Enabling the Epoxy-Based Polyurea with Adjustable Mechanical Properties, Recyclability, and 3D Shape Configuration

Thermosetting epoxy resins are frequently restricted by their inferior toughness, nonprocessability, and nonrecyclability resulting from their permanently cross-linked molecular network structure and the rigidity of their molecular chains, limiting the promotion of their additional value. Based on our previous research on the hindered urea bonds (HUBs), herein, we incorporated HUBs with isocyanates into the traditional epoxy network, synthesizing epoxy-based polyurea, namely, EHTPUs. The EHTPUs were synthesized by using commercial raw materials containing HDI-trimers, 2,6-dimethyl piperazine, and difunctional epoxides (E44 or PPGE) without a catalyst. By modulation of the proportion of epoxy monomers, these synthetic EHTPUs exhibit adjustable mechanical behavior, transitioning from soft elastomers to hard plastics. The dynamic HUBs can endow these EHTPUs with excellent recyclability, where their mechanical properties can be fully recovered (above 90%) after four cycles, elevating the versatility and long-term lifespan. Importantly, their dynamic mechanical properties, solvent resistance, and transmittance also can remain stable after four cycles. Meanwhile, the EHTPUs possess elastic shape memory and a 3D permanent shape reconfiguration capability in the same sample. Our work provides a fascinating way to design adjustable mechanical properties, recyclability, and multifunctionality thermosetting epoxy-based polymers, accelerating this category of recyclable polymers toward application and functionalization.