Modified polysilazane and preparation method thereof, silicon carbonitride ceramic and preparation method thereof

Abstract

This application relates to the field of polymer and ceramic materials technology, and particularly to modified polysilazane and its preparation method, and silicon carbon nitride ceramics and their preparation method. The modified polysilazane comprises a polysilazane backbone, isocyanate groups, and photosensitive groups. The carbon atoms of the isocyanate groups are bonded to at least a portion of the nitrogen atoms of the polysilazane backbone, and the photosensitive groups are bonded to the nitrogen atoms of the isocyanate groups. Using the isocyanate groups as a bridge between the polysilazane backbone and the photosensitive groups gives the modified polysilazane high ultraviolet light sensitivity. Therefore, modified polysilazane can greatly improve the efficiency of photocuring silicon carbon nitride ceramics and can also adjust the yield of photocured ceramics. The preparation method includes performing an addition reaction of raw materials comprising polysilazane and an isocyanate compound containing photosensitive groups in an inert atmosphere. In the preparation of silicon carbon nitride ceramics, raw materials comprising modified polysilazane and a photoinitiator can be subjected to ultraviolet light curing treatment in an inert atmosphere.

Description

1. Specification of Modified Polysilazane and its Preparation Method, Silicon Carbon Nitrogen Ceramics and their Preparation Methods Technical Field This application relates to the field of polymer and ceramic materials technology, and particularly to modified polysilazane and its preparation methods, silicon carbon nitrogen ceramics and their preparation methods. Background Technology Polysilazane compounds can be used as precursors to convert into silicon carbon nitrogen ceramics. In particular, the technical solution of using polyborosilicate as a precursor to convert into silicon borosilicate ceramics has many advantages over traditional sintered ceramics. On the one hand, compared with traditional powder-sintered silicon borosilicate ceramics, it has superior processing and forming performance and a lower preparation temperature; on the other hand, the obtained ceramics have excellent thermal stability, mechanical stability, and chemical stability at high temperatures. Precursor-converted silicon borosilicate ceramics have been developed into various applications in various fields, including high-temperature protection materials and electromagnetic wave absorbing materials in the aerospace field, and high-temperature resistant materials and functional materials in electrical engineering and nanoelectronics. The curing process of polyborosilicate preforms (mainly including thermosetting and photosetting) has a crucial impact on the morphology and properties of the final ceramic product. Thermal curing is unfavorable for preparing ceramic products with complex morphologies, while photocuring has inherent advantages in this area. Currently, there are two main methods for photocuring polyborosilazanes. One method involves introducing unsaturated groups such as vinyl groups into the chemical structure of the polyborosilazane to achieve photoinitiated free radical polymerization of carbon-carbon double bonds. However, the number of carbon-carbon double bonds that can be introduced is limited, and these bonds are not highly sensitive to ultraviolet light, resulting in a relatively slow curing rate. The other method involves physically mixing the polyborosilazane with ultraviolet-sensitive acrylate compounds to achieve a rapid curing reaction. However, this physical mixing inevitably leads to a decrease in ceramic yield. Other techniques for preparing silicon-carbon-nitrogen ceramics using polysilazanes also suffer from the aforementioned problems of low curing rates and low ceramic yields. HK 20138787 A 2 Summary of the Invention The purpose of this application is to provide modified polysilazane and its preparation method, as well as silicon carbon nitride ceramics and their preparation method, aiming to solve the problems of low curing rate and low ceramic yield when preparing silicon carbon nitride ceramics from polysilazane in the prior art. To achieve the above-mentioned purpose, the technical solution adopted in this application is as follows: Firstly, this application provides a modified polysilazane, comprising a polysilazane backbone, isocyanate groups, and photosensitive groups. The carbon atoms of the isocyanate groups are bonded to at least a portion of the nitrogen atoms of the polysilazane backbone, and the photosensitive groups are bonded