Ethylene-propylene block copolymers featuring dual crystalline networks: high-performance elastomers and sustainable high-density polyethylene/isotactic polypropylene blends upcycling

Abstract

The pursuit of high-performance polyolefins and sustainable recycling of their waste remain critical challenges in materials science, particularly for immiscible high-density polyethylene (HDPE) and isotactic polypropylene (iPP) blends with poor interfacial compatibility and mechanical deterioration. Here, we report a precision chain structure design strategy leveraging olefin block copolymers (OBCs) synthesized via coordination chain transfer polymerization (CCTP) using a bis(phenolate-ether) hafnium catalyst/chain transfer agent system, enabling concurrent enhancement of olefin elastomer properties and compatibilization of HDPE/iPP blends. Unlike conventional block copolymers with a single type of crystal, the OBCs form unique dual crystalline networks, where high-melting-temperature PE crystals (T_m ~ 130 °C) and low-T_m PP crystals (<110 °C) synergize with the amorphous regions. The PE crystals provide high-temperature structural stability and rigid frameworks, while PP crystals enhance room-temperature mechanical strength. Meanwhile, the amorphous regions connecting the two crystalline domains enhance the material's toughness. This well-designed structure not only endows the material with outstanding mechanical properties (tensile strength: 10–18 MPa, elongation at break: 1100–1600%) and thermally responsive shape memory but also significantly improves HDPE/iPP blend compatibility. As compatibilizers, the OBCs reduce the dispersed phase size and significantly enhance interfacial compatibility through dual crystalline anchoring effects, increasing the elongation at break of the blends from 10% to 600%. This work establishes a collaborative optimization paradigm of “catalytic system innovation”, “structural design”, and “application expansion”, providing an innovative solution for developing high-performance polyolefin elastomers and advancing sustainable upcycling of polyolefin waste resources.