A polyamide-imide containing a furan ring structure and its synthesis method and use

Abstract

The present invention provides a polyamide-imide containing a furan ring structure, a synthesis method, and uses thereof. The polyamide-imide containing a furan ring structure comprises a repeating structure as shown in Formula I: #imgabs0#, wherein 50 < n < 200 and is an integer; and Ar is one of the substituents containing an aromatic ring structure. The technical solution provided by the present invention has a short process flow, is simple to operate, and does not release hydrogen chloride during the preparation process, making it environmentally friendly. The resulting polyamide-imide containing a furan ring structure exhibits excellent mechanical properties and a low dielectric constant, and has great application potential in the field of electronic products.

Description

Technical Field

[0001] The present invention belongs to the field of polymers, and in particular relates to a polyamide-imide containing a furan ring structure, a synthesis method and application thereof. Background Art

[0002] Polyamide-imide (PAI) is a class of high-performance, high-temperature-resistant thermoplastic engineering plastics. Because its molecular backbone contains both heat-resistant imide and flexible amide groups, PAI products combine the heat resistance, low creep, high strength, high modulus, and solvent resistance of polyimide with the excellent mechanical properties and processability of polyamide. They can be molded using conventional injection molding, extrusion, and compression molding processes. Consequently, they are widely used in aerospace, military equipment, chemical equipment, electronic devices, and other fields, and hold broad development prospects.

[0003] Torlon (polyamide-imide) produced by Amoco Chemicals, Inc. in the United States usually adopts the acyl chloride method, that is, using trimellitic anhydride chloride (TMAc) and aromatic diamine as raw materials, and preparing PAI through condensation in a nitrogen-containing polar organic solvent. The acyl chloride method for producing PAI has been industrialized and the technology is relatively mature, but there are the following problems: (1) The key raw material trimellitic anhydride chloride is expensive and has poor storage stability, and its upstream raw material trimellitic anhydride (TMA) has been identified as a substance of very high concern by the European Union due to its respiratory sensitization; (2) The acyl chloride route involves process steps such as prepolymerization, powdering, and thermal imidization of polyamide acid. The route is long and the difficulty of controlling product performance stability increases; (3) The HCl released during the production process of the acyl chloride method will corrode the equipment and is difficult to separate completely from the product. The residual chloride ions seriously affect the insulation performance of electronic and electrical equipment, and the purification and removal of HCl will also greatly increase the production cost. Especially for electronic materials, the chloride ion content in the material directly affects the dielectric constant and dielectric loss coefficient of the material. These defects have largely become limiting factors in the development of PAI. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a polyamide-imide containing a furan ring structure and a synthesis method and use thereof, so as to solve the problems in the prior art.

[0005] To achieve the above-mentioned purpose and other related purposes, the present invention is achieved through the following technical solutions.

[0006] The first aspect of the present invention provides a polyamide-imide containing a furan ring structure, wherein the polyamide-imide comprises a repeating structure as shown in Formula I: Formula I; wherein, 50<n<200 and is an integer; Ar is one of the substituents containing an aromatic ring structure.

[0007] Preferably, Ar is selected from one of the following structures: 、 、 、 .

[0008] Preferably, the number average molecular weight of the polyamide-imide containing furan ring structure is 3×10 4 ~1.2×10 5 More preferably, the molecular weight of the polyamide-imide containing furan ring structure is 3×10 4 ~5.5×10 4 The number average molecular weight is obtained by GPC test. For example, the molecular weight is 3.1×10 4 ~5.5×10 4 , 3.6~5.0×10 4 .

[0009] A second aspect of the present invention provides a method for synthesizing the polyamide-imide containing a furan ring structure as described above, comprising the following steps:

[0010] 1) contacting an aromatic diamine containing a furan ring structure, an aromatic tetracarboxylic acid, a first catalyst, and water to carry out a polycondensation reaction to obtain an aqueous suspension, and dehydrating and drying the aqueous suspension to obtain a polyamic acid containing a furan ring structure;

[0011] 2) solid-phase thickening and high-temperature imidization of the polyamic acid to obtain the polyamide-imide containing a furan ring structure.

