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

Abstract

A polysulfide resin in which structural units including an adamantane structure are linked in a straight chain via a thioether bond.

Description

Technical Field

[0001] This invention relates to polysulfide resins, precursors, methods for manufacturing polysulfide resins, optical elements, optical systems, lenses for infrared cameras, and optical devices. This invention claims priority to Japanese Patent Application No. 2023-053432, filed March 29, 2023. For designated countries that recognize inclusion based on documentary reference, the contents of that application are incorporated herein by reference. Background Technology

[0002] For example, as disclosed in Patent Document 1, an infrared camera with a lens that focuses infrared light is known. As a lens for such an infrared camera, a low-cost resin material is required.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-77072 Summary of the Invention

[0006] The first aspect of the present invention is a polysulfide resin, wherein structural units comprising an adamantane structure are linked in a linear fashion via thioether bonds.

[0007] Another aspect of the present invention is a precursor, which is a precursor of the aforementioned polysulfide resin, wherein the precursor comprises a monomer of a dithiol compound and sulfur, and the addition rate of the sulfur in the precursor is 30% to 80% by mass.

[0008] Another aspect of the present invention is an optical element that uses the aforementioned polysulfide resin.

[0009] Another aspect of the invention is an optical system comprising the optical elements described above.

[0010] Another aspect of the present invention is a lens for an infrared camera, which includes the optical system described above.

[0011] Another aspect of the present invention is an optical device comprising the optical system described above.

[0012] Another aspect of the present invention is a method for manufacturing a polysulfide resin, comprising:

[0013] In the mixing process, the dithiol compound of formula (2) and sulfur are mixed at a molar ratio of 1:2.5 to 1:25 to obtain a mixture.

[0014] [Chemistry 1]

[0015]

[0016] (where l) 1 l 2 Each independently represents an integer from 0 to 2; and the reaction process, in which the above mixture is reacted at 120°C to 220°C for 12 to 48 hours. Attached Figure Description

[0017] Figure 1 This is a schematic structural diagram of an infrared digital camera when the optical device of this embodiment is configured as such.

[0018] Figure 2 This is a graph showing the proportion of thioether bonds in the polysulfide resin of this embodiment (monomer a: 30, 50, 70% by mass S addition rate).

[0019] Figure 3 This is a graph showing the proportion of thioether bonds in the polysulfide resin of this embodiment (monomers a, b, c: 50% by mass S addition rate). Detailed Implementation

[0020] Hereinafter, a detailed description will be given of a method for carrying out the present invention (hereinafter referred to as "this embodiment"). This embodiment is merely an example for illustrating the present invention and is not intended to limit the present invention to the following content.

[0021] <Polysulfide resins>

[0022] The polysulfide resin of this embodiment is a novel resin containing adamantane structural units linked in a linear fashion via thioether bonds. Such a resin is suitable as a component for use as a material in optical elements of infrared cameras, etc. Furthermore, by using this resin, optical elements with excellent far-infrared transmittance can be manufactured.

[0023] An example of the structural unit of the polysulfide resin in this embodiment is represented by the following formula (1).

[0024] [Chemistry 2]

[0025]

[0026] In the formula, l 1 l 2 Each can independently represent an integer from 0 to 2.

[0027] * indicates a bonding bond, which supports the thioether bond between the structural units shown in equation (1).

[0028] m represents the number of sulfur atoms in formula (1), and is an integer greater than or equal to 2. In this specification, compound (1) with m equal to 2 is denoted as compound (i):

[0029] [Chemistry 3]

[0030]

[0031] Let compound (1) with m = 3 be denoted as compound (ii):

[0032] [Chemistry 4]

[0033]

[0034] Compound (1) with m greater than 4 is denoted as (iii):

[0035] [Chemistry 5]

[0036]

[0037] It should be noted that the wavy part in the formula of compound (iii) represents the thioether bond when the number of sulfur atoms in compound (iii) further exceeds 4.

[0038] Compounds (i), (ii), and (iii) are linked in a straight chain via bonding bonds* through thioether bonds.

[0039] The content of compound (i) with m=2 in the polysulfide resin is 0 to 0.25 in mole fraction. The lower limit of the content of compound (i) is preferably 0.02, more preferably 0.05, and even more preferably 0.08. In addition, the upper limit of the content of compound (i) is preferably 0.20, more preferably 0.10, and even more preferably 0.05.

