CROSS REFERENCE

[0001] This application claims priority to U.S. Provisional Patent Application No. 62/203,567 filed August 11 , 2015, the specification(s) of which is/are incorporated herein in their entirety by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to polymeric compositions, in particular, to polymeric compositions prepared from elemental sulfur and thiocarbonyl-containing compounds.

BACKGROUND OF THE INVENTION

[0003] An incredible abundance of elemental sulfur, nearly 7-million tons is generated as a waste byproduct from hydrodesulfurization of crude petroleum feedstocks, which converts alkanethiols and other (organo) sulfur compounds into S ₈ . Before the invention of the inverse vulcanization process, there were only a limited number of synthetic methods available to utilize and modify elemental sulfur. Current industrial utilization of elemental sulfur is centered around sulfuric acid, agrochemicals, and vulcanization of rubber. For example, elemental sulfur is used primarily for sulfuric acid and ammonium phosphate fertilizers, where the rest of the excess sulfur is stored as megaton-sized, above ground sulfur towers.

[0004] While sulfur feedstocks are plentiful, sulfur is difficult to process. In its original form, elemental sulfur consists of a cyclic molecule having the chemical formulation S ₈ . Elemental sulfur is a brittle, intractable, crystalline solid having poor solid state mechanical properties, poor solution processing characteristics, and there is a limited slate of synthetic methodologies developed for it. Hence, there is a need for the production of new materials that offers significant environmental and public health benefits to mitigate the storage of excess sulfur.

[0005] Elemental sulfur has been explored for use in lithium-sulfur electrochemical cells. Sulfur can oxidize lithium when configured appropriately in an electrochemical cell, and is known to be a very high energy-density cathode material. The poor electrical and electrochemical properties of pure elemental sulfur, such as low cycle stability and poor conductivity) have limited the development of this technology. For example, one key limitation of lithium-sulfur technology is the ability to retain high charge capacity for extended numbers of charge-discharge cycles ("cycle lifetimes"). Cells based on present lithium ion technology has low capacity (180 mAh/g) but can be cycled for 500-1000 cycles. Lithium-sulfur cells based on elemental sulfur have very high initial charge capacity (in excess of 1200 mAh/g, but their capacity drops to below 400 mAh/g within the first 100-500 cycles. Hence, the creation of novel polymer materials from elemental sulfur feedstocks would be tremendously beneficial in improving sustainability and energy practices. In particular, improved battery technology and materials that can extend cycle lifetimes while retaining reasonable charge capacity will significantly impact the energy and transportation sectors and further mitigate dependence on fossil fuels.

[0006] There have been several recent attempts to form sulfur into nanomaterials for use as cathodes in lithium-sulfur electrochemical cells, such as impregnation into mesoporous carbon materials, encapsulation with graphenes, encapsulation into carbon spheres, and encapsulation into conjugated polymer spheres. While these examples demonstrate that the encapsulation of elemental sulfur with a conductive colloidal shell in a core/shell colloid can enhance electrochemical stability, these synthetic methods are challenging to implement to larger scale production required for industrial application. Hence, a new family of inexpensive, functional cathode materials obtained by practical methods is desirable.

[0007] Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.

SUMMARY OF THE INVENTION

[0008] An embodiment of the subject disclosure features a sulfur copolymer comprising one or more sulfur monomers and one or more thiocarbonyl-containing comonomers. The one or more thiocarbonyl-containing comonomers may be a thioaldehyde comonomer, a thioketone comonomer, a thionoester comonomer, a thioester comonomer, a dithioester comonomer, a thiocarbonyl S-oxide comonomer, a thioamide comonomer, a trithiocarbonyl comonomer, or combinations thereof. In another embodiment, the one or more thiocarbonyl-containing comonomers may be precursors, such as non-thiocarbonyl containing precursors, that generate thiocarbonyl groups in situ. In one embodiment, the sulfur copolymer may be synthesized by a method, comprising providing elemental sulfur, heating the elemental sulfur to form a molten sulfur, mixing one or more thiocarbonyl-containing comonomers with the molten sulfur, and polymerizing the one or more comonomers with the molten sulfur, thereby forming the sulfur copolymer.

[0009] The sulfur copolymers as will be further described herein is a suitable thermoplastic or thermoset for use in elastomers, resins, lubricants, coatings, antioxidants, cathode materials for electrochemical cells, dental adhesives/restorations (i.e. thermoplastic elastomer or thermoplastic resins. [0010] A unique and inventive technical feature of the present invention is the use of thiocarbonyl-containing comonomers that surprisingly and unexpectedly copolymerized with elemental sulfur to form the sulfur copolymer. None of the presently known prior references or work has the unique inventive technical feature of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 shows a reaction schematic of a sulfur ring (S ₈ ) opening and polymerizing.

[0012] FIG. 2 shows non-limiting examples of thiocarbonyl compounds.

