Third-order reaction type photopolymer holographic recording material and reinforceable grating thereof

Abstract

The invention relates to a three-order reaction type photopolymer holographic recording material, which is prepared from the following raw materials in parts by weight: 20 to 60 parts of thiol compound; 10 to 45 parts by weight of an isocyanate compound; 15-40 parts by weight of an alkene (alkyne) recording monomer; 15-40 parts by weight of an epoxy reinforcing monomer; 0.5-2 parts by weight of a free radical type photoinitiator; 0-0.5 part by weight of a photosensitizer; and 0-2 parts by weight of a photobase generator. According to the third-order reaction type photopolymer holographic recording material disclosed by the invention, a third-order reaction type photopolymer holographic recording material reaction system is constructed through three click reactions of sulfydryl-isocyanate, sulfydryl-alkene (alkyne) and thiol-epoxy, so that the refractive index modulation degree of a holographic grating is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of photopolymer holographic recording materials, in particular to an organic polymer system based on a third-order reactive photopolymer holographic recording material and an enhanced grating thereof. Background Art

[0002] Photopolymer holographic recording materials are organic polymer photosensitive materials that can achieve holographic recording through photopolymerization reactions. It can simultaneously record the phase and amplitude information of light waves in the form of volume holographic gratings inside the material. Compared with other holographic recording materials (such as silver halide emulsions, dichromated gelatin, photodegradable polymers, photorefractive materials, etc.), photopolymer holographic recording materials have advantages such as high photosensitivity, high spatial resolution, and high signal-to-noise ratio. The holographic gratings prepared using them have strong stability, high refractive index modulation, and low cost. This makes them widely used in the fields of optical storage, optical devices, sensing, anti-counterfeiting, solar energy, etc.

[0003] Photopolymer holographic recording materials usually contain film-forming resins, recording monomers, dyes, photoinitiators, etc. During holographic recording, the recording monomers in the coherent bright regions rapidly polymerize, while the recording monomers in the coherent dark regions do not react or react slowly. The concentration difference generated by the polymerization consumption of the recording monomers in the coherent bright regions drives the monomers in the coherent dark regions to continue to migrate to the coherent bright regions and participate in the polymerization, resulting in a refractive index difference between the coherent bright regions and the coherent dark regions in the material, forming a phase-type volume holographic grating. The maximum refractive index difference between the bright and dark regions of the grating is the refractive index modulation of the grating, which is an important indicator for measuring the performance of the grating.

[0004] The refractive index modulation of existing photopolymer gratings depends on the refractive index difference between the polymer formed by the recording monomer and the film-forming resin, and their correlation is shown in formula (1):

[0005]

[0006] In the formula, Δn is the refractive index modulation of the grating; SD is the migration ratio of the recording monomer, and its value range is 0% to 100%; is the volume fraction of the recording monomer; n photopolymer is the refractive index of the polymer formed by the recording monomer; n binder is the refractive index of the film-forming resin.

[0007] To increase the refractive index modulation (Δn) of the photopolymer holographic grating, traditional techniques usually increase the refractive index difference (n photopolymer -n binder) is achieved. The acquisition of high refractive index difference requires the use of monomer-resin combinations with significant molecular structural differences, but this structural difference leads to a sharp decrease in the compatibility between material components. Specifically, (1) high / low refractive index materials are prone to micro-region phase separation due to differences in polarity and molecular configuration, which significantly increases the material haze; (2) Insufficient compatibility directly restricts the maximum amount of monomer that can be added to the resin matrix. This results in a limited improvement in the actual Δn; (3) the microscopic defects formed by phase separation will reduce the uniformity and transmittance of the holographic grating. This contradiction between the refractive index difference and compatibility has become a key technical bottleneck restricting the performance breakthrough of traditional photopolymer holographic materials.

[0008] Therefore, developing new polymer material systems to break through the restrictive relationship between refractive index differences and material compatibility in existing technologies and achieve a synergistic improvement in high refractive index modulation and good material stability has become a core technical issue that needs to be urgently addressed in this field. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a photopolymer holographic recording material based on a third-order reaction mechanism, which innovatively introduces high / low refractive index recording monomers and enhancing monomers, and adopts a film-forming resin system containing active thiol sites. Different from the recording mechanism of traditional photopolymer holographic recording materials, the third-order reaction type photopolymer realizes holographic recording and grating refractive index modulation enhancement by reverse migration of recording and enhancing monomers to coherent bright areas and coherent dark areas respectively. This design has achieved a breakthrough in a non-traditional polymerization mechanism and self-enhanced photopolymer holographic recording material, which reduces the dependence on the refractive index difference between resin and monomer, improves the compatibility of components through chemical bonding, and effectively inhibits the micro-region phase separation phenomenon.

[0010] The first aspect of the present invention provides a third-order reaction type photopolymer holographic recording material, comprising: 20 to 60 parts by weight of a thiol compound; 10 to 45 parts by weight of an isocyanate compound; 15 to 40 parts by weight of an olefin (alkyne) recording monomer; 15 to 40 parts by weight of an epoxy reinforcing monomer; 0.5 to 2 parts by weight of a free radical type photoinitiator; 0 to 0.5 parts by weight of a photosensitizer; and 0 to 2 parts by weight of a photobase generator.

[0011] Furthermore, the content of the thiol compound is 30 to 50 parts by weight, preferably 30 to 45 parts by weight.

[0012] Furthermore, the content of the isocyanate compound is 20 to 40 parts by weight, preferably 15 to 25 parts by weight.

[0013] Furthermore, the content of the olefin (alkyne) recording monomer is 15 to 35 parts by weight, preferably 15 to 25 parts by weight.

[0014] Further, the content of the epoxy-based reinforcing monomer is 15 to 35 parts by weight, preferably 15 to 25 parts by weight.

[0015] Further, the molar ratio range of the (alkene / alkyne)-type recording monomer is 40 to 60%.

[0016] The molar amount of the (alkene / alkyne)-type recording monomer accounts for 40 to 60% of the sum of the molar amounts of the (alkene / alkyne)-type recording monomer and the epoxy-based reinforcing monomer. Among them, the molar ratio of the recording monomer = molar amount of the recording monomer / (molar amount of the recording monomer + molar amount of the reinforcing monomer).

[0017] The thiol compound is a bifunctional or polyfunctional thiol compound, and is selected from one or more of bis(mercaptoethyl) sulfide, 2,5-dimethylmercapto-1,4-dithiane, ethylene glycol bis(2-mercaptoacetate), ethylene glycol bis(3-mercaptopropionate), hexanediol bis(2-mercaptoacetate), hexanediol bis(3-mercaptopropionate), 4-mercaptomethyl-3,6-dithia-1,8-octanedithiol, triglycerol tris(2-mercaptoacetate), triglycerol tris(3-mercaptopropionate), trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), bis(mercaptomethyl)-3,6,9-trithianonane-1,11-dimercaptol, pentaerythritol tetra(2-mercaptoacetate), pentaerythritol tetra(3-mercaptopropionate), dipentaerythritol hexa(2-mercaptoacetate), and dipentaerythritol hexa(3-mercaptopropionate).