[0040] The content of compound (ii) with m=3 in the polysulfide resin is 0 to 0.25 in mole fraction. The lower limit of the content of compound (ii) is preferably 0.04, more preferably 0.07, and even more preferably 0.10. In addition, the upper limit of the content of compound (ii) is preferably 0.20, more preferably 0.15, and even more preferably 0.10.

[0041] The content of compound (iii) with m=4 or more in the polysulfide resin is 0.45 to 0.95 in mole fraction. The lower limit of the content of compound (iii) is preferably 0.50, more preferably 0.55, and even more preferably 0.60. In addition, the upper limit of the content of compound (iii) is preferably 0.90, more preferably 0.85, and even more preferably 0.80.

[0042] <Physical Properties of Polysulfide Resins>

[0043] The physical properties of the polysulfide resin of this embodiment will be described below.

[0044] The refractive index (n) of the polysulfide resin of this embodiment for the d-line d The refractive index (n) is 1.60–1.95. d The lower limit for refractive index (n) can be 1.65, 1.67, or 1.70. d The upper limit can be 1.88, 1.86, or 1.84.

[0045] The polysulfide resin of this embodiment has an external transmittance of 10% or more in the wavelength range of 8μm to 14μm (far-infrared region), preferably 15% or more, more preferably 20% or more, and even more preferably 24% or more.

[0046] The polysulfide resin of this embodiment has a film thickness of 0.3 mm 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.

[0047] <Manufacturing Method of Polysulfide Resins>

[0048] The polysulfide resin of this embodiment is manufactured, for example, by heating a monomer comprising a dithiol compound of formula (2) and a solid sulfur precursor to react and generate structural unit (1). The symbols in formulas (1) and (2) are as described above. The target polysulfide resin may also contain trace amounts of elemental sulfur that precipitate during the manufacturing process.

[0049] [Chemistry 6]

[0050]

[0051] In one example of the method for manufacturing the polysulfide resin according to this embodiment, the sulfur addition rate, in the monomer containing the dithiol compound and the sulfur precursor, 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%. Furthermore, 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 increase in refractive index cannot be obtained. On the other hand, if it exceeds 80% or more, the stability of the cured resin is lacking, and sulfur precipitates over time.

[0052] In one example of the method for manufacturing the polysulfide resin according to this embodiment, the method includes: a mixing step in which a monomer of a dithiol compound and sulfur are mixed at a molar ratio of 1:2.5 to 1:25 to obtain a mixture; and a reaction step in which the mixture is reacted at 120°C to 220°C for 12 to 48 hours. It should be noted that the molar ratio of the monomer of the dithiol compound to sulfur is expressed as the number of sulfur atoms relative to one monomer molecule.

[0053] The dithiol compound mixed in the mixing process preferably contains an adamantane structure, and more preferably is a dithiol compound represented by the monomers described below.

[0054] Monomer a (where l) 1 l 2 =2)

[0055] [Chemistry 7]

[0056]

[0057] Monomer b (where l) 1 l 2 =1)

[0058] [Chemistry 8]

[0059]

[0060] Monomer c (where l) 1 l 2 =0)

[0061] [Chemistry 9]

[0062]

[0063] Monomer a is synthesized, for example, by the following method.

[0064] [Chemistry 10]

[0065]

[0066] Monomer b is synthesized, for example, by the following method.

[0067] [Chemistry 11]

[0068]

[0069] Monomer c is synthesized, for example, by the following method.

[0070] [Chemistry 12]

[0071]

[0072] Detailed descriptions of the synthesis methods for monomers a, b, and c are provided in the examples described later. It should be noted that these monomers can also be synthesized using methods other than those described above. Furthermore, the reaction steps in the synthesis process can be performed using other reaction steps besides those described above, regardless of whether they are known or unknown.

[0073] The sulfur mixed in the mixing process is a powdered elemental form, which can be commercially available, for example, from companies such as Sigma-Aldrich.

[0074] In the mixing process, the molar ratio of the dithiol compound of formula (2) to sulfur is 1:2.5 to 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.

