Sulfur-or Selenium-containing Polymers Prepared From Elemental Chalcogen Via Multicomponent Polymerizations

As a group of functional materials,sulfur-or selenium-containing polymers have attracted much attention owing their wide applications in self-healing materials,precious-metal recovery,high refractive index materials,biotherapy,and optoelectronic devices.However,the lack of efficient synthetic methods and safe and economic monomers have restricted the development and practical application of sulfur-or selenium-containing polymers.Multicomponent polymerizations（MCPs）featured with simple operation,high efficiency,atomic economy,and structural diversity of polymer products are recently favored by polymer scientists.Meanwhile,elemental chalcogen is the ideal monomers for the preparation of sulfur-or selenium-containing functional polymers considering their advantages such as economic and safe.Therefore,the development of elemental chalcogen-based MCPs is expected to promote the development of sulfur-or selenium-containing polymers,which possesses both academic significance and industrial value.In this dissertation,we have developed three MCPs to synthesize a series of new sulfur-or selenium-containing functional polymers directly from elemental sulfur or selenium,and have explored the functionalities of these sulfur-or selenium-containing polymers.The detailed contents of this dissertation are as follows:Firstly,we have developed the catalyst-free MCPs of elemental selenium,diisocyanides,and diamines to synthesize polyselenoureas with well-defined structures,long-term stability,and good solubility.The polymerization can be completed in only 1 min at 100 ^oC or 45 min at40 ^oC,which is not only applicable for aliphatic or aromatic diisocyanides and aliphatic primary or secondary amines,the less nucleophilic aromatic diamines can also be polymerized smoothly,affording a series of polyselenoureas with high molecular weights（M_ws up to 96 900 g/mol）and high yields（>99%）.In addition,through the design and synthesis of polymer structure,polyselenoureas with aggregation-induced emission（AIE）feature and antibacterial property are obtained,revealing the potential application of polyselenoureas as luminescent materials and biological materials.Secondly,we have developed the MCPs of elemental selenium,diisocyanides,and dipropargyl alcohols at room temperature to prepare poly（oxyselenoalicyclic）s,as the first example of the construction of polymers with selenium-containing alicyclic structures.The polymerization could be carried out in the presence of DBU at room temperature for 4 h to prepare poly（oxyselenoalicyclic）s with well-defined structures,high molecular weights（M_ws up to 15 600 g/mol）,and high yields（up to 93%）.All the polymers possess excellent solubility and can be dissolved in common organic solvents such as tetrahydrofuran,dichloromethane,chloroform,or dimethyl sulfoxide.With the good thermal stability and acid/alkali resistance,the M_ws of the polymers could remain stable with the treatment of organic/inorganic acids or bases.Through structural design of the polymer products,poly（oxyselenoalicyclic）s with high refractive index（up to 1.8026 at 632.8 nm）and high light transmittance（>94%）are afforded,revealing the potential application of these selenium-containing polymer as optical materials.Thirdly,we have developed the MCPs of elemental sulfur,diisocyanides,and diols in the presence of Na OH to prepare poly（O-thiocarbamate）s.The polymerization was carried out at40 ^oC or room temperature to prepare poly（O-thiocarbamate）s with well-defined structures,high molecular weights（M_ws up to 32 500 g/mol）and high yields（up to 99%）.The polymerization enjoys wide monomer scope,including aliphatic or aromatic diisocynaides,and diols.Taking advantage of the strong coordination of sulfur and Au³⁺,the poly（O-thiocarbamate）s could be utilized to enrich Au³⁺from aqueous solution with high enrichment capacity(983 mg·Au³⁺/g)and high efficiency（>99.99%）in 1 min,demonstrating its industrial and economic value.Finally,we have designed and synthesized four types of sulfur-or selenium-containing polymers including polyselenoureas,polythiourea,poly（O-thiocarbamate）,and polythioamide with similar polymer skeletons and carefully characterized their chemical structures.The performance in gold enrichment under different conditions(such as different dosages,p H,temperatures,and Au³⁺initial concentrations)of the four types of sulfur-or selenium-containing polymers were investigated and compared.The poly（O-thiocarbamate）enjoys the highest enrichment capacity of 860 mg·Au³⁺/g.It’s demonstrated that these sulfur-or selenium-containing functional polymers have strong tolerance to the variable external environment.Furthermore,we also utilize polyselenoureas to recover Au³⁺from the leaching solution of discarded electronics and lake water.High selectively,sensitivity（<1μg/L）,efficiency（>99.99%）,and enrichment capacity(818.40 mg·Au³⁺/g)are realized within 1 min.The non-renewable resources of gold can be recovered from direct pyrolysis,affording 92.15 wt%gold content in the resultant residue.It is anticipated that these sulfur-or selenium-containing functional polymers may find their potential application in gold recovery with great economic and environmental implication.