Preparation Of Supramolecular Polymers Based On Hydrogen Bonding And Their Adhesion Applications

Supramolecular polymers are polymeric materials formed by the self-assembly of monomers through non-covalent interactions such as hydrogen bonds,host-guest recognition,and metal coordination bonds.As one of the non-covalent interactions,hydrogen bonding has the advantages of directionality,dynamic reversibility,and rich formation modes,and is widely used in the construction of functionalized supramolecular polymers.Moreover,hydrogen-bonded supramolecular polymers have many interesting properties,such as stimuli-responsiveness,high viscosity,self-adaptability,etc.,and have a wide range of applications in electronic skin,adhesives,drug delivery,and other fields,which has attracted widespread attention from researchers.In this paper,we synthesized a series of novel hydrogen-bonded supramolecular polymers from the design of functional monomers and supramolecular polymerization strategies,and applied them to adhesion and other aspects.In the first part,we combined the two different concepts of deep eutectic solvent and supramolecular polymerization and proposed a new strategy to prepare supramolecular polymer bulk materials.Cyclodextrins and natural organic acids were used as monomers,and a series of eutectic supramolecular polymers were obtained by one-pot method.During the preparation of supramolecular polymers,cyclodextrins and acids acted as both monomers and solvents.Hydrogen bonding interaction between cyclodextrins and carboxylic acids could disrupt their original crystalline structures and transform them from non-viscous solid powders to highly viscous gelatinous substances.Tensile test experiments showed that the eutectic supramolecular polymer exhibited excellent adhesion to various substrate surfaces（6.57 MPa for steel）.It was worth mentioning that the supramolecular polymer also showed high adhesion strength to the substrate surface in dichloromethane（3.25 MPa for steel）.Here,we proposed a simple and efficient strategy to prepare supramolecular polymer bulk materials,which enriches the preparation methods and types of supramolecular polymer bulk materials,and also expands the application scope of deep eutectic solvents.In the second part,we obtained a series of supramolecular polymers based on acids and sugars（acid@sugar supramolecular polymers）from natural small molecule sugars and organic acids.¹H NMR,two-dimensional nuclear magnetic resonance,FTIR,theoretical calculation and other methods were conducted to study in detail the intermolecular interactions within the polymer.It was found that the main interaction between monomers is hydrogen bonding.The abundant hydrogen bond network endows the supramolecular polymer with high viscosity,which could be used as a kind of adhesive material.This supramolecular polymer not only showed excellent adhesion performance to hydrophilic/hydrophobic surfaces at room temperature（5.42 MPa for steel）,but also had good adhesion strength at low or high temperature.At the same time,the acid@sugar adhesive material has thermal response characteristics,which makes it easy to process and recycle,and can be recycled for many times during the adhesion process.So,the waste of acid@sugar adhesion materials could be avoided.It was worth mentioning that the acid@sugar adhesion material had strong adhesion performance in low-polarity organic solvents.This work further expanded the application scope of supramolecular polymers,and also provided a new research idea for the preparation of organic solvent-resistant adhesives.In the third part,we selected natural nucleosides as monomers and prepared a series of low-molecular-weight supramolecular polymer glasses through a simple one-pot method.SAXS,PXRD,theoretical simulation calculations and other methods were performed to confirm that supramolecular glasses are a typical anisotropic substance.In other words,short range is ordered and long range is disordered in the system.Meanwhlie,supramolecular glasses had good processing properties,and its macroscopic morphology could be easily changed under heating conditions.Moreover,the supramolecular glasses also had high tensile strength（1.23 MPa）and compressive strength（3.3 MPa）due to its rich internal hydrogen bond network.Compared with commerical organic glass（PMMA）,supramolecular glasses showed more tolerant to common organic solvents.The formation process of supramolecular glasses was further explored using two-dimensinonal infrared spectral and theoretical calculations.It was found that high viscosity of supramolecular glasses could inhibit the precipitation of nucleoside crystals,which leaded to the formation of them.This work provided a new idea for the design of new low-molecular-weight supramolecular glasses.In the fourth section,we prepared a novel low-molecular-weight supramolecular adhesive material.This adhesive material had high adhesion strength to various substrate surfaces at low temperatures,including glass,iron,PMMA,and PTFE.Moreover,after long time（46 days）supramolecular adhesive still had good adhesion performance.Compared with traditional low-temperature-resistant adhesives,the supramolecular adhesive material could achieve low-temperature adhesion performance without adding other antifreeze components（such as glycerol or water）,which simplified the preparation process of the adhesion layer.In addition,various test substrates could be real-time adhered by the supramolecular adhesive in ice water,and the adhesion effect was strong.This work not only enriched the types of low-temperature-resistant supramolecular adhesive materials,but also provided a new idea for the design of underwater adhesive materials.In the fifth section,we prepared a novel low-molecular-weight gelator by the amide reaction between crown ether derivatives and fluorobenzoic acid.¹H NMR,DOSY,dynamical lighting scattering（DLS）and other methods were carried out to study low critical transition temperature（LCST）behavior of the gelator in aqueous solution or hydrogel.It was found that the gelation of gelator in water was mainly induced by its LCST behavior.When test temperature was higher than the cloud point temperature(T_cloud),the gelator was aggregated in water to form aggregates visible to the naked eye,and then the aggregates were further self-assembled into a three-dimensional network structure of hydrogel.This work provided a novel idea for studying the formation mechanism of supramolecular hydrogels.