Polycarbosilane and production method for high molecular weight polycarbosilane

Abstract

The present invention efficiently produces a high molecular weight PCS.　The present invention is a polycarbosilane in which a content rate of components having a molecular weight of 1000 or less is 25.0%-34.0%, and a weight average molecular weight (Mw) is 3300-5500. The present invention is a production method for a high molecular weight polycarbosilane, the production method comprising: a third step for heating a solidified polycarbosilane obtained using the polycarbosilane while maintaining a solid-phase state thereof, and removing low molecular weight components contained in the solidified polycarbosilane; and a fourth step for heating the polycarbosilane for solid-phase polymerization obtained in the third step and performing solid-phase polymerization.

Description

Method for producing polycarbosilane and high molecular weight polycarbosilane

[0001] The present invention relates to a method for producing polycarbosilane and high molecular weight polycarbosilane.

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

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

[0004] Thus, in various applications, PCS with a large molecular weight (hereinafter referred to as "high molecular weight PCS") is required. Conventionally, in order to obtain high molecular weight PCS (high molecular weight polycarbosilane), the PCS in the liquid phase state is heat-treated to increase its 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] Also, Patent Document 2 vaporizes an organosilicon compound in the liquid phase part of a liquid phase - gas phase thermal decomposition apparatus, cools the reaction product containing PCS generated by performing a thermal decomposition reaction in the gas phase part, returns it to the liquid phase part, heats it to polymerize PCS in the liquid phase, and repeats this circulation to synthesize high molecular weight PCS.

[0006] Japanese Patent Laid-Open No. 64-85225 International Publication No. 2,024 / 004,247

[0007] In polymerization methods of PCS (polycrystalline silicon) that involve heating in a liquid phase, the viscosity of the PCS increases as its molecular weight increases. As polymerization progresses, the high molecular weight PCS remains a highly viscous liquid even at high temperatures, making it difficult to remove and recover from the processing container. Furthermore, if the liquid PCS cools and solidifies within the processing container, it can cause the PCS to adhere to the inner wall of the container or form solidified material where the PCS particles are integrated, further complicating the PCS recovery process. Thus, conventional methods for producing high molecular weight PCS have challenges related to the workability of the process of removing the high molecular weight PCS from the processing container.

[0008] In view of the problems in polymerization methods that involve heating in a liquid phase, the present invention aims to provide a PCS that can be produced by solid-phase polymerization, and a method for producing high molecular weight PCS using the PCS, in order to improve the workability when recovering high molecular weight PCS from a processing container and to efficiently produce high molecular weight PCS.

[0009] The inventors have found that a specific PCS having a molecular weight ratio and weight-average molecular weight within a specific range is suitable as a raw material for producing high molecular weight PCS. Furthermore, they have found that by using the above-mentioned specific PCS, PCS in a molten state can be easily transported, components with a molecular weight of 1000 or less can be removed in a solid state, and high molecular weight PCS can be obtained by solid-phase polymerization using the PCS after the removal of such components, thus completing the present invention. Specifically, the present invention encompasses the following embodiments (1) to (7).

[0010] (1) A polycarbosilane having a content of 25.0% or more and 34.0% or less of components with a molecular weight of 1000 or less, and a weight-average molecular weight (Mw) of 3300 or more and 5500 or less.

[0011] (2) The polycarbosilane described in (1) above, wherein the viscosity at 450°C is 20.0 Pa·s or less.

[0012] (3) A method for producing a high molecular weight polycarbosilane using the polycarbosilane described in (1) or (2) above, comprising: a first step of preparing molten polycarbosilane in which the polycarbosilane is in a molten state, and then transferring the molten polycarbosilane; a second step of cooling the transferred molten polycarbosilane to prepare solidified polycarbosilane in a solid state; a third step of heating the solidified polycarbosilane obtained in the second step while maintaining its solid state to remove low molecular weight components contained in the solidified polycarbosilane; and a fourth step of heating the polycarbosilane for solid-phase polymerization obtained in the third step to perform solid-phase polymerization.

[0013] (4) The method for producing high molecular weight polycarbosilane as described in (3), wherein the heating temperature in the fourth step is 310°C or higher and 410°C or lower.

[0014] (5) The method for producing a high molecular weight polycarbosilane according to (3) or (4) above, wherein the heating temperature in the fourth step is equal to or greater than the heating temperature in the third step.

[0015] (6) The method for producing a high molecular weight polycarbosilane according to any one of (3) to (5) above, wherein the polycarbosilane obtained by the third step has a content of less than 25.0% of components with a molecular weight of 1000 or less.

[0016] (7) A method for producing a high molecular weight polycarbosilane according to any one of (3) to (6) above, wherein the ratio of the weight-average molecular weight (Mw2) of the high molecular weight polycarbosilane obtained in the fourth step to the weight-average molecular weight (Mw1) of the polycarbosilane obtained in the third step (Mw2 / Mw1) is 1.10 or more.

[0017] According to the present invention, it is possible to provide a PCS that can be transported in a molten state and that can maintain a solid state during the step of removing low molecular weight components. According to the present invention, it is possible to avoid the PCS adhering to the inner wall surface of the processing container and the formation of solidified material in which the PCS are integrated with each other, so the high molecular weight PCS obtained by solid-phase polymerization has fluidity. Therefore, the PCS can be easily removed and recovered from the processing container, improving work efficiency and enabling the efficient production of high molecular weight PCS.

[0018] This figure schematically shows a heat treatment apparatus for removing low molecular weight components or performing solid-phase polymerization in an inert gas atmosphere. This figure is a graph created to calculate an estimated viscosity of PCS at 450°C. This figure explains the relationship between the LMW component content (Lc) in PCS and the PCS softening point (TS). This figure explains the relationship between Mw of PCS and the PCS softening point (TS).

[0019] The embodiments of the present invention will be described in detail below. The present invention is not limited to the embodiments described below, 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".

[0020] 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).

[0021] The raw material polycarbosilane is in a solid state during the reaction, and it is preferable that the raw material polycarbosilane does not melt, 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-state raw material polycarbosilane via the melted portion.

[0022] When bulk PCS are formed, heat is not sufficiently transferred to the inside of the bulk, which may lead to a decrease in the efficiency of removing low-molecular-weight components and a decrease in the polymerization reaction rate. This tendency to decrease may become more pronounced as the total weight of bulk PCS increases. Therefore, 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.

[0023] (Method for calculating the proportion of bulk PCS) The proportion 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 bulk PCS is calculated. This total weight is then divided by the weight of the raw material PCS to calculate the proportion of bulk PCS, which can then be expressed as a percentage.

[0024] 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.

[0025] The PCS obtained by solid-phase polymerization may have a total weight of less than 50% by weight of the bulk PCS relative to the total weight of the polycarbosilane, and may contain the shape of the bulk PCS produced as described above.

[0026] 1. Polycarbosilane (PCS) PCS contains components with various molecular weights. The PCS according to this embodiment is characterized in that the content of components with a molecular weight of 1000 or less is 25.0% or more and 34.0% or less, and the weight-average molecular weight (Mw) is 3300 or more and 5500 or less. In this specification, the above-mentioned components with a molecular weight of 1000 or less may be referred to as "low molecular weight components" or "LMW components," and the PCS according to this embodiment may be referred to as "raw material PCS." PCS is a polymer having an amorphous structure and is a substance that does not clearly exhibit temperatures equivalent to the glass transition temperature and melting point of a crystalline polymer.

[0027] (Content of components with a molecular weight of 1000 or less) PCS with a content of components with a molecular weight of 1000 or less (low molecular weight components) of less than 25.0% has a high viscosity in the liquid phase in the molten state and insufficient fluidity, making it difficult to transfer to the second step in the first step of the method for producing high molecular weight PCS described later, which is to prepare solidified polycarbosilane in a solid phase state (hereinafter sometimes referred to as "solidified PCS"). On the other hand, if the content of low molecular weight components (LMW components) exceeds 34.0%, although the fluidity is good, the softening point is excessively low, making it difficult to maintain the solid phase state of the PCS when the low molecular weight components are removed from the solidified PCS in the third step of the method for producing high molecular weight PCS described later. Therefore, the content of LMW components is preferably 25.0% or more, more preferably 27.0% or more, and even more preferably 28.0% or more. On the other hand, the above content is preferably 34.0% or less, and more preferably 30.0% or less. The content of the above-mentioned LMW component may be set to any range obtained by arbitrarily combining the lower and upper limits shown above regarding the content. From the viewpoint of transporting the molten PCS and performing the LMW component removal treatment in the solid state of the PCS, the content of the above-mentioned LMW component is preferably 25.0 to 34.0%, more preferably 28.0 to 34.0%, and most preferably 28.0 to 30.0%.

