Method for producing polycarbosilane

Abstract

Provided is a method for producing a high molecular weight polycarbosilane (PCS) by solid-phase polymerization in order to improve the quality stability of the PCS and the workability of an extraction process.　The present invention relates to a method for producing a polycarbosilane having a high molecular weight by solid-phase polymerization, wherein using a raw material polycarbosilane as a raw material for polymerization, the raw material polycarbosilane is heated in a temperature range of 210-410°C to perform solid-phase polymerization of the raw material polycarbosilane.

Description

Method for producing polycarbosilane

[0001] The present invention relates to a method for producing polycarbosilane.

[0002] Polycarbosilane (PCS) is widely used as a precursor polymer for producing ceramics. It is used in the production of fibers, powders containing silicon carbide, silicon carbide-based composite materials, etc. In this specification, PCS may be hereinafter referred to as "PCS".

[0003] When producing silicon carbide fibers using PCS, silicon carbide fibers are produced by firing PCS fibers produced by spinning PCS. From the viewpoints of preventing fusion between fibers during firing of silicon carbide fibers and improving the mechanical strength of silicon carbide fibers, PCS having a large molecular weight is advantageous. Also, when producing a ceramic matrix composite material by firing a ceramic laminate impregnated with PCS, PCS having a large molecular weight is advantageous from the viewpoint of obtaining a dense composite material.

[0004] Thus, PCS having a large molecular weight (hereinafter referred to as "high molecular weight PCS") is required for various applications. Conventionally, in order to obtain high molecular weight PCS, the PCS in the liquid phase state is heat-treated to increase the molecular weight. For example, Patent Document 1 describes a method for producing PCS having a number average molecular weight of 1000 to 5000, which is a precursor of silicon carbide fibers, by thermally decomposing and polycondensing polysilane. Since Patent Document 1 returns the liquid separated from the gas by-produced during the thermal decomposition polycondensation reaction into the reaction system, the thermal decomposition polycondensation proceeds in the liquid phase state.

[0005] Further, Patent Document 2 describes a production method comprising a first step of thermally decomposing and polymerizing an organosilicon compound to obtain a low molecular weight polycarbosilane, and a second step of separating the obtained low molecular weight polycarbosilane from the reaction system and further polymerizing it to obtain a high molecular weight polycarbosilane. In the examples thereof, it is described that a low molecular weight polycarbosilane was distilled off to obtain a high molecular weight polycarbosilane, and the polymerization reaction proceeds in the liquid phase state.

[0006] JP-A No. 64-85225 JP-A No. 59-49234 Special Publication No. 2014-515423

[0007] In the polymerization method of PCS (polycrystalline silicate) that involves heating in the liquid phase, the viscosity of PCS increases as its molecular weight increases, making stirring for mixing within the reaction vessel difficult. Since the polymerization reaction that increases the molecular weight of PCS is highly dependent on the heating temperature, insufficient mixing and stirring makes it difficult to proceed with the polymerization reaction at a uniform temperature. Therefore, when the production scale is increased, there is a possibility of variations in the quality, such as molecular weight, of the produced PCS products.

[0008] In addition to the problems mentioned above, liquid PCS, which is high temperature and high viscosity, is difficult to remove and recover from the reaction vessel. If the liquid PCS cools and solidifies in the reaction vessel, it can cause the PCS to adhere to the inner wall of the reaction vessel or to form solidified masses of PCS, making the recovery process of the PCS even more difficult. Thus, conventional methods for producing high molecular weight PCS have various challenges, including the workability of the PCS removal process from the reaction vessel and the quality stability of the PCS product as the scale of production increases.

[0009] On the other hand, solid-phase polymerization, in which polymers are polymerized in a solid state, is known as a polymerization method for polymer materials. For example, Patent Document 3 describes a method for solid-phase polymerization of high molecular weight aliphatic polyesters, in which an aliphatic polyester prepolymer is polymerized under the flow of a gas containing a sulfonic acid catalyst ([Claim 1]). It also describes a method for solid-phase polymerization of polyesters, stating that it is a polymerization reaction carried out using a solid-phase oligomer at a temperature above its glass transition temperature and below the melting point of the polymer, and that it is a method applicable only to the polymerization of crystalline polyesters (paragraph

[0018] ). In contrast, PCS, unlike general polymers, is an amorphous polymer, and its thermal analysis shows that it does not clearly exhibit temperatures corresponding to the glass transition temperature and melting point of crystalline polymers. Patent Document 3 does not show a solid-phase polymerization method for increasing the molecular weight of polymers that do not have a clear glass transition temperature and melting point, such as PCS.

[0010] In view of the challenges in polymerization in the liquid phase, the present invention aims to provide a method for producing high molecular weight PCS by solid-phase polymerization in order to improve the stability of PCS quality and the workability of the extraction process.

[0011] The inventors of the present invention have discovered that by using PCS as a raw material and setting appropriate heating conditions, the polymerization reaction of PCS can be carried out in a solid state, and have completed the present invention. Specifically, the present invention encompasses the following embodiments (1) to (3).

[0012] (1) A method for producing a polycarbosilane having a high molecular weight by solid-phase polymerization, wherein a raw material polycarbosilane is used as a raw material for polymerization, and the raw material polycarbosilane is heated in a temperature range of 210°C or higher and 410°C or lower to perform solid-phase polymerization of the raw material polycarbosilane.

