Polychlorotrifluoroethylene and method for producing polychlorotrifluoroethylene

Abstract

Provided is a polytrifluorochlor oethylene containing trifluorochlor oethylene units, the content of the trifluorochlor oethylene units being 95.0-100 mol% with respect to the total monomer units, and the ratio ((A) / (B)) of the area (A) of a peak derived from a double bond to the area (B) of a peak derived from a main skeleton being 0.020% or less.

Description

Technical Field

[0001] This invention relates to polychlorotrifluoroethylene and a method for manufacturing polychlorotrifluoroethylene. Background Technology

[0002] Patent document 1 describes a method for improving the heat resistance of trifluorochloroethylene polymer, characterized by treating the trifluorochloroethylene polymer with a fluorinating agent.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 5-170811 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] The purpose of this invention is to provide polychlorotrifluoroethylene with excellent oxidation resistance.

[0008] Methods for solving problems

[0009] According to the present invention, a polychlorotrifluoroethylene is provided, which is a polychlorotrifluoroethylene containing trichlorotrifluoroethylene units, wherein the content of trichlorotrifluoroethylene units is 95.0 mol% to 100 mol% relative to all monomer units, and the ratio of the peak area (A) derived from the double bond to the peak area (B) derived from the main skeleton ((A) / (B)) is 0.020% or less.

[0010] Invention Effects

[0011] According to the present invention, polychlorotrifluoroethylene with excellent oxidation resistance can be provided. Detailed Implementation

[0012] The following describes specific embodiments of the present invention in detail, but the present invention is not limited to the following embodiments.

[0013] Polychlorotrifluoroethylene (PCTFE) is known as a fluoropolymer with excellent chemical resistance and gas barrier properties. Patent Document 1 describes improving the heat resistance of PCTFE by treating it with a fluorinating agent. However, to date, no method has been studied to improve the oxidation resistance of PCTFE.

[0014] If oxidants such as piranha solution come into contact with PCTFE, the durability of PCTFE against stress will decrease. The inventors conducted research and found that the double bonds present in PCTFE affect its oxidation resistance; by reducing the amount of double bonds present in PCTFE, the oxidation resistance of PCTFE is significantly improved.

[0015] That is, the PCTFE of the present invention is a PCTFE containing 95 mol% to 100 mol% of trifluorochloroethylene (CTFE) units relative to all monomer units, and having a ratio ((A) / (B)) of peak area (A) derived from double bonds to peak area (B) derived from the main framework of 0.020% or less.

[0016] The structure of the PCTFE of the present invention will be described in detail below.

[0017] (PCTFE)

[0018] The PCTFE of the present invention is characterized in that the ratio of the peak area (A) derived from the double bond to the peak area (B) derived from the main framework ((A) / (B)) is 0.020% or less.

[0019] The ratio (A) / (B) of the peak area derived from double bonds to the peak area derived from the main backbone represents the proportion of double bonds present in the main chain of PCTFE. A low ratio (A) / (B) indicates a low amount of double bonds present in the main chain of PCTFE. From the perspective of further improving the oxidation resistance of PCTFE, the ratio (A) / (B) is preferably 0.015% or less, more preferably 0.012% or less.

[0020] CTFE can be prepared, for example, by dechlorinating trifluorotrichloroethane. In this process, CF₂=CHCl and CF₂=CHF are inevitably generated as impurity monomers. When CTFE (CF₂=CFCl) is polymerized to produce PCTFE, if these impurity monomers enter the PCTFE backbone along with CTFE, dehydrofluorination or dechlorination reactions readily occur, forming double bonds in the PCTFE. The presence of these double bonds is currently found to be the cause of reduced oxidation resistance in PCTFE.

[0021] Peak area (A) of PCTFE 19 The area of ​​peaks originating from double bonds in the F-NMR spectrum. In the case of multiple peaks originating from double bonds, the areas of all peaks are summed. Peaks originating from double bonds typically appear in PCTFE. 19 Chemical shift regions of -144ppm to -153ppm and -176ppm to -188ppm in F-NMR spectra.

