Handedness switch of synthesized helical polyaniline nanofibers featuring the use of a single enantiomeric acid and aniline oligomers

The polymerization of aniline (AN) was assisted with an oligomer that possessed two amino end groups ( 2AO ) in the presence of a single enantiomeric acid, (1 S )-(+)-10-camphorsulfonic acid (( S ) CSA). The reaction produced helical polyaniline (PANI) nanofibers with the opposite helical sense due to the concentration changes of ( S ) CSA in the polymerization system. The similar dependence of the circular dichroism (CD) signal on the ( S ) CSA concentration was also observed in the oxidization of the oligomer 2AO by ammonium persulfate (APS) in the presence of ( S ) CSA. In addition, under a certain ( S ) CSA concentration, the 2AO- assisted polymerization at low and high temperatures also produced the PANI fibers with the opposite helical sense. It is likely that these result from the different interaction modes of ( S ) CSA with the 2AO at different ( S ) CSA concentration. As a consequence, the oxidized 2AO (oligomer seeds) with different chirality in the early stage of the polymerization control the helicity of the resulting PANI nanofibers.