[0028] The integrated molecular weight distribution of PCS can be obtained by analysis using gel permeation chromatography (GPC) equipped with a differential refractometer as a detector. The content of low molecular weight components in the PCS according to this embodiment is calculated using the above integrated molecular weight distribution. Specifically, the content can be identified by a value calculated by dividing the sum of signal intensities corresponding to molecular weights of 0 to 1000 by the total sum of signal intensities, based on the integrated molecular weight distribution calculated from the signal intensity of the differential refractometer.

[0029] (Weight-average molecular weight (Mw)) If the weight-average molecular weight of PCS increases, the viscosity of the molten PCS at the transfer temperature in the first step described below increases, making it difficult to transfer the molten PCS. For this reason, the weight-average molecular weight (Mw) of PCS is preferably 5500 or less, more preferably 5100 or less, and even more preferably 4500 or less. On the other hand, if the weight-average molecular weight of PCS is too small, it is difficult to maintain the solid state of PCS in the removal treatment of low molecular weight components in the third step described below, and the softening point of PCS does not rise sufficiently in the third step, making it difficult to proceed with the polymerization reaction of PCS while maintaining the solid state of PCS in the fourth step following the third step. For this reason, the weight-average molecular weight of PCS is preferably 3300 or more, more preferably 3500 or more, and even more preferably 3700 or more. The above weight-average molecular weight may be set within a range that is an arbitrary combination of the lower and upper limits shown above. The above weight-average molecular weight is preferably 3300 to 5500, more preferably 3500 to 5100, and even more preferably 3700 to 4500, from the viewpoint of transporting molten PCS and removing low molecular weight components in solid-state PCS.

[0030] As described above, the PCS according to this embodiment has a specific range with respect to the content of low molecular weight components and weight-average molecular weight, so that in the third step, low molecular weight components can be removed while maintaining the solid phase state. For this reason, the PCS according to this embodiment is preferably used as a raw material for solidified PCS in the third step.

[0031] When manufacturing PCS according to this embodiment, known manufacturing methods such as the liquid-gas phase thermal decomposition condensation method or thermal decomposition reaction using an autoclave can be used. By adjusting the reaction temperature or reaction time, PCS having a specific component content and molecular weight can be manufactured. As starting materials for 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.

[0032] When preparing the PCS according to this embodiment, one or more compounds selected from the group of linear polysilane compounds or cyclic silane compounds described above can be used as starting materials. For example, dodecamethylcyclohexasilane (DMCHS), a cyclic silane compound, can be used as a starting material to produce the raw material PCS by a liquid-gas phase thermal decomposition condensation method.

[0033] (Viscosity) In this embodiment, when transferring the molten liquid phase PCS to the next process, from the viewpoint of suppressing clogging of transfer pipes and the like and smoothly transferring the liquid phase PCS, the viscosity of the molten PCS at 450°C is preferably 20.0 Pa·s or less, more preferably 9.0 Pa·s or less, more preferably 7.0 Pa·s or less, even more preferably 5.0 Pa·s or less, and particularly preferably 4.0 Pa·s or less.

[0034] The degree of transferability of molten PCS can be evaluated based on the viscosity of the molten PCS at the transfer temperature. In this embodiment, the transferability of molten PCS was evaluated as good when the viscosity of the molten PCS at a transfer temperature of 450°C was 20.0 Pa·s or less. The transfer temperature used to evaluate transferability is not limited to 450°C, but can be set appropriately considering the quality of the PCS and the specifications of the equipment.

[0035] The viscosity of the PCS according to this embodiment is influenced by the content of low molecular weight components and the weight-average molecular weight of the PCS. As the content of low molecular weight components (molecular weight 1000 or less) decreases and the weight-average molecular weight of the PCS increases, the viscosity of the molten PCS at the transfer temperature increases, making it difficult to transfer the molten PCS.

[0036] The viscosity of the molten PCS according to this embodiment can be obtained using a general viscosity measuring device. However, because the applicability range of the measuring device is limited, it is difficult to measure the viscosity of molten PCS at temperatures higher than the usable temperature range of the device. Therefore, for the viscosity of the molten PCS in the temperature range of 400°C or higher (for example, 450°C) according to this embodiment, the estimated viscosity obtained by estimating based on the viscosity measured at a measurable temperature can be used.

[0037] In this embodiment, the so-called Andrade formula, shown in Equation 1 below, can be used as a method for estimating the viscosity of molten PCS from measured values. Specifically, the viscosity is measured at a measurable temperature, and then a graph is created in which the measured viscosity is plotted as a function of temperature based on Equation 1 below. By extrapolating this graph to the high-temperature range, the viscosity in the high-temperature range can be calculated as an estimated value. From the viewpoint of improving the accuracy of the calculated value, it is preferable that the number of plotted values ​​for the measured viscosity be three or more.

[0038] η = a × exp(B / RT) ...Equation 1 Here, the sign "η" is viscosity, the sign "R" is the gas constant, the sign "T" is the absolute temperature of the sample, and the signs "a" and "B" are material-specific coefficients.

[0039] Furthermore, as described in the examples below, the criteria for evaluating transferability based on viscosity can be determined based on the recovery rate obtained using a liquid with any viscosity. When performing such viscosity measurements, it is sufficient to select a liquid with a viscosity suitable for measurement, and the type of liquid is not limited. Regarding the transfer temperature, it may be carried out at room temperature if the viscosity at 450°C can be reproduced. The evaluation test of transferability at each viscosity according to this embodiment can be carried out at room temperature, for example, using an aqueous solution of "Metholose® 100" (manufactured by Shin-Etsu Chemical Co., Ltd.) with adjusted viscosity.

[0040] 2. Method for producing high molecular weight PCS (high molecular weight polycarbosilane) The method for producing high molecular weight PCS according to this embodiment is characterized by comprising: a first step of preparing molten polycarbosilane using a specific polycarbosilane as described in "1. Polycarbosilane (PCS)" above, and transferring the molten polycarbosilane; a second step of cooling the molten polycarbosilane to prepare solidified polycarbosilane in a solid state; a third step of heating the solidified polycarbosilane obtained in the second step while maintaining its solid state to remove low molecular weight components contained in the solidified polycarbosilane; and a fourth step of heating the polycarbosilane for solid-phase polymerization obtained in the third step to perform solid-phase polymerization.

[0041] (2.1) First step (Transfer of molten polycarbosilane) The PCS according to this embodiment, having a specific molecular weight, is prepared as molten PCS and then transferred to the next second step to be solidified. If the molten PCS solidifies during transfer, problems such as adhesion to the transfer piping may occur, so it is preferable to transfer the PCS while maintaining it in a molten state. Note that PCS heated above its softening point melts into a liquid. In this specification, this state exhibiting a liquid or liquid phase is referred to as the "molten state".

[0042] (Preparation of molten PCS) PCS having a specific component content and molecular weight obtained by a known production method is heated to a temperature above the softening point of the PCS in a preparation container to prepare molten PCS. The form of the PCS introduced into the preparation container may be in a solid state or may be in a previously melted state. It is preferable to stir and mix the molten PCS in the preparation apparatus so that the temperature becomes uniform.

[0043] (Transfer of molten PCS) In order to prepare solidified PCS, the molten PCS is transferred to the second step described below. The transfer means from the first step to the second step may be arbitrarily selected according to the viscosity and temperature of the molten PCS, the transfer speed, etc. For example, transfer means such as transfer by self-weight fall, transfer by a pump, or pressure feeding by a gas can be used. In the case of transfer by a pump, the installation position of the pump is not particularly limited. For example, a pump can be installed in the connection pipe connecting the preparation apparatus of the molten PCS and the cooling and solidifying apparatus of the molten PCS. In the case of pressure feeding by a gas, a gas may be introduced into the preparation apparatus of the molten PCS, and the molten PCS may be transferred through the above connection pipe. The gas used for the above pressure feeding is not particularly limited as long as it does not substantially affect the quality of the PCS. For example, an inert gas is preferable. In addition, in order to control the transfer amount of the molten PCS, a valve can be installed in the above connection pipe.

