Method for Preparing the Precursor

Abstract

A method for crosslinking an oligosilazane without inert gas control, comprising mixing an oligosilazane with a solvent and adding a soluble catalyst at an appropriate rate to ensure consistent release of gaseous by-products over the entire surface of the oligosilazane solution, said inert gas control including replacing the atmosphere above the solution with water and / or low oxygen gas, including reactions carried out in a glove box, using a Schlenk line, or with other purposeful addition of shielding gas such as nitrogen, argon, or dehumidified air. Also provided are polymers prepared by the method, preferably with low oxygen content, composites prepared from the polymers, and uses in the aerospace, automotive, and oil and gas industries.

Description

[Technical field]

[0001] The present invention relates to a method for preparing polymers for use in ceramics, and in particular to a method for producing preceramic polymers for Si-CN ceramics, and the products thereof. [Background technology]

[0002] Si-CN ceramic precursors require careful control of the atmosphere during synthesis because the polymer precursors contain a Si-N backbone that is reactive with water at ambient temperature, which hydrolyzes to form siloxanes, which can subsequently form Si-O ceramics upon thermal conversion (pyrolysis). Standard chemical methods teach that air- and moisture-sensitive reactions must be performed under highly controlled conditions, such as can be performed by a Schlenk line. Thus, prior art methods that specify additional nitrogen atmosphere generators to exclude moisture require a large amount of equipment to control moisture (e.g., Schlenk lines, glove boxes, solvent drying procedures, etc.). Specific prior art teachings in the manufacture of Si-CN ceramics include U.S. Pat. No. 10,385,234, which discloses a method for crosslinking polysilazane materials with a fluoride containing catalyst in tetrahydrofuran (THF), but emphasizes the requirement of excluding moisture to avoid side reactions. Reference O. Flores et al, J. Mat. Chem. A., 2013, 1, 15406 also explicitly teaches the need for moisture to be excluded, even to the extent of drying all organic solvents with sodium, and preparing all materials in a glove box. All references to raw materials include a note to use an inert atmosphere. Thus, one skilled in the art strives to take all control measures to exclude moisture, with the understanding that moisture can lead to hydrolysis of the reactive Si-N backbone, leading to the production of Si-O ceramics after further processing.

[0003] A further problem with prior art methods is that existing polymer derived ceramic (PDC) materials cannot be molded into large or complex shapes, and current processing methods are inadequate for existing composite manufacturing methods or newly developed methods, such as additive manufacturing. What is needed is a method for synthesizing Si-CN precursors that does not require the expense incurred by instrumentation for moisture removal, and new synthesis methods with improved scalability. A further problem with existing processes and materials is their inability to produce composite materials, for example due to poor viscosity to prevent leaching of fiber composites. Thus, the development of easily processable material polymer systems that allow the production of ceramic composites would also be of great value. Summary of the Invention

[0004] In accordance with the present invention, there is provided an improved method for crosslinking oligosilazanes without the use of inert gas control, comprising the steps of: mixing an oligosilazane with a solvent; adding a soluble catalyst at a suitable rate to ensure consistent release of gaseous by-products across the surface of the oligosilazane solution; Including, The control of the inert gas includes reactions carried out in a glove box, using a Schlenk line, or with other purposeful addition of shielding gases such as nitrogen, argon, or dehumidified air, and includes replacing the atmosphere above the solution with water and / or low oxygen gases. The catalyst may be a source of fluoride ions. The catalyst may be selected from tetraethylammonium fluoride or tetrabutylammonium fluoride. Preferably, the catalyst is tetrabutylammonium fluoride (TBAF).

