Comonomer Partition of PA6T/66 Random Copolymers Induced by Coupled Temperature and Pressure Fields

The semi‐aromatic co‐polyamide PA6T/66, known for its high thermal stability, low moisture absorption, and promising melt‐processability, is generally regarded as a typical eutectic copolymer. However, there is no adequate understanding of the eutectic behavior under the coupled field of temperature and pressure that widely exists in melt processing. In this work, a series of PA6T/66 samples crystallized under coupled temperature‐pressure fields were investigated using a combination of differential scanning calorimetry and in situ wide/small angle X‐ray scattering. Unexpected multi‐stage melting indicated comonomer partition across cocrystal domains, providing evidence of pseudo‐eutectic behavior. Under coupled temperature‐pressure fields, segments with long 6T sequences aggregated and formed cocrystals at a higher temperature, while the excluded segments with shorter 6T sequences subsequently formed cocrystals at a lower temperature. This led to the generation of cocrystals with different compositions of 6T repeat units. This work clarifies the structure evolution of PA6T/66 under coupled temperature‐pressure fields and provides an efficient strategy for the performance improvement of semi‐aromatic polyamide copolymer products.