History of Polyketones

The first palladium complex-catalyzed alternating copolymerization of ethylene and carbon monoxide was disclosed by Gough at ICI [8] in 1967. The polymer was produced at relatively low rates in severe reaction conditions (250 °C, 200 MPa). 

During the following 15 years, only small advances were achieved in increasing catalyst efficiencies. Independently, Fenton [9a] at Union Oil and Nozaki [9b] at Shell Development Company (USA) discovered several related palladium chlorides, palladium cyanides, and zero-valent palladium complexes as catalysts. Sen and co-workers [10] reported that cationic bis(triphenyl-phosphine)-palladium tetrafluoroborate complexes in aprotic solvents such as dichloromethane, produced ethylene/carbon monoxide copolymers under very mild conditions. The reaction rates were, however, very low, as were the molecular weights. 

Rhodium carbonyls have also been reported as catalysts for the alternating copolymerization of ethylene and carbon monoxide [11], but activities and yields as well as molecular weights were again very low. 

In addition to the synthesis problems mentioned above, unsurmountable processing problems were eneountered for the resulting polymers. Extensive erosslinking under melt proeessing eonditions led to a lack of significant thermoplastic properties of the resulting materials, and this also presented a major developmental hurdle. At the end of the 1970s, it was therefore concluded that the polymer baekbone of polyketone was inherently unstable and that polyketones eould not be efficiently produced. Both conclusions proved to be invalid. 

In the early 1980s, workers at Shell could demonstrate melt processability of polyketone produeed by palladium cyanide catalysts, after extensive extraction of catalyst residues from the polymers and blending these with other polymers such as styrene/acrylonitrile copolymer. From these studies, it was suggested that thermoplastic properties were possible in principle, and that the polyketone backbone was not inherently unstable in the melt as previously concluded. However, catalyst extraction did not offer a viable production option from a technical and economic viewpoint. 

---

The copolymerization of ethylene and carbon monoxide to give alternating copolymers has attracted considerable interest in both academia and industry over recent decades [1, 2]. Attention was focused on aliphatic polyketones such as poly(3-oxotrimethylene) (1) because of the low cost and plentiful availability of the simple monomers. The new family of thermoplastic, perfectly alternating olefin/ carbon monoxide polymers commercialized by Shell provides a superior balance of performance properties not found in other commercial materials the an ethylene/ propene/CO terpolymer is marketed by Shell imder the tradename Carilon . About the history of polyketones see Refs. [3-11],... 

---