[0013] (2) The method for producing polycarbosilane according to (1) above, wherein the polycarbosilane obtained by solid-phase polymerization has a molecular weight increase ratio, expressed as the ratio of the weight-average molecular weight (Mw) of the polycarbosilane after solid-phase polymerization to the weight-average molecular weight (Mw) of the raw material polycarbosilane before solid-phase polymerization, of 1.10 or more.

[0014] (3) The method for producing polycarbosilane according to (1) or (2) above, wherein the heating temperature of the raw material polycarbosilane is 10°C or more lower than the softening point.

[0015] According to the present invention, it is possible to avoid the adhesion of PCS to the inner wall surface of the reaction vessel and the formation of solidified products in which PCS are integrated with each other, so that the PCS obtained by solid-phase polymerization is fluid. Therefore, the PCS can be easily removed and recovered from the reaction vessel, improving work efficiency. Furthermore, unlike polymerization reactions in a high-viscosity liquid phase, the present invention is a solid-phase polymerization reaction, so stirring and mixing in the reaction vessel is easy. Therefore, it is possible to suppress uneven temperature distribution in the reaction vessel, contributing to improved quality of the PCS.

[0016] This figure schematically shows a first polymerization reactor for solid-phase polymerization in a nitrogen atmosphere using nitrogen gas. This figure schematically shows a second polymerization reactor for solid-phase polymerization in a reduced-pressure atmosphere. This figure shows the measurement results of the raw material PCS by powder X-ray diffraction.

[0017] The following describes specific embodiments of the present invention (hereinafter referred to as "these embodiments"). The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. In this specification, the notation "X to Y" (where X and Y are arbitrary numerical values) means "X or more and Y or less".

[0018] In the embodiments of the present invention, "solid phase" refers to the phase in which PCS is in a solid state, and "liquid phase" refers to the phase in which PCS heated above its softening point is in a liquid state (molten state).

[0019] (Solid-phase polymerization) The method for producing PCS according to this embodiment is a method for producing polycarbosilane having a high molecular weight by solid-phase polymerization, characterized in that raw material polycarbosilane is used as the raw material to be polymerized, and the raw material polycarbosilane is heated in a temperature range of 210°C or higher and 410°C or lower to perform solid-phase polymerization of the raw material polycarbosilane. The solid-phase polymerization of polycarbosilane according to this embodiment means a reaction in which the raw material polycarbosilane to be polymerized is increased in molecular weight while remaining in a solid state rather than a liquid state at the reaction temperature.

[0020] During the reaction, the raw material polycarbosilane is in a solid phase, and it is preferable that no melting of the raw material polycarbosilane occurs, or even if a portion of the raw material polycarbosilane melts, the total weight of the bulk PCS is less than 50% by weight of the total weight of the polycarbosilane. The raw material polycarbosilane may form multiple bulk PCS by joining with other coexisting solid-phase raw material polycarbosilane via the melted portion.

[0021] When bulk PCS are formed, heat transfer into the bulk may be insufficient, potentially leading to a localized decrease in the polymerization reaction rate. Therefore, as the total weight of bulk PCS increases, the decrease in the polymerization reaction rate may become more pronounced. From the viewpoint of rapidly completing the high molecular weight reaction, the ratio of the total weight of bulk PCS to the total weight of polycarbosilane is preferably 40% by weight or less, more preferably 30% by weight or less, and even more preferably 20% by weight or less.

[0022] (Method for calculating the proportion of bulk PCS) The proportion of the total weight of bulk PCS to the total weight of polycarbosilane can be calculated by measuring the weight of the generated bulk PCS. Specifically, the weight of each bulk PCS obtained after solid-phase polymerization is measured, and the total weight of the bulk PCS is calculated. This total weight is then divided by the total weight of polycarbosilane to calculate the proportion of bulk PCS, which can then be expressed as a percentage.

[0023] The above-mentioned bulk PCS refers to a form of mass in which at least a portion of the polycarbosilanes are joined together, and the mass constitutes 10% or more by weight of the raw material PCS. Because bulk PCS can have an irregular shape, it has a different form from the gravel-like, sandy, or pellet-like PCS described later.

[0024] The PCS obtained by solid-phase polymerization preferably has a total weight of less than 50% by weight of the total weight of the polycarbosilane, and may contain the above-mentioned bulk PCS shape.

[0025] (Raw Material Polycarbosilane) The raw material PCS used for solid-phase polymerization can be PCS produced by known PCS manufacturing methods. For example, PCS produced by liquid-gas phase thermal decomposition condensation or thermal decomposition reaction using an autoclave can be used. As starting materials for the raw material PCS, chain-like polysilane compounds having a skeleton in which silicon atoms are linked in a chain, and cyclic silane compounds having a skeleton in which silicon atoms are linked in a ring can be used. Examples of chain-like polysilane compounds include polydimethylsilane (PDMS), polymethylphenylsilane (PMPS), polydiphenylsilane (PDPS), and polymethylvinylsilane (PMVS). Examples of cyclic silane compounds include octamethylcyclotetrasilane, decamethylcyclopentasilane, dodecamethylcyclohexasilane, and tetradecamethylcycloheptasilane.

[0026] One or more compounds selected from the above-mentioned group of linear polysilane compounds and cyclic silane compounds can be used as starting materials. For example, the raw material PCS can be prepared by a liquid-gas phase thermal decomposition condensation method using dodecamethylcyclohexasilane (DMCHS), which is a cyclic silane compound.

