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 β-CD. To find the viability of other methods, we studied IC formation between β-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 β-CD aqueous solution at 80 °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 °C. Structures of the ICs in solution were confirmed by chemical shifts changes of cavity protons of β-CD in 1H NMR and the cross-peaks between aromatic protons and cavity protons in 1H-1H ROESY NMR. Job’s plot and NMR titration experiments were used to determine the stoichiometric ratio of host and guest in solution.芳香二胺是聚酰亚胺及诸多其他热固性聚合物的核心组成成分。近年来，将环糊精（cyclodextrins，CDs）穿入二胺单体以提升所得聚合物水溶性与热稳定性的研究日益受到关注。 共沉淀法常被用于分离芳香二胺与其他微溶于水的芳香客体分子和β-环糊精（β-CD）形成的包合物（inclusion complexes，ICs）。为探究其他方法的可行性，我们通过热水混合法、共沉淀法与固相研磨法，研究了β-环糊精与部分芳香二胺之间的包合物生成行为。 热水混合法制备包合物的具体操作为：将固体客体分散于80℃的β-环糊精水溶液中，辅以高速磁力搅拌。与之相对，固相研磨法则通过添加少量水来促进包合物的生成。 经热水混合法与固相研磨法制备的包合物，均通过降温至4℃从水中析出结晶。 溶液中包合物的结构，通过1H核磁共振谱（1H NMR）中β-环糊精空腔质子的化学位移变化，以及1H-1H旋转坐标系核Overhauser效应谱（1H-1H ROESY NMR）中芳香质子与空腔质子间的交叉峰得以确证。 我们采用Job图（Job’s plot）与核磁共振滴定实验，测定了溶液中主客体的化学计量比。