to the nitrogen atoms of the isocyanate groups. This application's modified polysilazane, by bonding the carbon atoms of the isocyanate groups to at least a portion of the N atoms of the polysilazane backbone and the photosensitive groups to the nitrogen atoms of the isocyanate groups, uses the isocyanate groups as a bridge between the polysilazane backbone and the photosensitive groups, thereby giving the modified polysilazane high ultraviolet light sensitivity.Compared to existing technologies that directly introduce carbon-carbon double bonds into polysilazane or directly mix it with acrylic monomers to prepare precursors for silicon-carbon-nitrogen ceramics, the modified polysilazane of this application can greatly improve the efficiency of photocuring for silicon-carbon-nitrogen ceramics. Simultaneously, the type and number of photosensitive groups can be adjusted, thereby regulating the yield of the photocured ceramics. Therefore, the modified polysilazane of this application can achieve dual optimization of efficiency and yield when used to prepare silicon-carbon-nitrogen ceramics. Secondly, this application provides a method for preparing the modified polysilazane described above, comprising the following steps: In an inert atmosphere, a raw material including polysilazane and an isocyanate compound containing photosensitive groups undergoes an addition reaction, causing the isocyanate groups of the isocyanate compound to graft onto the nitrogen atoms of the polysilazane backbone. Since the isocyanate groups in the isocyanate compound have high chemical reactivity, the above preparation method allows the isocyanate groups to efficiently undergo an addition reaction with the nitrogen-hydrogen bonds in the polyborosilicate, grafting the isocyanate groups onto the nitrogen atoms of the polysilazane backbone. Furthermore, photosensitive groups are efficiently introduced into the chemical structure of polysilazane to obtain the aforementioned modified polysilazane. Compared to existing methods such as directly introducing carbon-carbon double bonds into polysilazane or physically mixing with acrylic monomers, this preparation method offers more controllable processes. The photocuring rate and yield of the modified polysilazane used for ceramic preparation obtained through chemical modification are higher. Thirdly, this application provides a silicon-carbon-nitrogen ceramic, obtained by curing the modified polysilazane included in the above-described application or prepared by the above-described method. Since the silicon-carbon-nitrogen ceramic of this application is obtained by curing and pyrolyzing the aforementioned modified polysilazane, during the pyrolysis process, the modified polysilazane is transformed into a ceramic material containing silicon, carbon, and nitrogen elements. Depending on the type of polysilazane used, it may also contain elements such as boron and aluminum, forming various phase domain structures within the ceramic material. This results in strong high-temperature resistance, oxidation resistance, and microwave absorption properties, making it suitable for various technical fields. Fourthly, this application provides a method for preparing the silicon-carbon-nitrogen ceramic described above, comprising the following steps: In an inert atmosphere, raw materials including modified polysilazane and a photoinitiator are subjected to ultraviolet light curing treatment. In this preparation method, since the modified polysilazane contains photosensitive groups, under the action of the photoinitiator and ultraviolet light, the photosensitive groups in the modified polysilazane will crosslink and solidify, and the main chain of the polysilazane will also undergo cleavage, with silicon, nitrogen, carbon, and other elements in the polymer recombinating. Therefore, silicon-carbon-nitrogen ceramics can be obtained after ultraviolet light curing treatment of the raw materials of modified polysilazane and photoinitiator. This preparation method has a controllable process, the ultraviolet light curing rate is fast and controllable, the ceramic yield is high, and ceramic products with complex structures can be prepared.The accompanying drawings are provided to more clearly illustrate the technical solutions in the embodiments of this application. The drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 is a schematic diagram of the chemical reaction involved in the preparation of modified polysilazane in Example A1 of this application; Figure 2 is the Fourier transform infrared spectrum of the raw materials and the modified polysilazane obtained in Example A1 of this application; Figure 3 is the differential scanning calorimetry curve of modified polysilazane in Example A1 of this application with different amounts of photoinitiator and polyborosilicate KH-PSNB-1 in Comparative Example A1 with 2 wt.