[0022] Peak area (B) of PCTFE 19The area of ​​peaks originating from the main framework in the F-NMR spectrum. In the case of multiple peaks originating from the main framework, the areas of all peaks are summed. The main framework of PCTFE is a carbon chain backbone. Peaks originating from the main framework typically appear in the PCTFE spectrum. 19 The chemical shift region of the F-NMR spectrum is -75 ppm to -144 ppm.

[0023] From the perspective of further improving the oxidation resistance of PCTFE, the preferred flow value of PCTFE is 0.3 × 10⁻⁶. -3 centimeter 3 / second ~ 2.5×10 -3 centimeter 3 / second, more preferably 2.0×10 -3 centimeter 3 Below / second, further preferably 1.5 × 10 -3 centimeter 3 / second or less, and more preferably 1.0×10 -3 centimeter 3 / second or less.

[0024] The flow value of PCTFE can be determined using a high-performance flow meter under conditions of 230°C, a load of 980 N (100 kg), and a nozzle diameter of 1 mm φ. The flow value of PCTFE is the volume of PCTFE extruded from the nozzle per second.

[0025] The melting point of PCTFE is preferably 150°C or higher, more preferably 190°C or higher, more preferably 230°C or lower, and more preferably 217°C or lower. The melting point is the temperature corresponding to the maximum value in the heat of fusion curve when heated at a rate of 10°C / min using a differential scanning calorimeter [DSC].

[0026] As for PCTFE, there is no particular limitation as long as it contains CTFE units, it can be any of the following: CTFE homopolymer and polymers containing CTFE units and comonomer units (excluding CTFE units).

[0027] The content of CTFE units in PCTFE is 95.0 mol% to 100 mol% relative to all monomer units, preferably 98.0 mol% or more, more preferably 99.0 mol% or more, and even more preferably 99.9 mol% or more.

[0028] The comonomers that can constitute the comonomer units of PCTFE are not particularly limited as long as they can copolymerize with CTFE. Examples include ethylene, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, fluoro(alkyl vinyl ether), (perfluorobutyl)ethylene, (perfluorohexyl)ethylene, perfluoro(1,1,2-trihydro-1-hexene), and perfluoro(1,1,5-trihydro-1-pentene). In one embodiment, the comonomer is a monomer other than CF2=CHCl and CF2=CHF.

[0029] The monomer composition of PCTFE can be determined by... 19 The determination was performed using F-NMR.

[0030] (Manufacturing method of PCTFE)

[0031] The PCTFE of the present invention can be manufactured by using a monomer mixture in which the contents of CF2=CHCl and CF2=CHF are less than 250 mol ppm relative to the monomer mixture in a manufacturing method for manufacturing PCTFE by polymerizing a monomer mixture containing CTFE.

[0032] From the perspective of further improving the oxidation resistance of the obtained PCTFE, the content of CF2=CHCl and CF2=CHF in the monomer mixture is preferably 200 mol ppm or less, more preferably 160 mol ppm or less, and even more preferably 120 mol ppm or less relative to the monomer mixture. The lower limit of the content of CF2=CHCl and CF2=CHF is not particularly limited, and for example, it can be 0.1 mol ppm or more, 10 mol ppm or more, or 20 mol ppm or more.

[0033] The contents of CF2=CHCl and CF2=CHF in the monomer mixture can be determined by gas chromatography.

[0034] A monomer mixture with the contents of CF2=CHCl and CF2=CHF within the above range can be prepared, for example, by distilling a crude composition containing CTFE, CF2=CHCl and CF2=CHF to reduce the contents of CF2=CHCl and CF2=CHF in the crude composition.

[0035] Distillation of the crude composition can be carried out by known methods. For example, as described in Preparation Example 2 below, by using multiple distillation columns with high heating rates and high reflux ratios, the contents of CF2=CHCl and CF2=CHF in the crude composition can be sufficiently reduced.

[0036] A crude composition containing CTFE, CF2=CHCl, and CF2=CHF can be prepared by known methods such as dechlorination of trifluorotrichloroethane. In known methods for preparing CTFE, CF2=CHCl and CF2=CHF are typically generated naturally. Therefore, if known methods for preparing CTFE are used, CTFE is usually obtained as a crude composition containing CF2=CHCl and CF2=CHF in addition to CTFE.

[0037] The content of CF2=CHCl and CF2=CHF in the crude composition is usually greater than 250 mol ppm, and can be greater than 270 mol ppm or 300 mol ppm.

