Synthesis and properties of thermal-induced shape memory polyimide
Shape memory polyimides(SMPI)are new materials designed by combining polyimides with good thermal stabili-ty,excellent mechanical properties,corrosion resistance and radiation resistance with the shape memory effect that can be intelligent-ly deformed.Herein,the flexible diamine and twisted structure dianhydride were used as monomers to manufacture thermal-induced SMPI film by traditional two-step method.The structure,thermal properties and thermodynamics properties of the SMPI were analyzed by infrared spectrum,thermogravimetric and thermodynamics analysis.Moreover,the comprehensive shape memory prop-erties of the SMPI were reseached in detail by dual-,cyclical-,step-and flexural-shape memory tests.The results show that poly-imide is successfully prepared by diamine and dianhydride.The prepared polyimide exhibits excellent thermal properties,with a 5% weight loss temperature of 502℃ and 506℃ under air and nitrogen atmospheres,and a glass transition temperature of 267℃.In addition,the polymer segments with flexible twisted structure provided high strain for SMPI as a reversible phase above the glass transition temperature,while the π-π stacking and chain entanglement caused by the aromatic structure provided high shape memory fixation rate and recovery rate for SMPI as a fixed phase in the form of physical crosslinking points.The strain of SMPI during dual shape memory test is 121.9%,shape memory fixation ratio and recovery ratio of shape memory are 99.7% and 94.2%,respectively.In addition,polyimide exhibits multiple shape memory cycle stability,multi-stage and flexural shape memory proper-ties,and can be used as a new generation of high-temperature resistant intelligent deformation materials in deployable space struc-tures,intelligent jet propulsion systems,high-temperature sensors and other fields.
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