Compatibilization of iPP and PS blends with poly(styrene)-block-poly(ethylene-ran-ethylethylene)-block-poly(styrene) triblock copolymers

We have investigated the compatibilization performance of a series of symmetric poly(styrene)-block-poly(ethylene-ran-ethylethylene)-block-poly(styrene) (SXS) triblock copolymers with varying S block molecular weight in semi-crystalline/glassy iPP/PS blends. SXS triblock copolymers were prepared by sequential anionic polymerization of styrene, butadiene, and styrene followed by catalytic hydrogenation of the middle block to produce the X block that is iPP miscible. The incorporation of 3 wt% SXS (M_n = 1.5 x 10⁵ g/mol) into blends of commercial iPP (80 wt%) and general-purpose PS (20 wt%) led to strain at break of ε = 400%, while the neat blends exhibited ε = 60%. This enhancement is attributed to the “threading the needle” mechanism of the X loop^[1] along with the glassy chain entanglement of the S block at the interfaces of iPP/PS established during processing. Tuning the molecular weight of the S block revealed that 2­–3 glassy chain entanglements are required to prevent chain pullout under tensile stress, effectively mitigating interfacial failure of the compatibilized blends. This work explores the underlying mechanism driving compatibilization between glassy PS and semicrystalline iPP.



[1] Shen, L.; Gorbea, G. D.; Danielson, E.; Cui, S.; Ellison, C. J.; Bates, F. S. Threading-the-Needle: Compatibilization of HDPE/iPP Blends with Butadiene-Derived Polyolefin Block Copolymers. Proc. Natl. Acad. Sci. U.S.A. 2023, 120, e2301352120.