[0075] The reaction temperature in the reaction process is 120℃ to 220℃. The lower limit of the reaction temperature is preferably 140℃, more preferably 150℃, and even more preferably 160℃. The upper limit of the reaction temperature is preferably 220℃, more preferably 210℃, and even more preferably 200℃.

[0076] The reaction time in the reaction process 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.

[0077] After the reaction process, the target polysulfide resin can be obtained by naturally cooling at room temperature for 1 to 4 hours. The natural cooling period is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 4 hours or more. The polysulfide resin of this embodiment may also contain trace amounts of elemental sulfur.

[0078] Furthermore, as needed, for purposes such as clarification, coloring, decolorization, and fine-tuning of optical constants, known clarifying agents, colorants, defoaming agents, fluorinated compounds, etc., can be added to the resin composition in appropriate amounts. In addition, other components may be added within the range that achieves the effects of the polysulfide resin of this embodiment, without being limited to the above-mentioned components.

[0079] The preferred raw material is a high-purity product with a low impurity content. High-purity refers to a substance containing 99.85% or more of the component by mass. Using high-purity raw materials reduces impurities, resulting in a tendency to improve the internal transmittance of polysulfide resins.

[0080] <Uses of Polysulfide Resins>

[0081] From the above perspective, the polysulfide resin of this embodiment is suitable for use as an optical element in optical devices. Such optical elements include mirrors, lenses, prisms, filters, etc. Furthermore, examples of optical systems using these optical elements include objective lenses, condenser lenses, imaging lenses, and camera lenses. Moreover, these optical systems are suitable for use in various optical devices such as far-infrared cameras (8μm to 14μm), mid-infrared cameras (3μm to 5μm), and near-infrared cameras (0.7μm to 2.5μm).

[0082] Figure 1 This is a schematic structural 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, etc., a storage unit 103 storing image data acquired by the imaging unit, and a display unit 104 displaying the captured images. The lens unit 101 can use the polysulfide resin of this embodiment as the optical system.

[0083] Example

[0084] The invention is illustrated in more detail by way of the following embodiments, but the invention is not limited to any of the following embodiments.

[0085] Example 1 relates to a polysulfide resin (A) made from monomer a, Example 2 relates to a polysulfide resin (B) made from monomer b, and Example 3 relates to a polysulfide resin (C) made from monomer c.

[0086] The following details the steps involved in the synthesis of polysulfide resins, as well as the compounds generated in each step. 1 H-NMR (Bruker's "AVANCE III HD") 13 The results of C-NMR (using an AVANCEIII HD500 nuclear magnetic resonance apparatus) measurements are shown. Furthermore, the physical properties of the obtained polysulfide resins are presented in Tables 1-4.

[0087] <Example 1: Synthesis of polysulfide resin (A)>

[0088] Synthesis of monomer a

[0089] [Chemistry 13]

[0090]

[0091] Step 1-a

[0092] [Chemistry 14]

[0093]

[0094] To the molecular sieve 10.62 g (42.75 mmol) of an ethanol solution (100 mL) of 1,3-adamantanedicarboxylic acid (Tokyo Kasei Corporation) was added to a Soxhlet container, followed by the addition of concentrated sulfuric acid (0.454 g, 4.629 mmol) and reflux for 20 hours. After natural cooling to room temperature, 10 mL of NaHCO3 aqueous solution was added and the mixture was concentrated under reduced pressure. The mixture was extracted with CHCl3 (60 mL × 3) and water (50 mL), and the organic layer was washed with saturated brine (30 mL). The organic layer was dried with Na2SO4, filtered, and the solvent was removed by distillation under reduced pressure, yielding the target diester compound (13.19 g, 42.76 mmol) in 100% yield as a colorless, transparent liquid.