[0044] The recovery rate before and after the transfer from the first step to the second step is preferably 90.0% or more, more preferably 92.0% or more, and even more preferably 94.0% or more from the viewpoint of increasing the yield of the PCS obtained after the second step.

[0045] The transfer of the molten PCS is preferably carried out in an atmosphere containing an inert gas in order to keep the quality of the molten PCS substantially constant. The inert gas can be selected from the group consisting of nitrogen gas and rare gases (for example, argon gas). The atmosphere may contain a small amount of oxygen within a range that does not substantially affect the quality of the PCS. In addition, one type of inert gas may be used, or a combination of a plurality of types may be used.

[0046] (Viscosity of molten PCS) From the viewpoint of suppressing the adhesion of PCS to transfer pipes and the like and the blockage of pipes and smoothly transferring molten PCS, the viscosity of molten PCS at the transfer temperature is preferably 20.0 Pa·s or less, more preferably 9.0 Pa·s or less, still more preferably 7.0 Pa·s or less, further preferably 5.0 Pa·s or less, and particularly preferably 4.0 Pa·s or less.

[0047] Since the viscosity of molten PCS decreases according to Andrade's equation as the temperature of molten PCS increases, the transfer of molten PCS becomes easier. Therefore, from the viewpoint of imparting sufficient fluidity to molten PCS, the transfer temperature of molten PCS according to the present embodiment is preferably 300°C or higher, more preferably 400°C or higher, and still more preferably 425°C or higher. On the other hand, since the polymerization of PCS tends to proceed more easily in a higher temperature range, from the viewpoint of suppressing the deterioration of the quality of PCS due to excessive polymerization, the transfer temperature is preferably 550°C or lower, more preferably 500°C or lower, and still more preferably 485°C or lower. The transfer temperature may be set within a temperature range arbitrarily combining the above-mentioned lower limit and upper limit. From the above viewpoints, the transfer temperature is preferably 300 to 550°C, more preferably 400 to 500°C, and still more preferably 400 to 485°C.

[0048] (2.2) Second step (Preparation of solidified polycarbosilane) The molten PCS transferred from the first step is cooled and solidified in the second step, whereby solidified polycarbosilane in a solid state is prepared. The cooling method is not particularly limited as long as the temperature of molten PCS can be lowered below the softening point of PCS. For example, molten PCS can be supplied to an extruder cooled below the softening point of PCS and extruded while being solidified in the extruder. Alternatively, molten PCS may be extruded from the extruder into an atmosphere below the softening point of PCS or into a refrigerant such as water and solidified.

[0049] In this embodiment, the softening point of the PCS in each step is defined herein as "the temperature at which the PCS can no longer maintain a solid state, melts, integrates, and becomes transparent." Specifically, as described in the "Measurement of Softening Point" section of the examples below, when the light transmittance passing through a glass tube filled with PCS powder is measured using a melting point analyzer, the softening point of the PCS is defined as the temperature indicated corresponding to the state of the PCS where the above-mentioned light transmittance is 40% or more. The above-mentioned melting point analyzer is an analytical device whose measurement principle is that the light transmittance changes in accordance with the change in sample form before and after the melting point. As described above, by using a melting point analyzer, the temperature at which the PCS is in a molten state can be measured according to the change in light transmittance. The softening point of the PCS in this embodiment is a temperature that can be evaluated by the temperature corresponding to a light transmittance of 40% or more in the melting point analyzer.

[0050] The second step in this embodiment preferably includes a step of refining the solidified PCS to a granular or powdery size. The solidified PCS is then subjected to a third step, described later, to remove low molecular weight components. Furthermore, a solid-phase polymerization treatment is performed in a fourth step, described later.

[0051] The smaller the average particle size of the solidified PCS, the more efficiently low molecular weight components are removed from the PCS in the third step, and the more efficiently the polymerization reaction proceeds in the fourth step. From this viewpoint, the average particle size of the solidified PCS is preferably 1000.0 μm or less, more preferably 500.0 μm or less, and even more preferably 300.0 μm or less. On the other hand, as the particle size of the PCS powder decreases, it exhibits strong adhesion due to intermolecular forces. Therefore, from the viewpoint of smoothly transporting the PCS powder, the average particle size of the solidified PCS is preferably 1.0 μm or more, more preferably 5.0 μm or more, and even more preferably 10.0 μm or more. The above average particle size may be set within a range that is an arbitrary combination of the lower and upper limits shown above. From each of the above viewpoints, the average particle size of the solidified PCS is preferably 1.0 to 1000.0 μm, more preferably 10.0 to 500.0 μm, and even more preferably 15.0 to 300.0 μm.

[0052] The average particle size of the solidified PCS according to this embodiment is the volume-average diameter (MV) that can be calculated by the following equation 2. It is measured by the laser diffraction scattering method, which is excellent in terms of measurement accuracy and speed. MV = (V1・d1 + V2・d2 + ... + Vk・dk) / (V1 + V2 + ... + Vk) ...Equation 2 Here, d1, d2, ..., dk are the particle diameters of each particle when the particles contained in the powder are arranged in order from the smallest particle diameter, and V1, V2, ..., Vk are the volumes of the particles corresponding to d1, d2, ..., dk.

[0053] The second step is preferably carried out in an atmosphere containing an inert gas in order to maintain a nearly constant quality of the PCS. The inert gas can be selected from the group consisting of nitrogen gas and noble gases (e.g., argon gas). One type of inert gas may be used, or a combination of multiple types of inert gases may be used. The atmosphere may contain a small amount of oxygen, to the extent that it does not substantially affect the quality of the PCS.

[0054] The method of transferring the solidified PCS from the solidified PCS manufacturing apparatus to the third step's low-molecular-weight component removal apparatus is not particularly limited. The two apparatuses may be connected by piping with valves installed as needed, and the transfer may be continuous. Alternatively, the solidified PCS may be removed from the solidified PCS manufacturing apparatus and supplied to the low-molecular-weight component removal apparatus in a batch manner.

[0055] (2.3) Third step (removal of low molecular weight components) The solidified polycarbosilane obtained in the second step is subjected to a process in the third step in which it is heated while maintaining its solid state to remove the low molecular weight components contained in the solidified polycarbosilane. The PCS obtained in the third step is used as PCS for solid-phase polymerization and is then used in the next fourth step.

[0056] Low molecular weight (LMW) components are thought to have lower softening and boiling points compared to high molecular weight components. When heated to high temperatures, LMW components readily liquefy, and some or all of the solidified PCS may join together via the liquefied portions, forming lumpy PCS. When multiple lumpy PCS are formed, if the total weight of these lumpy PCS is 50% or more of the total weight of polycarbosilane, it may cause problems such as adhesion to the processing container. In addition, the presence of LMW components in the solidified PCS lowers the overall softening point of the PCS, and when heated to high temperatures, it may melt the entire solidified PCS. When solidified PCS melts, it is impossible to maintain the solid phase state, making it difficult to remove from the processing container.

[0057] Therefore, it is preferable to remove the LMW component from the solidified PCS before solid-phase polymerization in the next fourth step. PCS from which the LMW component has been removed can undergo polymerization while maintaining a solid state in the fourth step, thus enabling the production of high molecular weight PCS. Furthermore, unlike the production of PCS by liquid-phase polymerization, after solid-phase polymerization, it is possible to avoid the PCS adhering to the inner wall surface of the processing container and the formation of solidified products in which PCS are integrated with each other, so the PCS obtained by solid-phase polymerization has fluidity. As a result, the PCS can be easily removed and recovered from the reaction container, reducing the PCS recovery work. On the other hand, if the LMW component is not sufficiently removed, a large amount of LMW component will be present, causing fusion and melting of PCS during the solid-phase polymerization process, making it difficult to proceed with the polymerization reaction in a solid state.

[0058] In the third step, the removal of LMW components is preferably carried out using PCS in a solid phase state. If it is carried out using PCS in a liquid phase state, the molten PCS obtained after the LMW component removal treatment must be cooled and solidified again before the solid-phase polymerization treatment in the fourth step described below. This is undesirable because it adds work steps and equipment, leading to increased production costs.

