Abstract By chlorination of polyvinyl chloride in a water suspension, a number of samples of chlorinated polyvinyl chloride of varied chlorine content were prepared. The density, the temperature dependence of the dynamic modulus G' and the loss factor tg δ, as well as some mechanical properties of these samples were measured. The structure of the chlorinated PVC is discussed and the assumption expressed that the secondary maximum at − 10°C corresponds to the movements of the short chain interceptions of poly (1,2‐dichloroethylene). The tensile strength and flexural strength is growing linearly with the chlorine content. The impact strength from 65% Cl on is violently decreasing. By its behaviour, chlorinated polyvinyl chloride resembles a random copolymer of vinyl chloride and 1,2‐dichloroethylene.