[0005] The solvent may be tetrahydrofuran. The solvent may further be toluene. The solvent may further be 2-methyltetrahydrofuran. The solvent may further be dibutyl ether. The solvent may be any particular ratio of mixtures of tetrahydrofuran or toluene with or without an additional solvent selected from 2-methyltetrahydrofuran and dibutyl ether. The solvent may further be any other solvent known in the art that dissolves both the oligosilazane, the catalyst, and the quenching agent. The mass ratio of oligomer:solvent may be between 8:1 and 1:8. The mass ratio of oligomer:solvent may be more specifically in the range of 8:1 and 1:1, even more specifically in the range of 8:1 and 3:1, even more specifically in the range of 8:1 and 5:1. Alternatively, the mass ratio of oligomer:solvent may be in the range of 1:1 and 1:8, even more specifically in the range of 1:3 and 1:8, even more specifically in the range of 1:5 and 1:8. The mass ratio of oligomer:solvent may be preferably in the range of 1:3 and 3:1. More preferably, the mass ratio of oligomer:solvent may be 1:2 and 2:1. Even more preferably, the mass ratio may be 1:1.5 and 1:1. Most preferably, the mass ratio is 1:1. The molar ratio of the catalyst to the oligomer repeat unit is 1×10 -4 ~10×10 -4 More preferably, the molar ratio is between 2×10 -4 ~10×10 -4 Even more preferably, the molar ratio is between 2×10 -4 ~7×10 -4 Most preferably, the molar ratio is between 2×10 -4 ~6×10 -4 It may be between.

[0006] The catalyst addition rate is 10 to 100 (total catalyst %) per hour. -1 Preferably, the addition rate is between 15 and 35 (total catalyst %) per hour. -1 It may be between. The reaction may be carried out in a vessel with a height / width dimension ratio >1. The width / base dimension of the inlet opening of the vessel may be ≦0.5. The resulting crosslinked polymers can be pyrolyzed in an inert atmosphere at temperatures above 1200° C. to give ceramic materials without the need for high and uniform oxygen content. The catalyst may be added dropwise and the inhibitor may be added selectively throughout the course of the reaction. In a further aspect, the present invention provides polymers and composites comprising the polymers prepared according to the method of the present invention, and their use in the aerospace, automotive, and oil and gas industries. Preferably, the polymers and composites have a low oxygen content, e.g., less than 10 at% on average throughout the sample. In a particular embodiment of the invention, the solvent is THF, the catalyst is TBAF, the mass ratio of oligomer:solvent is between 1:1.5 and 1:1, and the molar ratio of catalyst:oligomer repeat units is 2×10 -4 ~4×10 -4 The catalyst averaged approximately 17 (total catalyst%) hours -1 will be added. In one particular embodiment, the solvent is THF, the catalyst is TBAF, the mass ratio of oligomer:solvent is 1:1, and the molar ratio of catalyst:oligomer repeat units is 3.6×10 -4 The catalyst was used for an average of about 17 (total catalyst%) hours. -1 will be added.

[0007] In another embodiment of the invention, the solvent is toluene, the catalyst is TBAF, the mass ratio of oligomer:solvent is between 1:1.5 and 1:1, and the molar ratio of catalyst:oligomer repeat units is 2×10 -4 ~6×10 -4 The catalyst averaged approximately 33 (total catalyst%) hours -1 will be added. In one particular embodiment, the solvent is toluene, the catalyst is TBAF, the mass ratio of oligomer:solvent is 1:1, and the molar ratio of catalyst:oligomer repeat units is 2.6×10 -4 The catalyst was used for an average of about 33 (total catalyst%) hours. -1 will be added. In a further embodiment, the solvent is toluene, the mass ratio of oligomer:solvent is 1:1.1, and the molar ratio of catalyst:oligomer repeat units is 5.2×10 -4 The catalyst was used for an average of about 33 (total catalyst%) hours. -1 will be added.

[0008] In one embodiment, the present invention provides a reactive F - We provide a method for chemically crosslinking a specific polysilazane (Durazane™ 1800, Merck) using an ion-containing catalyst (tetrabutylammonium fluoride, TBAF) to induce a number of reactions that result in high molecular weight polymeric materials. In particular, the process of the present invention is not carried out under dry inert gas; that is, in accordance with the present invention, an "inert" atmosphere is provided in situ (as far as moisture is concerned) by an arrangement in which sufficient hydrogen gas is generated during the reaction to displace the atmosphere above the reaction liquid. The actual extent of hydrolysis during the process of the present invention is also not believed to produce particularly high concentrations of siloxanes (and therefore oxygen) in the final ceramic material produced. A high concentration of oxygen may be defined as a significant amount, e.g., 15 mole %, of the final ceramic containing oxide. The method of the present invention, unlike the prior art methods, is characterized by the absence of a protection step, which provides a significant bonus to scalability. In a further aspect, the present invention further provides a crosslinked material made from the reaction of Durazane™ 1800 and TBAF in THF, followed by quenching with Ca(BH)·2THF to produce CaF and tetrabutylammonium borohydride by-products, followed by filtration and drying under vacuum to produce a ceramic precursor.

