Synergistic toughening of iso‐polypropylene with high‐density polyethylene and polycyclooctene synthesized by ROMP

Abstract

A series of different molecular weight Polycyclooctene(PCOE) rubber were synthesized via ROMP with G2 catalyst and Iso‐polypropylene (iPP), PCOE and high density polyethylene (HDPE) blends were prepared by micro twin‐screw extruder. The effects of PCOE molecular weight and content were investigated by studying the thermal, rheological and mechanical properties of the blends. We observed that the low molecular weight PCOE promoted the dispersion of HDPE, and as the molecular weight and content of PCOE rising, PCOE encapsulated HDPE particles entirely to form a connected core‐shell network structure in PP matrix and a certain degree of micro‐crosslinked structure which connected the PCOE ‘shell’. Micrographs of the fracture surfaces support the finding that PCOE promoted a finer dispersion and improved the morphological stability of the ternary blends as a compatibillizer. The increasing molecular weight of PCOE enhanced the molecular chains entanglement of the blends resulting in an increase on blends viscosity. The interfacial adhesion of PP/PCOE/HDPE ternary blends improved significantly as PCOE molecular weight increased from 12 kg/mol to 270 kg/mol. The impact strength of the PP/PCOE/HDPE blends increased by 3 times as compared with PP/HDPE blends owing to the addition of 15 wt% HDPE and 15 wt% PCOE(Mn = 270 kg/mol).