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 wit h 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 Ph2C HM possessed ill-controlled molecular weights and broad molecular weight di stributions (MWDs). On the other hand, poly(tBA)s having predicted molecula r 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 wi th Ph2CHK or Ph2CHCs in the presence of 10-20-fold excess R2Zn, although th e 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 i s 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 af ter 24 h. It is thus demonstrated that Ph2CHK or Ph2CHCs in conjunction wit h R2Zn induces the controlled anionic polymerization of tBA in THF at -78 d egrees C. By contrast, addition of R2Zn to the polymerization systems of me thyl, ethyl, and isopropyl acrylates showed little effects on the improveme nt 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 sequent ial addition of styrene, methyl methacrylate, or N,N-diethylacrylamide with tBA in the presence of R2Zn.