[0013] FIG. 3 shows non-limiting examples of reaction mechanisms where elemental sulfur reacts with a thiocarbonyl comonomer.

[0014] FIG. 4A shows a non-limiting reaction scheme of forming thiobenzophenone.

[0015] FIG. 4B shows a non-limiting reaction scheme of forming a sulfur copolymer from elemental sulfur and thiobenzophenone.

[0016] FIG. 5 and 5B show cycling experiments (C/5) of sulfur and thiobenzophenone as the cathode active material of two electrochemical cells. Excellent retention of charge capacity in Li- S batteries is demonstrated.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0017] As used herein, sulfur can be provided as elemental sulfur, for example, in powdered form. Under ambient conditions, elemental sulfur primarily exists in an eight-membered ring form (S8) which melts at temperatures in the range of 120°C -130 °C and undergoes an equilibrium ring-opening polymerization (ROP) of the S8 monomer into a linear polysulfane with diradical chain ends, as shown in schematic view in FIG. 1. As the person of skill in the art will appreciate, while S8 is generally the most stable, most accessible and cheapest feedstock, many other allotropes of sulfur can be used (such as other cyclic allotropes, derivable by melt- thermal processing of S8). Any sulfur species that yield diradical or anionic polymerizing species when heated as described herein can be used in practicing the present invention. As used herein, the term "sulfur copolymer" generally refers to any polymer or that contains sulfur monomers.

[0018] As used herein, the term "thiocarbonyl-containing monomer" is a monomer having one or more thiocarbonyl functional groups. As known to one of ordinary skill in the art, the term "thiocarbonyl" generally means that an oxygen atom has been replaced by a sulfur atom. More specifically, an oxygen atom of a carbonyl moiety is replaced by a sulfur atom. In some embodiments, the thiocarbonyl can have the structure -C=S. In the case of an ester or carboxylic acid functional group, either the oxygen atom of the carbonyl group, or the oxygen atom singly bonded to the carbonyl carbon, or both of the oxygen atoms may be replaced by a sulfur atom. For example, when the carbonyl oxygen is replaced by sulfur, the thiocarbonyl is referred to as a thionoester. When the oxygen singly bonded to the carbonyl carbon is replaced by sulfur, the thiocarbonyl is referred to as a thioester, which is an isomer of the thionoester. When both oxygens are replaced, the thiocarbonyl is referred to as a dithioester. As used herein, the terms "thiocarbonyl-containing co/monomer" and "thiocarbonyl co/monomer" may be used interchangeably. Non-limiting examples of thiocarbonyl compounds can include thioketones/thiones, thioaldehydes, thionoesters, thioethers, dithioesters, sulfines/thiocarbonyl oxide, thioamides, thionoacids/thio-acids, 1 ,2,4-trithiolanes, thiosulfinates, and thiosutfates. For example, FIG. 3 shows the basic structures of thiocarbonyls. Further examples of thiocarbonyl- containing monomer, but are not limited to, dithiooxamide, thioacetamide, vinylene trithiocarbonate, 2-cyanothioacetamide, dimethylthiocarbamoyl chloride, dimethyl trithiocarbonate, η,η-dimethylthioformamide, ethyl dithioacetate, diethylthiocarbamoyl chloride, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, o-phenyl chlorothionoformate, phenyl chlorodithioformate, thiobenzamide, o-(p-tolyl) chlorothionoformate, 4- methoxythiobenzamide, thiobenzophenone, thionobenzoate, thionocarbonates 4- methylbenzenethioamide, thioacetanilide, indole-3-thiocarboxamide, indole-3-thk>carboxamide, 3-(acetoxy)thiobenzamide, 3-ethoxythiobenzamide, 2-(phenylcarbonothioylthio)propanoic acid, 4'-hydroxybiphenyl-4-thiocarboxamide ₁ 4,4'-bis(dimethylamino)thiobenzophenone, and 4- biphenylthioamide.

[0019] As used herein, a "styrenic comonomer" is a monomer that has a vinyl functional group. The styrenic comonomer may comprise a styrene and at least one reactive functional group. As known to one of ordinary skill in the art, a styrene is a derivative of benzene ring that has a vinylic moiety. The sulfur diradicals can link to the vinylic moieties of the styrenic commoners to form the sulfur-styrenic polymer. In certain embodiments, the reactive functional group may be a halogen, an alkyl halide, an alkyl, an alkoxy, an amine, or a nitro functional group. Non-limiting examples of styrenic comonomers include bromostyrene, chlorostyrene, fluorostyrene, (trifluoromethyl)styrene, vinylaniline, acetoxystyrene, methoxystyrene, ethoxystyrene, methylstyrene, nitrostyrene, vinylbenzoic acid, vinylanisole, and vinylbenzyl chloride.

