Carbonyl polymerization

The polymerization of the carbonyl group in aldehydes yields polymers, referred to as poly-acetals, since they contain the acetal repeating structure 

Besides the carbon-carbon double bond, this is the only other unsaturated linkage whose polymerization has been successfully carried out to an appreciable extent [Furukawa and Saegusa, 1963 Kubisa et al., 1980 Vogl, 1967, 1976, 2000], The polymerization of formaldehyde has been studied much more intensely than that of other aldehydes. Although formaldehyde was successfully polymerized over a hundred years ago, it was not until much later that high-molecular-weight polymers of other aldehydes were obtained. 

Progress in the polymerization of the carbonyl linkage did not result until there was an understanding of the effect of ceiling temperature (Tc) on polymerization (Sec. 3-9c). With the major exception of formaldehyde and one or two other aldehydes, carbonyl monomers have low ceiling temperatures (Table 5-13). Most carbonyl monomers have ceiling temperatures at or appreciably below room temperature. The low Tc values for carbonyl polymerizations are due primarily to the AH factor. The entropy of polymerization of the carbonyl double bond in aldehydes is approximately the same as that for the alkene double bond. The enthalpy of polymerization for the carbonyl double bond, however, is appreciably lower. Thus AH for acetaldehyde polymerization is only about 29 kJ mol-1 compared to the usual 80-90 kJ mol-1 for polymerization of the carbon-carbon double bond (Table 3-14) [Hashimoto et al., 1076, 1978], 

Most of the early attempts to polymerize carbonyl compounds were carried out at temperatures that were, in retrospect, too high. The use of temperatures above Tc resulted in the absence of polymer formation, due to the unfavorable equilibrium between monomer and polymer. Carbonyl monomers were successfully polymerized to high polymer when the 

A characteristic of aldehyde polymerization is the precipitation, often with crystallization, of the polymer during polymerization. Depending on the solvent used, polymerization rate, state of agitation, and other reaction conditions, the polymerization can slow down or even stop because of occlusion of the propagating centers in the precipitated polymer. The physical state and surface area of the precipitated polymer influence polymerization by their effect on the availability of propagating centers and the diffusion of monomer to those centers. 

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This enantioselective PO carbonylation is still in its infancy. Ongoing experiments are being performed to understand the limitations of these catalysts in order to successfully generate highly active and selective catalysts for this interesting route. This pathway may become even more valuable, since Coates recently reported a one-pot synthesis of PHB from PO via carbonylative polymerization [ 132] (Fig. 45). 

Fig. 7. Scheme for propylene carbonylation-polymerization on H-MOR. Reproduced from Refs. (93,94). 

This monograph is not intended to provide a comprehensive view of all ruthenium-catalyzed reactions, as this metal and its numerous complexes are now involved in many useful catal3 tic transformations. For instance, ruthenium-catalyzed carbonylation, polymerization, enantioselective hydrogenation and cyclopropanation... have not been included in spite of their high interest in synthesis. 

Quinzler, D, Mecking, S., 2009. Renewable resource-based poly(dodecyloate) by carbonylation polymerization. Chemical Communications (Cambridge, England) 5400-5402. 

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