Inverse Vulcanized Polymers with Shape Memory, Enhanced Mechanical Properties, and Vitrimer Behavior.

The invention of inverse vulcanization provides great opportunities for generating functional polymers directly from elemental sulfur, an industrial by-product. However, unsatisfactory mechanical properties have limited the scope for wider applications of these exciting materials. Here, we report an effective synthesis method that significantly improves mechanical properties of sulfur-polymers and allows control of performance. A linear pre-polymer containing hydroxyl functional group was produced, which could be stored at room temperature for long periods of time. This pre-polymer was then further crosslinked by difunctional isocyanate secondary crosslinker. By adjusting the molar ratio of crosslinking functional groups, the tensile strength was controlled, ranging from 0.14±0.01 MPa to 20.17±2.18 MPa, and strain was varied from 11.85±0.88 % to 51.20±5.75 %. Control of hardness, flexibility, solubility and function of the material were also demonstrated. We were able to produce materials with suitable combination of flexibility and strength, with excellent shape memory function. Combined with the unique dynamic property of S-S bonds, these polymer networks have an attractive, vitrimer-like ability for being reshaped and recycled, despite their crosslinked structures. This new synthesis method could open the door for wider applications of sustainable sulfur-polymers.