[0059] In the third step, it is preferable to stir and uniformly heat the solidified PCS in the processing apparatus so that the removal of the LMW component proceeds uniformly.

[0060] The LMW component removal treatment is preferably carried out in an atmosphere containing an inert gas in order to suppress oxidation of the PCS. The inert gas can be selected from the group consisting of nitrogen gas and noble gases (e.g., argon gas). The atmosphere may contain a small amount of oxygen in a range that does not substantially affect the quality of the PCS. In addition, one type of inert gas may be used, or a combination of multiple types may be used.

[0061] The method for forming and maintaining an inert gas atmosphere is not particularly limited. For example, one method is to continuously supply and discharge an inert gas stream into the processing container. In such a method, the atmosphere formed by nitrogen gas may also be referred to as a "nitrogen atmosphere" in this specification.

[0062] The atmospheric pressure during the LMW component removal process is not particularly limited. For example, low molecular weight components can be removed under normal or reduced pressure. When using reduced pressure, a low pressure range of 10 torr or less may be selected.

[0063] In the third step, removing the LMW component from the PCS raises the softening point of the PCS, allowing the PCS to be heated to a high temperature range while maintaining its solid state in the subsequent fourth step.

[0064] The changes resulting from the removal of the LMW component can be evaluated by comparing the PCS before and after the removal treatment, based on the integrated molecular weight distribution obtained by measurement using gel permeation chromatography (GPC) (hereinafter referred to as "GPC measurement"), and assessing the degree to which the proportion of LMW component in the PCS decreases after the removal treatment. Specifically, it can be calculated by subtracting the proportion of LMW component in the PCS after the removal treatment from the proportion of LMW component in the PCS before the removal treatment. From the viewpoint of significantly increasing the softening point, the decrease in the LMW component content before and after the removal treatment is preferably 2.0% or more, more preferably 3.0% or more, and even more preferably 5.0% or more.

[0065] The content of LMW components in the PCS obtained after the LMW component removal treatment is preferably 25.0% or less, and more preferably 23.0% or less, in order to facilitate the solid-phase polymerization treatment in the next fourth step. On the other hand, the content of LMW components is preferably 15.0% or more, and more preferably 20.0% or more, in order to increase the production amount of high molecular weight PCS. The above content may be set within a range that is an arbitrary combination of the lower and upper limits shown above. The above content is preferably 15.0 to 25.0%, and more preferably 20.0 to 23.0%.

[0066] In the third step, the LMW component removal process involves heating the PCS while maintaining it in a solid state to efficiently remove the LMW component. Therefore, after reaching the heating start temperature described later, it is preferable to heat the PCS while increasing the temperature. If the heating rate is too fast, the heating rate may exceed the rate at which the PCS softens, making it impossible to maintain the PCS in a solid state. For this reason, the heating rate is preferably 30°C / 10min or less, more preferably 20°C / 10min or less, and even more preferably 15°C / 10min or less. On the other hand, from the viewpoint of shortening the processing time, the heating rate is preferably 3°C / 10min or more, more preferably 5°C / 10min or more, even more preferably 7°C / 10min or more, and particularly preferably 10°C / 10min or more. The heating rate may be set within a range that is an arbitrary combination of the lower and upper limits shown above. From the viewpoint of shortening the processing time and reacting the PCS in a solid state, the above heating rate is preferably 3 to 30°C / 10 min, more preferably 3 to 15°C / 10 min, even more preferably 5 to 15°C / 10 min, and particularly preferably 10 to 15°C / 10 min.

[0067] The heating start temperature in the third step is set to a temperature range lower than the softening point of the solidified PCS. From the viewpoint of efficiently removing the LMW component, it is preferable that the temperature be 230°C or higher, and more preferably 250°C or higher. On the other hand, if the heating start temperature is too high, the PCS will liquefy above its softening point, so from this viewpoint, the heating start temperature is preferably 350°C or lower, and more preferably 300°C or lower. The heating start temperature may be set to a range that is an arbitrary combination of the lower and upper limits shown above. From each of the above viewpoints, the heating start temperature is preferably 230 to 350°C, and more preferably 250 to 300°C.

[0068] The heating conditions up to the heating start temperature are not particularly limited. Heating may be performed at a rate higher than the above-mentioned heating rate. If heating is performed at a rate higher than the above-mentioned heating rate, the heating rate should be adjusted so that it reaches the above-mentioned heating rate after the heating start temperature is reached.

[0069] The heating termination temperature in the third step is preferably 230°C or higher, more preferably 250°C or higher, even more preferably 300°C or higher, and particularly preferably 320°C or higher, from the viewpoint of reducing the LMW component content to a level that does not melt during solid-phase polymerization. On the other hand, from the viewpoint of maintaining the PCS in a solid state during the LMW component removal process, the heating termination temperature is preferably 400°C or lower, and more preferably 350°C or lower. The above heating termination temperature may be set to a temperature range that is an arbitrary combination of the lower and upper limits shown above. From each of the above viewpoints, the above heating termination temperature is preferably 230 to 400°C, more preferably 250 to 350°C, even more preferably 300 to 350°C, and particularly preferably 320 to 350°C.

[0070] In the third step, the heating termination temperature is preferably higher than the heating start temperature, from the viewpoint of effectively removing the LMW component.

[0071] In the process of raising the temperature from the heating start temperature to the heating end temperature in the third step, steps may be provided to change the heating rate during the heating process, or to stop heating and hold it at a predetermined temperature, within a range that can maintain the solid state of the PCS. Multiple steps for holding the temperature may be provided. From the viewpoint of effectively removing the LMW component, the temperature in the temperature holding step is preferably 250°C to 320°C, more preferably 260°C to 300°C, and even more preferably 270°C to 280°C. Furthermore, from the viewpoint of effectively removing the LMW component, the time for holding the above temperature is preferably 1 hour to 9 hours, more preferably 2 hours to 9 hours, and even more preferably 3 hours to 9 hours.

[0072] When the processed PCS is transferred from the third step to the fourth step, the means of transfer are not particularly limited. The processing equipment in both steps may be connected by piping equipped with valves to continuously transfer the processed PCS, or the processed PCS may be taken out of the processing equipment in the third step and supplied to the processing equipment in the fourth step in a batch manner. Furthermore, from the viewpoint of reducing manufacturing costs, after the removal treatment in the third step, the solid-phase polymerization treatment in the fourth step may be carried out using the processing equipment in the third step.

[0073] (2.4) Fourth step (Solid-phase polymerization) The method for producing high molecular weight PCS according to this embodiment includes a fourth step in which a solid-phase polymerization treatment is performed on PCS for solid-phase polymerization, which has been treated to remove low molecular weight components, at a temperature range of 250°C or higher and 410°C or lower. The solid-phase polymerization of PCS according to this embodiment refers to a reaction in which the PCS to be polymerized is increased in molecular weight while remaining in a solid state at the reaction temperature.

[0074] In the fourth step of this embodiment, it is preferable to heat the PCS after the low molecular weight component removal treatment to 250°C or higher. If the heating temperature is below 250°C, the polymerization reaction proceeds slowly, making it difficult to increase the molecular weight of the PCS. On the other hand, heating at a temperature exceeding the softening point of the PCS is undesirable because the PCS transitions to a molten state, making it difficult to maintain the solid state. Therefore, the heating temperature in the solid-phase polymerization treatment of the fourth step is preferably 250°C or higher, and further, depending on the softening point of the PCS, it is also preferable to have a temperature of 300°C or higher, 310°C or higher, 320°C or higher, 330°C or higher, 340°C or higher, or 350°C or higher.

[0075] On the other hand, in the fourth step, solid-phase polymerization, it is necessary to heat the PCS at a temperature below its softening point. In addition to this, if the PCS is heated at a temperature exceeding 410°C, ultra-high molecular weight PCS that are insoluble in the solvent (hereinafter referred to as "solvent-insoluble PCS") are generated. These solvent-insoluble PCS have various adverse effects on the applications of the PCS, such as causing yarn breakage when dry spinning the PCS obtained after solid-phase polymerization, or becoming defect points in the silicon carbide fibers obtained after firing, thereby reducing the strength of the fibers. Therefore, the generation of these solvent-insoluble PCS is undesirable when using the 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 the PCS after solid-phase polymerization is dissolved in a solvent, the presence of these solvent-insoluble PCS in the solution makes it difficult to uniformly impregnate the ceramic material with the PCS, which is undesirable. Therefore, it is preferable that the upper limit of the heating temperature in the fourth step, solid-phase polymerization, be 410°C or lower.

