Construction Of Rigid-Flexible Block Supramolecular Aggregates Based On Imine Bonds

Supramolecular chemistry is the study of the process in which two or more molecules are driven by one or more forces and spontaneously arrange or aggregate from disorder to order,which can form a stable structure with a certain geometric structure.This process is usually dynamically balanced.The driving forces for supramolecular self-assembly include non-covalent interactions such as hydrogen bonding,?-? stacking,metal-coordination,van der Waals forces,dipole-dipole interactions,hydrophilic and hydrophobic interactions,host-guest interactions,and electrostatic interaction and so on.With the development of supramolecular chemistry,dynamic covalent chemistry has attracted widespread attention because it also has dynamic reversible characteristics and stronger interaction forces than non-covalent bond interactions.The use of dynamic covalent chemistry provides another feasible way for people to construct new stimuli-responsive structures,self-healing hydrogels,and nano-vesicle for drug delivery.Dynamic imine bonds have attracted widespread attention due to their fewer reaction by-products,but they are prone to hydrolyze in aqueous solutions.Therefore,the construction of an imine bond that can stably exist in an aqueous solution is crucial to its function in the living system.In this paper,we have successfully designed and synthesized amphiphilic rod-coil monomer molecules A1 and B1 with aromatic aldehyde as rigid units and polyethylene glycol(PEO)chains as flexible units.They react with Benzidine under different pH conditions,a series of polymers product with dynamic imine bonds TMa and TMb were obtained,and their characterization was determined by 1H-NMR and ATR-IR.It was confirmed that the imine bonds were hydrolyzed under strong acid conditions and could be not stabilized exist;under weak acid and alkaline conditions,aldehyde group and amino group react to form imine bonds and the content of imine bonds increases.Subsequently,the self-assembly behavior of imine bond formation in its aqueous solution was investigated by means of UV-FL spectroscopy,CD,TEM,and AFM.The experimental results show that in dilute solutions,the monomer molecules are assembled into short nanotubular structures,and the mixture still retains the nanotubular structure under strong acid conditions;in weak acid and alkaline conditions,increasing the value of pH and the content of imine bonds increases,its self-assembly changes from a short nanotubular structure to a nanosheet structure.Due to the the content of imine bonds increases,and the ?-? stacking effect is enhanced,which makes the polymer structure tend to be planar,which is conducive to the formation of nano-sheet structures.When the pH was reduced to acidic,the DLS results showed that the size of the self-assembled aggregates changed dynamically and reversibly.