Sodium-Benzophenone Eetyl as an Initiator of Anionic Polymerization of Methyl Methacrylate

Abstract

The anionic polymerization of methyl methacrylate in tetrahydrofuran initiated by sodium-benzophenone ketyl was studied in rigorously purified systems by means of optical absorption measurements as well as conventional polymerization techniques to elucidate the initiation process involved. It was concluded, on the basis of kinetic behavior of the ketyl anion in reacting with the monomer and the UV absorption of the product polymer, that the addition of the ketyl anion to the monomer forms a propagating carbanion and thus initiates the polymerization. The addition reaction shows an activation energy of 13 kcallmol and a rate constant of 1.2x 10-2 M-1 sec-1 at -10°C. It was also found that no termination reaction occurs, so that the propagating chains are long-lived, though the chain transfer reaction takes place very slowly. The chain transfer reaction is brought about by electron transfer from the propagating carbanion to the benzophenone present in excess in the reaction system to regenerate the initiator.

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

“…By determining the concentration of the former ketyl in the THF solution relative to that of the latter, it was found that the solution of 1.2 x 10 20 spinsjl of magnesium-benzophenone ketyl gave an optical density of 0.888 at 610 nm for a 0.5 em optical path. Thus, the extinction coefficient of the magnesium-benzophenone ketyl was determined to be 18,000 M-1 cm- 1 • Throughout the present investigation, the concentration of the initiator was determined by doubling the concentration of the magnesium ketyl obtained on the basis of this extinction coefficient. Figure 2 shows the Beer-Lambert plot for the ketyl at the absorption maximum at 610 nm.…”

“…was typically 2). 1 It should be noted that the value as high as 2. 7 is obtained for the ratio of the number of polymer chains to the number of the initiator fed.…”

“…MMA, THF and benzophenone were purified as described previously. 1 Mercury of reagent grade (Wako Pure Chemicals Ind. Co., Ltd.) was used as received without further purification.…”

“…The solution of magnesium-benzophenone ketyl was prepared in a glass apparatus similar to that shown in Figure 1 in the previous paper. 1 In the present study however, the ampoule containing the sodium mirror was replaced with a side-arm through which mercury and magnesium are put into the vessel A. The whole apparatus was connected to a vacuum line, evacuated and flamed thoroughly.…”

“…Polymerization was carried out by mixing the monomer into the solution of magnesiumbenzophenone ketyl in vacuo through a break 424 seal as described previously. 1 The product polymer was precipitated in methanol. Either a GPC or a viscometric method was used in determining the molecular weight of the polymer and its distribution.…”