[0095] 1 H-NMR (500MHz, CDCl3) 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, CDCl3) δ177.7,60.0,48.6,47.3,41.6,35.9,33,5,29.0,14.5

[0096] Step 2-a

[0097] [Chemistry 15]

[0098]

[0099] Under a nitrogen atmosphere, anhydrous THF (20 mL) was added to LiAlH4 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. The mixture was heated to room temperature and stirred under reflux for 20 hours. After natural cooling to room temperature, the container was cooled in an ice bath, and water (2 mL) was added dropwise. A 20% NaOH aqueous solution (1 mL) was added, and the mixture was stirred at room temperature for 2 hours. The pH was adjusted to 3–4 with 6M HCl aqueous solution, and the precipitated solid was filtered through a glass filter and then washed with THF (50 mL). After concentrating the solution under reduced pressure, the precipitated solid was dissolved by heating with 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 dried with Na2SO4, filtered, and the solvent was removed by vacuum distillation, thus giving the target diol compound (6.80 g, 30.31 mmol) as a white solid in 94% yield.

[0100] 1 H-NMR (500MHz, CDCl3) δ3.71 (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, CDCl3) δ58.9,48.3,47.0,42.3,36.6,32.7,29.1

[0101] Step 3-a

[0102] [Chemistry 16]

[0103]

[0104] A CHCl3 solution (100 mL) containing 4.41 g (19.65 mmol) of the diol compound was added, followed by triethylamine (13.6 mL, 98.1 mmol), and then methanesulfonyl chloride (6.1 mL, 78.8 mmol). After stirring at room temperature for 2 days, 1 M HCl aqueous solution (100 mL) was added, and the mixture was extracted with CHCl3 (50 mL × 3). The organic layer was washed with saturated brine (30 mL). The organic layer was dried with Na2SO4, filtered, and the solvent was removed by vacuum distillation, yielding a crude product of the dimethylsulfonyl 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 recorded during purification). It was a liquid immediately after purification but became a solid after being left at room temperature for a period of time.

[0105] 1 H-NMR (500MHz, CDCl3) 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, CDCl3) δ66.4,47.3,42.4,41.6,37.5,36.0,32.5,28.6

[0106] Step 4-a

[0107] [Chemistry 17]

[0108]

[0109] Potassium thioacetate (6.96 g, 60.94 mmol) was added to a MeCN solution (280 mL) of the crude dimethylsulfonyl compound (9.91 g), 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 solution was extracted with EtOAc (60 mL × 3) and water (30 mL), and the organic layer was washed with saturated brine (30 mL). The organic layer was dried with Na₂SO₄ and filtered. The solvent was removed by distillation under reduced pressure to obtain the crude product. The crude product was purified by column chromatography, yielding the target dithioacetyl compound (6.517 g, 19.14 mmol) as an orange liquid in 97% yield (combined yields of steps 3-a and 4-a).

[0110] 1 H-NMR (500MHz, CDCl3) 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, CDCl3) δ196.1,46.7,43.6,41.6,36.5,33.7,30.7,29.0,23.7

[0111] Step 5-a

[0112] [Chemistry 18]

[0113]

[0114] Under a nitrogen atmosphere, 15 mL of anhydrous THF was added to LiAlH4 powder (1.45 g, 38.21 mmol). A 35 mL THF solution of dithioacetyl compound (6.52 g, 19.13 mmol) was added dropwise, and the mixture was heated under reflux for 20 hours. After cooling to room temperature, 15 mL of water and 5 mL of 2 M NaOH aqueous solution were added, and the mixture was stirred for 30 minutes. The solution was concentrated under reduced pressure, and the precipitated solid was removed using a glass filter. The residue was washed with hot EtOAc (150 mL), and the organic layer was washed with saturated brine (20 mL) + 1 M HCl aqueous solution (20 mL). The aqueous layer was extracted with EtOAc (15 mL × 2), and the combined organic layers were washed with saturated brine (20 mL). The organic layer was dried with Na2SO4 and filtered. The solvent was removed by vacuum distillation to obtain the crude product. The crude product was purified by column chromatography, yielding the target dithiol compound (3.20 g, 12.48 mmol) (monomer a) in 65% yield as a colorless, transparent liquid.

[0115] 1 H-NMR (500MHz, CDCl3) 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, CDCl3) δ49.3,47.0,41.6,36.4,33.8,28.8,18.9

[0116] Monomer a and sulfur (Sigma-Aldrich) were weighed and added into a PFA reaction vessel according to the molar ratio and sulfur content shown in Table 1. The mixture was stirred at 200°C for 3–6 hours. After stirring, it was further heated at 200°C for 18–21 hours (a total of 24 hours of heating), and then naturally cooled to room temperature to obtain a liquid. Then, it was allowed to stand at room temperature for approximately 3 hours to obtain polysulfide resins (1A–5A).

