Hyperbranched polysiloxane acrylate-based materials and devices and methods

Abstract

The present application relates to holographic projection display technical field, more particularly, to a kind of based on hyperbranched polysiloxane acrylate material and device and method, and total amount of hyperbranched polysiloxane acrylate and reactive comonomer is 100 mass parts, including: hyperbranched polysiloxane acrylate 40~50 parts, reactive comonomer 50~60 parts, RAFT reagent 0.1~0.3 parts, nematic liquid crystal 30~50 parts, photoinitiator 0.5~5 parts, co-initiator 0.5~5 parts, the number average molecular weight of hyperbranched polysiloxane acrylate is 2000~6000, and the number of polymerizable groups carried by each molecule is 10~30;Reactive comonomer is at least one of monofunctional acrylate and multifunctional acrylate. Holographic grating device can be prepared using the material, and it is helpful to consider higher diffraction efficiency and lower transmission haze under the condition of higher exposure light intensity and practical film thickness.

Description

Technical Field

[0001] This invention relates to the field of holographic projection display technology, and more specifically, to a material, device, and method based on hyperbranched polysiloxane acrylate. Background Technology

[0002] Holographic polymer-dispersed liquid crystal (HPDLC) gratings are periodic refractive index-modulated optical elements formed by laser interference photopolymerization inducing the separation of liquid crystal and polymer phases. Based on the Bragg diffraction effect, they can couple incident light to specific diffraction orders with extremely high efficiency, showing key application prospects in augmented reality (AR) diffraction waveguide coupling gratings, transparent displays, and holographic optical elements.

[0003] The fabrication of HPDLC gratings is essentially a photopolymerization-induced phase separation (PIPS) process: a homogeneous mixed solution containing photosensitive monomers, liquid crystals, and initiators is poured into a liquid crystal cell and exposed using dual-beam laser interference. In the bright region, the monomers undergo photopolymerization, increasing in molecular weight and decreasing their compatibility with the liquid crystals. This drives the liquid crystals to diffuse and enrich in the dark region, ultimately forming a refractive index grating with periodically alternating polymer-rich and liquid crystal-rich regions.

[0004] Currently, the main technical approaches to optimizing the performance of HPDLC materials focus on the dimension of "regulating the phase separation process." Specific methods include: altering the polymerization rate and gel point by adjusting the ratio of acrylate monomers and crosslinking agents with different functionalities, thereby affecting the liquid crystal diffusion window; or adding chain transfer agents such as thiols to the system to reduce the polymer molecular weight and delay gelation. The starting point of these techniques is to optimize the macroscopic phase separation between the liquid crystal and the polymer by regulating the polymerization reaction kinetics, thereby increasing refractive index modulation and improving diffraction efficiency.

[0005] Recent research has explored the introduction of reversible addition-fragmentation chain transfer (RAFT) reagents or hyperbranched polymers into HPDLC systems, aiming to improve polymerization controllability or crosslinking efficiency, respectively. However, when the preparation conditions of HPDLC shift from laboratory parameters (such as 3 μm film thickness and low light intensity) to the practical conditions required for industrialization (film thickness ≥ 8 μm to ensure sufficient absolute diffraction efficiency and light intensity ≥ 80 mW / cm² to achieve mass production speed), the transmission haze of the grating often increases significantly, thus affecting its practical application in fields such as AR waveguides. Existing technologies still have room for further improvement in achieving both high diffraction efficiency and low transmission haze under conditions of high light intensity and practical film thickness. Summary of the Invention

[0006] The present invention aims to overcome at least one of the defects (deficiencies) of the prior art and provide a material, device and method based on hyperbranched polysiloxane acrylate, so as to improve the problem that the existing HPDLC system is difficult to balance diffraction efficiency and transmission haze under high light intensity and practical film thickness conditions.

[0007] One object of the present invention is to provide a holographic polymer-dispersed liquid crystal material based on hyperbranched polysiloxane acrylate, wherein the total amount of hyperbranched polysiloxane acrylate and reactive comonomer is 100 parts by mass, and the holographic polymer-dispersed liquid crystal material comprises: 40-50 parts of hyperbranched polysiloxane acrylate, 50-60 parts of reactive comonomer, 0.1-0.3 parts of RAFT reagent, 30-50 parts of nematic liquid crystal, Photoinitiator 0.5-5 parts, Total initiator 0.5-5 parts, in, The number-average molecular weight of the hyperbranched polysiloxane acrylate is 2000-6000. The reactive comonomer is at least one of monofunctional acrylate and polyfunctional acrylate.

