The synthesis of poly(acrylonitrile)-block-poly-(ethylene glycol)-block-poly(acrylonitrile) copolymers has been carried out using a redox system consisting of ceric ion and poly(ethylene glycol)s of various molecular weights in aqueous medium. The generation of intermediate radicals in the redox process has been confirmed by ESR spectroscopy and the polymerization progressing through ’blocking from’ mechanism has been postulated. The formation of the block copolymers has been confirmed by chemical tests and fractional precipitation technique as well as by FT-IR and FT-NMR [H-1 and C-13-(H-1)] spectroscopic techniques. The triblock nature of the block copolymers has been ascertained through the cleavage of ether linkage of the PEG segment. TG/DTA studies of the block copolymers with PEG molecular weights of 1000 and above revealed two-stage decomposition, while their DSC traces exhibited a shift in the melting peak of PEG. GPC investigations of the block copolymers manifested a high homogeneity with unimodal distribution of molecular weights. SEM studies indicated significant changes in the morphological characteristics of the block copolymers.