[0117] <Example 2: Synthesis of polysulfide resin (B)>

[0118] Synthesis of monomer b

[0119] [Chemistry 19]

[0120]

[0121] Step 1-b

[0122] [Chemistry 20]

[0123]

[0124] To the molecular sieve 30.65 g (136.67 mmol) of an ethanol solution (220 mL) of 1,3-adamantanedicarboxylic acid (Tokyo Kasei Corporation) was added to a Soxhlet container, followed by the addition of concentrated sulfuric acid (1.39 g, 14.17 mmol) and reflux for 22 hours. After natural cooling to room temperature, an aqueous solution of NaHCO3 (30 mL) was added and the mixture was concentrated under reduced pressure. Extraction was performed with CHCl3 (100 mL × 3) and water (50 mL), and the organic layer was washed with saturated brine (30 mL). The organic layer was dried with Na2SO4 and filtered. The solvent was removed by reduced pressure distillation, yielding the target diester compound (38.2 g, 136.25 mmol) in 100% yield as a pale yellow transparent liquid.

[0125] 1 H-NMR (500MHz, CDCl3) 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, CDCl3) δ73.6,40.6,38.8,36.8,35.2,28.3

[0126] Step 2-b

[0127] [Chemistry 21]

[0128]

[0129] Under a nitrogen atmosphere, anhydrous THF (30 mL) was added to LiAlH4 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 dropwise using a dropping funnel. After all additions were completed, the temperature was raised to room temperature, and the mixture was stirred under reflux for 24 hours. After naturally cooling to room temperature, the container was cooled in an ice bath, and water (10 mL) was added dropwise. A 10% NaOH aqueous solution (5 mL) was added, and the mixture was stirred at room temperature for 30 minutes. The pH was adjusted to 4–5 with 2 M HCl aqueous solution, and the precipitated solid was filtered through a glass filter. The solution was then concentrated under reduced pressure. The residue was washed with THF (100 mL), and the solution was concentrated under reduced pressure. The solution was extracted with hot EtOAc (100 mL × 3) and water (100 mL), and the mother liquor was washed with saturated brine (20 mL). The organic layer was dried with Na2SO4 and filtered. The solvent was removed by vacuum distillation, thereby giving the target 1,3-adamantanediethanol (9.27 g, 47.2 mmol) as a white solid in 94% yield.

[0130] 1H-NMR (500MHz, CDCl3) 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, CDCl3) δ73.6,40.6,38.8,36.8,35.2,28.3

[0131] Step 3-b

[0132] [Chemistry 22]

[0133]

[0134] ZnBr2 (5.63 g, 25.00 mmol) and 30% HBr-AcOH solution (15 mL) were added to 1,3-adamantanediethanol (0.981 g, 5.00 mmol). The mixture was stirred at room temperature for 15 minutes, followed by stirring at 110 °C for 5 hours. After cooling naturally to room temperature, the mixture was allowed to stand overnight. The precipitated solid was filtered off using a glass filter, and the residue was washed with water (30 mL × 3). The mixture was dried under reduced pressure to give the target 1,3-dimethylene adamantane (1.46 g, 4.53 mmol) as a white solid in 91% yield.

[0135] 1 H-NMR (500MHz, CDCl3) δ3.19(2,4H),2.12(s(br),2H),1.58(s(br),2H),1.46-1.55(m,10H); 13 C-NMR (125MHz, CDCl3) δ47.4,43.8,40.1,35.9,34.6,28.7

[0136] Step 4-b

[0137] [Chemistry 23]

[0138]

[0139] Potassium thioacetate (1.55 g, 13.57 mmol) was added to a DMF-water (4:1, 30 mL) solution of 1,3-dimethylene adamantane (1.457 g, 4.524 mmol) and stirred at 110 °C for 18 hours. After cooling to room temperature, water (70 mL) was added and the mixture was extracted with Et₂O (30 mL × 3). The organic layer was washed with saturated brine (15 mL × 2). The organic layer was dried over Na₂SO₄ and filtered. The solvent was removed by vacuum distillation to obtain the crude product. The crude product was purified by column chromatography to give the target dithioacetyl compound (1.247 g, 3.991 mmol) as an orange liquid in 88% yield.

