Control of molecular weight distribution in propylene polymerization with Ziegler-Natta/metallocene catalyst mixtures

Abstract

Propylene polymerization was investigated with a sequential addition of Ziegler-Natta and metallocene catalysts. From the fact that the molecular weights of polypropylene (PP) produced with Ziegler-Natta and with metallocene catalysts differ, it was possible to control the molecular weight distribution (MWD) of PP with a sequential addition of methylaluminoxane and rac-ethylenebis(indenyl)zirconium dichloride followed by triethylaluminum and magnesium dichloride-supported titanium tetrachloride catalyst. The obtained PP exhibited a wide MWD curve with shoulder peak. The position and height of each peak was controlled with the variation of polymerization time for each catalyst as well as the amount of each catalyst. The MWD of PP prepared with sequential addition of catalysts was much wider than that of PP obtained from each catalyst.

Recent Advances in Olefin Polymerization Using Binary Catalyst Systems

“…(iii) The third method utilizes the variation of operation conditions, such as temperature, comonomer concentration, and hydrogen pressure (non-steady-state polymerization), in a single reactor during polymerization. [4] This process is effective for laboratory-scale reactors, but is unlikely to be applied to the production of commodity polyolefins. (iv) Finally, the fourth method consists of combining two or more types of catalysts to produce polymers with different and controlled MW and MWD in a single reactor.…”

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

“…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 ].…”

Bimodal polypropylene through binary metallocene catalytic systems: comparison between hybrid and mixed heterogeneous catalysts

“…However, this method involves additional processes and increases costs considerably [9], and 3) Combination of a binary or multicomponent catalytic system in a single reactor with the subsequent cost saving. This last method can comprise a combination of a heterogeneous Ziegler-Natta catalyst and a homogeneous metallocene catalyst providing a means to control the MWD and polydispersity of the polyolefin [10] but a disadvantage of this particular binary system comes from triethyl-aluminium (TEA) used to activate Ziegler-Natta since it has a serious detrimental effect on metallocene active sites [11] Therefore, an economical and attractive route is to use two or more metallocenes simultaneously yielding a polypropylene mixture consisting on the polymer fractions produced by each metallocene [12][13][14][15][16]. In this sense, it is important to decide which metalocenes will be present in the catalytic system, since they should have different kinetic responses, such as different propagation and termination rate constants, in order to produce a blend of polymeric chains with different predominant molecular weights.…”