Nickel salicylaldiminato catalysts for olefin polymerization in organic and aqueous media.

摘要

There has been increased interest in late transition metal catalyzed olefin polymerizations. This is due, in part, to the ability of late transition metal catalysts to yield new polymers. Among them, neutral nickel salicylaldiminato catalysts have gained importance in recent years due to their functional group tolerance. Schiff's base chemistry was employed to synthesize a wide variety of ligand frameworks. These ligands, combined with discrete metal precursors led to the synthesis of neutral nickel salicylaldiminato catalysts 11-13. A phosphine sponge was needed to activate these catalysts for olefin polymerization. An inexpensive phosphine sponge such as copper (I) halide was successfully used as a cocatalyst to perform polymerization of ethylene in organic media. The functional group tolerance of the catalyst and cocatalyst allowed for polymerization of ethylene in water leading to polyethylene latexes. The polymerizations were performed under moderate conditions of pressure and temperature to yield low molecular weight polyethylene with up to 100 branches/1000 C atoms. The effect of the nature of the ligand framework on the activity of the catalyst and the molecular weight of the polymer obtained was studied. Copolymerization of ethylene with functional monomers was performed in organic or aqueous media leading to polyolefins with incorporated functionality. Norbornene was also polymerized by complexes 11-13 with either a borane or methyl aluminoxane (MAO) cocatalysts. The microstructure of the polynorbornene obtained was found to be dependent on the nature of the cocatalyst. A wide variety of functionalized norbornenes were also effectively copolymerized with norbornene. A variety of chain transfer agents such as 1-octene and 5-bromo-1-pentene were used to control the molecular weight of polynorbornenes. These chain transfer agents were also used successfully to control the molecular weight of the copolymers of norbornene with functional norbornenes. All of the polymers were characterized by spectroscopic and thermal methods of analysis.