Polysulfide resin, precursor, method for producing polysulfide resin, optical element, optical system, lens for infrared camera, and optical device

Abstract

Provided is a polysulfide resin in which structural units including an adamantane structure are linearly linked via a sulfide bond.

Description

Polysulfide resin, precursor, method for producing polysulfide resin, optical element, optical system, lens for infrared camera, optical device

[0001] The present invention relates to a polysulfide resin, a precursor, a method for producing a polysulfide resin, an optical element, an optical system, a lens for an infrared camera, and an optical device. The present invention claims priority from Japanese Patent Application No. 2023-053432 filed on March 29, 2023, and the contents of that application are incorporated by reference into this application in designated states where incorporation by reference of documents is permitted.

[0002] For example, an infrared camera equipped with a lens that focuses infrared light is known, as disclosed in Patent Document 1. Lenses for such infrared cameras are required to be made of low-cost resin materials.

[0003] Japanese Patent Application Laid-Open No. 2018-77072

[0004] A first aspect of the present invention is a polysulfide resin in which structural units containing an adamantane structure are linearly linked via sulfide bonds.

[0005] Another aspect of the present invention is a precursor of the above-mentioned polysulfide resin, comprising a dithiol compound monomer and sulfur, wherein the sulfur content in the precursor is 30 to 80% by mass.

[0006] Another aspect of the present invention is an optical element using the above polysulfide resin.

[0007] Another aspect of the present invention is an optical system including the optical element described above.

[0008] Another aspect of the present invention is a lens for an infrared camera including the optical system described above.

[0009] Another aspect of the present invention is an optical device including the optical system described above.

[0010] Another aspect of the present invention is a dithiol compound of formula (2)

[0011] (In the formula, l １ , l ２and each independently represent an integer of 0 to 2.) with sulfur in a molar ratio of 1:2.5 to 1:25 to obtain a mixture, and a reaction step of reacting the mixture at 120°C to 220°C for 12 to 48 hours.

[0012] Fig. 1 is a schematic diagram of a far-infrared digital camera as an optical device according to this embodiment. Fig. 2 is a diagram showing the proportions of sulfide bonds in the polysulfide resin according to this embodiment (monomer a: 30, 50, and 70 mass% S addition rate). Fig. 3 is a diagram showing the proportions of sulfide bonds in the polysulfide resin according to this embodiment (monomer a, b, and c: 50 mass% S addition rate).

[0013] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content.

[0014] <Polysulfide Resin> The polysulfide resin according to this embodiment is a novel resin in which structural units containing an adamantane structure are linearly linked via sulfide bonds. Such a resin can be suitably used as one component of materials for optical elements of infrared cameras, etc. Furthermore, the use of such a resin can result in optical elements, etc., having excellent far-infrared transmittance.

[0015] An example of the structural unit of the polysulfide resin according to the present embodiment is represented by the following formula (1):

[0016] It is expressed as:

[0017] In the formula, l １ , l ２ each independently represents an integer of 0 to 2.

[0018] * represents a bond and serves as a sulfide bond between the structural units represented by formula (1).

[0019] m represents the number of sulfur atoms contained in formula (1) and is an integer of 2 or more. In this specification, compound (1) in which m is 2 is referred to as compound (i):

[0020] Compound (1) in which m is 3 is converted into compound (ii):

[0021] Compound (1) in which m is 4 or more is treated with (iii):

[0022] The wavy line in the formula of compound (iii) represents the outline of an additional sulfide bond when the number of sulfur atoms contained in compound (iii) is more than four.

[0023] Compounds (i), (ii), and (iii) are randomly linked in a linear chain via the bonds * through sulfide bonds.

[0024] The content of compound (i) in which m is 2 in the polysulfide resin is 0 to 0.25 in terms of molar fraction. The lower limit of the content of compound (i) is preferably 0.02, more preferably 0.05, and even more preferably 0.08. The upper limit of the content of compound (i) is preferably 0.20, more preferably 0.10, and even more preferably 0.05.

[0025] The content of compound (ii) in which m is 3 in the polysulfide resin is 0 to 0.25 in terms of molar fraction. The lower limit of the content of compound (ii) is preferably 0.04, more preferably 0.07, and even more preferably 0.10. The upper limit of the content of compound (ii) is preferably 0.20, more preferably 0.15, and even more preferably 0.10.

[0026] The content of compound (iii) in which m is 4 or greater in the polysulfide resin is 0.45 to 0.95 in terms of molar fraction. The lower limit of the content of compound (iii) is preferably 0.50, more preferably 0.55, and even more preferably 0.60. The upper limit of the content of compound (iii) is preferably 0.90, more preferably 0.85, and even more preferably 0.80.

