Research On Molecular Design And Performance Of Highly Adhesive Elastomers

Supramolecular polymer networks can be designed with precisely tailored properties for a variety of applications ranging from electronics to medicine.Based on metal-ligand complexation,Mussel adhesion is mediated by foot proteins(mfps)rich in a catecholic amino acid,3,4-dihydroxyphenylalanine(dopa),capable of forming strong bidentate interactions with a variety of surfaces.However,Liquid adhesive suffers from the emission of volatile organic compounds(VOCs)that have detrimental effects on human beings.Based on hydrogen bonding,self-healing materials have attracted considerable attention because of their improved safety,lifetime,energy efficiency and environmental impact.However,development of a polymeric material with good mechanical performance as well as self-healing capacity is very challenging.In this study,two self-healing polyurethane(PU)elastomers were developed from polytetrahydrofuran(PTMEG),isophorone diisocyanate(IPDI),diphenylmethane diisocyanate(MDI)and 2-hydroxy-4-amino-6methylpyrimidine(Py).(1)Poly(ether amine)(PEA)and 3,4-dihydroxybenzaldehyde(dhba)is utilized to synthesize catechol-terminated PEA,and subsequent complexation by Fe3+ results in the supramolecular component(PEA-dhba-Fe3+).The Fourier transform infrared(FTIR)spectrum together with the UV-vis spectrum reveal the existence of quinone converted from catechol.Raman spectra prove the existence of a successful complex of PEA-dhba with Fe3+.The tri-complex is found to be the predominant mode and can successfully form into clusters,serving as a physical cross-linking network.The PEA-dhba-Fe3+exhibits strong adherence to metal substrates compared to polymeric substrates,with its shear strength reaching as high as 1.36±0.14 MPa when the pH of the glue is adjusted to 8.The obvious improvement of adhesion originates from the formation of interfacial coordination bonds between quinone/catechol and metal atoms,as well as their cations,as revealed by X-ray photoelectron spectroscopy(XPS)and theoretical calculations.With consideration of its merits,including strong adhesion and the minor emission of VOCs compared to commercial epoxy and acrylic adhesives.(2)In order to study the role of hydrogen bonding as the center of the crosslinking network,we selected Py to form self-complementary quadruple hydrogen bonding structures(UPy).Polytetrahydrofuran(PTMEG)and isophorone diisocyanate(IPDI)were used as starting materials,polymers with supramolecular properties were successfully synthesized by polymerization.Experiments show that Py acts as both a chain extender and an end-capping agent in the polymerization reaction.By changing the molecular weight of PTMEG and constructing linear and cross-linked branched polyurethane elastomers with 3-hydroxymethylpropane(TMP)as the chemical cross-linking center,the tensile strength of blue fluorescent PUIP1000 is 0.34 MPa,and will not break during the stretching process,after being placed at room temperature for 6 hours,the repair efficiency can reach more than 80%.The material is characterized by the ability to identify defects by the fluorescence effect and to take measures to repair them.(3)In order to improve the mechanical properties of the material and ensure the self-healing ability of the material,we replaced IPDI with a large sterically hindered and symmetrical high-activity diphenylmethane diisocyanate MDI.The tensile strength of PUM-2.3 is increased to 5.16 MPa.After 4 hours of repair,the healing efficiency of elongation at break can reach 91.33%.In addition,the bonding strength of PUM-2.3 elastomer on the steel plate substrate is 9.29±0.58 MPa,and the bonding strength on the epoxy plate substrate is 7.54±0.58 MPa.