True model linear poly(styrene-b-dimethylsiloxane) PS-b-PDMS copolymers were synthesized by using sequential addition of monomers and anionic polymerization (high-vacuum techniques), employing the most recent experimental procedures that allow the controlled polymerization of each monomer to obtain blocks with controlled molar masses. The model diblock copolymers obtained were analyzed by using different techniques, such as size-exclusion chromatography, H-1 NMR, Fourier transform infrared spectroscopy, small angle X-rays scattering (SAXS), and wide angle X-rays scattering (WAXS). The PS-b-PDMS copolymers obtained showed narrow molar mass distribution and variable PDMS content, ranging from 2 up to 55 wt %. Compacted powder samples were investigated by SAXS to reveal their structure and morphology changes on thermal treatment in the interval from 30 to 200 degrees C. The sample with the highest PDMS content exhibits a lamellar morphology, whereas two other samples show hexagonally packed cylinders of PDMS in a PS matrix. For the lowest PDMS content samples, the SAXS pattern corresponds to a disordered morphology and did not show any changes on thermal treatment. Detailed information about the morphology of scattering domains was obtained by fitting the SAXS scattering curves. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3119-3127, 2010