[0008] In this technical solution, the hyperbranched polysiloxane acrylate (HPSiA) is the main resin of the material system, with a number-average molecular weight of, for example, 2500, 3000, or 4000. Each molecule carries an average of 10 to 30 polymerizable groups (the sum of grafted acrylate groups and backbone vinyl groups); wherein the grafted acrylate groups are introduced by hydrosilylation grafting from an allyl compound containing acrylate groups, and the backbone vinyl groups originate from the repeating methyl vinylsiloxane unit in the starting material; for example, the average number of polymerizable groups carried per molecule is, for example, 16, 18, 20, 21, 22, 24, or 26. The RAFT reagent is a reversible addition-fragmentation chain transfer reagent, which acts as a polymerization kinetic regulator. The photoinitiator and co-initiator are preferably 1 to 3 parts each; the RAFT reagent is preferably 0.12 to 0.15 parts, and the nematic liquid crystal is preferably 35 to 40 parts.

[0009] Through systematic experiments, the inventors have found that using the aforementioned hyperbranched acrylate containing polysiloxane segments as the main resin, combined with dithiobenzoate or xanthate-based RAFT reagents, can achieve a combination of low haze and high diffraction efficiency under conditions of high light intensity and practical film thickness. In the embodiments of this invention, the combination of the aforementioned HPSiA with dithiobenzoate or xanthate-based RAFT reagents yields the preferred effect of achieving a haze H not exceeding 2.0% and a diffraction efficiency not less than 89% under the tested conditions.

[0010] Furthermore, the hyperbranched polysiloxane acrylate is prepared by reacting hydroxyl-terminated hyperbranched polymethylvinylsiloxane with an allyl compound containing acrylate groups in the presence of a hydrosilylation catalyst; and the molar ratio of the allyl compound containing acrylate groups to the Si-H groups in the hydroxyl-terminated hyperbranched polymethylvinylsiloxane is 0.45:1 to 0.9:1.

[0011] In this technical solution, the hyperbranched polysiloxane acrylate is obtained by grafting acrylate groups onto the terminal hydroxyl hyperbranched polymethylvinylsiloxane via a hydrosilylation reaction.

[0012] Furthermore, the terminal hydroxyl hyperbranched polymethylvinylsiloxane contains 50% to 80% mol% methylvinylsiloxane repeating units based on the total number of repeating units, has a number average molecular weight of 1500 to 4000, a hydroxyl value of 1.5 to 3.5 mmol / g, and a Si-H group content of 0.20 to 0.40 mol / 100g.

[0013] Furthermore, the hyperbranched polysiloxane acrylate accounts for 40% to 50% of the total mass of the hyperbranched polysiloxane acrylate and the reactive comonomer.

[0014] Furthermore, the RAFT reagent is selected from dithiobenzoic acid esters or xanthate esters.

[0015] Through systematic experiments, the inventors discovered that not all types of RAFT reagents can achieve low haze when combined with HPSiA. Under the same HPSiA system and preparation conditions, dithiobenzoate and xanthate RAFT reagents showed better results; while trithiocarbonate RAFT reagents exhibited significantly higher transmission haze under the same conditions. This indicates that the type of RAFT reagent selected in this invention has good compatibility with HPSiA.

[0016] Furthermore, the RAFT reagent is selected from one or more of 2-cyano-2-propylbenzene dithioester, 4-cyanopentanoic acid dithiobenzoate, and O-ethyl xanthoxyethyl acetate.

[0017] Further, the reactive comonomer is selected from one or more of isobornyl acrylate (IBOA), lauryl acrylate (LA), ethoxylated trimethylolpropane triacrylate (EO3-TMPTA), trimethylolpropane triacrylate (TMPTA), tripropylene glycol diacrylate (TPGDA), 1,6-hexanediol diacrylate (HDDA), and pentaerythritol triacrylate (PETA); and / or, The nematic liquid crystal is selected from E7 (Δn=0.224, n o =1.521), E8, E44, 5CB, 8CB, or one or more of these; and / or, The photoinitiator is selected from zeatan-based photosensitizers; and / or, The co-initiator is selected from amine compounds and / or organic sulfonic acid compounds.

[0018] In this technical solution, the photoinitiator is specifically selected from one or more of Rose Bengal (RB), Methylene Blue (MB), Erythrosin B, and Eosin Y.

[0019] The co-initiator is selected from one or more of N-phenylglycine (NPG), triethanolamine (TEOA), methyldiethanolamine (MDEA), and p-toluenesulfonic acid hydrate (p-TsOH).

