Organic polysulfide polymers and uses thereof

Abstract

A method of producing an organic polysulfide polymer is disclosed. The method comprises dissolving elemental sulfur in a solvent to form a sulfur solution. An unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer is added to the sulfur solution to produce a reaction mixture. The reaction mixture is treated under conditions to copolymerize sulfur and the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer to produce the organic polysulfide polymer. A prepared organic polysulfide polymer is recovered from the reaction mixture and, optionally, the prepared organic polysulfide polymer is further cured.

Description

ORGANIC POLYSULFIDE POLYMERS AND USES THEREOFPRIORITY DOCUMENT

[0001] The present application claims priority from Australian Provisional Patent Application No. 2024902135 title “ORGANIC POLYSULFIDE POLYMERS AND USES THEREOF” and filed on 10 July 2024, the content of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates to sulfur containing polymers, and to methods of, and an apparatus for, producing the polymers. The present disclosure also relates to sulfur containing polymers that are infrared (IR) transmissible and the use of the polymers in components for IR imaging applications.BACKGROUND

[0003] The synthesis of organic polysulfide polymers has found use in recent years in providing novel cathodes materials for lithium sulfur batteries,1-2materials for thermal imaging and infrared optics,3-7and metal binding.8-11The high sulfur content of these materials (typically 30% of the mass of the material or higher) is critical in these applications as it imparts the required redox activity,2refractive index,12transparency to mid-wave and long-wave infrared light,12and affinity for heavy and precious metals.10-11,

[0004] The sulfur content in these organic polysulfides often presents challenges in the synthesis and processing of these polymers. In particular, the low solubility of these sulfur-rich polymers in many solvents can result in challenging issues of phase separation and inhomogeneity in the synthesis,14-15particularly during large scale synthesis.16This problem is exacerbated in cases where the organic component of these polymers also has low solubility or high crystallinity.4

[0005] One method of making organic polysulfides that has found increasing use in the last several years is inverse vulcanization.1This polymerization features the reaction of elemental sulfur with an organic comonomer.13, 17-18The organic comonomer is often a diene or polyene,18but can also include organic monomers with alkynes19or C-H groups that can be functionalized with elemental sulfur.20These reactions often use molten sulfur as a reagent. In such cases, the organic comonomer is not always miscible with the molten sulfur, resulting in a two-phase reaction at the start of the polymerization.8-9, 16The multi-phase nature of this copolymerization presents challenges in homogeneity. Specifically, if the reaction mixture vitrifies or gels before the monomers have been consumed, the product can becontaminated with elemental sulfur, unreacted organic monomer, short oligomers, or multiple polymer species with different chemical compositions. These incomplete reactions can also result in phase separation of organic and sulfur-rich components of the mixture.15

[0006] An inhomogeneous product of inverse vulcanization and related polymerizations can be detrimental to the intended applications. Even subtle changes in the reaction conditions and homogeneity are known to cause wide variation in the polymer properties.21For infrared optics applications,12inhomogeneous poly sulfide polymers will decrease the optical quality of the material and change its material properties.22In cases where unreacted sulfur is present or forms in the polymer over time through depolymerization or other degradation pathways,22it may scatter light, and cause unwanted variations in transparency and refractive index. For other general applications of polymers made by inverse vulcanization,13’17 18inhomogeneity creates problems in batch-to-batch reproducibility of the product.

[0007] Inverse vulcanization reactions are also inhomogeneous in other aspects of the polymer structure. For instance, the stereochemistry of the C-S bonds formed are not typically controlled when they are formed.23The high temperature and reactive intermediates of inverse vulcanization also can result in complex rearrangements, chain transfer reactions, C-H abstraction or oxidation of the organic monomer, and other side reactions that complicate structural analysis and batch-to-batch reproducibility.8,20, 24

[0008] There is thus a need to provide methods for producing organic polysulfide polymers the overcome or ameliorate problems associated with prior art methods.SUMMARY

[0009] According to a first aspect, there is provided a method of producing an organic polysulfide polymer, the method comprising: dissolving elemental sulfur in a solvent to form a sulfur solution; adding, to the sulfur solution, an unsaturated organic comonomer and / or a cyclic poly sulfide organic comonomer to produce a reaction mixture; treating the reaction mixture under conditions to copolymerize sulfur and the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer to produce the organic polysulfide polymer; recovering a prepared organic polysulfide polymer from the reaction mixture; and optionally, further curing the prepared organic polysulfide polymer.

[0010] It will be appreciated from the foregoing that the method of the first aspect is a solution phase inverse vulcanization method. Advantageously, the method of the first aspect may overcome problems ofpremature vitrification or precipitation, phase separation and unreacted monomers contaminating the product associated with prior art methods that are not carried out in a solvent.

[0011] In certain embodiments, the solvent used in the first aspect is selected from one or more of the group consisting of amide-containing solvents, polar aprotic solvents, chlorohydrocarbons, and aromatic solvents. The solvent may be a mixture of these solvents. Specific amide-containing solvents that may be used include, but are not limited to, dimethylformamide (DMF), N-methyl-2 -pyrrolidone (NMP), and dimethylacetamide (DMAc). Specific polar aprotic solvents that may be used include, but are not limited to, propylene carbonate, acetonitrile, N,N’ -dimethylpropylene urea (DMPU), and dimethyl sulfoxide (DMSO). Specific chlorohydrocarbon solvents that may be used include, but are not limited to, tetrachloroethylene. Specific aromatic solvents that may be used include, but are not limited to, toluene, and xylene. In certain embodiments, the solvent used in the first aspect is selected from one or more of the group consisting of dimethylformamide, tetrachloroethylene, and xylene.

[0012] In certain embodiments, the sulfur concentration in the sulfur solution is about 1 g per 10 mb of solvent.

[0013] In certain embodiments, the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer is reacted in the solvent at a temperature of from about 100 to about 160 °C.

[0014] The prepared organic polysulfide polymer may be recovered from the reaction mixture by precipitation using an antisolvent or the solvent can be evaporated or distilled to provide the product.

[0015] A final curing step can be carried out after the solvent is removed to complete the polymerization or crosslinking process where required.

[0016] In certain embodiments, the unsaturated organic comonomer is selected from the group consisting of organic alkene, organic alkyne, organic diene, or organic polyene. In certain specific embodiments, the unsaturated organic comonomer is a non-aromatic cyclic diene or polyene hydrocarbon. Examples of non-aromatic cyclic diene or polyene hydrocarbons can comprise, consist essentially of, or consist of, either singly or in any combination, cyclobutadiene, cyclopentadiene, cyclohexadiene, cyclooctadiene, norbomadiene, vinylcyclohexene, vinylnorbomene, cyclooctatetraene, ethylidene norbomene and cyclopentadiene dimer. In certain specific embodiments, the unsaturated organic comonomer comprises norbomadiene.

[0017] Advantageously, when the organic comonomer is a low molecular weight, rigid, organic cyclic monomer, the resulting organic polysulfide polymer may be transparent to mid-wave infrared (MWIR) light and long-wave infrared (LWIR) light. For example, in some embodiments described herein, organicpolysulfide polymers with LWIR transmittance exceeding 20% for 1 mm thick windows in the range of 7 pm and 14 pm are formed.

[0018] Also advantageously, some organic polysulfide polymers formed according to embodiments described herein have a high glass transition temperature such as, for example, a Tgfrom 133 °C to 196 °C.

[0019] Furthermore, some organic polysulfide polymers formed according to embodiments described herein are insoluble or have low solubility in common organic solvents.

[0020] In certain embodiments of the method of the first aspect, the organic comonomer is a cyclic polysulfide. The cyclic polysulfide may contain 3 to 5 sulfur atoms in a cyclic ring attached to the organic comonomer structure. The cyclic polysulfide organic monomer may have the general structure: n = 1 -3cyclic or polycyclic / carbon framework

[0021] In certain specific embodiments, the cyclic polysulfide is formed by reaction of sulfur with an unsaturated organic comonomer. The unsaturated organic comonomer used to form the cyclic polysulfide may be a non-aromatic cyclic diene hydrocarbon. One or both of the alkene moieties in the diene may be reacted with sulfur to form the cyclic polysulfide. The cyclic polysulfide may be formed by reaction of sulfur with butadiene (1,3-butadiene), isoprene, 1,5 -hexadiene, 1,7-octadiene, cyclobutadiene, cyclopentadiene, cyclohexadiene, cyclooctadiene, norbomadiene, vinylcyclohexene, vinylnorbomene, divinylbenzene, ethylidene norbomene or cyclopentadiene dimer. In certain specific embodiments, the cyclic polysulfide is formed by reaction of sulfur with norbomadiene to form a cyclic polysulfide of formula (2) or formula (3):(2) (3)

[0022] The organic cyclic polysulfide can be reacted with elemental sulfur in solvents with varying combinations and concentrations to form copolymers. Advantageously, this polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur.

[0023] The organic cyclic polysulfide may comprise a pre-formed cyclic polysulfide and an alkene or other unsaturated functional group. Thus, the organic monomer contains both a cyclic polysulfide and a group of unsaturation such as an alkene. These organic cyclic polysulfides can be reacted with elemental sulfur in solvents to form copolymers. This polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur. In this reaction, the cyclic polysulfide, sulfur, and alkene groups all react to form the polysulfide polymer and the reaction is complete after a curing step.

[0024] The method of the first aspect provides the first synthetic access to polymer (1):

[0025] Thus, according to a second aspect, there is provided a polymer comprising repeating units of formula (1):wherein: a, b, c and d are each integers independently selected from 1, 2, 3, 4, 5, 6, 7, and 8; and p is an integer greater than or equal to 2.

[0026] Organic cyclic polysulfide monomers can also be used to form organic polysulfide polymers by thermal ring opening polymerization without the use of elemental sulfur in the polymerization reaction. Thus, in a third aspect, there is provided a method of producing an organic polysulfide polymer, the method comprising: dissolving an organic cyclic polysulfide monomer in a solvent to form a reaction solution; heating the reaction solution under conditions to initiate thermal ring opening polymerization to produce the organic polysulfide polymer; recovering a prepared organic polysulfide polymer from the reaction mixture; and curing the prepared organic polysulfide polymer.

[0027] Organic cyclic polysulfide monomers can also be used to form organic polysulfide polymers by copolymerization in molten sulfur. Thus, in a fourth aspect, there is provided a method of producing an organic polysulfide polymer, the method comprising: combining an organic cyclic polysulfide monomer and elemental sulfur to form a reaction mixture; heating the reaction mixture under conditions to produce the organic polysulfide polymer; and curing the prepared organic polysulfide polymer.

[0028] Molten sulfur is the solvent and comonomer in this reaction. The preinstalled cyclic trisulfides render the organic comonomer soluble in the molten sulfur comonomer, which is an advantage over many other bulk copolymerizations with sulfur because the organic monomer is often insoluble in sulfur. This polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur.

[0029] In a fifth aspect, provided herein is a component for use in infrared (IR) imaging applications, the component composed of, or comprising, the cured organic polysulfide polymer as described herein.

