Synthesis of Ethylene–Styrene Multiblock Copolymers Possessing High Strength and Toughness Using Binuclear Scandium Catalysts

Abstract

Synthesizing materials with both high strength and toughness has been a promising but challenging research project. Syndiotactic polystyrene (sPS) is known for its high strength while encountering serious brittleness and processing problems. Introducing flexible ethylene units into rigid polystyrene chains can solve these issues, but copolymer regularity and sequence distribution need to be controlled to balance strength and toughness. Herein, we report the copolymerization of styrene and ethylene using alkyl-bridged fluorenyl binuclear scandium catalysts. The resulting copolymers show superior tensile strength (60.0 MPa) and impact resistance (119.6 kJ m^–2), surpassing sPS and high-density polyethylene (HDPE), respectively. These properties are mainly attributed to their unique chain structures composed of long syndiotactic polystyrene and long polyethylene multiblocks, forming an interpenetrating network without phase separation. The PE sequence lengths were measured by successive self-annealing procedures. The density functional theory simulation revealed the mechanisms. The binuclear active species of homo sPS-attached Sc³⁺ species (Cat_Sc2-nSt) prefer styrene insertion due to low insertion energy and thermostable intermediate. Homo PE-attached Sc³⁺ ions (Cat_Sc2-nE) favor ethylene insertion, where the agoistic interaction of H---Sc³⁺ prevents styrene insertion. The hetero sPS and PE-attached Sc³⁺ ions (Cat_Sc2-nESt) provide the opportunity to form sPS–PE joints in the copolymer chain.