[0140] 1 H-NMR (500MHz, CDCl3) 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, CDCl3) δ195.7,45.2,41.9,40.6,35.9,34.1,30.8,28.7

[0141] Step 5-b

[0142] [Chemistry 24]

[0143]

[0144] Under a nitrogen atmosphere, 10 mL of anhydrous THF was added to LiAlH4 powder (0.227 g, 5.982 mmol). A 20 mL solution of THF containing a dithioacetyl compound (0.932 g, 2.982 mmol) was added dropwise, and the mixture was heated under reflux for 20 hours. After cooling naturally to room temperature, 2 mL of water, 1 mL of 15% NaOH aqueous solution, and 10 mL of THF were added, and the mixture was stirred at room temperature for 1.5 hours. The pH was adjusted to 3–4 with 6 M HCl aqueous solution, and the precipitate was filtered through a glass filter. The residue was washed with 50 mL of THF. After concentrating the solution under reduced pressure, it was diluted with 80 mL of EtOAc, and the organic layer was washed with 15 mL of saturated brine. The organic layer was dried with Na2SO4 and filtered. The solvent was removed by vacuum distillation, yielding the crude product. The target dithiol compound (0.657 g, 2.876 mmol) (monomer b) was separated and purified by column chromatography and obtained as a colorless, transparent liquid in 96% yield.

[0145] 1H-NNR(500MHz, CDCl3)DCl3)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

[0146] Monomer b and sulfur (Sigma-Aldrich) were weighed and added into a PFA reaction vessel according to the molar ratio and sulfur content shown in Table 2. The mixture was stirred at 200°C for 3–6 hours. After stirring, it was further heated at 200°C for 18–21 hours (a total of 24 hours of heating), and then naturally cooled to room temperature to obtain a liquid. Afterward, it was allowed to stand at room temperature for approximately 3 hours to obtain polysulfide resins (1B–4B).

[0147] <Example 3: Synthesis of polysulfide resin (C)>

[0148] Synthesis of monomer C

[0149] [Chemistry 25]

[0150]

[0151] In a 10L four-necked flask, thiourea (906g, 11.9mol) was added to a concentrated hydrochloric acid aqueous solution (~12M, 3Kg, 30W equivalent) of 1,3-adamantanediol (100g, 0.6mol) (Tokyo Chemical Industry). 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 reactor wall. The precipitated solid was scraped off with a spatula and allowed to fall back into the reaction solution). After naturally cooling to room temperature, 1.6L of 48% NaOH aqueous solution (internal temperature: maximum 39°C) was added dropwise over 1 hour 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 naturally cooling to room temperature, 200mL of concentrated hydrochloric acid aqueous solution was added dropwise while cooling in an ice bath to adjust the pH to 1. CHCl3 (3L) was added and stirred, and the precipitated solid (thiourea and its residue and NaCl) was filtered off. The filtered solid was washed with CHCl3 (1L×3), and the organic layer combined with the mother liquor was washed in the order of water (5L) and saturated brine (5L). The organic layer was concentrated to obtain the coarse substance (1).

[0152] The crude material (1) was washed with CHCl3 (230 mL) and then transferred back to the reactor. Thiourea (906 g, 11.9 mol) and concentrated hydrochloric acid aqueous solution (~12 M, 3 kg, 30 w equivalent) were added, and the mixture was heated and stirred at an internal temperature of 97 °C. The CHCl3 that was initially refluxed was removed as much as possible using a Dean-Stark apparatus (distillate: 140 mL), and the mixture was heated and stirred overnight, then allowed to cool naturally. While cooling the mixture in an ice bath, 48% NaOH aqueous solution (1.7 L) was added dropwise over 90 minutes (internal temperature: maximum 39 °C) to adjust the pH to 12. The mixture was heated to an internal temperature of 97 °C and stirred for 3 hours. After the mixture was allowed to cool naturally to room temperature, concentrated hydrochloric acid aqueous solution (330 mL) was added dropwise while cooling in an ice bath to adjust the pH to 2. CHCl3 (3 L) was added and stirred, and the precipitated solids (thiourea and its residue and NaCl) were filtered off. The filtered solid was washed with CHCl3 (1L×3), and the organic layer combined with the mother liquor was washed in the order of water (5L) and saturated brine (5L). The organic layer was concentrated to obtain the coarse substance (2).