[0018] Further, the isocyanate compound is a bifunctional or polyfunctional isocyanate, and is selected from one or more of 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthalene 1,5-diisocyanate, p-phenylene diisocyanate, butane-1,4-diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, dimethylbiphenyl diisocyanate, tetramethylm-xylylene diisocyanate, cyclohexane dimethylene diisocyanate, norbornane dimethylene diisocyanate, dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, hexamethylene diisocyanate trimer, and isophorone diisocyanate trimer.

[0019] Further, the refractive index difference between the (alkene / alkyne)-type recording monomer and the epoxy-based reinforcing monomer is greater than 0.1, preferably greater than 0.15, and more preferably greater than 0.2.

[0020] Further, the structure of the (alkene / alkyne)-type recording monomer is as shown in formula (I):

[0021]

[0022] x is an integer from 1 to 6; y is an integer from 1 to 3.

[0023] Wherein RIG is a Refractive Index Group, which plays a role in regulating the refractive index of the whole molecule. Preferably, RIG is one or more of aryl group, halogenated aryl group, heteroaryl group, group containing sulfide bond, alkane group, chloroalkane group, bromoalkane group, iodoalkane group, siloxane group, alkane group, fluoroalkane group, etc.

[0024] Wherein CG is a Connecting Group in the structure, which is used to connect RIG and RAG functional groups in the record of monomer molecular structure, and regulates the solubility and crystallinity of the molecule by introducing rigid or flexible structures. Specifically, CG is one or more of alkyl groups, ester groups, amide groups, aromatic groups, groups containing ether bonds, groups containing sulfide bonds, cycloalkane groups, and heterocyclic groups formed by lacking (x + y) hydrogens. Preferably, it is one or more of ester groups, amide groups, and groups containing sulfide bonds.

[0025] Wherein RAG is a Radical Additional Group that can undergo radical addition with thiol group, and is a group with unsaturated carbon-carbon double bond or carbon-carbon triple bond. Preferably, RAG is a carbon-carbon double bond or triple bond with small steric hindrance and connected with an electron-donating group. More preferably, RAG is an electron-rich, small steric hindrance monosubstituted carbon-carbon double bond.

[0026] In some embodiments of the present invention, the ene (yne) - type recording monomer is one or more of 2,4,6 - tribromophenol allyl ether, 4,4'-thiodiphenol diallyl ether, phenoxyacetic acid allyl ester, N - vinylcarbazole, N - allylcarbazole.

[0027] Furthermore, the structure of the epoxy - type enhancing monomer is shown in formula (II):

[0028]

[0029] x' is an integer from 1 to 6; y' is an integer from 1 to 3.

[0030] Wherein RIG' is a refractive index contribution group, which plays a role in regulating the refractive index of the whole molecule. Preferably, RIG' is one or more of aryl group, halogenated aryl group, heteroaryl group, group containing sulfide bond, alkane group, chloroalkane group, bromoalkane group, iodoalkane group, siloxane group, alkane group, fluoroalkane group, etc.

[0031] Among them, CG’ is a linking group in the structure, which is used to connect the RIG’ and ROAG functional groups in the enhanced monomer molecule, and regulate the solubility and crystallinity of the molecule by introducing a rigid or flexible structure. Specifically, CG’ is an alkyl group, an ester group, an amide group, an aryl group, a group containing an ether bond, a group containing a thioether bond, a cycloalkane group, or a heterocyclic group formed by lacking (x’ + y’) hydrogens; preferably, it is one or more of an ester group, an amide group, and a group containing a thioether bond.

[0032] Among them, ROAG (Ring-Opened Additional Group) is a group that can undergo ring-opening addition reaction with a thiol group under base catalysis. Preferably, it is a group with a large ring strain, including but not limited to one or several of an ethylene oxide group, an oxetane group, and a cyclohexene oxide group. Preferably, ROAG is one or more of an ethylene oxide group and an oxepinyl group.

[0033] Furthermore, the refractive indices of the RIG and RIG’ groups are different. Specifically, when RIG is a high refractive index group, RIG’ should be a low refractive index group. Conversely, when RIG is a low refractive index group, RIG’ should be a high refractive index group.

[0034] The high refractive index groups include aryl groups, non-fluorinated halogenated aryl groups, heteroaryl groups, groups containing a thioether bond, chloroalkyl groups, bromoalkyl groups, and iodoalkyl groups. Further preferably, it is one or more of non-fluorinated halogenated aryl groups and heteroaryl groups.

[0035] The low refractive index groups include siloxane groups, alkane groups, and fluoroalkane groups. Further preferably, it is a fluoroalkane group.

[0036] In some embodiments of the present invention, the epoxy-based enhanced monomer is one or several of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-epoxypropane, 3-(2,2,3,3,4,4,5,5-octafluoropentyloxy)-1,2-epoxypropane, n-butyl glycidyl ether, and 1,3-bis(3-glycidyletheroxypropyl)tetramethyldisiloxane.

[0037] Furthermore, the molar amount of the mercapto group in the thiol compound should satisfy formula (2), that is, it is equal to the sum of the molar amount of the isocyanate group in the isocyanate compound, the molar amount of the alkene / alkyne group in the alkene (alkyne) type recording monomer, and the molar amount of the epoxy group in the epoxy-based enhanced monomer.

[0038] ∑n thiol f thiol =∑n isocyanate f isocyanate +∑n ene f ene +2×∑n yne fyne +∑n epoxy f epoxy (2)

[0039] where n thiol 、n isocyanate 、n ene 、n yne 、n epoxy are the molar amounts of the thiol compound, isocyanate compound, olefinic recording monomer, acetylenic recording monomer, and epoxy strengthening monomer, respectively; f thiol 、f isocyanate 、f ene 、f yne 、f epoxy are the functionalities of the thiol compound, isocyanate compound, olefinic recording monomer, acetylenic recording monomer, and epoxy strengthening monomer, respectively.

[0040] Furthermore, the radical photoinitiator is a compound that can generate radicals after absorbing light of a certain wavelength and initiate the thiol-ene / yne radical addition. It includes but is not limited to one or more of thioxanthone compounds, anthraquinone compounds, benzil compounds, benzoin ether compounds, acylphosphine oxide compounds, benzoin ether compounds, benzoyl ketal compounds, acetophenone compounds, benzophenone compounds, organometallic compounds.