[0030] The component may be a sheet, window, sample cell, waveguide or filter. The component may have a thickness equal to, or less than, about 2 mm. The component may have a thickness equal to, or less than, about 1 mm. For example, the component may be a lens.BRIEF DESCRIPTION OF DRAWINGS

[0031] Embodiments of the present disclosure will be discussed with reference to the accompanying drawings wherein:

[0032] Figure 1 shows photographs showing solventless reaction between sulfur and norbomadiene with 58 % sulfur, (a) Reaction set up showing condenser and sulfur in 21 m scintillation vial, (b-c) images showing solid material formed after addition of norbomadiene. (d-e) Images showing heterogeneous material from solventless reaction after curing for 24 hours at 140 °C. The light and dark regions are consistent with a heterogeneous product, phase separation, and unreacted elemental sulfur;

[0033] Figure 2 shows a differential scanning calorimetry thermogram of the cured product formed according to Example 1;

[0034] Figure 3 shows an infrared spectrum of the cured product formed according to Example 2;

[0035] Figure 4 shows GC-MS traces of reduced products formed according to Example 2;

[0036] Figure 5 shows a differential scanning calorimetry thermogram of the cured product formed according to Example 3;

[0037] Figure 6 shows an ATR FTIR spectrum of the cured product formed according to Example 3;

[0038] Figure 7 shows ’H NMR spectra of the reaction mixture of Example 4 over time;

[0039] Figure 8 shows the results of GC-MS analysis of the organic layer formed in the reaction of Example 5;

[0040] Figure 9 shows an ATR FTIR spectrum of the cured product formed according to Example 6;

[0041] Figure 10 shows photographs showing reaction between sulfur and norbomadiene using TCE as a solvent and according to Example 6. (a) Reaction set up before sulfur and TCE is added to heat, (b) Reaction after 10 minutes of heating sulfur and TCE. (c) Reaction shortly after addition of norbomadiene (NBD). (d) Reaction after a reaction time of 90 minutes, (e) Polymer after cure;

[0042] Figure 11 shows an ATR FTIR spectrum of the cured product formed according to Example 7;

[0043] Figure 12 shows photographs showing reaction between sulfur and norbomadiene using xylene as a solvent and according to Example 7. (a) Reaction set up before sulfur and xylene is added to heat, (b) Reaction after 10 minutes of heating sulfur and xylene, (c) Reaction shortly after addition of norbomadiene (NBD). (d) Reaction after a reaction time of 90 minutes, (e) Polymer after cure;

[0044] Figure 13 shows photographs showing reaction between sulfur and norbomadiene using 50-50 DMF-TCE as a solvent and according to Example 8. (a) Reaction set up before sulfur and DMF-TCE is added to heat, (b) Reaction after 10 minutes of heating sulfur and DMF-TCE. (c) Reaction shortly after addition of norbomadiene (NBD). (d) Reaction after a reaction time of 90 minutes, (e) Polymer after cure;

[0045] Figure 14 shows photographs showing reaction between sulfur and norbomadiene using 50-50 DMF-xylene as a solvent and according to Example 8. (a) Reaction set up before sulfur and DMF-xylene is added to heat, (b) Reaction after 10 minutes of heating sulfur and DMF-xylene. (c) Reaction shortlyafter addition of norbomadiene (NBD). (d) Reaction after a reaction time of 90 minutes, (e) Polymer after cure;

[0046] Figure 15 shows ATR FTIR spectra of the cured products formed according to Example 8 using DME-TCE (left) or DMF-xylene (right) as solvent;

[0047] Figure 16 shows photographs showing prepolymers before curing and formed according to Example 10 using the amount of sulfur indicated;

[0048] Figure 17 shows (a) a 3D representation of a die set for molding a polymer made by solutionphase copolymerization of sulfur and norbomadiene according to Example 11 ; (b) a cross section view of the die set shown in (a); (c) photographs of a die set for molding a polymer made by solution-phase copolymerization of sulfur and norbomadiene according to Example 11; (d) a representative polymer window formed in accordance with Example 11 ;

[0049] Figure 18 shows plots of sulfur content vs MWIR transmittance (top) and sulfur content vs LWIR transmittance (bottom) for polymers formed according to Example 12;

[0050] Figure 19 shows (a) GC trace of norbomene trisulfide; (b)1H NMR spectmm of norbomene trisulfide; and (c)13C NMR spectmm of norbomene trisulfide formed according to Example 13;

[0051] Figure 20 shows (a)1H NMR spectmm; and (b)13C NMR spectmm of bis (cyclic trisulfide) monomer from norbomene formed according to Example 13;

[0052] Figure 21 shows an infrared spectmm (left) and DSC (right) of a polymer formed by solutioncopolymerization of sulfur with a monomer containing two cyclic trisulfides and formed according to Example 15;

[0053] Figure 22 shows an infrared spectmm (left) and DSC (right) of a polymer formed by solutioncopolymerization of sulfur with a monomer containing a cyclic trisulfide and an alkene and formed according to Example 16;

[0054] Figure 23 shows an infrared spectmm (left) and DSC (right) of a polymer formed by solutioncopolymerization of a monomer containing two cyclic trisulfides and formed according to Example 17;

[0055] Figure 24 shows infrared spectra (left) and DSC (right) of polymers formed by solvent-free copolymerization of 72% sulfur (upper), 81% sulfur (middle), 85% (lower) sulfur with a monomer containing two cyclic trisulfides and formed according to Example 18;

[0056] Figure 25 shows an infrared spectrum (left) and DSC (right) of a polymer formed by solvent- free copolymerisation of sulfur with a monomer containing a cyclic trisulfide and an alkene and formed according to Example 19;

[0057] Figure 26 shows an infrared spectrum (left) and DSC (right) of a polymer formed by solvent- free polymerization of a monomer containing two cyclic trisulfides and formed according to Example 20;

[0058] Figure 27 shows photographs showing the formation of a silicon mould used for forming a polymer window as described in Example 21 ;

[0059] Figure 28 shows plots of sulfur content vs MWIR transmittance (top) and sulfur content vs LWIR transmittance (bottom) for polymers formed according to Example 21;

[0060] Figure 29 shows plots of refractive index vs wavelength for polymers formed using 85% sulfur (blue line) and 81% sulfur (black line) and formed according to Example 21;

[0061] Figure 30 shows FLIR images obtained through a polymer window formed according to Example 21 using 81% sulfur (middle row) and 85% sulfur (lower row);

[0062] Figure 31 shows photographs showing the formation of piano convex lenses as described in Example 21;

[0063] Figure 32 shows a photograph of a system for testing the IR transmission and imaging using piano convex lenses formed as described in Example 21 ;

[0064] Figure 33 shows FLIR images obtained through piano convex lenses formed according to Example 21 using 81% sulfur (top two rows) and 85% sulfur (lower two rows). The abbreviation ‘CT’ used in the figure refers to centre thickness which is the thickness of the lens at its centre;

[0065] Figure 34 shows FLIR images obtained through piano convex lenses at different temperatures and formed according to Example 21 using 81% sulfur (top two rows) and 85% sulfur (lower two rows). The abbreviation ‘CT’ used in the figure refers to centre thickness which is the thickness of the lens at its centre;

[0066] Figure 35 shows photographs of polymer windows prepared according to Example 22;

[0067] Figure 36 shows plots of average MWIR and LWIR transparencies across a range of window thicknesses as described in Example 23;

[0068] Figure 37 shows (left) photographs of the polymer 1 windows, (middle) LWIR images taken through the polymer windows, and (right) FTIR spectra through polymer 1 of Example 23 at different thicknesses;

[0069] Figure 38 shows (left) table of parameters, (middle) photographs, and (right) plan and cross section drawings of lenses formed according to Example 24;

[0070] Figure 39 shows 3D printed holder designs and integration into a FLIR Lepton 3.5 thermal camera module as described in Example 25;

[0071] Figure 40 shows masks used in Example 26 to investigate the imaging when using the polymer lenses;

[0072] Figure 41 shows the imaging station used to test imaging in Example 26;

[0073] Figure 42 shows thermal sensitivity testing of lens 7 on a FLIR Lepton 3.5 according to Example 27;

[0074] Figure 43 shows thermal sensitivity testing of lens 6 on a FLIR Lepton 3.5 according to Example 27;

[0075] Figure 44 shows thermal sensitivity testing of lens 5 on a FLIR Lepton 3.5 according to Example 27;

[0076] Figure 45 shows thermal sensitivity testing of lens 4 on a FLIR Lepton 3.5 according to Example 27;

[0077] Figure 46 shows thermal sensitivity testing of lens 3 on a FLIR Lepton 3.5 according to Example 27;

[0078] Figure 47 shows thermal sensitivity testing of lens 2 on a FLIR Lepton 3.5 according to Example 27;

[0079] Figure 48 shows thermal sensitivity testing of lens 1 on a FLIR Lepton 3.5 according to Example 27;

[0080] Figure 49 shows an overview of all images obtained from thermal sensitivity testing with each of the lenses according to Example 28;

[0081] Figure 50 shows design and disassembly of heated compression mold on Autodesk Inventor;

[0082] Figure 51 shows compression molded lenses from polymer 1. (a) Hydraulic press used to compress die. (b) Aluminum die used for compression molding, (c) Insert for compression mold, (d) 2.5 g of polymer 1 after being ground into pellets with an approximate diameter of 2 mm. (e) Polymer 1 pellets placed on insert before compression, (f) Polymer 1 disk after compression before removal from insert, (g- h) Disk of polymer 1 after removal from insert, (i) Individual lens after separation from compression molded lens array; and

[0083] Figure 52 shows LWIR Images taken with poly-1 lenses on a FLIR Lepton 3.5 thermal imaging module.DESCRIPTION OF EMBODIMENTS

[0084] The present disclosure arises from the inventors’ research that provides first access to polymer (1).

[0085] In particular, the inventors have developed methods for forming polymer (1) that avoid rearrangement reactions, including avoiding formation of cyclopropane groups in the polymer that are detrimental to infrared transparency.

[0086] The methods disclosed herein provide the first experimental verification of the long-wave infrared (LWIR) transparency of polymer (1) (with LWIR transmittance exceeding 20% for 1 mm thick windows in the range of 7 pm and 14 pm), its high glass transition temperature (7„ ranged from 133 to 196 °C depending on the composition and synthesis method) and its insolubility in common organic solvents.

[0087] The research has also provided solution-based methods for the copolymerization of sulfur and norbomadiene. While this reaction does not avoid the rearrangement that results in cyclopropane formation, the method is the first general copolymerization method for sulfur and norbomadiene that provides a material that can be fashioned into optical components for thermal imaging.

[0088] The synthetic methods in this disclosure address homogeneity challenges for inverse vulcanization and related polymerizations. The methods provide techniques for homogenouscopolymerization of elemental sulfur with comonomers that contain unsaturation and / or cyclic polysulfides, overcoming the problem of premature vitrification or precipitation, phase separation and unreacted monomers contaminating the product. The methods also provide strategies for avoiding rearrangements of the organic monomer and / or controlling the stereochemistry of the C-S bond in target organic polysulfide polymers, particularly for norbomadiene derivatives. These methods are exemplified in the copolymerization of sulfur and norbomadiene, the copolymerization of sulfur and sulfurized norbomene derivatives, and related polymerizations that provide organic polysulfides with a norbomane organic component. However, the methods can also be readily applied to other unsaturated organic comonomers based on the details provided herein.

[0089] Provided herein is a method of producing an organic polysulfide polymer. The method comprises dissolving elemental sulfur in a solvent to form a sulfur solution. An unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer is added to the sulfur solution to produce a reaction mixture. The reaction mixture is treated under conditions to copolymerize sulfur and the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer to produce the organic polysulfide polymer. A prepared organic polysulfide polymer is recovered from the reaction mixture and, optionally, the prepared organic polysulfide polymer is further cured.

[0090] The method is carried out in a solution phase and the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer is added to the sulfur solution.

[0091] The solvent may be any solvent in which both elemental sulfur and the unsaturated organic comonomer and / or the cyclic polysulfide organic comonomer is soluble. Suitable solvents include amide- containing solvents, polar aprotic solvents, chlorohydrocarbons, and aromatic solvents. The solvent may also be a mixture of these solvents.

[0092] Specific amide -containing solvents that may be used include, but are not limited to, dimethylformamide (DMF), N-methyl-2 -pyrrolidone (NMP), and dimethylacetamide (DMAc).

[0093] Specific polar aprotic solvents that may be used include, but are not limited to, propylene carbonate, acetonitrile, N,N’ -dimethylpropylene urea (DMPU), and dimethyl sulfoxide (DMSO).

[0094] Specific chlorohydrocarbon solvents that may be used include, but are not limited to, tetrachloroethylene .

[0095] Specific aromatic solvents that may be used include, but are not limited to, toluene, and xylene.

[0096] In certain embodiments, the solvent may be one or more of dimethylformamide, tetrachloroethylene, and xylene.

[0097] As used herein, the term “xylene” is intended to include ortho xylene, meta xylene, para xylene, or any combination of any two or more of these.

[0098] These solvents can provide efficient mixing and solvation of sulfur and unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer, especially at elevated temperatures (typically 100-160 °C).

[0099] Tetrachloroethylene can provide a non-flammable reaction medium in processes where this is desirable. As inverse vulcanization can lead to exotherms and runaway reactions,27-28the tetrachloroethylene solvent provides a non-flammable reaction medium. Notably, tetrachloroethylene (even though it contains an alkene), does not react with elemental sulfur under the conditions of inverse vulcanization.

[0100] The solvent may be a mixture of different solvents and the solvent mixtures can vary from 0 to 100% by volume.

[0101] In certain embodiments, the sulfur concentration in the sulfur solution is equal to or less than about 1 g per 10 mb of solvent, such as about 1 g per 10 mb of solvent, about 0.9 g per 10 mb of solvent, about 0.8 g per 10 mb of solvent, about 0.7 g per 10 mb of solvent, about 0.6 g per 10 mb of solvent or about 0.5 g per 10 mb of solvent. For most solvents, about 1 g per 10 mb of solvent is the solubility limit of elemental sulfur in the solvent.