[0009] The prior art does not disclose or teach crosslinked materials prepared by methods involving crosslinking of polysilazanes under ambient pressure conditions. The solution provided by the present invention relies on the inherent atmosphere generated by the synthesis for shielding purposes, and control of the synthesis time to ensure that sufficient H2 is released to remove H2O from the reaction vessel atmosphere. A particular advantage of the present invention is that it does not require any laborious infrastructure requirements for gas supply to the reaction vessel, cleaning, or drying procedures for gases and solvents. Any form of modification or addition can be added to the reaction without the need to employ complex gas-sensitive techniques that are inherently a small-scale solution in synthesis. Thus, the synthesis is much more flexible and scalable. Potential applications of the improved PDC precursors according to the present invention include: High temperature ceramics for aerospace applications: leading edges, exhaust ducts High temperature resistant materials - energy materials, automobiles, aerospace Hard materials - abrasives, bearings, cutting tools / machining tools Chemical Engineering - Catalyst Supports, Food and Biotechnology Functional Materials - Electrical Engineering, Micro / Nanoelectronics

[0010] Thus, the methods and products of the present invention have application in a variety of industries including automotive, aerospace, oil and gas, etc. The methods of the present invention can also be used in combination with other processes, if desired. The features of any aspect or embodiment of the present invention may be used alone or in any combination with the other aspects and embodiments, where appropriate. The invention will now be described in more detail, by way of example only, with reference to the following schematic drawings in which: [Brief description of the drawings]

[0011] [Figure 1]1 shows energy dispersive spectroscopy (EDS, elemental analysis) data of ceramic composites made from precursors of the method of the present invention. [Diagram 2] 1 shows the experimental setup of a round bottom flask. [Diagram 3] 1 shows the wide-rimmed vessel experimental setup. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention is described more fully hereinafter with reference to the accompanying examples and drawings, in which embodiments of the invention are shown. The invention should not be construed as being limited to the embodiments described herein. EXAMPLES

[0013] Example 1 400 g of oligosilazane, Durazane™ 1800 (Merck Life Sciences, India) was added in a 1:1 mass ratio to THF (Sigma-Aldrich, Gillingham, UK) in a 3 L round bottom flask at room temperature under magnetic stirring. The vessel had a height of 24.3 cm, a width of 18.8 cm, a high curvature and a neck opening diameter of 2.5 cm. No reflux condenser or gas line was attached. After homogenization, tetrabutylammonium fluoride (TBAF) 1 M in THF (Sigma Aldrich, Gillingham, UK) was added dropwise. The rate of addition was controlled to prevent the release of excessive amounts of H2 gas, defined as the entire surface being covered by bubbles without widespread obstruction of the surface by larger bubbles. The total amount of TBAF solution added was 2.3 cm over the course of approximately 6 hours, including periods during which no addition was made due to the appearance of complete surface bubbles. 3 The addition of catalyst to the top of the bubbles may cause overpolymerization of the thin bubble film, resulting in the formation of an insoluble coating. This corresponds to a final TBAF concentration of 0.00282M, and the addition rate was 0.00038 mol h -1The final molar ratio of TBAF:oligosilazane repeat units was 0.000356.

[0014] The mixture was stirred until gas evolution ceased. A final 0.1 cm 3 of TBAF solution was added. Ca(BH4)2·2THF (Sigma Aldrich, Gillingham, UK) was used as a suspension for F - in a molar ratio of 1.5:1 to THF (approximately 5 cm 3 The suspension was stirred for 10 min, then filtered to remove any aggregates, and the filtrate was collected and used as is in solution for composite applications after synthesis. Example 2 300 g of oligosilazane, Durazane™ 1800, was dissolved in TBAF 1M in THF (1.7 cm) as described in Example 1. 3 ) solution and Ca(BH4)2·2THF. This corresponds to a final TBAF concentration of 0.00278M, and the addition rate was 0.00028 mol h -1 The final molar ratio of TBAF:oligosilazane repeat units was 0.000351. The solution was then concentrated at 85° C. in a rotary evaporator at a pressure between 800 and 300 mBar until a pale yellow oil was obtained, which solidified to a pale glassy solid upon cooling to room temperature.

