Selective Growth of Conformational Polymorphs with Distinct Morphologies by Adding Different Polymers

Understanding the relationship between polymorphs and crystal growth is crucial for polymorph control. Here, the polymorph growth of pimelic acid (DA7) was investigated in aqueous solutions containing different polymers. The stable form III was obtained in an aqueous solution at a supersaturation level of S = 1.3 at 298.15 K. However, DA7-crystallized into form II in the presence of polyacrylamide (PAM) or poly(vinyl alcohol) (PVA). Moreover, form II developed distinct morphologies in PAM and PVA aqueous solutions. Face indexing according to single-crystal X-ray diffraction (SCXRD) revealed that two form II crystals had completely different faces. In situ crystal growth monitoring confirmed that the specific growth of faces was the key factor in determining the resulting polymorph. The preferential adsorption of additives on certain faces governed their growth according to molecular dynamics simulation. Additionally, the additives can modify the surface roughness of the crystals, thereby affecting their growth. Our work demonstrated that the crystallization of the targeted polymorph product can be achieved via varied growth pathways.