[0020] As used herein, the term "amine monomer" is a monomer that has an amine functional group. In one embodiment, aromatic amines and multi-functional amines may be used. Amine monomers include, but are not limited to, aromatic amines, vinylaniline, m-phenylenediamine, and p-phenylenediamine. The various types of phenylenediamines are inexpensive reagents due to their wide-spread use in the preparation of many conventional polymers, e.g., polyureas, polyamides. [0021] As used herein, the term "thiol monomer" is a monomer that has a thiol functional group. Thiol monomers include, but are not limited to, 4,4'-thiobisbenzenethiol and the like. The term "sulfide monomers" are monomers that have sulfide functional groups.

[0022] As used herein, an alkynylly unsaturated monomer is a monomer that has an alkynylly unsaturated functional group (i.e. triple bond). The term "alkynylly unsaturated monomer" does not include compounds in which the alkynyl unsaturation is part of a long chain alkyl moiety (e.g., unsaturated fatty acids, or carboxylic salts, or esters such as oleates, and unsaturated plant oils). In one embodiment, aromatic alkynes, both internal and terminal alkynes, multifunctional alkynes may be used. (Examples of alkynylly unsaturated monomers include, but are not limited to, ethynylbenzene, 1-phenylpropyne, 1 ,2-diphenylethyne, 1 ,4-diethynylbenzene, 1 ,4- bis(phenylethynyl)-benzene, and 1 ,4-diphenylbuta-1 ,3-diyne.

[0023] As used herein, the term "nitrone monomer" is a monomer that has a nitrone groups. In one embodiment, nitrones, dinitrones, and multi-nitrones may be used. (Examples include, but are not limited to, N-benzylidene-2-methylpropan-2-amine oxide.

[0024] As used herein, an "aldehyde monomer" is a monomer that has an aldehyde functional group. In one embodiment, aldehydes, dialdehydes, and multi- aldehydes may be used.

[0025] As used herein, the term "ketone monomer" is a monomer that has a ketone functional group. In one embodiment, ketones, di-ketones, and multi-ketones may be used.

[0026] As used herein, the term "epoxide monomer" is a monomer that has epoxide functional groups. Non-limiting examples of such monomers include, generally, mono- or polyoxiranylbenzenes, mono- or polyglycidylbenzenes, mono- or poly-glycidyloxybenzenes, mono- or polyoxiranyl(hetero)aromatic compounds, mono-or polyglycidyl(hetero)aromatic compounds, mono- or polyglycidyloxy(hetero)aromatic compounds, diglyckjyl bisphenol A ethers, mono- or polyglycidyl(cyclo)alkyl ethers, mono- or polyepoxy(cyclo)alkane compounds and oxirane-terminated oligomers. In one preferred embodiment, the epoxide monomers may be benzyl glycidyl ether and tris(4-hydroxyphenyl)methane triglycidyl ether. In certain embodiments, the epoxide monomers may include a (hetero)aromatic moiety such as, for example, a phenyl, a pyridine, a triazine, a pyrene, a naphthalene, or a polycyclic (hetero)aromatic ring system, bearing one or more epoxide groups. For example, in certain embodiments, the one or more epoxide monomers are selected from epoxy(hetero)aromatic compounds, such as styrene oxide and stilbene oxide and (hetero)aromatic glycidyl compounds, such as glycidyl phenyl ethers (e.g., resorcinol diglyckjyl ether, glycidyl 2-methylphenyl ether), glycidylbenzenes (e.g., (2,3- epoxypropyl)benzene) and glycidyl heteroaromatic compounds (e.g., N-(2,3- epoxypropyl)phthalimide). In certain desirable embodiments, an epoxide monomer will have a boiling point greater than 180 °C, greater than 200 °C, or even greater than 230 °C at the pressure at which polymerization is performed (e.g., at standard pressure, or at other pressures).

[0027] As used herein, the term "thiirane monomer" is a monomer that has a thirane functional group. Non-limiting examples of thiirane monomers include, generally, mono- or polythiiranylbenzenes, mono- or polythiiranylmethylbenzenes, mono- or polythiiranyl(hetero)aromatic compounds, mono- or polythiiranylmethyl(hetero)-aromatic compounds, dithiiranylmethyl bisphenol A ethers, mono- or polydithiiranyl (cyclo)alkyl ethers, mono- or polyepisulfide(cyclo)alkane compounds, and thiirane-terminated oligomers. In some embodiments, thiirane monomers may include a (hetero)aromatic moiety such as, for example, a phenyl, a pyridine, a triazine, a pyrene, a naphthalene, or a poly cyclic (hetero)aromatic ring system, bearing one or more thiirane groups. In certain desirable embodiments, a thiirane monomer can have a boiling point greater than 180 °C, greater than 200 °C, or even greater than 230 °C at the pressure at which polymerization is performed (e.g., at standard pressure).