[0041] Furthermore, the photosensitizer is a dye that can efficiently transfer energy or electrons to the above radical photoinitiator after absorbing light of a certain wavelength, and is used to broaden the photosensitive range of the material. When the light source wavelength used for holographic recording is adapted to the absorption wavelength of the radical photoinitiator, the photosensitizer can be not added. The photosensitizer includes but is not limited to: cyanine dyes, fluorescein dyes, coumarinone dyes, nitrogen-containing aromatic heterocyclic compounds, aromatic amine compounds, benzylidene cycloalkanone compounds, or any proportion mixture of these compounds. For example, it includes one or several of new methylene blue, thionine, basic yellow, pinacyanol chloride, rhodamine 6G, gallocyanine, ethyl violet, victoria blue R, celestine blue, methylene blue, basic orange G, eosin, darrow red, pyrrole red Y, basic red 29, quinidine red, crystal violet, ethyl violet, bright green, azure A, crystal violet nitrile, malachite green nitrile, etc.

[0042] Furthermore, the photo-base generator can generate a strong base after absorbing light of a certain wavelength (such as ultraviolet light), and is used to catalyze the ring-opening addition reaction of thiol-epoxy. When the used thiol and epoxy-based reinforcing monomers both have high activities and can achieve a catalyst-free addition reaction under heating conditions, the photo-base generator can be not added. It should be noted that in order to avoid the reaction of epoxy-based reinforcing monomers during holographic recording in the second stage, the photo-base generator should have no absorption in the light band for holographic recording, and the above-mentioned photosensitizer has no sensitization effect or a weak sensitization effect on the photo-base generator.

[0043] The photo-base generator includes, but is not limited to, one or more of the following compounds: carbamate, O-acyl oxime ester, O-carbamoyl oxime ester, α-aminoketone, benzoylmethanamide, reduced formamidine, cobalamin complex, quaternary ammonium salt, tetraphenylborate, carboxylate, etc.

[0044] Optionally, the photopolymer holographic recording material of the present invention further includes other additives in an amount of 0 to 2 parts by weight; the other photo-additives are one or several of a leveling agent, a plasticizer, an ultraviolet light absorber, a polymerization inhibitor, a chain transfer agent, and an antifoaming agent.

[0045] Furthermore, the third-order reaction-type photopolymer holographic recording material of the present invention constructs a third-order reaction-type photopolymer holographic recording material system through three click reactions of thiol-isocyanate, thiol-ene (alkyne), and thiol-epoxy, thereby enhancing the refractive index modulation of the holographic grating.

[0046] Furthermore, to satisfy the thiol-isocyanate polycondensation reaction of the isocyanate compound and the thiol compound to form a crosslinked network, the molar amounts of the isocyanate compound and the thiol compound should satisfy formula (3).

[0047]

[0048] In the formula, N thiol and N isocyanate are the molar amounts of the thiol compound and the isocyanate compound respectively, and f isocyanate is the functionality of the isocyanate compound.

[0049] According to formula (3), in order to form a crosslinked network, when the isocyanate compound used in the present invention is bifunctional, its molar amount should not be less than 100% of the molar amount of the thiol compound; when the isocyanate compound is trifunctional, its molar amount should not be less than 50% of the molar amount of the thiol compound; when the isocyanate compound is tetrafunctional, its molar amount should not be less than 33% of the molar amount of the thiol compound.

[0050] Preferably, in order to obtain a film-forming resin with more stable morphology, when using multiple isocyanate compounds with different functionality degrees simultaneously, the molar amount of the isocyanate compound and the molar amount of the thiol compound should satisfy formula (4).

[0051]

[0052] When the isocyanate compound used is bifunctional, its molar amount should not be less than 120% of the molar amount of the thiol compound; when the isocyanate compound used is trifunctional, its molar amount should not be less than 60% of the molar amount of the thiol compound; when the isocyanate compound used is tetrafunctional, its molar amount should not be less than 40% of the molar amount of the thiol compound.

[0053] In the second aspect of the present invention, there is provided a method for preparing the third-order reaction-type photopolymer holographic recording material described in the first aspect, which is obtained by the thiol-isocyanate reaction between the mercapto group in the thiol compound and the isocyanate group in the isocyanate compound.

[0054] Furthermore, a method for preparing a third-order reaction-type photopolymer holographic recording material includes the following steps:

[0055] 1) Mixing: Mix each component evenly to form a precursor solution of the third-order reaction-type photopolymer holographic recording material;

[0056] 2) Curing and film-forming: Cure the precursor solution at 20 - 40 °C for 8 - 16 h to form a film-forming resin.

[0057] Optionally, it further includes loading the film-forming resin onto a substrate.

[0058] The substrate includes PET, PC, PMMA transparent sheets, glass substrates, etc.

[0059] In the third aspect of the present invention, there is provided a grating enhancer, which is formed by performing holographic recording exposure using the above-mentioned third-order reaction-type photopolymer holographic recording material.

[0060] The holographic recording exposure causes a thiol-ene (yne) radical addition reaction between the ene (yne)-type recording monomer and the mercapto group on the film-forming resin of the holographic recording material to obtain a grating enhancer.

[0061] In an embodiment of the present invention, the holographic recording exposure treatment is carried out with the aid of two coherent light beams. The two coherent light sources are s-polarized laser beams with an optical intensity of 1 - 5 mW / cm 2 , a diameter of 8 - 12 mm, a wavelength of 400 - 600 nm, a grating period of 400 - 1000 nm, and an exposure time of 40 - 60 s.

[0062] Further, under ultraviolet and / or heating conditions, an epoxy-based enhancing monomer in the raw material undergoes a thiol-epoxy ring-opening addition reaction with the residual thiol groups on the film-forming resin of the holographic recording material, enhancing the refractive index modulation of the grating.

[0063] The ultraviolet conditions are as follows: wavelength 100 - 405 nm, intensity 10 - 50 mW / cm 2 , and time 10 - 50 minutes;

[0064] The heating conditions are as follows: temperature 60 - 100 °C, and time 8 - 16 h.

[0065] In one embodiment of the present invention, the raw materials of the third-order reactive photopolymer holographic recording material are mixed, coated on a substrate, cured into a film, and holographically recorded and exposed to form an enhanced holographic grating, and with the action of ultraviolet and / or heating, the refractive index modulation of the grating is enhanced.

