AbstractThe ultrasonic attenuation of PVCz in 1,2‐dichloroethane solution was investigated as a function of temperature and frequency. The relaxation observed is assigned to segmental motions of the chain. The activation enthalpy of this process and the enthalpy difference between the two states are ΔH2* = 14.2 kJ/mol and ΔH0 = 39 kJ/mol, respectively. The high enthaply difference ΔH0 hits at high thermal “stiffness” of the PVCz‐chains. This can be explained by the formation of intramolecular sandwich complexes in PVCz by conformational changes of the relevant carbazole side groups.