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

Abstract

Summary: Propylene was polymerized by three homogenous metallocene catalytic systems: rac-Me 2 Si (Ind) 2 ZrCl 2 (CAT-1), rac-Et(Ind) 2 ZrCl 2 (CAT-2) and rac-Me 2 Si(2-Mebenzoind) 2 ZrCl 22 ZrCl 2 (CAT-3) at 50 8C. In function of the molecular-average weight results of poly(propylene)s obtained, rac-Et(Ind) 2 ZrCl 2 (CAT-2) and rac-Me 2 Si(2-Mebenzoind) 2 ZrCl 2 (CAT-3) were combined in different proportions (wt %/wt %) of (CAT-2/CAT-3) for obtaining a new poly(propylene) with a bimodal molecular weight distribution consisting in clearly separated low and high molecular weight polymer fractions with a difference between them of an order of magnitude. The polymers obtained were compared with those coming from melt mixing of two poly(propylene)s with different molecular weights in an extruder. Both methods allow obtaining bimodal poly(propylene)s, but polymer melt blending shows partial miscibility effects and less crystallinity while binary catalytic systems have several advantages such as lower costs and easier to process that can be controlled to tailor properties together with intimate mixing of high and low molecular weight components.

From Multisite Polymerization Catalysis to Sustainable Materials and All-Polyolefin Composites

“…The higher molar mass of the iso-rich PP was attributed to the Zr sites, whereas the lower molecular-weight fraction was synthesized on the Ti sites . By combining three different isospecific bridged metallocenes, Paredes varied the MWD of isotactic polypropylene . According to studies by Rytter − and Soares of ethylene polymerization on homogeneous dual-site catalysts, precise control of polyethylene MWDs via the molar ratios of the catalyst components is possible when taking into account the influence of various other parameters such as monomer type, temperature, pressure, comonomer, hydrogen, the presence of trimethylaluminum, and diffusion problems associated with the precipitation of polyethylene during polymerization.…”

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

“…As is well-established, MW is responsible for the mechanical properties and MWD is highly influential on the processability and rheological properties of the final polymer. In many applications, such as blow molding, extrusion and packaging, polymers with bimodal MWD are needed to attain a product with high mechanical strength, stiffness and impact strength and also a good level of processability [ 24 , 25 , 26 ]. Since each of the catalysts within the binary catalyst systems is able to produce a unique polymer, it would be possible to achieve PPs with bimodal or broad MWDs if the catalyst system is properly designed.…”

“…Since each of the catalysts within the binary catalyst systems is able to produce a unique polymer, it would be possible to achieve PPs with bimodal or broad MWDs if the catalyst system is properly designed. Therefore, some of the researchers used both homogeneous and heterogeneous binary metallocene silica-supported catalysts with different stereo-specificities to synthesize PPs with broad and bimodal MWD as well as stereoblock structures with different melting points [ 16 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. Numerous studies have been conducted on the microstructural characterization of PPs synthesized by binary or hybrid catalyst systems as well as the effects of type and composition of catalysts on their microstructures through different characterization techniques [ 15 , 35 , 36 , 37 ].…”