[0066] Specifically, the raw materials of the third-order reactive photopolymer holographic recording material are mixed to form a homogeneous mixture. After standing for a period of time, the first-order reaction is initiated and cured into a thin film; and it is placed in a laser interference field for holographic recording and exposure to initiate the second-order reaction (exposure intensity 1 - 5 mW / cm 2 , exposure time 40 - 60 seconds) to obtain an enhanced grating; placed under ultraviolet light (wavelength 100 - 405 nm, intensity 10 - 50 mW / cm 2 , time 10 - 50 minutes), under the action of a photo-base generator and / or under heating conditions (60 - 100 °C, heating for 8 - 16 h), the third-order reaction is initiated to enhance the refractive index modulation of the holographic grating.

[0067] For the enhanced grating of the present invention, an isocyanate compound and an excessive thiol compound in the third-order reactive photopolymer holographic recording material undergo a thiol-isocyanate Michael addition (optionally a trace amount of base catalyst can be added) to form a film-forming resin cross-linked network containing a large number of active thiol sites (completing the first-order reaction); with the help of holographic recording conditions, the ene(yne)-type recording monomer migrates to the coherent bright region and undergoes a thiol-ene(yne) radical addition with the thiol groups on the film-forming resin in the bright region (completing the second-order reaction); under the action of a photo-base generator or heat, the epoxy-based enhancing monomer migrates to the dark region and undergoes a thiol-epoxy ring-opening addition with the residual thiol groups on the film-forming resin (completing the third-order reaction), using the third-order reaction to enhance the refractive index modulation of the photopolymer holographic recording material.

[0068] In the third-order reaction process provided by the present invention, in the first stage, a solvent-free film-forming process is adopted, and a highly transparent film is rapidly cross-linked through thiol-isocyanate to avoid the defects caused by the volatilization of traditional solvents; in the second stage, a thiol-ene (alkyne) click reaction is used to achieve high-resolution, low-shrinkage, and high-sensitivity holographic grating recording, significantly improving sensitivity and edge clarity; in the third stage, the refractive index modulation of the grating is directionally enhanced by controllably triggering the thiol-epoxy reaction, breaking through the performance bottleneck of traditional materials.

[0069] To ensure the enhanced effect of holographic recording of the material, the stoichiometric relationship of each component should satisfy the above formulas (2)-(3).

[0070] The third-order reactive photopolymer holographic recording material described in the present invention is different from the traditional holographic system based on free radical polymerization. It realizes the construction of an enhanced volume holographic grating through the reverse migration mechanism of ene (alkyne) - type recording monomers and epoxy - type enhancing monomers, as well as the multi - level bonding reaction of the active thiol (-SH) of the film - forming resin, and has the following technical advantages: ① High resolution: The active thiol of the film - forming resin bonds with the monomer, inhibiting the diffusion of oligomers and photoactive substances to the non - exposed area (dark area), eliminating the grating edge blur effect, and improving the spatial resolution; ② Efficient monomer migration: Avoiding the gelation phenomenon of the system caused by the growth of polymer chains, the monomer migration rate from the dark area to the bright area can reach more than 90%; ③ Low haze: The recording monomer, enhancing monomer, and resin are covalently connected through thioether bonds, realizing molecular - level interfacial bonding, inhibiting the generation of micro - phase separation, and reducing the haze of the material; ④ Low shrinkage and anti - distortion: Based on the two low - molar - shrinkage reactions of thiol - ene (alkyne) free - radical addition and thiol - epoxy ring - opening addition, the volume shrinkage rate of the holographic recording material is reduced, the deformation rate of the formed grating is reduced, and it is not easy to be distorted.

[0071] Furthermore, the refractive index modulation generation mechanism of the third - order reactive photopolymer holographic recording material is also different from that of the traditional photopolymer holographic recording material. Its final grating refractive index modulation results from the reverse migration of the recording monomer and the enhancing monomer, as Figure 1 shown, and its final refractive index modulation can be shown by formula (5):

[0072]

[0073] In the formula, Δn3 is the refractive index modulation after all three stages of the material have reacted; ID is the degree of reverse migration of the recording monomer and the enhancing monomer; and are the volume fractions of the ene (alkyne) - type recording monomer and the epoxy - type enhancing monomer respectively; n r and n eThe refractive indices of the vinyl (acetylene) - type recording monomers and epoxy - type reinforcing monomers are respectively measured. It can be seen that for the grating obtained from the third - order reactive holographic recording material, the refractive index modulation degree is independent of the refractive index of the film - forming resin. The structural design of the film - forming resin in the present invention is no longer restricted by the refractive index, reducing the dependence on the refractive index difference between the resin and the monomer.

[0074] In the fourth aspect of the present invention, a method for enhancing the refractive index modulation degree of a grating is provided. The raw materials of the above - mentioned third - order reactive photopolymer holographic recording material are mixed, cured into a film, holographically recorded and exposed, and a thiol - epoxy ring - opening addition reaction occurs under the conditions of ultraviolet light and / or heating, enhancing the refractive index modulation degree of the grating.

[0075] In the fifth aspect of the present invention, a use for enhancing a grating is provided. The grating that can be enhanced in the present invention can be used in various holographic display systems in the art and can be used alone or in combination with other optical elements.

[0076] Furthermore, the grating that can be enhanced in the present invention can be used in holographic optical waveguide display devices and is particularly suitable for head - mounted display devices for augmented reality (AR), such as AR display glasses.

[0077] Advantages of the present invention:

[0078] The present invention provides a third - order reactive photopolymer holographic recording material. By introducing a high / low refractive index recording monomer and a reinforcing monomer synergistic system, and using a film - forming resin containing active thiol (-SH), the thiol - vinyl (acetylene) radical addition reaction and thiol - epoxy ring - opening addition reaction are used to replace the traditional free - radical polymerization. In the holographic exposure and volume holographic grating enhancement stages, the vinyl (acetylene) - type recording monomers and epoxy - type reinforcing monomers respectively migrate reversely to the thiol sites in the coherent bright area and coherent dark area of the resin, and the monomers are anchored to the film - forming resin through an addition reaction. It realizes precise regulation of performance in stages and dynamic enhancement of optical properties by constructing a holographic recording material system based on the synergistic effect of thiol - isocyanate, thiol - vinyl (acetylene), and thiol - epoxy third - order click reactions.

[0079] The enhanced grating recorded by using the third-order reactive photopolymer holographic recording material of the present invention is formed after raw material mixing, film curing, and holographic recording, and its performance is enhanced by exciting the third-order thiol-epoxy ring-opening reaction. It utilizes the synergistic effect of the thiol-ene(yne) addition reaction in the second stage and the thiol-epoxy ring-opening reaction in the third stage to construct an interpenetrating network structure. The refractive index modulation degree of the grating is increased by more than 50% after being triggered by the third-order reaction. The enhanced holographic grating has excellent light transmittance (haze < 0.03%) and environmental stability while achieving a high refractive index difference, successfully providing a novel solution to the problem that it is difficult to balance refractive index modulation and material compatibility in traditional systems, and providing an innovative material basis with both high-efficiency diffraction and long-term stability for the fields of high-density holographic storage, programmable optical devices, and precision optical sensing.

