Olefin Polymerization with Polar Ligands

II. Mechanism of Olefin Polymerization with Polar Ligands. 61... 

This review will feature the kinetics and mechanism of RLi-initiated, homo- and copolymerization of hydrocarbon diene and olefin monomers, with and without polar ligands. Hydrocarbon olefin homopolymerization in nonpolar media will not be discussed per se because simple olefins such as ethylene do not polymerize under such conditions, and such reactive, hydrocarbon a-olefins as styrene behave similarly to dienes in... 

Alkenes and/or alkynes can be dimerized, telomerized, and polymerized under palladium-catalysis. In an effort to copolymerize polar co-monomers, Johnson et al. investigated catalysts based upon palladium. These catalysts were referred to as postmetallocene catalysts. They were based upon complexes bearing bulky, neutral, alpha-diimine (or diketimine) ligands. They have been commercialized as DuPont s Versipol olefin polymerization system. The commercial synthesis of 1-octene (starting in 2007) is a palladium-catalyzed telomerization of butadiene with methanol. ... 

Brookhart and co-workers [79-81] introduced catalysts based largely on chelating, nitrogen-based ligands that are active for the homopolymerization of ethylene and the copolymerization of ethylene with 1-olefins and polar comonomers (31). Ni, Co, Fe or Pd are used as late transition metals. The diimine ligands have big substituents to prevent 6-hydride elimination. Ni(II) or Pd(II) complexes form cations by combination with MAO and polymerize ethylene to highly branched polymers with molecular weights up to one million. The activities reach TON... 

The choice of the most effective catalyst system is highly dependent on the type of olefin under consideration. Polymerization of CO and aliphatic a-olefines is most suitably carried out employing a catalytic system modified with a symmetrical, Cs-bridged aryldiphosphine ligand (2,71). However, these systems are not suitable for copolymerization of CO and styrene (41). For this reaction palladium(II)-based catalysts modified with a conjugated diimine (39,41), a bisoxazoline (43,44), a phosphine-phosphite (43), or a phosphine-imine ligand (43) have been employed, in, under chain-transfer conditions, combination with an oxidant promotor, such as 1,4-benzoquinone or 1,4-naphthoquinone (39-47,72), or a polar, acidic type of solvent (73,74). 

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