The anionic polymerization of tert-butyl acylate (tBuA) initiated by tert-butyl α-lithioisobutyrate was investigated in THF at 25°C. The individual oligomers were isolated and characterized by UV, IR and NMR spectroscopy. The distribution of products was determined in the range of reaction times 0,02 s ≤ t ≤ 1800 s. The oligomerization is extremely fast. Even after 0,02 s at -30°C, no residual monomer could be detected. After short reaction times the reaction mixture almost exclusively consists of linear oligomers of tBuA. This indicates that there is no termination reaction by Claisen condensation during polymerization. Nevertheless, the molecular weight distribution is rather broad (M̄w/M̄n = 2,15). The very large amount of dimer observed is an indication of its low reactivity. A two-state mechanism is proposed to account for the high polydispersity. Only after longer reaction times side products are formed by Claisen condensation (“back-bitting”). The termination product of the trimer is an enolized cyclic β-ketoester.