Role of organometallic complexes in olefin polymerization: a review report

Abstract

• A detailed discussion on various organometallic complexes used for olefin polymerization, has been done. • Regulation on composition and microstructure of the polymer products can be done by altering the metal center and the auxiliary ligand of an organometallic complex. • The organometallic catalysts of group 3 metals for the polymerization of olefins are still less discovered and very uncommon and group 4 metal-based catalysts holding diverse auxiliary ligands have been widely researched and investigated. • Increase in performance of homogeneous catalysts by introducing them on metalasiloxanes. The chemistry of catalytic polymerization of ethylene and propylene employing titanium complexes and aluminum-alkyls as co-catalysts is well known since last 50 years. Thorough studies show that invention of homogeneous organometallic complexes as catalysts such as metallocenes and other transition metal complexes with methylaluminoxane (MAO) as co-catalyst for the polymerization of olefins has achieved a lot of interest in this area as compared to the well-known and conventional heterogeneous catalysts i.e. Ziegler–Natta and Phillips catalyst. The possibilities of controlling the polymer composition, microstructure, tacticity, stereoregularity and special properties with high precision are found to be high in homogeneous catalysts. Availability of single active accessible site on metallocene catalysts in contrast to their classical equivalents is responsible for improved catalytic polymerization. Furthermore, these single-site catalysts, such as half titanocenes/MAO, zirconocenes, and other single-site catalysts, can control important parameters like co-monomer distribution, molecular weight, molecular weight distribution, molecular architecture, stereo-specificity, degree of linearity, polymer branching etc . The purity in products found less when Ziegler–Natta catalysts were used. This review summarises and compares the recent advances in the polymerization of various olefins (especially ethylene or α-olefins) using various organometallic catalysts consist of rare-earth elements and lanthanides, group 4 metals, and other transition metals (V,Cr and Ni). At the end the review discusses modulation of catalytic activity to control polymerization reactions and concludes the study with future challenges in the area.