[0027] The raw material PCS according to this embodiment may be in a solid phase state. Its form is not particularly limited. For example, PCS in the form of powder, gravel, sand, or pellets can be used.

[0028] (Heating Temperature) In the method for producing PCS according to this embodiment, it is preferable to heat the raw material PCS to a temperature range of 210°C or higher and below the softening point of the raw material PCS for solid-phase polymerization. If the heating temperature is below 210°C, the polymerization reaction proceeds slowly, making it difficult to increase the molecular weight of the PCS. On the other hand, if heated to a temperature above the softening point of the PCS, the PCS will begin to transition to a molten state.

[0029] In addition to the above, when the raw material PCS is heated to a temperature exceeding 410°C in a solid state, the molecular weight of the PCS may increase excessively, resulting in the formation of ultra-high molecular weight PCS that are insoluble in the solvent (hereinafter referred to as "solvent-insoluble PCS"). Such solvent-insoluble PCS can cause yarn breakage when the PCS obtained after solid-phase polymerization is dry-spun, or become defects in the silicon carbide fibers obtained after firing, reducing the strength of the fibers, thus having various adverse effects on the applications of the PCS. Therefore, the formation of solvent-insoluble PCS is undesirable when using PCS after solid-phase polymerization as a raw material for silicon carbide fibers. Furthermore, when creating a ceramic composite material by impregnating a ceramic material with a solution in which PCS after solid-phase polymerization is dissolved in a solvent, the presence of solvent-insoluble PCS in the solution is undesirable because it makes it difficult to uniformly impregnate the ceramic material depending on the solution state.

[0030] When performing the dry spinning described above or when creating ceramic composite materials, a solvent with high solubility for PCS (hereinafter referred to as the "applicable solvent") is generally used to dissolve the PCS. Therefore, it is preferable that no components insoluble in the applicable solvent are generated in the PCS after solid-phase polymerization. Examples of the applicable solvent include aromatic hydrocarbons such as benzene, toluene, xylene, and mesitylene; halogen-containing hydrocarbons such as chloroform and dichloromethane; and cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran.

[0031] Therefore, from the viewpoint of efficiently carrying out the solid-phase polymerization reaction and increasing the molecular weight of PCS, the heating temperature for the raw material PCS is preferably 210°C or higher, and may be 230°C or higher, 250°C or higher, 270°C or higher, 300°C or higher, 320°C or higher, or 340°C or higher. These heating temperatures can also be set according to the softening point of the raw material PCS. Furthermore, the temperature at which the polymerization reaction is carried out may be increased in steps, or maintained within multiple temperature ranges. On the other hand, from the viewpoint of keeping PCS in a solid state and suppressing the generation of components insoluble in the applicable solvent, the upper limit of the above heating temperature is preferably 410°C or lower. The above heating temperature may be set within a range arbitrarily created by combining the lower and upper limits shown above. From each of the above viewpoints, the above heating temperature is preferably 210 to 410°C, more preferably 230 to 410°C, even more preferably 270 to 410°C, and particularly preferably 320 to 410°C.

[0032] As described above in the background technology, PCS is an amorphous polymer that does not clearly exhibit temperatures corresponding to the glass transition temperature and melting point of crystalline polymers. Furthermore, the method for producing PCS according to this embodiment is characterized by polymerizing the PCS in a solid state. The softening point of the raw material PCS according to this embodiment is defined as the temperature at which "the PCS can no longer maintain a solid state, melts, integrates, and becomes transparent." Specifically, the softening point is defined as the temperature indicated when measuring with a melting point analyzer, as described in the "Measurement of Softening Point" section of the examples below, and corresponds to the state of PCS where the light transmittance passing through a glass tube filled with PCS powder is 40% or more. A melting point analyzer is an analytical device whose measurement principle is that the light transmittance changes with changes in sample form before and after the melting point. As described above, by using a melting point analyzer, the temperature at which PCS is in a softened state can be measured according to the change in light transmittance. The softening point according to this embodiment is a temperature that can be evaluated by the temperature corresponding to a light transmittance of 40% or more in a melting point analyzer.

[0033] Furthermore, the temperature range that can be increased may be limited depending on the performance of the melting point measuring instrument used. Therefore, in the case of PCS with a high softening point, the PCS may not soften or melt even when the maximum temperature that can be increased is reached. In such cases, it is difficult to clearly determine the softening point of the PCS using a melting point measuring instrument, so in this embodiment, the softening point of the PCS may be defined as a temperature higher than the maximum temperature of the melting point measuring instrument.

[0034] When raw material PCS is heated near its softening point to carry out a polymerization reaction, partially melted raw material PCS joins with other solid-state PCS via the melted portion, thereby forming bulk PCS. If multiple bulk PCS are formed, and the total weight of these bulk PCS exceeds 50% by weight of the raw material PCS (excessive formation of bulk PCS), it may cause problems such as adhesion to the reactor. Furthermore, some of the melted PCS may remain in a molten state without joining with other solid-state PCS, which can lead to a decrease in the polymerization reaction rate. Therefore, from the viewpoint of avoiding such excessive formation of bulk PCS, it is preferable to perform solid-state polymerization by heating at a low temperature away from the softening point. Specifically, regarding the difference between the softening point of the raw material PCS and the heating temperature, it is preferable to select a heating temperature that is 10°C or more lower than the softening point, and more preferably 20°C or more lower.

