Morphology and properties of PP in-reactor alloys prepared with a MgCl₂/TiCl₄/diisobutyl phthalate/phosphate tris-methylphenyl ester catalyst system

Abstract

A series of polypropylene(PP)/poly(ethylene-co-propylene) in-reactor alloys with different ethylene con-tents was prepared through a two-stage polymerization process using a MgCl₂/TiCl₄/diisobutyl phthalate/phosphate tris-methylphenyl ester catalyst system. The ethylene content, particle shape, fractured surface, and glass-transition temperature(T _g) of the obtained PP in-reactor alloys were characterized by means of nuclear magnetic resonance, scanning electron microscopy(SEM), and dynamic mechanical analysis(DMA). The ethylene content of the PP alloys increased from 2.34% to 26.69% when the propylene/ethylene feed ratio was increased from 66/34 to 54/46(molar ratio). Morevoer, the increment in ethylene content increased the notched Izod impact strength of the resulting PP al-loys. The impact strength of the PP alloy with an ethylene content of 26.69% was 55.8 kJ/m², which is 12.7 times that of isotactic polypropylene. The results of DMA and SEM analysis reveal that ethylene-propylene random copoly-mer(EPR) in the PP alloy has a low T _g of ca.‒50 °C and a high interface compatibility with the PP matrix. The ex-cellent impact performance of the PP alloy can be attributed to the uniform dispersal of EPR in the alloy particles and PP matrix.

Keywords

Polypropylene in-reactor alloy / Phosphate / Ziegler-Natta catalyst / Ethylene-propylene random copolymer / Toughening mechanism

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