[0027] <Physical Properties of Polysulfide Resin> The physical properties of the polysulfide resin according to this embodiment will be described below.

[0028] The refractive index (n ｄThe refractive index (n ｄ The lower limit of the refractive index (n ｄ The upper limit of ) may be 1.88, 1.86, or 1.84.

[0029] The external transmittance of the polysulfide resin according to this embodiment at wavelengths of 8 to 14 μm (far-infrared region) is 10% or more, preferably 15% or more, more preferably 20% or more, and even more preferably 24% or more.

[0030] The film thickness of the polysulfide resin according to this embodiment is 0.3 to 2.0 mm. The lower limit of the film thickness is preferably 0.5 mm, more preferably 0.6 mm, and even more preferably 0.7 mm. The upper limit of the film thickness is preferably 2.0 mm, more preferably 1.8 mm, and even more preferably 1.5 mm.

[0031] <Method for producing polysulfide resin> The polysulfide resin according to this embodiment is produced, for example, as shown below, by heating a precursor containing a dithiol compound monomer of formula (2) and solid sulfur to cause a reaction and produce structural unit (1). The symbols in formulas (1) and (2) are as described above. The target polysulfide resin may contain a trace amount of elemental sulfur that precipitates during the production process.

[0032]

[0033] In one example of the method for producing a polysulfide resin according to this embodiment, the sulfur addition rate in a precursor containing a dithiol compound monomer and sulfur is 30 to 85% by mass. The lower limit of the sulfur addition rate is preferably 35%, more preferably 40%, and even more preferably 45%. The upper limit of the sulfur addition rate is preferably 80%, more preferably 75%, and even more preferably 70%. If the sulfur addition rate is less than 30%, a sufficient effect of improving the refractive index cannot be obtained. On the other hand, if the sulfur addition rate exceeds 80%, the cured resin lacks stability, and sulfur precipitates over time.

[0034] An example of a method for producing a polysulfide resin according to this embodiment includes a mixing step of mixing a dithiol compound monomer with sulfur at a molar ratio of 1:2.5 to 1:25 to obtain a mixture, and a reaction step of reacting the mixture at 120 to 220° C. for 12 to 48 hours. The molar ratio of the dithiol compound monomer to sulfur is expressed as the number of sulfur atoms per one monomer molecule.

[0035] The dithiol compound mixed in the mixing step preferably contains an adamantane structure, and more preferably contains a monomer a (wherein: l １ , l ２ =2)

[0036] Monomer b (wherein: l １ , l ２ =1)

[0037] Monomer c (wherein: l １ , l ２ = 0)

[0038] These are dithiol compounds such as those represented by the following formula:

[0039] Monomer a can be synthesized, for example, by the following method.

[0040]

[0041] Monomer b can be synthesized, for example, by the following method.

[0042]

[0043] Monomer c can be synthesized, for example, by the following method.

[0044]

[0045] The details of the synthesis methods of the above-mentioned monomers a, b, and c will be described later in the Examples. These monomers may be synthesized by methods other than those described above, and each reaction step during the synthesis may also be a reaction step other than those described above, whether known or unknown.

[0046] The sulfur mixed in the mixing step is in the form of a powder, which is commercially available from, for example, Sigma-Aldrich Corporation.

[0047] The molar ratio of the dithiol compound of formula (2) to sulfur mixed in the mixing step is 1:2.5 to 1:25. When the dithiol compound is monomer a, the molar ratio is preferably 1:5.0, more preferably 1:8.0, and even more preferably 1:12.0. When the dithiol compound is monomer b, the molar ratio is preferably 1:3.5, more preferably 1:7.0, and even more preferably 1:10.5. When the dithiol compound is monomer c, the molar ratio is preferably 1:6.0, more preferably 1:10.0, and even more preferably 1:14.5.

[0048] The reaction temperature in the reaction step is 120 to 220° C. The lower limit of the reaction temperature is preferably 140° C., more preferably 150° C., and even more preferably 160° C. The upper limit of the reaction temperature is preferably 220° C., more preferably 210° C., and even more preferably 200° C.

[0049] The reaction time in the reaction step is 12 to 48 hours. The lower limit of the reaction time is preferably 16 hours, more preferably 20 hours, and even more preferably 24 hours. The upper limit of the reaction time is preferably 48 hours, more preferably 36 hours, and even more preferably 24 hours.

[0050] After the reaction step, the target polysulfide resin can be obtained by allowing the reaction mixture to cool at room temperature for 1 to 4 hours. The cooling period is preferably 1 hour or longer, more preferably 2 hours or longer, and even more preferably 4 hours or longer. The polysulfide resin according to this embodiment may contain a trace amount of elemental sulfur.