[0076] 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.

[0077] The heating temperature for solid-phase polymerization may be set to a temperature range that is an arbitrary combination of the lower and upper limits shown above. From the viewpoint of suppressing the formation of solvent-insoluble PCS while allowing the polymerization reaction to proceed, the heating temperature is preferably 250 to 410°C, and more preferably 300 to 410°C, 310 to 410°C, 320 to 410°C, 330 to 410°C, 340 to 410°C, or 350 to 410°C, depending on the softening point of the raw material PCS.

[0078] In the fourth step, if the PCS is heated near its softening point to carry out the polymerization reaction, some of the raw material PCS may melt and form bulky PCS. If multiple bulky PCS are formed, and the total weight of these bulky PCS is 50% or more of the total weight of polycarbosilane, it may cause problems such as adhesion to the processing container. Furthermore, since some of the bulky PCS exist in the liquid phase, it may cause a decrease in the polymerization reaction rate. Therefore, solid-phase polymerization may be carried out by heating at a low temperature away from the softening point. For example, the heating temperature for solid-phase polymerization can be selected to be 10°C or more lower, or 20°C or more lower, than the softening point of the PCS to be used in the fourth step.

[0079] In the fourth step, the polymerization reaction can be accelerated by heating at a temperature range higher than the heating completion temperature in the third step's low molecular weight component removal treatment to perform solid-phase polymerization. From this perspective, it is preferable that the heating temperature for solid-phase polymerization is higher than or equal to the heating completion temperature in the third step.

[0080] In the fourth step, depending on the softening point of the PCS, steps may be provided to change the heating rate during heating, or to stop heating and maintain a predetermined temperature, within a range where no solvent-insoluble PCS are generated or fusion occurs.

[0081] Furthermore, PCS with increased molecular weight tend to have a higher softening point as the molecular weight increases. 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 a high softening point for the PCS used in the fourth step, from the viewpoint of setting a higher temperature for solid-phase polymerization to rapidly increase molecular weight. The weight-average molecular weight of the PCS used in the fourth step is preferably 3700 or higher, more preferably 4000 or higher, even more preferably 4500 or higher, particularly preferably 5000 or higher, and most preferably 6000 or higher, from the viewpoint of obtaining PCS with a high molecular weight conversion rate after solid-phase polymerization in a short time.

[0082] The heating time in the fourth step, the solid-phase polymerization treatment, is not particularly limited. It can be set appropriately according to various conditions such as the type of PCS, heating temperature, and high molecular weight conversion rate. As the high molecular weight conversion rate increases 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 longer heating time may be selected.

[0083] The fourth step, solid-phase polymerization, is preferably carried out in an atmosphere containing an inert gas in order to suppress oxidation of the PCS. The inert gas can be selected from the group consisting of nitrogen gas and noble gases (e.g., argon gas). The atmosphere may also contain a small amount of oxygen, as long as it does not hinder the increasing molecular weight of the PCS.

[0084] 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.

[0085] The method for forming and maintaining an inert gas atmosphere is not particularly limited. For example, a method of continuously supplying and discharging an inert gas flow into a processing container can be used. In this specification, the atmosphere formed by nitrogen gas in such a method may be referred to as the "nitrogen atmosphere" below.

[0086] In the method for producing high molecular weight PCS according to this embodiment, the following heat treatment apparatuses can be used in the third or fourth step.

[0087] (Heat Treatment Apparatus) Figure 1 schematically shows a heat treatment apparatus as an example of a solid-phase polymerization apparatus used to carry out solid-phase polymerization under the nitrogen atmosphere described above. A similar apparatus can also be used in the third step described above. The configuration of the heat treatment apparatus 1 is broadly divided into a processing section for removing low molecular weight components or carrying out the solid-phase polymerization reaction, and an atmosphere forming section for forming the atmosphere.

[0088] As shown in Figure 1, the former processing section includes a processing container 2, a heater 3, and a thermocouple 4. The processing container 2 is a component that houses PCS (not shown) and is used for removing low molecular weight components from each PCS or for solid-phase polymerization. The heater 3 is a component that is arranged around the processing container 2 and is used to heat each PCS in the processing container 2. The thermocouple 4 is a component that measures the heating temperature of the processing container 2. The operation of the heater 3 is controlled based on the measurement value from the thermocouple 4. The processing container 2 may also be equipped with stirring means for mixing the raw material PCS during heating (not shown).

[0089] The latter atmosphere formation section, as shown in Figure 1, includes a gas supply passage 5, a gas discharge passage 6, a flow meter 7, and a cooling pipe 8. The gas supplied to the processing container 2 from the gas supply passage 5 passes through the processing container 2 and is then discharged to the outside from the gas discharge passage 6.

[0090] For example, when a nitrogen atmosphere is formed in the processing container 2 using a heating device, the nitrogen gas is continuously supplied into the processing container 2 from the gas supply passage 5 and then continuously discharged from the gas discharge passage 6, allowing a nitrogen gas flow to pass through the processing container 2. This maintains a nitrogen atmosphere filled with nitrogen gas inside the processing container 2. Even if air enters from the outside, that air can be discharged by the nitrogen gas flow.

[0091] The heating apparatus maintains the atmosphere inside the processing container 2 while heating the PCS at each stage of the process within the processing container 2 using heaters 3 surrounding the processing container 2. The heating is increased until each PCS reaches a predetermined temperature, and the heating is maintained for a predetermined time as needed, after which the heating is stopped. After the processing container 2 is cooled, the PCS inside the processing container 2 are recovered. However, if the removal of low molecular weight components and solid-phase polymerization are performed in the same apparatus, the series of operations may be carried out continuously without recovery.

[0092] (High molecular weight conversion rate) In the method for producing high molecular weight PCS according to this embodiment, it is preferable that the high molecular weight conversion rate, expressed as the ratio (Mw2 / Mw1) of the weight-average molecular weight (Mw1) of the polycarbosilane after solid-phase polymerization to the weight-average molecular weight (Mw1) of the polycarbosilane before solid-phase polymerization, is 1.10 or higher. PCS with a high high molecular weight conversion rate corresponds to a large proportion of high molecular weight PCS polymerized from the PCS before solid-phase polymerization. Therefore, the high molecular weight conversion rate is preferably 1.10 or higher, more preferably 1.20 or higher, even more preferably 1.50 or higher, and particularly preferably 2.00 or higher.

[0093] On the other hand, if the molecular weight conversion rate is too high, some of the obtained high molecular weight PCS may form ultra-high molecular weight PCS (solvent-insoluble PCS) that are insoluble in the 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. Thus, 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, for example, 1.10 to 20.00, more preferably 1.20 to 15.00, even more preferably 1.50 to 10.00, and particularly preferably 2.00 to 10.00.

[0094] The following describes examples of the present invention. The present invention is not limited to the following description.

[0095] (PCS) The PCS used in the following experiment was synthesized using the cyclic silane compound dodecamethylcyclohexasilane (DMCHS) as a starting material, by a liquid-gas phase thermal decomposition condensation method at atmospheric pressure in a liquid-gas phase thermal decomposition apparatus.

[0096] (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 was connected and used so that the liquid flowed through them in this order from the pump side (all manufactured by Resonaq 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%

[0097] (Determination regarding the formation of toluene-insoluble components) PCS obtained by solid-phase polymerization is generally used by dissolving it in the 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 that are toluene-insoluble may be referred to as "toluene-insoluble components" below.

[0098] Specifically, the turbidity (unit: NTU) of the toluene solution prepared to measure the molecular weight of PCS was measured using a digital turbidimeter (manufactured by APERA INSTRUMENTS Co., Ltd.). When the turbidity exceeded 40 NTU, toluene-insoluble components were visually confirmed. Therefore, it was determined that toluene-insoluble components are generated in PCS with a turbidity exceeding 40 NTU, and that toluene-insoluble components are substantially not generated in PCS with a turbidity of 40 NTU or less. Hereafter, cases where toluene-insoluble components are generated will be described as "insoluble components present," and cases where toluene-insoluble components are substantially not generated will be described as "insoluble components absent."