[0012] Water is used as the reaction medium in the present application. Since the polyamic acid prepared in step 1) has poor solubility in water, the formed polyamic acid suspension is easily dehydrated by centrifugation. The steps are simple and the recovery efficiency of the polyamic acid product is high.

[0013] Preferably, the structural formula of the aromatic diamine containing a furan ring structure is as shown in Formula II: Formula II.

[0014] Preferably, the aromatic tetracarboxylic acid is selected from one or more of pyromellitic acid, biphenyltetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid and 4,4-oxydiphthalic acid.

[0015] Preferably, in step 1), the water content is 80-90% based on the total weight of the aromatic diamine containing a furan ring structure, the aromatic tetracarboxylic acid and water; and the molar ratio of the aromatic diamine to the aromatic tetracarboxylic acid is 1.01-1.05:1.

[0016] For example, based on the total weight of the aromatic diamine containing a furan ring structure, the aromatic tetracarboxylic acid, and water, the water content may be 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90%. For example, the molar ratio of the aromatic diamine to the aromatic tetracarboxylic acid may be 1.01:1, 1.02:1, 1.03:1, 1.04:1, or 1.05:1.

[0017] Preferably, based on the total weight of the aromatic diamine containing a furan ring structure, the aromatic tetracarboxylic acid and water, the added amount of the first catalyst is 0.2-1.5 wt ‰, such as 0.2-1.0 wt ‰ or 1.0-1.5 wt ‰.

[0018] The molar ratio of the aromatic diamine containing a furan ring structure and the aromatic tetracarboxylic acid is not arbitrarily limited. If the content of the aromatic diamine containing a furan ring structure is low, the reaction is incomplete, resulting in a low yield of the product; if the content of the aromatic diamine containing a furan ring structure is too high, the end-capping effect is obvious during the reaction, and only oligomer products can be obtained in the end.

[0019] Preferably, the first catalyst is a hypophosphite catalyst.

[0020] More preferably, the hypophosphite catalyst is selected from one or more of sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, and magnesium hypophosphite.

[0021] Preferably, in step 1), the polycondensation reaction includes a first stage and a second stage.

[0022] Preferably, the first stage reaction temperature is 100-150°C and the first stage reaction time is 3-6 hours. For example, the reaction temperature may be 100-120°C or 120-150°C and the reaction time may be 3 hours, 4 hours, 5 hours or 6 hours.

[0023] Preferably, the second stage reaction temperature is 130-180°C and the second stage reaction time is 3-6 hours. For example, the reaction temperature may be 130-150°C or 140-180°C and the reaction time may be 3 hours, 4 hours, 5 hours or 6 hours.

[0024] Preferably, the pressure of the second stage reaction is 0.5-1.5 MPa. For example, the pressure can be 0.5-1.2 MPa or 1.2-1.5 MPa.

[0025] Preferably, in step 1), the polycondensation reaction is also stirred at a rate of 50 to 400 r / min, for example, 50 to 200 r / min or 200 to 400 r / min.

[0026] Preferably, in step 1), the polycondensation reaction is carried out in an inert gas environment.

[0027] Preferably, in step 1), a centrifugal separator is used for the dehydration and drying.

[0028] Preferably, the polycondensation reaction is carried out in a high-pressure polymerization reactor.

[0029] Preferably, in step 2), the temperature of the solid phase viscosity enhancement reaction is 200-260° C. For example, the temperature of the solid phase viscosity enhancement reaction can be 200° C., 210° C., 220° C., 230° C., 240° C., 250° C., or 260° C.

[0030] Preferably, in step 2), the solid phase viscosity increasing reaction time is 4 to 10 hours. For example, the reaction time can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0031] Preferably, in step 2), the solid phase viscosity increasing reaction is carried out under vacuum conditions, wherein the vacuum degree is 40-80 Pa. For example, the vacuum degree may be 50-60 Pa, 40-60 Pa, or 50-80 Pa.

