| Abstract: | The kinetics and degree of polymerization of the radiation-induced polymerization of styrene were investigated at dose rates up to 3 Mrads per sec. It was found that both the polymerization rates and the molecular weights at high dose rates lie well above the values predicted by extrapolation from low dose rate studies where the mechanism is primarily free radical in nature. The evidence obtained indicates that with increasing dose rate there is an increase in the ionic contribution to the polymerization mechanism. At the highest dose rates investigated, 3 Mrads per sec, the ionic mechanism dominates while the free-radical mechanism contributes insignificantly. There was no inhibition of the polymerization of styrene by dissolved air at the higher dose rates. Investigation of the polymerization of styrene saturated with water tends to support the ionic mechanism via free cations. Investigation of equimolar solutions of styrene and methyl methacrylate further support the ionic mechanism, yielding predominately polystyrene and a small amount of 50–50 copolymer. In the intermediate dose rate range, 1000 rads per sec, there is evidence that the high dose rate free-radical kinetic mechanism is the principal mechanism. |