[0038] The polymerization of monomer mixtures containing PCTFE can be carried out by known polymerization methods. There are no particular limitations on the polymerization method; it can be solution polymerization, suspension polymerization, emulsion polymerization, etc. However, from the viewpoint of successfully producing PCTFE, suspension polymerization is preferred. For example, the suspension polymerization method described in Japanese Patent Publication No. 47-44031 can be cited as an example.

[0039] In one embodiment, polymerization can be carried out as follows: a monomer mixture containing CTFE is added to a polymerization reactor, the contents of the reactor are stirred, the reactor is then maintained at a predetermined polymerization temperature, and a polymerization initiator is added to initiate the polymerization reaction. Before the polymerization reaction begins, solvents, additives, etc., can be added to the reactor as needed. After the polymerization reaction begins, solvents, monomer mixtures, polymerization initiators, chain transfer agents, etc., can be added as needed.

[0040] From the perspective of further improving the oxidation resistance of the obtained PCTFE, the polymerization temperature of the monomer mixture containing CTFE is preferably below 25°C, more preferably below 20°C, and even more preferably below 15°C.

[0041] The polymerization time for monomer mixtures containing CTFE is typically 1 hour to 60 hours.

[0042] In the case of PCTFE production by suspension polymerization, a slurry of PCTFE is usually obtained. Therefore, the slurry is recovered from the reactor and subjected to post-processing such as washing and drying as desired, thereby obtaining PCTFE powder.

[0043] (Material for molding)

[0044] The present invention also relates to molding materials containing the above-mentioned PCTFE.

[0045] The molding material of the present invention can be in the form of, for example, powder, granulated powder, granules, flakes, pellets, cubes or beads.

[0046] The molding material of the present invention can have an extremely low metal content. In one embodiment, the content of Co, Cr, Cu, Fe, Mn, and Ni in the molding material of the present invention is 500 ppb by mass or less, preferably 400 ppb by mass or less, more preferably 300 ppb by mass or less, further preferably 250 ppb by mass or less, even more preferably 220 ppb by mass or less, particularly preferably 200 ppb by mass or less, and can be 0.01 ppb by mass or more or more. By keeping the metal content in the molding material within the above range, for example, even when the molded body obtained from the molding material is used as a component in the semiconductor manufacturing field, metal contamination of the semiconductor can be suppressed.

[0047] The molding material of the present invention contains PCTFE with a low ratio ((A) / (B)) of peak area (A) derived from double bonds to peak area (B) derived from the backbone, thus reducing the likelihood of hydrogen fluoride and hydrogen chloride formation from PCTFE. In particular, PCTFE obtained by polymerizing a monomer mixture with low contents of CF2=CHCl and CF2=CHF is less prone to hydrogen fluoride and hydrogen chloride formation. Therefore, even when metal manufacturing equipment is used to manufacture PCTFE or prepare the molding material, the equipment is less susceptible to corrosion, resulting in a molding material with extremely low metal content.

[0048] Regarding the metal content in the molding material, accurately weigh 1g of the molding material and place it in a platinum crucible (platinum purity 99.9%). Ash the sample using a gas burner, or ash it at 500°C for 30 minutes using an electric furnace. Dissolve the remaining ash in 10% nitric acid to obtain a solution. The resulting solution can be measured using an ICP-based luminescence analyzer (SPS3000, manufactured by Seiko Instruments) or a flameless atomic absorption spectrophotometer.

[0049] Furthermore, when the metal content in the molding material is extremely low (e.g., less than 0.1 ppb by mass), the metal content can be determined using a method different from the above-mentioned methods. For example, it can be determined using the ashing method described in International Publication No. 94 / 28394. In the ashing method, the molding material can be accurately weighed in the range of 2 mg to 6 mg, ashed in a graphite test tube by heating at 1100°C for 180 seconds, and analyzed using an atomic absorption spectrophotometer (polarized Zeeman atomic absorption spectrophotometer (Z-8100), manufactured by Hitachi, Ltd.).

[0050] The molding material of the present invention may contain various additives such as conductive materials, reinforcing agents, fillers, ultraviolet absorbers, heat stabilizers, and pigments.

[0051] (Molded body)

[0052] A molded body can be obtained by molding the above-mentioned PCTFE or molding material.

