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关键组成成分。近年来，将环糊精(cyclodextrins, CDs)穿接至二胺单体以提升所得聚合物水溶性与热稳定性的研究逐渐受到广泛关注。
通常采用共沉淀法分离得到芳香二胺与其他微溶于水的芳香客体分子和β-CD形成的包合物(inclusion complexes, ICs)。为探究其他制备方法的可行性，我们通过热水混合法、共沉淀法与固态研磨法，研究了β-CD与部分芳香二胺之间的包合物形成过程。
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-CD水溶液中，辅以高速磁力搅拌。与之相对，固态研磨法则通过添加少量水以促进包合物生成。
经热水混合法与固态研磨法制得的包合物，均通过冷却至4 ℃从水溶液中结晶析出。
溶液中包合物的结构通过以下两种方式得以验证：一是β-CD空腔质子在氢核磁共振波谱(¹H NMR)中的化学位移变化，二是氢-氢旋转坐标系核奥弗豪泽增强谱(¹H-¹H ROESY NMR)中芳香质子与空腔质子之间的交叉峰。
我们采用Job作图法(Job’s plot)与核磁共振滴定实验(NMR titration experiments)，测定了溶液中主客体的化学计量比。