[0102] The sulfur solution may be formed by heating elemental sulfur in the solvent. The solution may be formed by heating at a temperature of from about 100 °C to about 160 °C, such as about 100 °C, about 101 °C, about 102 °C, about 103 °C, about 104 °C, about 105 °C, about 106 °C, about 107 °C, about 108 °C, about 109 °C, about 110 °C, about 111 °C, about 112 °C, about 113 °C, about 114 °C, about 115 °C, about 116 °C, about 117 °C, about 118 °C, about 119 °C, about 120 °C, about 121 °C, about 122 °C, about 123 °C, about 124 °C, about 125 °C, about 126 °C, about 127 °C, about 128 °C, about 129 °C, about 130 °C, about 131 °C, about 132 °C, about 133 °C, about 134 °C, about 135 °C, about 136 °C, about 137 °C, about 138 °C, about 139 °C, about 140 °C, about 141 °C, about 142 °C, about 143 °C, about 144 °C, about 145 °C, about 146 °C, about 147 °C, about 148 °C, about 149 °C, about 150 °C, about 151 °C, about 152 °C, about 153 °C, about 154 °C, about 155 °C, about 156 °C, about 157 °C, about 158 °C, about 159 °C or about 160 °C. In certain embodiments, the sulfur solution is formed by heating at a temperature of about 140 °C. The sulfur solution is formed when substantially all of the elemental sulfur has dissolved.

[0103] Once the sulfur solution is formed, the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer added to the solution. When the comonomer is an unsaturated organic comonomer, the weight ratio of unsaturated organic comonomer to elemental sulfur used in the reaction is from about 1: 1 to about 1: 10. For example, the weight ratio of unsaturated organic comonomer to elemental sulfur used in the reaction may be about 1: 1 to about 1:2. When the comonomer is a cyclic polysulfide organic comonomer, the weight ratio of cyclic polysulfide organic comonomer to elemental sulfur used in the reaction is from about 1 : 1 to about 10: 1. For example, the weight ratio of cyclic polysulfide organic comonomer to elemental sulfur used in the reaction may be about 2: 1 to about 7: 1.

[0104] After addition, the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer is reacted in the solvent at a temperature of from about 100 °C to about 160 °C, such as about 100 °C, about 101 °C, about 102 °C, about 103 °C, about 104 °C, about 105 °C, about 106 °C, about 107 °C, about 108 °C, about 109 °C, about 110 °C, about 111 °C, about 112 °C, about 113 °C, about 114 °C, about 115 °C, about 116 °C, about 117 °C, about 118 °C, about 119 °C, about 120 °C, about 121 °C, about 122 °C, about 123 °C, about 124 °C, about 125 °C, about 126 °C, about 127 °C, about 128 °C, about 129 °C, about 130 °C, about 131 °C, about 132 °C, about 133 °C, about 134 °C, about 135 °C, about 136 °C, about 137 °C, about 138 °C, about 139 °C, about 140 °C, about 141 °C, about 142 °C, about 143 °C, about 144 °C, about 145 °C, about 146 °C, about 147 °C, about 148 °C, about 149 °C, about 150 °C, about 151 °C, about 152 °C, about 153 °C, about 154 °C, about 155 °C, about 156 °C, about 157 °C, about 158 °C, about 159 °C or about 160 °C. In certain embodiments, the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer is reacted in the solvent at a temperature of about 140 °C.

[0105] The unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer is reacted with sulfur in solution for a time that is sufficient to allow for substantially complete reaction. The progress of the reaction can be monitored using techniques known in the art, such as thin layer chromatography or gas chromatography. Typically, the unsaturated organic comonomer and / or a cyclic poly sulfide organic comonomer is reacted with sulfur in solution for a period of from about 5 minutes to about 180 minutes, or from about 30 minutes to about 150 minutes, such as about 30 minutes, about 90 minutes or about 15 minutes.

[0106] The prepared organic polysulfide polymer may be recovered from the reaction mixture by precipitation using an antisolvent or the solvent can be evaporated or distilled to provide the product.

[0107] After recovery, or as part of the recovery step, the prepared organic polysulfide polymer may be washed to remove residual solvent, for example, by washing with water. The water washed prepared organic polysulfide polymer may then be dried, for example by lyophilisation.

[0108] A final curing step can be carried out on the recovered prepared organic polysulfide polymer to complete the polymerization or crosslinking process where required. The curing step may be a thermalcuring step. For example, the recovered prepared organic polysulfide polymer may be heated to a temperature for a time to complete the curing step. The temperature used in the curing step may be from about 100 °C to about 160 °C, such as about 100 °C, about 101 °C, about 102 °C, about 103 °C, about 104 °C, about 105 °C, about 106 °C, about 107 °C, about 108 °C, about 109 °C, about 110 °C, about 111 °C, about 112 °C, about 113 °C, about 114 °C, about 115 °C, about 116 °C, about 117 °C, about 118 °C, about 119 °C, about 120 °C, about 121 °C, about 122 °C, about 123 °C, about 124 °C, about 125 °C, about 126 °C, about 127 °C, about 128 °C, about 129 °C, about 130 °C, about 131 °C, about 132 °C, about 133 °C, about 134 °C, about 135 °C, about 136 °C, about 137 °C, about 138 °C, about 139 °C, about 140 °C, about 141 °C, about 142 °C, about 143 °C, about 144 °C, about 145 °C, about 146 °C, about 147 °C, about 148 °C, about 149 °C, about 150 °C, about 151 °C, about 152 °C, about 153 °C, about 154 °C, about 155 °C, about 156 °C, about 157 °C, about 158 °C, about 159 °C or about 160 °C. In certain embodiments, the curing step is carried out at a temperature of about 140 °C.

[0109] The curing step may be carried out for a time that is sufficient to allow for substantially complete curing of the polymer. Typically, the curing step can be carried out for a period of from about 1 hour to about 48 hours, such as about 24 hours.

[0110] The cured organic polysulfide polymer may have a sulfur content of between about 40% w / w and about 90% w / w. The sulfur content may be between about 50% w / w and about 85% w / w.

[0111] The unsaturated organic comonomer may be selected from the group consisting of organic alkene, organic alkyne, organic diene, or organic polyene. In certain specific embodiments, the unsaturated organic comonomer is a non-aromatic cyclic diene or polyene hydrocarbon. Examples of non-aromatic cyclic diene or polyene hydrocarbons can comprise, consist essentially of, or consist of, either singly or in any combination, cyclobutadiene, cyclopentadiene, cyclohexadiene, cyclooctadiene, norbomadiene, vinylcyclohexene, vinylnorbomene, cyclooctatetraene, ethylidene norbomene or cyclopentadiene dimer. In certain specific embodiments, the unsaturated organic comonomer comprises norbomadiene.

[0112] As used herein, norbomadiene (NBD) means any compound that includes at least one norbomene or substituted norbomene moiety, including without limitation norbomene, substituted norbomene(s), norbomadiene, substituted norbomadiene(s), polycyclic norbomenes, and substituted polycyclic norbomene(s).

[0113] Copolymerization of sulfur and norbomadiene or sulfur and norbomadiene derivatives is particularly challenging.4The reaction is complicated by the volatility of norbomadiene, its high crystallinity, and its propensity to rearrange when reacted directly with elemental sulfur. In a publication by Norwood, Pyun and co-workers, it was stated that “due to the volatility of NBD (boiling point: « 89°C), these compounds could not be used with liquid sulfur in the inverse vulcanization process (T > 130 °C).”4For this reason, the authors synthesized a norbomene dimer with a higher boiling point that could be directly copolymerized with sulfur.4In this publication4and a related patent application (W02020191340),25Pyun and Norwood describe the useful optical properties of the polymers derived from the norbomene dimers and related derivatives, particularly for the use in mid-wave infrared imaging and long-wave infrared imaging. With that said, the norbomadiene dimer requires lengthy reaction times in its synthesis before it can be used in the key polymerization.

[0114] In W02020191340, the norbomane core is specified as a key structural component of the featured polymer. This is one of the organic structures formed, in principle, from the reaction of sulfur with norbomadiene. However, the reaction between norbomadiene (and its substituted derivatives) and elemental sulfur under inverse vulcanization conditions results in significant rearrangement to a cyclopropane structure, among other unwanted side products. These rearrangement products are detailed in this disclosure. Therefore, nobomadiene and sulfur cannot be used to make a polysulfide polymer that contains norbomane as the sole organic component. Furthermore, the reaction between norbomadiene and elemental sulfur vitrifies before the desired polymer can form, resulting in unreacted alkenes and an inhomogenous reaction and product mixtures. These outcomes were demonstrated in W0202020191340, in which a substituted norbomadiene reacted with elemental sulfur under inverse vulcanization conditions to provide polymers containing cyclopropane products of rearrangement, unreacted alkenes, and inhomogenous products and reaction mixtures. All of these unwanted side reactions result in detrimental effects for infrared imaging, including increased absorbance in the MWIR and LWIR region due to unreacted alkenes and the cyclopropane group.

[0115] A summary of the inverse vulcanization or norbomadiene and sulfur and its current limitations are summarized below:Norbomadiene is too volatile for inverse vulcanization;Neat reaction of norbomadiene and sulfur leads to rapid vitrification and inhomogenous product; Norbomadiene rearranges to form cyclopropanes on reaction with sulfur Therefore, polymer (1) cannot be formed by inverse vulcanizationPyun analog of (1): prepare dimer of norbomadiene and react dimer with sulfur in inverse vulcanization This process addresses volatility and rearragement problems with using norbomadiene directly W02020191340 and Angew. Chem. Int. Ed. 2019, 58, 17656-17660.

[0116] The target polymer (1) is an idealized polymer that contains a norbomane as the organic component of the polymer, with polysulfide groups connecting the norbomane domains. This norbomane core is also referred to as a bicyclo[2.2.1]heptane unit. This class of polymer is expected, on theoretical grounds,4to have desirable transparency to infrared light, particularly long-wave infrared light (LWIR, 7- 14 pm), which makes it of potential utility in thermal imaging optics. However, these applications have not been realized because:• No general methods have been reported for the copolymerization of norbomadiene and elemental sulfur that allow processing into materials for infrared optics. Even with the issue of rearrangement that leads to cyclopropane, a general and scalable method for this reaction has not been reported. Therefore, the evaluation of this polymer in infrared thermal imaging has not been reported..No general methods have been reported for the synthesis of 1 from any monomers

[0117] As the inverse vulcanization process typically features the reaction of a diene with elemental sulfur, it is reasonable to consider that norbomadiene and sulfur could react to form polymer 1. However, this reaction has not been realized due to several problems, as discussed above and summarized below:• First: norbomadiene is volatile so it is not practical to react it with neat, molten sulfur in the inverse vulcanization process. Regarding this issue, Norwood and Pyun commented that “due to the volatility of NBD (boiling point: « 89 °C), these compounds could not be used with liquid sulfur in the inverse vulcanization process (T> 130 °C).”4• Second: in an attempt to react molten sulfur with norbomadiene at 140 °C (using a reflux condenser to recover and return volatilized norbomadiene back into the reaction, example 1), the reaction vitrified prematurely, resulting in unreacted sulfur, unreacted norbomadiene, and generally inhomogeneous material. The premature vitrification prevents conventional stirring and unreacted alkenes remain in the product; the alkenes are detrimental to LWIR transparency. This experiment corroborates Norwood and Pyun’s assertion that inverse vulcanization using norbomadiene cannot be done with the usual inverse vulcanization protocols.• Third: during inverse vulcanization and related reactions with elemental sulfur, norbomadiene rearranges to form a cyclopropane group, which exhibits a strong absorption at 800 cm1, which lowers the LWIR transparency of the polymer (see examples 2-11 in this filing for evidence for cyclopropane formation, and IR spectra; see example 11 for reduced MWIR and LWIR transparency due to the cyclopropoane). This cyclopropane formation was reported by Pyun and Norwood for substituted norbomadiene derivatives in W0202020191340 (but not for norbomadiene itself).25

[0118] For the reasons outlined above (norbomadiene volatility, premature vitrification during the reaction of molten sulfur with norbomadiene, and rearrangement processes that result in cyclopropane formation), the synthesis of polymer 1 has not been achieved. No general method has been reported for the preparation of polymer 1 and therefore its use in infrared imaging and optics has not been realized in experiment or practice.

[0119] Relatedly, no general copolymerization technique of sulfur and norbomadiene has been reported. Notably, an attempted copolymerization of elemental sulfur and norbomadiene was attempted using ball milling, as reported by He and Xia.26However, this process results in a product with significant infrared absorbances >3000 cm'1and strong absorbance at 800 cm1. Although not considered by the authors, this is very likely due to the formation of the cycloproprane rearrangement product. Furthermore, the authors report a glass transition temperatures ranging from 36-45 °C depending on the sulfur content, which is far lower than expected for the branched or cross-linked structure in 1, which is reported in this disclosure to reach up to 196 °C depending on the composition and method of synthesis. He and Xia also report soluble fractions exceeding 15% of the mass of their product for multiple solvents, which is not consistent with the crosslinked structure of 1. While the ball milling method appears to provoke thereaction of sulfur and the alkenes of norbomadiene, these physical data are not consistent with the formation of polymer 1. Therefore, ball milling is not a general method for the synthesis of 1.