[0080] In the present invention, "functionality" refers to the number of reactive groups (such as hydroxyl -OH, epoxy group, double bond, mercapto -SH, etc.) that can participate in reactions in a single molecule. "Mono-functional" means that the molecule contains 1 reactive group (such as acrylic monomer contains 1 double bond). "Di-functional" means that the molecule contains 2 reactive groups (such as bisphenol A type epoxy resin contains 2 epoxy groups). "Multi-functional" (≥3) means that the molecule contains 3 or more reactive groups (such as pentaerythritol contains 4 hydroxyl groups).

[0081] In the present invention, the mercapto group, also known as the hydrogen sulfide group or thiol group, is a monovalent functional group composed of a sulfur atom and a hydrogen atom, with the chemical formula -SH.

[0082] The ene(yne) - type recording monomer of the present invention refers to an ene - type recording monomer and / or a yne - type recording monomer.

[0083] In the examples of the present invention, potassium bromide transparent plates are used as the substrate, mainly for infrared test to verify the process and principle of the third - order reaction. Description of the Drawings

[0084] Figure 1 It is a schematic diagram of the mechanism for the enhancement of the refractive index modulation degree of the volume holographic grating that can be enhanced in the second stage recording and the grating in the third stage of the third - order reactive photopolymer holographic recording material proposed by the present invention;

[0085] Figure 2 It is the infrared test results of different stages of each step of the third - order reactive photopolymer holographic recording material prepared in Example 1;

[0086] Figure 3 It is a graph showing the change of the angular selectivity curve of the third - order reactive photopolymer volume holographic grating prepared in Example 2 with the heating time.

[0087] Figure 4Infrared test results of the third-order reactive photopolymer volume holographic grating material prepared in Example 2 at different heating times.

[0088] Figure 5 Refractive index modulation degrees of the third-order reactive photopolymer volume holographic gratings prepared in Examples 3 to 6 in the second and third stages.

[0089] Figure 6 Refractive index modulation degrees of the third-order reactive photopolymer volume holographic gratings prepared in Examples 7 to 10 in the second and third stages. Detailed implementation manners

[0090] The technical solutions in the embodiments of the present invention will be described in detail below in conjunction with specific invention embodiments. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention.

[0091] The raw materials or chemical reagents used in the embodiments of the present invention are all commercially available products. In the third-order reactive photopolymer holographic recording materials of Examples 1 to 10, the amounts of the raw materials all satisfy Formulas (2) and (3).

[0092] Example 1

[0093] In this example, a potassium bromide holographic recording sample was prepared to verify the reaction properties of each stage of the third-order reactive photopolymer holographic recording material.

[0094] A third-order reactive photopolymer holographic recording material, comprising: 38 g of dipentaerythritol hexa(3-mercaptopropionate), 15 g of hexamethylene diisocyanate isocyanurate trimer, 5 g of hexamethylene diisocyanate, 5 g of allyl phenoxyacetate, 15 g of allyl 2,4,6-tribromophenol ether, 15 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-epoxypropane, 5 g of n-butyl glycidyl ether, 1 g of photoinitiator 784, 1 g of WPBG-018 (as shown in Table 1).

[0095] 1) Under light-shielded or red light conditions, the above-mentioned raw material components were sequentially added to a brown sample bottle and stirred at room temperature for 1 hour to obtain a clear solution; the solution was filtered through a 0.45 μm organic filter membrane to remove dust and other insoluble impurities, and 0.01 wt% of polystyrene microspheres with a diameter of 15 μm were added according to the mass of the solution and dispersed evenly by ultrasonic treatment to obtain a precursor solution of the third-order reactive photopolymer holographic recording material.

[0096] 2) Take 5 μL of the above-mentioned precursor solution and sandwich it between two potassium bromide salt tablets of 10 mm × 10 mm × 1 mm to obtain an uncured potassium bromide sample of the third-order reactive photopolymer holographic recording material, denoted as "uncured precursor solution".

[0097] 3) Cure the uncured potassium bromide sample of the third-order reactive photopolymer holographic recording material described in step 2) into a film at room temperature, in a dark environment, and under dehumidification conditions for 12 hours, denoted as "film formation in the first stage of curing".

[0098] 4) Perform holographic recording exposure on the cured potassium bromide sample of the third-order reactive photopolymer holographic recording material in step 3). The light source for holographic recording exposure is two coherent s-polarized laser beams with an optical intensity of 1.5 mW / cm 2 , a diameter of 10 mm, and a wavelength of 532 nm; the two laser beams intersect at an angle of 30.8° on the sample, and the normal of the sample bisects the angle between the two laser beams. The exposure time is 60 s. After the holographic recording exposure is completed, it is denoted as "completion of the second stage of exposure".

[0099] 5) Act on the potassium bromide sample of the third-order reactive photopolymer holographic recording material that has completed holographic recording exposure in step 4) under an LED lamp with a power of 20 mW and a wavelength of 405 nm for 30 min to stimulate the photoacid generator to generate base, and then place it in an oven at 70 °C for 12 h to promote the reaction in the third stage and complete the enhancement of the refractive index modulation degree, denoted as "enhancement of the grating in the third stage".

[0100] Table 1

[0101]

[0102] Example 2

[0103] A third-order reactive photopolymer holographic recording material, comprising: 34 g of dipentaerythritol hexa(3-mercaptopropionate), 14 g of hexamethylene diisocyanate isocyanurate trimer, 4 g of isophorone diisocyanate, 5 g of allyl phenoxyacetate, 18 g of N-vinylcarbazole, 17 g of 3-(2,2,3,3,4,4,5,5-octafluoropentyloxy)-1,2-epoxypropane, 6 g of n-butyl glycidyl ether, 1 g of photoinitiator 1,2'-bis(2-chlorophenyl)-tetraphenyl benzimidazole, 0.1 g of photosensitizer 2,5-bis[4-(diethylamino)-benzylidene]cyclopentanone, 0.9 g of WPBG-018 (as shown in Table 2).

[0104] 1) Under light - shielding or red - light conditions, add the above - mentioned raw material components into a brown sample bottle in sequence, stir for 1 hour at room temperature to obtain a clear solution; filter with a 0.45 - μm organic filter membrane to remove dust and other insoluble impurities, add polystyrene microspheres with a diameter of 15 μm and a content of 0.01 wt% according to the mass of the solution, and disperse evenly by ultrasonic treatment to obtain a precursor solution of the third - order reactive photopolymer holographic recording material.

