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.