% photoinitiator in the process of preparing ceramics by ultraviolet curing; Figure 4 is the thermogravimetric curve of modified polyborosilicate obtained in Example A1 of this application and polyborosilicate in Comparative Example A1 in the process of preparing ceramics by ultraviolet curing; Figure 5 is the thermogravimetric curve and differential thermal analysis curve of modified polyborosilicate obtained in Comparative Example A3. Detailed Description To make the technical problems, technical solutions and beneficial effects to be solved by this application clearer, the following describes this application in further detail with reference to the embodiments. It should be understood that the specific embodiments described herein are merely for explaining this application and are not intended to limit this application. In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. In this application, "at least one" refers to one or more, and "more" refers to two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. It should be understood that in the various embodiments of this application, the sequence number of the above processes does not imply the order of execution. Some or all steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component (HK 20138787 A 5), but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature. A first aspect of the embodiments of this application provides a modified polysilazane, comprising a polysilazane backbone, isocyanate groups, and photosensitive groups, wherein the carbon atoms of the isocyanate groups are bonded to at least a portion of the nitrogen atoms of the polysilazane backbone, and the photosensitive groups are bonded to the nitrogen atoms of the isocyanate groups. The modified polysilazane of this application improves ultraviolet light sensitivity by combining carbon atoms of isocyanate groups with at least a portion of the nitrogen atoms of the polysilazane backbone and photosensitive groups with the nitrogen atoms of the isocyanate groups. This uses the isocyanate groups as a bridge between the polysilazane backbone and the photosensitive groups. Compared to existing technologies that directly introduce carbon-carbon double bonds into polysilazane or directly mix it with acrylic monomers to prepare precursors for silicon-carbon-nitrogen ceramics, the modified polysilazane of this application significantly improves the efficiency of photocuring for silicon-carbon-nitrogen ceramics. Furthermore, the type and number of photosensitive groups can be adjusted to regulate the yield of the photocured ceramics. Therefore, the modified polysilazane of this application achieves dual optimization of efficiency and yield when used to prepare silicon-carbon-nitrogen ceramics. In some embodiments, the modified polysilazane comprises repeating units as shown in the general chemical formula (I): HK 20138787 A 6 (I). In formula (I), isocyanate groups are seen bonded to the N atoms of the polysilazane backbone. In some embodiments, R3 is a photosensitive group, which includes at least one of acrylate groups and methacrylate groups; "includes" here means "contains," as in the example, the photosensitive group includes acrylate groups, but this does not mean that R3 is only an acrylate group; R3 can also be a group containing acrylate and alkyl segments. These photosensitive groups can be cross-linked and cured under ultraviolet light. By bonding to the nitrogen atoms of the isocyanate groups and the carbon atoms of the isocyanate groups to the polysilazane backbone, the modified polysilazane has high ultraviolet light sensitivity, which can improve the curing efficiency and yield of silicon carbon nitride ceramics. In some embodiments, a is 5 to 10; in exemplary embodiments, it may include, but is not limited to, any value of 5, 7, 8, 10 or any range between two values. The value of a represents the degree of polymerization of the silazane backbone. The larger the value of a, the higher the degree of polymerization, the larger the polymer scale, and the slower the subsequent curing rate, but the yield will be higher. Choosing a suitable value for the silazane backbone is beneficial to balance these properties.In some embodiments, R1 and R2 may be the same or different, including at least one of alkyl, hydrogen, vinyl, and phenyl. In some embodiments, the polysilazane backbone includes at least one of polyboron silazane backbone, polyaluminum silazane backbone, and polyboron aluminum silazane backbone; polysilazane is a general term