[0028] As used herein, an ethylenically unsaturated monomer is a monomer that contains an ethylenically unsaturated functional group (i.e. double bond). The term "ethylenically unsaturated monomer" does not include compounds in which the ethylenic unsaturation is part of a long chain alkyl moiety (e.g. unsaturated fatty acids such as oleates, and unsaturated plant oils).

[0029] Non-limiting examples of ethylenically unsaturated monomers include vinyl monomers, acryl monomers, (meth)acryl monomers, unsaturated hydrocarbon monomers, and ethylenically- terminated oligomers. (Examples of such monomers include, generally, mono- or polyvinylbenzenes, mono- or polyisopropenylbenzenes, mono- or polyvinyl(hetero)aromatic compounds, mono- or polyisopropenyl(hetero)-aromatic compounds, acrylates, methacrylates, alkylene di(meth)acrylates, bisphenol A di(meth)acrylates, benzyl (meth)acrylates, phenyl(meth)acrylates, heteroaryl (meth)acrylates, terpenes (e.g., squalene) and carotene. In some embodiments, non-limiting examples of ethylenically unsaturated monomers that are non- homopolymerizing include allylic monomers, isopropenyls, maleimides, norbornenes, vinyl ethers, and methacrylonitrile. In other embodiments, the ethylenically unsaturated monomers may include a (hetero)aromatic moiety such as, for example, phenyl, pyridine, triazine, pyrene, naphthalene, or a polycyclic (hetero)aromatic ring system, bearing one or more vinylic, acrylic or methacrylic substituents. Examples of such monomers include benzyl (meth)acrylates, phenyl (meth)acrylates, divinylbenzenes (e.g., 1 ,3-divinylbenzene, 1 ,4-divinylbenzene), isopropenylbenzene, styrenics (e.g., styrene, 4-methylstyrene, 4-chlorostyrene, 2,6- dichlorostyrene, 4-vinylbenzyl chloride), diisopropenylbenzenes (e.g., 1,3- diisopropenylbenzene), vinylpyridines (e.g., 2-vinylpyridine, 4-vinylpyridine), 2,4,6-tris((4- vinylbenzyl)thk))-1 ,3,5-triazine and divinylpyridines (e.g., 2,5-divinylpyridine). In certain embodiments, the ethylenically unsaturated monomers (e.g., including an aromatic moiety) bear an amino (i.e., primary or secondary) group, a phosphine group or a thiol group. One example of such a monomer is vinykJiphenylphosphine. In certain desirable embodiments, an ethylenically unsaturated monomer will have a boiling point greater than 180 °C, greater than 200 °C, or even greater than 230 °C at the pressure at which polymerization is performed (e.g., at standard pressure).

[0030] As used herein, the term "self-healing" is defined as to enable a material to repair damage with minimum intervention. In some embodiments, mechanisms and techniques to enable self-healing may include covalent bonding, supramolecular chemistry, H-bonding, ionic interactions, π-π stacking, chemo-mechanical repairs focusing on encapsulation, remote self- healing, or shape memory assisted polymers. In one preferred embodiment, self-healing utilizes thermal reformation. As used herein, thermal reformation involves the use of heat to reform the bonds or cross-links of a polymeric material.

[0031] As used herein, an "elemental carbon material" is a material that is primarily formed as an allotrope of carbon, with a minor amount of chemical modification. For example, graphene, graphene oxide, graphite, carbon nanotubes, fullerenes, carbon black, carbon flakes and carbon fibers are examples of elemental carbon materials. Such materials can be made, for example, by first dispersing the elemental carbon material in molten sulfur, then copolymerizing the molten sulfur with one or more monomers (e.g., one or more polyfunctional monomers). As a general guideline for the person of skill in the art to use in formulating such materials, up to about 15 wt% elemental carbon material can be dispersed in sulfur at temperatures high enough that the sulfur is molten, but low enough that significant ring opening and polysutfide polymerization does not occur (e.g., at temperatures in the range of about 120 °C to about 160 °C). Higher loadings of elemental carbon materials in sulfur can be achieved by pre-dissolution of the sulfur and dispersion of the elemental carbon material into a suitable solvent (e.g., carbon disulfide) followed by removal of the solvent under reduced pressure to yield a blended composite powder which can be melted and allowed to with the one or more monomers. To induce curing of the dispersed carbon, or other nanoinclusions with the sulfur matrix, direct heating of the dispersion affords a polymerized nanocomposite.

[0032] As used herein, the term "functional" in correlation with a polymer refers to functional polymers that have specified physical, chemical, biological, pharmacological, or other properties or uses that are determined by the presence of specific chemical functional groups, which are usually dissimilar to those of the backbone chain of the polymer.

