvents, the target photocurable resin P8 can be obtained, and its structural formula is shown in Formula 22.

[0115]

[0116] Example 9: Preparation of high refractive index photocurable resin (Formula 23)

[0117] The synthesis method of the high refractive index photocurable resin (Formula 23) is basically the same as that of Example 1, except that in the first step, the starting raw materials 2-vinylanthracene, bis(2-(vinylthio)ethyl)sulfane, and 4-methylstyrene are dissolved in dimethylformamide in a molar ratio of 5:5:1 to form a 10% mass fraction solution; then, a free radical initiator azobisisobutyronitrile is added, the mass of which is 5% of the total mass of the raw materials, the reaction temperature is 70°C, the reaction time is 2 h, and a small amount of benzenethiophenol methanol solution is added to terminate the reaction.

[0118] The post-treatment process of the first step reaction and the second step reaction are the same as those in Example 1. After removing all the solvents, the target photocurable resin P9 can be obtained, and its structural formula is shown in Formula 23.

[0119]

[0120] Example 10: Preparation of photocurable resin (P10)

[0121] The preparation of light-curing resin P10 uses commercially available high-refractive index monomers as raw materials. The specific preparation method is as follows:

[0122] (1) First step reaction: The starting raw materials, biphenyl acrylate (BPMA, purchased from Meiyuan), bis(2-(vinylthio)ethyl)sulfane (synthesized in the same manner as in Example 1), and 4-methylstyrene were dissolved in dimethylformamide at a molar ratio of 10:5:1 to prepare a 10% mass fraction solution; then, a free radical initiator, azobisisobutyronitrile, was added at a mass ratio of 5% of the total mass of the raw materials. The reaction temperature was 70°C, the reaction time was 2 h, and a small amount of benzenethiophenol methanol solution was added to terminate the reaction.

[0123] (2) The post-treatment process of the first step reaction and the second step reaction are the same as those in Example 1. After removing all the solvents, the target photocurable resin P10 can be obtained.

[0124] Example 11: Performance test of high refractive index photocurable resin

[0125] The key to the preparation of high-refractive index photocurable resins lies in the introduction of high polarizability groups. The introduction of advanced polarizability groups such as aromatic groups and sulfur atoms can greatly increase the refractive index of the resin. The greater the weight proportion of the advanced polarizability groups, the more effective the improvement in the refractive index, but it will also reduce the flexibility of the resin, resulting in an increase in the viscosity of the resin. Therefore, this example examines the performance differences of the photocurable resins prepared from different types of raw materials or different raw material ratios in Examples 1-10. The performance tests include refractive index test, viscosity test, Young's modulus test, imprint performance test and curing activity test. The specific test methods are as follows:

[0126] (1) Refractive index test: Use Abbe refractometer to test the refractive index of the resin, and select the refractive index at 589nm light source.

[0127] (2) Viscosity test: Use a viscometer to test the viscosity of the resin, and test at a controlled temperature of 25 degrees.

[0128] (3) Young's modulus test: The photocurable resins of Examples 1-9 were poured into dumbbell-shaped resin molds respectively, and irradiated with a 395 nm LED light source of 100 mJ / cm 2 , 30s, and after complete curing, the dumbbell-shaped resin strip was taken out and tested in the dynamic thermomechanical analysis (DMA) tensile mode to characterize the Young's modulus of the material.

[0129] (4) Elongation test: The photocurable composition of the embodiment was poured into a dumbbell-shaped resin mold and irradiated with a 395 nm LED light source of 100 mW / cm 2 , 30s, after complete curing, take out the dumbbell-shaped resin strip and use a tensile testing machine to test the elongation of the material.

[0130] (5) Curing activity test: By fixing the light intensity and time, the curing activity of the glue is evaluated based on the touch surface dryness as the standard.

[0131] The test results of refractive index, viscosity, Young's modulus, elongation and curing activity are shown in Table 1. The test results of refractive index of the photocurable resin P1 prepared in Example 1 are shown in Table 1. Figure 1 shown.