[0015] Example 3 400 g of the oligosilazane, Durazane™ 1800, was treated with TBAF and Ca(BH4)2·2THF as described in Example 1. This corresponded to a final TBAF concentration of 0.00282 M, with an addition rate of 0.00038 mol h -1 The final molar ratio of TBAF:oligosilazane repeat units was 0.000351. The suspension was then filtered to remove any coagulants and the filtrate was collected. The solution was then concentrated in a rotary evaporator at 85°C and between 850-700 mBar pressure for a total of 15 minutes until a pale yellow liquid was obtained, which contained 22 wt% retained THF solvent. This liquid was used in composite applications as a viscous oil.

[0016] Example 4 30 g of oligosilazane, Durazane™ 1800 (Merck Life Sciences, India) was added in a 1:1 mass ratio to toluene (Sigma-Aldrich, Gillingham, UK) in a 0.4 L round bottom flask of 13.5 cm height, 10 cm width and 2.5 cm diameter at the neck opening under magnetic stirring at room temperature. No reflux condenser or gas line was attached. After homogenization, 1M tetrabutylammonium fluoride (TBAF) in THF (Sigma Aldrich, Gillingham, UK) was added dropwise after diluting it twice with toluene. The addition rate was controlled to prevent the release of excessive H2 gas. The total volume of TBAF solution added was 0.25 cm 3 The mixture was stirred until gas evolution ceased. A final 0.05 cm 3 of TBAF solution was added, which corresponds to a final TBAF concentration of 0.00202 M, and the addition rate was 2.08 × 10 -5 molh -1 The final molar ratio of TBAF:oligosilazane repeat units was 0.000258.

[0017] Ca(BH4)2·2THF (Sigma Aldrich, Gillingham, UK) was used as a suspension for F - in a molar ratio of 1.5:1 to THF (approximately 5 cm 3 The suspension was stirred for 10 min, then filtered to remove aggregates, and the filtrate was collected and concentrated in a rotary evaporator at 85° C. and 80 mBar. A pale yellow gel was obtained at room temperature. Example 5 30 g of oligosilazane, Durazane™ 1800 (Merck Life Sciences, India) was added in a 1:1 mass ratio to toluene (Sigma-Aldrich, Gillingham, UK) in a 1 L round bottom flask at room temperature under magnetic stirring without a reflux condenser or gas line. After homogenization, tetrabutylammonium fluoride (TBAF) 1M in THF (Sigma Aldrich, Gillingham, UK) was added dropwise. The rate of addition was controlled to prevent the release of excessive amounts of H2 gas. The total volume of TBAF solution added was 0.15 cm 3 The mixture was stirred until gas evolution ceased. A final 0.05 cm 3 of TBAF solution was added, which corresponds to a final TBAF concentration of 0.00403 M, and the addition rate was 8.33 × 10 -5 molh -1 The final molar ratio of TBAF:oligosilazane repeat units was 0.000516.

[0018] Ca(BH4)2·2THF (Sigma Aldrich, Gillingham, UK) was used as a suspension for F - in a molar ratio of 1.5:1 to THF (approximately 5 cm 3 The suspension was stirred for 10 minutes, then filtered to remove coagulates, and the filtrate was collected and concentrated in a rotary evaporator at 85° C. and 80 mBar for 3 minutes. The product was recovered as a viscous pale liquid at room temperature. Example 6 A layer of oil from Example 3 was extracted and spread evenly on a layer of plastic release film. A layer of Torayca COR8112 fiber was placed on the oil layer. The coating was applied using an extruder and rolling equipment. Additional layers of fiber and oil were applied in sequence until a total of 25 fiber plies were laid up. An additional layer of release film was placed on top of the laminate and the laminate was placed between two steel plates separated by a spacer at 4.6 mm. The width of the laminate as made was 5 mm.

