Post-Printing Manipulation of Material Mechanical Properties via Synergistic Engineering of Dynamic Polymer Network and Phase Separation.

The coupling of 3D printing process constraints and material molecular design makes it difficult to simultaneously achieve sophisticated structural fidelity and desirable mechanical performance. Topological reconfiguration of dynamic covalent polymer networks imparts materials with the capability to modulate their properties as needed post fabrication. However, prior studies had only achieved a limited modulation range because material properties depend solely on the polymer network structure. Herein, we introduce phase separation into a 3D printable dynamic covalent polymer network to enable significant mechanical property modulation in geometrically complex 3D objects. Specifically, the printing resin precursor comprises a crosslinker functionalized with dynamic hindered urea bonds and non-photocurable polyethylene glycol monomethyl ether. A rigid construct is first obtained via photopolymerization-induced phase separation during printing. Subsequent activation of dynamic bond exchange reactions enables simultaneous tailoring of both the network topology and phase morphology, realizing broad-range mechanical tunability with a modulus spanning three orders of magnitude from 0.47 GPa to 0.5 MPa. This remarkable on-demand rigid-to-soft transition allows 100 μm printing resolution to be readily achieved, overcoming the limitations of 3D printing in fabricating soft functional materials with high structural fidelity.