for silazane polymers, and in addition to the polysilazane backbone, it may also contain various doping elements to form rich side chains, constituting a variety of polymers with different forms. In the example, when the polysilazane is polyboron silazane, it can be referred to the following formula (II): HK 20138787 A 7 (II) Wherein, R4 and R5 may be the same or different, including at least one of alkyl, hydrogen, vinyl, and phenyl. b is 5 to 10. Introducing these boron and aluminum elements can greatly improve the performance of ceramics made from modified polysilazane. Among them, the introduction of boron can greatly reduce the molecular diffusion coefficient of silicon and nitrogen elements and increase the crystallization temperature of the ceramics. Simultaneously, BN bonds can inhibit ceramic crystallization and Si3N4 decomposition, significantly improving the high-temperature resistance and density of the prepared ceramics, and reducing surface porosity and grain size. In some embodiments, the grafting rate of isocyanate groups on the polysilazane backbone is 5%–20%. This grafting rate refers to the proportion of isocyanate groups to the total number of monomer units in the polysilazane backbone. The grafting rate of isocyanate groups will affect the content of photosensitive groups in the modified polysilazane, thereby affecting the ultraviolet light sensitivity of the modified polysilazane, and affecting the rate and yield of photocuring ceramics. The grafting rate of these isocyanate groups is beneficial to ensuring the rate and yield of ceramic preparation from modified polysilazane. In some embodiments, the above-mentioned modified polyborosilicate is a low-viscosity fluid to resin-type solid, easily soluble in a variety of organic solvents, and can be used to prepare high-temperature resistant composite materials, ceramic precursors, high-performance protective coatings, high-temperature resistant adhesives, etc. Ceramic products or polymer products with complex structures can be prepared by 3D printing, photolithography, etc., according to actual needs. The second aspect of this application provides a method for preparing the modified polysilazane described in the above application, comprising the following steps: S10: In an inert atmosphere, a raw material including polysilazane and an isocyanate compound containing a photosensitive group (HK 20138787 A 8) undergoes an addition reaction, causing the isocyanate group of the isocyanate compound to be grafted onto the nitrogen atom of the polysilazane backbone. Since the isocyanate group in the isocyanate compound has high chemical reactivity, the above preparation method allows the isocyanate group to efficiently undergo an addition reaction with the nitrogen-hydrogen bond in the polysilazane, grafting the isocyanate group onto the nitrogen atom of the polysilazane backbone. This efficiently introduces the photosensitive group into the chemical structure of the polysilazane, obtaining the aforementioned modified polysilazane.Compared to existing methods that directly introduce carbon-carbon double bonds into polysilazanes or physically mix them with acrylic monomers, this preparation method offers more controllable processes. The modified polysilazanes obtained through chemical modification exhibit higher photocuring rates and yields for ceramic preparation. In some embodiments, the polysilazane includes at least one of polyborosilazane, polyaluminasilazane, polyaluminasilazane, and polyboroaluminasilazane; wherein, the polyborosilazane may include at least one of perhydropolyborosilazane, hyperbranched polyborosilazane, and carborane-alkyl polyborosilazane; among which, hyperbranched polyborosilazane possesses high solubility and good rheological properties, which is beneficial for the molding of complex ceramic structures, and its three-dimensional spherical topology helps retain boron elements during the curing process. Perhydropolyborosilazane exhibits higher ceramic yields and can effectively reduce the shrinkage rate during pyrolysis. The carborane in carborane-alkyl polyborosilicates has a high boron content, thus the boron content of carborane-alkyl polyborosilicates can be widely controlled. The rigid structure of carborane itself can significantly improve the ceramic yield of polyborosilicates. Polyalumina silazines can include at least one of polyalumina silazines and polyboronalumina silazines. Among them, the silicon-alumina carbonitridium ceramics obtained by the pyrolysis of polyalumina silazines have excellent high-temperature oxidation resistance. Compared with silicon-alumina carbonitridium ceramics, silicon-boron carbonitridium aluminum ceramics obtained