Additive-free ultrafast-curing-enabled 3D printing of high-strength blocked polyurethane elastomer

• Develops an additive-free, ultrafast-curing blocked polyurethane elastomer exhibiting a curing rate 28.6-fold faster than conventional systems. • Proposes a progressive curing-enabled extrusion printing process for rapid structural stabilization. • Produces as-printed components with tensile strength twice that of cast-molded counterparts. Single-component blocked polyurethane (BPU) elastomers have garnered significant interest in three-dimensional (3D) printing due to their controllable reactivity, environmental friendliness, and storage stability. However, their extremely slow curing rates significantly limit practical applications. Existing 3D printing strategies primarily incorporate additional components to enhance material printability, which increases formulation complexity, fails to fundamentally address the issue of slow curing, and in some cases compromises mechanical properties. To address this challenge, we develop an ultrafast-curing BPU (UBPU) elastomer through reactivity-optimized formulation design, achieving additive-free processing. The UBPU system attains a gelation time of approximately 3.15 min at the deblocking temperature, representing a 28.6-fold faster curing rate relative to conventional BPU systems. The UBPU also demonstrates a high evaporation rate of the blocking agent. Accordingly, we propose a progressive curing-enabled extrusion printing (PCEEP) method, wherein the UBPU elastomer is preheated in extruder to further accelerate blocking agent evaporation during layer-by-layer deposition, thereby enabling the rapid stabilization of printed structures. This enhanced evaporation mechanism improves tensile strength of as-printed UBPU parts by 2-fold compared to cast-molded counterparts. Our study provides an additive-free strategy and novel insights into high-performance thermosetting polyurethane (TSPU) elastomers for advanced 3D printing applications.