Radiation-induced polymerization of 3-octylthiophene

► Polymerization of 3-octylthiophene by irradiation of γ-ray was found. ► G-values of the monomer conversion by the polymerization are from 10 to 445. ► The G-values increased with decreasing the irradiated dose. ► The G-values were large and cannot be explained by the widely accepted mechanism. ► A new mechanism is proposed, which is a chain reaction of cations.