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.