Supramolecular Adhesives Based On Crown Ether

Through non-covalent bond interactions(including hydrogen bonding,host-guest recognition,van der Waals forces,metal complexation,hydrophilicity and hydrophobicity,?-?stacking,etc.),supramolecular adhesives could not only increase the intermolecular cohesion,but also facilitate the adhesion of a variety of substrates or biological tissues.Compared with most polymer adhesives which are difficult to recycle,supramolecular adhesives show good recycling performance which can save energy and reduce pollution.At present,supramolecular polymer adhesives are mainly formed by non-covalent interactions such as hydrogen bonding,host-guest recognition,and metal coordination.In addition,supramolecular adhesives based on small molecules have appeared.In recent years,we have also developed water-induced crown ether-based supramolecular polymer adhesives,providing new methods and ideas for the preparation of recyclable adhesives.In order to further broaden the application of crown ether-based supramolecular polymers as adhesives,we conducted the following explorations:In the second part,dibenzo-24-crown-8(DB24C8)was introduced into pentaerythritol through condensation reaction to obtain the four-arm compound P1with low molecular weight.P1 has good long-term adhesion properties on various surfaces,and its maximum adhesion strength reached to 4.174 MPa.The supramolecular adhesive not only exhibits stable and long-term adhesion in high humidity and water environment,but also exhibits excellent adhesion in seawater.In addition,we can use P1 to quickly prepare a uniform adhesive layer by electrospinning technology,which can save energy and reduce pollution.The application of this adhesive to repair holes quickly and the long-term underwater adhesion experiments show that the low-molecular-weight adhesive has great application potential as a water-resistant,moisture-proof and marine adhesive.In the third part,we designed and synthesized the pillar[5]arene-crown ether hybrid monomer PC.The introduction of water molecules and the formation of hydrogen bonds not only initiated the supramolecular polymerization,but also gave PC-water copolymer the low temperature resistance.In the supramolecular polymer system,the content of water molecules plays a vital role in the adhesion behavior at low temperature.At low temperature,the water molecules in high-water-content samples tend to aggregate into clusters and there is obvious phase separation,making PC-water copolymer only exhibit adhesion behavior similar to pure water.However,supramolecular copolymers triggered by a small amount of water molecules will not cluster even at very low temperature.In this circumstance,water is structural water.Dielectric spectroscopy,low-temperature rheology and molecular dynamics simulations prove that water molecules are still part of the copolymer without phase separation at extremely low temperatures.This is also the key reason why supramolecular polymers have strong adhesion at extremely low temperature environment,even in liquid nitrogen.The systhesis of the extremely low-temperature-resistant supramolecular adhesive provides a new method and a new idea for the design of supramolecular adhesive applied in extreme environment.In the fourth part,the 1,3,5-benzoic acid derivative TC7 self-assembled into one-dimensional supramolecular aggregates in chloroform,and then the aggregates formed cross-linked supramolecular polymers via host-guest complexation between B21C7 and secondary ammonium salts.After the concentration of TC7 was fixed,the optimal molar ratio of TC7 to bis-secondary ammonium salt was determined by NMR titration with gradual addition of bis-secondary ammonium salt.The crosslinked polymer was detected by concentration dependent ~1H NMR,DOSY,D_Hand viscosity tests.Compared with one-dimensional linear supramolecular polymer,cross-linked supramolecular polymer has higher viscosity and lower diffusion coefficient,and soft viscoelastic fiber is prepared from its concentrated solution.The introduction of bis-secondary ammonium salt crosslinking agent not only makes the supramolecular polymer form macro aggregates,but also facilitates the stimulation response.These supramolecular polymers provide us with a new understanding of supramolecular polymerization process.In the fifth part,we obtained AABB monomer J-click by click reaction.The AABB monomer self-assembled into a network supramolecular polymer by heating.The polymer not only can adhere to hydrophilic substrate,but also has high temperature resistance.In contrast,the linear supramolecular polymer(B-click)can withstand higher temperature to some extent,but it is obviously weaker than the network supramolecular polymer.In addition,J-click is insoluble in water and has long-term adhesion even in salt solutions such as sodium chloride,ferric chloride and copper chloride.In addition,the adhesion-deadhesion process of supramolecular adhesives can be inversely controlled by doping micro multi-wall carbon nanotubes,which provides a new design idea for the preparation of supramolecular adhesives for stimulus responsive applications.