We present the synthesis strategy of polymers containing single quaternary ammonium ion per chain at an arbitrary position using controlled anionic polymerization technique and the structure characterization results of the quaternary-ammonium-containing polymers in bulk and hydrated states. The placement of single quaternary ammonium group in a polymer chain was achieved by using amine-functionalized diphenylethylene (A-DPE) that has unique polymerization kinetics, i.e., the A-DPE monomer cannot self-polymerize due to the large steric hindrance but can initiate polymerization of vinyl monomers with less steric hindrance. We successfully synthesized monomodal and nearly monodisperse polystyrene polymers containing single A-DPE monomer at the one end of chains and the middle of the chains. The X-ray scattering characterization shows that the polymers containing quaternary ammonium in the middle of chains form smaller ion aggregates.