Selective Laser Sintering (SLS) is one of the most mature and engineered polymeric 3D printing technologies, and the produced part is characterized by homogeneous polymorphism, which make the sintered material possess an ordered crystalline phase distribution and thus present a self-formed composite structure. This is due in large part to the special processing method during the SLS process. However, molecular motion mechanism between different phases remain unclear and further exploration is needed. Therefore, this paper firstly investigates the molecular motion mechanism concerning special composite phase structure of SLS-processed PA6 based on 2D correlation fourier transform mid-infrared (FT-MIR) spectra. The results show that although the crystal structure of the LT-α phase is less-ordered, the groups in LT-α change later than those in HT-α as the temperature increases. The overall movement sequence is: HT-α ˃ interphase ˃ LT-α, and the motion mode in the individual phase is the skeleton movement of carbon chains driven by H-bonds whereas the movement of interphase H-bonds is driven by the synergistic effect of the chain in HT-α. Besides, the symmetric methylene (v_s(CH₂)) vibrates firstly both for HT-α and LT-α, and then is the stretching vibration of asymmetric methylene (v_as(CH₂)).

选择性激光烧结（SLS）是最成熟和工程化的聚合物3D打印技术之一，所生产的零件具有均质多态性的特征，使烧结后的材料具有有序的结晶相分布，从而呈现出自形成的复合结构。这在很大程度上是由于SLS过程中的特殊处理方法。但是，不同相之间的分子运动机理尚不清楚，需要进一步探索。因此，本文首先基于二维相关傅里叶变换中红外光谱（FT-MIR），研究了SLS处理的PA6的特殊复合相结构的分子运动机理。结果表明，尽管LT-α相的晶体结构较不规则，随着温度的升高，LT-α中的基团变化比HT-α中的基团变化晚。整体运动顺序为：HT-α˃相间˃LT-α，单个相中的运动模式是由H键驱动的碳链的骨架运动，而相间H键的运动则由协同作用驱动HT-α中链的位置。此外，对称亚甲基v _s（CH ₂））首先对HT-α和LT-α振动，然后是不对称亚甲基（v _{a s}（CH ₂））的拉伸振动。