Acetone polysulfide copolymer synthesis

Abstract

The invention relates to the acetone polysulfide copolymer obtained after combining acetone and elemental sulfur (S8), dimethyl sulfoxide (DMSO) solvent and its production. The method used for the synthesis is a type of catalyst-free dispersion polymerization driven by inverse vulcanization. Said copolymer is a hydrophilic sulfur copolymer in powder form with an oxygen content of approximately 10-15% and a polymeric sulfur content of 45-55% by weight.

Description

[0001] ACETONE POLYSULFIDE COPOLYMER SYNTHESIS

[0002] Technical Field of the Invention

[0003] The invention relates to an acetone-polysulfide copolymer synthesized by a catalyst- free dispersion polymerization process involving acetone and elemental sulfur (S8) in dimethyl sulfoxide (DMSO) solvent. This process can be considered a type of inverse vulcanization. The said copolymer is a hydrophilic sulfur copolymer containing 10-15% oxygen by weight and 45-55% polymeric sulfur by weight (based on Energy Dispersive X-ray Spectroscopy) and can be obtained in powder form.

[0004] State of the Art

[0005] Polysulfides are chemical compounds consisting of chains in which two or more sulfur atoms are connected to each other with -S-S- bonds. These compounds can combine with organic or inorganic groups and have a wide chemical structure. While organic polysulfides generally combine with carbon-based compounds, inorganic polysulfides combine with metal atoms. The structure of polysulfides can vary depending on the number of sulfur atoms they contain, which affects their chemical and physical properties. For example, short-chain polysulfides generally have lower viscosity, while long-chain ones are more viscous and can be used in different applications including energy storage.

[0006] Polysulfides are divided into two main categories, organic and inorganic, based on their structural diversity. Organic polysulfides are formed by the combination of carbonbased compounds with sulfur chains. Such polysulfides have properties such as flexibility and adhesiveness, and are often used in elastomeric materials, sealants and coatings. In particular, polyurethanes and polysulfide rubbers used in sealants are examples of organic polysulfides. Inorganic polysulfides are formed by the combination of metal atoms and sulfur chains. Compounds such as sodium polysulfides are used as whitening agents in the paper industry and for cleaning metal surfaces. Inorganic polysulfides can also generally act as catalysts or solvents in chemical reactions.

[0007] Polysulfides offer significant advantages in various industrial applications. Their chemical resistance provides long-term resistance to corrosive substances, solvents and oxidative substances. This feature makes polysulfides an ideal material for reactor coatings and chemical transport vessels in the chemical and pharmaceutical industries. In addition, the high resistance of polysulfides to water and weather conditions allows them to be widely used in the construction and automotive sectors. These materials provide effective sealing in buildings and vehicles by means of their flexibility and adhesive properties. High flexibility makes polysulfide sealants resistant to structural movements and vibrations.

[0008] Inverse vulcanization / free radical polymerisation is a type of polymerisation frequently used for polysulfide copolymer synthesis. In conventional vulcanization, small amounts of elemental sulfur binds long organic polymer chains together to obtain cross-linked polymers with sulfur bridges, while in inverse vulcanization, organic materials crosslink sulfur bridges, and they are obtained from elemental sulfur and organic materials that contain vinyl groups. In inverse vulcanization, hydrophobic comonomers are generally the choice, due to their compatibility with sulfur. When hydrophobic comonomers react with elemental sulfur, the copolymers produced often maintain the water-resistant nature of their precursor materials. However, since many industrially important hydrophilic monomers (methacrylates, etc.) are not compatible with inverse vulcanization. The number of hydrophilic polysulfide copolymers is limited. Another reason why some comonomers cannot be used is their low boiling points. A limited number of studies have shown that polymerisation with polar monomers is possible using nucleophilic activators. The reason why these compounds are called activators is because they activate reactants. The activators used in reverse vulcanization are generally organic compounds containing nitrogen atoms. In addition, the comonomer used in one of the limited number of hydrophilic sulfur copolymer production procedures is 2-carboxyethyl acrylate, which is not obtained from sustainable sources and are relatively expensive.

