Magnesium—Benzophenone Ketyl as an Initiator of Anionic Polymerization of Methyl Methacrylate

Abstract

Polymerization of methyl methacrylate was studied in tetrahydrofuran with magnesium-benzophenone ketyl as initiator. According to the results of optical absorption studies on the reaction of the initiator as well as of conventional polymerization experiments; it is concluded that (1) the polymerization proceeds via the anionic mechanism, (2) the initiation reaction between the ketyl anion and the monomer shows an activation energy of 4 kcallmol and a rate constant of 1.6 x 10-2 M-lsec-1 at-25°C, and (3) the chain-transfer reaction occurs slowly through electron transfer to benzophenone in the reaction system with an activation energy of 2 kcallmol and a rate constant of 1.3 x 10-1 M-1 sec-1 at-25°C. The results also suggested that the initiation efficiency is not much lower than unity and that the propagation rate constant is as low as 10-1 M-1sec-1 at-20°C.