AbstractThe polymerisation of dec‐1‐ene has been studied using catalysts prepared by mixing titanium tetrachloride and triethylaluminium. The properties of the polymers vary with the ratio of the two components used to prepare the catalyst, with the concentration of the catalysts, and with the reaction temperature. When the catalyst is prepared by mixing the components at molar ratios of lower than about 0.8:1, liquid polymers are obtained. At catalyst ratios greater than 1:1, waxy polymers are formed. The difference may arise from a difference in the reaction mechanism which is considered to be predominantly cationic at the lower ratios (1:1). Evidence for this conclusion is discussed. Under the cationic conditions the polymerisation is sensitive to solvent and when benzene is used it is involved chemically in the polymerisation. At high ratios benzene acts as an inert solvent. The properties of the polymers obtained using Ziegler catalysts are compared with those obtained using catalysts based on aluminium chlor