[0032] Preferably, in step 2), a second catalyst is added during the solid phase viscosity increasing reaction, and the second catalyst is selected from one or more of diisopropylamine, 4-dimethylaminopyridine and triphenylphosphine.

[0033] Preferably, in step 2), based on the total mass of the polyamic acid, the amount of the second catalyst added is 0.2-1.5 wt‰, such as 0.2-1.0 wt‰ or 1.0-1.5 wt‰.

[0034] Preferably, in step 2), a vacuum drum reactor is used to carry out the solid phase viscosity increasing reaction.

[0035] A third aspect of the present invention provides a use of the polyamide-imide containing a furan ring structure as described above in preparing a low dielectric film, or in preparing a substrate for electronic products, or as an insulating material.

[0036] A fourth aspect of the present invention provides a low dielectric film prepared using the polyamide-imide containing a furan ring structure as described above.

[0037] Preferably, the polyamide-imide containing a furan ring structure is dissolved in an organic solvent to form a solution, the solution is applied to a glass plate, and dried at high temperature to obtain the low dielectric film. Preferably, the organic solvent includes NMP.

[0038] Preferably, the high-temperature drying temperature is 60-300°C.

[0039] Preferably, the dielectric constant of the low-dielectric film is 2.6 to 3.2, such as 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, or 3.2.

[0040] Preferably, the low-dielectric film has a tensile strength of 220-290 MPa, such as 220-250 MPa, 240-290 MPa, 230-270 MPa, or 220-280 MPa. Preferably, the low-dielectric film has an elongation at break of 2.2-2.7%, such as 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, or 2.7%.

[0041] The beneficial effects of the present invention are as follows: 1) The present invention uses aromatic diamines containing a furan ring structure and aromatic tetracarboxylic acid as reaction raw materials to prepare PAI through polycondensation reaction and high-temperature imidization, abandoning the technical solution of using halogen-containing monomers as reaction raw materials in the prior art, so that no HCl is released during the reaction process, and the synthesis process is green and friendly.

[0042] 2) The technical solution of the present invention does not involve chloride ions in the process of preparing polyamide-imide (PAI). Therefore, the dielectric constant of the product is low and the application prospects in the field of electronic products are broad.

[0043] 3) In this technical solution, the synthesis of polyamide-imide containing a furan ring structure can be completed in only two steps, which is a short route and easy to operate.

[0044] 4) In the present invention, the molecular weight of the polyamide-imide product can be adjusted by changing the process parameters of the solid phase viscosity enhancement, while the distribution coefficient of the molecular weight of the polyamide-imide product is reduced, and the product properties are more excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The aromatic diamine containing a furan ring structure used in the present invention is shown 1 H-NMR spectrum.

[0046] Figure 2 The aromatic diamine containing a furan ring structure used in the present invention is shown 13 C-NMR spectrum.

[0047] Figure 3Shown is the infrared spectrum of the polyamide-imide containing a furan ring structure prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0048] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0049] Before further describing the specific embodiments of the present invention, it should be understood that the scope of the present invention is not limited to the specific embodiments described below. It should also be understood that the terminology used in the examples is intended to describe specific embodiments and is not intended to limit the scope of the present invention. The experimental procedures in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0050] When the embodiments provide numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the understanding of the prior art by those skilled in the art and the description of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention may also be used to implement the present invention.

[0051] The present application does not impose any specific limitation on the preparation method of the aromatic diamine containing a furan ring structure, as long as the aromatic diamine containing a furan ring structure as shown in Formula II can be obtained. Formula II.

[0052] In the following examples of this application, the aromatic diamines containing a furan ring structure were prepared by the following preparation method: a) Dissolve 90 mmol of triethylamine and 90 mmol of p-nitroaniline in 50 mL of DMAc and stir at room temperature until completely dissolved. Under a nitrogen atmosphere, add dropwise 37.5 mL of a DMAc solution containing 40 mmol of 2,5-furandicarbonyl chloride and stir at room temperature for 24 hours to obtain a mixed solution. The mixed solution is then added dropwise to water to form a precipitate, which is collected by filtration, washed with water, and dried in vacuo at 95°C to obtain a dinitro compound.