[0051] In addition, if necessary, suitable amounts of known clarifying agents, coloring agents, defoaming agents, fluorine compounds, and other components may be added to the resin composition for the purpose of clarifying, coloring, decoloring, fine adjustment of optical constants, etc. Furthermore, other components may be added in addition to the above components as long as the effects of the polysulfide resin according to the present embodiment can be obtained.

[0052] It is preferable to use high-purity raw materials with low impurity content. A high-purity raw material is one containing 99.85 mass% or more of the component. The use of high-purity raw materials reduces the amount of impurities, which tends to increase the internal transmittance of the polysulfide resin.

[0053] <Uses of Polysulfide Resin> From the above-mentioned viewpoint, the polysulfide resin according to this embodiment can be suitably used, for example, as an optical element provided in an optical device. Such optical elements include mirrors, lenses, prisms, filters, and the like. Examples of optical systems in which the optical elements are used include objective lenses, condenser lenses, imaging lenses, and camera lenses. These optical systems can be suitably used in various optical devices such as far-infrared cameras (8 to 14 μm), mid-infrared cameras (3 to 5 μm), and near-infrared cameras (0.7 to 2.5 μm).

[0054] 1 is a schematic diagram of a far-infrared digital camera 1. The far-infrared digital camera 1 includes a lens unit 101, an imaging unit 102 equipped with a CMOS image sensor or the like, a memory unit 103 for storing image data acquired by the imaging unit, and a display unit 104 for displaying the captured image. The lens unit 101 can use the polysulfide resin according to this embodiment as an optical system.

[0055] The present invention will be explained in more detail by the following examples, but the present invention is not limited to these examples in any way.

[0056] Example 1 relates to a polysulfide resin (A) produced from monomer a, Example 2 relates to a polysulfide resin (B) produced from monomer b, and Example 3 relates to a polysulfide resin (C) produced from monomer c.

[0057] Details of each step in the synthesis of polysulfide resin and the compounds produced in each step １ H-NMR (Bruker "AVANCE III HD") １３The results of C-NMR (nuclear magnetic resonance spectrometer AVANCEIII HD500) measurement are shown below. The physical properties of the obtained polysulfide resin are shown in Tables 1 to 4.

[0058] Example 1: Synthesis of polysulfide resin (A)

[0059] Synthesis of Monomer a

[0060]

[0061] Step 1-a

[0062]

[0063] A Soxhlet vessel packed with 3Å molecular sieves was charged with 10.62 g (42.75 mmol) of 1,3-adamantanedicarboxylic acid (Tokyo Chemical Industry Co., Ltd.) in ethanol (100 mL), and concentrated sulfuric acid (0.454 g, 4.629 mmol) was added, followed by heating under reflux for 20 hours. After allowing to cool to room temperature, NaHCO ３ Aqueous solution (10 mL) was added and concentrated under reduced pressure. ３ (60 mL x 3) and water (50 mL), and the organic layer was washed with saturated brine (30 mL). ２ SO ４ The extract was dried at 400°C, filtered, and the solvent was evaporated under reduced pressure to give the target diester compound (13.19 g, 42.76 mmol) as a colorless, transparent liquid in a yield of 100%.

[0064] １ H-NMR (500MHz, CDCl ３ ) δ4.11 (q, 4H, J = 7.1Hz), 2.12-2.17 (m, 2H), 2.02 (s, 2H), 1.81-1.90 (m, 8H), 1.66-1.69 (m, 2H), 1.24 (t, 6H, J = 7.1Hz); １３ C-NMR (125MHz, CDCl ３ ) δ177.7, 60.0, 48.6, 47.3, 41.6, 35.9, 33, 5, 29.0, 14.5

[0065] Step 2-a

[0066]

[0067] ​Under a nitrogen atmosphere, LiAlH ４ Anhydrous THF (20 mL) was added to the powder (0.578 g, 7.619 mmol). The solution was cooled in an ice bath, and a THF solution (30 mL) of the diester compound (2.450 g, 7.619 mmol) was added. After warming to room temperature, the mixture was stirred for 20 hours under reflux. After cooling to room temperature, the container was cooled in an ice bath, and water (2 mL) was added dropwise. A 20% aqueous NaOH solution (1 mL) was added, and the mixture was stirred at room temperature for 2 hours. After adjusting the pH to 3-4 with a 6 M aqueous HCl solution, the precipitated solid was filtered through a glass filter and washed with THF (50 mL). The solution was concentrated under reduced pressure, and the precipitated solid was dissolved by heating in EtOAc (60 mL). The organic layer was extracted with saturated brine (20 mL), and the aqueous layer was extracted with EtOAc (20 mL). The combined organic layers were washed with Na ２ SO ４ The mixture was dried at 400°C, filtered, and the solvent was evaporated under reduced pressure to obtain the target diol compound (6.80 g, 30.31 mmol) as a white solid in a yield of 94%.

