Convert Elemental Sulfur To Sulfur-containing Functional Polymers Through Transition Metal Catalyst-free Multicomponent Polymerizations

Sulfur is the third most abundant element in the earth's crust.The annual production of elemental sulfur is about 83 million tons,but its consumption is limited,and sulfur is mainly used in the preparation of sulfuric acid.Due to the flammable nature of sulfur and its gradual oxidation in air,the storage of sulfur can cause serious safety issues and environmental problems.On the other hand,sulfur-containing polymer materials play important roles in the fields of metal ion coordination,energy storage,self-healing materials,and biological imaging.Therefore,the preparation of sulfur-containing functional polymers directly from elemental sulfur is an ideal choice.However,the efficient transformation and utilization of sulfur is still quite challenging because of the poor solubility of sulfur in organic solvents and its toxicity to transition metal catalysts or free radical initiators.In recent years,multicomponent polymerizations?MCPs?have gradually become a class of highly efficient polymer synthetic methods,owing to their advantages such as simple operation and high efficiency,which are expected to be developed into effective approach for sulfur conversion.This thesis aims to explore elemental sulfur-based MCPs for the efficient construction of sulfur-containing functional polymer materials.Firstly,we developed multicomponent polymerizations of elemental sulfur,dicarboxylic acids,and diamines to prepare functional polythioamides.All monomers of the MCP are commercially available,and no transition metal catalyst is involved in the polymerization,enabling scalable preparation of polythioamides with a great diversity of well-defined structures,high M_ws?up to 86 200 g/mol?,and high yields?up to 99%?.In addition to the aliphatic diamine monomers which are commonly used in previously reported sulfur-based MCPs,aromatic diamine monomers are also suitable for this MCP,furnishing polythioamide structures with unique rigid structures and advanced functionalities.Furthermore,these polythioamides can be utilized in the efficient?>99.99%?,fast?1 min?,sensitive?10 ppb?,and selective extraction of Au³⁺from complex aqueous solutions with high extraction capacity of up to 0.6 g·Au³⁺/g.Elemental gold can be facilely recovered by pyrolyzing the polythioamide-Au³⁺complexes.These MCPs can not only utilize the abundantly existed industrial waste sulfur by converting it to sulfur-containing functional polymers on a large scale,but also can find application for the polymer products in the recovery of trace amount of precious metals in electronic wastes,demonstrating their great potential in resource utilization.Secondly,we developed base-catalyzed MCPs of elemental sulfur,diisocyanides,and diamines to prepare functional polythioureas.The addition of base enables the aromatic amines with low reactivity to be successfully applied to the polymerization.From these MCPs,12 polythioureas with great structural diversity and high M_ws of up to 107 700 g/mol were obtained in high yields of up to 99%.These polythioureas can efficiently remove Hg²⁺from aqueous solution,and the adsorption effect of the polythioureas prepared from aromatic diamines are generally better than that of the polythioureas prepared from aliphatic diamines,proving the importance of realizing the synthesis of polythioureas with rigid skeleton and conjugated structure.In addition,we designed a series of small molecular model reactions and proved that in the presence of base,the thiourea molecules can undergo transamination reactions,which could be used in the degradation of polythioureas.The dynamic covalent bond property of thiourea moieties could bring important guidance for the design of new sulfur-containing functional materials.This thesis mainly introduces two types of transition metal-free multicomponent polymerizations of sulfur to realize one-step conversion from elemental sulfur to sulfur-containing functional polymers under mild conditions.A group of polythioamides and polythioureas with great structural diversity were successfully synthesized from these MCPs,which were further applied in the selective adsorption of metal ions.The MCPs can not only lay the foundation for the convenient,efficient,and scalable synthesis of sulfur-containing functional materials,but also provide solutions for the problems regarding to sulfur utilization,gold enrichment,and mercury pollution.