Compatibilization of iPP/PS Blends with Diblock and Triblock Copolymers

Mechanical recycling of plastics benefits from block copolymer compatibilizers, yet limited understanding of optimal molecular design restricts their broader applications. In this study, we synthesized poly(styrene)-block-poly(ethylene-ran-ethylethylene) (SX) diblock and SXS triblock copolymers via sequential anionic polymerization followed by catalytic hydrogenation and investigated their effectiveness in compatibilizing semicrystalline isotactic polypropylene (iPP) blended with glassy polystyrene (PS). By varying the S block molecular weight (10−80 kDa) and block architecture (diblock vs. triblock), we explored the underlying compatibilization mechanisms. Our findings corroborate the recently proposed “threading-the-needle” mechanism describing engagement between X block loops and iPP homopolymer chains near domain interfaces. Additionally, a new mechanism for creating ductility in the semicrystalline iPP matrix without stress transfer across the phase separated interface with PS was revealed in SX diblock-compatibilized blends. Remarkably, incorporating only 0.1 wt% SX diblock enhances ductility in blends containing 20 wt% PS (strain at break, ε_b > 400%) by dissipating strain energy and suppressing void formation during deformation. This study provides insights into the design of block copolymer compatibilizers for recycled polymer blends.