[0009] Inverse vulcanization typically requires comonomers with vinyl groups. Additionally, hydrophilic comonomers with particularly low boiling points are generally unsuitable for this process, and the available comonomers are often expensive and not sustainably produced. Therefore, advancements in hydrophilic sulfur polymer synthesis via inverse vulcanization have become necessary. Furthermore, solution-based synthesis is known to be limited and inadequate for inverse vulcanization, partly due to challenges in selecting appropriate solvents. However, with the use of suitable solvents, inverse vulcanization becomes possible, allowing the synthesis of sulfur copolymers with unconventional comonomers, even those that do not contain vinyl groups.

[0010] Brief Description and Aims of the Invention

[0011] This invention is a single-step polymer production technique based on a type of dispersion polymerization or free radical polymerization process carried out in dimethyl sulfoxide (DMSO) solvent, in which sulfur (S8), produced in excess as an unwanted by-product of the petrochemical industry, is reacted with acetone, a cheap, readily available, and simple organic compound that is a by-product of the cumene process. With this technique, the fact that there is no need for inert atmosphere or synthesis in pressurised containers emphasises the suitability of this method for mass production.

[0012] One aim of the invention is to eliminate the necessity of using comonomers containing vinyl groups as reaction inputs. For this, the polymerisation of acetone and elemental sulfur, which are not normally likely to react with a solvent such as DMSO, has been made possible.

[0013] Another aim of the invention is to produce hydrophilic polysulfide in an environmentally friendly and economical way. For this reason, acetone -a cheap, readily available, and simple organic compound, which is a by-product of the sulphur and cumene process- was used in the synthesis. The second starting material, sulfur, an excess and largely unwanted by-product of the petrochemical industry, was also utilized. In addition, using DMSO instead of other reaction activating compounds or solvents, such as nitrogencontaining ones, may produce more positive results, as DMSO is more environmentally friendly. Because DMSO has lower acute and chronic toxicity for animals, plants, and aquatic life compared to nitrogen-containing activators.

[0014] Another aim of the invention is the use of acetone polysulfide as a cathode active material in lithium-sulfur (Li-S) batteries. The first aim would be expected from a electroactive cathode material in Li-S batteries is to contain high amount of polymerized sulfur, which can be realised in acetone polysulfide copolymers. Another aim is to prevent the diffusion of catholyte (lithium polysulphide molecules dissolved in the electrolyte) formed during discharge to the anode. A material is needed that interacts with the catholyte (lithium polysulfides) and prevents its diffusion. Oxygen-bearing functional groups on acetone polysulfide and Lewis acid-base interactions with lithium polysulfides can enable the adsorption of the molecules forming the catholyte on the acetone polysulfide surface. As a result, instead of using elemental sulfur, lithium-sulfur batteries derived from acetone polysulfide could enable the production of longer-lasting lithium-sulfur batteries.

[0015] Description of Drawings

[0016] Figure 1 shows the possible formation reactions of acetone polysulfide copolymer.

[0017] Figure 2 shows the X-ray diffraction results of sulfur and acetone polysulfide copolymer.

[0018] Figure 3 shows: A) thermal gravimetric analysis and B) differential thermal analysis results of elemental sulfur and acetone polysulfide copolymer.

[0019] Figure 4 shows the Raman spectra of elemental sulfur and acetone polysulfide copolymer.

[0020] Figure 5 shows the differential scanning calorimetry (DSC) curves of elemental sulfur and acetone polysulfide copolymer.

[0021] Figure 6 shows the Fourier transform infrared spectrum of acetone polysulfide copolymer.

[0022] Figure 7 shows the energy dispersive X-ray spectrum of acetone polysulfide copolymer and inset is the elemental analysis results obtained from this spectrum.

[0023] Figure 8 shows the water vapour adsorption isotherms of elemental sulfur and acetone polysulfide copolymer obtained at 30°C.

