Radiation‐induced ionic polymerization of isoprene

The γ‐ray‐induced polymerization of isoprene was investigated in the temperature range of ‐78° to 40°C. The following variables were studied: the dependence of polymerization rate on temperature; the effects of DPPH and pyridine on the polymerization at various temperatures; the dependence of the polymerization rate on dose rate at ‐78° and 20°C.; and the structure of the polyisoprenes obtained at various temperatures. the following results were obtained: (1) Although the Arrhenius plot of the polymerization rate did not yield a linear relation, the total polymerization rate was successfully separated into radical and ionic contributions. (2) The polymerization rate was proportional to the square root of dose rate at 20°C., whereas it was proportional to the first power of the dose rate at ‐78°C. (3) The structure of polyisoprene prepared at ‐78°C. is closely similar to that of cationically polymerized polyisoprene. The partially ionic mechanism of the radiation‐induced polymerization of isoprene was elucidated in this investigation. It was concluded that a cationic mechanism is operative at low temperatures whereas a radical mechanism predominates at higher temperatures.