[0035] Furthermore, from the viewpoint of avoiding the excessive formation of bulk PCS and efficiently carrying out polymerization, the heating temperature of the raw material PCS is preferably 210°C or higher, at least 10°C lower than the softening point; more preferably 230°C or higher, at least 10°C lower than the softening point; even more preferably 230°C or higher, at least 20°C lower than the softening point; particularly preferably 270°C or higher, at least 20°C lower than the softening point; and most preferably 320°C or higher, at least 20°C lower than the softening point.

[0036] Furthermore, the softening point of PCS tends to increase with increasing molecular weight. Low molecular weight PCS may be liquid or a viscous resinous substance at room temperature. Since the polymerization reaction is accelerated at higher heating temperatures, it is preferable to use PCS with a high molecular weight and high softening point as the raw material PCS from the viewpoint of rapidly increasing molecular weight by setting a higher temperature for solid-phase polymerization. Therefore, the weight-average molecular weight of the raw material PCS is preferably 3000 or higher, and more preferably 4000 or higher, 5000 or higher, 6500 or higher, or 7000 or higher. In addition, the softening point of the raw material PCS is preferably 210°C or higher, more preferably 290°C or higher, even more preferably 350°C or higher, and particularly preferably 400°C or higher.

[0037] (Heating time) The heating time is not particularly limited. It can be set appropriately according to various conditions such as the type of raw material PCS, heating temperature, and high molecular weight conversion rate. Since the high molecular weight conversion rate tends to increase with increasing heating time, the heating time should be set within the range of the required high molecular weight conversion rate. For example, a heating time of 3 to 15 hours may be selected, or a heating time longer may be selected.

[0038] (Atmosphere) In the method for producing PCS according to this embodiment, it is preferable to carry out solid-phase polymerization in an atmosphere containing an inert gas. Nitrogen gas, argon gas, etc. can be selected as the inert gas. In addition, the atmosphere may contain a small amount of oxygen, as long as it does not substantially inhibit the high molecular weight of the PCS.

[0039] The atmospheric pressure during solid-phase polymerization is not particularly limited. For example, solid-phase polymerization can be carried out under normal pressure or reduced pressure. When using reduced pressure, a low-pressure range of 10 torr or less may be selected.

[0040] The method for forming and maintaining the atmosphere is not particularly limited. For example, a method can be used to maintain an inert gas atmosphere in a reaction vessel by continuously supplying and discharging an inert gas stream into the reaction vessel. In this specification, the atmosphere formed by nitrogen gas in such a method may be referred to as the "nitrogen atmosphere".

[0041] Alternatively, a method of reducing the pressure inside the reaction vessel by any pressure reducing means and maintaining a reduced-pressure atmosphere may be used. The atmosphere formed by such a method may also be referred to as an "atmosphere under reduced-pressure conditions" in this specification.

[0042] In addition to the methods described above, a method of maintaining an inert gas atmosphere inside the reaction vessel by replacing the inside of the reaction vessel with an inert gas and then blocking the flow of the inert gas between the inside and the outside of the reaction vessel may be applied.

[0043] The production method according to the present embodiment can cause the solid-phase polymerization of the raw material PCS to proceed under a predetermined atmosphere and the pressure inside the reactor by maintaining an inert gas atmosphere, an atmosphere under reduced-pressure conditions, etc. inside the reaction vessel.

[0044] Examples of the polymerization reactor for carrying out the production method of PCS according to the present embodiment include a first polymerization reactor and a second polymerization reactor as shown below.

[0045] (First Polymerization Reactor) FIG. 1 schematically shows a first polymerization reactor as an example of a solid-phase polymerization apparatus used for carrying out solid-phase polymerization under the above-described nitrogen atmosphere. The configuration of the first polymerization reactor 1 is roughly divided into a reaction part for carrying out a solid-phase polymerization reaction and an atmosphere-forming part for forming an atmosphere. As shown in FIG. 1, the former reaction part includes a reaction vessel 2, a heater 3, and a thermocouple 4. The reaction vessel 2 is a component for accommodating the raw material PCS (not shown) and carrying out the solid-phase polymerization of PCS. The heater 3 is arranged around the reaction vessel 2 and is a component for heating the raw material PCS in the reaction vessel 2. The thermocouple 4 is a component for measuring the heating temperature of the reaction vessel 2. The operation of the heater 3 is controlled based on the measurement value by the thermocouple 4. Note that the reaction vessel 2 may be provided with stirring means for mixing the raw material PCS during heating (not shown).

[0046] The latter atmosphere-forming part includes a gas supply line 5, a gas discharge line 6, a flow meter 7, and a cooling pipe 8 as shown in FIG. 1. The gas supplied into the reaction vessel 2 from the gas supply line 5 is discharged to the outside from the gas discharge line 6 after passing through the inside of the reaction vessel 2.

[0047] For example, when forming a nitrogen atmosphere of nitrogen gas in the reaction vessel 2 by the first polymerization reactor, after continuously supplying nitrogen gas from the gas supply path 5 into the reaction vessel 2, it is continuously discharged from the gas discharge path 6 to allow a nitrogen gas flow to pass through the reaction vessel 2, thereby maintaining a nitrogen atmosphere in the reaction vessel 2 filled with nitrogen gas. Even if air enters the reaction vessel 2 from the outside, the air can be discharged by the nitrogen gas flow.

