Synthesis and Applications of High Sulfur Content Polymeric Materials/Yüksek Kükürt İçerikli Polimerik Malzemelerin Sentezi ve Uygulamaları

Sulfur has been used in various applications. With approximately 70 million tonnes produced each year from petroleum refining, elemental sulfur is widely available and inexpensive (∼$120 USD per tonne). A significant portion of sulfur is used in the production of sulfuric acid. Although elemental sulfur is not toxic, it is a flammable solid so finding productive uses for this stockpiled material under the open air is important. Finding large-scale uses for this sulfur, such as conversion to useful polymers, would be an important advance. Polymerization of elemental sulfur has long been studied. Sulfur polymerizes above 159 oC. Unfortunately, the polymeric sulfur undergoes depolymerization since elemental sulfur is more stable thermodynamically at room temperature. As a solution for this problem, in Pyun’s pioneering study, an alkene was used as an organic cross-linker via inverse vulcanization method. In this study, sulfur was heated to 185 °C to initiate ring-opening polymerization and then, addition of alkene resulted in cross-linking. Because of the high sulfur content (50-90 wt%) and the corresponding polysulfur copolymers represented several interesting chemical, material, and optical properties: redox acitivity (cathode materials for Li-S batteries), a high refractive index and a mid IR region of transparency (night vision, thermal imaging), self healing, heavy metal ions remediation, etc. These usage areas have inspired further exploration of inverse vulcanization with a variety of unsaturated cross-linkers to obtain polysulfides with various properties. On the other hand, today vegetable oils are the most important renewable raw material for the chemical industry. About 80% of the global oil and fat production is vegetable oil. These oils make highly pure fatty acids available such as oleic acid (OA) from sunflower, linoleic acid (LA) from soybean, linolenic acid (LnA) from linseed, and ricinoleic acid from castor oil (Figure 1.1(a)). Vegetable oils are expected to play a key role during the 21st century to synthesize polymers from renewable sources. Within this contribution, the project is aimed at the synthesis and application of new high sulfur content polymeric materials using fatty acids (Figure 1.1(a)). Figure 1. (a) Chemical structures of some fatty acids, (b) the synthesis and chemical modification (poly(S-r-OA)-PE) of a polsulfur copolymer (poly(S-r-OA)) via inverse vulcanization. Due to the presence of double bonds, these pure fatty acids will be used firstly for cross-linking by using inverse vulcanization method (Figure 1.1(b)). Correponding copolymers are expected to be soluble in common organic solvents, processable and electroactive. In particular, the effect of double bonds and the free alkyl chains on the polysulfur copolymers will be investigated systematically by using OA, LA and LnA. Another feature of the copolymers obtained from these fatty acids will be the presence of reactive functional units (-COOH), which makes it possible to make chemical modifications (amide, ester, etc. linkages) of the polysulfur copolymers and to convert them into new polymers with different properties. With this project, the first examples of high sulfur content derivatives of polyesters and polyamides (like poly(S-r-OA)-PE) may have been synthesized by the chemical modification (esterification and amidation) of polysulfur copolymers. After inverse vulcanization process, the characterization of the obtained polysulfur copolymers will be done by using NMR, Raman, FTIR, UV, GPC, SEM, DSC, TGA etc., techniques. Electrochemical, optical, and material properties of the polymers will be investigated and tested as potential promising materials for use in Li-S batteries, heavy metal ions remediation and photocatalytic dye removal. The properties of obtained polymers will be compared with each other as well as with the literature data. Lastly, studies will be carried out to produce polymers in kg scale, and the applicability of the method to be applied to the industry will be tested. With reaching the project targets, it will be possible to polymerize elemental sulfur with the renewable vegetable fatty acids; therefore, huge amounts of sulfur can be used more effectively and an important step for sustainable synthesis/production in the polymer industry will be realized.