[0020] Furthermore, each molecule of the hyperbranched polysiloxane acrylate carries an average of 10 to 30 polymerizable groups. These polymerizable groups are the sum of grafted acrylate groups and backbone vinyl groups. The grafted acrylate groups are introduced by hydrosilylation grafting of an allyl compound containing acrylate groups, and the backbone vinyl groups originate from the methyl vinyl siloxane repeating unit in the hydroxyl-terminated hyperbranched polymethyl vinyl siloxane of the starting material.

[0021] Furthermore, the hydrosilylation grafting reaction is carried out in the presence of a free radical polymerization inhibitor to suppress the free radical addition side reaction between the backbone vinyl group and the grafted acrylate double bond; the free radical polymerization inhibitor is selected from one or more of p-methoxyphenol (MEHQ), hydroquinone, and 2,6-di-tert-butyl-p-cresol (BHT), and the amount used is 50 to 500 ppm of the total mass of the reaction system; and / or, the hydrosilylation reaction is carried out under inert gas protection; and / or, the allyl compound containing the acrylate group is added dropwise at a temperature of 40 to 70°C, and the reaction is maintained at 50 to 70°C after the addition is complete.

[0022] In one or more embodiments of the present invention, the total mass of the reaction system is the total mass of the reaction mixture, including the solvent, and the free radical polymerization inhibitor is p-methoxyphenol (MEHQ), used in an amount of 100 ppm of the total mass of the silane reaction system.

[0023] Another object of the present invention is to provide a holographic grating device, which is made of any of the above-mentioned holographic polymer-dispersed liquid crystal materials.

[0024] Another object of the present invention is to provide a method for fabricating the above-mentioned holographic grating device, comprising the following steps: The components of the holographic polymer liquid crystal dispersion material are mixed and poured into a liquid crystal cell. After exposure under the interference light field formed by a dual-beam light source, it is placed under uniform light for post-curing to obtain the holographic grating device.

[0025] Furthermore, the thickness of the liquid crystal cell is 8~12μm; and / or, The irradiation power of the interference exposure is 80~150 mW / cm²; and / or, The post-curing time is 20-40 minutes; and / or, The interference exposure time is 1 to 5 minutes.

[0026] In some embodiments of the present invention, the above-mentioned holographic polymer-dispersed liquid crystal material premix is ​​poured into a liquid crystal cell with a cell thickness of 8 μm, and exposed by a 532 nm laser with a period of 450 nm using a laser of 80-150 mW / cm². After being cured for 20 minutes by uniform light of 405 nm with 50 mW / cm², the transmission haze of the resulting grating region to 550 nm visible light (measured according to GB / T2410 standard, after deducting the contribution of the glass substrate) can be no higher than 2.0%, and the first-order diffraction efficiency can be no less than 89%.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The material system of the present invention exhibits good comprehensive optical performance under exposure light intensity of 80-150 mW / cm² and film thickness of 8 μm. According to the embodiments, the obtained HPDLC grating can have a transmission haze of not more than 2.0% and a first-order diffraction efficiency of not less than 89%.

[0028] (2) The material system of the present invention exhibits a wide exposure application window in the range of 80 to 150 mW / cm², and its performance fluctuates little under the test conditions.

[0029] (3) The HPSiA described in this invention can be prepared according to the feeding ratio, starting material specifications and reaction conditions recorded in the specification. The device performance can be evaluated by diffraction efficiency and haze test, and it has good feasibility. Detailed Implementation

[0030] To enable those skilled in the art to better understand this solution, the present invention will be further described in detail below with reference to specific embodiments. Unless otherwise specified, the process methods used in the embodiments are conventional methods; and unless otherwise specified, the materials used are commercially available.

[0031] Table 1

[0032] Example 1 of raw material preparation (Preparation of hydroxyl-terminated hyperbranched polymethylvinylsiloxane) This preparation example follows the A2+B3 one-step polycondensation strategy reported by Chen et al. (Kelong Chen, Tong Zhang, Yi Cui, Zhiyong Wang, Bin Li. OH- and NH2-Terminated Hyperbranched Polysiloxanes: Controlled Synthesis, Characterization, Toughening, and Reinforcing Epoxy Resin. Macromolecular Chemistry and Physics, 2018, 219, 1800200). Hydroxyl-terminated hyperbranched polymethylvinylsiloxanes were prepared via polycondensation using diethylene glycol (DEG, A2 monomer) and organoalkoxysilanes as raw materials. It should be noted that Chen et al. (Macromolecular Chemistry and Physics, 2018, 219, 1800200) originally used aminopropyltriethoxysilane (KH550) as the B3 monomer. In this invention, it is replaced with vinyl-containing / hydrogen-containing silanes to introduce subsequently graftable vinyl and Si-H sites into the backbone. The raw materials, their specifications, and uses are shown in Table 2. Table 2