[0105] Steps 2) - 3) are the same as those in Example 1.

[0106] 4) Expose the third - order reactive photopolymer holographic recording material sample cured in step 3) to holographic recording. The holographic recording exposure light source is two coherent s - polarized laser beams with a light intensity of 1.5 mW / cm 2 , a diameter of 10 mm, and a wavelength of 532 nm; the two laser beams intersect at the sample at an angle of 44.6°, the normal of the sample bisects the angle between the two laser beams, the corresponding grating period is 700 nm, and the exposure time is 60 s.

[0107] 5) Expose the third - order reactive photopolymer holographic recording material sample that has completed holographic recording exposure in step 4) under an LED lamp with a power of 20 mW and a wavelength of 405 nm for 30 min to excite the photo - base - generating agent to generate base, and then place it in an oven at 70 °C for a certain period of time to promote the third - stage reaction and complete the enhancement of the refractive index modulation degree.

[0108] Table 2

[0109]

[0110]

[0111] Examples 3 - 6

[0112] Change the dosage ratio of the isocyanate compound in the third - order reactive photopolymer holographic recording material, and investigate the influence of different cross - linking densities of the film - forming resin.

[0113] 1) A third-order reactive photopolymer holographic recording material, including the raw materials and ratios in Table 3 (Example 3: 38 g of dipentaerythritol hexa(3-mercaptopropionate), 18 g of HDI trimer curing agent, 22 g of N-vinylcarbazole, 20 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide, 0.9 g of 1,2'-bis(2-chlorophenyl)-tetraphenylbenzimidazole, 0.1 g of 1,5-dicondensed (9-formyljulolidine) cyclopentanone, 1 g of WPBG-018; Example 4: 38 g of dipentaerythritol hexa(3-mercaptopropionate), 21 g of HDI trimer curing agent, 20 g of N-vinylcarbazole, 19 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide, 0.9 g of 1,2'-bis(2-chlorophenyl)-tetraphenylbenzimidazole, 0.1 g of 1,5-dicondensed (9-formyljulolidine) cyclopentanone, and 1 g of WPBG-018;; Example 5: 38 g of dipentaerythritol hexa(3-mercaptopropionate), 24 g of HDI trimer curing agent, 19 g of N-vinylcarbazole, 17 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide, 0.9 g of 1,2'-bis(2-chlorophenyl)-tetraphenylbenzimidazole, 0.1 g of 1,5-dicondensed (9-formyljulolidine) cyclopentanone, 1 g of WPBG-018; Example 6: 38 g of dipentaerythritol hexa(3-mercaptopropionate), 27 g of HDI trimer curing agent, 17 g of N-vinylcarbazole, 16 g of 3-(2,2,3,3-tetrafluoropropoxy)-1,2-propylene oxide, 0.9 g of 1,2'-bis(2-chlorophenyl)-tetraphenylbenzimidazole, 0.1 g of 1,5-dicondensed (9-formyljulolidine) cyclopentanone, 1 g of WPBG-018).

[0114] 2) Under light-shielded or red light conditions, add each component in Table 3 into a brown sample bottle in sequence, stir at room temperature for 1 hour to obtain a clear solution; use a 0.45 μm organic filter membrane to filter out dust and other insoluble impurities, add polystyrene microspheres with a diameter of 15 μm at 0.01 wt% according to the solution mass, and use ultrasonic dispersion to make it uniform to obtain a precursor solution of the third-order reactive photopolymer holographic recording material.

[0115] Steps 3)-5) are the same as those in Example 1.

[0116] Table 3

[0117]

[0118]

[0119] Examples 7-10

[0120] Change the ratio of the recording monomer to the enhancing monomer in the third-order reactive photopolymer holographic recording material, and investigate the effects of different ratios of the recording monomer to the enhancing monomer.

[0121] 1) A third-order reactive photopolymer holographic recording material, comprising the raw materials and ratios in Table 4 (Example 7: 39 g of dipentaerythritol hexa(3-mercaptopropionate), 19 g of HDI trimer curing agent, 12 g of N-allylcarbazole, 7 g of 4,4'-thiobis(phenol diacrylate ether), 21 g of 1,3-bis(3-glycidyletheroxypropyl)tetramethyldisiloxane, 0.9 g of 1,2'-bis(2-chlorophenyl)-tetraphenylbenzimidazole, 0.1 g of 1,5-dicondensed(9-formyljulolidine) cyclopentanone, 1 g of WPBG-018; Example 8: 39 g of dipentaerythritol hexa(3-mercaptopropionate), 19 g of HDI trimer curing agent, 13 g of N-allylcarbazole, 8 g of 4,4'-thiobis(phenol diacrylate ether), 19 g of 1,3-bis(3-glycidyletheroxypropyl)tetramethyldisiloxane, 0.9 g of 1,2'-bis(2-chlorophenyl)-tetraphenylbenzimidazole, 0.1 g of 1,5-dicondensed(9-formyljulolidine) cyclopentanone, 1 g of WPBG-018; Example 9: 39 g of dipentaerythritol hexa(3-mercaptopropionate), 19 g of HDI trimer curing agent, 14 g of N-allylcarbazole, 8 g of 4,4'-thiobis(phenol diacrylate ether), 18 g of 1,3-bis(3-glycidyletheroxypropyl)tetramethyldisiloxane, 0.9 g of 1,2'-bis(2-chlorophenyl)-tetraphenylbenzimidazole, 0.1 g of 1,5-dicondensed(9-formyljulolidine) cyclopentanone, 1 g of WPBG-018; Example 10: 39 g of dipentaerythritol hexa(3-mercaptopropionate), 19 g of HDI trimer curing agent, 15 g of N-allylcarbazole, 9 g of 4,4'-thiobis(phenol diacrylate ether), 16 g of 1,3-bis(3-glycidyletheroxypropyl)tetramethyldisiloxane, 0.9 g of 1,2'-bis(2-chlorophenyl)-tetraphenylbenzimidazole, 0.1 g of 1,5-dicondensed(9-formyljulolidine) cyclopentanone, 1 g of WPBG-018).

[0122] 2) Under light avoidance or red light conditions, add each component in Table 4 into a brown sample bottle in sequence, stir at room temperature for 1 hour to obtain a clear solution; filter with a 0.45 μm organic filter membrane to remove dust and other insoluble impurities, add polystyrene microspheres with a diameter of 15 μm at 0.01 wt% according to the solution mass, and use ultrasonic dispersion to make it uniform to obtain a precursor solution of the third-order reactive photopolymer holographic recording material.

[0123] Steps 3)-5) are the same as those in Example 1.