[0099] The integrated molecular weight distribution was calculated from the detector signal intensity obtained by GPC measurement. The content of low molecular weight components with a molecular weight of 1000 or less in PCS is calculated based on the above integrated molecular weight distribution by dividing the total amount of distribution corresponding to molecular weights of 0 to 1000 by the total amount of distribution, and is expressed as a percentage (%).

[0100] (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.

[0101] 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 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%. Three of the glass tubes were inserted into the tube insertion port of the melting point analyzer.

[0102] The glass tube was heated to an initial temperature. At this initial temperature, it was confirmed that the PCS powder had not softened or melted and was maintaining a solid state. Subsequently, the temperature was increased 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 was used to measure the PCS in six glass tubes, and the lowest temperature recorded among the obtained measurement results was adopted as the PCS softening point. If the PCS in the glass tube remained in powder form 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 PCS softening point described above, a softening point of ">410°C" means a temperature above 410°C.

[0103] The initial temperature was set to be below the expected softening point temperature, and the difference between the initial temperature and the expected softening point temperature was set to 30°C or more. For example, if the expected softening point temperature was 210-240°C, the initial temperature was set to 180°C, and if the expected softening point temperature was 240-270°C, the initial temperature was set to 210°C.

[0104] (Measurement of average particle size) The average particle size of the raw material PCS used in each example and comparative example was measured by the following procedure. PCS dispersion was prepared by adding PCS powder to water and subjecting it to ultrasonic treatment. Then, the dispersion was put into a particle size distribution analyzer (Microtrac-Bell Co., Ltd.) and the volume average diameter (MV) was measured.

[0105] (Calculation of viscosity at 450°C) Three or more temperatures were selected within the temperature range of 150°C to 380°C, and the viscosity of PCS at each temperature was measured using the method described below. • Equipment name: MCR 702 MultiDrive SN82511319 (manufactured by Anton Paar) • Strain amount: 0.30% • Angular frequency: 13 rad / s • Shear rate: 50 s －１

[0106] For viscosity measurement, the PCS to be measured was packed into a cylindrical mold with a diameter of 25 mm. While the mold was heated to 50°C, the PCS inside the mold was compressed and pressed to produce a tablet-shaped sample with a diameter of 25 mm and a thickness of 1 mm. Using the obtained sample, the viscosity of the PCS was measured at three or more temperatures within the measurable range. The relationship between the measured viscosity and the reciprocal of the absolute temperature was plotted, and an approximate straight line based on a linear regression equation was created using the least squares method. Based on Andrade's equation shown in Equation 1 below, 450°C is in a higher temperature range than the measurable temperature range of the viscometer. Therefore, the estimated viscosity of the PCS at 450°C was calculated by extrapolating the above approximate straight line to the high-temperature range.

[0107] η = a × exp(B / RT) ...Equation 1 Here, the sign "η" is viscosity, the sign "R" is the gas constant, and the sign "T" is the absolute temperature of the sample. The signs "a" and "B" are material-specific coefficients and can be calculated from the slope and intercept in the above linear regression equation.

[0108] (Evaluation of the transferability of viscous liquids) In order to establish evaluation criteria for the transferability of viscous liquids, various viscosities of simulated liquids and a container equipped with a discharge valve at the bottom were prepared. After pouring the simulated liquid into the container, the discharge valve was opened to full capacity at room temperature, and the simulated liquid was discharged. Subsequently, under all conditions, it was confirmed that the simulated liquid in the piping was empty after 100 minutes, so it was determined that the transfer was complete, and the weight of the discharged simulated liquid was measured at that time. Five aqueous solutions of "Metrol 100 (registered trademark)" (manufactured by Shin-Etsu Chemical Co., Ltd.) with concentrations of 2.5 wt%, 5.0 wt%, 6.0 wt%, 7.5 wt%, and 8.0 wt% were used as simulated liquids. The viscosities of these aqueous solutions (simulated liquids) at room temperature were 0.1 Pa·s, 1.7 Pa·s, 9.3 Pa·s, 22.9 Pa·s, and 30.2 Pa·s, respectively.

[0109] According to the measurement results of the above extraction test, the weight of the simulated liquid poured into the container, the weight of the simulated liquid recovered by opening the extraction valve, and the recovery rate were as follows: (1) For a simulated solution of 0.1 Pa·s, 246.10 g (input), 231.94 g (recovered), recovery rate 94.2% (2) For a simulated solution of 1.7 Pa·s, 215.66 g (input), 206.71 g (recovered), recovery rate 95.8% (3) For a simulated solution of 9.3 Pa·s, 234.51 g (input), 216.04 g (recovered), recovery rate 92.1% (4) For a simulated solution of 22.9 Pa·s, 252.16 g (input), 225.76 g (recovered), recovery rate 89.5% (5) For a simulated solution of 30.2 Pa·s, 223.18 g (input), 184.29 g (recovered), recovery rate 82.5%

[0110] According to the results of the above sampling test, when the viscosity at room temperature exceeds 20 Pa·s, the recovery rate of the simulated liquid falls below 90.0%, indicating poor transferability. Based on the above test results, the PCS according to this embodiment was evaluated as having poor transferability when the viscosity exceeds 20 Pa·s, making smooth transfer in transfer piping difficult.

[0111] (Example 1) As the raw material PCS, powdered PCS having the physical properties such as the softening point shown in Table 1 was used. In Table 1 and Tables 2 to 4 described below, the softening point is indicated by the symbol "TS", and the content of low molecular weight components (LMW components) is indicated by the symbol "Lc". To calculate the viscosity at 450°C, the viscosity of molten PCS at 280°C, 300°C, 320°C, and 340°C was measured. Based on Equation 1, the measured value of viscosity (η, unit Pa·s) was expressed as the reciprocal of the temperature (1 / T, unit K). －１ The values ​​were plotted against the given values ​​to create a graph as shown by "E1" in Figure 2. The vertical axis in Figure 2 is shown on a logarithmic scale of viscosity. The upper horizontal axis in Figure 2 is shown in degrees Celsius (Tc) and the lower horizontal axis is shown in the reciprocal of absolute temperature, 1 / T (K). －１ This was shown as follows. According to the extrapolation of the "E1" graph in Figure 2, the estimated viscosity of the molten PCS at 450°C was 1.5 Pa·s.

[0112] Next, the LMW component of the raw PCS was removed using a reaction apparatus as shown in Figure 1. As the raw PCS, powdered PCS having the physical properties such as the softening point shown in Table 1 was used, and the raw PCS was placed into the processing container 2. Then, nitrogen gas was continuously supplied into the processing container 2 from the gas supply passage 5 at a rate of 500 mL / min and continuously discharged from the gas discharge passage 6, thereby passing nitrogen gas through the processing container 2 and creating a nitrogen atmosphere that filled the processing container 2 with nitrogen gas.

[0113] While maintaining the nitrogen atmosphere described above, the PCS powder inside the processing container was heated by a heater surrounding the container to remove the LMW component. After the PCS temperature reached 250°C, the temperature was increased to 280°C at a rate of 10°C / 10 min. It was then held at 280°C for 3 hours. After that, the temperature was increased again to 320°C at a rate of 10°C / 10 min. Heating was stopped when it reached 320°C, and it was allowed to cool to room temperature (25°C) to obtain a sample for analysis. During the LMW component removal process, the PCS remained in a solid state.

[0114] Next, to carry out solid-phase polymerization of PCS using the same processing container, the nitrogen gas supply was increased to 100 mL / min and heating was started again. After reaching 320°C, heating was continued at 320°C for 3 hours to solidify the PCS. During this solid-phase polymerization process, the PCS remained in a solid state. After the processing container was allowed to cool to room temperature, the high molecular weight PCS in the processing container was recovered. After the solid-phase polymerization reaction, the PCS did not adhere to the inner wall surface of the processing container, and no solidified material of integrated PCS was formed. Therefore, the obtained PCS was fluid, and it was possible to easily remove and recover the PCS from the processing container.

