Preparation And Properties Of Self-healing Polyurethanes With Dynamic Bonding And Multiple Hydrogen Bonds

With the development of polymer science,polymer materials are widely used in people’s clothing,food,housing and transportation.Polyurethane materials are widely used in coatings,adhesives,automotive parts and other fields because of their good chemical stability,easily adjustable structure and excellent mechanical properties.In the process of daily use,polyurethane materials will inevitably be damaged by external forces,reducing the safety and shortening the service life of the material.Self-healing materials are those that can spontaneously recover the mechanical properties as they are damaged.If polyurethane materials are endowed with self-healing properties,they will be of great significance to expand their application areas.However,there is still a challenge for the self-healing materials to combine good mechanical properties and high self-healing efficiency.To solve the contradictory problem between good mechanical properties and high repair efficiency,this paper prepares a series of high-strength self-healing polyurethanes by introducing chemical dynamic bonds and multiple hydrogen bonds into the polyurethane materials by the structural design.The main contents are as follows:（1）The isocyanate-capped prepolymer was facilely synthesized by the reaction of polytetrahydrofuran ether diol（PTMEG）with isophorone diisocyanate（IPDI）.Then,as the chain expansion reagents,2,5-furandimethanol and adipic acid dihydrazide were added in.Finally,the products with dynamic bonds were synthesized by the cross-linker,4,4’-bismaleimide diphenylmethane.The nuclear magnetic hydrogen spectroscopy（¹H NMR）,Fourier transform infrared spectroscopy（FT-IR）and gel permeation chromatography（GPC）were used to characterize the structure of products.The thermal reversibility of the polyurethanes（PUs）was demonstrated by differential scanning calorimetry（DSC）and dynamic thermomechanical method（DMA）.The results showed that,with the increase of chemical cross-linking degree,the glass transition temperatures（T_gs）of the PUs slightly increased.Such as,the tensile strength and the elongation at break of PU_F50-A50 were 56.87±0.53 MPa and 1320.93±113.23%,respectively,which means the introduction of multi-hydrogen bonds can effectively improve their mechanical properties.As the typical thermal reversible bonds,D-A bonds and hydrogen bonds,can repair the damaged materials without some special repair conditions.The self-healing effective and the tensile strength of PU_F50-A50 have reached 70%and 39.55 MPa,at 120°C for 30 min and 100°C for 2 h.Based on the reversible performance of dynamic networks,polymers have the good reprocessability and retrievability.（2）An imine group-containing diol was prepared by Mannich reaction between terephthalaldehyde and 6-amino-1-hexanol.Then,its structure was characterized using ¹H NMR,¹³C NMR,and FT-IR measurements.A series of PU elastomers(PU_I25-A75-PU_I65-A35)with high transparency and good mechanical strengths were prepared by varying the mole ratio of terminal hydroxyimino diol and adipic dihydrazide.The elastomer structures were characterized by ¹H NMR,FT-IR,and GPC measurements.Their thermomechanical properties were characterized by DMA and rheometer,and their mechanical properties as well as repair results were characterized by an electronic universal tensile tester.With the increasing of imine bonds,the tensile strength decreased.However,its self-healing efficiency increased.For example,the original tensile strength of PU_I50-A50was 13.07±0.23MPa and the tensile strength and self-healing efficiency of the healed PU_I50-A50 were 13.05±0.62 MPa and 99.84%,respectively,at 80°C for 1 h.（3）The incorporation of reversible disulfide bonds into polymers can endow their good self-healing properties.However,the disulfide bonds have the poor strength and toughness.A series of linear polyurethane-polyurethanes containing dynamic disulfide bonds were prepared by adding 4,4’-dithiodiphenylamine（DTDA）and adipic acid dihydrazide（AD）as the chain extenders.The structure of as-prepared linear polyurea-polyureas were characterized by ¹H NMR,FT-IR,and GPC tests.The T_gs of polyurea-polyurea was characterized by DSC and DMA measurements.The tensile strength,elongation at break and toughness were 60.24 MPa,1489.2%and 257.24 MJ m^-3,respectively.After healing at30°C for 5 h and with the assistance of normal solvents,the tensile strength,strain and toughness of the healed samples were as high as 44.4 MPa,1254.4%and 179.52 MJ m^-3,respectively.At the same time,the healing efficiency can reach 73.6%.