Polyketone synthesis

Palladium catalysts also promote copolymerization of SO2 with alkenes analogously to copolymerization of CO and alkenes (Eq. 7.24) [119]. The catalyst activities for the polysulfone synthesis are lower by an order of magnitude than those for the polyketone synthesis. Perfectly alternating copolymers can be obtained by use of cationic methylpalladium(II) complexes, [PdMe(CH3CN)L2]BF4 (L2 = l,3-bis(diphenylphosphino)propane and 1,2-bis(2,5-dimethylphosphinolato)benzene), in contrast to a lower degree of alternation provided by a radical polymerization [120]. 

Yang J, Gibson HW (1999) A polyketone synthesis involving nucleophilic substitution via carbanions derived from bis(a-aminonitrile)s. 5. A new, well-controlled route to long bisphenol and activated aromatic dihalide monomers. Macromolecules 32 8740-8746... 

Recently developed catalyst systems make it possible to construct carbon (.v/>2 )-catbon (sp3) bonds and carbon-nitrogen bonds under mild conditions (Scheme 9.14).19,20 These new developments have also been incorporated into step-growth polymerization. Kanbara et al. reported the synthesis of polyanilines and related polymers in 1996 (Scheme 9.15).21 Wang and Wu reported the synthesis of polyketones in 1999 (Scheme 9.16).22... 

Although only several reports appeared employing these reactions for polymerization, they could potentially be used for the synthesis of different types of polyamines and polyketones, including optically active ones with main-chain chirality. 

The copolymerization of carbon monoxide and a-olefins is one of the most challenging problems in polymer synthesis. Sen and his coworkers discovered that some cationic palladium compounds catalyze this alternative copolymerization, giving polyketones (Eq. 13). 

The most common alkenes employed in the Pd-catalysed synthesis of alternating polyketones are ethene, styrene, propene and cyclic alkenes such as norbomene and norbornadiene. Even though the mechanism does not vary substantially with the alkene, the reactions of the various co-monomers are here reported and commented on separately, starting with the ethene/CO copolymerisation, which is still the most studied process. As a general scheme, the proposed catalytic cycles are presented first, then the spectroscopic experiments that have allowed one to elucidate each single mechanistic step. 

The application of polyketone-derived anions to the synthesis of oxygen heterocycles has much to offer a comprehensive review of this area has been published (77T2159). 

As pointed out in the introduction, because of the ease with which the carbonyl group can be chemically modified, the polyketones should be excellent starting materials for the synthesis of other classes of functionalized polymers. Indeed, a large number of derivatives of the C2H4—CO copolymer has been prepared and, not surprisingly, the vast majority of these are described in the patent literature. Patents concerning the use of these derivatives in polymer blends have also appeared but these are outside the scope of this review. 

While certain intereshng aspects have been recently discovered, the potential of BVMO-mediated biooxygenation of multifunctional substrates and, in particular, of polyketone compounds, is yet to be fully investigated. Further studies in this area certainly contain the prospect of high impact contributions for the further improvement and increase in efficiency for future applications in single-operation multistep synthesis. 

These complexes result from the coordination of tri-, tetra- or polyketonates to two or more metal centers (138-140). Because these topics have been reviewed widely and recently and, in addition, the methods of synthesis are not different from those outlined above, only a few of them will be discussed. 

Also, the carbonyl group can be derivatized to a variety of interesting new materials. Significant advances in technological synthesis and processing made by Shell over the past decade have now moved aliphatic polyketones to commercial reality [2]. 

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. 

This discovery of the combined importance for high catalyst activity of biden-tate ligands and weakly coordinating anions around a cationic palladium(II) center has, for the first time, given access to efficient synthesis of polyketones. These new catalysts opened the way to economically attractive production and, equally important, provided much more stable polymers with catalyst residues now measured in parts per million rather than percentages. Polyketone thermoplastics have been developed to be easily melt-processable, and could therefore be shown to exhibit a unique set of desirable engineering thermoplastic properties [2]. 

Money, Scott and coworkers utilized a similar strategy of protecting the labile polyketone as a pyrone ring. As shown in equation (ISO), pyranopyrone (133) reacts with aqueous base to give orsellinic acid, presumably by way of the intermediate triketo diacid (134).174 The procedure was found to be quite general equation (151) shows a further application in the synthesis of pinosylvin, (135).175... 

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