Towards fast relaxation rates and creep resistance in disulfide vitrimer-like materials

Reaching a delicate balance between polymer flow for reprocessing and mechanical robustness at service temperatures remains a challenge in designing dynamic polymer networks. The demand for creep-resistant materials with fast relaxation rates at relatively low temperatures is a crucial research topic in the academic world. In this study, we present the preparation of a series of disulfide vitrimeric materials by curing two commercially available aromatic and aliphatic epoxy resins and cystamine. Through careful variation of the proportions between the epoxy resins, the properties of the final materials can be properly tailored. The completion of the curing was confirmed using FTIR spectrometry, and the thermal stability of all materials was evaluated by TGA. The thermomechanical properties were investigated using DMA analysis, obtaining glass transition temperatures (Tgs) above 60 degrees C and high rigidity in the glassy state depending on the proportion of the aromatic resin. Extensive stress relaxation tests unveiled remarkable vitrimeric behavior, with all materials capable of relaxing 63% of the initial stress in less than 2 min at 140 degrees C. The in-depth creep experiments not only allowed for determining material viscosity at high temperatures and the topology freezing temperatures (Tvs) but also offered control over dynamic stability at room temperature, depending on the initial formulation composition. Dilatometry and tensile tests provided further insights into the materials' characteristics. The self-healing and self-welding behavior enabled by the disulfide metathesis exchange reactions were also evaluated, revealing a total self-healing recovery process with short times and comparable tensile modulus in the welded samples. The facile preparation, commercial availability of monomers, and excellent thermosetting and vitrimeric properties highlight the immense potential of this series of materials.