Recent Advances in Olefin Polymerization Using Binary Catalyst Systems (original) (raw)

A few considerations on some catalysts for olefin polymerization

Makromolekulare Chemie. Macromolecular Symposia, 1993

Among many precursors and catalysts for alpha‐olefins polymerization, one seems to be particularly interesting, because it has not been completely clarified yet.We refer especially to precursors obtained via reaction between Mg‐alkyls and SiCl4.The products of this reaction are not well known; in fact, under some operating conditions, a special form of MgCl2 is obtained, showing x‐ray diffraction peaks in the angular region lower than 15° (2 theta), which corresponds to the 5.9 A interplanar spacing, characteristic of alpha‐MgCl2.Under other conditions, MgCl2 is obtained in the well known and strongly disordered delta structure.By employing these precursors, some catalytic systems for alpha‐olefins polymerization have been prepared.In this paper, the peculiar aspects of these precursors and catalysts are described, particularly focusing on the correlation between structure and performances in ethylene and propylene polymerization.

Catalysts for olefins polymerization

Catalysis Today, 1998

Polyole®ns are still protagonist of an exciting innovation, due to a continuous development of new catalysts, processes and products. The positive solutions given by polyole®ns to the environmental and energetic issues are among the factors responsible for their success. The most relevant breakthrough occurred in the last years is the discovery of metallocenes, and more in general, of single centre catalysts. They are, in most cases, highly active catalysts and are already employed on the industrial scale for the preparation of both``drop-in'' products with improved properties, and of totally new materials. # 1998 Elsevier Science B.V. All rights reserved.

Polymer support of “single-site” catalysts for heterogeneous olefin polymerization

Progress in Polymer Science, 2011

The discovery of metallocenes and post-metallocenes has revived olefin polymer chemistry as these single-site catalysts enable the production of (co)polyolefins with tunable molecular structures, stereochemistries and molecular weight distributions. To be used in industry, however, such catalysts have to be manipulated under conditions already common to existing polyolefin production processes. This means, in particular, that their heterogenization is required to produce beads of polyolefins and prevent reactor fouling, and this in turn leads to the use of supports for these catalysts. The large majority of supports currently used in industry are inorganic-based, with silica being the most important. Organic supports are also of interest as they are expected to be more versatile and less expensive. This review presents a detailed survey of the different routes to immobilizing single-site catalysts on organic supports. The various methods as well as the different types of supports are described. The influence of the organic support on the catalytic activity and main features of the thus formed polyolefin viz. molecular weight, dispersity and morphology, are also considered.

Covalently Linked Heterobimetallic Catalysts for Olefin Polymerization

Organometallics, 2004

This contribution describes the synthesis and polymerization characteristics of the covalently linked heterobinuclear constrained-geometry polymerization catalyst (µ-CH 2 CH 2-3,3′){(η 5-indenyl)[1-Me 2 Si(t BuN)]-(TiMe 2)}{(η 5-indenyl)[1-Me 2 Si(t BuN)](ZrMe 2)} (Ti 1 Zr 1). When activated with Ph 3 C + B(C 6 F 5)-4 , it is competent to produce long-chain (gC 6) branched polyethylenes in ethylene homopolymerization, in sharp contrast to control experiments with mixtures of analogous but mononuclear Zr and Ti CGC catalysts.

Polymerization of Ethylene with Catalyst Mixture in the Presence of Chain Shuttling Agent

Chemistry & Chemical Technology, 2012

Mixture of two catalysts in one reactor for ethylene/α-olefin copolymerization in the solution process can result in the combination of microstructures related to both catalysts in the polymer framework. Thus, novel polymer configuration is synthesized, which is characterized by containing sequences of monomers produced with each catalyst in the same polymer chain. Adding a reversible transfer agent (CSA) to the binary system enables the production of new block copolymers with enhanced properties. Late transition metal catalysts, such as α-diimine nickel catalyst when activated with methylaluminoxane (MAO) show high activity towards olefin polymerization and produces highly branched homopolymers. On the other hand, C 2 symmetry metallocene catalysts produce linear polyethylenes. This paper describes the synthesis of ethylene homopolymer with amorphous and crystalline blocks using a binary mixture containing a nickel catalyst with α-diimine ligand, which produces ф highly branched polyethylene (soft PE) and a metallocene (rac-ethylene bis(H 4-indenyl)ZrCl 2) that converts ethylene into polyethylene with high activities and melting temperatures (hard PE). The influence of polymerization temperature and CSA concentration were investigated. The polymeric materials were characterized by density, thermal properties, X-ray diffractometry and dynamic-mechanical properties.

Effect of monomer diffusion in the polymerization of olefins over Ziegler-Natta catalysts

1989

By using an extremely high stereospecific catalyst, three kinds of copolymerizations were carried out with combinations of monomers which differ in thecrystallinity of the homopolymers. Addition of a small quantity of comonomer to the homopolymerization systems producing very high crystalline polymers was found to cause a remarkable increase in the apparent polymerization rate as well as a marked decrease in the polymer crystallinity. Such an irregular increase in the polymerization activity was, however, not observed when a small amount of comonomer was added to the homopolymerization systems producing low-crystalline or amorphous polymers. These observations have led to the conclusion that resistance of monomer diffusion through the polymer film should be one of the significant parameters for the apparent polymerization rate when very high crystalline polymers, like high density polyethylene, isotactic polypropylene etc., are produced.