[0068] １ H-NMR (500MHz, CDCl ３ ) δ 3.71 (t, 4H, J = 7.5Hz), 2.01 (t, 2H, J = 2.91Hz), 1.47-1.60 (m, 8H), 1.38-1.45 (m, 8H), 1.29 (s, 2H); １３ C-NMR (125MHz, CDCl ３ ) δ58.9, 48.3, 47.0, 42.3, 36.6, 32.7, 29.1

[0069] Step 3-a

[0070]

[0071] Diol compound (4.41 g, 19.65 mmol) in CHCl ３ The solution (100 mL) was added, and triethylamine (13.6 mL, 98.1 mmol) and then mesyl chloride (6.1 mL, 78.8 mmol) were added. After stirring at room temperature for 2 days, 1 M aqueous HCl solution (100 mL) was added and CHCl ３ (50 mL x 3), and the organic layer was washed with saturated brine (30 mL). ２ SO​４ The mixture was dried at 77°C, filtered, and the solvent was evaporated under reduced pressure to give the crude dimesyl compound (9.91 g) as a pale yellow, transparent liquid. The crude product was used in the next step without further purification (peak assignments are those at the time of purification). Immediately after purification, the product was liquid, but after standing at room temperature for a while, it became solid.

[0072] １ H-NMR (500MHz, CDCl ３ ) δ4.29 (t, 4H, J=7.8Hz), 3.00 (s, 6H), 2.06 (s, 2H), 1.49-1.62 (m, 10H), 1.41-1.47 (m, 4H), 1.31 (s, 2H); １３ C-NMR (125MHz, CDCl ３ ) δ66.4, 47.3, 42.4, 41.6, 37.5, 36.0, 32.5, 28.6

[0073] Step 4-a

[0074]

[0075] Potassium thioacetate (6.96 g, 60.94 mmol) was added to a solution (280 mL) of the crude dimesyl compound (9.91 g) in MeCN, and the mixture was stirred under reflux for 24 hours. After cooling to room temperature, water (50 mL) was added and the solution was concentrated under reduced pressure. The mixture was extracted with EtOAc (60 mL x 3) and water (30 mL), and the organic layer was washed with saturated brine (30 mL). The organic layer was then washed with Na ２ SO ４ The mixture was dried at 75°C and filtered. The solvent was evaporated under reduced pressure to give a crude product. The crude product was purified by column chromatography to give the target dithioacetyl compound (6.517 g, 19.14 mmol) as an orange liquid in a 97% yield (total yield of Step 3-a and Step 4-a).

[0076] １ H-NMR (500MHz, CDCl ３ ) δ2.80-2.84 (m, 4H), 2.31 (s, 6H), 2.04 (s, 2H), 1.59 (s, 2H), 1.38-1.44 (m, 8H), 1.32-1.37 (m, 4H), 1.26 (s, 2H); １３ C-NMR (125MHz, CDCl ３ ​​)δ196.1, 46.7, 43.6, 41.6, 36.5, 33.7, 30.7, 29.0, 23.7

[0077] Step 5-a

[0078]

[0079] Under a nitrogen atmosphere, LiAlH ４ Anhydrous THF (15 mL) was added to the powder (1.45 g, 38.21 mmol). A THF solution (35 mL) of the dithioacetyl compound (6.52 g, 19.13 mmol) was added dropwise, and the mixture was heated to reflux for 20 hours. After cooling to room temperature, water (15 mL) and 2 M NaOH aqueous solution (5 mL) were added, and the mixture was stirred for 30 minutes. The solution was concentrated under reduced pressure, and the precipitated solid was filtered off using a glass filter. The residue was washed with hot EtOAc (150 mL), and the organic layer was washed with saturated brine (20 mL) and 1 M HCl aqueous solution (20 mL). The aqueous layer was extracted with EtOAc (15 mL x 2), and the combined organic layer was washed with saturated brine (20 mL). The organic layer was washed with Na ２ SO ４ The mixture was dried at 75°C and filtered. The solvent was removed by distillation under reduced pressure to obtain a crude product. The crude product was purified by column chromatography to obtain the target dithiol compound (3.20 g, 12.48 mmol) as a colorless, transparent liquid in a yield of 65% (monomer a).

