New Thermoplastic Elastomers based on Ethylene‐Butadiene‐Rubber (EBR) by Switching from Anionic to Coordinative Chain Transfer Polymerization

Olefin triblock copolymers based on glassy polystyrene (PS), ethylene butadiene rubber (EBR) and highly crystalline polyethylene (PE) segments were prepared for the first time using a switch strategy from anionic polymerization to coordinative chain transfer (co)polymerization (CCT(co)P). PS chains obtained by anionic polymerization were transmetalated with mesitylmagnesium bromide (BrMgMes) to act as macromolecular chain transfer agents (macro-CTA, PS-MgMes) in the CCTcoP of ethylene and butadiene using {Me2Si(C13H8)2Nd(BH4)2Li(THF)}2 complex (1). Further chain extension by CCTP using pure ethylene in the monomer feed afforded well-defined PS-b-EBR-b-PE triblock copolymers. The structural, rheological and mechanical properties of these materials demonstrate excellent balance between properties and easy processability at moderate temperatures (> 150 °C). We demonstrate that such triblock copolymers behave effectively as low-viscosity PS-b-EBR diblock copolymers above the melting point of PE domains and high performance thermoplastic elastomers (TPEs) upon crystallization of PE segments.