[0053] There are no particular limitations on the molding method; examples include melt molding, extrusion molding, injection molding, transfer molding, blow molding, compression molding, and other well-known methods. The appropriate molding method should be selected based on the shape of the resulting molded product.

[0054] The molded articles of this invention are suitable for use in the semiconductor manufacturing, chemical product manufacturing, and electronic component manufacturing fields. For example, the molded articles of this invention can be used as sealing materials such as seals and gaskets; pump components such as housings, impellers, valves, and plugs; liquid tubing; and component materials for use in cryogenic fluids, such as butterfly valves for cryogenic applications.

[0055] The molded articles of the present invention have excellent oxidation resistance, and are therefore particularly suitable for use as components that come into contact with aqueous solutions of acids such as sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid, as well as pharmaceutical solutions such as hydrogen peroxide.

[0056] The molded articles of the present invention exhibit excellent oxidation resistance, making them particularly suitable for use as components constituting semiconductor manufacturing apparatuses. Examples of such components include turntables for processing silicon wafers, peripheral components such as wafer guides, silicon wafer cleaning guides, connectors for chemical solution piping, valves, and joints; etc. For example, a turntable in a semiconductor cleaning apparatus can be cited as an example.

[0057] The embodiments have been described above, but it is understood that various changes can be made to the methods and details without departing from the spirit and scope of the claims.

[0058] <1> According to a first aspect of the present invention, a polychlorotrifluoroethylene is provided, which is a polychlorotrifluoroethylene containing trichlorotrifluoroethylene units, wherein the content of trichlorotrifluoroethylene units is 95.0 mol% to 100 mol% relative to all monomer units, and the ratio of the peak area (A) derived from the double bond to the peak area (B) derived from the main skeleton ((A) / (B)) is 0.020% or less.

[0059] <2> According to a second aspect of the present invention, a polychlorotrifluoroethylene based on the first aspect is provided, having a flow value of 0.3 × 10⁻⁶. -3 centimeter 3 / second ~ 2.5×10 -3 centimeter3 / Second.

[0060] <3> According to a third aspect of the present invention, a polychlorotrifluoroethylene based on the first or second aspect is provided, wherein the content of the chlorotrifluoroethylene unit is 99.9 mol% to 100 mol% relative to all monomer units.

[0061] <4> According to a fourth aspect of the present invention, a molding material is provided, which contains polychlorotrifluoroethylene based on any one of the first to third aspects.

[0062] <5> According to a fifth aspect of the present invention, a molding material based on the fourth aspect is provided, which is a powder, a granulated powder, a granule, a sheet, a pellet, a cube, or a bead.

[0063] <6> According to a sixth aspect of the present invention, a molding material based on the fourth or fifth aspect is provided, wherein the contents of Co, Cr, Cu, Fe, Mn and Ni are 500 ppb by mass or less.

[0064] <7> According to a seventh aspect of the present invention, a molded body is provided, which is obtained by molding polychlorotrifluoroethylene based on the first or second aspect, or a molding material based on any one of the fourth to sixth aspects.

[0065] <8> According to the eighth aspect of the present invention, a method for manufacturing polychlorotrifluoroethylene is provided, which manufactures polychlorotrifluoroethylene by polymerizing a monomer mixture containing trichlorotrifluoroethylene, wherein the content of CF2=CHCl and CF2=CHF in the monomer mixture is less than 250 mol ppm relative to the monomer mixture.

[0066] <9> According to a ninth aspect of the present invention, a manufacturing method based on the eighth aspect is provided, wherein the monomer mixture is prepared by distilling a crude composition containing trifluorochloroethylene to reduce the content of CF2=CHCl and CF2=CHF in the crude composition.

[0067] <10> According to a tenth aspect of the present invention, a manufacturing method based on an eighth or ninth aspect is provided, wherein the polymerization temperature is below 25°C.

[0068] Example

[0069] Next, embodiments will be given to illustrate the implementation of the present invention, but the present invention is not limited to these embodiments.

[0070] The values ​​in the examples were measured using the following methods.