[0033] Referring now to FIG. 1-5B, the present invention features a sulfur copolymer comprising one or more sulfur monomers at least about 50 %wt of the sulfur copolymer, and one or more thiocarbonyl-containing comonomers at about 5 to 50 %wt of the sulfur copolymer. In some embodiments, the one or more thiocarbonyl-containing comonomers may be a thioaldehyde comonomer, a thioketone comonomer, a thionoester comonomer, a thioester comonomer, a dithioester comonomer, a thiocarbonyl S-oxide comonomer, a thioamide comonomer, a trithiocarbonyl comonomer, or combinations thereof. In another embodiment, the one or more thiocarbonyl-containing comonomers may be precursors, such as non-thiocarbonyl containing precursors, that generate thiocarbonyl groups in situ. For example, the thiocarbonyl-containing comonomers are thioketone comonomers such as thiobenzophenone. In other embodiments, the sulfur monomers are according to the formula: S-S _n -S, with "n" ranging from about 1 to 10.

[0034] Preferably, a sulfur moiety of the sulfur monomer is bonded to a functional moiety of the thiocarbonyl-containing comonomers. The functional moiety may be a carbon, such as the thiocarbonyl carbon, an amine, a halogen, a hydrogen, or oxygen, or any appropriate reactive functional group of the thiocarbonyl-containing comonomers. For example, the sulfur moiety of the sulfur monomers is bonded to a functional moiety of the thioketone. The functional moiety may be a carbon, such as the thiocarbonyl carbon, of the thioketone.

[0035] In some embodiments, the sulfur monomers are about 10 to 30%wt of the copolymer, 30 to 40%wt of the copolymer, 40 to 60%wt of the copolymer, 60 to 80%wt of the copolymer, or 80 to 95%wt of the copolymer. For example, the sulfur monomers are at least about 80% wt of the sulfur copolymer. In other embodiments, the thiocarbonyl-containing comonomers are about 5 to 20%wt of the copolymer, 20 to 40%wt of the copolymer, or 40 to 60%wt of the copolymer. For instance, the thiocarbonyl-containing comonomers are about 20%wt of the sulfur copolymer.

[0036] For example, the present invention may feature a sulfur copolymer comprising one or more sulfur monomers at about 10 to 95%wt of the sulfur copolymer, and one or more thioketone comonomers at about 5 to 90%wt of the sulfur copolymer. In other embodiments, the thioketone comonomers are about 5 to 20%wt of the copolymer, 20 to 40%wt of the copolymer, 40 to 60%wt of the copolymer, 60 to 80%wt of the copolymer, or 80 to 90%wt of the copolymer.

[0037] In some embodiments, the sulfur copolymer may further comprise one or more termonomers at about 5 to 50%wt of the sulfur copolymer. In further embodiments, the termonomers may be about 5 to 15%wt of the copolymer, 15 to 25%wt of the copolymer, 25 to 35%wt of the copolymer, or 35 to 50%wt of the copolymer.

[0038] In one embodiment, the termonomer may be a vinyl monomer, an isopropenyl monomer, an acryl monomer, a methacryl monomer, an unsaturated hydrocarbon monomer, an epoxide monomer, a thiirane monomer, an alkynyl monomer, a diene monomer, a butadiene monomer, an isoprene monomer, a norbornene monomer, an amine monomer, a thiol monomer, a sulfide monomer, an alkynylly unsaturated monomer, a nitrone monomer, an aldehyde monomer, a ketone monomer, a thiocarbonyl-containing monomer, or an ethylenically unsaturated monomer.

[0039] In another embodiment, the termonomers may be a polyvinyl monomer, a polyisopropenyl monomer, a polyacryl monomer, a polymethacryl monomer, a polyunsaturated hydrocarbon monomer, a polyepoxide monomer, a polythiirane monomer, a polyalkynyl monomer, a polydiene monomer, a polybutadiene monomer, a polyisoprene monomer, a polynorbornene monomer, a polyamine monomer, a polythiol monomer, a polysutfide monomer, a polyalkynylly unsaturated monomer, a polynitrone monomer, a polyaldehyde monomer, a polyketone monomer, a polythiocarbonyl-containing monomer, and a polyethylenically unsaturated monomer.

[0040] In still other embodiments, the sulfur copolymer may further comprise an elemental carbon material dispersed in the sulfur copolymer. The carbon material may be at most about 50 wt% of the sulfur copolymer. For example, the carbon material is about 20 wt% of the sulfur copolymer.

[0041] In some embodiments, the sulfur monomers may comprises dynamic sulfur-sulfur (S-S) bonds. Preferably, when the dynamic S-S bonds of the sulfur copolymer are broken, the S-S bonds can be reconnected by thermal reforming.

[0042] In one embodiment, the sulfur copolymer may be a thermoplastic or a thermoset for use in elastomers, resins, lubricants, coatings, antioxidants, cathode materials for electrochemical cells, dental adhesives/restorations. For example, the sulfur copolymer may be a thermoplastic rubber or a thermoplastic elastomer. In another embodiment, the sulfur copolymer may be in a form of a polymeric film. For example, the sulfur copolymer may be a thin film coating for a surface of a substrate.

