Effect of the Combined External Electron Donors on the Structure and Properties of Polypropylene/Poly(ethylene-co-propylene) In-Reactor Alloys Prepared by High-Efficiency Industrial Ziegler-Natta Catalyst

In this work, a series of isotactic polypropylene/ethylene-propylene rubber (iPP/EPR) in-reactor alloys were prepared by high efficiency industrial Ziegler-Natta catalyst with diphenyldimethoxysilane/dicyclopentyldimethoxysilane (DDS/D-donor) mixtures as external electron donors. The effects of the external electron donor on the structure and mechanical properties of the iPP/EPR in reactor alloys were studied. According to the characterization results, the iPP/EPR in reactor alloys were mainly composed of random poly(ethylene-co-propylene), multiblock poly(ethylene-co-propylene), and highly isotactic PP. For DDS/D-donor mixtures as external electron donors and triethylaluminum (TEA) as the cocatalyst, as the amount of D-donor in DDS/D-donor mixtures increased, the molecular weight of polypropylene homopolymer and the structural uniformity of multiblock poly(ethylene-co-propylene) increased, whereas when D-donor alone was used as the external electron donor, they decreased. However, the isotacticity of polypropylene homopolymer increased as the amount of D-donor in the DDS/D-donor mixtures increased. Therefore, as the amount of D-donor in the DDS/D-donor mixtures increased, the impact strength of the iPP/EPR in reactor alloy increased, but when D-donor alone was used as the external electron donor, the impact strength of the alloy decreased. An optimum feed ratio between DDS and D-donor was found, namely, DDS/D-donor = 1:3 (Si/Ti = 5). The iPP/EPR in-reactor alloy prepared under these conditions was the toughest. The influence of the external electron donor on the flexural modulus and flexural strength could be ignored.