[0071] <Amount of impurity monomers in the monomer mixture>

[0072] In this embodiment, the impurity monomers refer to CF2=CHCl and CF2=CHF. The amount of impurity monomers (the content of CF2=CHCl and CF2=CHF) in the monomer mixture, relative to CTFE, was determined using a gas chromatograph GC8A (manufactured by Shimadzu Corporation), a SUS 3mm φ × 10m column, Octoil S packing material, under the following conditions: column temperature 45°C, detector temperature 80°C, carrier pressure 160 kPa, carrier gas He, and sample volume 1 cc.

[0073] In addition, the CTFE content in the raw material monomer mixture is the value obtained by subtracting the content of components other than CTFE, such as CF2=CHCl and CF2=CHF, from 100 mol%

[0074] <Flow value of PCTFE>

[0075] Using a high-performance flow meter CFT-500D (manufactured by Shimadzu Corporation), the volume of resin flowing per second (cm³) was measured under the conditions of 230°C, a load of 980 N (100 kg), and a nozzle diameter of 1 mm. 3 / Second).

[0076] <Peak area ratio ((A) / (B))>

[0077] Through melting 19 F-NMR method to obtain PCTFE 19 F-NMR spectroscopy. Measurements were performed using an AVANCE NEO400 nuclear magnetic resonance apparatus (manufactured by BRUKER) at 376.51 MHz, 240 °C, and 500 cycles.

[0078] Peak area (A): The sum of peak areas appearing in the ranges of -144ppm to -153ppm and -176ppm to -188ppm.

[0079] Peak area (B): The total peak areas appearing in the range of -75ppm to -144ppm

[0080] <Fatigue Test>

[0081] (Production of the experimental film)

[0082] PCTFE was melt-compressed at 280°C for 20 minutes to produce 1.5 mm sheets, which were then punched using ASTM D638 type IV dumbbells to produce test pieces.

[0083] (Immersion in piranha solution)

[0084] Arrange the test pieces in a container, and pour in hydrogen peroxide and sulfuric acid in a 1:3 ratio (30% hydrogen peroxide to 98% sulfuric acid). Immerse the test pieces in the solution for 24 hours. After immersion, rinse the test pieces with running water and wipe off the moisture.

[0085] (Fatigue test)

[0086] Using test pieces immersed in a piranha solution and an EHF-LV020k1 fatigue testing machine (manufactured by Shimadzu Corporation), tests were conducted under tensile conditions, R=0.1 (stress ratio R=minimum stress / maximum stress), maximum stress at 60% of the yield point of the tensile test, and 5Hz. The number of repetitions until the test piece broke was measured. Test pieces with a high number of fracture repetitions exhibited excellent oxidation resistance.

[0087] (Metal content)

[0088] Regarding the metal content of the granules, accurately weigh 1g of granules and place them in a platinum crucible (platinum purity 99.9%). Ash the sample using a gas burner or ash it at 500°C for 30 minutes using an electric furnace. Dissolve the ash remaining in the platinum crucible in 10% nitric acid to obtain a solution. Use the obtained solution and an ICP-based luminescence analyzer (SPS3000, manufactured by Seiko Instruments) to determine the contents of Co, Cr, Cu, Fe, Mn, and Ni.

[0089] Preparation Example 2 (Preparation of CTFE)

[0090] Use a mixture of raw material monomers with the following composition.

[0091] CTFE content: 99.8 mol%

[0092] CF2=CHF content: 300 mol ppm

[0093] CF2=CHCl content: 700 mol ppm

[0094] A monomer mixture containing CTFE is prepared by distillation of the raw monomer mixture. The raw monomer mixture is fed to the first distillation column at a rate of 175 kg / h. The fraction containing impurities is distilled from the top of the first distillation column at a rate of 1 kg / h, and the fraction containing CTFE is distilled from the bottom of the first distillation column at a rate of 174 kg / h.

[0095] The first distillation column

[0096] Theoretical number of trays: 25 trays

[0097] Heating capacity: 2500 kcal / h

[0098] Reflux ratio: 147 moles

[0099] Pressure: 0.90 MPaG

[0100] Tower top temperature: 38.1℃

[0101] Temperature at the bottom of the tower: 41.0℃

[0102] Next, the fraction distilled from the bottom of the first distillation column is fed to the second distillation column at a rate of 174 kg / h. The fraction containing impurities is distilled from the bottom of the second distillation column at a rate of 1 kg / h, and the fraction containing CTFE is distilled from the top of the second distillation column at a rate of 173 kg / h.

