We report a synthetic method for the preparation of well-defined poly(styrene-b-butadiene) (PS-PB)n multiblock copolymers using a combination of living anionic polymerization and urethane based polycondensation along with an assessment of the associated microphase morphology and thermal and mechanical properties. The prepolymers, α,ω-dihydroxy polystyrene (HO-PS-OH) and α,ω-dihydroxy polybutadiene (HO-PB-OH), were prepared using a protected initiator, followed by deprotection and condensation with isophorone diisocyanate (IPDI) leading to the (PS-PB) n multiblock copolymers. Two types of block sequences were generated, one with random block sequences (PS-ran-PB)n and the second with alternating (PS-alt-PB)n block architectures. Size exclusion chromatography (SEC), 1H nuclear magnetic resonance (NMR), and Fourier transform infrared spectrometry (FTIR) confirmed that the synthetic procedures yielded the desired products. Differential scanning calorimetry (DSC) revealed microphase separation and small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) demonstrated that the multiblock materials, containing between 69% and 85% by volume glassy PS, are characterized by a disordered bicontinuous-like morphology. Tensile tests demonstrated yielding followed by necking and an overall ductility that translates into much greater toughness than that typically found in glassy continuous SBS triblock copolymers.