Water‐soluble random copolymer ammonium ionenes with in the range of 17.4 to 20.8 kg mol−1 and various charge densities are synthesized from 1,12‐dibromododecane, N,N,N′,N′‐tetramethyl‐1,6‐hexanediamine, and 1,12‐bis(N,N‐dimethylamino)dodecane. Anion exchange of the bromine counterion forms ionenes with TFSI, TFO, and BF4 anions. The nature of the counteranion and charge density tailor the thermal and rheological properties of 12,6/12‐ionenes, respectively. X‐ray scattering reveals microphase separation with a correlation length of ≈7 nm for ionenes with 50 to 90% N,N,N′,N′‐tetramethyl‐1,6‐hexanediamine content. Ionene copolymers display polyelectrolyte behavior in methanol based on a predicted scaling relationship between specific viscosity (ηsp) and concentration.