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 (Ph2CHM) and dimethylzinc or diethylzinc in THP at -78 degrees C. In the absence of dialkylzinc (R2Zn), the poly(tBA)s produced with Ph2CHM 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 Ph2CHK or Ph2CHCs in the presence of 10-20-fold excess R2Zn, although the polymers obtained with Ph2CHLi/R2Zn 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 R2Zn at -78 degrees C for 1 h, but 56% deactivation occurred after 24 h. It is thus demonstrated that Ph2CHK or Ph2CHCs in conjunction with R2Zn induces the controlled anionic polymerization of tBA in THF at -78 degrees C. By contrast, addition of R2Zn 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 R2Zn.