Chain Propagation Mechanisms

Abstract

The copolymers of olefins with carbon monoxide are of great interest from at least four standpoints [1. First, as a monomer, carbon monoxide is particularly plentiful and inexpensive. Second, the presence of the carbonyl chromophore in the backbone makes them photodegradable [2], A third reason for the interest in olefin-carbon monoxide copolymers is that, because of the ease with which the carbonyl group can be chemically modified, the polyketones serve as excellent starting materials for other classes of functionalized polymers. In fact, about two dozen polymers incorporating a variety of functional groups have been previously synthesized [la] from the random ethylene-carbon monoxide copolymer (C₂H₄:CO>1) made through radical-initiated polymerization. Since carbon monoxide does not homopolymerize, the alternating olefin-carbon monoxide copolymers (olefin: CO = 1) have the highest possible concentration of the reactive carbonyl groups. Moreover, the 1,4-arrangement of the carbonyl groups in the alternating olefin-carbon monoxide copolymers provides additional functionalization pathways [3]. Finally, specific interest in the alternating ethylene-carbon monoxide copolymer stems from its high mechanical strength which results from its high crystallinity [1c,d,4]. To date, the metal ions that have been found to be active for the copolymerization and cooligomerization of vinyl monomers with carbon monoxide are palladium(II), nickel(II), and rhodium(I). The mechanistic pathways through which chain growth occurs at these metal centers are discussed below.