Well-defined syndiotactic polystyrene-b-atactic polystyrene stereoblock polymers

Abstract

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.