The anionic bulk polymerization of α-methylstyrene (αMS) has been carried out using tert-butyllithium (t-BuLi) as initiator with or without N,N,N′,N′-tetramethylethylenediamine (TMEDA). In absence of TMEDA, the "living ends" are rapidly deactivated at 62 °C whereas they are relatively more stable at 25 °C. The "living ends" are much more stable in presence of TMEDA; however, their stability is a function of the order in which t-BuLi and TMEDA are added to αMS. The stability of "living ends" is also a function of the ratio r = [TMEDA]/[t-BuLi] and best results are obtained with a one to one ratio. At high temperature, the formation of species with absorption bands at 390 and 424 nm and the broadening of the molecular weight distribution are observed. These results are explained in terms of a transfer reaction to the monomer or to the deactivated polymer.