Bimodal Poly(propylene) through Binary Metallocene Catalytic Systems as an Alternative to Melt Blending

Correlation of Microstructure, Rheological and Morphological Characteristics of Synthesized Polypropylene (PP) Reactor Blends Using Homogeneous Binary Metallocene Catalyst

A novel binary homogeneous catalyst system based on (I): rac-Me₂Si(2-Me-4-PhIn)₂ZrCl₂ and (II): (2-PhIn)₂ZrCl₂ catalysts at various molar ratios was utilized for the synthesis of polypropylene (PP) reactor blends with bimodal molecular weight distribution (MWD). The results of gel permeation chromatography analyses revealed that the catalyst (I) was responsible for the production of i-PP with high molecular weight (MW) while the individual use of catalyst (II) led to the production of an elastomeric PP with relatively low MW. However, application of the binary catalyst system led to high MW bimodal MWD products being highly dependent on the catalysts’ molar ratios. Increasing the molar ratio of catalyst (II) to catalyst (I) resulted in a notable enhancement of the products’ complex viscosity due to the increased MW, a higher level of chains’ entanglements and formation of amorphous blocks along the polymer chains. All products exhibited a single relaxation that shifted towards longer times upon changing the catalysts’ molar ratios. Scanning electron microscopy results revealed that the fracture surface of the blends, synthesized by the binary catalyst system, became more heterogeneous in comparison with the products obtained by the individual use of the catalyst (I). The observed heterogeneity was found to increase by increasing the amount of catalyst (II). Such morphological change was further corroborated by the dynamic rheological data, indicating a promising correlation between the linear rheological results and the morphological features of the synthesized PP reactor blends.