[0120] Due to the challenges in the direct polymerization of sulfur and norbomadiene reported by Pyun, including the norbomadiene volatility, premature vitrification, and rearrangements to give cyclopropane products,4’25no synthetic methods have been reported that provide polymer 1. And while the reaction of norbomadiene and sulfur in a ball mill has been reported,26the physical and optical properties of the product (including its infrared spectmm, solubility and glass transition temperature) are not consistent with the structure of 1 and the product was not evaluated in the context of thermal imaging. Therefore, there is still an outstanding problem of making the sulfur-norbomadiene copolymer in a form that can be processed as a lens, window or other optical device.

[0121] In contrast to prior art methods, the method of the first aspect provides the first synthetic access to polymer (1):

[0122] Thus, provided herein is a polymer comprising repeating units of formula (1):wherein: a, b, c and d are each independently integers selected from 1, 2, 3, 4, 5, 6, 7, and 8; and p is an integer greater than or equal to 2.

[0123] Advantageously, when the organic comonomer is a low molecular weight, rigid, organic cyclic monomer, such as polymer (1), the resulting organic poly sulfide polymer may be transparent to mid-wave infrared (MWIR) light and long-wave infrared (LWIR) light. For example, in some embodiments described herein, organic polysulfide polymers with LWIR transmittance exceeding 20% for 1 mm thick windows in the range of 7 pm and 14 pm are formed.

[0124] Also advantageously, some organic polysulfide polymers formed according to embodiments described herein have a high glass transition temperature such as, for example, a Tgfrom 133 °C to 196

[0125] Furthermore, some organic polysulfide polymers formed according to embodiments described herein are insoluble or have low solubility in common organic solvents.

[0126] In certain embodiments, the organic comonomer is a cyclic polysulfide. The cyclic polysulfide organic comonomer may contain 3 to 5 sulfur atoms in a cyclic ring attached to the organic comonomer structure. The cyclic polysulfide organic monomer may have the general structure: n = 1-3 cyclic or polycycliccarbon framework

[0127] The cyclic polysulfide organic comonomer may be formed by reaction of sulfur with an unsaturated organic comonomer. The unsaturated organic comonomer used to form the cyclic polysulfide organic comonomer may be a non-aromatic cyclic diene hydrocarbon. One or both of the alkene moieties in the diene may be reacted with sulfur to form the cyclic polysulfide organic comonomer. The cyclic polysulfide may be formed by reaction of sulfur with butadiene (1,3 -butadiene), isoprene, 1,5 -hexadiene, 1,7-octadiene, cyclobutadiene, cyclopentadiene, cyclohexadiene, cyclooctadiene, norbomadiene, vinylcyclohexene, vinylnorbomene, divinylbenzene, ethylidene norbomene or cyclopentadiene dimer. For example, cyclic polysulfide organic comonomer may be formed by reaction of sulfur with norbomadiene to form a cyclic polysulfide of formula (2) or formula (3):

[0128] Thus, the cyclic polysulfide organic comonomer may comprise a pre-formed cyclic polysulfide and an alkene or other unsaturated functional group.

[0129] The cyclic polysulfide organic comonomer can be reacted with elemental sulfur in solvents as previously described with varying combinations and concentrations to form organic polysulfide polymers. Advantageously, this polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur. In this reaction, the cyclic polysulfide, sulfur, and alkene groups all react to form the polysulfide polymer and the reaction is complete after a curing step.

[0130] Cyclic polysulfide organic comonomers as described herein can also be used to form organic polysulfide polymers by thermal ring opening polymerization without the use of elemental sulfur in the polymerization reaction. Thus, provided herein is a method of producing an organic polysulfide polymer. The method comprises dissolving an organic cyclic polysulfide monomer in a solvent to form a reaction solution. The reaction solution is then heated under conditions to initiate thermal ring opening polymerization to produce the organic polysulfide polymer. The prepared organic polysulfide polymer is then recovered from the reaction mixture and cured.

[0131] As before, the cyclic polysulfide organic comonomer may be formed by reaction of sulfur with an unsaturated organic comonomer. The unsaturated organic comonomer used to form the cyclic poly sulfide organic comonomer may be a non-aromatic cyclic diene hydrocarbon. One or both of the alkene moieties in the diene may be reacted with sulfur to form the cyclic polysulfide organic comonomer. The cyclic polysulfide may be formed by reaction of sulfur with butadiene (1,3-butadiene), isoprene, 1,5 -hexadiene, 1,7-octadiene, cyclobutadiene, cyclopentadiene, cyclohexadiene, cyclooctadiene, norbomadiene, vinylcyclohexene, vinylnorbomene, divinylbenzene, ethylidene norbomene or cyclopentadiene dimer. For example, cyclic polysulfide organic comonomer may be formed by reaction of sulfur with norbomadiene to form a cyclic poly sulfide of formula (2) or formula (3):(2) (3)

[0132] The solvent may be selected from one or more of the group consisting of dimethylformamide, tetrachloroethylene, and xylene. The solvent may be a mixture of different solvents and the solvent mixtures can vary from 0 to 100% by volume. In certain embodiments, the solvent comprises dimethylformamide and xylene. The mixture may comprise 50% by volume dimethylformamide and 50% by volume xylene.

[0133] A reaction solution comprising organic cyclic polysulfide monomer dissolved in the solvent can be formed by mixing the cyclic polysulfide organic comonomer and the solvent.

[0134] The reaction solution is then heated under conditions to initiate thermal ring opening polymerization to produce the organic polysulfide polymer. The temperature used in the polymerization may be from about 100 °C to about 160 °C, such as about 100 °C, about 101 °C, about 102 °C, about 103 °C, about 104 °C, about 105 °C, about 106 °C, about 107 °C, about 108 °C, about 109 °C, about 110 °C, about 111 °C, about 112 °C, about 113 °C, about 114 °C, about 115 °C, about 116 °C, about 117 °C, about 118 °C, about 119 °C, about 120 °C, about 121 °C, about 122 °C, about 123 °C, about 124 °C, about 125°C, about 126 °C, about 127 °C, about 128 °C, about 129 °C, about 130 °C, about 131 °C, about 132 °C, about 133 °C, about 134 °C, about 135 °C, about 136 °C, about 137 °C, about 138 °C, about 139 °C, about140 °C, about 141 °C, about 142 °C, about 143 °C, about 144 °C, about 145 °C, about 146 °C, about 147 °C, about 148 °C, about 149 °C, about 150 °C, about 151 °C, about 152 °C, about 153 °C, about 154 °C, about 155 °C, about 156 °C, about 157 °C, about 158 °C, about 159 °C or about 160 °C. In certain embodiments, the polymerization is carried out at a temperature of about 140 °C.

[0135] The reaction solution may be heated for a period of from about 5 minutes to about 180 minutes, or from about 30 minutes to about 150 minutes, such as about 90 minutes.

[0136] The prepared organic polysulfide polymer may be recovered from the reaction mixture by precipitation using an antisolvent or the solvent can be evaporated or distilled to provide the product.

[0137] A final curing step can be carried out on the recovered prepared organic polysulfide polymer to complete the polymerization or crosslinking process where required. The curing step may be a thermal curing step. For example, the recovered prepared organic polysulfide polymer may be heated to a temperature for a time to complete the curing step. The temperature used in the curing step may be from about 100 °C to about 160 °C, such as about 100 °C, about 101 °C, about 102 °C, about 103 °C, about 104 °C, about 105 °C, about 106 °C, about 107 °C, about 108 °C, about 109 °C, about 110 °C, about 111 °C, about 112 °C, about 113 °C, about 114 °C, about 115 °C, about 116 °C, about 117 °C, about 118 °C, about 119 °C, about 120 °C, about 121 °C, about 122 °C, about 123 °C, about 124 °C, about 125 °C, about 126 °C, about 127 °C, about 128 °C, about 129 °C, about 130 °C, about 131 °C, about 132 °C, about 133 °C, about 134 °C, about 135 °C, about 136 °C, about 137 °C, about 138 °C, about 139 °C, about 140 °C, about141 °C, about 142 °C, about 143 °C, about 144 °C, about 145 °C, about 146 °C, about 147 °C, about 148 °C, about 149 °C, about 150 °C, about 151 °C, about 152 °C, about 153 °C, about 154 °C, about 155 °C, about 156 °C, about 157 °C, about 158 °C, about 159 °C or about 160 °C. In certain embodiments, the curing step is carried out at a temperature of about 140 °C.

[0138] The curing step may be carried out for a time that is sufficient to allow for substantially complete curing of the polymer. Typically, the curing step can be carried out for a period of from about 1 hour to about 48 hours, such as about 24 hours.

[0139] Cyclic polysulfide organic comonomers can also be used to form organic polysulfide polymers by copolymerization in molten sulfur. Thus, also provided herein is a method of producing an organic polysulfide polymer. The method comprises combining an organic cyclic polysulfide monomer and elemental sulfur to form a reaction mixture. The reaction mixture is then heated under conditions to produce the organic polysulfide polymer and the prepared organic polysulfide polymer is cured.

[0140] Molten sulfur is the solvent and comonomer in this reaction. The preinstalled cyclic trisulfides render the organic comonomer soluble in the molten sulfur comonomer, which is an advantage over many other bulk copolymerizations with sulfur because the organic monomer is often insoluble in sulfur. This polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur.

[0141] As before, the cyclic poly sulfide organic comonomer may be formed by reaction of sulfur with an unsaturated organic comonomer. The unsaturated organic comonomer used to form the cyclic poly sulfide organic comonomer may be a non-aromatic cyclic diene hydrocarbon. One or both of the alkene moieties in the diene may be reacted with sulfur to form the cyclic polysulfide organic comonomer. The cyclic polysulfide may be formed by reaction of sulfur with butadiene (1,3-butadiene), isoprene, 1,5 -hexadiene, 1,7-octadiene, cyclobutadiene, cyclopentadiene, cyclohexadiene, cyclooctadiene, norbomadiene, vinylcyclohexene, vinylnorbomene, divinylbenzene, ethylidene norbomene or cyclopentadiene dimer. For example, cyclic polysulfide organic comonomer may be formed by reaction of sulfur with norbomadiene to form a cyclic poly sulfide of formula (2) or formula (3):(2) (3)

[0142] The organic cyclic polysulfide monomer and elemental sulfur are combined to form a reaction mixture. The reaction mixture is then heated to a temperature of from about 100 °C to about 160 °C, such as about 100 °C, about 101 °C, about 102 °C, about 103 °C, about 104 °C, about 105 °C, about 106 °C, about 107 °C, about 108 °C, about 109 °C, about 110 °C, about 111 °C, about 112 °C, about 113 °C, about 114 °C, about 115 °C, about 116 °C, about 117 °C, about 118 °C, about 119 °C, about 120 °C, about 121 °C, about 122 °C, about 123 °C, about 124 °C, about 125 °C, about 126 °C, about 127 °C, about 128 °C, about 129 °C, about 130 °C, about 131 °C, about 132 °C, about 133 °C, about 134 °C, about 135 °C, about 136 °C, about 137 °C, about 138 °C, about 139 °C, about 140 °C, about 141 °C, about 142 °C, about 143 °C, about 144 °C, about 145 °C, about 146 °C, about 147 °C, about 148 °C, about 149 °C, about 150 °C, about 151 °C, about 152 °C, about 153 °C, about 154 °C, about 155 °C, about 156 °C, about 157 °C, about 158 °C, about 159 °C or about 160 °C. In certain embodiments, the reaction mixture is heated to a temperature of about 140 °C.

[0143] The reaction mixture may be heated for a period of from about 5 minutes to about 180 minutes, or from about 30 minutes to about 150 minutes, such as about 90 minutes.

[0144] A final curing step can be carried out on the recovered prepared organic polysulfide polymer to complete the polymerization or crosslinking process. The curing step may be athermal curing step. For example, the recovered prepared organic polysulfide polymer may be heated to a temperature for a time to complete the curing step. The temperature used in the curing step may be from about 100 °C to about 160 °C, such as about 100 °C, about 101 °C, about 102 °C, about 103 °C, about 104 °C, about 105 °C, about 106 °C, about 107 °C, about 108 °C, about 109 °C, about 110 °C, about 111 °C, about 112 °C, about 113 °C, about 114 °C, about 115 °C, about 116 °C, about 117 °C, about 118 °C, about 119 °C, about 120 °C, about 121 °C, about 122 °C, about 123 °C, about 124 °C, about 125 °C, about 126 °C, about 127 °C, about 128 °C, about 129 °C, about 130 °C, about 131 °C, about 132 °C, about 133 °C, about 134 °C, about 135 °C, about 136 °C, about 137 °C, about 138 °C, about 139 °C, about 140 °C, about 141 °C, about 142 °C, about 143 °C, about 144 °C, about 145 °C, about 146 °C, about 147 °C, about 148 °C, about 149 °C, about 150 °C, about 151 °C, about 152 °C, about 153 °C, about 154 °C, about 155 °C, about 156 °C, about 157 °C, about 158 °C, about 159 °C or about 160 °C. In certain embodiments, the curing step is carried out at a temperature of about 140 °C.