[0080] １ H-NMR (500MHz, CDCl ３ ) δ2.46-2.51 (m, 4H), 2.02 (s, 2H), 1.57 (s, 2H), 1.34-1.48 (m, 12H), 1.30 (t, 2H, J = 2.4Hz), 1.20 (s, 2H); １３ C-NMR (125MHz, CDCl ３ )δ49.3, 47.0, 41.6, 36.4, 33.8, 28.8, 18.9

[0081] ​Monomer a and sulfur (Sigma-Aldrich) were weighed into a PFA reaction vessel so that the molar ratio and sulfur content were as shown in Table 1. The mixture was stirred at 200°C for 3 to 6 hours. After stirring, the mixture was further heated at 200°C for 18 to 21 hours (a total of 24 hours of heating) and then allowed to cool to room temperature to obtain a liquid. The mixture was then allowed to stand at room temperature for approximately 3 hours to obtain polysulfide resins (1A to 5A).

[0082] Example 2: Synthesis of polysulfide resin (B)

[0083] Synthesis of Monomer b

[0084]

[0085] Step 1-b

[0086]

[0087] A solution (220 mL) of 30.65 g (136.67 mmol) of 1,3-adamantanedicarboxylic acid (Tokyo Chemical Industry) in ethanol was placed in a Soxhlet-equipped vessel packed with 3Å molecular sieves, and concentrated sulfuric acid (1.39 g, 14.17 mmol) was added, followed by heating under reflux for 22 hours. After allowing to cool to room temperature, NaHCO ３ Aqueous solution (30 mL) was added and concentrated under reduced pressure. ３ (100 mL x 3) and water (50 mL), and the organic layer was washed with saturated brine (30 mL). ２ SO ４ The solvent was evaporated under reduced pressure to give the target diester compound (38.2 g, 136.25 mmol) as a pale yellow, transparent liquid in a yield of 100%.

[0088] １ H-NMR (500MHz, CDCl ３ ) δ3.25 (s, 4H), 2.11 (s, 2H), 1.65 (s, 2H), 1.42-1.54 (m, 10H), 1.29 (s, 2H); １３ C-NMR (125MHz, CDCl ３ ) δ73.6, 40.6, 38.8, 36.8, 35.2, 28.3

[0089] Step 2-b

[0090] ​

[0091] Under a nitrogen atmosphere, LiAlH ４ Anhydrous THF (30 mL) was added to the powder (3.81 g, 100.4 mmol). The solution was cooled in an ice bath, and a THF solution (150 mL) of the diester compound (14.02 g, 50.01 mmol) was added using a dropping funnel. After the dropwise addition was completed, the temperature was raised to room temperature and the mixture was stirred for 24 hours under reflux. After cooling to room temperature, the container was cooled in an ice bath, and water (10 mL) was added dropwise. 10% aqueous NaOH solution (5 mL) was added, and the mixture was stirred at room temperature for 30 minutes. After adjusting the pH to 4-5 with 2 M aqueous HCl solution, the precipitated solid was filtered through a glass filter, and the solution was concentrated under reduced pressure. The residue was washed with THF (100 mL), and the mixture was concentrated under reduced pressure. The mixture was extracted with hot EtOAc (100 mL x 3) and water (100 mL), and the mother liquor was washed with saturated brine (20 mL). The organic layer was then cooled in an ice bath and water (10 mL) was added dropwise. ２ SO ４ The solvent was evaporated under reduced pressure to give the target 1,3-adamantanedimethanol (9.27 g, 47.2 mmol) as a white solid in a yield of 94%.

[0092] １ H-NMR (500MHz, CDCl ３ ) δ3.25 (s, 4H), 2.11 (s, 2H), 1.65 (s, 2H), 1.42-1.54 (m, 10H), 1.29 (s, 2H); １３ C-NMR (125MHz, CDCl ３ ) δ73.6, 40.6, 38.8, 36.8, 35.2, 28.3

[0093] Step 3-b

[0094]

[0095] 1,3-Adamantane dimethanol (0.981 g, 5.00 mmol) with ZnBr ２ ​(5.63 g, 25.00 mmol) and a 30% HBr-AcOH solution (15 mL) were added and stirred at room temperature for 15 minutes, and then stirred at 110°C for 5 hours. After cooling to room temperature, the mixture was left standing overnight. The precipitated solid was filtered off using a glass filter, and the residue was washed with water (30 mL x 3). After drying under reduced pressure, the target 1,3-dimethylenebromoadamantane (1.46 g, 4.53 mmol) was obtained as a white solid in a yield of 91%.

