A polybutadiene(19)-block-poly(ethylene oxide)(94) (PB-PEO) has been modified by free-radical additions of 2-ethylhexanethiol, 1-decanethiol, and 1-dodecanethiol separately to the PB block. The block copolymers were characterized by DSC, SAXS, XRD and AFM measurements. Above the melting temperature of PEC, PB-PEO showed hexagonal morphology having PB cylinders in the PEO matrix. The addition of alkyl side chains decreased the volume fraction of PEO and the morphology changed to lamellar for ethylhexyl side chains and to reversed hexagonal morphology with PEO cylinders in the PB/alkyl chain matrix for decyl and dodecyl side chains. Below the melting temperature of PEO, all polymers showed lamellar morphology. In the case of dodecyl side chains, the lamellar morphology Oriented perpendicular to the air/film interface and was stable against high temperature annealing. (c) 2008 Elsevier Ltd. All rights reserved.