THE REACTION OF ORGANIC COMPOUNDS OF LOW MOLECULAR WEIGHT INITIATED BY COBALT-60 GAMMA-RADIATION. VII. DOSE RATE EFFECT OF RADIATION POLYMERIZATION OF METHYL METHACRYLATE

Methyl methacrylate was subjected to polymerization reactions initiated by the Co-60 gamma rays in the absence or presence of additives over the temperature range from 10 to 30 deg C and the dose rate effect of gamma irradiation was observed. The dose rate of this work is about 3 x 10/sup 18/ ev/ ml/hr. The rate of the polymerization reaction and the molecular weight of the polymer thus obtained depend on the irradiation temperature and dose rate, and the overall activation energy of polymerization of the pure monomer was found to be 4 kcal/mole. The rate of polymerization of the monomer increases with increasing dose rate, but the molecular weight of the polymer decreases with increasing dose rate. Each of 50 kinds of additives was added to the monomer. The value of R/sub E/ (that is, the product of R/sub p/ and R/sub M/, where R/sub p/ is the ratio of the polymerization rates and R/sub M/ is the ratio of the viscosity average molecular weights of the polymer with and without an additive under the same experimental conditions) remains almost constant so long as the additives possess the same kinds of functional groups and also same concentrations (0.1 mole/1).more » Additives thus examined are in the following decreasing order of the values of R/sub E/: Acids and their anhydrides > Hydroxy > Nitrogen containing compounds > Halogenated compounds > Nitro compounds. The values of R/sub p/, R/sub M/, and hence R/sub E/ change with the concentration of the additive, but it seems that they are independent of the change of the dose rate of gamma rays. (auth)« less