[0145] The curing step may be carried out for a time that is sufficient to allow for substantially complete curing of the polymer. Typically, the curing step can be carried out for a period of from about 1 hour to about 48 hours, such as about 24 hours.

[0146] Organic polysulfide polymers produced herein may advantageously be transparent to mid-wave infrared (MWIR) light and long-wave infrared (LWIR) light. For example, the cured organic polysulfide polymer may have a % transmittance of MWIR light of greater than about 50% at a thickness of about 1 mm, or greater than about 60% at a thickness of about 1 mm. In another example, the cured organic polysulfide polymer may have a % transmittance of LWIR light of greater than or equal to about 15% at a thickness of about 1 mm.

[0147] Also provided herein is a component for use in infrared (IR) imaging applications, the component composed of, or comprising, the cured organic polysulfide polymer as described herein.

[0148] The component may be a sheet, window, sample cell, waveguide or filter. The component may have a thickness equal to, or less than, about 2 mm. The component may have a thickness equal to, or less than, about 1 mm. For example, the component may be a lens.

[0149] The methods disclosed herein on one or more of the following:• Solvent compositions that promote homogeneous copolymerization of sulfur and unsaturated organic monomers. These solvents include dimethylformamide, tetrachloroethylene, and xylenes, and mixtures of these solvents. Here “xylenes” can be any combination of ortho, meta, or para xylene. The solvent mixtures can vary from 0 to 100% by volume and be used as a solvent in the reaction of elemental sulfur and a comonomer. These solvent compositions can provide efficient mixing andsolvation, especially at elevated temperatures (typically 100-160 °C). Tetrachloroethylene can provide a non-flammable reaction medium in processes where this is desirable. As inverse vulcanization can lead to exotherms and runaway reactions,27-28the tetrachloroethylene solvent is proposed as a non-flammable reaction medium. Importantly, tetrachloroethylene (even though it contains an alkene), does not react with elemental sulfur under the conditions of inverse vulcanization so it can be used as a solvent for this reaction.• Homogeneous, solution polymerization of elemental sulfur and unsaturated organic monomers such as alkenes, alkynes, dienes and polyenes. In solvent compositions containing dimethylformamide, tetrachloroethylene, and / or xylenes, elemental sulfur can be dissolved for a solutionphase reaction with an organic comonomer. In these reactions, the sulfur concentration is typically 1 g per 10 mb of solvent. Above these concentrations the sulfur is not fully soluble. For the solution copolymerization of sulfur with an organic alkene, alkyne, diene, or polyene, the comonomers are reacted in the solvent or solvent mixture at a temperature of 100-160 °C. This method constitutes a solution phase method for the copolymerization of elemental sulfur and an unsaturated organic comonomer. After all monomers have been consumed and converted into oligomer or polymer products, these products can be precipitated by an antisolvent or the solvent can be evaporated or distilled to provide the product. A final curing step can be carried out after the solvent is removed to complete the polymerization or crosslinking process where required.• Solution copolymerization of elemental sulfur and an organic monomer or monomers containing one or more pre-formed cyclic polysulfides. In this technique, the organic monomer contains one or more cyclic polysulfides. These cyclic polysulfides can contain 3-5 sulfiir atoms. These organic cyclic polysulfides can be reacted with elemental sulfiir in solvents with varying combinations and concentrations of dimethylformamide (DMF), xylenes or tetrachloroethylene to form copolymers. This polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur.29This is an important point as any added initiator, base or nucleophile would have to be removed after the reaction, complicating the polymer work-up. In the reaction example shown below, the stereochemistry of the C-S bonds is set in the starting material (before polymerization) and the norbomane core does not rearrange. The organic monomer also does not contain any alkenes. All of these features of this reaction distinguish the process from inverse vulcanization17and other ring-opening polymerizations of sulfur- containing monomers.29• Solution copolymerization of elemental sulfur and an organic monomer or monomers containing a pre-formed cyclic polysulfide and an alkene or other unsaturated functional groups. In this technique, the organic monomer contains both a cyclic polysulfide and a group of unsaturation such as an alkene. These organic cyclic polysulfides can be reacted with elemental sulfur in solvents with varying combinations of dimethylformamide (DMF), xylenes or tetrachloroethylene to form copolymers. This polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur.29In this reaction, the cyclic polysulfide, sulfur, and alkene groups all react to form the polysulfide polymer containing the norbomane core; the reaction is complete after a curing step. No rearrangement of the norbomene group to form a cyclopropane occurs using this method.• Solution polymerization of a single monomer containing one or more pre-formed cyclic polysulfides. In this technique, the thermal ring-opening polymerization of a pre-formed cyclic polysulfide monomer is carried out in the specified solvent compositions. The C-S stereochemistry of the monomer is set and defined before the polymerization. No elemental sulfur is used in this reaction. This polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur.29In the example below, a monomer with two cyclic trisulfides reacts with itself to form a polymer. Removal of the solvent and curing provides an organic polysulfide with a norbomane core, devoid of cyclopropane groups.• Solvent-free copolymerization of elemental sulfur and an organic monomer or monomers containing one or more pre-formed cyclic polysulfides. In this technique, an organic monomer with a cyclic polysulfide is copolymerized in molten sulfur. Molten sulfur is the solvent and comonomer in this reaction. In the example shown below, the preinstalled cyclic trisulfides render the organic comonomer soluble in the molten sulfur comonomer, which is an advantage over many other bulk copolymerizations with sulfur because the organic monomer is often insoluble in sulfur. Furthermore, the organic comonomer has the C-S stereochemistry set and defined before the polymerization. This polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur.29The norbomane group is conserved in the copolymer and no cyclopropane groups are formed.(no solvent)• Solvent-free copolymerization elemental sulfur and an organic monomer or monomers containing a pre-formed cyclic polysulfide and an alkene or other unsaturated functional groups. In this reaction, the organic monomer contains two different functional groups that can react with sulfur: a cyclic polysulfide and an alkene. In the example below, the pre-installed cyclic trisulfide renders the organic monomer soluble in the molten sulfur comonomer. Both the cyclic trisulfide and the alkene can react with the molten sulfur. This polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ringopening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur.29The norbomane core structure stays intact and no cyclopropane groups form.(no solvent)• Solvent-free melt polymerization of an organic monomer or monomers containing one or more pre-formed cyclic polysulfide. In this technique, an organic monomer is subject to thermal ringopening polymerization and crosslinking. No solvent is required and no elemental sulfur is used in this polymerization method. The C-S stereochemistry is set in the monomer, before polymerization. This polymerization does not require any additional reagents or initiators such as acids, bases or nucleophiles, which distinguishes this method from previous methods of ring-opening polymerization of polysulfides such as anionic or cationic ring-opening polymerization of cyclic polysulfides with sulfur.29The resulting polymer contains the norbomane core and no cyclopropane groups are formed.(no solvent)EXAMPLES

[0150] In the following examples, copolymerizations were carried out in organic solvents that allow homogeneous reactions of elemental sulfur with dienes such as norbomadiene. These examples illustrate solvent compositions that can be used to fully dissolve and react elemental sulfur with an organic diene comonomer. If such solvent compositions are not used, monomers, oligomers, and products can precipitate and lead to inhomogeneity.

[0151] Example 1 - Norbornadiene is not suitable for solvent-free copolymerization with sulfur(no solvent) premature vitrification,+ S8- ► heterogeneous product,140 °C unreacted sulfur

[0152] Sulfur (3.00 g, 93.8 mmol S atoms) was added to a 21 mL scintillation vial with a magnetic stirrer. The vial was connected to a condenser and lowered into a 140 °C oil bath. The sulfur was heated with constant stirring for three minutes, over which time it melted into a yellow liquid. Norbornadiene (2.160 g, 23.4 mmol, 2.38 mL) was slowly added by volumetric pipette through the top of the condenser. Within 4-5 minutes of adding the norbornadiene, the sulfur formed a soft yellow solid. Norbornadiene was observed to reflux on the surface of the solid, but would no longer mix with the bulk material. Over time, the surface of the solid would darken and the bottom would remain yellow. After 90 minutes of heating, the material was removed from the scintillation vial and then cured at 140 °C for 24 hours. The final product was not homogenous and had regions of black or dark color material, and regions of yellow material (Figure 1). Differential scanning calorimetry showed a melting point for unreacted sulfur at 119 °C. Elemental analysis of a sample of the top layer of the solid formed upon vitrification only had 42% sulfur by mass. The bottom layer of the solid formed at vitrification had 95% sulfur by mass. This is evidence for premature vitrification, phase separation, and a heterogeneous product.

[0153] Figure 2 shows a differential scanning calorimetry thermogram of the cured product. A melting point for unreacted sulfur is clearly detected at 119 °C. This indicates the reaction is not complete.

[0154] Example 2 - Ball milling norbornadiene and sulfur does not produce polymer 1

[0155] Ball milling was performed using a Planetary Ball Mill PM 100 (Retsch). Norbornadiene (6.00 g, 65. 1 mmol) and Sx (14.0 g, 54.6 mmol) were added to a 250 mL agate grinding jar with 45 agate grinding balls (o 10 mm). The mixture was ball milled for 3 hours at 500 RPM with rotation inversion cycles of 15 minutes and 5 second pauses between inversion cycles. The jar was opened, and solid material was dislodged from the walls of the reactor vessel using a spatula. Milling was resumed for 3 hours at 500 RPM with rotation inversion cycles of 15 minutes and 5 second pauses between inversion cycles. The jar was opened, and the grinding balls were observed to be clumped together with solid material; they were dislodged from each other by hand. Milling was resumed for 1 hour at 600 RPM with rotation inversion cycles of 15 minutes and 5 second pauses between inversion cycles. A final milling for 1 hour at 100 RPM with rotation inversion cycles of 10 minutes and 10 minute pauses between inversion cycles was performed. The solid material was collected for further analysis; material stuck to the agate balls was dislodged using a hammer. A total of 12.542 g of a beige-brown solid were recovered and further analyzed. The infrared spectrum (Figure 3) of this material contained a strong absorbance at 812cm1, which is due to a cyclopropane product of rearrangement. When the product was reduced with NaBH4, the cyclopropane units were further confirmed by GC-MS analysis.

[0156] Reduction of the polysulfide products followed by GC-MS analysis (Figure 4) reveals the microstructures formed in the polymerization. The top three polymers all contain cyclopropane microstructures as the major products. This is evidence that the direct reaction of sulfur and norbornadiene (either in a ball mill or in solution) does not provide polymer 1. In contrast, polymer 1 is made from the reaction of monomer 3 and sulfur. After reduction of polymer 1, GC-MS analysis shows the expected products and no cyclopropane products (Figure 4 bottom GC trace).

[0157] Example 3 - Solution-copolymerization of sulfur and norbornadiene in dimethylformamide (DMF)

[0158] Sulfur (1.00 g, 31.3 mmol S atoms) and DMF (10 mb) were added to a 21 mb vial and connected to a water-cooled condenser. The vial was lowered into a 140 °C oil bath and heated for 10 minutes with constant stirring provided by a magnetic stir bar. After 10 minutes, all sulfur had dissolved. Next, norbornadiene (0.72 g, 7.81 mmol) was added down the condenser. The reaction was then heated for 90 minutes at 140 °C. The sample was removed from the heating source and the solvent was removed by rotary evaporation. The polymer was washed with water and lyophilized to remove any remaining DMF and water. The product was then placed in a silicone container and cured in an oven at 140 °C for 24 hours to cure to provide a black polymer. DSC analysis of the material indicated no elemental sulfur was present (Figure 5 and Figure 6).

[0159] Example 4 - Evidence for reaction of the norbornadiene alkenes when reacted with sulfur in deuterated dimethylformamide (DMF-d7) at 140 °C

[0160] Sulfur (100 mg, 3.1 mmol S atoms) and DMF-d7 (1 mL) were added to a 21 mL vial and connected to a water-cooled condenser. The vial was lowered into a 140 °C oil bath and heated for 10 minutes with constant stirring provided by a magnetic stir bar. After 10 minutes, all sulfur had dissolved. Next, norbomadiene (72 mg, 0.78 mmol) was added. The reaction was then heated for 30, 90, or 150 minutes at 140 °C.JH NMR analysis of the reaction mixture (Figure 7) indicated that alkene signals from norbomadiene and intermediates from 6.0-7.0 ppm are reduced over the course of the reaction due to reaction. >80% conversion is observed after 90 minutes. This experiment is evidence for alkene consumption in the reaction of elemental sulfur with norbomadiene in DMF at 140 °C.