[0033] Preparation steps: Under nitrogen protection, diethylene glycol (DEG) and organoalkoxysilane monomers were fed into a four-necked flask using the A2+B3 one-step method described in the reference. For example, using 95.51 g (0.90 mol) of DEG, the total amount of organoalkoxysilane monomers was 0.77 mol, including 68.5 g (0.36 mol) of vinyltriethoxysilane (VTES), 19.6 g (0.11 mol) of methyltriethoxysilane (MTES), and 40.3 g (0.3 mol) of methyldiethoxysilane (MDES). The molar ratio of VTES to MTES can be adjusted according to the target proportion of repeating methylvinylsiloxane units, and the amount of MDES can be adjusted according to the target Si-H content. The reaction was carried out under a gradient temperature program with stirring: 120℃ for 60 minutes, 130℃ for 20 minutes, 140℃ for 20 minutes, 150℃ for 20 minutes, and finally raised to 170℃ and held for about 1 hour. The byproduct ethanol was continuously distilled off during the reaction, with the distillation temperature controlled at 78±2℃. Heating was stopped when the distillate decreased significantly and the viscosity of the system increased markedly. The reaction solution was cooled to room temperature to obtain a pale yellow, transparent, viscous liquid, which is the hydroxyl-terminated hyperbranched polymethylvinylsiloxane.

[0034] Synthesis Example 1 (Synthesis of HPSiA-1) Under nitrogen protection, 100 g of hydroxyl-terminated hyperbranched polymethylvinylsiloxane prepared in Example 1 was added to a four-necked flask equipped with a mechanical stirrer, thermometer, dropping funnel, and condenser. The polymer had a hydroxyl value of 2.8 mmol / g, a Si-H content of 0.30 mol / 100 g, and a number-average molecular weight of approximately 2200. 250 mL of anhydrous toluene was added to the flask to dissolve the polymer completely, followed by the addition of 100 ppm of p-methoxyphenol (MEHQ, based on the total mass of the reaction system) as a free radical polymerization inhibitor.

[0035] 0.10 mmol of Karstedt catalyst was added to the above solution at room temperature, and after stirring, the temperature was raised to 55 °C. 0.16 mol of allyl acrylate was dissolved in 50 mL of anhydrous toluene to prepare a dropping solution. The dropping rate was controlled, and the solution was slowly added dropwise to the reaction system over 1.5 hours to allow the allyl groups to undergo catalytic hydrosilylation with the Si-H groups. After the addition was complete, the reaction was continued at 55–60 °C for 4 hours. After the reaction was stopped and cooled to room temperature, the solution was filtered through activated carbon adsorption, and the solvent and unreacted monomers were removed by vacuum distillation at 40 °C to obtain a light yellow viscous liquid, HPSiA-1. Based on the Si-H content of the starting materials (0.30 mol / 100 g), number-average molecular weight (approximately 2200), and allyl acrylate feed amount (0.16 mol), 100 g of hydroxyl-terminated hyperbranched polymethylvinylsiloxane corresponds to approximately 0.0455 mol of polymer molecules. Therefore, the starting polymer theoretically contains approximately 6.6 Si-H sites per molecule on average. In Synthesis Example 1, the allyl acrylate feed amount was 0.16 mol. If we assume that one allyl group consumes one Si-H site, then the average number of acrylate groups grafted onto each hyperbranched polysiloxane molecule is approximately 3.5. On the other hand, based on the molar ratio of vinyltriethoxysilane (VTES) to methyldiethoxysilane (MDES) in Raw Material Preparation Example 1 (approximately 1.1:1), each molecule retains approximately 7 to 8 skeletal vinyl groups derived from the repeating unit of the skeletal methylvinylsiloxane. In summary, the average total number of polymerizable groups per molecule, that is, the sum of grafted acrylate groups and backbone vinyl groups, is approximately 10 to 12.

