Polymerization of methyl methacrylate by triethylboron–oxygen mixtures

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Abstract
The effect of oxygen on the rate of polymerization of methyl methacrylate catalyzed by triethylboron has been investigated at temperatures in the range 0–52°C. In the absence of oxygen polymerization does not occur, but formation of polymer begins immediately on admission of oxygen. Polymerization is characterized by a decrease in rate with increasing conversion which is most pronounced when the concentrations of oxygen and triethylboron are greatly different. The initial rate of polymerization is proportional to the square root of the oxygen concentration and inversely proportional to the degree of polymerization of poly(methyl methacrylate) formed, confirming the radical nature of the polymerization. The apparent activation energy for the polymerization was unusually low, only 4 kcal./mole. A mechanism in which initiating radicals are produced by a sequence of reactions involving autoxidation of the boron alkyl to peroxide followed by induced decomposition of the peroxide by excess boron alkyl is suggested.