Synthesis And Properties Of Novel Electrochromic Polymers

Electrochromic is the phenomenon of reversible color change of materials under applied voltage or electric field.In essence,reversible redox reactions of the polymer film prepared under a given voltage in an electrolyte solution.The transmittance of light was changed by the gain and loss of electrons in conducting polymers.Organic electrochromic materials have attracted much attention due to their desirable properties through molecular design.Electrochromic materials have bright prospects for application and wide range of applications,from automotive anti-glare rearview mirrors,building smart windows,color changing glasses to aerospace materials.The introduction of triphenylamine is due to nitrogen atoms turn to the oxidation state under voltage or electric field,the formation of radical cations and accompanied by color changes.Triphenylamine has a very stable structure,because the three benzene rings connected by nitrogen atoms reduce the tension of the center of free radical.These two properties make the triphenylamine and its derivatives possess high hole transport capacity,and can be applied to electrochromic devices,organic solar cells and so on.In this paper,the di-acid monomers containing imide structure were synthesized by three steps,They undergo high temperature poly-condensation with three di-amine monomers with different aromatic structures.A series of novel redox active poly(amide-imide)s with triphenylamine and phenoxy structure were successfully synthesized,respectively.The structure of PAIs,thermal stability,solubility,electrochemical and electrochromic properties were tested respectively.The purity and reaction of monomers and polymers were confirmed by nuclear magnetic resonance(NMR)and thin layer chromatography(TLC).The functional groups and characteristic absorption peaks of monomers and polymers were confirmed by Fourier transform infrared spectroscopy and UV Vis spectra,The solubility of the polymer was confirmed by dissolving the polymer in different solvents,Thermogravimetric analysis(TGA)showed that the polymer had high thermal stability.Electrochemical tests(cyclic voltammetry)and electrochromic properties(UV-vis-NIR)of the polymer films were carried out to prove the polymer film had good performance and bright color change.From neutral yellow to semi oxidized light green,and then to full oxidation of green,and finally back to the light colored reduction state.The coloring time range of the three PAIs films is 8-20 s,and the fading time is about 4s.At about 800 nm,the change of transmittance of the three PAIs films at the optimum voltage was 68%,37%,60%.,respectively.These polymers exhibit high optical contrast and long-term redox and electrochromic reversibility,and can be used as an electrochromic material in the field of optoelectronics due to their proper HOMO values.