Well‐defined Syndiotactic Polystyrene‐ b ‐Atactic Polystyrene Stereoblock Polymers

New well‐defined syndiotactic polystyrene–atactic polystyrene (sPS‐ b ‐aPS) stereoblock polymers were synthesized in a two‐step process using a combination of “pseudo‐living” Ziegler‐Natta and atom transfer radical polymerizations. Under specific conditions, the one‐pot termination with N ‐bromosuccinimide of syndioselective styrene polymerization catalyzed by Cp*Ti(CH 2 Ph) 3 /B(C 6 F 5 ) 3 /Al( n ‐Oct) 3 (1:1:1) provided sPS‐Br polymers almost perfectly (97%) end‐capped with bromine atoms. These sPS‐Br were used as macroinitiators in the ATRP of styrene affording sPS‐ b ‐aPS with a broad range of compositions. Characterizations by 1 H and 13 C NMR spectroscopy, HT‐GPC and DSC confirmed the formation and identity of the new materials. Preliminary studies on the crystallization behavior under both isothermal and non‐isothermal conditions showed that these sPS‐ b ‐aPS stereoblock polymers crystallize faster than the corresponding blends made of sPS and aPS with a similar composition; this effect is amplified at high contents (80%) of aPS in the stereoblock materials.