Compatibilization of HDPE and iPP blends with hydrogenated polybutadiene block copolymers

Aiming at the global plastic waste crisis, we have investigated the performance of a series of polybutadiene (PB)-derived saturated hydrocarbon block copolymers for HDPE/iPP compatibilization. EX diblock and EXE triblock copolymers were prepared by anionic polymerization of butadiene followed by catalytic hydrogenation, where X refers to an iPP melt miscible poly(ethylene–ran-ethylethylene) random copolymer and E is hydrogenated 1,4-PB. Whereas blends of commercial HDPE (70%) and iPP (30%) exhibit a strain at break of ε = 10%, addition of just 1 wt% of a M_n = 2.2x10⁵ g/mol EXE triblock during melt blending resulted in ε = 600%. This behavior is attributed to the threading of iPP chains through the X loops at the interfaces in the melt state, leading to topological constraints upon iPP crystallization, along with the cocrystallization of the E blocks with HDPE homopolymer. This “threading the needle” mechanism is supported by relatively poor ductility (ε = 30%) with comparable molecular weight EX diblock copolymer, which does not form X-block loops at the domain interfaces. This work exposes an economically viable approach to recycling polyethylene and polypropylene.