[0048] The first polymerization reactor heats the raw material PCS in the reaction vessel 2 by the heater 3 surrounding the reaction vessel 2 while maintaining the atmosphere in the reaction vessel 2. After raising the temperature until the raw material PCS reaches a predetermined temperature and holding it for a predetermined time, the heating is stopped. Then, after cooling the reaction vessel 2, the polymerized PCS in the reaction vessel 2 is recovered.

[0049] (Second Polymerization Reactor) Fig. 2 schematically shows a second polymerization reactor as an example of a solid-phase polymerization apparatus used for performing solid-phase polymerization under the atmosphere of the above reduced-pressure conditions. The configuration of the second polymerization reactor 11 is roughly divided into a reaction part for performing the solid-phase polymerization reaction and an atmosphere formation part for forming the atmosphere. As shown in Fig. 2, the former reaction part includes a reaction vessel 12, a heater 13, and a thermocouple 14. The reaction vessel 12 is a component for accommodating the raw material PCS (not shown) and performing the solid-phase polymerization of PCS. The heater 13 is arranged around the reaction vessel 12 and is a component for heating the raw material PCS in the reaction vessel 12. The thermocouple 14 is a component for measuring the heating temperature of the reaction vessel 12. The operation of the heater 13 is controlled based on the measurement value by the thermocouple 14. Note that the reaction vessel 12 may be provided with stirring means for mixing during heating of the raw material PCS (not shown).

[0050] The latter atmosphere formation section, as shown in Figure 2, includes a gas supply passage 15, a gas discharge passage 16, a three-way valve 17, a flow meter 21, a valve 22, a control valve 23, a pressure reducing pump 24, and a pressure reducing meter 25. The three-way valve 17 has three valves: a valve 18 on the gas supply side, a valve 19 on the reaction vessel side, and a valve 20 on the gas discharge side. It is connected to the reaction vessel 12 via the valve 22 and serves as a means of switching the gas flow. The control valve 23, pressure reducing pump 24, and pressure reducing meter 25 are connected to the reaction vessel 12 and serve as means of discharging gas from inside the reaction vessel 12 and reducing the pressure inside the reaction vessel 12.

[0051] For example, the following describes the case in which a reduced-pressure atmosphere is formed in the reaction vessel using a second polymerization reactor. First, the three valves 18, 19, 20 and valve 22 of the three-way valve 17 are closed, and the inside of the reaction vessel 12 is depressurized using the depressurizing pump 24 and the control valve 23. Next, after stopping the depressurizing pump 24, the valve 18 on the gas supply side and the valve 19 and valve 22 on the reaction vessel side of the three-way valve 17 are opened to introduce nitrogen gas into the reaction vessel 12 and restore pressure. This depressurization and restoration process is repeated to replace the inside of the reaction vessel 12 with nitrogen gas. After that, the three valves 18, 19, 20 and valve 22 of the three-way valve 17 are closed, and the inside of the reaction vessel 12 is depressurized using the depressurizing pump 24 and the control valve 23. By continuing the depressurization operation until the vacuum level shown on the depressurizing gauge 25 is reached, a reduced-pressure atmosphere can be formed inside the reaction vessel 12.

[0052] The second polymerization reactor maintains the atmosphere inside the reaction vessel 12 while heating the raw material PCS inside the reaction vessel 12 with a heater 13 surrounding the reaction vessel 12. The raw material PCS is heated until it reaches a predetermined temperature and held at that temperature for a predetermined time, after which the heating is stopped. After the reaction vessel 12 is cooled, the polymerized PCS inside the reaction vessel 12 is recovered.

[0053] (High molecular weight conversion rate) In the method for producing PCS according to this embodiment, it is preferable that the high molecular weight conversion rate, expressed as the ratio of the weight-average molecular weight (Mw) of the polycarbosilane after solid-phase polymerization to the weight-average molecular weight (Mw) of the raw material polycarbosilane before solid-phase polymerization, is 1.10 or higher. PCS with a high high molecular weight conversion rate corresponds to a PCS in which a large proportion of high molecular weight PCS is polymerized from the raw material PCS. Therefore, a high molecular weight conversion rate of 1.10 or higher, 1.20 or higher, or 1.50 or higher is more preferable, and 2.00 or higher is even more preferable.

[0054] On the other hand, if the molecular weight conversion rate is too high, some of the resulting high molecular weight PCS may form ultra-high molecular weight PCS that are insoluble in the applied solvent, which may adversely affect the use of the PCS in various applications. Therefore, the molecular weight conversion rate is preferably 20.00 or less, more preferably 15.00 or less, and even more preferably 10.00 or less. From the viewpoint of producing high molecular weight PCS with a large molecular weight while suppressing the formation of solvent-insoluble PCS, the molecular weight conversion rate is preferably 1.10 to 20.00, more preferably 1.10 to 10.00, and even more preferably 1.10 to 5.00.

[0055] The following describes embodiments of the present invention. The present invention is not limited to the following description.

[0056] (Raw material PCS) The raw material PCS used in the following test examples A to D was synthesized using a liquid-gas thermal decomposition condensation method at atmospheric pressure with a liquid-gas thermal decomposition apparatus, using dodecamethylcyclohexasilane (DMCHS), a six-membered ring silane compound, as the starting material.

