Comparative study of inclusion complex formation between β-cyclodextrin (host) and aromatic diamines (guests) by mixing in hot water, co-precipitation, and solid-state grinding methods

Aromatic diamines are essential components of polyimide and many other thermosetting polymers. Recent attention has been growing on the threading of cyclodextrins (CDs) onto diamine monomers intended to improve the solubility in water and thermal stability of resultant polymers. The co-precipitation method is often used to isolate inclusion complexes (ICs) of aromatic diamines and other sparingly water-soluble aromatic guest molecules with beta-CD. To find the viability of other methods, we studied IC formation between beta-CD and some aromatic diamines by mixing in hot water, co-precipitation, and solid-state grinding. ICs formation in water was carried out by solid guest dispersion into the beta-CD aqueous solution at 80 degrees C with high-speed magnetic stirring. In contrast, solid-state grinding was employed by adding a small amount of water to promote IC formation. Thus, ICs prepared by mixing in hot water and solid-state grinding methods were crystallized from water by cooling to 4 degrees C. Structures of the ICs in solution were confirmed by chemical shifts changes of cavity protons of beta-CD in H-1 NMR and the cross-peaks between aromatic protons and cavity protons in H-1-H-1 ROESY NMR. Job's plot and NMR titration experiments were used to determine the stoichiometric ratio of host and guest in solution.

Automated summary

Aromatic diamines play a crucial role in polyimide and other thermosetting polymers. This study focuses on the threading of cyclodextrins onto diamine monomers to improve the solubility and thermal stability of resulting polymers. The co-precipitation method is commonly used to isolate inclusion complexes (ICs), but other methods were explored in this study. The formation of ICs between beta-cyclodextrin and aromatic diamines was investigated using hot water mixing, co-precipitation, and solid-state grinding.