[0161] Example 5 - Evidence for cyclopropane formation in the solution copolymerization of sulfur and norbomadiene in DMF

[0162] The polymer prepared in Example 3 was reduced with sodium borohydride to provide small molecules which could be analyzed by GC-MS. Polymer (30 mg) was ground into a powder and added to a flame dried round bottomed flask. Sodium borohydride (94 mg) was added under a stream of nitrogen. The round bottomed flask was then connected to a condenser and purged with nitrogen. After purging, 5 mL of anhydrous tetrahydrofuran (THF) was added, and the round bottomed flask was heated to 50 °C. The reaction was heated for 24 hours with constant stirring. After this time, the round bottomed flask was removed from heat and cooled on an ice bath. Hydrochloric acid (5 mL of a 1 M solution) was injected slowly under a stream of nitrogen to quench the reaction. The HC1 was added slowly as hydrogen gas is formed. Hexane (5 mL) was then added into the round bottomed flask and stirred for an additional hour to extract the products. The organic layer was then separated and analyzed by GC-MS (Figure 8). Three major products were detected, which correspond to reducing the S-S bonds in the polymer. The signal at a retention time of 14.3 min is consistent with the reaction of sulfur at both alkenes in the original copolymerization. The peak at 10. 1 mins corresponds to a rearrangement of norbomadiene to form a molecule with a cyclopropane. The peak at 10.0 minutes corresponds to domains where only one alkene of the norbomadiene has reacted. Other minor products may reflect other microstmctures of the polymer and other products of overreduction by excess sodium borohydride. A peak for butylated hydroxytoluene (BHT) is present at 11.15 mins. This peak is due to the stabilizer in the THF solvent.

[0163] Example 6 - Solution-copolymerization of sulfur and norbornadiene in tetrachloroethylene

[0164] Sulfur ( 1.00 g, 31.2 mmol S atoms) was added into a 21 mL vial with 10 mL of tetrachloroethylene. The vial was attached to a water cooled reflux condenser and lowered into a 140 °C oil bath. The reaction was heated for 10 minutes with constant stirring provided by a magnetic stirring bar. Over this time, the sulfur completely dissolved, giving a yellow solution. Norbornadiene (0.72 g, 7.81 mmol) was then added through the top of the reflux condenser using a volumetric pipette. The reaction was then heated for a total of 90 minutes and slightly darkened over this time to a brown colour. After removal from heat, the TCE was removed by rotary evaporation. To remain consistent with the reactions in DMF, the prepolymer was then washed thoroughly in water and then lyophilized. The prepolymer was then transferred into a silicone mould and cured in an oven at 140 °C for 24 hours. After curing, the polymer took on the appearance of an orange, slightly transparent material (Figure 10).

[0165] Example 7 - Solution-copolymerization of sulfur and norbornadiene in xylenes

[0166] Sulfur (1.00 g, 31.2 mmol S atoms) was added into a 21 mL vial with 10 mL of xylenes. The xylene solvent was a mixture of isomers (64% meta, 21% ortho, 15% para). The vial was attached to a water cooled reflux condenser and lowered into a 140 °C oil bath. The vial was heated for 10 minutes with constant stirring provided by a magnetic stirring bar. Over this time, the sulfur completely dissolved, giving a yellow solution. Norbornadiene (0.72 g, 7.81 mmol) was added through the top of the reflux condenser using a volumetric pipette. The reaction was then heated at 140 °C for a total of 90 minutes. The initially yellow solution slowly darkened over time. The vial was removed from heat and xylene was evaporated using rotary evaporation. To remain consistent with the reactions in DMF, the prepolymer was then washed thoroughly in water and then lyophilized. The prepolymer was transferred into a silicone mold and cured in an oven at 140 °C for 24 hours. The polymer material was brittle and dark brown. Figure 12 demonstrates the homogeneous solution phase reaction, and the final polymer after curing.

[0167] Example s - Solution-copolymerization of sulfur and norbornadiene in mixed solvent systems

[0168] The reaction between sulfur and norbornadiene was performed using mixed solvents comprised of DMF and an equal volume of either TCE or xylenes. Sulfur ( 1.00 g, 31.2 mmol S atoms) was added to a 21 mL vial. 5 mL of DMF was added along with 5 mb of either TCE or xylenes. The vial was connected to a condenser and added to a 140 °C oil bath. The vial was heated for 10 minutes, over which time, the sulfur completely dissolved. Norbornadiene (0.72 g, 7.81 mmol) was then added down the condenser. The reactions were heated at 140 °C for a total of 90 minutes, over which time they would darken. The reactions would go notably darker when DMF was used instead of just TCE or xylene. The vial was then removed from the oil bath and the solvents were removed by rotary evaporation. The prepolymer was then thoroughly washed with water and lyophilized. The resulting black prepolymer was added to a silicone mould and cured in an oven at 140 °C for 24 hours. Figures 13 and 14 demonstrate the homogeneous solution phase reaction, and the final polymers after curing.

[0169] Example 9 - Solution-copolymerization of sulfur and norbornadiene in a mixture of DMF and xylenes. Elemental analysis of product reflects feed ratio

[0170] The copolymerization of sulfur and norbornadiene in a mixture of DMF and xylenes (1: 1 by volume) was consistently effective in preventing precipitation and ensuring a homogeneous reaction. As described above, Sulfur (1.00 g, 31.2 mmol S atoms) was added to a 21 m vial. 5 m of DMF was added along with 5 mb of xylenes. The vial was connected to a condenser and added to a 140 °C oil bath. The vial was heated for 10 minutes, over which time, the sulfur would completely dissolve. Norbornadiene (0.72 g, 7.81 mmol) was then added down the condenser. The reactions were heated at 140 °C for a total of 90 minutes, over which time they would darken. No precipitate or phase separation was observed over this period. The vial was then removed from the oil bath and the solvents were removed by rotary evaporation. The prepolymer was then thoroughly washed with water and lyophilized. The resulting black prepolymer was added to a silicone mould and then cured in an oven at 140 °C for 24 hours. Elemental analysis was carried out to determine the relative amount of carbon, hydrogen and sulfur. The composition reflected the monomer feed ratio (Table 1), which is consistent with a homogeneous, solution-phase reaction in which there is no precipitate or phase-separated substance formed.

[0171] Table 1 - Elemental analysts of polymer reflects feed ration of monomer

[0172] Example 10 - Copolymerization of sulfur and norbomadiene in a mixture of DMF and xylene with varying sulfur content

[0173] Sulfur (5.00 g, 156 mmol S atoms) was added to a 250 mL round bottomed flask with 25 mL of DMF and 25 mL xylene. The flask was connected to a condenser and added to a 140 °C oil bath. The flask was heated for 30 minutes with constant stirring, over which time, the sulfur completely dissolved. Norbomadiene was then added down the condenser. The amount of norbomadiene was varied from 14 to 59 wt% relative to sulfur. The reaction was heated for 90 minutes after the addition of norbomadiene. The solvents were then removed by rotary evaporation to give a black prepolymer (Figure 16). The prepolymer was washed thoroughly in water and then lyophilized. The prepolymer with 41% sulfur content was brittle and not easy to mold. The polymers with 58-83% sulfur content could be molded by heating to 60 °C. The prepolymer with 85% sulfur or higher was yellow due to unreacted Ss. This experiment indicates that a prepolymer made from sulfur and norbomadiene can be made in solution using equal volumes of DMF and xylenes, and the sulfur content can vary from 41-83%. Curing these products for 24 h at 140 °C provided polymer products with glass transition temperatures ranging from 37 °C to 120 °C, as shown in Table 2.

[0174] Table 2 - Dependence of glass transition temperature on sulfur percentage

[0175] Example 11 - Molding a polymer made by solution-phase copolymerization of sulfur and norbornadiene

[0176] Copolymers were prepared by the reaction of sulfur and norbornadiene using a mixed solvent system (1: 1 volume of DMF:xylenes) and sulfur content varying from 58% to 83%. The amount of solvent was such that the amount of sulfur was 1 g per 10 m of solvent. The prepolymers were cured for 24 hours. The cured polymers were then crushed into a powder to use for molding. An aluminum die was used to mold the polymer into windows. A dry PTFE spray was used as a mould release agent to ensure the samples did not stick to the aluminium disks. The die was preheated to 140 °C and approximately 500 mg of polymer was loaded into the die. Using a hot press, the die was heated at 140 °C and 20 MPa of pressure for 10 minutes. The aluminum die was then removed from the press and left to cool. After cooling to approximately 40 °C, the polymer window was removed from the press. The die could be used to make windows of three thicknesses: 0.75 mm, 1 mm, and 1. 1 mm. The die set and a representative window are shown in Figure 17.

[0177] Example 12 - Infrared transparency of polymer windows made from the copolymerization of sulfur and norbornadiene

[0178] The windows prepared in Example 11 were measured for infrared transparency from 2 pm to 20 pm using a Perkin Elmer Frontier FTIR (Figure 18). The transmittance was integrated over the mid wave infrared (3 pm - 5 pm) and the long wave infrared (7 pm - 14 pm) then divided by the wavelength range to obtain an average. In general, the transmittance increased with sulfur content. MWIR transmittance ranged from ~10 to 45%. LWIR transmittance ranged from <1 to 9% for these polymer windows.

[0179] Methods to access polymer that avoid the formation of cyclopropane and other rearrangement products.

[0180] The structure of the monomers was designed to avoid the rearrangements encountered when norbornadiene reacts with elemental sulfur. As seen in Example 12, these rearrangements cause IR absorption that reduces transparencies in the LWIR region to «10 % for windows on the order of 1 mm thick. The formation of cyclopropane rearrangement is detrimental for LWIR transmittance. Avoiding this rearrangement provides access the norbomane core of polymer 1. The examples below feature alternative monomers to norbornadiene in the synthesis of 1. Solvents are used in some of these examples, such as the 1: 1 DMF:xylenes solvent system disclosed earlier. Additional examples include polymerizations that do not use solvent, and examples that use elemental sulfur as both a comonomer and solvent.

[0181] Example 13 - Synthesis of cyclic trisulfide monomer from norbornadiene and sulfur120 °C, 90 min

[0182] A 250 mL round botomed flask was charged with sulfur (4.725 g, 147.4 mmol S atoms), norbornadiene (5 mL, 4.53 g, 49.2 mmol) and [Ni(NH3)6]CL (228 mg, 0.98 mmol). 50 mL of DMF and 50 mL of toluene were added along with a magnetic stirrer. The reaction was heated to 120 °C and stirred for 90 minutes. After the reaction, the mixture was cooled to room temperature and the solution was poured into a beaker containing 250 mL of hexane and 250 mL of water. Polymeric material precipitated and setled in the water layer. The solution was then filtered over celite, and the filtrate was collected. The orange-coloured filtrate was washed three times with 250 mL of distilled water to remove any DMF. The solution was then dried with magnesium sulfate, filtered, and concentrated by rotary evaporation to provide a crude mixture of sulfurized species (5.55 g). This mixture was purified further by flash column chromatography, eluting with hexanes. The first fraction contained the cyclic trisulfide product, which could be further purified by crystallising the neat solution at 4 °C. These crystals were triturated with cold hexane, and then extracted with chloroform. Concentrating under reduced pressure provided the pure trisulfide product as yellow crystals (m.p. = 138 °C, yield = 18 %). A GC trace and NMR spectra of the purified trisulfide are shown in Figures 19(a) and 19(b) and 19(c), respectively.

[0183] 'H NMR (600 MHz, CDC13) 5 6.38 (m, 2H), 4.05 (d, J= 1.9 Hz, 2H), 2.91 (m, 2H), 2.48 (app. d, J= 9.3, 1H), 1.72 (m, 1H).13C NMR (151 MHz, CDCh) 5 139.38, 70.81, 46.21, 43.32.

[0184] Example 14 - Synthesis ofbis(cyclic trisulfide) monomer from norbornadiene120 °C, 24 h

[0185] A 250 mL round botomed flask was charged with sulfur (9.450 g, 294.7 mmol S atoms), norbornadiene (5 mL, 4.53 g, 49.15 mmol) and [Ni(NH3)e]C12 (228 mg, 0.98 mmol). 50 mL of DMF and 50 mL of toluene were added along with a magnetic stirrer. The reaction was heated to 120 °C and stirred for 24 hours. After this time, the reaction was cooled to room temperature and poured into a beakercontaining 250 mL of hexane and 250 mL of water. Polymeric material precipitated and settled in the water layer. The solution was then fdtered over celite, and the fdtrate was collected. The orange-coloured filtrate was washed three times with 250 mL of distilled water to remove DMF. The solution was then dried with magnesium sulfate, filtered, and collected in a round bottom flask. The washing and filtering steps were done quickly as the bis(trisulfide) precipitates readily. The flask was sealed and the bis(trisulfide) precipitated as a yellow powder over 24 hours. The hexane was carefully decanted and the bis(trisulfide) was further purified by recrystallization in hot hexane (yellow crystals, m.p. = 179 °C). Yields up to 10% from norbomadiene were obtained with this method. NMR spectra for the bis(trisulfide) are shown in Figure 20.

