Anionic polymerizations of 4-chlorostyrene (1), 4-bromostyrene (2), and 4-iodostyrene (3) were carried out in tetrahydrofuran (THF) at -78 degrees C for 5 min using sec-butyllithium (sec-BuLi) or oligo(alpha-methylstyryl)lithium (alpha MSLi) as the initiator. Poly(1)s having broad molecular weight distribution (MWD, D-M, M-w/M-n similar to 2) were quantitatively obtained using sec-BuLi and alpha MSLi, and the molecular weights could be controlled by the molar ratios between 1 and the initiators. Complete consumption of 2 was also realized using alpha MSLi under similar conditions. The conversion of 2 was only 8.8% when initiated with sec-BuLi, and the resulting poly(2) possessed broad multimodal MWD. No polymeric product of 3 was produced using sec-BuLi, indicating the presence of major side reactions involving the electrophilic C-Br and C-I bonds. On the other hand, well-defined poly(1) and poly(2) were quantitatively obtained using alpha MSLi in the presence of 10-fold cesium phenoxide (PhOCs) as an additive. The polymerization using alpha MSLi/PhOCs was completed within few minutes, and the resulting poly(1)s and poly(2) possessed narrow MWD (M-w/M-n <1.1) and predictable molecular weights. In the case of 3, the alpha MSLi/PhOCs initiator quantitatively produced poly(3) having predictable molecular weight and relatively narrow MWD (M-w/M-n = 1.2-1.3). The stability of the propagating carbanions was demonstrated at -78 degrees C by the quantitative efficiency of the sequential copolymerization of 1 or 2 and styrene as well as that of 1 and 2 in any addition order. The observed difference in polymerization behaviors of 1-3 can be explained by the relative reactivity of the carbon-halogen bonds in the monomer structures.