Elemental Sulfur-Based Scalable Synthesis of Functional Polythioureas and co-Polythioureas with Tunable Mechanical...

Polythioureas with fascinating features have attracted widespread attention recently, owing to their high refractive index, excellent metal coordination ability, adhesive property, self-healing ability, and so on. However, their systematic property investigation was hindered by synthetic approaches for large-scale preparation. Herein, facile synthesis of 120 g-scale polythioureas was realized through the design of an efficient and robust base-free multicomponent polymerization of elemental sulfur, malonic acid, and diamines in DMSO. The polymerization could be applied to both aromatic and aliphatic amine monomers, affording a series of functional aromatic and aliphatic polythioureas with high molecular weights (M_w up to 65,100 g/mol) in excellent yields (up to 99%). Multicomponent copolymerization using different diamine monomers was investigated, and 25 different polythioureas or copolythioureas with well-defined structures were successfully obtained. An interesting odd-even effect was observed for aliphatic polythioureas with different alkyl chain spacers on their molecular weight, thermal property, processability, and so on. The mechanical property of most of these aliphatic polythioureas/copolythioureas was first reported, which showed excellent mechanical performance with tensile strength (σ_B) of 37 MPa and elongation at break (ε_B) of 365%. Their tensile strength could be dramatically enhanced to 70.0 MPa after uniaxial extension deformation, and excellent adhesive performance was proved on copper substrate with a large room-temperature adhesion strength of 12.8 MPa. The aromatic polythioureas possessed high refractive indices up to 1.8661 at 589 nm and good transmittance, showing potential as advanced optical materials. Benefiting from the three facilely available economic industrial monomers, simple one-pot operation, robust base-free condition in air, and high efficiency of the multicomponent polymerization, the facile preparation of large-scale and diversified polythioureas was realized, paving the way for functionality and application exploration of these promising sustainable sulfur-containing polymer materials.