[0186] Example 15 - Solution-copolymerization of sulfur with a monomer containing two cyclic trisulfides

[0187] The bis(trisulfide) monomer (87 mg, 0.31 mmol) and a stirring bar was added to a 5 mL vial, followed by 500 pL DMF and 500 pL xylenes. Sulfur (13 mg, 0.41 mmol S atoms) was then added to the vial. The vial was attached to a condenser and then placed in an oil bath preheated to 140 °C. The reaction mixture was stirred at 140 °C for 90 minutes. After this time, the vial was removed from the oil bath and the magnetic stir bar was extracted. The solvent was evaporated using rotary evaporation and the vial was added to an oven at 140 °C for 24 hours. DSC indicated there was no unreacted elemental sulfur and the product had a glass transition temperature of 142 °C. The infrared spectrum (Figure 21) did not have signals at 800 and 3060 cm1, indicating that no cyclopropane formation had occurred.

[0188] Example 16 - Solution-copolymerisation of sulfur with a monomer containing a cyclic trisulfide and an alkene

[0189] The trisulfide monomer (69 mg, 0.37 mmol) and a stirring bar was added to a 5 mL vial, followed by 500 pL DMF and 500 pL xylenes. Sulfur (31 mg, 0.97 mmol S atoms) was then added to the vial. The vial was attached to a condenser and then placed in an oil bath preheated to 140 °C. The reaction mixture was stirred at 140 °C for 90 minutes. After this time, the vial was removed from the oil bath and the magnetic stir bar was extracted. The solvent was evaporated using rotary evaporation and the vial was added to an oven at 140 °C for 24 hours. DSC indicated there was no unreacted elemental sulfur and theproduct had a glass transition temperature of 191 °C. The infrared spectrum did not have signals at 800 and 3060 cm1, indicating that no cyclopropane formation had occurred. No alkene was detected in the infrared spectrum either (Figure 22), indicating the alkene had reacted.

[0190] Example 17 - Solution-polymerization of a monomer containing two cyclic trisulfides

[0191] The bis(trisulfide) monomer (100 mg, 0.35 mmol) and a stirring bar was added to a 5 mb vial, followed by 500 pL DMF and 500 pL xylenes. The vial was attached to a condenser and then placed in an oil bath preheated to 140 °C. The reaction mixture was stirred at 140 °C for 90 minutes. After this time, the vial was removed from the oil bath and the magnetic stir bar was extracted. The solvent was evaporated using rotary evaporation and the vial was added to an oven at 140 °C for 24 hours. DSC indicated a glass transition temperature of 156 °C. The infrared spectrum (Figure 23) did not have signals at 800 and 3060 cm1, indicating that no cyclopropane formation had occurred.

[0192] Example 18 - Solvent-free copolymerization of sulfur with a monomer containing two cyclic trisulfides(no solvent)

[0193] Three polymer compositions were prepared with different relative amounts of sulfur. These corresponded to 72 %, 81 % and 85 % sulfur by mass. All reactions had atotal mass of 100 mg of reactant. The mass of the bistrisulfide monomer was 87 mg, 60 mg and 53 mg and the mass of sulfur was 13 mg, 40 mg and 47 mg respectively for the three reactions. The bis(trisulfide) monomer and a stirring bar were added to a 5 m vial, followed by sulfur. For the 72 % sulfur sample, the vial was placed in an oil bath preheated to 185 °C for 5 minutes to melt the reactants. This step was not necessary for the other reactions. The reaction mixture was then moved to an oil bath preheated to 140 °C for 90 minutes. After this time, the vials were removed from the oil bath and the magnetic stir bar was extracted. The product was then cured in an oven at 140 °C for 24 hours. DSC (Figure 24) indicated there was no unreacted elemental sulfur and the products had glass transition temperatures of 164 °C, 137 °C and 133 °C for the samples with 72 %, 81 % and 85 % sulfur, respectively. The infrared spectrum (Figure 24) did not have signals at 800 and 3060 cm1, indicating that no cyclopropane formation had occurred.

[0194] Example 19 - Solvent-free copolymerisation of sulfur with a monomer containing a cyclic trisulfide and an alkene(no solvent)

[0195] The trisulfide monomer (69 mg, 0.37 mmol) and a stirring bar were added to a 5 mL vial, followed by sulfur (31 mg, 0.97 mmol S atoms). The vial was capped and then placed in an oil bath preheated to 140 °C. The reaction mixture was stirred at 140 °C for 90 minutes. After this time, the vial was removed from the oil bath and the magnetic stir bar was extracted. The product was then cured in an oven at 140 °C for 24 hours. DSC (Figure 25) indicated there was no unreacted elemental sulfur and the product had a glass transition temperature of 196 °C. The infrared spectrum (Figure 25) did not have signals at 800 and 3060 cm1, indicating that no cyclopropane formation had occurred.

[0196] Example 20 - Solvent-free polymerization of a monomer containing two cyclic trisulfides °(no solvent)

[0197] The bis(trisulfide) monomer (100 mg, 0.35 mmol) and a stirring bar was added to a 5 mL vial. The vial was placed in an oil bath preheated to 185 °C for 5 minutes to melt the reactant. The reaction mixture was then moved to an oil bath preheated to 140 °C for 90 minutes. After this time, the vials were removed from the oil bath and the magnetic stir bar was extracted. The product was then cured in an oven at 140 °C for 24 hours. DSC (Figure 26) indicated the product had a glass transition temperature of 181 °C. The infrared spectrum (Figure 26) did not have signals at 800 and 3060 cm1, indicating that no cyclopropane formation had occurred.

[0198] Example 21 - Formation of a polymer window made from norbornane sulfur polymer (1)(no solvent)

[0199] Sulfur (300 mg, 9.36 mmol S atoms) was added to a vial with a magnetic stirrer. The vial was added to a preheated oil bath at 140 °C. The sulfur was left for 3 minutes to melt. The bis(trisulfide)monomer (445 mg, 1.56 mmol or 267 mg, 0.94 mmol) was then added into the vial. The norbomane bistrisulfide rapidly dissolved in the molten sulfur. The reaction was heated in the oil bath for 5 minutes at 140 °C and then poured into a silicone mould preheated to 140 °C. To reduce bubbles, the molten prepolymer should be poured from one end and allowed to fill into the mould. The mould was the placed in a 140 °C oven and cured 24 hours. (Note: the prepolymer vitrifies within 7 minutes at 140 °C so it must be poured quickly into the mould).

[0200] Example 21 - Formation of piano convex lenses made from norbornane sulfur polymer (1)

[0201] The polymers made from norbomane bistrisulfide and sulfur were used to make piano convex lenses. Moulds (Figure 27) were prepared using glass lenses as a negative. Two lenses were purchased from Edmund Optics. The first lens had a diameter of 2mm, a focal length of 2 mm and a centre thickness of 0.8 mm. The second lens had a diameter of 2.5 mm, a focal length of 5 mm and a centre thickness of 0.8 mm. To make the moulds, the lenses were each placed in a 3D printed part. The 3D part created the negative for a funnel section and an outlet. Silicone resin was slowly poured into the 3D printed part and left for 24 hours to cure. When removed, the silicone mould would have the features of the convex side of the lens. The piano side of the mould was prepared using a 20 mm by 20 mm 3D printed part. This part was placed on a glass slide and silicone resin was poured in. The two silicone parts were held together with a clamp to make a mould.

[0202] Sulfur (300 mg, 9.36 mmol S atoms) was measured into a vial with a magnetic stirrer. The vial was added to a preheated oil bath at 140 °C. The sulfur was left for 3 minutes to melt. Norbomane bistrisulfide was then poured into the vial (the amount of norbomane bistrisulfide was either 444 mg (1.56 mmol) or 267 mg (0.94 mmol)) to obtain polymers with 81% or 85% sulfiir by mass. The norbomane bistrisulfide rapidly dissolved in the molten sulfiir. The reaction was heated in the oil bath for 5 minutes and was then poured into the preheated mould at 140 °C. The mould and polymer were placed in a 140 °C oven for 24 hours to cure. After cure, the two parts of the mould were separated, and the polymer lens was removed. The funnel and outlet parts were removed by scoring the part and carefully breaking them off.

[0203] The polymer lenses were mounted onto a FLIR Lepton 3.5 LWIR camera. The shutter and the silicon lens were removed from the lepton and the polymer lens was mounted using a custom 3D printed mount. This is the first thermal imaging camera in which the lens is made from polymer 1.

[0204] Imaging was done using a 100 °C hotplate with a mask that was laser cut from 3 mm thick acrylic. The mask was placed 5 cm from the hotplate and the LWIR camera was placed 20 cm from the mask. Each lens for first tested for focal length by adjusting the distance from the sensor using custom mounts. After the focal length was determined, imaging of several masks and a person was done witheach lens. Thermal sensitivity was tested by adjusting the hotplate temperature from 30 °C to 100 °C and taking LWIR images using each of the polymer lenses.

[0205] Example 22 - Synthesis of polymer 1 using two different cyclic sulfide monomers

[0206] Sulfur (300 mg, 1.17 mmol S 8) was measured into a 5 mL vial. The vial was added to a preheated oil bath at 140 °C. The sulfur was left for 3 minutes to melt. After this point, the vial was transferred to a preheated vacuum oven at 140 °C. The pressure in the oven was decreased to approximately 2 mbar for 30 minutes. After degassing the sulfur, the sulfur was transferred back to the 140 °C oil bath at ambient pressure. The mixture of cyclic sulfide monomers was then added and dissolved in the molten sulfur over approximately 15 seconds. The reaction was stirred carefully with a heated metal spatula to prevent gas from becoming trapped which would cause bubbles in the polymer. The reaction was stirred for a total of 30 seconds (stirring was stopped at a reaction time of 45 seconds). After a total reaction time of 60 seconds, the prepolymer was poured into a silicone mold which had been preheated to 140 °C. The mold was then placed in a 100 °C oven where it was left for 1 hour to cure. Figure 35 shows images of polymer windows prepared using this method. The polymer was yellow and transparent. In this example, the ratio of monomers and sulfur was such that the total sulfur content in the final polymer was 81%.

[0207] Example 23 - MWIR and LWIR transparency across a range of thicknesses for polymer 1 windows (81% sulfur)

[0208] A 1.62 mm thick, 13 mm diameter window of polymer 1 (81% sulfur) was cast into a silicone mold. Its surfaces were polished using micromesh sandpaper ranging from 1500 to 12000 grit. After polishing, the infrared spectrum was analyzed using a Bruker Vertex 80 V. Images through the window were also taken with a standard visible light camera and with a FLIR E6 thermal camera. The FLIR E6 used wavelengths ranging from 7.5 pm to 13 pm, making it completely in the LWIR region. To reduce the thickness of the window, one side was lightly sanded using the 1500 grit micromesh sandpaper before once again being polished. This process reduced the thickness of the window by approximately 50 pm to 150 pm. After every reduction in thickness, the polymer window was analyzed using the same method as the initial window. A total of 16 thickness were tested ranging from 1.62 mm to 0.15 mm. The results are shown in Figure 36. For LWIR transmission, an average of 11.3 % was observed for windows 1.6 mm thick; 19.4 % at 1.0 mm thick, and 58.7 % for windows 0. 15 mm thick. An average MWIR transmission of 48.6% was measured for 1 mm thick windows.

[0209] Photos of the polymer 1 windows, LWIR images taken through the polymer windows, andFTIR spectra through polymer 1 at different thicknesses are shown in Figure 37.

[0210] Example 24 - Seven lens designs made from polymer 1 (all 81% sulfur)

[0211] The lenses shown in Figure 38 were prepared by casting the polymer 1 reaction mixture in a suitable silicone mold and curing at 100 °C for 1 hour.

[0212] Example 25 -Mounting polymer 1 lenses on the FLIR Lepton 3.5 module, replacing the silicon lens for a polymer 1 lens

[0213] The FLIR Lepton 3.5 had an internal thread with a pitch of 350 pm. The holder was designed to thread into this part of the camera. The thread not only provided a secure fitting for the holder but also allowed for fine control of the distance from the sensor to the bottom of the holder. This was used to find the optimal focus of each lens. The holders had a hole through the middle and an opening where the lens could be placed. After inserting the lens, a press fit cap could be inserted. The cap ensured that the lens was held securely and did not move or fall out of the holder. For all but one example, the distance between the bottom edge of the holder and the lens was maintained at 500 pm. As there was a range of focal length lenses, several different holders were prepared which controlled the height at which the lens was held. After removing the shutter and lens from the FLIR Lepton 3.5, the holder could be directly threaded into the module, allowing the lens to be used for imaging. As the shutter was removed, the camera would need manual full field calibration between each image. The calibration was done by coving the lens with an opaque material and calibrating in the Lepton User App.