[0036] Synthesis Example 2 (Synthesis of HPSiA-2) Using 100 g of the same hydroxyl-terminated hyperbranched polymethylvinylsiloxane, the allyl acrylate addition was adjusted to 0.14 mol (equivalent to a Si-H group molar ratio of 0.47:1), and the remaining operations were the same as in Synthesis Example 1, to obtain HPSiA-2. The number average molecular weight (Mn) of the obtained product HPSiA-2 was approximately 2500. Based on the feed ratio, it is estimated that there are approximately 3.1 grafted acrylate groups per molecule on average, and approximately 10–11 polymerizable groups (the sum of the grafted acrylate and the backbone vinyl groups).

[0037] Synthesis Example 3 (Synthesis of HPSiA-3) Using 100 g of the same hydroxyl-terminated hyperbranched polymethylvinylsiloxane as in Synthesis Example 1, the allyl acrylate addition was adjusted to 0.24 mol (equivalent to a Si-H group molar ratio of 0.8:1). The remaining operations were the same as in Synthesis Example 1, and HPSiA-3 was finally synthesized. The number-average molecular weight (Mn) of the obtained product HPSiA-3 was approximately 2700. Based on the feed ratio, it is estimated that approximately 5.3 acrylate groups are grafted per molecule on average, and approximately 12–13 polymerizable groups are present.

[0038] Comparative Example 1 (Preparation of control resin HPSiA-C, non-polysiloxane backbone) 100g of commercially available hydroxyl-terminated hyperbranched polyester (Boltorn H40 type, hydroxyl value 4.8 mmol / g, Mn approximately 2800, backbone of COC ester bonds, without Si-O segments) was dissolved in 250 mL of anhydrous dichloromethane. 0.22 mol of acryloyl chloride and 0.25 mol of triethylamine were added, and the mixture was reacted in an ice bath for 2 hours, then at room temperature for 24 hours. After washing with water, drying, and vacuum distillation, a light yellow viscous liquid, HPSiA-C, was obtained. Mn = 3100. Based on the feed ratio, it is estimated that each molecule contains approximately 6 grafted acrylate groups (this control resin has a hydrocarbon backbone and does not contain skeletal vinyl groups, therefore the polymerizable groups are also approximately 6). This resin was used only for comparative experiments.

[0039] The specifications of the starting material for the synthesis of HPSiA, "hydroxyl-terminated hyperbranched polymethylvinylsiloxane", such as hydroxyl value, Si-H content, number-average molecular weight, and the proportion of repeating units of methylvinylsiloxane, can be provided by the supplier or determined using conventional characterization methods in the field.

[0040] Regarding the acrylate functionality of the product HPSiA, in this invention, "polymerizable groups" refers to the average total number of polymerizable groups carried per molecule, which is the sum of grafted acrylate groups and backbone vinyl groups. The grafted acrylate groups are introduced by hydrosilylation of an allyl compound containing acrylate groups, while the backbone vinyl groups originate from the methyl vinyl siloxane repeating units in the hydroxyl-terminated hyperbranched polymethyl vinyl siloxane of the starting material. The number of polymerizable groups can be theoretically estimated as follows: based on the measured Si-H content of the starting material, the number-average molecular weight of the starting material, and the molar ratio, the average number of acrylate groups grafted per molecule is estimated, and combined with the estimated number of vinyl repeating units in the backbone, the average total number of polymerizable groups carried per molecule is obtained. It should be noted that this value is a theoretical estimate, based on a reasonable expectation that the hydrosilylation reaction will proceed sufficiently under the catalytic conditions, and can be used to characterize the structural features of the product. For those skilled in the art, the reproducibility of HPSiA synthesis is guaranteed by the feed ratio and starting material specifications—operating according to the feed ratio and synthesis conditions described in the specification will yield HPSiA products with the same structural features. Furthermore, as shown in the examples below, HPSiA synthesized in different batches can achieve grating performance with a haze H not exceeding 2.0% and a diffraction efficiency η not less than 89% under the same formulation and preparation conditions. From the perspective of the final effect, this fully verifies the reproducibility of the synthesis method and the consistency of the product structure.

[0041] Furthermore, during the hydrosilylation grafting process, the double bonds of the backbone vinyl group and the grafted acrylate may undergo free radical addition side reactions under the influence of heat, light, or residual free radicals, leading to an increase in product molecular weight, crosslinking, or even gelation, which in turn affects the phase separation and final haze of HPDLC. To address this, this invention incorporates a free radical polymerization inhibitor (such as p-methoxyphenol MEHQ) into the grafting reaction, employs inert gas protection, controls the monomer dropping rate and reaction temperature, and slowly adds the allyl compound containing the acrylate group to suppress the aforementioned free radical side reactions, ensuring controllable product structure and batch stability. The reproducibility of the synthesis method is ensured by the feed ratio, starting material specifications, and the aforementioned side reaction control measures.

