This work studies the electrical, rheological, and thermal characteristics for polyurethane (PU) capped with tetraaniline as a new material, tetraaniline-containing poly(urethane–urea) (TAPU). The conductivities can be increased from less than 10−10 S/cm for pure PU to 10−4 S/cm for TAPU, independently of the length of the soft segment in the TAPU backbone chain. The tensile strength and modulus are increased when PU is copolymerized with tetraaniline. The viscoelastic creep can be effectively simulated using a Burgers model. Additionally, TAPU has higher viscosity, higher retardation time, and lower compliance J1 than regular PU. Restated, TAPU exhibits less elastic but superior permanent deformation than PU because tetraaniline functions as a chain holder. The thermogravimetric analytic (TGA) results reveal that TAPU has lower Td, smaller Tmw1 and Tmw2, and higher char yield because the dehydration of the urea-containing polymer produces a thin layer from a nitrogen compound on the polymer’s surface, which insulates the underlying polymer from heat and oxygen.