Quasiliving Carbocationic Polymerization. Xi: an Interpretation of Solvent Effects by Donor and Acceptor Numbers

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Counteranion/solvent interactions (counteranion solvation) profoundly influence each and every elementary step of carbocationic polymerizations and are just as important as the commonly emphasized cation/solvent interactions (cation solvation). Counteranion solvation and carbocation solvation have been characterized by Gutmann' s acceptor number AN and donor number DN, respectively. Analysis of earlier data leads to the conclusion that the effect of monomer concentration on the rate, molecular weight, and molecular weight distribution obtained in cationic olefin polymerizations in “polar” solvents are in fact due to subtle changes in solvent concentration. Indeed, olefin monomers behave as “nonpolar” solvents and by changing the monomer concentration the character of the medium may profoundly change. It is further concluded that quasiliving polymerizations cannot be achieved in batch operations because the conditions that prevail in the initial charge, although possibly suitable for quasiliving polymerizations, must continuously change with the diminishing monomer concentration, i.e., by continuously changing the solvent character of the system. In contrast, in continuous systems initial conditions in the charge suitable for the attainment of living or quasiliving conditions can be maintained even for long periods of time by continuously replenishing the consumed monomer. By the use of these concepts, heretofore unexplained observations made in the course of quasiliving polymerization studies have been accounted for and, beyond this, new insight into solvation phenomena in cationic polymerizations is generated.

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Journal of Macromolecular Science: Part A - Chemistry





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