[0132] Table 1 Performance test results of different light-curing resins

[0133]

[0134]

[0135] After a large number of experimental verifications, it was found that the higher the mechanical strength of a photocurable resin with a high refractive index, the better. However, it is only when its elongation is between 5-10% that it has good flexibility, achieving a balance between mechanical strength and flexibility. According to the results in Table 1, it can be found that compared with the resin (P10) prepared with aromatic acrylate compounds as raw materials, the refractive index of the resins (P1-P9) prepared with aromatic vinyl compounds is significantly higher, and the mechanical strength is also improved to a certain extent, indicating that the introduction of monomers with a higher refractive index into the preparation raw materials can significantly improve the refractive index of the resin. However, by comparing the performance of P1-P6, it can be found that the specific structure of the rigid monomer, flexible monomer and active monomer in the molecular structure of the photocurable resin will also significantly affect the refractive index and comprehensive performance of the resin. The refractive index of the resin prepared by Example 1 after curing is the highest, reaching 1.72, and its mechanical strength is the highest, the flexibility is good, and a better balance state is achieved, with the best performance, followed by the photocurable resin P2 of Example 2.

[0136] Comparing the three resins P1-P3, it can be found that although the starting raw materials of the resins all use the same flexible monomer and reactive monomer, the refractive index of the resins prepared using the rigid monomers N-vinylcarbazole and 4-vinylbiphenyl (P2 and P3) is lower, and the Young's modulus of the P3 resin also decreases slightly. This shows that although 2-vinylanthracene, N-vinylcarbazole, and 4-vinylbiphenyl are all aromatic monomers with advanced groups, there are differences in the refractive index of the specific groups and the rigidity of the monomers. Therefore, there are certain differences in the refractive index and strength of the prepared resins. Based on the above results, it can be seen that in order to achieve the purpose of improving the refractive index of the photocurable resin while balancing the rigidity and flexibility of the resin, using 2-vinylanthracene, bis(2-(vinylthio)ethyl)sulfane, and 4-methylstyrene as the starting raw monomers for preparing the resin is a more preferable choice.

[0137] Comparing the test results of P1 and P4-P6, it can be seen that after replacing bis(2-(vinylthio)ethyl)sulfane or 4-methylphenyl styrene with other flexible monomers or reactive monomers as starting materials, the refractive index of the resulting resin decreases to below 1.7, and the Young's modulus and elongation decrease. This indicates that the molecular chains of 1,2-bis(vinylthio)ethane and 4-hydroxyphenyl styrene are not flexible enough and the refractive index of the material itself is low. Therefore, the refractive index and flexibility of the prepared resin are poor, and the strength of the resin is also insufficient. Therefore, the photocurable resin prepared in Example 1 is preferred.

[0138] The greater the weight proportion of higher-grade groups such as aromatic groups and sulfur atoms, the more effective the improvement in refractive index. Comparing the results of P1, P7-P9, it can be found that when the proportion of the rigid monomer 2-vinylanthracene in the starting material is increased (P7, P8), the refractive index of the resin after curing is significantly improved, the Young's modulus increases, but the elongation decreases, the viscosity increases, and the fluidity of the resin deteriorates. Among them, the overall performance of the photocurable resin P8 decreases more significantly; and when the addition ratio of 2-vinylanthracene is reduced (P9), the refractive index and Young's modulus of the resin after curing are significantly reduced. This shows that when the addition ratio of rigid monomers and flexible monomers in the starting material exceeds a certain ratio, although the refractive index of the resin can be increased, the obtained resin has too high stiffness, poor flexibility, and is prone to brittle cracking. When it is below a certain ratio, the refractive index and stiffness of the resin cannot meet the requirements. Therefore, only when the molar ratio of the rigid monomer, the flexible monomer and the active monomer is 10:5:1, that is, the group R1:R2:R3=10:5:1 (m:n:l=10:5:1), can the balance between strength and flexibility be achieved while increasing the refractive index of the resin.