[0153] The crude compound (2) was separated and purified by column chromatography, thereby yielding the target 1,3-adamantane dithiol compound (73.1 g, 0.365 mol) (monomer c) as a white solid in a yield of 61%.

[0154] 1 H-NMR (500MHz, CDCl3) δ2.14(s,2H),2.08(s,2H),1.83(m,8H),1.73(s,2H),1.58(s,2H); 13 C-NMR (125MHz, CDCl3) δ57.3,45.8,43.9,34.2,31.6

[0155] Monomer C can be synthesized using the following methods.

[0156] [Chemistry 26]

[0157]

[0158] Trifluoromethanesulfonic acid (0.52 mL, 5.89 mmol) was added to a 25 mL solution of 1,3-adamantanediol (9.943 g, 59.10 mmol) in thioacetic acid, and the mixture was stirred at 50 °C for 22 hours. After cooling to room temperature, the mixture was diluted with 150 mL of CHCl3, washed with 300 mL of NaHCO3 aqueous solution, and washed with 200 mL of CHCl3. The combined organic layers were washed with 20 mL of saturated brine. The organic layers were dried with Na2SO4 and filtered. The solvent was removed by vacuum distillation to obtain a crude product (19.8 g). The crude product was used in the next step without further purification.

[0159] Under a nitrogen atmosphere, 100 mL of anhydrous THF was added to LiAlH4 powder (6.77 g, 178.4 mmol). Anhydrous THF solution (80 mL) of the crude product was added dropwise while the container was cooled in an ice bath. After heating to room temperature, the mixture was stirred under reflux for 20 hours. After natural cooling to room temperature, the container was cooled in an ice bath, and water (12 mL) and 20% NaOH aqueous solution (6 mL) were added dropwise in sequence. Then, THF (150 mL) was added, and the mixture was stirred at room temperature for 1 hour. The pH was adjusted to 3–4 with 12 M HCl aqueous solution, and the precipitated solid was filtered through a glass filter. The residue was washed with THF (250 mL). After concentrating the solution under reduced pressure, it was diluted with EtOAc (300 mL) and washed successively with water (100 mL) and saturated brine (50 mL). The organic layer was dried with Na2SO4 and filtered. The solvent was removed by vacuum distillation to obtain the crude product. Purification was performed by column chromatography (hexane / toluene) to obtain the target 1,3-adamantane dithiol (8.461 g, 42.23 mmol) (monomer c) in a two-step process with a yield of 71%.

[0160] Monomer C and sulfur (Sigma-Aldrich) were weighed and added into a PFA reaction vessel according to the molar ratio and sulfur content shown in Table 3. The mixture was stirred at 200°C for 3–6 hours. After stirring, it was further heated at 200°C for 18–21 hours (a total of 24 hours of heating), and then naturally cooled to room temperature to obtain a liquid. Afterward, it was allowed to stand at room temperature for approximately 3 hours to obtain a polysulfide resin (1C–3C).

[0161] <Physical Property Evaluation of Polysulfide Resins>

[0162] For the obtained polysulfide resins A (1A~5A), B (1B~4B), and C (1C~3C), the refractive index n was measured. d Far-infrared transmittance and film thickness were also measured. Additionally, the refractive index and transmittance in the terahertz region were measured for polysulfide resins 3A, 2B, 1C, and 3C.

[0163] Refractive index n d The d-line (587.6 nm) was measured using a prism coupler (Metricon). The refractive index in the terahertz region was measured using a terahertz spectrophotometer (sample, measurement band: 0.1–1.5 THz, frequency resolution: approximately 5 GHz, spatial resolution: approximately 100 μm) and time-domain spectroscopy (THz-TDS). In addition to the transmittance spectrum described later, 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)).

