Polyacrylonitriles (PANs) were synthesizid both by atom transfer radical polymerization (ATRP) and free radical polymenzation in ionic liquid 1-buty-3-methylimidazolium chloride ([bmim]Cl).[bmim]Cl demonstrates to be a preferable solvent for ATRP of acrylonitrile (AN).The polymerization maintains the usual advantages of ATRP with molecular weight agrees well withtheoretical value and low polydispersity (PDI=1.15).It is also shown the higher conversion and lower molecular weight dispersion in ionic liquid than in dimethylformamide (DMF).From FTIR and NMR analysis,it is confirmed that the chemical structures of PANs synthesized in [bmlm]Cl were identical with that obtained in DMF.In atom transfer radical polymerization,the methine and cyan carbon atoms in isotactic configuration for PAN preduced in [bmim] Cl have a configuration consisting of about 55.5% isotactic diads.It is higher than that obtained in DMF which is 52.2%,So,ionic liquid has effect on the stereostmcture of PANs.Further analysis of 13C NMR spectra indicated that the isotacticity of PAN synthesized by free radical polymerization was lower than that of PAN prepared by ATRP,although both of them were random in stereoregularity.Besides the pentad tacticities of PANs also suggested that the sequence distributions of them all obey Bernoulli statistics.