Controlled Anionic Polymerization of tert-Butyl Acrylate with Diphenylmethyl Anions in the Presence of Dialkylzinc

The anionic polymerization of tert -butyl acrylate (tBA) was carried out with a binary initiator system prepared from diphenylmethyllithium, -potassium, or -cesium (Ph 2 CHM) and dimethylzinc or diethylzinc in THF at −78 °C. In the absence of dialkylzinc (R 2 Zn), the poly(tBA)s produced with Ph 2 CHM possessed ill-controlled molecular weights and broad molecular weight distributions (MWDs). On the other hand, poly(tBA)s having predicted molecular weights based on the molar ratio of monomer to initiators and narrow MWDs ( M w / M n < 1.15) were obtained in quantitative yields by the initiation with Ph 2 CHK or Ph 2 CHCs in the presence of 10−20-fold excess R 2 Zn, although the polymers obtained with Ph 2 CHLi/R 2 Zn still possessed broad MWDs ( M w / M n = 2). The growing chain end of poly(tBA) associated with cesium counterion is completely stable to reinitiate the further polymerization of tBA in the presence of R 2 Zn at −78 °C for 1 h, but 56% deactivation occurred after 24 h. It is thus demonstrated that Ph 2 CHK or Ph 2 CHCs in conjunction with R 2 Zn induces the controlled anionic polymerization of tBA in THF at −78 °C. By contrast, addition of R 2 Zn to the polymerization systems of methyl, ethyl, and isopropyl acrylates showed little effects on the improvement of polymer yields and the molecular weight controls. Well-defined block copolymers, poly(styrene- b -tBA), poly(methyl methacrylate- b -tBA), and poly(tBA- b - N,N -diethylacrylamide), were also anionically prepared by the sequential addition of styrene, methyl methacrylate, or N,N -diethylacrylamide with tBA in the presence of R 2 Zn.