[0096] １ H-NMR (500MHz, CDCl ３ ) δ 3.19 (2,4H), 2.12 (s (br), 2H), 1.58 (s (br), 2H), 1.46-1.55 (m, 10H); １３ C-NMR (125MHz, CDCl ３ ) δ47.4, 43.8, 40.1, 35.9, 34.6, 28.7

[0097] Step 4-b

[0098]

[0099] Potassium thioacetate (1.55 g, 13.57 mmol) was added to a solution of 1,3-dimethylenebromoadamantane (1.457 g, 4.524 mmol) in DMF-water (4:1, 30 mL) and stirred at 110° C. for 18 hours. After cooling to room temperature, water (70 mL) was added and the mixture was diluted with Et ２ The organic layer was washed with saturated brine (15 mL x 2). ２ SO ４ The mixture was dried at 75°C and filtered. The solvent was removed by distillation under reduced pressure to obtain a crude product. The crude product was isolated and purified by column chromatography to obtain the target dithioacetyl compound (1.247 g, 3.991 mmol) as an orange liquid in a yield of 88%.

[0100] １ H-NMR (500MHz, CDCl ３ ) δ2.72 (s, 4H), 2.32 (s, 6H), 2.01 (s, 2H), 1.53 (s, 2H), 1.33-1.46 (m, 8H), 1.22 (s, 2H); １３ C-NMR (125MHz, CDCl ３ ​​) δ195.7, 45.2, 41.9, 40.6, 35.9, 34.1, 30.8, 28.7

[0101] Step 5-b

[0102]

[0103] Under a nitrogen atmosphere, LiAlH ４ Anhydrous THF (10 mL) was added to the powder (0.227 g, 5.982 mmol). A solution of the dithioacetyl compound (0.932 g, 2.982 mmol) in THF (20 mL) was added dropwise, and the mixture was heated to reflux for 20 hours. After cooling to room temperature, water (2 mL), 15% aqueous NaOH solution (1 mL), and THF (10 mL) were added, and the mixture was stirred at room temperature for 1.5 hours. After adjusting the pH to 3-4 with 6 M aqueous HCl, the precipitate was filtered through a glass filter, and the residue was washed with THF (50 mL). The solution was concentrated under reduced pressure, diluted with EtOAc (80 mL), and the organic layer was washed with saturated brine (15 mL). The organic layer was then washed with Na ２ SO ４ The mixture was dried at 75°C and filtered. The solvent was removed by distillation under reduced pressure to obtain a crude product. The crude product was isolated and purified by column chromatography to obtain the target dithiol compound (0.657 g, 2.876 mmol) as a colorless, transparent liquid in a yield of 96% (monomer b).

[0104] １ H-NNR (500MHz, CDCl ３ ) DC ３ ) δ2.34 (d, 4H, J = 8.7Hz), 2.10 (m, 2H), 1.39-1.51 (m, 8H), 1.28 (s, 2H), 1.33-1.46 (m, 8H), 1.11 (t, 2H, J = 8.7Hz); １３ C-NMR (125MHz, CDCl3) δ44.4, 40.5, 38.3, 36.3, 34.2

[0105] Monomer b and sulfur (Sigma-Aldrich) were weighed into a PFA reaction vessel so as to obtain the molar ratio and sulfur content shown in Table 2. The mixture was stirred at 200°C for 3 to 6 hours. After stirring, the mixture was further heated at 200°C for 18 to 21 hours (a total of 24 hours of heating) and allowed to cool to room temperature to obtain a liquid. The mixture was then allowed to stand at room temperature for approximately 3 hours to obtain polysulfide resins (1B to 4B). ​

[0106] Example 3: Synthesis of polysulfide resin (C)

[0107] Synthesis of Monomer c

[0108]

[0109] Thiourea (906 g, 11.9 mol) was added to a concentrated aqueous hydrochloric acid solution (approximately 12 M, 3 kg, 30 W equivalents) of 1,3-adamantanediol (100 g, 0.6 mol) (Tokyo Chemical Industry Co., Ltd.) in a 10 L four-neck flask, and the mixture was heated and stirred overnight at an internal temperature of 97°C. (The reaction solution changed from a white suspension to a colorless solution, and a white solid precipitated on the walls of the reactor. As much of the precipitated solid as possible was scraped off with a spatula and dropped into the reaction solution.) After allowing to cool to room temperature, 48% aqueous NaOH solution (1.6 L) was added dropwise over 1 hour (internal temperature: maximum 39°C) to adjust the pH to 12. The reaction solution was then heated to an internal temperature of 97°C and stirred for 1 hour. After allowing the reaction solution to cool to room temperature, concentrated aqueous hydrochloric acid solution (200 mL) was added dropwise while cooling in an ice bath to adjust the pH to 1. CHCl ３ (3 L) was added and stirred, and the precipitated solid (thiourea, its residue, and NaCl) was filtered off. The filtered solid was dissolved in CHCl ３ The organic layer combined with the mother liquor was washed with water (5 L) and saturated brine (5 L) in this order, and the organic layer was concentrated to obtain crude product (1).