by the pyrolysis of polyboronalumina silazines have higher thermal stability and anti-crystallization properties. In some embodiments, the isocyanate compounds include at least one of ethyl acrylate-2-isocyanate and isocyanoethyl methacrylate. These isocyanate compounds not only contain isocyanate groups, which can be grafted onto polysilazines through addition reactions, but also contain photosensitive groups, which is beneficial for the preparation of ceramics by photocuring of the modified polysilazines. In some embodiments, the mass ratio of polysilazane to isocyanate compound is (5-20):1; in exemplary cases, it may include, but is not limited to, any value of 5:1, 7:1, 8:1, 9:1, 10:1, 20:1, or any range between two values. These mass ratios of raw materials are beneficial for the addition reaction, increasing the yield of modified polysilazane. Simultaneously, the mass ratio of polysilazane to isocyanate compound also affects the content of photosensitive groups in the obtained modified polysilazane, thereby affecting the rate and yield when used for photocuring ceramics. By adjusting this mass ratio, the rate of subsequent photocuring ceramic preparation can be controlled. Compared with the two prior art techniques, the preparation method of this application improves controllability, allowing for reasonable design during raw material preparation according to the requirements of the final application. The inert atmosphere for the addition reaction can be nitrogen, helium, argon, etc.In some embodiments, the addition reaction temperature is 20–100°C, and the reaction time is 1–20 hours. These reaction temperatures and times are favorable for the addition reaction to proceed and for the isocyanate groups of the isocyanate compounds to be fully grafted onto the N atoms of the polysilazane backbone. In some embodiments, the addition reaction can be carried out in a solvent to improve the uniformity of the raw material dispersion. The reaction solvent can be an ultra-dry anhydrous solvent, which may include at least one of tetrahydrofuran, n-hexane, and xylene. During the addition reaction, appropriate stirring can be performed to facilitate a uniform and stable addition reaction. After the reaction is completed, the reaction solvent in the system can be removed at 20–80°C by means such as vacuum distillation to obtain the modified polysilazane. A third aspect of this application provides a silicon-carbon-nitrogen ceramic, which is obtained by curing and pyrolyzing the modified polysilazane included in the embodiments of the above application or the modified polysilazane prepared by the preparation method of the embodiments of the above application. The silicon-carbon-nitrogen ceramics in this application are obtained by curing and pyrolyzing the modified polysilazane described in the above embodiments. During the pyrolysis process, the modified polysilazane is transformed into a ceramic material containing silicon, carbon, and nitrogen elements. Depending on the type of polysilazane used, it may also contain elements such as boron and aluminum, which can form multiple phase domain structures in the ceramic material. It has strong high-temperature resistance, oxidation resistance, and wave absorption properties, and can be used in a variety of different technical fields. In some embodiments, the silicon-carbon-nitrogen ceramics can be silicon-boron-carbon-nitrogen ceramics, which contain phase domain structures such as BN or B4C, and the high-temperature resistance can reach above 2000℃. Moreover, it can still maintain good oxidation resistance at high temperatures and is not easily oxidized. It also contains self-generated silicon carbide, which conforms to the impedance matching structural design principle, which is beneficial to the absorption of electromagnetic waves. The fourth aspect of this application provides a method for preparing the silicon-carbon-nitrogen ceramics described in the above application, including the following steps: S20: In an inert atmosphere, the raw materials including the modified polysilazane and the photoinitiator are subjected to ultraviolet light curing treatment. In the preparation method of this application, since the modified polysilazane contains photosensitive groups, these groups will crosslink and solidify under the action of a photoinitiator and ultraviolet light. Simultaneously, the main chain of the polysilazane will also break down, and the silicon, nitrogen, carbon, and other elements in the polymer will recombine. Therefore, silicon-carbon-nitrogen ceramics can be obtained by ultraviolet curing of the modified polysilazane and photoinitiator. This preparation method is process-controllable, the