[0057] (Evaluation of Crystallinity of Raw Material PCS) The synthesized raw material PCS was analyzed using powder X-ray diffraction (XRD). As a result, no sharp diffraction peaks were observed, and as shown in Figure 3, broad peaks were observed, confirming that it is an amorphous polymer with an amorphous structure. The measurement conditions for powder X-ray diffraction were a wavelength of 0.154 nm for the CuKα X-ray source, a voltage of 45 kV, a current of 40 mA, and a scanning range (2θ) of 5 to 100°.

[0058] (Molecular Weight Measurement) The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of PCS were measured by gel permeation chromatography (GPC) using the method described below. PCS was dissolved in toluene to prepare a solution of approximately 0.5 wt%, and 20 μL of this solution was used for analysis. The analytical instruments and conditions were as follows: • Instrument name: HPLC manufactured by Shimadzu Corporation • Columns: LF-404, KF-402, KF-401 (one of each) connected in this order from the pump side (all manufactured by Resonac Holdings Co., Ltd.) • Solvent: Toluene • Flow rate: Analytical section and reference: 0.30 mL / min • Oven: 40°C • Detector: Differential refractometer (RID-20A manufactured by Shimadzu Corporation) • Sample solution: 0.5 wt%

[0059] (Determination regarding the formation of toluene-insoluble components) PCS obtained by solid-phase polymerization is generally used by dissolving it in an applicable solvent. Therefore, if toluene-insoluble components are formed in the applicable solvent, it is undesirable for the use of PCS. In this example, we confirmed whether or not toluene-insoluble components are formed when PCS is dissolved in toluene, one of the applicable solvents. Components insoluble in toluene may hereafter be referred to as "toluene-insoluble components". Specifically, the turbidity of the toluene solution was measured using a digital turbidimeter (manufactured by APERA INSTRUMENTS Co., Ltd.) with a toluene solution prepared to measure the molecular weight of PCS. When the turbidity exceeded 40 NTU, toluene-insoluble components were also confirmed visually. Therefore, it was determined that toluene-insoluble components are formed in PCS with a turbidity exceeding 40 NTU, and that toluene-insoluble components are substantially not formed in PCS with a turbidity of 40 NTU or less. In the following, cases where toluene-insoluble components are generated will be described as "insoluble components present," and cases where toluene-insoluble components are not substantially generated will be described as "insoluble components absent."

[0060] (Measurement of softening point) First, the sample for measurement was prepared according to the following procedure. A glass tube with an inner diameter of 1 mm (manufactured by Nippon Rikagakukikai Co., Ltd.) was filled with PCS powder to a height of 5 mm. A metal rod with a diameter of approximately 1 mm was inserted into the glass tube, and the PCS powder was compressed to a height of 3 to 4 mm. Six such glass tubes were prepared in this manner.

[0061] Next, the softening point of the PCS powder was measured using a melting point analyzer (manufactured by Buchi) according to the procedure shown below. The melting point analyzer is an analytical device that uses the change in light transmittance due to the change in sample morphology before and after the melting point as its measurement principle. The melting point analyzer used in this example can be heated up to 410°C. To avoid the influence of oxygen in the air, the melting point analyzer (manufactured by Buchi) and the glass tubes filled with PCS powder were placed inside a glove box, and then the inside of the box was replaced with nitrogen to achieve an oxygen concentration of 0.0 vol%. After that, three of the glass tubes were inserted into the tube insertion port of the melting point analyzer.

[0062] Next, heating of the glass tube was started and the temperature was raised to the initial temperature. After confirming that the PCS powder remained in a powder state without softening or melting at this initial temperature, the temperature was raised to 410°C at a heating rate of 10°C / min. The temperature at which the light transmittance passing through the glass tube exceeded 40% during heating was automatically measured and recorded using a melting point analyzer. The same procedure as above was used to measure the PCS in the six glass tubes, and the lowest temperature recorded among the obtained measurement results was adopted as the softening point of the PCS. If the PCS in the glass tube remained in a powder state up to 410°C and the light transmittance did not exceed 40%, the measurement result was recorded as ">410°C". According to the procedure for calculating the softening point of the PCS described above, a softening point of ">410°C" means a temperature above 410°C.

[0063] The initial temperature was set to be below the expected softening temperature, and the difference between the initial temperature and the expected softening temperature was 30°C or more. For example, if the expected softening temperature was 210 to 240°C, the initial temperature was set to 180°C, and if the expected softening temperature was 240 to 270°C, the initial temperature was set to 210°C.

[0064] (1) Test Example A (Atmospheric pressure and nitrogen atmosphere with nitrogen gas; atmosphere α) The reaction vessel was filled with nitrogen gas, and then solid-phase polymerization of PCS was carried out.

[0065] (Example 1) Solid-phase polymerization of the raw material PCS was carried out at atmospheric pressure using a polymerization reactor as shown in Figure 1. Using powdered PCS as the raw material PCS, 10 g of the above raw material PCS was placed into the reaction vessel 2. Thereafter, nitrogen gas was continuously supplied into the reaction vessel 2 from the gas supply passage 5 at a rate of 100 mL / min and continuously discharged from the gas discharge passage 6, thereby passing nitrogen gas through the reaction vessel 2 and creating a nitrogen atmosphere that filled the reaction vessel 2 with nitrogen gas.

