Intrinsic High-performance Self-healing Polymers Based On Reversible Covalent Crosslinking

Intrinsic self-healing polymers have attracted great attention owing to their excellent structural designability and ability to repeatedly heal the damage.However,currently available self-healing polymers exist two problems.One is that it's difficult for them to own both high mechanical strength and good self-healing ability at the same time,and the other is that they don't have addition function.Aiming at overcoming above two problems above,high mechanical strength self-healing materials are developed,and then the self-healing polymers with reversible cross-linking networks are further modified for two important applications.The specific research contents of this thesis include two following parts:Firstly,to solve the problem that the reported self-healing polyacrylate resins can't obtain both high mechanical strength and great self-healing ability,one novel polyacrylate resin with fast healing ability is developed.One linear polyacrylate(LFP)with furan group on side chain was synthesized,which was then reacted with hyperbranched polysiloxane terminated with maleimide to construct the crosslinking network based on Diels-Alder reversible bond,followed by adding polydopamine particles(PDAP).As a result,one new kind of crosslinked polyacrylate coating(HPA)with good mechanical strength is developed,which also can fast heal the damage under the NIR laser radiation.The effect of the reversible covalent crosslinking network on the mechanical strength of HPA were systematically studied,and the effects of PDAP on the mechanical properties,thermal properties,and photothermal conversion capabilities of HPA were also investigated.When the content of PDAP is 0.3 wt%,the obtained resin(HPA3)has the best comprehensive mechanical properties.Its tensile strength,elongation at break and toughness are 12.9±0.7 MPa,23.9±1.6%,and 2.63±0.10.MPa,respectively.In addition,after 2.5 min of near-infrared light irradiation,the self-healing efficiency of HPA3 reaches above 87.6%,showing the great healing ability of the material.Secondly,the overlays of high-sensitive flexible touch panels should be colorless,transparent,flexible,self-healable and have high dielectric constant.To meet above requirements,one novel polyurethane film is developed.One isocyanate-terminated oligomer with disulfide group was prepared using isophorone diisocyanate,hydroxy-terminated polycarbonate and 2-hydroxyethyl disulfide as monomers.Then the oligomer was reacted with 1,1,1-tris(hydroxymethyl)propane(Tri-OH)to build the reversible crosslinking network based on disulfide bond.In order to improve the dielectric constant of the polymer while keeping its colorlessness and transparency,lithium bis(trifluoromethane)sulfonimide(LiTFSI)and 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)were introduced,and a series of polyurethane film(PULEs)was fabricated.The effects of LiTFSI and EMTFSI contents on mechanical,dielectric and self-healing properties of PULEs were systematically studied.When the content of LiTFSI and EMTFSI are 5wt%and 7.5%respectively,the obtained film PULE7.5 has the best comprehensive properties,which can be freely switched between bending,curling and S-shape,and its tensile strength,toughness and Young's modulus are 19.6±1.6 MPa,819.5±16.5 MJ m-3,and 85.5±6.0 MPa,respectively.What's more the dielectric constant(9.6-6.1)in the frequency range of 104-106 Hz is comparable to that of glass,the commercial used overlay.The healing efficiency of PULE7.5 is above 92.7%,the mechanical property recovery rate after remodeling is higher than 91.8%,and the transmittance at 550 nm is 90.7%.The outstanding comprehensive performance of PULE7.5 shows its broad application prospects in preparing cover materials for flexible touch panels.