[0124] Table 4

[0125]

[0126] Comparative Example 1

[0127] The formulation and dosage of the photopolymer holographic recording material in Comparative Example 1 are similar to those in Example 4, except that the epoxy reinforcing monomer component in Comparative Example 1 is replaced by an equal weight of the low refractive index inert component 3-methoxytetrafluoropropionic acid methyl ester (as shown in Table 5), and the specific operation steps are the same as those in Example 4.

[0128] Comparative Example 2

[0129] The formulation and dosage of the photopolymer holographic recording material of Comparative Example 2 are shown in Table 5. The difference from Example 4 is that no epoxy reinforcing monomer is added. The specific operation steps are the same as those of Example 4.

[0130] Table 5

[0131]

[0132] Test Example 1

[0133] Example 1 was evaluated to verify the reaction mechanism of each component of the three-stage reaction type photopolymer holographic recording material.

[0134] The evaluation method comprises the following steps: infrared tests are performed on the "uncured precursor solution" in step 2) of Example 1, the "first stage cured film" in step 3), the "second stage exposure completed" sample in step 4), and the "third stage grating enhancement" sample in step 5), respectively. The results are as follows: Figure 2 shown.

[0135] from Figure 2 It can be seen that the mercapto peak is at 2560 cm -1 At the three stages, the mercapto peak decreased, indicating that the thiol compounds participated in the reaction in the three stages. The isocyanate peak was at 2269 cm -1 The peak disappears after the sample is cured, indicating that the isocyanate compound reacts with the thiol compound in the first stage to cure the material into a film. The double bond peak is at 1615 cm -1 The peak disappears after the sample completes holographic recording, indicating that the olefin (alkyne) recording monomer reacts with thiol in the second stage to complete the holographic recording. The epoxy peak is at 895cm -1 The above results verify that the present invention can enhance the refractive index modulation of holographic grating materials through the three-stage reaction process of mercapto-isocyanate, mercapto-ene (alkyne), and mercapto-epoxy to enhance the refractive index modulation.

[0136] Test Example 2

[0137] Evaluate the samples of Example 2 to further verify the mechanism and effect of the enhancement of the refractive index modulation of the third-order reaction-type photopolymer holographic recording material in the third stage. The results are as follows Figures 3 - 4 shown

[0138] When the oven heating time in step 5) of Example 2 is 0, 1, 4, 8, 12, 20, 36 h, respectively, test the angular selectivity curve of the sample and the infrared absorption of the mercapto group at 2560 cm -1 and the epoxy group at 895 cm -1 of the sample

[0139] Among them, the test method of the angular selectivity curve: use a laser beam with a total power of 10 mW, a diameter of 1 mm, and a wavelength of 532 nm to irradiate the above grating within the range of Bragg angle ±10°. The incident light passes through the grating, and part of the light is transmitted and part of the light is diffracted. Use a photometer to measure the transmitted light intensity and diffracted light intensity at different incident angles, and calculate the diffraction efficiency of the grating at different incident angles through formula (6).

[0140]

[0141] In the formula, η is the diffraction efficiency, I d is the diffracted light intensity, and I t is the transmitted light intensity

[0142] Draw a diffraction efficiency-angle curve according to the incident angle and the measured diffraction efficiency, fit the curve using the Kogelnik coupling theory, and calculate the refractive index modulation of the grating (DOI: 10.1002 / j.1538-7305.1969.tb01198.x).

[0143] From Figure 3 it can be seen that as the heating time increases, the refractive index modulation gradually increases; from Figure 4 the infrared test results of

[0144] it can be seen that the corresponding mercapto absorption peak and epoxy absorption peak both decrease with the increase of time, indicating that the increase of the refractive index modulation of the grating is closely related to the reaction of the above two groups Figures 3 - 4 Comprehensive

[0145] Test Example 3

[0146] Evaluate Examples 3 to 10 to verify and compare the holographic recording performance of the third-order reactive photopolymer holographic recording material under different formulations, as well as the enhancement effect of recording holographic gratings.

[0147] Steps 1)-3) of Examples 3 to 10 are the same as those of Example 1;

[0148] 4) Perform holographic recording exposure on the third-order reactive photopolymer holographic recording material sample in step 3). The holographic recording exposure light source is two coherent s-polarized laser beams with a light intensity of 1.5 mW / cm 2 , a diameter of 10 mm, and a wavelength of 532 nm. The two laser beams intersect at the sample at angles of 30.8°, 44.6°, and 83.4° respectively. The normal of the sample bisects the angle between the two laser beams, and the corresponding grating periods are 1000 nm, 700 nm, and 400 nm respectively. The exposure time is 60 s.

[0149] Using the method in Test Example 2, measure the grating refractive index modulation of the sample in step 4) "Completion of the second-stage exposure" and the sample in step 5) "Third-stage grating enhancement" respectively, and record them as the second-order refractive index modulation and the third-order refractive index modulation respectively, and calculate the enhancement ratio of the refractive index modulation. The test results are shown in Tables 6 to 7, Figures 5 - 6 as shown.

[0150] Table 6 Influence of the crosslinking density of the film-forming resin on the third-order reactive photopolymer holographic recording material in Examples 3 to 6

[0151]

[0152] Table 7 Influence of different ratios of recording monomers on the third-order reactive photopolymer holographic recording material in Examples 7 to 10

[0153]

[0154]

[0155] * Proportion of recording monomer = molar amount of recording monomer / (molar amount of recording monomer + molar amount of enhancing monomer)

[0156] From Tables 6 to 7 and Figures 5 - 6 it can be seen that for the third-order reactive photopolymer holographic recording material of the embodiments of the present invention, under the conditions of appropriate raw material components and ratios, with the help of the third-order reaction, at different grating periods, the refractive index modulation of the grating has a significant enhancement effect, and the enhancement effect can reach 40% to 80%. In addition, the enhancement ratio of the grating refractive index modulation increases with the increase of the proportion of the recording monomer; when the proportion of the recording monomer is 50%, the final refractive index modulation of the grating is the largest.

[0157] Test Example 4

[0158] Evaluate Comparative Examples 1 and 2 to verify the holographic recording performance of a photopolymer holographic recording material without introducing third-order reactions, as well as the enhancement effect of the recorded holographic grating. The test method is the same as that in Test Example 3, and the test results are shown in Table 8.

[0159] Table 8

[0160]

[0161] As can be seen from Table 8, in Comparative Example 1, since the epoxy-based enhancing monomer was replaced with an inert low-refractive-index component, even under the action of a photo-base generator, the third-order thiol-epoxy click reaction did not occur, and the inert low-refractive-index component did not undergo back migration. Therefore, the refractive index modulation degree of the holographic grating recorded by the photopolymer holographic recording material without introducing third-order reactions is relatively low, and there is no refractive index modulation enhancement effect.

