Organic Versus Inorganic Supports for Metallocenes: The Influence of Rigidity on the Homogeneity of the Polyolefin Microstructure and Properties

Abstract

A procedure to obtain very uniform polyolefin copolymers by supported metallocenes is presented. Conventional metallocene or Ziegler–Natta catalysts, both immobilized on inorganic supports, yield only copolymers with inhomogeneous comonomer incorporation and broad short-chain branching distribution. The main reasons are diffusional limitations of the monomers or the multisite character of the catalysts. By comparing inorganic and organic supports, we demonstrate that metallocenes immobilized on organic supports solve these problems. In this regard, organic and soft nanosized polystyrene particles (nPS) versus industrially used, hard, and inorganic SiO2 were used to support [Me2Si­(Ind)2ZrCl2/MAO (I) and Me2Si­(Benz­[e]-Ind)2ZrCl2/MAO (BI)] catalysts for ethylene/1-hexene copolymerization. In the inorganic case, the catalyst systems show a substantial inconsistency in the copolymers’ branching distribution, resulting in phase separation. One phase is hexene-poor with high melting temperature (T m) and high molecular weight (MW). The second, hexene-rich phase, however, shows lower T m and MW. By using organic supports, comonomers are uniformly inserted into the polymer chain and homogeneous microstructured copolymers are obtained. These findings are mainly attributed to diffusion processes of the monomers into the soft organic material. To prove this conclusion and to elucidate the structure of the catalyst system, various characterization techniques such as time-of-flight secondary ion mass spectrometry and scanning electron microscopy–energy-dispersive X-ray were performed.

Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst

“…Homogeneous single-site catalysts, such as metallocene and half-metallocene, and post-metallocene catalysts are actively used in the production of polyethylene (PE) and polypropylene (PP), although most PE and PP is still produced by suing heterogeneous Ziegler-Natta catalysts [1,2]. While homogeneous catalysts can be directly used in a solution process where polymers (e.g., polyolefin elastomer (POE) with high α-olefin content) are formed by dissolution in solvent, they should be immobilized on an inorganic support, e.g., silica, in order to be applied in a slurry-process or a gas-phase process, where the morphology of the generated polymer particles is of importance for stable operation [3][4][5][6][7][8][9][10][11]. When a homogeneous catalyst is injected, as dissolved, into a slurry-or gas-phase reactor, the shape and size of the generated polymer particles are irregularly uncontrolled, making stable operation impossible (termed 'fouling') as well as causing low productivity due to low bulk density.…”

Porous Organic Polymers-Supported Zeigler-Natta Catalysts for Preparing Highly Isotactic Polypropylene with Broad Molecular Weight Distribution

“…However, the inorganic support components would eventually incorporate extra impurities and surface acidic groups in the final product, which might limit its applications in high value-added fields, such as the electronics and medical industries. As a potential clean and green alternative composed mainly of C, H and O atoms, etc., porous organic polymers (POPs) have received extensive attention in heterogeneous catalysis, including olefin polymerization, owing to their high surface area and controllable pore structure, flexible synthesis strategy and functionality [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Moreover, the less hydrophilic surface of POPs allows them to endure higher impurity contents of moisture and oxygen in the polymerization medium, need no fastidious pre-treatment, and provides a polymerization medium more close to homogeneous catalysis [ 31 , 32 ].…”

Immobilized Polyolefin Catalysts: Organic Versus Inorganic Supports

“…Klapper and co-workers [12] have revealed that the inorganic and organic supports based metallocene catalysts can impose substantial inconsistency in the incorporation of comonomer and short chain branching (SCB) [22]. The SCB distribution of the prepared PE copolymer from silica gel-supported metallocene is inhomogeneous, while by comparison, 1-hexene insertion is quite uniform in all the PE chains from the organic PS-based metallocene.…”