ultraviolet curing rate is fast and controllable, the ceramic yield is high, and ceramic products with complex structures can be prepared. In some embodiments, the photoinitiator includes at least one of free radical photoinitiators such as phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone; these photoinitiators are beneficial for ultraviolet curing, making the ceramic preparation process fast and controllable, and improving the ceramic yield.In some embodiments, the mass ratio of modified polysilazane to photoinitiator is 100:(0.1-5). In exemplary embodiments, this may include, but is not limited to, any value or a range between any two of 100:0.1, 100:0.5, 100:1, 100:2, and 100:5. In some embodiments, the ultraviolet wavelength used for ultraviolet curing is 365-405 nm; in some embodiments, the power of the ultraviolet lamp used for ultraviolet curing is 0.01-200 W, which covers the laser power for micro / nano printing and the ultraviolet power for macroscopic bulk curing, adapting to different preparation processes. The following description is based on specific embodiments. Example A1 This embodiment provides a modified polysilazane and its preparation method. The modified polysilazane is a modified polyborosilazane, with isocyanate groups grafted onto the N atoms of the polyborosilazane backbone, and acrylic acid groups also bonded to the isocyanate groups. Please refer to Figure 1. The preparation method includes the following steps S1 to S2: HK 20138787 A 11 Raw materials: The polyborosilazane is commercially available polyborosilazane KH-PSNB-1, the isocyanate compound containing the photosensitive group is ethyl 2-isocyanate (IEA), and the organic solvent is tetrahydrofuran (THF). S1: Replace the air in the 100 mL reaction flask equipped with a magnetic stirrer with nitrogen as an inert gas. Add 30 mL of tetrahydrofuran, 41.62 g of polyborosilazane KH-PSNB-1, and 4.23 g of ethyl 2-isocyanate (IEA) to the reaction flask. The stirring speed is 900 rpm, and the reaction is carried out at 60°C for 4 hours. S2: At room temperature, remove the tetrahydrofuran from the system by vacuum distillation to obtain the modified polyborosilazane. Example A2 This example provides a modified polysilazane and its preparation method. The only difference between the preparation method and Example A1 is that the reaction solvent in step S1 is changed to 15 mL tetrahydrofuran, and the reaction raw materials are changed to 16.8 g of polyborosilazane KH-PSNB-1 and 1.9 g of ethyl 2-isocyanate acrylate (IEA). All other aspects are the same. Example A3 This example provides a modified polysilazane and its preparation method. The only difference between the preparation method and Example A1 is that the reaction raw materials in step S1 are changed to 43.71 g of polyborosilazane KH-PSNB-1 and 4.36 g of ethyl isocyanate methacrylate (IEM). All other aspects are the same. Example A4 This example provides a modified polysilazane and its preparation method. The only difference between the preparation method and Example A1 is that in step S1, ethyl 2-isocyanate acrylate is replaced with the same mass of ethyl isocyanate methacrylate. All other aspects are the same.Example A5 This example provides a modified polysilazane and its preparation method. The difference between the preparation method and Example A1 is only that in step S1, ethyl 2-isocyanate is replaced with the same mass of isocyanoethyl methacrylate; all other aspects are the same. Example A6 This example provides a modified polysilazane and its preparation method. The difference between the preparation method and Example A1 is only that in step S1, polyborosilazane KH-PSNB-1 is replaced with the same mass of perhydropolysilazane; all other aspects are the same. Example A7 This example provides a modified polysilazane and its preparation method. The difference between the preparation method and Example A1 is only that in step S1, polyborosilazane KH-PSNB-1 is replaced with the same mass of carborane-alkyl polysilazane; all other aspects are the same. Example A8 This example provides a modified polysilazane and its preparation method. The difference between the preparation method and Example A1 is only that in step S1, polyborosilazane KH-PSNB-1 is replaced with the same mass of polyboroaluminosilicate; all other steps are the same. Comparative Example A1 This comparative example provides a polysilazane, namely the polyborosilazane KH-PSNB-1 in Example 1, without any modification treatment. Comparative Example A2 This comparative example provides a modified polysilazane, which is a physical mixture. The raw material is the polyborosilazane KH-PSNB-1 in Example 1, along with acrylic monomer. At