[0053] b) 3.155 g of the dinitro compound obtained in step a) was dissolved in 30 mL of DMAc and 65.6 mg of a Pd / C catalyst was added to obtain a reaction solution. Then, 6 mL of 50% hydrazine hydrate was slowly added dropwise to the reaction solution at 100°C and stirred under a nitrogen atmosphere for 24 hours. After the reaction, the Pd / C catalyst was removed by filtration. The filtrate was added dropwise to water to produce a yellow precipitate, which was then dried in vacuo at 60°C overnight to obtain an aromatic diamine containing a furan ring structure as shown in Formula II.

[0054] The applicant used nuclear magnetic resonance technology to analyze and detect the aromatic diamine containing a furan ring structure, and its NMR spectrum is as follows: Figure 1 and Figure 2 shown.

[0055] Depend on Figure 1 and Figure 2 It can be seen that the above preparation method can indeed obtain an aromatic diamine containing a furan ring structure with the structural formula shown in Formula II.

[0056] Example 1

[0057] This embodiment provides a method for synthesizing a polyamide-imide containing a furan ring structure, which specifically includes the following steps: 1) dissolving 200.24 g of an aromatic diamine containing a furan ring structure, 148 g of pyromellitic acid (molar ratio of 1.02:1), and 2.9 g (1 wt‰) of sodium hypophosphite in 2554 ml of water, and adding the mixture to a reactor (the reactor is equipped with a mechanical stirrer, a condenser, and a thermometer), stirring at a temperature of 120°C, and carrying out a first-stage reaction for 5 hours at a mechanical stirring speed of 200 r / min.

[0058] After the first stage of reaction, the air in the reactor was displaced by vacuuming and then passing high-purity argon gas. This cycle was repeated six times until a pressure of 0.2 MPa remained in the reactor after the displacement step. Under the protection of high-purity argon, the temperature in the reactor was raised to 180°C at a heating rate of 2°C / min, and the pressure in the reactor was raised to 1.2 MPa. The mechanical stirring speed was 200 r / min, and the second stage of reaction was carried out for 3 hours to obtain a polyamic acid aqueous suspension.

[0059] After the second stage reaction is completed, the temperature in the reactor is cooled to room temperature, and the polyamic acid aqueous suspension is discharged from the bottom of the reactor and dehydrated and dried by a centrifuge to obtain polyamic acid.

[0060] 2) 300 g of the polyamic acid prepared in step 1) was added to a vacuum drum reactor, imidized at 200° C., and viscosity-increasing for 6 h. During the process, vacuum was continuously drawn and water was removed, and the vacuum degree of the drum reactor was maintained at 50 Pa to obtain the polyamide-imide containing a furan ring structure. The molecular weight of the polyamide-imide containing a furan ring structure was 3.1×10 4 .

[0061] The furan ring structure polyamide imide prepared in this embodiment was subjected to infrared spectrum analysis. The results are as follows: Figure 3 shown.

[0062] Depend on Figure 3 It can be seen that 3325 cm -1 The peak at 1742 cm is the stretching vibration absorption peak of NH in the amide bond; -1 The absorption peak at 1700 cm is the symmetrical stretching vibration absorption peak of -CO-N-CO- in the imine ring; -1 The absorption peak at 1666 cm is the asymmetric stretching vibration absorption peak of -CO-N-CO- in the imine ring; -1 The peak at 1600 cm is the stretching vibration absorption peak of C=O in the amide bond; -1 and 1500 cm -1 The peak at 1375 cm is the vibration absorption peak of the benzene ring; -1 The stretching vibration absorption peak of CN in the imine ring is at 725 cm -1 The absorption peak is the bending vibration of -CO-N-CO- in the imine ring.