[0042] Example 1 This embodiment provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a fabrication method, specifically including the following steps: (1) Preparation of holographic polymer-dispersed liquid crystal materials Under light-protected conditions, 45 parts by mass of HPSiA-1, 40 parts by mass of isobornyl acrylate (IBOA), and 15 parts by mass of ethoxylated trimethylolpropane triacrylate (EO3-TMPTA) were weighed sequentially and stirred until homogeneous and transparent. Then, 38 parts by mass of nematic liquid crystal E7, 2 parts by mass of photoinitiator RB, 2 parts by mass of co-initiator NPG, and 0.15 parts by mass of RAFT reagent 2-cyano-2-propylphenyl dithioester were added. The mixture was stirred in a 30°C water bath until completely dissolved, and then filtered through a 0.2 μm filter to obtain a homogeneous premix, i.e., the holographic polymer-dispersed liquid crystal material.

[0043] (2) Fabrication of HPDLC grating devices The premixed liquid was poured into an 8 μm thick, unoriented planar liquid crystal cell under darkroom conditions. A 532 nm solid-state laser was used for dual-beam split-interference exposure, with the interference angle corresponding to the formation of a holographic grating with a period of 450 nm. The total incident light power density was 100 mW / cm². Exposure was stopped after the first-order diffraction efficiency stabilized, with an exposure time of approximately 3 min. Then, post-curing was performed for 20 min with uniform light at 405 nm and 50 mW / cm² to obtain the HPDLC grating device.

[0044] (3) Performance testing Transmitted haze: According to GB / T 2410 standard, it is measured using a haze meter with a collimated beam of 550 nm. After subtracting the haze of the glass substrate, H=1.8%.

[0045] First-order diffraction efficiency: η = 90.5% was measured using a grating diffraction efficiency meter with collimated probe light at a Bragg angle of 550 nm.

[0046] Example 1 - Batch Repeat 1 Following the same feed ratio and operating conditions as in Example 1, a second batch of HPSiA-1 was synthesized. Using the exact same formulation and preparation conditions as in Example 1, HPDLC grating devices were fabricated using this batch of HPSiA-1. Test results were obtained using the same testing methods: η = 90.2%, H = 1.9%.

[0047] Example 1 - Batch Repeat 2 Following the same feed ratio and operating conditions as in Example 1, a third batch of HPSiA-1 was synthesized. Using the exact same formulation and preparation conditions as in Example 1, HPDLC gratings were fabricated using this batch of HPSiA-1. Test results were obtained using the same testing methods: η = 90.6%, H = 1.7%.

[0048] The performance data of the gratings fabricated by the above three batches of HPSiA-1 are summarized in Table 3.

[0049] Table 3 Performance repeatability of HPSiA-1 from different batches

[0050] As shown in Table 3, the HPDLC gratings prepared from the three independently synthesized batches of HPSiA-1 exhibited highly consistent diffraction efficiencies and haze (η fluctuation ≤ 0.4%, H fluctuation ≤ 0.2%). These results fully demonstrate that, following the feed ratio and synthesis steps provided in this invention, the obtained HPSiA products exhibit good batch-to-batch reproducibility in achieving the aforementioned grating performance, and the consistency of the product structure was effectively verified by the final performance.

[0051] Example 2 This embodiment provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a preparation method. The difference from Example 1 is that HPSiA-1 in Example 1 is replaced with an equal mass of HPSiA-3, and the RAFT reagent in Example 1 is replaced with an equal mass of 4-cyanopentanoic acid dithiobenzoate. All other aspects are identical. Test results obtained using the same testing method are: H = 1.9%, η = 90.0%.

[0052] Example 3 This embodiment provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a preparation method. The difference from Example 1 is that HPSiA-1 in Example 1 is replaced with an equal mass of HPSiA-2 (provided by Synthesis Example 2), the reactive comonomers are adjusted to 40 parts of lauryl acrylate (LA) and 15 parts of trimethylolpropane triacrylate (TMPTA), and the RAFT reagent is replaced with 0.12 parts by mass of ethyl O-ethyl xanthate. The rest is the same as in Example 1. Test results were obtained using the same testing method: H = 2.0%, η = 89.8%.

[0053] Example 4 This embodiment provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a preparation method thereof. The difference from Embodiment 1 is that the total incident light power density is set to 80 mW / cm², while the rest is the same as in Embodiment 1. Performance tests were conducted using the same methods, and the test results were obtained as follows: H = 1.5%, η = 91.2%.