[0043] Another embodiment of the present invention features a method of synthesizing the sulfur copolymer described herein. In an exemplary embodiment, the method may comprise providing elemental sulfur, heating the elemental sulfur to form a molten sulfur, adding one or more thiocarbonyl-containing comonomers with the molten sulfur, and polymerizing the one or more thiocarbonyl-containing comonomers with the molten sulfur, thereby forming the sulfur copolymer. The technique of polymerizing can be free radical polymerization, controlled radical polymerization, ring-opening polymerization, ring-opening metathesis polymerization, step- growth polymerization, or chain-growth polymerization. The elemental sulfur may be heated to a temperature of about 120 to 230 °C to form the molten sulfur. The molten sulfur may comprise sulfur radicals, such as sulfur diradicals, that, upon addition of the thiocarbonyl-containing comonomers, can copolymerize with the thiocarbonyl-containing comonomers.

[0044] In one embodiment, the elemental sulfur is at least 50 %wt of the sulfur copolymer. In another embodiment, the thiocarbonyl-containing comonomers are about 5 to 50 wt% of the sulfur copolymer, and can be a thioaldehyde comonomer, a thioketone comonomer, a thionoester comonomer, a thioester comonomer, a dithioester comonomer, a thiocarbonyl S- oxide comonomer, a thioamide comonomer, a trithiocarbonyl comonomer, or combinations thereof. In yet another embodiment, the one or more thiocarbonyl-containing comonomers may be non-thiocarbonyl containing precursors that generate thiocarbonyl groups in situ.

[0045] In one embodiment, the sulfur and thiocarbonyl-containing comonomer mixture may be heated to a temperature in the range of about 120 °C to about 230 °C, e.g., in the range of about 120 °C to about 150 °C, to polymerize the mixture and form the sulfur copolymer. A person of skill in the art will select conditions that provide the desired level of polymerization. In certain embodiments, the polymerization reaction is performed under ambient pressure. However, in other embodiments, the polymerization reaction can be performed at elevated pressure (e.g., in a bomb or an autoclave). Elevated pressures can be used to polymerize more volatile comonomers, so that they do not vaporize under the elevated temperature reaction conditions. In further embodiments, the thiocarbonyl-containing comonomers may be reacted directly with the liquid molten sulfur, or in another reaction medium with the sulfur. The reaction medium can be any solution, such as a multiphasic solution.

[0046] In another embodiment, the method may further comprise reacting an available reactive functional group of the sulfur copolymer with one or more second comonomers to form a terpolymer. The reaction mechanism may be oxidative coupling, polymerization, or copolymerization. In some embodiments, the second comonomers are about 5 to 50 %wt of the terpolymer. In one embodiment, the second comonomer may be a vinyl monomer, an isopropenyl monomer, an acryl monomer, a methacryl monomer, an unsaturated hydrocarbon monomer, an epoxide monomer, a thiirane monomer, an alkynyl monomer, a diene monomer, a butadiene monomer, an isoprene monomer, a norbornene monomer, an amine monomer, a thiol monomer, a sulfide monomer, an alkynylly unsaturated monomer, a nitrone monomer, an aldehyde monomer, a ketone monomer, a thiocarbonyl-containing monomer and an ethylenically unsaturated monomer.

[0047] In yet another embodiment, the second comonomer may be a polyvinyl monomer, a polyisopropenyl monomer, a polyacryl monomer, a polymethacryl monomer, a polyunsaturated hydrocarbon monomer, a polyepoxide monomer, a polythiirane monomer, a polyalkynyl monomer, a polydiene monomer, a polybutadiene monomer, a polyisoprene monomer, a polynorbomene monomer, a polyamine monomer, a polythiol monomer, a polysutfide monomer, a polyalkynylly unsaturated monomer, a polynitrone monomer, a polyaldehyde monomer, a polyketone monomer, a polythiocarbonyl-containing monomer, and a polyethylenically unsaturated monomer.

[0048] In other embodiments, the method may further comprise dispersing an elemental carbon material in the sulfur copolymer. The carbon material may be at most about 50 wt% of the sulfur copolymer.

[0049] The present invention may further feature a method of making an article formed from any of the sulfur copolymers described herein. The method may comprise heating the sulfur copolymer to a temperature in the range of about 120°C to about 230°C to form a prepolymer, forming the prepolymer into a shape of the article to yield a formed prepolymer, and curing the formed prepolymer to yield the article. In some embodiments, the method may further comprise mixing the prepolymer with a solvent prior to forming. In other embodiments, the prepolymer may be coated and cured as a thin film on a substrate. In still other embodiments, the prepolymer can be shaped and cured using a mold.

[0050] Another embodiment of the present invention features a method of forming an article from any of the sulfur copolymer described herein. The method may comprise admixing the copolymer material in a solvent, forming the admixed copolymer material into a shape of the article, and removing the solvent from the copolymer material to yield the article.

