Syndiotactic polystyrene catalysts and polymerization

Abstract

After the first preparation of syndiotactic polystyrene in 1985, the synthesis of this polymer has gained much interest in the last decade especially in catalyst and polymerization research and has led to a fast commercialization of this product. This literature review gives a comprehensive overview on the catalytic systems and especially on the transition metal complexes investigated in the syndiospecific homopolymerization of styrene. It includes the polymerization activity of the catalysts itself, the syndiotacticity and other properties of the polymers received with these catalysts as well as the discussion of the relationships between structure and properties. The mechanism of the syndiospecific polymerization is summarized and discussed in a separate chapter. The review of the catalytic systems for the syndiospecific polymerization of styrene comprises transition metal complexes, cocatalysts (methylalumoxanes and boron compounds), activators and chain transfer agents, and supported catalysts. Transition metal complexes contain first transition metal complexes, group 4 metal complexes (mono- and bis-cyclopentadienyl complexes, metal complexes with other ring systems and binuclear catalysts, non-metallocene complexes), and metal complexes of other transition metals. The chapter on mono- and bis-cyclopentadienyl complexes gives an overview of the influence of the transition metal, mono- or bis-cyclopentadienyl substitution, variation of the structure of the cyclopentadienyl ligand, and the influence of other complex ligands besides cyclopentadienyl. The chapter on the mechanism of the syndiospecific polymerization includes an overview of the mechanism, the initiation reaction and the active species, the propagation reaction (mode of addition to the double bond, monomer insertion into the metal–carbon bond, chain-end control mechanism, active site of propagation), chain transfer and termination reactions and kinetic parameters.