A study of chain transfer in homologous vinyl esters

Abstract

The principal complication arising out of free radical‐initiated polymerizations involving vinyl acetate has been the chain transfer to monomer and polymer which results in a highly branched polymer chain. Some evidence has also been presented to show that the degree of branching in polyvinyl esters increases with an increasing number of carbon atoms in the vinyl ester. It was of interest, therefore, to obtain a relative measure of the chain transfer constants for successive members of the homologous series of vinyl esters and to relate the constants to the actual structure of the respective polyvinyl ester. Accordingly, the study of the chain transfer in the benzoyl peroxideinitiated polymerizations of vinyl acetate in the presence of a homologous series of ethyl esters of fatty acids was made. Chain transfer constants versus number of carbon atoms in the carboxylate portion of the fatty acid ester resulted in a linear relationship which can be expressed as where n is the number of non‐α‐methylene groups in the side chain. A concurrent study of the influence of monomer chain lengths of selected vinyl esters on molecular weight of the derived homopolymer was also carried out. The results obtained provide a basis for predicting the trends for changes in branching and degree of polymerization within the homologous series of vinyl esters.

Intrinsic viscosity‐number average molecular weight relationship for poly (n‐Octadecyl acrylate) and poly (N‐n‐octadecylacrylamide)

“…It might be that a small difference in radical reactivities, accruing for every added methylene across the homologous series, might cause this difference. An analogous situation has been noted for differences observed between transfer to monomer for vinyl ester homologs, and transfer to ethyl esters of the same chain length by vinyl acetate (28). In this instance, also, the difference in transfer constants was by a factor of about 2.…”

Chain transfer to monomer and polymer in the radical polymerization of vinyl neo-decanoate

“…1 The data is not reliable, as the average degrees of polymerizations were not extrapolated to zero initiator concentration or rate of polymerization, as is the case with the commonly used Mayo method. Furthermore, the average degree of polymerization was calculated assuming the same relationship between viscosity and average degree of polymerization as for vinyl acetate.…”

“…3 As with the Mayo method, polymer formed at low conversion and low initiator concentrations could be used to find C M under conditions such that transfer to polymer or adventitious chain transfer agent are negligible. Clay and Gilbert demonstrated that the instantaneous number distribution P(N) under these conditions would be given by (1) The cumulative distribution will be equal to P(N) as C M is independent of conversion, and the slope of a logarithmic plot of P(N) as a function of N equal to C M . As termination was not negligible at low N for most experimental conditions they recommended that the slope at high N, where a linear plot could be obtained, should be used to calculate C M .…”