[0115] The PCS obtained after the removal of the LMW components described above was dissolved in toluene to prepare a toluene solution for GPC measurement. Using this toluene solution, the molecular weight, such as weight-average molecular weight (Mw1), and the softening point were measured. In addition, the high molecular weight PCS obtained after the solid-phase polymerization reaction described above was also dissolved in toluene to prepare a toluene solution for GPC measurement. The molecular weight, such as weight-average molecular weight (Mw2), and the softening point were measured.

[0116] (Example 2) In Example 2, high molecular weight PCS was obtained using the same procedure as in Example 1, except that the heating conditions in the LMW component removal treatment and the solid-phase polymerization conditions were different. Since Example 2 used the same raw material PCS as Example 1, the measured viscosity of the PCS was estimated by extrapolating the graph shown in "E1". The estimated viscosity of the molten PCS at 450°C was 1.5 Pa·s. During the LMW component removal treatment and the solid-phase polymerization treatment, the PCS maintained a solid state. For the PCS after the LMW component removal treatment and the high molecular weight PCS after the solid-phase polymerization reaction, the molecular weight and softening point of the PCS were measured using the same method as in Example 1.

[0117] (Example 3) In Example 3, high molecular weight PCS was obtained using the same procedure as in Example 1, except that the raw material PCS used, the heating conditions in the LMW component removal treatment, and the solid-phase polymerization conditions were different. The measured viscosity of the PCS was calculated using the same method as in Example 1, and the graph shown as "E3" in Figure 2 was created. Extrapolating the "E3" graph in Figure 2, the estimated viscosity of the raw material PCS dissolved at 450°C was 0.3 Pa·s. During the LMW component removal treatment and the solid-phase polymerization treatment, the PCS maintained a solid state. For the PCS after the LMW component removal treatment and the high molecular weight PCS after the solid-phase polymerization reaction, the molecular weight and softening point of the PCS were measured using the same method as in Example 1.

[0118] (Example 4) Example 4 obtained high molecular weight PCS using the same procedure as in Example 1, except that the raw material PCS used, the evaluation method for the transportability of PCS at 450°C, the heating conditions in the LMW component removal treatment, and the solid-phase polymerization conditions were different.

[0119] The transportability of PCS at 450°C was evaluated by actually transporting the raw material PCS, in addition to estimating the viscosity of molten PCS at 450°C as performed in Example 1. The measured viscosity for estimating the viscosity of PCS at 450°C was measured at temperatures of 290°C, 300°C, 320°C, and 340°C. Based on these measurement results, a graph shown as "E4" in Figure 2 was created. Extrapolating the "E4" graph in Figure 2, the estimated viscosity of molten PCS at 450°C of the raw material PCS was 3.5 Pa·s.

[0120] In evaluating the transportability of PCS, the same apparatus as that used for evaluating the transportability of viscous liquids was used, except that a receiving container for recovering PCS was connected to the lower part of the extraction valve. Specifically, the processing container was equipped with an extraction valve at its lower part, and the outlet side of the extraction valve was connected to the receiving container. 411.15 g of raw PCS was placed in the processing container, and both the processing container and the receiving container were filled with nitrogen gas. Then, the processing container and the extraction valve were heated to 450°C. After the internal temperature of the processing container reached 450°C, the extraction valve was fully opened, and the PCS was extracted into the receiving container. After 100 minutes, the PCS recovered in the receiving container was allowed to cool to room temperature to solidify, and the weight of the obtained PCS was measured. The measured weight was 389.72 g, so the PCS recovery rate was 94.5%, indicating good transportability. Therefore, we confirmed that the actual PCS extraction results can be substituted for evaluation using estimated values.

[0121] In the LMW component removal treatment and solid-phase polymerization treatment, the solidified PCS recovered by the above-mentioned transportability evaluation test was used in a finely powdered form. As a result, the PCS maintained its solid state. For the PCS after the LMW component removal treatment and the high molecular weight PCS after the solid-phase polymerization reaction, the molecular weight and softening point of the PCS were measured using the same method as in Example 1.

[0122] (Examples 5 and 6) Examples 5 and 6 obtained high molecular weight PCS using the same procedure as in Example 1, except that the raw material PCS used and the heating conditions in solid-phase polymerization were different. The raw material PCS used had an Mw of 5035 and an Mn of 1263, with an LMW component content of 25.5%. The PCS maintained its solid state during the LMW component removal treatment and solid-phase polymerization treatment. The molecular weight of the high molecular weight PCS after the solid-phase polymerization reaction was measured using the same method as in Example 1.

[0123] (Comparative Example 1) Comparative Example 1 obtained high molecular weight PCS using the same procedure as in Example 1, except that the raw material PCS used, the measurement temperature for the measured viscosity to estimate the viscosity of PCS at 450°C, and the heating conditions in the LMW component removal treatment were different. The measured viscosity was measured at temperatures of 150°C, 160°C, 170°C, 190°C, and 210°C. Based on the measurement results, a graph shown as "CE1" in Figure 2 was created. According to the extrapolation of the "CE1" graph in Figure 2, the estimated viscosity of the molten PCS at 450°C of the raw material PCS was less than 0.001 Pa·s.

[0124] In the subsequent LMW component removal treatment, the temperature was increased to 320°C at a rate of 10°C / 10 min after reaching 120°C. However, the PCS could not maintain its solid state during this heating process and exhibited a liquid state. The PCS remained in a liquid state during the subsequent solid-phase polymerization treatment, and the resulting PCS was a highly viscous liquid. After cooling, the PCS adhered to the inner wall of the treatment container, making it difficult to recover the polymerized PCS.

[0125] (Comparative Example 2) In Comparative Example 2, the viscosity of the raw material PCS at 450°C was calculated using the same procedure as in Example 1, except that the raw material PCS used and the measurement temperature for the measured viscosity used to estimate the viscosity at 450°C were different. The measured viscosity was measured at temperatures of 320°C, 340°C, 360°C, and 380°C. Based on the measurement results, a graph shown as "CE2" in Figure 2 was created. According to the extrapolation of the "CE2" graph in Figure 2, the estimated viscosity of the molten PCS at 450°C was 894.6 Pa·s. Based on this viscosity value, the transportability of the molten PCS was evaluated as poor. Therefore, the obtained molten PCS did not proceed to the subsequent cooling and solidification treatments.

[0126] (Comparative Example 3) In Comparative Example 3, PCS after removal of the LMW component was prepared using the same procedure as in Comparative Example 1, except for the heating conditions in the LMW component removal treatment. However, the PCS after the LMW component removal treatment showed no substantial change in either the number-average molecular weight (Mn) or the weight-average molecular weight (Mw) compared to before the removal treatment, confirming that the LMW component had not been removed. Therefore, the PCS after the above removal treatment was not subjected to the subsequent solid-phase polymerization treatment.

[0127] (Comparative Example 4) In Comparative Example 4, a high molecular weight PCS was obtained using the same procedure as in Example 5, except that the heating conditions in solid-phase polymerization were different. During the LMW component removal treatment and solid-phase polymerization treatment, the PCS maintained its solid state. When the PCS obtained after the solid-phase polymerization treatment was dissolved in toluene, the turbidity of the toluene solution was determined to indicate the presence of insoluble components. Since the molecular weight of a toluene solution containing insoluble components cannot be accurately measured by GPC, molecular weight measurement was not performed on the PCS after the solid-phase polymerization reaction.

[0128] Tables 1 and 2 show the test details and measurement results for Examples 1 to 6 and Comparative Examples 1 to 4. In the "Removal Treatment of LMW Components" column of Table 1, the symbols No. 1 to No. 5 shown in the "Heating Method" column of "Heat Treatment" refer to the following heating methods (1) to (5) performed in the Examples and Comparative Examples. The numerical values ​​shown in the "Heating Rate" column refer to the heating rate between each temperature used in heating methods No. 1 to No. 4. (1) No. 1: Heat from 250°C to 280°C, hold at 280°C for 3 hours, and then heat from 280°C to 320°C. (2) No. 2: Heat from 250°C to 320°C. (3) No. 3: Heat from 230°C to 250°C, hold at 250°C for 3 hours, heat from 250°C to 280°C, hold at 280°C for 3 hours, and heat from 280°C to 320°C. (4) No. 4: Heat from 120°C to 230°C. (5) No. 5: Hold at 145°C for 6 hours.

