The living free-radical copolymerizations of styrene (St) with the polar monomers (methyl methacrylate (MMA), ethyl methacrylate (EMA), butyl methacrylate (BMA), methyl acrylate (M-A), ethyl acrylate (EA), butyl acrylate (BA), 2-hydroxyethyl acrylate (HEA), and vinyl acetate (VAc)) mediated by TEMPO and BPO as initiator at 1.25 degrees C had been analyzed by H-1 NMR and gel permeation chromatography (GPC). The data from GPC showed that the polydispersities of the resulted copolymers were below 1.5, and the rate of polymerization increased, while the polydispersity declined with increase in St molar fraction in the feed. Monomer reactivity ratios had been determined by expanded Kelen-Tudos method. r(St) = 1.32, r(MA) = 0.14; r(St) = 1.17, r(EA) 0.23; r(St) = 0.83, r(BMA) 0.20; r(St) = 0.74, r(MMA) = 0.25; r(St) 0.76, r(EMA) = 0.30; r(St) 1.27, r(BMA) = 0.59; r(St) = 1.67, r(VAc) = 1.05; and r(St) = 0.28, r(HEA) = 0.43. In the copolymerization of St with acrylates the monomer reactivity ratio 0 (St) decreases and in the copolymerization of St with methacrylates the monomer reactivity ratio r1 (St) increases while the length of the substituted group increases. (c) 2006 Wiley Periodicals, Inc.