Preparation And Properties Of Self-healing Polyurethane With Hydrazone Bonds In Soft Section

Polyurethane is a kind of polymer with hard and soft segments.The hard segment is composed of isocyanate,chain extender and crosslinking agent,while the soft segment is composed of long chain polyols.At present,domestic and foreign studies on self-repairing polyurethanes based on reversible covalent bonds mostly focus on introducing different functional groups,and the functional groups are mostly located in the hard segment of polyurethanes,while there are few reports on self-repairing polyurethanes containing functional groups in the soft segment.In this paper,a special long-chain diol containing hydrazone bonds was synthesized by taking hydrazone bonds as the self-repairing functional group,which were introduced into the polyurethane system to prepare a self-repairing polyurethane with hydrazone bonds on the soft segment(PUPGHE-HDI).It was found that the self-repairing polyurethane with hydrazone bonds in the soft segment also had a certain self-repairing function.The synthesis of long chain diol(PGHE)with hydrazone bond was characterized by IR and1 HNMR.It was proved that its structure was consistent with that of the designed reaction product.The performance of the polyurethane was tested,and the experimental results were as follows: DSC test showed that PUPGEH-HDI soft segments in the part of the glass transition temperature was 12.56 ?,the hard segment part of the glass transition temperature was 48.65 ?.It was an elastomer with a high elastic state and an interconnected structure at room temperature.The tensile test showed that the tensile strength of the self-repairing polyurethane with hydrazone bonds on the soft segment was 1.01 MPa,and the elongation at break was 177.29%.The strength of the polyurethane spline repaired for1 h was too low to be measured.The tensile strength of the repaired 6h polyurethane spline was 0.20 MPa,and the recovery rate was 19.80%.The elongation at break was14.74% and recovered to 8.31%.The tensile strength of the repaired 24 h polyurethane spline was 0.15 MPa,recovering 14.85%.The elongation at break was 17.37% and recovered to 9.80%.The equilibrium swelling rate and gel content of the synthesized polyurethane PUPGHE-HDI were tested and found to be 139.86% and 55.39%,respectively.The structure of the polyurethane was partially crosslinked.At the same time,in this paper,a self-repairing polyurethane(PMM-HDI)with a bond concentration of 5.3*10-4mol/g of acylhydrazone was synthesized in advance.and compared with the self-repairing polyurethane with acylhydrazone bonds on the soft segment,the experiment found that: The equilibrium swelling rate and gel content of the synthesized polyurethane PMM-HDI were tested and found to be177.34% and 70.51% respectively.The SEM microphase separation structure of the polyurethane was observed by electron microscopy.DSC test showed that the soft segment of the polyurethane has two glass transition temperatures,they are1,4-butanediol as chain extender synthetic glass transition temperature of polyurethane Tg1 = 52.31 ? and PM as the synthesis of polyurethane chain extender the glass transition temperature of Tg1'= 34.81 ? respectively.The hard segment part of the glass transition temperature was 63.58?.The test results showed that the polyurethane was an crosslinked structure.The self-repairing performance of the polyurethane was tested,and the results showed that under the condition of 80 ? ice acetic acid stimulation,disconnect the polyurethane spline reconnecedt.The tensile properties of polyurethane before and after repair were tested.The tensile strength of the spline before repair was 0.95 MPa,and the elongation at break was 258.40%.The strength of the repaired 1h polyurethane spline was too low to be measured.The tensile strength of the repaired 6h polyurethane spline was 0.33 MPa,and the recovery rate was 34.73%.The elongation at break was 60.34% and the recovery was 23.35%.The tensile strength of the repaired 24 h polyurethane spline was 0.54 MPa,and the recovery rate was 56.84%.The elongation at break was 160.49% and recovered to 62.11%.It can be seen that the repair rate increases with time.The self-repairing polyurethane with hydrazone bonds on the soft segment and hard segment had lower glass transition temperature,so it had better elasticity and low temperature resistance.Polyurethane materials that are likely to be used in low-temperature environments,polyurethane materials used in repairing bone fractures,polyurethane materials used in car shockproof cushions,and the application of polyurethane materials used under acidic conditions has certain potential value.