[0024] Figure 9 shows the contact angle measurements of elemental sulfur and acetone polysulfide copolymer (t = seconds).

[0025] Figure 10 shows back scattered electron microscope image of sulfur and acetone polysulfide obtained with a backscattered electron detector and, from left to right, elemental maps of oxygen, sulfur and carbon obtained with energy dispersive X-ray spectroscopy.

[0026] Detailed Description of the Invention

[0027] The invention is a hydrophilic sulfur copolymer that can be obtained in powder form, containing 10-15% oxygen and 45-55% polymeric sulfur by weight. The amount of sulfur or oxygen is dependent on the reaction conditions such as how better the reactor is sealed from the environment.

[0028] In the synthesis of said polymer, elemental sulfur (Ss) and acetone are used as reacting components and dimethyl sulfoxide (DMSO) is used as a solvent. During the synthesis, DMSO solvent acts as an activator so that acetone without vinyl group could be used directly as reaction input.

[0029] Acetone can be transformed into a state that will have a (C=C) functional group during the synthesis by converting it to enol or enolate form, or it can be achieved by the reaction of two acetone molecules and their conversion to ct-|3 unsaturated hydrocarbons because of the aldol reaction. Since DMSO is a polar molecule, it enables acetone to dissolve in it and since it has basic properties, it creates an environment where the enolate form of acetone can be formed at high temperatures. In addition, DMSO can dissolve elemental sulfur in excess of 10 g.L1at a temperature of 100°C and above.

[0030] In said reaction, enolate formation occurs in DMSO at 130°C and acetone molecules turns into ct-|3 unsaturated hydrocarbons. Since DMSO has nucleophilic properties, it promotes formation of higher amounts of sulfur radicals in DMSO at 130°C compared to undissolved sulfur. The reaction of unsaturated hydrocarbons with sulfur radicals in DMSO which enables the production of a polymeric material, referred to as acetone polysulfide by inverse vulcanization method, which is a type of free radical polymerization mechanism, takes place in a closed container isolated from the external environment (screw-lidded Pyrex bottle or a lidded vial) at 130°C for 24 hours. Then, the material was subjected to curing at 130 °C for 2 hours.

[0031] Possible formation reactions of acetone polysulfide through free radical mechanism are shown in Figure 1. All reactions occur in a single synthesis step: a) Possible formation mechanism of unsaturated carbonyl compounds derived from acetone, b) formation of sulfur diradicals by opening the ring opening reaction of elemental sulfur, c) formation of cross-linked carbonyl compounds between sulfur chains as a result of the reaction of unsaturated hydrocarbon and sulfur diradicals, and production of acetone polysulfide copolymer.

[0032] The diffraction patterns of cured acetone polysulfide and elemental sulfur are presented in Figure 2. There is no information about presence of elemental sulfur in the diffraction pattern of acetone polysulfide.

[0033] The results of thermal gravimetric analysis of acetone polysulfide and sulfur in nitrogen gas atmosphere and differential thermal analysis derived from these curves are presented in Figure 3. Elemental sulfur sublimes below 400°C depending on the heating temperature. The thermal stability of acetone polysulfide is higher than elemental sulfur due to cross-linked structure.

[0034] The Raman spectra of acetone polysulfide and elemental sulfur are presented in Figure 4. The peaks at 157 cnr1and 221 cm-1are indicative of elemental sulfur. The peaks at 157 cm’1and 221 cm’1are not present in the structure of acetone polysulfide. Acetone polysulfide has a broad peak at 400-500 cm1. This peak indicates the presence of -S-S- bonds belonging to polymerised sulfur.

[0035] DSC curves of elemental sulfur and acetone polysulfide are shown in Figure 5. The endothermic peak at 105°C indicates the transformation from orthorhombic sulfur to monoclinic sulfur crystal structure. The peak at 121 °C indicates the melting process of sulfur. The presence of the above-mentioned endothermic peaks was not detected in cured acetone polysulfide. DSC analysis shows that acetone polysulfide is amorphous and does not contain elemental sulfur.