[0063] This indicates that the synthesis method provided in this example successfully prepared polyamide-imide containing a furan ring structure.

[0064] Example 2

[0065] 1) Step 1) is the same as in Example 1, obtaining polyamic acid;

[0066] 2) 300 g of the polyamic acid prepared in step 1) was added to a vacuum drum reactor, imidized at 240° C., and viscosity-increasing for 7 h. During the process, vacuum was continuously drawn and water was removed, and the vacuum degree of the drum reactor was maintained at 60 Pa to obtain the polyamide-imide containing a furan ring structure. The molecular weight of the polyamide-imide containing a furan ring structure was 3.8×10 4 .

[0067] Example 3

[0068] 1) Step 1) is the same as in Example 1, obtaining polyamic acid;

[0069] 2) 300 g of the polyamic acid prepared in step 1) and 0.3 g of diisopropylamine were added to a vacuum drum reactor, imidized at 260° C., and viscosity increased for 8 h. During the process, vacuum was continuously drawn and water was removed, and the vacuum degree of the drum reactor was maintained at 50 Pa to obtain the furan ring structure-containing polyamide-imide. The molecular weight of the furan ring structure-containing polyamide-imide was 5×10 4 .

[0070] Example 4

[0071] 1) The raw materials in Example 1 were replaced with: 200.24 g of an aromatic diamine containing a furan ring structure, 191 g of biphenyltetracarboxylic acid (molar ratio of 1.01:1), and 2.6 g (1 wt‰) of sodium hypophosphite dissolved in 2216 ml of water and added to the reactor. The remaining steps were exactly the same to obtain polyamic acid;

[0072] 2) 300 g of the polyamic acid prepared in step 1) was added to a vacuum drum reactor, imidized at 260° C., and viscosity-increasing for 8 h. During the process, vacuum was continuously drawn and water was removed, and the vacuum degree of the drum reactor was maintained at 50 Pa to obtain the polyamide-imide containing a furan ring structure. The molecular weight of the polyamide-imide containing a furan ring structure was 3.6×10 4 .

[0073] Example 5

[0074] 1) Step 1) is the same as step 4 to obtain polyamic acid;

[0075] 2) 300 g of the polyamic acid prepared in step 1) and 0.3 g of diisopropylamine were added to a vacuum drum reactor, imidized at 260° C., and viscosity increased for 8 h. During the process, vacuum was continuously drawn and water was removed, and the vacuum degree of the drum reactor was maintained at 50 Pa to obtain the furan ring structure-containing polyamide-imide. The molecular weight of the furan ring structure-containing polyamide-imide was 5.5×10 4 .

[0076] The applicant also soaked the glass plate in acetone for 1 hour, rinsed it with deionized water, and oven-dried it. The furan ring-containing polyamide-imide prepared in Examples 1-5 was then added to NMP to form a PAI solution with a solids content of 18%. A 100 μm thick PAI coating was then formed on the glass plate using a wet film preparation apparatus. The coating was then maintained at temperatures of 60°C, 80°C, 120°C, 150°C, 200°C, 250°C, and 300°C for 2 hours. After cooling, the glass plate was immersed in deionized water and peeled off to obtain a pale yellow PAI film.

[0077] With reference to GB / T 1040.3–2006, the tensile strength and elongation at break of the PAI film were measured using an electronic universal materials testing machine, and the dielectric constant was measured using a Concept 40 broadband dielectric tester. The specific results are shown in Table 1 below.

[0078] Table 1

[0079] tensile strength Elongation at break Dielectric constant Example 1 220 MPa 2.2% 3.2 Example 2 252 MPa 2.4% 3.0 Example 3 276 MPa 2.6% 2.6 Example 4 243 MPa 2.4% 2.9 Example 5 290 MPa 2.7% 3.0

[0080] As shown in Table 1, the film made from the polyamide-imide containing a furan ring structure provided by the present invention has good mechanical properties, with a tensile strength of 220 MPa to 290 MPa and an elongation at break of 2.2 to 2.7%. It also has a low dielectric constant of 2.6 to 3.2, and has great application potential in the field of electronic products.