[0103] Second distillation column

[0104] Theoretical number of trays: 50 trays

[0105] Heating capacity: 60000 kcal / h

[0106] Reflux ratio: 9 moles

[0107] Pressure: 0.45 MPaG

[0108] Tower top temperature: 18.5℃

[0109] Temperature at the bottom of the tower: 28.4℃

[0110] The combined content of CF2=CHCl and CF2=CHF in the fraction (monomer mixture) distilled from the top of the second distillation column was 80 mol ppm.

[0111] Preparation Example 8 (Preparation of CTFE)

[0112] The heating rate of the second distillation column was changed to 20,000 kcal / h, and the reflux ratio was changed to 2 moles. Otherwise, the process was the same as in Preparation Example 2 to prepare a monomer mixture containing CTFE. The combined content of CF2=CHCl and CF2=CHF in the monomer mixture was 354 moles per ppm.

[0113] Preparation Examples 1, 3-7 (Preparation of CTFE)

[0114] The monomer mixtures obtained in Preparation Example 2 and Preparation Example 8 were mixed in any proportion to prepare a monomer mixture having the amount of impurity monomers listed in Table 1.

[0115] Example 1 (Manufacturing of PCTFE)

[0116] PCTFE was manufactured using the suspension polymerization method described in Japanese Patent Publication No. 47-44031. The monomer mixture obtained in Preparation Example 1 was polymerized at a polymerization temperature of 12°C and a polymerization time of 42 hours to obtain powdered PCTFE. The results are shown in Table 1.

[0117] Examples 2-6 and Comparative Examples 1-2

[0118] The monomer mixtures obtained in Preparation Examples 2-8 were used instead of the monomer mixture obtained in Preparation Example 1. The monomer mixtures were polymerized at the polymerization temperature and polymerization time recorded in Table 1, and otherwise the same procedure was followed as in Example 1 to obtain powdered PCTFE. The results are shown in Table 1.

[0119] In addition, powdered PCTFE was extruded at 310°C to produce granules, and the metal content (Co, Cr, Cu, Fe, Mn, and Ni) in the granules was determined. The results are shown in Table 2.

[0120] [Table 1]

[0121]

[0122] [Table 2]

[0123]

Claims

1. A type of polychlorotrifluoroethylene, which is a polychlorotrifluoroethylene containing trifluorochloroethylene units, wherein, The content of trichlorofluoroethylene units is 95.0 mol% to 100 mol% relative to all monomer units. The ratio of the peak area (A) derived from the double bond to the peak area (B) derived from the main framework, i.e., (A) / (B), is less than 0.020%.

2. The polychlorotrifluoroethylene according to claim 1, having a flow value of 0.3 × 10⁻⁶. -3 centimeter 3 / second ~ 2.5×10 -3 centimeter 3 / Second.

3. The polychlorotrifluoroethylene according to claim 1 or 2, wherein, The content of trichlorofluoroethylene units is 99.9 mol% to 100 mol% relative to all monomer units.

4. A molding material comprising polychlorotrifluoroethylene as described in any one of claims 1 to 3.

5. The molding material according to claim 4, wherein it is a powder, a granulated powder, a granule, a sheet, a pellet, a cube, or a bead.

6. The molding material according to claim 4 or 5, wherein, The contents of Co, Cr, Cu, Fe, Mn and Ni are below 500 ppb by mass.

7. A molded body obtained by molding the polychlorotrifluoroethylene according to any one of claims 1 to 3 or the molding material according to any one of claims 4 to 6.

8. A method for manufacturing polychlorotrifluoroethylene, wherein polychlorotrifluoroethylene is manufactured by polymerizing a mixture of monomers containing trifluorochloroethylene, wherein, The content of CF2=CHCl and CF2=CHF in the monomer mixture is less than 250 mol ppm relative to the monomer mixture.

9. The manufacturing method according to claim 8, wherein, The monomer mixture is prepared by distilling a crude composition containing trifluorochloroethylene to reduce the content of CF2=CHCl and CF2=CHF in the crude composition.

10. The manufacturing method according to claim 8 or 9, wherein, The polymerization temperature is below 25℃.

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