[0054] Example 5 This embodiment provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a fabrication method. The difference from Embodiment 1 is that the total incident light power density is set to 120 mW / cm², while the rest is the same as in Embodiment 1. Test results were obtained using the same testing method: H = 1.9%, η = 90%.

[0055] Example 6 This embodiment provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a preparation method thereof. The difference from Embodiment 1 is that the total incident light power density is set to 150 mW / cm², while the rest is the same as in Embodiment 1. Test results were obtained using the same testing method: H = 2.0%, η = 89.2%.

[0056] The performance of Examples 1, 4-6 under different exposure light intensities is summarized in Table 4.

[0057] Table 4

[0058] Comparative Example 1 (HPSiA-free - conventional linear acrylate system) This comparative example provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a preparation method. The difference from Example 1 is that HPSiA-1 in Example 1 is replaced with 60 parts by mass of linear bifunctional aliphatic polyurethane acrylate (CN991, Sartomer), and the composition of the reactive comonomer is adjusted accordingly to include 30 parts by mass of IBOA and 10 parts by mass of EO3-TMPTA. The rest is the same as in Example 1. Test results obtained using the same testing method are: η = 79.5%, H = 10.8%.

[0059] Comparative Example 2 (Polysiloxane-free backbone - hyperbranched polyester acrylate + RAFT) This comparative example provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a preparation method. The difference from Example 1 is that HPSiA-1 in Example 1 is replaced with an equal mass of HPSiA-C provided in Comparative Example 1; otherwise, the methods are the same as in Example 1. Test results obtained using the same testing methods are: η = 83.2%, H = 6.5%.

[0060] Comparative Example 3 (without RAFT) This comparative example provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a preparation method. The difference from Example 1 is that the RAFT reagent 2-cyano-2-propylphenyl dithioester is not added; otherwise, it is the same as Example 1. Test results obtained using the same testing method are: η=88%, H=5.2%.

[0061] Comparative Example 4 (RAFT reagent is a trithiocarbonate) This comparative example provides a holographic polymer-dispersed liquid crystal material, an HPDLC grating device, and a preparation method. The difference from Example 1 is that the RAFT reagent in Example 1 is replaced with an equal mass of S,S'-bis(α,α'-dimethyl-α''-acetic acid) trithiocarbonate (a trithiocarbonate-based RAFT reagent). The rest is the same as in Example 1. Test results obtained using the same testing method are: η=86%, H=4.8%.

[0062] Table 5 summarizes the performance of the HPDLC grating devices of Examples 1 to 6 and Comparative Examples 1 to 4.

[0063] Table 5

[0064] Comparative Example 1 shows that when conventional linear acrylates are used instead of the HPSiA of the present invention, the combination of low haze and high diffraction efficiency cannot be obtained under the same preparation conditions.

[0065] Comparative Example 2 shows that even with a hyperbranched topology, if the framework does not contain polysiloxane segments, the transmitted haze of the resulting device is still significantly increased, making it difficult to achieve the overall performance comparable to that of the embodiments of the present invention. It is worth noting that both the control resins HPSiA-C and HPSiA-1 have hyperbranched structures, and under the same conditions as the RAFT reagent and other components, the haze of the resulting devices was 6.5% and 1.8%, respectively, showing a significant difference. This result indicates that the performance difference mainly stems from the structural difference between the polysiloxane and non-polysiloxane frameworks, and not solely from the estimated number of polymerizable groups.

[0066] Comparative Example 3 shows that adding the RAFT reagent to the system helps reduce transmission haze and improve the overall performance of the device.

[0067] Comparative Example 4 shows that not all types of RAFT reagents can be combined with HPSiA to achieve low haze. Compared with the trithiocarbonate RAFT reagents tested, dithiobenzoate and xanthate RAFT reagents showed better results.

[0068] Table 5 shows that, under the tested conditions, the haze values ​​of the embodiments of the present invention and batch-to-batch repeatability were all no higher than 2.0%, and the diffraction efficiency was no lower than 89%. Comparative data indicates that when using a resin without a polysiloxane backbone, without adding RAFT reagents, or selecting an incompatible RAFT type, the overall performance of the device decreased to varying degrees. The above experimental results demonstrate that the combination of hyperbranched acrylate (HPSiA) containing polysiloxane segments with dithiobenzoate or xanthate-based RAFT reagents is the preferred technical solution for achieving lower haze and higher diffraction efficiency under the tested conditions.

