The combination of potassium tert-butoxide (tBuOK) and triisobutylaluminum (iBU(3)Al) (the tBuOK/iBU(3)Al system) initiated the anionic polymerization of tert-butyl acrylate (tBA) and methyl methacrylate (MMA) and controlled the polymerization with respect to molecular weights and molecular weight distributions (MWDs). Poly(tBA)s (M-n = 20 000-80 000) with narrow MWDs (M-w/M-n = 1.05-1.12) were obtained quantitatively in toluene at 0 degreesC for 1-2 h. The controlled character of the polymerization remained intact even at high temperatures up to 50 degreesC. MALDI-TOF-MS analyses of a low molecular weight poly(tBA) prepared with the initiating system revealed that the polymer had hydrogens at both chain ends. Block copolymerizations of tBA and MMA were also successful in toluene at 0 degreesC by using the initiating system, giving poly(tBA-b-MMA)s with various compositions of the two monomer units and narrow MWDs in high yield. Although the tBuOK/iBu(3)Al system failed to control the homopolymerization of MMA in toluene or THF, the use of diethyl ether (Et2O) as a solvent for the polymerization coupled with cesium fluoride (CsF) resulted in the quantitative formation of high molecular weight poly(MMA)s with narrow MWDs.