Active Segment Polymerization of 1,3-Propanediamine Enables Low-Melting-Point Polyamides for High-Precision 3D Printing

Abstract The preparation of ultra-short-chain diamine-based polyamides by melt polycondensation remains a formidable challenge in polyamide synthesis, with 1,3-propanediamine (DAP) serving as a representative monomer. To date, the fundamental reasons why this monomer fails to yield satisfactory polymeric products via melt polycondensation remain unclear. Here, we employed quantum chemical calculations to identify DAP polymerization transition states, reaction pathways, and energy barriers, thereby elucidating the molecular origins of the polymerization challenges. The theoretical predictions were further validated by experimental results. Based on the above mechanistic insights, we developed a living chain-segment polymerization strategy that effectively suppresses side reactions, enabling the facile synthesis of a novel structurally tunable low-melting-point polyamide (LMPA), PAX(12312). These LMPAs exhibit exceptional mechanical properties, including a tensile strength of 55 MPa, an elongation at break exceeding 500%, and an impact strength retention of 13.9 kJ/m2 at –30 °C, along with a tunable melting range. Notably, they also feature a low saturated water absorption of 1.25%, a narrow molecular weight distribution of 1.6–2.0, and superior processability. The low processing temperature and high melt stability of these LMPAs confer unique advantages for 3D printing, enabling the fabrication of warp-free, high-precision components.