room temperature and in an inert atmosphere, 50.23 g of borosilazane and 5.11 g of acrylic monomer (mass ratio approximately 10:1) are mixed by magnetic stirring at a speed of 900 rpm for 4 hours to obtain a physically mixed modified polysilazane. Comparative Example A3: This comparative example provides a modified polysilazane, which is a physical mixture. The only difference from Comparative Example A2 is that it uses 50.23 g of borosilicate and 10.2 g of acrylic monomer (mass ratio approximately 5:1), while all other components are the same. The differences between Examples A1 to A9 and Comparative Examples A1 to A3 are shown in Table 1.Table 1. Case Study: Polysilazane Modified Raw Material - Polysilazane to Modified Raw Material Mass Ratio HK 20138787 A 13 Example A1: Polyborosilazane KH-PSNB-1 - Ethyl 2-isocyanate 10:1 Example A2: Polyborosilazane KH-PSNB-1 - Ethyl 2-isocyanate 9:1 Example A3: Polyborosilazane KH-PSNB-1 - Ethyl 2-isocyanate 10:1 Example A4: Polyborosilazane KH-PSNB-1 - Ethyl 2-isocyanate 10:1 Example A5: Polyborosilazane KH-PSNB-1 - Ethyl methacrylate 10:1 Example A6: Perhydro-hydrogenated polysilazane - Ethyl 2-isocyanate 10:1 Example A7: Carboronyl alkyl polysilazane - Ethyl 2-isocyanate 10:1 Example A8 Polyboron aluminum silazane ethyl acrylate 10:1 Comparative Example A1 Polyboron silazane KH-PSNB-1 None Comparative Example A2 Polyboron silazane KH-PSNB-1 physically mixed with acrylic monomer 10:1 Comparative Example A3 Polyboron silazane KH-PSNB-1 physically mixed with acrylic monomer 5:1 Silicon carbon nitrogen ceramic examples: Silicon carbon nitrogen ceramics were prepared by mixing the polysilazane and modified polysilazane provided in Examples A1 to A8 and Comparative Examples A1 to A3 as follows: In an inert atmosphere, the samples provided in each case were mixed with phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (photoinitiator) at a mass ratio of 100:2 and cured under ultraviolet light at 365 nm and 100 W to obtain the corresponding silicon carbon nitrogen ceramics. In this study, Example A1 modified polysilazane to prepare Example B1 silicon carbon nitrogen ceramic, Example A2 modified polysilazane to prepare Example B2 silicon carbon nitrogen ceramic, and so on, up to Comparative Example A3 modified polysilazane to prepare Comparative Example B3 silicon carbon nitrogen ceramic. Related performance tests and result analysis: 1. Fourier transform infrared (FT-IR) testing: The raw materials and products in Examples A1 to A8 and Comparative Examples A1 to A3 were tested using a Fourier transform infrared spectrometer to obtain Fourier transform infrared (FT-IR) spectra. The FT-IR spectra of KH-PSNB-1, IEA, and the modified polysilazane sample in Example A1 are shown in Figure 2.Figure 2 shows the signal peaks as follows: 3381 cm⁻¹ (NH); 3047 cm⁻¹ + 3008 cm⁻¹ (CH=); HK 20138787 A 14 2957 cm⁻¹ + 2883 cm⁻¹ (CH⁻); 2276 cm⁻¹ + 1356 cm⁻¹ (-CNO); 2130 cm⁻¹ (Si-H); 1727 cm⁻¹ (C=O); 1639 cm⁻¹ (CC=C); 1593 cm⁻¹ (Si-C=C); 3320 cm⁻¹ + 1690 cm⁻¹ + 1537 cm⁻¹ + 1464 cm⁻¹ (CO-NH); 1403 cm⁻¹ + 1360 cm⁻¹ (BN); 1260 cm⁻¹ (Si-CH₃); 990 cm⁻¹ (Si-N-Si). The disappearance of the signal peak representing the -CNO group and the appearance of the signal peaks representing CC=C, C=O, and CO-NH groups in the FTIR spectrum of the modified polysilazane in Example A1 indicate that the isocyanate compound underwent an addition reaction with the polysilazane, and the photosensitive group was successfully introduced into the chemical structure of the polyborosilicate, rather than a simple physical mixture. 2. Differential Scanning Calorimetry (DSC) Photo-DSC curves of silicon-carbon-nitrogen ceramics prepared by photocuring in each case were plotted using a differential scanning calorimeter (DSC). Figure 3 shows the Photo-DSC curves of polyborosilicate KH-PSNB-1 (with 2 wt.% photoinitiator added) in Comparative Example A1 and the modified polysilazane in Example A1 with different amounts of photoinitiator (0.5 wt.%, 1 wt.%, 2 wt.%) during the UV curing process for ceramics. It can be seen that within a certain range, the more photoinitiator added, the higher the photocuring efficiency. Furthermore, KH-PSNB-1 polyborosilicate itself also contains vinyl groups (common knowledge in the industry). KH-PSNB-1 from Comparative Example A1 can be directly mixed with a photoinitiator for UV curing pyrolysis to prepare ceramics. However, as shown in Figure 3, this method has extremely low photocuring efficiency. When 2.wt.% of a photoinitiator is added, the modified polyborosilicate in Example A1 has significantly higher photocuring efficiency compared to the unmodified polyborosilicate in Comparative Example A1. 