[0129] In Table 1, the "PCS Transferability at 450°C" column under the "Raw Material PCS" column is indicated by the symbols "A (Good)" or "B (Poor)". "A" indicates that the viscosity at 450°C is 20 Pa·s or less, and the transferability is evaluated as good. "B" indicates that the viscosity at 450°C is greater than 20 Pa·s, and the transferability is evaluated as poor.

[0130] In Table 2, the "Heat Treatment" column under "Solid-Phase Polymerization Treatment" indicates a process in which heating conditions 1 to 3 are performed consecutively at predetermined temperatures and durations.

[0131] (Reference Example 1) Powdered PCS (Mn1084, Mw3879, low molecular weight component content 31.6%, softening point 282°C) was placed into the processing container 2 as the raw material PCS. Then, nitrogen gas was continuously supplied into the processing container 2 from the gas supply passage 5 at a rate of 500 mL / min and continuously discharged from the gas discharge passage 6, thereby passing nitrogen gas through the processing container 2 and creating a nitrogen atmosphere that filled the processing container 2 with nitrogen gas.

[0132] While maintaining the nitrogen atmosphere described above, the PCS powder inside the processing container was heated by a heater surrounding the container to remove the LMW component. After 10 minutes from the start of heating, the temperature of the PCS reached 170°C, and thereafter, heating was continued at 170°C for 3 hours. Next, it was allowed to cool to room temperature (25°C), and a sample for analysis was obtained. During the heating of the PCS, the PCS remained in a solid state. Using the analytical sample, the content of Mn, Mw, and LMW components, as well as the softening point, were measured using the same method as in Example 1.

[0133] (Reference Example 2) Reference Example 2 was carried out using the same procedure as Reference Example 1, except that the PCS was heated at 200°C for 3 hours.

[0134] (Reference Example 3) Reference Example 3 was carried out using the same procedure as in Reference Example 1, except that the PCS was heated at 230°C for 3 hours.

[0135] (Reference Example 4) Reference Example 4 was carried out using the same procedure as Reference Example 1, except that the PCS was heated at 250°C for 3 hours.

[0136] Table 3 shows the test procedures and measurement results for Reference Examples 1 to 4. In Table 3, the "Heating Conditions" column in the "LMW Component Removal Treatment" section indicates the treatment performed by heating and holding at a predetermined temperature and time.

[0137] (Reference Examples 5-1 to 5-7) Using DMCHS as a raw material, multiple PCSs with different molecular weights were synthesized by a liquid-gas thermal decomposition condensation method at atmospheric pressure using a liquid-gas thermal decomposition apparatus. The content of Mn, Mw, and LMW components, and the softening point of the obtained PCS were measured using the same method as in Example 1. The measurement results are shown in Table 4. Based on the measurement results in Table 4, Figure 3 shows a graph plotting the softening point (TS) against the content of the LMW component (Lc), and Figure 4 shows a graph plotting the softening point (TS) against Mw. As shown in Figures 3 and 4, it was shown that there is an almost linear relationship between the softening point and the content of the LMW component or Mw.

[0138]

[0139]

[0140]

[0141]

[0142] As shown in Tables 1 and 2, Examples 1 to 4, which used PCS within the scope of this embodiment, exhibited good transferability of molten PCS. Furthermore, the solidified PCS powder maintained its solid state even after LMW component removal treatment and solid-phase polymerization treatment, yielding high molecular weight PCS with a high molecular weight ratio of 1.10 or higher after solid-phase polymerization. Moreover, since the PCS could be easily recovered after solid-phase polymerization, it was confirmed that the recovery workability was also excellent.

[0143] The transportability evaluation test conducted in Example 4 demonstrated a close correlation between the estimated viscosity obtained based on the transport conditions and the actual transportability of the PCS. Therefore, the transportability of the PCS can be easily evaluated.

[0144] As shown in Table 1, Examples 1 to 4 used heating methods No. 1 to No. 3 to remove LMW components and reduce the LMW component content. Multiple heating conditions can be selected for the LMW component removal treatment.

[0145] The PCS after the LMW component removal treatment was subjected to solid-phase polymerization. As shown in Table 2, in Examples 1 to 6, high molecular weight PCS with a large high molecular weight conversion rate was prepared by using multiple heating conditions in the solid-phase polymerization treatment. Multiple heating conditions can be selected in the solid-phase polymerization treatment of PCS.

[0146] In contrast, in Comparative Example 1, when heated at the same temperature as in Example 1 during the polymerization treatment, the PCS failed to maintain a solid state and exhibited a liquid state. In Comparative Example 2, the viscosity at 450°C was high, and the transferability of the molten PCS was poor. In Comparative Example 3, because the heating temperature was low, neither the removal of the LMW component nor the increase in the softening point occurred substantially.

[0147] Next, we examined the effect of heating temperature on the LMW component removal treatment. As shown in Table 3, in Reference Examples 1 and 2, where the heating temperature was less than 230°C, the decrease in the low molecular weight component content was less than 2.0%, and the increase in the PCS softening point was less than 10°C. In contrast, in Reference Examples 3 and 4, where the heating temperature was 230°C or higher, the decrease in the LMW component content was 2.0% or more, and the increase in the PCS softening point was 10°C or higher. Furthermore, the increase in the PCS softening point tended to expand with increasing heating temperature. Thus, it was confirmed that heating PCS at a temperature of 230°C or higher during the LMW component removal treatment can significantly increase the PCS softening point.

[0148] As shown in the graph in Figure 3 based on the test results in Table 4, PCS with an LMW component content (Lc) of 34.0% or less had a softening point of 230°C or higher. Therefore, it was confirmed that by using PCS with an LMW component content (Lc) of 34.0% or less, it is possible to heat the PCS without melting it when raising its softening point during the LMW component removal process.

[0149] As shown in the graph in Figure 4 based on the test results in Table 4, PCS with an Mw of 3300 or higher had a softening point of 230°C or higher. Therefore, it was confirmed that by using PCS with an Mw of 3300 or higher, it is possible to heat the PCS without melting it when raising its softening point during the LMW component removal process.

[0150] As shown in the test results in Tables 3 and 4, it was confirmed that the heating start temperature for the third step is preferably 230°C or higher, and that for PCS that do not melt at 230°C, the LMW component content (Lc) in the PCS is preferably 34.0% or less, and the Mw of the PCS is preferably 3300 or higher.

[0151] 1. Heating apparatus 2. Processing container 3. Heater 4. Thermocouple 5. Gas supply channel 6. Gas discharge channel 7. Flow meter 8. Cooling tube

Claims

1. A polycarbosilane having a content of 25.0% or more and 34.0% or less of components with a molecular weight of 1000 or less, and a weight-average molecular weight (Mw) of 3300 or more and 5500 or less.

2. The polycarbonate silane according to claim 1, wherein the viscosity at 450°C is 20.0 Pa·s or less.

3. A method for producing a high molecular weight polycarbosilane using the polycarbosilane described in claim 1 or 2, comprising: a first step of preparing molten polycarbosilane in which the polycarbosilane is in a molten state, and then transferring the molten polycarbosilane; a second step of cooling the transferred molten polycarbosilane to prepare solidified polycarbosilane in a solid state; a third step of heating the solidified polycarbosilane obtained in the second step while maintaining its solid state to remove low molecular weight components contained in the solidified polycarbosilane; and a fourth step of heating the polycarbosilane for solid-phase polymerization obtained in the third step to perform solid-phase polymerization.

4. The method for producing a high molecular weight polycarbosilane according to claim 3, wherein the heating temperature in the fourth step is 310°C or higher and 410°C or lower.

5. The method for producing a high molecular weight polycarbosilane according to claim 3, wherein the heating temperature in the fourth step is equal to or greater than the heating temperature in the third step.

6. The method for producing a high molecular weight polycarbosilane according to claim 3, wherein the polycarbosilane obtained by the third step has a content of less than 25.0% of components with a molecular weight of 1000 or less.

7. The method for producing a high molecular weight polycarbosilane according to claim 3, wherein the ratio of the weight-average molecular weight (Mw2) of the high molecular weight polycarbosilane obtained in the fourth step to the weight-average molecular weight (Mw1) of the polycarbosilane obtained in the third step (Mw2 / Mw1) is 1.10 or more.

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