Synthesis and Characterization of Diolefin/Propylene Copolymers by Ziegler-Natta Polymerization

Summary Diolefins can be used as comonomers in propylene copolymerizations in order to modify some of the final properties of the obtained poly(propylene) (PP) resins. Although reduction of catalyst activity can be expected when such copolymerizations are performed with standard heterogeneous Ziegler- Natta catalysts, copolymers containing 1,5-hexadiene (HD) and 1,7-octadiene (OD) can be produced at high rates when the comonomer content is sufficiently low (below 2 mol%); however, the presence of very small amounts of 5-ethylidene-2-norbornene (ENB) leads to complete catalyst inhibition. It is shown that incorporation of dienes lead to decrease of the melting point of the final product, especially in presence of ENB. When compared to HD, addition of OD causes more pronounced modification of the melt flow index and weight-average molecular weight, although the xylene solubles is less sensitive to the comonomer feed when the comonomer composition is low. Obtained results indicate that small amounts of dienes can be used at plant site to modify the final properties of PP resins produced with standard heterogeneous Ziegler-Natta polymerizations.