[0110] This crude product (1) was dissolved in CHCl ３ The contents were transferred to the reactor again while being washed with 230 mL of thiourea. Thiourea (906 g, 11.9 mol) and a concentrated aqueous solution of hydrochloric acid (about 12 M, 3 kg, 30 wt equivalents) were added to the reactor, and the mixture was heated and stirred at an internal temperature of 97°C. CHCl ３ The reaction mixture was removed as much as possible using a Dean-Stark flask (distillate volume: 140 mL). After heating and stirring overnight, the reaction mixture was allowed to cool. While the reaction mixture was cooled in an ice bath, 48% aqueous NaOH solution (1.7 L) was added dropwise over 90 minutes (internal temperature: maximum 39°C) to adjust the pH to 12. The reaction mixture was heated to an internal temperature of 97°C and stirred for 3 hours. After allowing the reaction mixture to cool to room temperature, concentrated aqueous hydrochloric acid solution (330 mL) was added dropwise while cooling in an ice bath to adjust the pH to 2. CHCl ３ (3 L) was added and stirred, and the precipitated solid (thiourea, its residue, and NaCl) was filtered off. The filtered solid was dissolved in CHCl３ The organic layer combined with the mother liquor was washed with water (5 L) and saturated brine (5 L) in this order, and the organic layer was concentrated to obtain crude product (2).

[0111] The crude product (2) was purified by column chromatography to obtain the target 1,3-adamantanedithiol compound (73.1 g, 0.365 mol) as a white solid in a yield of 61% (monomer c).

[0112] １ H-NMR (500MHz, CDCl ３ ) δ2.14 (s, 2H), 2.08 (s, 2H), 1.83 (m, 8H), 1.73 (s, 2H), 1.58 (s, 2H); １３ C-NMR (125MHz, CDCl ３ ) δ57.3, 45.8, 43.9, 34.2, 31.6

[0113] Monomer c may be synthesized by the following method.

[0114]

[0115] Trifluoromethanesulfonic acid (0.52 mL, 5.89 mmol) was added to a solution of 1,3-adamantanediol (9.943 g, 59.10 mmol) in thioacetic acid (25 mL), and the mixture was stirred at 50° C. for 22 hours. After allowing to cool to room temperature, CHCl ３ (150 mL) and diluted with NaHCO ３ The aqueous layer was washed with CHCl ３ The combined organic layer was washed with saturated brine (30 mL x 2). ２ SO ４ The mixture was dried at 77°C and filtered. The solvent was removed under reduced pressure to give a crude product (19.8 g), which was used in the next step without further purification.

[0116] Under a nitrogen atmosphere, LiAlH ４ ​Anhydrous THF (100 mL) was added to the powder (6.77 g, 178.4 mmol). A solution of the above crude product in anhydrous THF (80 mL) was added dropwise while the container was cooled in an ice bath. After warming to room temperature, the mixture was stirred for 20 hours under reflux. After cooling to room temperature, the container was cooled in an ice bath, and water (12 mL) and a 20% aqueous NaOH solution (6 mL) were added dropwise in this order. THF (150 mL) was then added, and the mixture was stirred at room temperature for 1 hour. After adjusting the pH to 3-4 with 12 M aqueous HCl, the precipitated solid was filtered through a glass filter, and the residue was washed with THF (250 mL). The solution was concentrated under reduced pressure, diluted with EtOAc (300 mL), and washed with water (100 mL) and saturated brine (50 mL) in this order. The organic layer was then washed with Na ２ SO ４ The residue was dried at 70°C and filtered. The solvent was distilled off under reduced pressure to obtain a crude product. The crude product was purified by column chromatography (hexane / toluene) to obtain the target 1,3-adamantanedithiol (8.461 g, 42.23 mmol) in a two-step yield of 71% (monomer c).

[0117] Monomer c and sulfur (Sigma-Aldrich) were weighed into a PFA reaction vessel so that the molar ratio and sulfur content were as shown in Table 3. The mixture was stirred at 200°C for 3 to 6 hours. After stirring, the mixture was further heated at 200°C for 18 to 21 hours (a total of 24 hours of heating) and allowed to cool to room temperature to obtain a liquid. The mixture was then allowed to stand at room temperature for approximately 3 hours to obtain polysulfide resins (1C to 3C).

[0118] <Evaluation of Physical Properties of Polysulfide Resins> The refractive index n ｄ The refractive index and transmittance in the terahertz region were also measured for the polysulfide resins 3A, 2B, 1C, and 3C.

[0119] Refractive index n ｄThe refractive index was measured for the d-line (587.6 nm) using a prism coupler (Metricon). The refractive index in the terahertz region was measured using time-domain spectroscopy (THz-TDS) with a terahertz spectroscopic imaging device (prototype, measurement frequency band: 0.1 to 1.5 THz, frequency resolution: approximately 5 GHz, spatial resolution: approximately 100 μm). In addition to the transmittance spectrum described below, the phase difference spectrum was also measured simultaneously, and the refractive index spectrum was derived from these results (Reference: K. Sakai, "Terahertz Optoelectronics," Topics Appl. Phys. 97, 203 (2005)).