[0081] In summary, the technical solution provided by the present invention is convenient, has a short preparation process, is simple to operate, and does not release HCl during the preparation process, making it environmentally friendly. The obtained polyamide-imide containing a furan ring structure has good mechanical properties and a low dielectric constant, and has great application potential in the field of electronic products.

[0082] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for synthesizing a polyamide-imide containing a furan ring structure, characterized in that: The following steps are involved: 1) contacting an aromatic diamine containing a furan ring structure, an aromatic tetracarboxylic acid, a first catalyst, and water to carry out a polycondensation reaction to obtain an aqueous suspension, and dehydrating and drying the aqueous suspension to obtain a polyamic acid containing a furan ring structure; 2) solid-phase thickening and high-temperature imidization of the polyamic acid to obtain the polyamide-imide containing a furan ring structure; In step 1), the polycondensation reaction includes a first stage and a second stage; The first stage reaction temperature is 100-150°C; the first stage reaction time is 3-6 hours; The reaction temperature of the second stage is 130-180°C; the reaction time of the second stage is 3-6 hours; The pressure of the second stage reaction is 0.5~1.5MPa; The polyamide-imide containing a furan ring structure includes a repeating structure as shown in Formula I: Formula I; wherein 50<n<200 and is an integer; Ar is one of the substituents containing an aromatic ring structure; In step 1), the water content is 80-90% based on the total weight of the aromatic diamine containing a furan ring structure, the aromatic tetracarboxylic acid and water; The molar ratio of the aromatic diamine to the aromatic tetracarboxylic acid is 1.01-1.05:1; The amount of the first catalyst added is 0.2 to 1.5 wt‰ based on the total weight of the aromatic diamine containing a furan ring structure, the aromatic tetracarboxylic acid and water; In step 2), the temperature of the solid phase viscosity increasing reaction is 200-260°C; In step 2), the solid phase viscosity enhancement reaction time is 4 to 10 hours; In step 2), the solid phase viscosity increasing reaction is carried out under vacuum conditions, wherein the vacuum degree is 40-80 Pa; The first catalyst is a hypophosphite catalyst.

2. The synthesis method according to claim 1, wherein The Ar is selected from one of the following structures: 、 、 、 ； And / or, the number average molecular weight of the polyamide-imide containing furan ring structure is 3×10 4 ~1.2×10 5 .

3. The synthesis method according to claim 1, wherein The structural formula of the aromatic diamine containing a furan ring structure is shown in Formula II: Formula II; And / or, the aromatic tetracarboxylic acid is selected from one or more of pyromellitic acid, biphenyltetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid and 4,4-oxydiphthalic acid.

4. The synthesis method according to claim 1, characterized in that The hypophosphite catalyst is selected from one or more of sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, and magnesium hypophosphite.

5. The synthesis method according to claim 3, characterized in that In step 1), the polycondensation reaction is also stirred at a stirring rate of 50 to 400 r / min; and / or, carrying out the polycondensation reaction in an inert gas environment; and / or, using a centrifugal separator to carry out the dehydration and drying; And / or, the polycondensation reaction is carried out in a high-pressure polymerization reactor.

6. The synthesis method according to claim 3, characterized in that In step 2), a second catalyst is added during the solid phase viscosity increasing reaction, wherein the second catalyst is selected from one or more of diisopropylamine, 4-dimethylaminopyridine and triphenylphosphine; And / or, in step 2), a vacuum drum reactor is used to carry out the solid phase viscosity increasing reaction.

7. Use of the polyamide-imide containing a furan ring structure synthesized by the synthesis method according to any one of claims 1 to 6 in preparing a low dielectric film, a substrate for electronic products, or as an insulating material.

8. A low dielectric film, characterized in that The polyamide-imide containing a furan ring structure is prepared by the synthesis method according to any one of claims 1 to 6.

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