[0162] In Comparative Example 2, since the enhancing epoxy monomer was not added, even under the action of a photo-base generator, the thiol-epoxy third-order enhancement reaction still did not occur. Therefore, the refractive index modulation degree of the grating is still relatively low, and the enhancement effect cannot be formed.

[0163] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A third-order reactive photopolymer holographic recording material, characterized in that, The raw materials include: 20 to 60 parts by weight of a thiol compound; 10 to 45 parts by weight of an isocyanate compound; 15 to 40 parts by weight of an olefin (alkyne) recording monomer; 15 to 40 parts by weight of an epoxy reinforcing monomer; 0.5 to 2 parts by weight of a radical photoinitiator; 0 to 0.5 parts by weight of a photosensitizer; 0 to 2 parts by weight of a photoacid generator.

2. The third-order reaction-type photopolymer holographic recording material according to claim 1, characterized in that, The content of the thiol compound is 30 to 50 parts by weight, preferably 30 to 45 parts by weight; The content of the isocyanate compound is 20 to 40 parts by weight, preferably 15 to 25 parts by weight; The content of the olefin (alkyne) recording monomer is 15 to 35 parts by weight, preferably 15 to 25 parts by weight; The content of the epoxy reinforcing monomer is 15 to 35 parts by weight, preferably 15 to 25 parts by weight.

3. The third-order reactive photopolymer holographic recording material according to claim 1 or 2, characterized in that, The molar amount of the olefin (alkyne) recording monomer accounts for 40 to 60% of the sum of the molar amounts of the olefin (alkyne) recording monomer and the epoxy reinforcing monomer.

4. The third-order reactive photopolymer holographic recording material according to claim 1 or 2, characterized in that, The thiol compound is a bifunctional or polyfunctional thiol compound; the isocyanate compound is a bifunctional or polyfunctional isocyanate; the refractive index difference between the olefin (alkyne) recording monomer and the epoxy reinforcing monomer is greater than 0.

1.

5. The third-order reaction-type photopolymer holographic recording material according to claim 4, characterized in that, The thiol compound is selected from one or more of bis(2-mercaptoethyl) sulfide, 2,5-dimethylmercapto-1,4-dithiane, ethylene glycol bis(2-mercaptoacetate), ethylene glycol bis(3-mercaptopropionate), hexylene glycol bis(2-mercaptoacetate), hexylene glycol bis(3-mercaptopropionate), 4-mercaptomethyl-3,6-dithia-1,8-octanedithiol, glyceryl tris(2-mercaptoacetate), glyceryl tris(3-mercaptopropionate), trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), bis(mercaptomethyl)-3,6,9-trithiaundecane-1,11-dithiol, pentaerythritol tetra(2-mercaptoacetate), pentaerythritol tetra(3-mercaptopropionate), dipentaerythritol hexa(2-mercaptoacetate), and dipentaerythritol hexa(3-mercaptopropionate); The isocyanate compound is a bifunctional or polyfunctional isocyanate, selected from one or more of 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthalene 1,5-diisocyanate, p-phenylene diisocyanate, butane-1,4-diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, dimethylbiphenyl diisocyanate, tetramethylm-xylene diisocyanate, cyclohexane diisocyanate, norbornane diisocyanate, dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, hexamethylene diisocyanate trimer, and isophorone diisocyanate trimer; 6. The third-order reactive photopolymer holographic recording material according to claim 4, wherein The structure of the olefin (alkyne) recording monomer is shown in formula (I): x is an integer from 1 to 6; y is an integer from 1 to 3; wherein RIG is one or more of aryl, haloaryl, heteroaryl, a group containing a thioether bond, an alkane group, a chloroalkane group, a bromoalkane group, an iodoalkane group, a siloxane group, an alkane group, a fluoroalkane group, etc.; CG is one or more of an alkyl group formed by lacking (x + y) hydrogens, an ester group, an amide group, an aromatic group, a group containing an ether bond, a group containing a thioether bond, a cycloalkane group, a heterocyclic group; RAG is a group with an unsaturated carbon-carbon double bond or carbon-carbon triple bond; The structure of the epoxy-based enhancing monomer is shown in formula (II): x' is an integer from 1 to 6; y' is an integer from 1 to 3; RIG' is selected from one or more of aryl, haloaryl, heteroaryl, a group containing a thioether bond, an alkane group, a chloroalkane group, a bromoalkane group, an iodoalkane group, a siloxane group, an alkane group, a fluoroalkane group, etc.; CG' is an alkyl group, an ester group, an amide group, an aryl group, a group containing an ether bond, a group containing a thioether bond, a cycloalkane group, a heterocyclic group formed by lacking (x' + y') hydrogens; preferably one or more of an ester group, an amide group, a group containing a thioether bond; ROAG is selected from one or more of an epoxyethyl group, an oxetanyl group, an oxidation cyclohexene group.

7. The third-order reactive photopolymer holographic recording material according to claim 5 or 6, characterized in that, The molar amount of the mercapto group in the thiol compound satisfies formula (2) ∑n thiol f thiol = ∑n isocyanate f isocyanate + ∑n ene f ene + 2 × ∑n yne f yne + ∑n epoxy f epoxy (2) where n thiol , n isocyanate , n ene , n yne , n epoxy are the molar amounts of the thiol compound, isocyanate compound, vinyl recording monomer, alkyne recording monomer, and epoxy reinforcing monomer, respectively; f thiol , f isocyanate , f ene , f yne , f epoxy are the functionalities of the thiol compound, isocyanate compound, vinyl recording monomer, alkyne recording monomer, and epoxy reinforcing monomer, respectively.

8. The third-order reactive photopolymer holographic recording material according to claim 7, characterized in that, For the thiol-isocyanate polycondensation reaction between the isocyanate compound and the thiol compound, the molar amounts of the isocyanate compound and the thiol compound should satisfy formula (3): Wherein, N thiol and N isocyanate are the molar amounts of the thiol compound and the isocyanate compound respectively, and f isocyanate is the functionality of the isocyanate compound.

9. A grating-enhanced product is formed by holographic recording exposure using the third-order reactive photopolymer holographic recording material according to any one of claims 1-8; In the holographic recording exposure, a thiol-ene(yne) radical addition reaction occurs between the ene(yne)-type recording monomer and the mercapto group on the film-forming resin; In the grating-enhanced product, under the conditions of ultraviolet and / or heating, a thiol-epoxy ring-opening addition reaction occurs between the epoxy-based enhancing monomer in the raw material and the remaining mercapto group on the holographic material film-forming resin, enhancing the refractive index modulation degree of the grating.

10. The use of the enhanced grating according to claim 9, characterized in that, The grating-enhanced product is used in a holographic display system.

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