[0069] Those skilled in the art will understand that the molecular weight and number of polymerizable groups of HPSiA can be controlled by adjusting the molecular weight of the raw materials and the feed ratio; the proportion of HPSiA and the amount of RAFT reagent will affect the crosslinking density and polymerization kinetics. Based on the verified parameter ranges in the examples, including Mn, the number of polymerizable groups, the feed ratio, the mass fraction of HPSiA, the amount of RAFT reagent, etc., and in combination with conventional experimental methods in the art, those skilled in the art can determine the specific implementation conditions for achieving the purpose of this invention within the scope defined by the claims.

[0070] The above embodiments of the present invention are merely examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A holographic polymer-dispersed liquid crystal material based on hyperbranched polysiloxane acrylate, characterized in that, Based on a total mass of 100 parts by weight of hyperbranched polysiloxane acrylate and reactive comonomer, the holographic polymer-dispersed liquid crystal material comprises: 40-50 parts of hyperbranched polysiloxane acrylate, 50-60 parts of reactive comonomer, 0.1-0.3 parts of RAFT reagent, 30-50 parts of nematic liquid crystal, Photoinitiator 0.5-5 parts, Total initiator 0.5-5 parts, in, The number-average molecular weight of the hyperbranched polysiloxane acrylate is 2000-6000. The reactive comonomer is at least one of monofunctional acrylate and polyfunctional acrylate; The reactive comonomer is selected from one or more of isobornyl acrylate, lauryl acrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, and pentaerythritol triacrylate.

2. The holographic polymer-dispersed liquid crystal material based on hyperbranched polysiloxane acrylate according to claim 1, characterized in that, Each molecule of the hyperbranched polysiloxane acrylate carries an average of 10 to 30 polymerizable groups.

3. The holographic polymer-dispersed liquid crystal material based on hyperbranched polysiloxane acrylate according to claim 1, characterized in that, The hyperbranched polysiloxane acrylate is prepared by reacting hydroxyl-terminated hyperbranched polymethylvinylsiloxane with an allyl compound containing acrylate groups in the presence of a hydrosilylation catalyst; and the molar ratio of the allyl compound containing acrylate groups to the Si-H groups in the hydroxyl-terminated hyperbranched polymethylvinylsiloxane is 0.45:1 to 0.9:

1.

4. The holographic polymer-dispersed liquid crystal material based on hyperbranched polysiloxane acrylate according to claim 3, characterized in that, The hydrosilylation grafting reaction is carried out in the presence of a free radical polymerization inhibitor; the free radical polymerization inhibitor is selected from one or more of p-methoxyphenol, hydroquinone, and 2,6-di-tert-butyl-p-cresol, and the amount of the free radical polymerization inhibitor is 50–500 ppm of the total mass of the hydrosilylation reaction system; and / or, The hydrosilylation reaction is carried out under an inert gas atmosphere; and / or, In the hydrosilylation reaction, the allyl compound containing acrylate groups is added dropwise to the reaction system of terminal hydroxyl hyperbranched polymethyl vinyl siloxane at a temperature of 40–70°C, and the reaction is maintained at 50–70°C after the addition is complete.

5. The holographic polymer-dispersed liquid crystal material based on hyperbranched polysiloxane acrylate according to claim 3, characterized in that, The terminal hydroxyl hyperbranched polymethylvinylsiloxane contains 50% to 80% mol% methylvinylsiloxane repeating units based on the total number of repeating units, has a number average molecular weight of 1500 to 4000, a hydroxyl value of 1.5 to 3.5 mmol / g, and a Si-H group content of 0.20 to 0.40 mol / 100g.

6. The holographic polymer-dispersed liquid crystal material based on hyperbranched polysiloxane acrylate according to claim 1, characterized in that, The RAFT reagent is selected from dithiobenzoate compounds or xanthate compounds.

7. A holographic grating device, characterized in that, The holographic grating device is made from the holographic polymer-dispersed liquid crystal material as described in any one of claims 1 to 6.

8. A method for fabricating a holographic grating device according to claim 7, characterized in that, Includes the following steps: The components of the holographic polymer-dispersed liquid crystal material are mixed and poured into a liquid crystal cell. After exposure under the interference light field of a dual-beam light source, the material is placed under uniform light for post-curing to obtain the holographic grating device.

9. The preparation method according to claim 8, characterized in that, The thickness of the liquid crystal cell is 8~12μm; and / or, The irradiation power of the interference exposure is 80~150 mW / cm²; and / or, The post-curing time is 20-40 minutes.

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