[0051] According to yet another embodiment, the present invention features an electrochemical cell comprising an anode comprising metallic lithium, a cathode comprising any of the sulfur copolymer described herein, and a non-aqueous electrolyte interposed between the cathode and the anode. Without wishing to limit the present invention to a particular theory or mechanism, the sulfur copolymer can generate soluble additive species in situ upon discharge, which are co-deposited with lower sulfide discharge products onto the cathode by an electrochemical reaction or a non-electrochemical reaction. Referring to FIGS. 5A and 5B, the use of the sulfur copolymer as a cathode material can provide for an electrochemical cell that has a capacity of about 800 - 1400 mAh/g, and an increased volumetric energy density.

[0052] EXAMPLE 1. Non-limiting procedure for preparing an exemplary sulfur- thiocarbonyl-containing copolymer

[0053] To a vial equipped with a magnetic stir bar was loaded with sulfur and the thiocarbonyl- containing compound. The mixture was heated in an oil bath and stirred at a temperature of about 130°C to yield a liquid. The reaction was cooled to yield the sulfur copolymer. [0054] EXAMPLE 2. Copolymerization of elemental sulfur and thiobenzophenone

[0055] To a vial equipped with a magnetic stir bar was loaded with about 80 wt% elemental sulfur and about 20 wt% thiobenzophenone. The mixture was heated in an oil bath and stirred at a temperature of about 175°C to yield a liquid for about 10-15 minutes. The mixture of elemental sulfur and thiobenzophenone was miscible. The reaction was then cooled to yield a blue sulfur copolymer.

[0056] A person of skill in the art will select thiocarbonyl-containing comonomers and relative ratios thereof in order to provide the desired properties to the sulfur copolymer. A polyfunctional monomer is one that includes more than one (e.g., 2 or 3) polymerizable amine, thiol, sulfide, alkynylly unsaturated, nitrone and/or nitraso, aldehyde, ketone, thiirane, ethylenically unsaturated, and/or epoxide moieties. In some embodiments, polyfunctional monomers can be used to cross-link the sulfur copolymer to adjust the properties of the polymer, as would be understood by the person of skill in the art. The multiple polymerizable groups of a polyfunctional monomer can be the same or different.

[0057] The copolymers described herein can be partially cured to provide a more easily processable material, which can be processed into a desired form (e.g., into a desired shape, such as in the form of a free-standing shape or a device), then fully cured in a later operation. For example, one embodiment of the invention is a method of making an article formed from a sulfur copolymer as described herein. The prepolymer can be formed, for example, by conversion of the one or more thiocarbonyl-containing comonomers at a level in the range of about 20 to about 50 mol%. For example, the heating is performed for a time in the range of about 20 seconds to about five minutes, for example, at a temperature in the range of about 175 °C to about 195 °C. The person of skill in the art will determine the desired level of comonomer conversion in the prepolymer stage to yield a processable prepolymer material, and will determine process conditions that can result in the desired level of comonomer conversion.

[0058] In one embodiment, the prepolymer can be provided as a mixture with a solvent for forming, e.g., via casting, molding or printing. The prepolymers described herein can form miscible mixtures or solutions with a variety of solvents, such as non-polar high-boiling aromatic solvents, including, for example, haloarene solvents such as di- and trichlorobenzene (e.g., 1 ,2,4-trichlorobenzene). The solvent can be added, for example, after the prepolymer is prepared, to provide a softened or flowable material suitable for a desired forming step (e.g., casting, molding, or spin-, dip- or spray-coating.) In some embodiments, the prepolymer/solvent mixture can be used at elevated temperatures (e.g., above about 100 °C, above about 120 °C or above about 140 °C) to improve flow at relatively low solvent levels (e.g., for use in casting or molding processes). In other embodiments, the prepolymer/solvent mixture can be used at a lower temperature, for example, at ambient temperatures (e.g., for use in spin-coating processes). Unlike molten sulfur, the prepolymers described herein can remain soluble even after the solvent cools.

[0059] In one embodiment, the prepolymer is coated and cured as a film on a substrate. While S ₈ is typically intractable due to its crystallinity, the materials described herein can be formed as to be amenable to solution processing (e.g., in molten or solvent-admixed form) to fabricate thin film materials. Mixtures of molten prepolymer and solvent can be diluted to the concentration desired for a given spin-coating process.

[0060] When forming thin films of the materials described herein on substrates, it can often be desirable to use a polyimide primer layer. Thus, a solution of a polyamic precursor (e.g., polypyromellitamic ackJ-4,4'-dianiline, or compounds with oxyaniline linkages), or similar copolymer derivatives can be deposited onto a substrate and cured (e.g., by heating at a temperature in the range of about 120 to about 220 °C) to form a thin polyimide layer (e.g., as thin as 2 nm), upon which the materials described herein can be formed. Moreover, in many embodiments, even fully cured copolymers as described herein can be melt processed or suspended or dissolved in solvent and deposited on to substrates in a manner similar to those described for prepolymeric materials.

