Aromatic Polymers: Synthesis via Nickel Catalyzed Coupling of Aryl Chlorides

A new method for the formation of high molecular weight aromatic polymers via the nickel coupling of aromatic dichlorides will be described. The novel polymerization is performed in a dry aprotic solvent (e.g., in DMAC) using catalytic amounts of zero-valent nickel, triphenylphosphine or bipyridyl ligands, and excess zinc metal. The reaction must be performed under an inert atmosphere and in the absence of water. In order to obtain high polymer, one must use low amounts of nickel, high triphenylphosphine/nickel ratios, excess zinc metal and moderate temperatures (70 degrees C). Variables such as the choice of ligand or co-ligand, salt addition, ligand and zinc concentrations, allow for optimization of the reaction efficiency. Critical features of the polymerization mechanism will also be reviewed. The method is general and allows for the preparation of novel monomers and an almost infinite variety of polymers. The two prerequisites for a successful preparation of high molecular weight product are solubility of the monomer, and more particularly of the obtained polymer, in the reaction medium; and the necessity that any functional group(s) present in the monomer(s) (and in the resulting polymer) be inert toward zinc/nickel system. Materials that were prepared via the novel method include polyarylethersulfones, polyaryletherketones, polyphenylenes and polyamides. The approach is particularly suited for the synthesis of biphenylene based resins, e.g., polybiphenylene ethersulfone, because coupling of a chlorophenyl moiety creates a biphenyl unit. The latter display a number of highly attractive characteristics, such as high glass transition temperatures, low moisture absorption and extremely high impact strengths and toughness. An intriguing feature of the nickel coupling polymerizations and copolymerizations is encountered in instances that involve aryl chloro dichlorides possessing dissimilar chloro moieties. A number of sequence distributions are then possible in the resulting polymer. In some instances, different microstructures were indeed obtained under different experimental conditions when such "asymmetric" dichlorides were used.