[0139] Example 12: Screening and Optimization of Reaction Conditions

[0140] In the preparation process of photocurable resin, the first reaction is particularly critical, specifically involving the concentration of monomers and initiators, reaction time, and temperature. The monomer concentration and initiator concentration determine the molecular weight of the photocurable resin. The higher the monomer concentration, the larger the molecular weight of the photocurable resin, while the higher the initiator concentration, the smaller the molecular weight of the photocurable resin. The reaction temperature and reaction time also affect the molecular weight and molecular weight distribution of the photocurable resin. The number average molecular weight (Mn) of the photocurable resin needs to be maintained at 1000-3000. In order to obtain a suitable molecular weight (1000-3000) and a narrow molecular weight distribution, it is necessary to optimize the monomer concentration, reaction time, and temperature.

[0141] 1. Monomer concentration

[0142] This example employed a preparation method substantially identical to that of Example 1, wherein the monomer solution concentrations were controlled at 5%, 10%, and 20% by mass, respectively, to produce three types of photocurable resins. The number average molecular weight (Mn) and polydispersity index (PDI) of the resins were determined by gas chromatography. The results are shown in the table below.

[0143] Table 2 Test results of photocurable resins with different monomer concentrations

[0144] Monomer concentration Mn PDI 5% mass fraction 800 3.3 10% mass fraction 2200 1.5 20% mass fraction 8000 2.5

[0145] From the results in Table 2, it can be seen that when the concentration of the monomer solution is 5% by mass, the molecular weight of the obtained photocurable resin is too small. When the monomer concentration is controlled at 20% by mass, the number average molecular weight of the obtained photocurable resin reaches 8000, the solubility drops sharply, and the subsequent application is limited. In addition, under these two conditions, the molecular weight distribution of the polymer is relatively wide, indicating that the controllability of the polymerization reaction process is poor. A concentration of 10% by mass is preferred.

[0146] 2. Initiator Screening

[0147] (1) Type of initiator

[0148] Since the controllability of the molecular weight of the photocurable resin is mainly affected by the free radical initiator, in order to select a suitable free radical initiator, this embodiment further adopts a preparation method basically the same as that of Example 1 to prepare the photocurable resin, wherein the free radical initiators are dibenzoyl peroxide, tert-butyl hydroperoxide, azobisisobutyronitrile, and azobisisoheptanenitrile, respectively.

[0149] The Mn and PDI of the resin were detected by gas chromatography, and the results are shown in Table 3.

[0150] Table 3 Test results of photocurable resins with different types of free radical initiators

[0151] Free radical initiators Mn PDI Benzoyl peroxide 5000 3.1 tert-Butyl hydroperoxide 400 3.8 Azobisisobutyronitrile 2200 1.5 Azobis(2,2-diisoheptylnitrile) 4000 2.6

[0152] If the initiator initiates polymerization too quickly, the molecular weight will increase too quickly, making the experimental process difficult to control; if the initiator initiates polymerization too slowly, the polymerization time will be too long, resulting in low preparation efficiency. Within the same reaction time, a larger molecular weight indicates a faster reaction, while a smaller molecular weight indicates a slower reaction. Among them, dibenzoyl peroxide has a low thermal decomposition temperature, usually starting to decompose significantly at 60-80°C. The decomposition product is benzoyloxy free radicals, which can further disproportionately generate benzoic acid and benzene free radicals. The free radical activity is high and it is suitable for bulk polymerization. Tert-butyl hydroperoxide is a high-temperature initiator with a decomposition temperature of approximately 120-140°C, which is suitable for high-temperature polymerization reactions. Azobisisobutyronitrile has a thermal decomposition temperature of approximately 50-70°C. During the decomposition process, nitrogen is released (which can serve as a marker of the reaction progress) to generate isobutyronitrile free radicals. The free radical activity is moderate and it is suitable for solution polymerization and suspension polymerization of monomers such as styrene, acrylonitrile, and vinyl acetate, and is particularly suitable for preparing polymers with a narrow molecular weight distribution. Azobisisoheptylnitrile has a lower thermal decomposition temperature, approximately 40-60°C, and a faster decomposition rate and activity close to that of AIBN. Combined with the results of the examples, Table 3 shows that using dibenzoyl peroxide results in a photocurable resin with an excessively high molecular weight. Using tert-butyl hydroperoxide as a free radical initiator results in a photocurable resin with an excessively low molecular weight, leading to a slow reaction. Using azobisisobutyronitrile as an initiator results in a relatively high molecular weight. Only by using azobisisobutyronitrile can the molecular weight of the photocurable resin be effectively controlled and its molecular weight distribution narrowed within the same reaction time, resulting in highly controllable polymerization. Therefore, azobisisobutyronitrile is the preferred free radical initiator.