[0066] While maintaining the nitrogen atmosphere described above, the PCS powder inside the reaction vessel was heated by a heater surrounding the vessel. The temperature of the PCS was raised until it reached 250°C, and after being held at 250°C for 3 hours, the heating was stopped. The reaction vessel was then allowed to cool to room temperature, and the PCS inside the reaction vessel was recovered. The resulting PCS after the solid-phase polymerization reaction was dissolved in toluene to prepare a toluene solution for measurement. The turbidity of the toluene solution was measured. Next, the molecular weight of the PCS after the polymerization reaction was measured using gel permeation chromatography (GPC) (hereinafter referred to as "GPC measurement"). Furthermore, after the polymerization reaction, the PCS did not adhere to the inner wall surface of the reaction vessel, and no solidified product of integrated PCS was formed. Therefore, the obtained PCS was fluid, and it was possible to easily remove and recover the PCS from inside the reaction vessel.

[0067] (Examples 2, 3, 5, 6) Examples 2, 3, 5, and 6 obtained solid-phase polymerized PCS using the same procedure as in Example 1, except that the heating temperature or the raw material PCS used differed. The turbidity of the toluene solution in which the PCS after the polymerization reaction was dissolved was measured. Then, the molecular weight of the PCS after the polymerization reaction was measured by GPC measurement.

[0068] (Example 7) In Example 7, PCS was obtained by solid-phase polymerization using the same procedure as in Example 1, except that the heating temperature and the raw material PCS used were different. The turbidity of the toluene solution in which the PCS after polymerization was dissolved was measured. Next, the molecular weight of the PCS after polymerization was measured by GPC measurement. Furthermore, after the polymerization reaction, the PCS did not adhere to the inner wall surface of the reaction vessel, and no solidified product of integrated PCS was formed, so the obtained PCS was fluid and could be easily removed and recovered from the reaction vessel. In addition, since no formation of bulk PCS was confirmed in the PCS after polymerization, the total weight of bulk PCS was 0% by weight relative to the total weight of polycarbosilane.

[0069] (Example 8) In Example 8, PCS was obtained by solid-phase polymerization using the same procedure as in Example 1, except that the heating temperature, heating time, and the use of PCS obtained by solid-phase polymerization in Example 7 as the raw material PCS. The turbidity of the toluene solution in which the PCS after polymerization was dissolved was measured. Next, the molecular weight of the PCS after polymerization was measured by GPC measurement.

[0070] (Example 9) In Example 9, PCS was obtained by solid-phase polymerization using the same procedure as in Example 1, except that the heating temperature, heating time, and the use of PCS obtained by solid-phase polymerization in Example 8 as the raw material PCS. The turbidity of the toluene solution in which the PCS after polymerization was dissolved was measured. Next, the molecular weight of the PCS after polymerization was measured by GPC measurement.

[0071] (Comparative Examples 1-5) Comparative Examples 1-3 obtained PCS by solid-phase polymerization using the same procedure as in Example 1, except that the heating temperature was different. Comparative Examples 4 and 5 also obtained PCS by solid-phase polymerization using the same procedure as in Example 1, except that the heating temperature, heating time, and the raw material PCS used were different. For Comparative Examples 1, 4, and 5, the turbidity of the toluene solution in which the PCS after polymerization was dissolved was measured. Then, the molecular weight of the PCS after polymerization was measured. On the other hand, Comparative Examples 2 and 3 were determined to have "insoluble components" based on the turbidity measurement results of the toluene solution. Since toluene solutions containing insoluble components are not suitable for molecular weight measurement by GPC, molecular weight measurement was not performed on the PCS obtained after polymerization in Comparative Examples 2 and 3.

[0072] (2) Test Example B (Atmosphere under reduced pressure; Atmosphere β) The reaction vessel was subjected to a reduced pressure atmosphere of 10 torr or less, and then solid-phase polymerization of PCS was carried out.

[0073] (Example 4) Solid-phase polymerization of the raw material PCS was carried out using a polymerization reactor as shown in Figure 2. Using powdered PCS as the raw material PCS, 10 g of the above raw material PCS was placed into the reaction vessel 12. Then, with the three valves 18, 19, 20 and valve 22 of the three-way valve 17 closed, the pressure inside the reaction vessel 12 was reduced using the depressurizing pump 24 and the control valve 23. Next, the valve 18 on the gas supply side and the valve 19 and valve 22 on the reaction vessel side of the three-way valve 17 were opened, and nitrogen gas was introduced into the reaction vessel 12 to restore pressure. This depressurization and restoration process was repeated three times to replace the inside of the reaction vessel 12 with nitrogen gas. Then, after closing the three valves 18, 19, 20 and valve 22 of the three-way valve 17, the depressurizing pump 24 and the control valve 23 were used to create a reduced pressure atmosphere of 10 torr or less inside the reaction vessel 12.

[0074] While maintaining the above reduced pressure conditions, the PCS powder inside the reaction vessel was heated by a heater surrounding the vessel. The temperature of the PCS was raised until it reached 320°C, and after being held at 320°C for 3 hours, the heating was stopped. The reaction vessel was then allowed to cool to room temperature, and the PCS inside the reaction vessel was recovered. The turbidity of the toluene solution in which the resulting PCS after polymerization was dissolved was measured. Next, the molecular weight of the PCS after polymerization was measured by GPC measurement. Furthermore, after polymerization, no PCS adhered to the inner wall surface of the reaction vessel, and no solidified material formed from the PCS particles was generated. Therefore, the obtained PCS was fluid and could be easily removed and recovered from the reaction vessel.