[0120] The far-infrared transmittance was measured using FT-IR (Thermo Fischer, Nicolet 6700) from 4000 to 400 cm －１ was measured by the transmission method. The resolution was 2 and the number of integrations was 30. The average transmittance was calculated in the wavelength range of 8 to 14 μm. The unit is wave number cm －１ The transmittance was calculated by summing the data using the quadrature method of pieces and then averaging them. The refractive index in the terahertz range was measured using time-domain spectroscopy (THz-TDS) with a terahertz spectroscopic imaging device (prototype). The spectroscopic spectrum was acquired using spectroscopic imaging, and the transmittance was calculated by comparing it with reference data (Teflon (registered trademark) substrate).

[0121] The film thickness was measured at the center using a constant pressure thickness measuring device (TECLOCK, PG-01) (the thickness was also measured at the periphery (four locations) to confirm uniformity of the thickness). The measuring device mentioned above complies with JIS K6250.

[0122] The measurement results for polysulfide resin A are shown in Table 1: Example 1 (Examples 1-1 to 1-5), the measurement results for polysulfide resin B are shown in Table 2: Example 2 (Examples 2-1 to 2-4), and the measurement results for polysulfide resin C are shown in Table 3: Example 3 (Examples 3-1 to 3-3). Furthermore, the measurement results for refractive index and transmittance in the terahertz range are shown in Table 4. Furthermore, Figs. 2 and 3 show the proportion of sulfide bonds (abundance ratio of m numbers) in polysulfide resins when the monomer and sulfur addition rate are changed. The abundance ratio of m numbers is １ H-NMR (500MHz, CDCl３ ) was calculated from the results. For example, in the case of monomer a, -CH ２ The peak derived from SH is detected at δ = 2.48, at δ = 2.58-2.65 for m = 2, at δ = 2.85 for m = 3, and at δ = 2.97 for m ≥ 4. The sum of the integral ratios of these peaks is used as the denominator and the integral ratio of the corresponding peak as the numerator to give the m number abundance ratio. For monomer b, the exact peak positions are different, but the calculation was similar. For monomer c, in addition to the overall peak position shift, the peak positions of m = 2 and m = 3 overlap, so separation was not performed.

[0123]

[0124]

[0125]

[0126]

[0127] As shown in Tables 1 to 3, it was confirmed that the polysulfide resins of Examples 1 to 3 had higher refractive indexes and far-infrared transmittances as the sulfur content increased.

[0128] 1... far-infrared digital camera, 101... lens unit, 102... imaging unit, 103... storage unit, 104... display unit

Claims

1. A polysulfide resin in which structural units containing an adamantane structure are linked in a linear chain via sulfide bonds.

2. The polysulfide resin according to claim 1 , wherein the structural unit is represented by formula (1): 【Chemistry 1】 (In the formula, l １ , l ２ each independently represents an integer of 0 to 2, m represents an integer of 2 or more, and * represents a bond.

3. The contents of the compound i in which m is 2, the compound ii in which m is 3, and the compound iii in which m is 4 or more are, in terms of mole fraction, Compound i: 0 to 0.25, Compound ii: 0 to 0.25, Compound iii: 0.45-0.95 The polysulfide resin according to claim 2, wherein

4. Refractive index (n ｄ 3. The polysulfide resin according to claim 1, wherein the saturation modulus (S) is 1.60 to 1.

95.

5. The polysulfide resin according to any one of claims 1 to 2, having a transmittance of 10% or more in the far-infrared region (wavelength 8 to 14 µm).

6. The polysulfide resin according to any one of claims 1 and 2, having a thickness of 0.3 to 2.0 mm.

7. A precursor of the polysulfide resin according to claim 1 or 2, containing a dithiol compound monomer and sulfur, A precursor in which the loading rate of the sulfur in the precursor is 30 to 80% by mass.

8. An optical element using the polysulfide resin according to claim 1 or 2.

9. An optical system comprising the optical element according to claim 8.

10. An infrared camera lens comprising the optical system of claim 9.

11. An optical device comprising the optical system of claim 9.

12. Dithiol compounds of formula (2) 【Chemistry 2】 (In the formula, l １ , l ２ each independently represents an integer of 0 to 2) and sulfur in a molar ratio of 1:2.5 to 1:25 to obtain a mixture; a reaction step of reacting the mixture at 120 to 220°C for 12 to 48 hours; A method for producing a polysulfide resin having the formula:

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