[0153] (2) Initiator concentration

[0154] Three photocurable resins were prepared using a method essentially identical to that of Example 1, except that the concentrations of the free radical initiator, azobisisobutyronitrile, were controlled at 1%, 5%, and 10% of the total monomer mass, respectively. The Mn and PDI of the resins were determined by gas chromatography. The results are shown in Table 4.

[0155] Table 4 Test results of photocurable resin with different initiator concentrations

[0156] Initiator concentration Mn PDI 1% of the total monomer mass 3800 2.5 5% of the total monomer mass 2200 1.5 10% of the total monomer mass 500 3.2

[0157] According to the results in Table 4, when the initiator solution concentration is 1% and 10% of the total monomer mass, the resulting photocurable resin has a broad molecular weight distribution, with number average molecular weights of 3800 and 500, respectively, making it unsuitable for subsequent applications. However, selecting an initiator concentration of 5% of the total monomer mass maintains the molecular weight of the photocurable resin within the range of 1000-3000, with a narrower molecular weight distribution.

[0158] 3. Reaction time and temperature

[0159] This example further controls the time and temperature of the first step reaction, using a preparation method substantially the same as that of Example 1, wherein the reaction time is controlled to 1 h, 2 h, and 3 h, respectively, and the reaction temperature is controlled to 60° C., 70° C., and 80° C., respectively. Single-variable control experiments are set up with temperature and time to prepare light-curable resins, and the Mn and PDI of the resins are tested. The results are shown in Table 5.

[0160] Table 5 Effect of reaction time and temperature on the molecular weight of photocurable resin

[0161] temperature Mn PDI 60℃ 400 3.5 70℃ 2200 1.5 80℃ 6500 2.5 time Mn PDI 1h 500 3.3 2h 2200 1.5 3h 5100 2.3

[0162] According to the results in Table 5, it can be found that only when the reaction temperature is 70°C and the reaction time is 2 h, the number average molecular weight of the prepared photocurable resin is in the range of 1000-3000 and has a narrow molecular weight distribution. Therefore, a reaction temperature of 70°C and a reaction time of 2 h are preferred.

[0163] Example 13: Preparation of light-curing glue

[0164] The high-refractive index photocurable resins prepared in Examples 1-9 were respectively added with initiator IGM-TPO (purchased from Agenmon), diluent OPPEA (purchased from Changxing), and crosslinker trimethylolpropane triacrylate (SR-351NS, purchased from Sartomer), wherein the weight proportions of resin, initiator, diluent, and crosslinker were 80%, 1%, 10%, and 9%, respectively. Stirring was carried out in the dark for 3 hours until completely dissolved. After mixing, light curing was carried out. Curing conditions: LED 365nm light source, 100mW / cm 2 , 30s.

[0165] The comprehensive properties of the nine prepared photocurable adhesives were tested, including refractive index, elongation, Young's modulus, curing activity, viscosity, and embossing performance, using the same testing methods as in Example 11. For the embossing performance test, a ruler grating imprinted with the adhesive on a 2-inch glass substrate was selected, and the grating microstructure was characterized using a scanning electron microscope (SEM).

[0166] The test results are shown in Table 6, where the refractive index test results and the imprinting performance test results of the light-curing glue prepared by the light-curing resin P1 are shown in Table 6. Figure 2 and Figure 3 shown.

