Investigation of crystal habit of N,N′-dicyclohexylterephthalamide and its influence on the crystallization behavior of isotactic polypropylene

In this paper, the N,N′-dicyclohexylterephthalamide (DCHT) with various morphologies and sizes was prepared by antisolvent precipitation at room temperature, and DCHT single crystals were also grown. Among them, DCHT crystals precipitated from deionized water (H₂O), alcohol (C₂H₅OH) and N′N-dimethylformamide (DMF) are particle-like crystallites (DCHT-H₂O), cuboid (DCHT-C₂H₅OH) and large rectangular crystals (DCHT-DMF), respectively. The powder XRD results show that the (002) plane is the dominant growth plane of the DCHT crystals, and the diffraction peak intensity of (100) plane is negatively correlated with the size of the DCHT crystals. The single-crystal XRD results show that the minimum distance between the two nearest DCHT molecules is the hydrogen bond distance (2.21 Å), and the (100) crystal plane is the plane of hydrogen bonding between DCHT molecules. Thus, it is speculated that the hydrogen bonding interaction is the main driving force for the growth of DCHT crystals. Further, the effect of different morphologies and sizes of DCHT on isotactic polypropylene (iPP) crystallization was investigated. Non-isothermal crystallization studies revealed that the DCHT size plays a decisive role in increasing the crystallization temperature of iPP. Through isothermal crystallization, it was found that the upper critical temperature of β-α growth “transition” of iPP could be related to the morphology of DCHT. Finally, the iPP film was attached to the surface of DCHT single crystal, and its crystallization behavior was studied. It is confirmed that the (001) plane is the epitaxial plane of DCHT to the β-iPP molecular chain, while the epitaxial plane of β-iPP is the (110) plane.