Study On The Synthesis And Properties Of Polyurethanes With Boron-Nitrogen Coordination

Nitrogen-coordinated boronic esters have been widely used to build the self-healing and reprocessable cross-linked polymers.The boron-nitrogen(B-N)coordination bonds,which forming between the boronic esters and its ortho-amino,or between the boronic esters and electron riched nitrogen-containing small molecular additives,significantly improve the water-resistance and reversibility of boronic esters,but merely contribute to the strength enhancement of the polymer materials.Supramolecular interactions,such as metal-ligand and hydrogen bonds,have significant advantages in building robust self-healing and reprocessable intelligent materials,and several advanced functional materials with excellent performance have been developed.Herein,we propose a novel strategy of synergistically functionalized boronic esters and B-N coordination in polymers to achieve high performance.The dihydroxyl-bearing boronic ester and nitrogen-containing diol are separately incorporated into the backbone of polyurethanes,in which the formation of B-N coordination bonds dramatically enhances the interaction between the polyurethane chains.The room temperature self-healing,high energy absorption and reprocessablility in polyurethanes are successfully implemented,while their structure-property relationships are systematically investigated.The main contents of this thesis include the following three aspects.1)The preparation and study of reprocessable polyurethanes containing nitrogen-coordinated boronic ester structures.A dihydroxyl-bearing boronic ester was successfully synthesized and the spatial structure of the boronic esters and the influence of B-N coordination on the dynamic characteristics of boronic esters were investigated by the density functional theory(DFT),and the calculated results show the length of B-O bonds was increased from 1.369(?)to1.451(?),indicating that the dissociation of boronic esters was accelerated and easily due to the formation of B-N coordination.In further,we explored the application of nitrogen-coordinated boronic esters in the construction of reprocessable cross-linked polyurethanes.The tensile test results demonstrate that B-N coordination bonds significantly improve the mechanical properties of polyurethanes,and the cross-linked polyurethanes with nitrogen-coordinated boronic esters can quickly relax the stress,the sample with cross-linking index of 10(PU-10)can relax its stress to zero within 1 h.The recycled PU-10,which was obtained by hot-pressing for 30 min,shows the similar mechanical properties to the initial one.In addition,the cross-linked polyurethanes based on nitrogen-coordinated boronic esters demonstrate self-healing ability with the aid of water at room temperature.2)The preparation and properties of room temperature self-healing polyurethanes.A series of novel polyurethanes are developed by separately incorporating boronic esters and B-N coordination into their backbone.The rheological results and deformation-rate-dependent tensile behaviors verify two kinds of B-N coordination,which dramatically enhance the intermolecular and intramolecular interactions.The intramolecular coordination results in the folding of the polyurethane chains,which enables a very high chain extension ratio(?14000%),and the intermolecular coordination contributes to the formation of the transient network,which dramatically enhances the mechanical strength(?10.5 MPa).Meanwhile,the reversible breakage and recombination of B-N coordination bonds can effectively dissipate the applied energy,which contributes to the superior notch insensitivity and outstanding puncture resistance(-72100J m^-2).The high reversibility of boronic esters,B-N coordination bonds and hydrogen bonds endow the polyurethanes with excellent room temperature self-healing characteristics,the tensile strength reaches to 5.2 MPa after self-healing 24 h at room temperature,and increases to 8.6 MPa with the aid of water in 36 h,which is greater than the majority of room temperature self-healing polymer materials reported in literature.3)Study on the preparation and properties of high water-resistant and energy absorption polyurethanes.A series of high water-resistant and energy absorption polyurethanes are developed by incorporating hydrophobic polydimethylsiloxane(PDMS)into polyurethane chains,the tensile strength of HMDI-(PTMEG)_0.6-(PDMS)_0.4 shows little change after it was exposed in RH75 environment for 48h.The testing results of cyclic tensile demonstrate that B-N coordination bonds dramatically improves the tensile strength(?27.3MPa)and energy absorption capacity,and the energy absorption efficiency(?92.2%)is almost unaffected by the deformation rate and tensile strain.In addition,the obtained polyurethanes also show excellent resilience,the absorbed energy of samples that experienced five cycles can recover to 83.8%of the original after relaxing for 2 h at room temperature.