[0164] Far-infrared transmittance was measured using FT-IR (Thermo Fischer, Nicolet 6700) at a range of 4000–400 cm⁻¹ via transmission method. -1 Measurements were performed. The resolution was 2, and the number of measurements was 30. Average transmittance was calculated in the wavelength range of 8 μm to 14 μm. Units were kept to wavenumbers (cm). -1 The transmittance was calculated by averaging the summed values ​​using the discriminant quadrature method. The refractive index in the terahertz region was measured using a terahertz spectrophotometer (prototype) and time-domain spectroscopy (THz-TDS). The transmittance was derived by comparing the spectrophotometer obtained using spectrophotometry with reference data (Teflon substrate).

[0165] The film thickness was measured at the center using a constant pressure thickness gauge (TECLOCK, PG-01) (and also at the perimeter (4 points) to confirm thickness uniformity). It should be noted that the above measuring device is based on JISK6250.

[0166] The measurement results for polysulfide resin A are shown in Table 1: Examples 1 (Examples 1-1 to 1-5); the measurement results for polysulfide resin B are shown in Table 2: Examples 2 (Examples 2-1 to 2-4); and the measurement results for polysulfide resin C are shown in Table 3: Examples 3 (Examples 3-1 to 3-3). Furthermore, the measurement results for refractive index and transmittance in the terahertz region are shown in Table 4. Figure 2 and Figure 3 The figure shows the proportion (m-number ratio) of thioether bonds in the polysulfide resin when the monomer and sulfur addition rates are varied. The m-number ratio is determined by... 1 The results were obtained from H-NMR (500MHz, CDCl3). Taking monomer a as an example, the result is derived from -C H2The peak of SH was 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 was used as the denominator, and the corresponding integral ratio of the peaks was used as the numerator, to determine the m-number ratio. In the case of monomer b, the exact peak positions differed, but the results were calculated similarly. For monomer c, apart from the overall peak position shift, the peak positions of m = 2 and m = 3 overlapped, therefore no separation was performed.

[0167] [Table 1]

[0168]

[0169] [Table 2]

[0170]

[0171] [Table 3]

[0172]

[0173] [Table 4]

[0174]

[0175] As shown in Tables 1-3, it was confirmed that the higher the sulfur addition rate of the polysulfide resins in Examples 1-3, the higher the refractive index and far-infrared transmittance.

[0176] Symbol Explanation

[0177] 1… Far-infrared digital camera, 101… Lens unit, 102… Camera unit, 103… Storage unit, 104… Display unit.

Claims

1. A polysulfide resin, wherein, The structural units containing the adamantane structure are linked in a straight chain via thioether bonds.

2. The polysulfide resin according to claim 1, wherein, The structural unit is represented by equation (1). [Chemistry 1] In the formula, l 1 l 2 Each of them independently represents an integer from 0 to 2, m represents an integer greater than 2, and * represents a associative bond.

3. The polysulfide resin according to claim 2, wherein, The content of compound i (m=2), compound ii (m=3), and compound iii (m=4), expressed as mole fractions, is as follows: Compound i: 0–0.25 Compound ii: 0~0.25, Compound iii: 0.45–0.

95.

4. The polysulfide resin according to any one of claims 1 to 3, wherein, Refractive index n d It ranges from 1.60 to 1.

95.

5. The polysulfide resin according to any one of claims 1 to 4, wherein, The transmittance in the far-infrared region with wavelengths of 8μm to 14μm is over 10%.

6. The polysulfide resin according to any one of claims 1 to 5, wherein the thickness is 0.3 mm to 2.0 mm.

7. A precursor, which is a precursor of the polysulfide resin according to any one of claims 1 to 6, wherein, The precursor comprises a monomer of a dithiol compound and sulfur. The sulfur addition rate in the precursor is 30% to 80% by mass.

8. An optical element that uses the polysulfide resin according to any one of claims 1 to 6.

9. An optical system comprising the optical element of claim 8.

10. A lens for an infrared camera, comprising the optical system of claim 9.

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

12. A method for manufacturing a polysulfide resin, comprising: In the mixing process, the dithiol compound of formula (2) and sulfur are mixed at a molar ratio of 1:2.5 to 1:25 to obtain a mixture. [Chemistry 2] In the formula, l 1 l 2 Each independently represents an integer from 0 to 2; and The reaction process involves reacting the mixture at 120°C to 220°C for 12 to 48 hours.

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