Preparation And Electromagnetic Properties Of Chiral Conducting Polyaniline

Chiral Polyaniline(PANI)is a special conductive polymer and has apeared potential application in diverse areas,such as electrochemical asymmetric synthesis,chiral chromatography,membrane separation technology and microwave absorbents,etc.In this paper,the chiral polyaniline are synthesized by re-doping emeraldine base(EB)with chiral acid.The maicrostructures and chirality of the samples are characterized by means of Fourier transform infrared (FT-IR)spectra,element analysis,x-ray diffractor(XRD),circular dichroism spectroscopy(CD),ultraviolet visible spectrophotometer(UV-vis).The results indicate that the EB can be induced by chiral camphorsulfonic acid(CSA)with specific electrostatic and hydrogen bond between the PANI chains and the enantiomeric dopant CSA~- anions,inspiring the PANI chains rearranged and preferentially adopting a one-handed helical screw to form the chiral PANI.The electrical conductivity,magnetic property and electromagnetic behavior of the samples are intensively investigated.The results indicate that PANI are fully doped with CSA and have the maximum chirality with the maximum conductivity is 0.58 S/cm in case that the molar ratio of tetramer unit of EB and CSA is approximately 1:3.The test of conductivity shows no obvious dependence on different helical orientation.The as-synthesized chiral PANI possesses unique room-temperature ferromagnetism and behaves superparamagnetism at 50 K and 100 K.The magnetization curves of the samples apear typical magnetic hysteresis loop at 300 K and 200 K with saturation magnetization of 0.031 emu/g and 0.032 emu/g,respectively,and the corresponding coercivity is 70 Oe and 80 Oe,respectively.The above magnetic properties found in the chiral PANIs are attributed to the chiral helical conformation of the main chain.This chiral PANI without any metal inpurity is recognized as organomagnet.It is also found that the chiral PANI exhibits dielectric loss at 2～12 GHz and magnetic loss at 12～18 GHz,respectively,which is mainly arisen from the chiral helical conformation. The microwave absorption of chiral PANI has superiority over that of the regular PANI.The effective absorption bandwidth(＞-5dB)of the chiral PANI slab with 2 mm thickness could be obtaied as 7 GHz with the maxium electromagnetic wave attenuation -10.8 dB peak value.