[0075] (3) Test Example C (Liquid Phase State, Atmosphere α) (Comparative Examples 6-8) Comparative Examples 6-8 were subjected to the polymerization reaction by heating the raw material PCS in the same procedure as in Example 1, except that the heating temperature and the raw material PCS used were different. Since the heating temperature was higher than the softening point of the raw material PCS, the PCS could not maintain a solid state during heating and remained in a molten liquid state at all times. The turbidity of the toluene solution in which the polymerized PCS was dissolved was measured. Next, the molecular weight of the polymerized PCS was measured by GPC measurement.

[0076] Table 1 shows the polymerization reaction conditions for Examples 1 to 9 and Comparative Examples 1 to 8, and Table 2 shows the measurement results. The "Raw Material PCS" column in Table 1 shows the physical properties of the raw material PCS used, including the softening point (°C), average molecular weight (number average molecular weight (Mn), weight average molecular weight (Mw)), and the ratio of average molecular weight (Mw / Mn) for each PCS. ">410" in the "Softening Point" column indicates that the softening point is in a temperature range above 410°C.

[0077] The "Reaction Conditions" column in Table 1 shows the atmosphere, heating temperature (°C), and heating time (h) during the heat treatment. The column labeled "TD" shows the difference (°C) between the softening point and the heating temperature, calculated by subtracting the heating temperature from the softening point. For example, ">210" means a value greater than 210°C. Next, the "α" and "β" labels in the "Atmosphere" column indicate the atmosphere applied in Test Examples A to C above. Specifically, "α" refers to a nitrogen atmosphere at normal pressure using nitrogen gas, and "β" refers to a reduced pressure atmosphere of 10 torr or less. The terms "Solid Phase" and "Liquid Phase" in the "Reaction System" column indicate the form of the PCS when heated.

[0078] The "PCS after polymerization" column in Table 2 shows the physical properties of the PCS recovered after heat treatment. The "High molecular weight ratio" column shows the value calculated by dividing the Mw of the PCS after polymerization by the Mw of the raw material PCS. The "Toluene-insoluble components" column shows the result of the determination of toluene-insoluble components by a turbidimeter; "Present" indicates "Insoluble components present," and "-" indicates "Insoluble components absent."

[0079]

[0080]

[0081] As shown in Tables 1 and 2, Examples 1 to 9, which are included in the scope of this embodiment, had a high molecular weight conversion rate of 1.10 or higher, and high molecular weight PCS were obtained from low molecular weight PCS. In all cases, there were "no insoluble components." In all cases, after the polymerization reaction, the PCS remained in a powdery form without adhering to the inner wall surface of the reaction vessel or forming solidified products of integrated PCS. Therefore, the obtained PCS was fluid and could be easily removed and recovered from the reaction vessel.

[0082] Furthermore, since Examples 1 to 9, where the TD was 10°C or higher, obtained a high molecular weight conversion rate of 1.10 or higher, it was confirmed that solid-phase polymerization at a temperature 10°C or higher below the softening point is preferable from the viewpoint of increasing the high molecular weight conversion rate. In addition, since the amount of bulk PCS produced in Example 7 was 0%, it was confirmed that solid-phase polymerization at a temperature 10°C or higher below the softening point is preferable from the viewpoint of avoiding the excessive production of bulk PCS.

[0083] In contrast, Comparative Examples 1, 4, and 5 showed lower molecular weight conversion rates than Examples 1-9, even after solid-phase polymerization. Comparative Examples 2 and 3 produced components insoluble in the solvent toluene. Furthermore, in Comparative Examples 6-8, the polymerization reaction proceeded in the liquid phase, making it difficult to recover the PCS after cooling as it fused to the reaction vessel.

[0084] 1. First polymerization reactor 2. Reaction vessel 3. Heater 4. Thermocouple 5. Gas supply line 6. Gas discharge line 7. Flow meter 8. Cooling pipe 11. Second polymerization reactor 12. Reaction vessel 13. Heater 14. Thermocouple 15. Gas supply line 16. Gas discharge line 17. Three-way valve 18. Valve on the gas supply side 19. Valve on the reaction vessel side 20. Valve on the gas discharge side 21. Flow meter 22. Valve 23. Control valve 24. Pressure reducing pump 25. Pressure reducing gauge

Claims

1. A method for producing a polycarbosilane having a high molecular weight by solid-phase polymerization, wherein a raw material polycarbosilane is used as the raw material for polymerization, and the raw material polycarbosilane is heated in a temperature range of 210°C or higher and 410°C or lower to perform solid-phase polymerization of the raw material polycarbosilane.

2. The method for producing polycarbosilane according to claim 1, wherein the polycarbosilane obtained by solid-phase polymerization has a molecular weight increase ratio, expressed as the ratio of the weight-average molecular weight (Mw) of the polycarbosilane after solid-phase polymerization to the weight-average molecular weight (Mw) of the raw material polycarbosilane before solid-phase polymerization, of 1.10 or more.

3. The method for producing polycarbosilane according to claim 1 or 2, wherein the heating temperature of the raw material polycarbosilane is 10°C or more lower than the softening point.

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