3. Thermogravimetric Analysis Figure 4 shows the thermogravimetric curves of KH-PSNB-1 polyborosilicate in Comparative Example A1 (UV irradiation for 60 minutes) and the modified polyborosilicate in Example A1 (UV irradiation for 10 minutes) during UV curing to prepare ceramics. Figure 4 shows that compared to the unmodified polyborosilicate, introducing isocyanate compounds containing photosensitive groups into the chemical structure of polyborosilicate did not decrease the ceramic yield but rather increased it.Figure 5 shows the thermogravimetric analysis (TGA) curves and differential thermal analysis (DTA) curves of the modified polyborosilazane prepared in Comparative Example A3. The DTA curves show the curing and pyrolysis temperatures, and the TGA curves show a very low ceramic yield. The above description is merely a preferred embodiment of this application and is not intended to limit the application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application (HK 20138787 A 15) should be included within the scope of protection of this application. HK 20138787 A 1 Claims 1. A modified polysilazane, characterized in that it comprises a polysilazane backbone, isocyanate groups, and photosensitive groups, wherein the carbon atoms of the isocyanate groups are bonded to at least a portion of the nitrogen atoms of the polysilazane backbone, and the photosensitive groups are bonded to the nitrogen atoms of the isocyanate groups. 2. The modified polysilazane according to claim 1, characterized in that: the modified polysilazane comprises repeating units represented by the following general chemical formula (I): (I) In general formula (I), R3 is the photosensitive group; a is 5 to 10; R1 and R2 may be the same or different and include at least one of alkyl, hydrogen atom, vinyl, and phenyl. 3. The modified polysilazane according to claim 1 or 2, characterized in that: the polysilazane backbone comprises at least one of polyboron silazane backbone, polyaluminum silazane backbone, and polyboron aluminum silazane backbone; and / or, the grafting rate of the isocyanate group on the polysilazane backbone is 5% to 20%; and / or, the photosensitive group comprises at least one of acrylate group and methacrylate group. 4. A method for preparing the modified polysilazane according to any one of claims 1 to 3, characterized in that it comprises the following steps: In an inert atmosphere, a raw material comprising polysilazane and an isocyanate compound containing the photosensitive group is subjected to an addition reaction, such that the isocyanate group of the isocyanate compound is grafted onto the nitrogen atom of the main chain of the polysilazane. HK 20138787 A 2 5. The preparation method according to claim 4, characterized in that: the mass ratio of the polysilazane to the isocyanate compound is (5-20):1; and / or, the polysilazane comprises at least one of perhydropolyborosilicate, hyperbranched polyborosilicate, carborane-alkyl polyborosilicate, polyaluminasilazane, and polyborosilicate; and / or, the isocyanate compound comprises at least one of ethyl acrylate-2-isocyanate and isocyanoethyl methacrylate. 6. The preparation method according to claim 4 or 5, characterized in that: the temperature of the addition reaction is 20-100°C; and / or the time of the addition reaction is 1-20 hours; and / or the reaction solvent of the addition reaction includes at least one of tetrahydrofuran, n-hexane, xylene, and toluene.7. A silicon-carbon-nitrogen ceramic, characterized in that it is obtained by curing and pyrolyzing a modified polysilazane comprising any one of claims 1 to 3 or a modified polysilazane prepared by the preparation method according to any one of claims 4 to 6. 8. A method for preparing the silicon-carbon-nitrogen ceramic according to claim 7, characterized in that it comprises the following steps: subjecting a raw material comprising the modified polysilazane and a photoinitiator to ultraviolet light curing treatment in an inert atmosphere. 9. The preparation method according to claim 8, characterized in that the photoinitiator comprises at least one of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone; and / or, the mass ratio of the modified polysilazane to the photoinitiator is 100:(0.1-5). 10. The preparation method according to claim 8 or 9, characterized in that: the wavelength of the ultraviolet light used in the ultraviolet curing treatment is 365-405 nm; and / or, the power of the ultraviolet lamp used in the ultraviolet curing treatment is 0.01-200 W. HK 20138787 A 1 Specification Drawings Figure 1 Figure 2 HK 20138787 A 2 Figure 3 Figure 4 HK 20138787 A 3 Figure 5 HK 20138787 A.

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