[0036] In Figure 6, the presence of carbonyl groups (C=O) in the structure of acetone polysulfide is proven by the presence of a peak in the infrared spectrum at 1705 cm’1.

[0037] The EDS analysis result of acetone polysulfide, prepared in a screw-capped Pyrex bottle, is shown in Figure 7. It is seen that the material contains both oxygen (13% by weight) and sulfur (46% by weight) in its structure, and the rest is carbon. The elemental composition of the polymer varies depending on the extent to which the reaction chamber (bottle or vial) leaks or retains the reaction inputs over time. In Figure 8, the water vapour adsorption isotherms of acetone polysulfide and elemental sulfur obtained at 30°C are presented. The obtained acetone polysulfide shows a much higher water vapour adsorption capacity compared to elemental sulfur, which is indicative of its hydrophilic properties.

[0038] Figure 9 presents the contact angle measurement of elemental sulfur and acetone polysulfide with water. The contact angle of elemental sulfur was found to be 92 degrees. A water drop can remain in sulfur for a long time without being absorbed. When water was dropped onto the acetone polysulfide pellet, the contact angle was found to be below 90 degrees. The contact angle measured at 0.6 seconds was 70 degrees. A water drop on acetone polysulfide tends to be absorbed by the material immediately and disappear. The contact angle measurements indicate that acetone polysulfide is a hydrophilic material.

[0039] The backscattered electron image and EDS mapping of acetone polysulfide are shown in Figure 10. The backscattered electron image taken at 7 kV shows that acetone polysulfide particles are chemically homogeneous. Sulfur and oxygen elemental mappings indicate that these elements are distributed homogeneously within each particle.

[0040] A hydrophilic sulfur polymer that can be synthesized without the need for a vinyl group- containing input is synthesised using acetone, elemental sulfur (S8), and dimethyl sulfoxide (DMSO) as reaction inputs. The polymer comprises 10-15% oxygen by weight and 45-55% polymeric sulfur by weight.

[0041] The production method of a hydrophilic sulfur polymer that can be synthesised without the need for a reaction input containing vinyl group comprises the process steps of: a) adding 1 x mole of elemental sulfur (Ss), 4 x mole of acetone and 25 x mole of DMSO solvent to a lidded glass bottle or glass vial and seal the bottle / vial, b) stirring the reaction at 130°C and with a magnetic stirring bar rotating 500 times per second for 24 hours, c) cooling the bottle by immersing it in a room temperature water bath at the end of the reaction, d) opening the lid of the reaction bottle after the cooling process, and slowly pouring 30 ml of pure water onto the reaction products and mixing, e) centrifuging the resulting reaction product liquid in centrifuge tubes held at a 45-degree angle at 5500 rpm with water, repeating this process 4 times for 45 minutes each, and removing the polymer precipitate formed at the bottom of the tube from the supernatant structure as a result of the centrifugation, f) then mixing the polymer precipitate with water to obtain a fluid but viscous black liquid, g) pouring the product into glass petri dishes and drying it in a drying oven at 100°C for 12-16 hours, h) then grinding the obtained product with a pestle and mortar, and i) after the grinding process, curing the polymer powder at 130°C for 2 hours.

[0042] An embodiment of the production method of a hydrophilic sulfur polymer that can be synthesised without the need for a reaction input containing vinyl group comprises the process steps of: a) adding 0.312 g of elemental sulfur (Ss), 2.89 ml of acetone and 17.3 ml of DMSO solvent to a screw lidded Pyrex bottle and closing the lid of the bottle, b) stirring the reaction at 130°C and with a magnetic stirring bar rotating 500 times per second for 24 hours, c) cooling the bottle by immersing it in a room temperature water bath at the end of the reaction, d) opening the lid of the reaction bottle after the cooling process, and slowly pouring 30 ml of pure water onto the reaction products and mixing, e) filling the reaction product liquid mixed with water into 4 centrifuge tubes of 15 ml, f) carrying out the centrifugation process in centrifuge tubes held at a 45- degree angle at 5500 rpm for 45 minutes, g) centrifuging the liquid in centrifuge tubes held at a 45-degree angle at 5500 rpm with water 4 times for 45 minutes and removing the polymer precipitate formed at the bottom of the tube from the supernatant structure as a result of the centrifugation process, h) then mixing the polymer precipitate with water to obtain a fluid but viscous black liquid, i) pouring the product into glass petri dishes and drying it in a drying oven at 100 °C for 12-16 hours, j) then grinding the obtained product with a pestle and mortar, and k) after the grinding process, curing the polymer powder at 130°C for 2 hours.

