Green polysulfides from renewable monomers: a challenge towards sustainability

Large volumes of elemental sulfur derived from oil industry are stored unused, causing the global "excess sulfur problem". In the last few years an interest in exploring the use of sulfur as a low cost starting material for the synthesis of sulfur rich-polymers with interesting optical, electrical and antibacterial properties has emerged. [1-4] Here, the catalytic inverse vulcanization of low cost monomers, including monomers coming from renewable sources or by-products and waste, to obtain sustainable materials is reported. Epoxides such as limonene oxide (LO), epoxidated vegetable oil, and dipentene and grape seed oil have been explored as monomers. The synthesis of poly(S-dipentene), poly(S-epoxides) with a sulfur content higher than 50 wt % in the presence of zinc-based accelerators which act reducing the mixing time between monomer and melted sulfur was investigated. Accelerators, probably acting as phase transfer, reduced the time required for mixing of dipentene and melted sulfur and the best results were obtained with zinc tetrabutyl-bis(phosphorodithioate). [5] Poly(S-dipentene) stability was improved adding a second bio-based crosslinker such as garlic oil (GO), diallyl disulfide (DAS) and myrcene (MYR). The ter-polysulfides obtained are soft solids with glass transition temperature (Tg) ranging from -1 to 4 °C with wax-like aspect. In order to give them shape persistence for possible applications, polystyrene-polysulfide blends were obtained. Porous polystyrene blends, prepared via the salt templating technique, have shape persistence and Tg value of 44 °C. They were found to be able to remove ferric ions from aqueous solution for applications in wastewater purification. [5] The synthesis and characterization of poly(S-LO), and of polysulfide-based on grape seed oil and soybean oil will be also reported.