Two series of well-defined multiblock four-arm tapered star copolymers with "arms" of the type poly(styrene)-block-poly(isoprene-grad-styrene), (SI/S)(4), were synthesized on a multigram scale with short reaction times. Targeted molecular weight (M) values ranged from 80 to 240 kg mol(-1) with polystyrene (PS) compositions of 40 and 60 wt %. Narrowly distributed (D = 1.04-1.12) copolymers were obtained regardless of M and without additional purification beyond precipitation. At sufficiently high M, members of the 40 wt % PS series possessed either a cylindrical or bicontinuous morphology, whereas the 60 wt % PS series yielded lamellae. The star copolymers outperformed their corresponding linear analogues with respect to ultimate toughness and elongation at break. Young's moduli of up to 304 +/- 11 MPa were reached, and the overall toughest (83 +/- 2 MJ/m(3)) star copolymer exhibited the highest strain at break (1198 +/- 34%). Catalytic hydrogenation of the PI segments was achieved selectively without saturation of styrene units at conversions of >= 98%. More pronounced strain hardening occurred upon hydrogenation. Modulus, toughness, and ultimate strength of the linear tapered copolymer increased substantially upon hydrogenation to poly(styrene)-block-poly((ethylene-alt-propylene)-grad-styrene), SEP/S. However, these mechanical properties for the star copolymer were found to decrease upon hydrogenation to (SEP/S)(4). These materials, particularly the unsaturated multiblock stars of the highest M, are promising candidates for future advanced materials that require extremely tough elastomers.