[0061] In certain embodiments, the prepolymer can be shaped and cured using a mold. For example, in one embodiment, the prepolymer (i.e., in molten or solvent-admixed form) can be deposited (e.g., by pouring) into a TEFLON or silicone (e.g., polydimethylsiloxane (PDMS)) mold, then cured to form a desired shape. In another embodiment, a softened prepolymer material (e.g., swollen with solvent and/or softened by heat) can be imprinted by stamping with a mold bearing the desired inverse surface relief, then cured and allowed to cool. Moreover, in many embodiments, even fully cured copolymers as described herein can be shaped with a mold in a manner similar to those described for prepolymeric materials. Sulfur terpolymers and more complex copolymer materials, such as in the form of cross-linked polymers, or non- crosslinked, intractable polymers, can be reprocessed by thermal or other stimuli activation of dynamic S-S bonds in the polymer system.

[0062] As described above, soluble copolymers can be made by the person of skill in the art, for example, using relatively higher fractions of organic comonomer(s). Such copolymers can be solution processed to fabricate articles. For example, another aspect of the invention is a method of forming an article formed from the sulfur copolymer as described herein, the method comprising admixing the sulfur copolymer with a solvent, such as a nonpolar organic solvent (e.g., to make a suspension or solution), forming the admixed the sulfur copolymer into the shape of the article, and removing the solvent from the sulfur copolymer to yield the article. The admixture with solvent can, for example, dissolve the sulfur copolymer. Various process steps can be performed at elevated temperatures, for example, to decrease viscosity of the admixed sulfur copolymer and to aid in evaporation of solvent.

[0063] For example, in one embodiment, a room temperature solution of any sulfur copolymer described herein (e.g., in prepolymeric form) is poured into a TEFLON or PDMS mold. A decrease in viscosity at elevated temperatures (e.g., > about 140 °C) can allow sufficient flow into even intricate mold shapes. Once the mold is filled, it can be placed in a vacuum oven at increased temperature (e.g., about 210 °C) under ambient pressure to cure and to drive off solvent. For thicker molded samples, vacuum can be pulled on the solution when it is in a low viscosity state in order to ensure the removal of bubbles. The mold is then removed from the oven and allowed to cool before removal from the mold. A person of ordinary skill in the art will understand that other suitable methods, such as injection molding, compression molding, and melt casting, can be used in forming articles from the materials described herein.

[0064] According to one embodiment, the present invention features a sulfur composite material comprising at least about 50 %wt of elemental sulfur and about 5 to 50 %wt of a thiocarbonyl- containing compound. Preferably, the elemental sulfur is miscible with the thiocarbonyl- containing compound such that sulfur composite material is an intimately mixed composite.

[0065] A further embodiment of the present invention features a method of producing the sulfur composite material. The method may comprise providing at least about 50 %wt of elemental sulfur, heating the elemental sulfur to form molten sulfur, and adding and mixing about 5 to 50 %wt of a thiocarbonyl-containing compound to the molten sulfur such that the thiocarbonyl- containing compound is miscible with the molten sulfur, thereby forming the sulfur composite material. In one embodiment, the elemental sulfur is heated to about 130-180°C.

[0066] In one embodiment, the thiocarbonyl-containing compound is selected from a group consisting of a thioaldehyde, a thioketone, a thionoester, a thioester, a dithioester, a thiocarbonyl S-oxide, a trithiocarbonyl, thioamides, and a precursor that generates a thiocarbonyl group in situ. For example, the thioketone may be a thiobenzophenone.

[0067] In some embodiments, the sulfur composite material may be used as a cathode for an electrochemical cell. For example, in one embodiment, the electrochemical cell may comprise an anode comprising metallic lithium, a cathode comprising the sulfur composite material, and a non-aqueous electrolyte interposed between the cathode and the anode. The sulfur composite material can generate soluble additive species in situ upon discharge. These soluble additive species are co-deposited with lower sulfide discharge products onto the cathode by an electrochemical reaction or a non-electrochemical reaction. Preferably, the sulfur composite material can provide for an electrochemical cell that has an increased volumetric energy density and a capacity ranging from about 800 to about 1400 mAh/g.

[0068] As used herein, the term "about" refers to plus or minus 10% of the referenced number. Various modifications of the invention, in addition to those described herein, will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. Each reference cited in the present application is incorporated herein by reference in its entirety.

[0069] Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims. In some embodiments, the figures presented in this patent application are drawn to scale, including the angles, ratios of dimensions, etc. In some embodiments, the figures are representative only and the claims are not limited by the dimensions of the figures. In some embodiments, descriptions of the inventions described herein using the phrase "comprising" includes embodiments that could be described as "consisting of, and as such the written description requirement for claiming one or more embodiments of the present invention using the phrase "consisting of is met.