Lauric acid/pentaerythrityl monolaurate: a model melt esterification. Part 2.—Statistical distribution of products

Abstract

The esterification of lauric acid, LA, with pentaerythrityl monolaurate (PEML) has previously been shown to exhibit a positive kinetic substitution effect in the PEML moiety: each OH previously esterified in PEML (or in pentaerythritol, PE, itself) accelerates the esterification of any remaining OH in the same PEML unit (first-shell substitution effect, FSSE) by a factor of about 1.3–1.4. This corresponds to a small difference in activation free energy (2–3 kJ mol^–1), but a similar effect in polycondensations of PE with dibasic acids causes substantial changes in gel points, network structure and physical properties, so that the thorough investigation of the simple model system LA/PEML is of value. The substitution effect is here confirmed by comparing gel permeation chromatographic measurements of the composition as a function of conversion with the statistical theory of the FSSE. The mechanism of esterification in undiluted melts is briefly reviewed. In ungelled systems, no evidence for diffusion control, for effects due to the size of reagent species, or due to the change in medium with increasing conversion, is generally found.