Compatibilization of iPP/PS Blends with Diblock and Triblock Copolymers

Mechanical recycling of plastics benefits from block copolymer compatibilizers, yet a limited understanding of optimal polymer design hinders widespread 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 tuning the S block molecular weight (10–80 kDa) and block architecture (diblock vs. triblock), we probed the underlying compatibilization mechanisms. Our findings corroborate the recently proposed "threading-the-needle" mechanism of engagement between the X block and iPP. A new mechanism for creating ductility in the semicrystalline iPP matrix without stress transfer across the phase-separated interface with PS is demonstrated with SX diblock copolymer. Remarkably, incorporating just 0.1 wt % SX diblock enhances ductility in blends containing 20% PS (strain at break εb > 400%) through dissipating strain energy thereby suppressing void formation upon deformation. This study provides fresh insights into the design of block copolymers for blend compatibilization and toughening.