[0019] The laminate was dried in an oven at ambient conditions at 160 °C and then pyrolyzed in Ar(g) at 1280 °C for 1 h. The samples were then flexurally tested according to ASTM C1341 and energy dispersive spectroscopy (Oxford Instruments, Oxford, UK) was then performed in a scanning electron microscope (SEM) on the matrix of the fractured ceramic composite. Figure 1: Atomic percentages of each of the major constituents Si, C, N, and O for a fixed number of test sites. O was variously introduced as a contaminant during synthesis or pyrolysis. Superimposed on the experimental data points are box plots displaying the median and interquartile range of the atomic percentage distribution of data collected across test sites.

[0020] From Figure 1, it is clear that all the observed elements are position dependent and present in abundance. However, statistically speaking, oxygen is present in negligible amounts at most throughout the composite. In contrast to the abundant silicon, the average stoichiometric number of the matrix is ​​Si 1±0.48 C 1.58±0.61 N 0.68±0.57 O 0.11±0.11, suggesting that the ceramic is primarily a Si-C glass containing some N, with a statistically negligible oxygen content. Some spots of higher oxygen content may be due to localized oxygen-rich regions formed during strength testing or pyrolysis due to insufficiently dry inert gas feed. Global hydrolysis of the precursors may be manifested as a significant increase in the average oxygen content compared to that observed here. Thus, it is believed that the method of the present invention can produce Si-CN ceramics with minimal oxygen content without many of the procedural inefficiencies and scalable complications associated with handling air-sensitive chemicals. Example 7 Six additional composite samples were prepared following the method described in Example 6. The weights of these composites and their components are shown in Table 1.

[0021] [Table 1] The average precursor ceramic yield was calculated to be 74±4%, with variability attributed to inconsistencies in gas flow rates and temperatures at all points in the heat treatment furnace.

[0022] Comparative Example 1 A mixture of oligosilazane, Durazane™ 1800 (Merck Life Sciences, India) and THF (Sigma Aldrich, Gillingham, UK) was prepared in a wide-rimmed dish, both 11 cm in width and opening diameter, and mixed with a glass rod until homogenous. The total volume was approximately 10 ml. With vigorous stirring, a few drops of TBAF (1 M in THF) were added to the mixture. The fluid evolved copious amounts of gas and formed insoluble white brittle aggregates.

Claims

1. 1. A method for crosslinking oligosilazanes without inert gas control, comprising: mixing an oligosilazane with a solvent; adding a soluble catalyst at an appropriate rate to ensure consistent release of gaseous by-products across the surface of the oligosilazane solution; Including, The inert gas control includes techniques where the atmosphere above the solution is replaced with water and / or low-oxygen gas, including reactions carried out in a glove box, using a Schlenk line, or with other purposeful addition of shielding gases such as nitrogen, argon, or dehumidified air; the molar ratio of catalyst to oligomeric repeat units is between 1×10 −4 and 10×10 −4 ; A process wherein the catalyst addition rate is between 10 and 100 (total % catalyst hr −1 ).

2. The method of claim 1 wherein the catalyst is a source of fluoride ions.

3. 3. The method of claim 2, wherein the catalyst is tetrabutylammonium fluoride.

4. 2. The method of claim 1, wherein the solvent is selected from tetrahydrofuran, toluene, 2-methyltetrahydrofuran, dibutyl ether, or a mixture thereof.

5. 10. The method of claim 1, wherein the weight ratio of oligomer to solvent is between 8:1 and 1:

8.

6. 10. The method of claim 1, wherein the reaction is carried out in a vessel having a height / width dimension ratio >1.

7. 2. The method of claim 1, wherein the width / base dimension of the inlet opening of the container is ≦0.

5.

8. 10. The method of claim 1, wherein the resulting crosslinked polymer upon pyrolysis above 1200°C in an inert atmosphere provides a ceramic material without the need for a large and uniform oxygen content.

9. 10. The method of claim 1, wherein the catalyst is added dropwise and the inhibitor is added selectively throughout the course of the reaction.

10. 10. The process of claim 1, wherein the solvent is tetrahydrofuran or toluene or a mixture thereof.

11. 10. A polymer prepared by the method of claim 1, preferably with low oxygen content.

12. A composite prepared with the polymer of claim 11.

13. 13. Use of a polymer or composite prepared according to claim 11 or 12 in the aerospace, automotive, oil and gas industries.

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