[0043] A hydrophilic sulfur polymer that can be synthesized without the need for a reaction input containing a vinyl group can be used as a cathode active material in lithium-sulfur batteries due presence of electroactive sulfur in the polymer.

Claims

CLAIMS1. A hydrophilic sulfur polymer that can be synthesised without the need for a vinyl group-containing reaction input, wherein the hydrophilic sulfur polymer is synthesised with acetone, elemental sulfur (Ss) and dimethyl sulfoxide (DMSO) as reaction inputs and comprises 10-15 wt% oxygen and 45-55 wt% polymerized sulfur.

2. The production method of a hydrophilic sulfur polymer that can be synthesised without the need for a reaction input containing vinyl group according to Claim 1 , comprising the process steps of: a) adding 1 x mole of elemental sulfur (S8), 4 x mole of acetone and 25 x mole of DMSO solvent to a screw lidded Pyrex bottle and closing the lid of the bottle, b) stirring the reaction at 130°C and with a magnetic stirring bar rotating 500 times per second for 24 hours, c) cooling the bottle by immersing it in a room temperature water bath at the end of the reaction, d) opening the lid of the reaction bottle after the cooling process, and slowly pouring 30 ml of pure water onto the reaction products and mixing, e) centrifuging the resulting reaction product liquid in centrifuge tubes held at a 45-degree angle at 5500 rpm with water, repeating this process 4 times for 45 minutes each, and removing the polymer precipitate formed at the bottom of the tube from the supernatant structure as a result of the centrifugation, f) then mixing the polymer precipitate with water to obtain a fluid but viscous black liquid, g) pouring the product into glass petri dishes and drying it in a drying oven at 100 °C for 12-16 hours, h) then grinding the obtained product with a pestle and mortar, and i) after the grinding process, curing the polymer powder at 130°C for 2 hours.

3. The production method of a hydrophilic sulfur polymer that can be synthesised without the need for a reaction input containing vinyl group according to Claim 1 , comprising the process steps of: a) adding 0.312 g of elemental sulfur (Ss), 2.89 ml of acetone and 17.3 ml of DMSO solvent to a screw lidded Pyrex bottle and closing the lid of the bottle, b) stirring the reaction at 130°C and with a magnetic stirring bar rotating 500 times per second for 24 hours, c) cooling the bottle by immersing it in a room temperature water bath at the end of the reaction, d) opening the lid of the reaction bottle after the cooling process, and slowly pouring 30 ml of pure water onto the reaction products and mixing, e) filling the reaction product liquid mixed with water into 4 centrifuge tubes of 15 ml, f) carrying out the centrifugation process in centrifuge tubes held at a 45- degree angle at 5500 rpm for 45 minutes, g) centrifuging the liquid in centrifuge tubes held at a 45-degree angle at 5500 rpm with water 4 times for 45 minutes and removing the polymer precipitate formed at the bottom of the tube from the supernatant structure as a result of the centrifugation process, h) then mixing the polymer precipitate with water to obtain a fluid but viscous black liquid, i) pouring the product into glass petri dishes and drying it in a drying oven at 100 °C for 12-16 hours, j) then grinding the obtained product with a pestle and mortar, and k) after the grinding process, curing the polymer powder at 130°C for 2 hours.

4. The production method of a hydrophilic sulfur polymer that can be synthesised without the need for a reaction input containing vinyl group according to Claim 1 , wherein it is used as cathode active material in lithium-sulfur batteries.

Images