[0167] Table 6 Performance comparison of light-curing glue prepared by different light-curing resins

[0168]

[0169] Table 6 shows that when light-curing resins with different structures are combined with crosslinkers, diluents, and initiators to prepare light-curing adhesives, the cured adhesives exhibit an overall lower refractive index, decreased viscosity, and increased elongation compared to the resins. The curing energy remains unchanged, but the overall performance trends among the different light-curing adhesives are similar to those of the resins, indicating that the light-curing resins significantly influence the viscosity, refractive index, and mechanical strength of the adhesives. When the elongation is between 5% and 10%, the light-curing adhesive exhibits good flexibility, and a higher Young's modulus indicates improved mechanical strength.

[0170] Because the refractive index, stiffness, and flexibility of rigid and flexible monomers primarily determine the refractive index, Young's modulus, and elongation of the resin, the results in Table 2 indicate that photocurable adhesives prepared from photocurable resins with different rigid, flexible, and reactive monomer structures exhibit significant differences in refractive index, mechanical strength, and flexibility. The adhesive prepared from resin P1 exhibits the highest refractive index, reaching 1.69, a Young's modulus of 3200, an elongation of 5%, and moderate viscosity. This demonstrates that the introduction of resin P1 achieves a high refractive index and a high crosslink density in the photocurable adhesive, while maintaining a high level of mechanical strength.

[0171] By comparing the comprehensive performance of the glue prepared by the photocurable resins P7-P9, it can be seen that the refractive index and Young's modulus of the glue obtained by the resin with a high addition ratio of rigid monomer (P7, P8) are improved, but the elongation is reduced. The stiffness of the glue after curing is too high and it is easy to break during use. By reducing the addition amount of rigid monomer and increasing the addition amount of flexible monomer (P9), the mechanical strength and refractive index of the obtained glue are significantly reduced, which cannot meet the use requirements.

[0172] In summary, the photocurable resin prepared in Example 1, that is, 2-vinylanthracene (rigid monomer), bis(2-(vinylthio)ethyl)sulfane (flexible monomer), and 4-methylolstyrene (reactive monomer) are selected as the starting monomers for preparing the resin, and the molar ratio of rigid monomer: flexible monomer: reactive monomer is 10:5:1, the comprehensive performance of the prepared photocurable glue is optimal.

[0173] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

Claims

1. A high refractive index photocurable resin, characterized in that: It has the general structural formula shown in Formula 1: Wherein R1 is an aromatic group, R2 is a sulfur-containing alkyl group, R3 is an aromatic group or an alkyl group, and R4 is a photocurable active functional group.

2. The high refractive index photocurable resin according to claim 1, wherein The R1 is selected from any one or more of the following formulas 2 to 6:

3. The high refractive index photocurable resin according to claim 1, wherein The R2 is selected from any one or more of the following formulas 7 to 9:

4. The high refractive index photocurable resin according to claim 1, wherein The R4 is selected from any one or more of the following formulas 12 to 14:

5. The high refractive index photocurable resin according to claim 4, wherein The structural formula of the high refractive index photocurable resin is shown in any one or more of Formulas 15 and 16:

6. A method for preparing a high refractive index photocurable resin, characterized in that: It is prepared by the following chemical formula: Among them, R1 is an aromatic group, R2 is a sulfur-containing alkyl group, R3 is an aromatic group or an alkyl group, and R4 is a photocurable active functional group.

7. The preparation method according to claim 6, wherein The Cl-R4 is one of acryloyl chloride, methacryloyl chloride and epichlorohydrin.

8. The preparation method according to claim 7, wherein described It is prepared by the following chemical formula:

9. The preparation method according to claim 8, wherein The free radical initiator includes any one of cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl hydroperoxide, azobisisobutyronitrile, and azobisisoheptanenitrile.

10. The preparation method according to claim 8, characterized in that The following steps are involved: S1: dissolving the aromatic vinyl compound and vinyl sulfide raw materials in dimethylformamide, and adding azobisisobutyronitrile as a free radical initiator to fully react; S2: After the reaction is terminated, the solvent is removed, eluted, and impurities are removed to obtain oligomers; S3: dissolving the oligomer in dichloromethane, adding triethylamine dropwise and then adding acryloyl chloride or methacryloyl chloride or epichlorohydrin dropwise and stirring. After the reaction is terminated, extracting, drying and evaporating to remove the solvent to obtain a high refractive index photocurable resin.

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