Decoupling Shape Retention from Polymerization Kinetics Enables Ambient-Temperature 3D Printing of Polystyrene

Polystyrene (PS) is a widely used polymer with numerous structural and functional applications, yet its additive manufacturing remains highly constrained. Conventional Fused Deposition Modeling (FDM) relies on the extrusion of pre-polymerized thermoplastic filaments at temperatures exceeding 230 °C, due to the high softening point of PS, and cannot produce crosslinked architectures. This aspect limits design freedom, energy efficiency, and material performance. Here, we introduce a paradigm-shifting approach for ambient-temperature extrusion of PS using an oil-in-water high internal phase emulsion (HIPE) ink composed of styrene and divinylbenzene dispersed in an aqueous phase. UV irradiation during deposition induces instantaneous crosslinking of the continuous phase, forming a thin hydrogel scaffold that confers structural integrity, while subsequent thermal curing converts the oil phase into dense PS. This dual-curing strategy decouples shape retention from polymerization kinetics, allowing for the printing of complex constructs at room temperature. Compression tests reveal exceptional mechanical performance, with a yield stress comparable to that of benchmark FDM polymers (ABS and PETG) and a maximum compressive stress exceeding their values by more than twofold, highlighting the robustness of interlayer cohesion achieved through in-situ crosslinking. Beyond PS, this versatile approach could unlock new possibilities for scalable, energy-efficient manufacturing of advanced polymer architectures, redefining the boundaries of additive manufacturing.