[0214] 3D printed holder designs and integration into a FLIR Lepton 3.5 thermal camera module are shown in Figure 39.

[0215] Example 26 - Masks for testing thermal sensitivity and resolution of polymer 1 lenses in the FLIR Lepton 3.5 module

[0216] To investigate the imaging when using the polymer lenses, several masks were prepared (Figure 40). These masks were cut from 3 mm thick acrylic using a Rayjet 300EDU laser cutter. A 3D printed holder with a thread allowed these masks to be attached to an optical rail. The masks were then positioned in front of a hotplate for imaging. The imaging station used to test imaging using lenses 1-7 (made from polymer 1), mounted on the FLIR Lepton 3.5 camera is shown in Figure 41.

[0217] The first mask was a USAF target which utilizes line pairs with varying thickness and separation. The maximum resolution of the camera can be determined by the smallest set of three lineswhich can be resolved. The number of line pairs per millimeter and the width of each line is determined by the element and group number. The group number is written next to every set of 6 lines while the element is written next to its associated group. The elements and groups used for the target as well as their dimensions can be seen in the Table 3.

[0218] Table 3 - Elements and groups used for the USAF target

[0219] The second mask has three sets of 6 lines. For each set, three lines were horizontal and three were vertical. The widths of the lines were 1 mm, 2 mm, 3 mm for the first second and third sets respectively. The horizontal and vertical lines in each set had three different lengths with 3 mm, 7.5 mm and 12 mm and the distance between the outer edges of each group of vertical or horizontal lines was 12 mm. This target is useful to show general imaging and demonstrate the focus of the lens. The range of line widths also gives an indication on the resolution of the imaging system.

[0220] The final mask was a star mask. This mask consisted of a 60 mm diameter circle broken into 36 sectors. This gave it a 10 ° pitch with each sector being 5 °. In the center, there was a circle with a diameter of 10 mm. This mask is useful to see any astigmatism or focusing effects. If there was any warping or inconsistency in the lens focus, the sectors would no longer be straight.

[0221] These masks were useful for investigating the imaging with the polymer lenses. However, there were some limitations. The first is that the masks had a thickness of 3 mm. This meant that if the mask was not perfectly aligned with the camera, the gaps may become obscured due to parallax effects. For this reason, the lines or openings may appear smaller than the dimensions of the mask. It is possible that thethickness of the masks may also block much of the non-parallel light from reaching the camera, potentially affecting the focus of the lens. The second limitation of the masks is that they can heat up over time while being close to the heat source. As the masks heat up, they may emit long wave infrared light of their own. As this occurs, the contrast in the images of the masks may decrease. Overall, these limitations mean that the resolution and thermal sensitivity determined using these masks is the lower-bound estimate of performance.

[0222] Example 27 - Thermal sensitivity testing using polymer 1 lenses

[0223] The polymer lens was focussed using the imaging testing station shown in Example 26 and the hot plate temperature was varied. A LWIR image was taken every 10 °C between 30 °C and 100 °C (Figures 42 to 48). For all tests, the room temperature was approximately 25 °C. The thermal sensitivity testing was only qualitative as access to the intensity values for the FLIR Lepton was not possible, but it showed the lowest temperature differential at which clear images can be taken with the camera using the polymer-based lenses. The lenses with a lower f-number had greater thermal sensitivity. This can be seen most clearly with lens 7 which had a f-number of 2 while all other lenses had a f-number below 1.2. Lens 7 did not have the same contrast as the other lenses at low temperatures.

[0224] Example 28 - Summary of imaging using polymer 1 lenses on the FLIR Lepton 3.5 Module

[0225] Figure 49 shows an overview of all the images taken with each of the lenses on the FLIRLepton 3.5. The LWIR images of the masks were all taken using the same set up described in the previous two Examples. The hotplate was at 100 °C for all the mask images. To go with the images of the masks, images were taken of a person and a hand. The top set of images is a control using the stock silicon doublet lens supplied with the FLIR Lepton 3.5 camera. This is an optimized doublet lens made from high quality silicon with an anti -reflection coating on all surfaces. The f-number of this lens was 1.1 and it had a focal length of 1.77 mm. While there was some loss in intensity, the images using the piano convex polymer-based lenses compare very well to the silicon doublet.

[0226] LWIR Images taken with polymer 1 lenses on a FLIR Lepton 3.5 thermal camera. The images of the targets were all taken using a 100 °C hotplate as a black body radiation source. The target was placed 5 cm from the hotplate and the camera was placed 20 cm from the target.

[0227] Example 29 - Molding multiple lenses of polymer 1 in a single step by reactive compression molding

[0228] A custom compression mold was designed to demonstrate the scalability of lens manufacture (Figure 50). The same lens design as lens 5 was employed with a focal length of 2.5 mm and a f-numberof 1. To give the desired radius of the curved side, an array of 89 lens indents were machined into an aluminum disk. The disk had a flash ring so that excess polymer would flow into a designated area in the die. The polymer was placed on this piece before another disk was placed on top. These pieces made up the die insert. The insert was placed into a cylinder heating block and heated to the compression temperature. A push rod was then placed in the top and the entire die would be compressed using a hydraulic jack. A figure showing the compression mold design can be seen below. This compression die was designed on Autodesk Inventor and machined by the engineering staff at Flinders University from aluminum. To use the compression mold, a total of 2.5 g of polymer 1 (81% sulfur) was ground into pellets of approximately 2 mm diameter. The flash ring was pressed onto the bottom disk of the insert, the polymer was placed within the flash ring and the top disk was placed on top. Two 65 W heating cartridges and a thermocouple were inserted into holes in the heating cylinder. The push rod and bottom piece were assembled with the heating cylinder, but the insert and polymer were left separate. The die was preheated to 185 °C over approximately 10 minutes. Using heat proof gloves, the push rod was removed, and the insert was added to the preheated die. The push rod was replaced on top, and the press was left for 1 minute for the temperature in the insert to equilibrate. The die was transferred to a hydraulic press and compressed to 10 MPa for a total of 1 minute. The die was then removed from the press and the insert was extracted. Without disassembling the insert, it was transferred to a pair of water-cooled aluminum plates. The insert was cooled for an additional seven minutes, returning to approximately room temperature. Accounting for 1 minute to of handling the die, the total cycle time was 10 minutes. However, the cylinder and press rod are not cooled so multiple inserts could be used to reduce the cycle time to below 5 minutes.

[0229] To remove the polymer disk from the insert, the top disk was removed. The flashing was separated using a scalpel and the flash ring was pried off the bottom disk. The poly-1 disk would usually stay within the flash ring as it was removed. A 3D print was used to gently remove the polymer disk from the flash ring. Following removal from the press, the flat side of the disk was polished with a range of micromesh sandpapers. The lenses were then separated.

[0230] The lenses prepared using the compression mold had a square carrier material, rather than circle like the cast lenses. A slightly modified mount was used to accommodate the change in shape of the lens. The compression molded lens was mounted on the FUIR Uepton 3.5 and the same imaging experiments were performed as the cast lenses.

[0231] Compression molded lenses made from polymer 1 are shown in Figure 51.

[0232] Example 30 - Thermal imaging using polymer 1 lens (81% sulfur) made by reactive compression molding

[0233] LWIR Images taken with poly-1 lenses on a FLIR Lepton 3.5 thermal imaging module are shown in Figure 52. The top images were taken using the lens made by casting into a silicone mold. The bottom images were taken using the lenses made by reactive compression molding. The images of the masks were all taken using a 100 °C hotplate as a black body radiation source. This demonstrates that many lenses could be manufactured in parallel using preformed polymer 1 and that they can be used in imaging with comparable performance to individually cast lenses.

[0234] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

[0235] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0236] In some cases, a single embodiment may, for succinctness and / or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

[0237] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and / or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.REFERENCES

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Claims

1. CLAIMS1. A method of producing an organic polysulfide polymer, the method comprising: dissolving elemental sulfur in a solvent to form a sulfur solution; adding, to the sulfur solution, an unsaturated organic comonomer and / or a cyclic poly sulfide organic comonomer to produce a reaction mixture; treating the reaction mixture under conditions to copolymerize sulfur and the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer to produce the organic polysulfide polymer; recovering a prepared organic polysulfide polymer from the reaction mixture; and optionally, further curing the prepared organic polysulfide polymer.

2. The method according to claim 1, wherein the solvent is selected from one or more of the group consisting of dimethylformamide, tetrachloroethylene, and xylene.

3. The method according to claim 2, wherein the solvent comprises a mixture of two or more solvents.

4. The method according to any one of claims 1 to 3, wherein the sulfur concentration in the sulfur solution is about 1 g per 10 mL of solvent.

5. The method according to any one of claims 1 to 4, wherein the unsaturated organic comonomer and / or a cyclic polysulfide organic comonomer is reacted in the solvent at a temperature of from about 100 to about 160 °C.

6. The method according to any one of claims 1 to 5, wherein the prepared organic polysulfide polymer is recovered from the reaction mixture by precipitation using an antisolvent.

7. The method according to any one of claims 1 to 5, wherein the prepared organic polysulfide polymer is recovered from the reaction mixture by solvent evaporation or distillation.

8. The method according to any one of claims 1 to 7, wherein a final curing step is carried out after the solvent is removed to complete the polymerization or crosslinking process.

9. The method according to any one of claims 1 to 8, wherein the unsaturated organic comonomer is selected from the group consisting of organic alkene, organic alkyne, organic diene, or organic polyene.

10. The method according to claim 9, wherein the unsaturated organic comonomer is a non-aromatic cyclic diene or polyene hydrocarbon.

11. The method according to claim 10, wherein the unsaturated organic comonomer is cyclobutadiene, cyclopentadiene, cyclohexadiene, cyclooctadiene, norbomadiene, vinylcyclohexene, vinylnorbomene, cyclooctatetraene, ethylidene norbomene or cyclopentadiene dimer.

12. The method according to claim 11, wherein the unsaturated organic comonomer comprises norbomadiene.

13. The method according to any one of claims 1 to 12, wherein the organic polysulfide polymer is transparent to mid-wave infrared (MWIR) light and long-wave infrared (LWIR) light.

14. The method according to any one of claims 1 to 8, wherein the organic comonomer is a cyclic polysulfide.

15. The method according to claim 14, wherein the cyclic polysulfide contains 3 to 5 sulfur atoms in a cyclic ring attached to the organic comonomer structure.

16. The method according to claim 15, wherein the cyclic poly sulfide has the following structure:cyclic or polycycliccarbon framework17. The method according to claim 16, wherein the cyclic polysulfide is formed by reaction of sulfur with butadiene (1,3 -butadiene), isoprene, 1,5-hexadiene, 1,7-octadiene, cyclobutadiene, cyclopentadiene, cyclohexadiene, cyclooctadiene, norbomadiene, vinylcyclohexene, vinylnorbomene, divinylbenzene, ethylidene norbomene or cyclopentadiene dimer.

18. The method according to claim 17, wherein the cyclic polysulfide is formed by reaction of sulfur with norbomadiene to form a cyclic poly sulfide of formula (2) or formula (3):(2) (3)19. A polymer comprising repeating units of formula (1):wherein: a, b, c and d are each independently integers selected from 1, 2, 3, 4, 5, 6, 7, and 8; and p is an integer greater than or equal to 2.

20. The polymer according to claim 19, comprising 85 wt% sulfur.

21. The polymer according to claim 20, wherein the LWIR transparency of the polymer (7 pm - 14 pm) is >30% for a 0.55 mm thick window, >20% for a 0.75 mm thick window, and >20% for a 1.0 mm thick window.

22. A method of producing an organic polysulfide polymer, the method comprising: dissolving an organic cyclic polysulfide monomer in a solvent to form a reaction solution; heating the reaction solution under conditions to initiate thermal ring opening polymerization to produce the organic polysulfide polymer; recovering a prepared organic polysulfide polymer from the reaction mixture; and curing the prepared organic polysulfide polymer.

23. A method of producing an organic polysulfide polymer, the method comprising: combining an organic cyclic polysulfide monomer and elemental sulfur to form a reaction mixture; heating the reaction mixture under conditions to produce the organic polysulfide polymer; and curing the prepared organic polysulfide polymer.

24. A component for use in infrared (IR) imaging applications, the component composed of, or comprising, a cured organic polysulfide polymer formed according to the method of any one of claims 1 to 18, 22 or 23, or according to any one of claims 19 to 21.

Images