Preparation And Properties Of Responsive Self-healing Poly(Dimethylsiloxane) Elastomers

Polysiloxane is a vital member of organosilicone,which has been extensively used in aviation,national defense and medical industry due to its excellent properties such as high-and-low temperature endurance,corrosion resistance and biocompatibility.However,macroscopic or microscopic damage always appear in operation period,causing performance deterioration,lowering service life and even bringing about security risks.Responsive polymer is a kind of material that undergo physical and chemical changes upon external stimuli.This unique property allows real-time display of environmental changes,not only providing visual multifunction sensing,but also holding great promise for applications in early warning of material failure.In this paper,a responsive self-healing poly(dimethylsiloxane)(PDMS)elastomer was prepared based on spiropyran(SP)mechanophore and reversible hydrogen bonds to realize the force-,heat-and light-induced color conversion.Firstly,2,3,3-Trimethylindolenine(TMI)and 3-chloromethyl-5-nitrosalicylaldehyde(CNA)were used to synthesize SP possessing two alkane hydroxyl groups(SP-(OH)₂).Then,carbinol(hydroxyl)-terminated polydimethylsiloxane(HO-PDMS-OH),SP-(OH)₂,4,4'-diphenylmethane diisocyanate(MDI),isophorone diisocyanate(IPDI)and 1,4-butanediol(BDO)were used to synthesized the PDMS elastomer(PDMS-MDI-IPDI)by the reaction between isocyanate and hydroxyl groups.Chemical structure of SP-(OH)₂ was characterized by ¹H NMR.It was confirmed that two alkoxy groups attach to indole ring and pyran ring respectively.UV-Vis and fluorescence spectra verified the photochromic property of SP-(OH)₂.FTIR analysis of PDMS-MDI-IPDI confirmed the reaction between isocyanate and hydroxyl groups.Tensile tests and UV-Vis spectra indicated that PDMS-MDI-IPDI indeed have the function of mechanochromic.It starts to exhibit a color variation from yellow to purple at 300%strain,which can recover rapidly by white light illumination after unloading.Similar reversible color change occurred under heating or UV.PDMS-MDI-IPDI also have excellent mechanical properties and self-healing efficiency.Its tensile strength is up to 10.5 MPa and elongation at break reaches 785%.After heat treatment at 60?for24 h,self-healing efficiency of both strength and elongation at break exceeds 90%.