Ion aggregation in magnesium‐neutralized polyester resins — Small angle X‐ray scattering study

Abstract

Evidence for ion aggregation was found in SAXS studies of models of unsaturated polyester resins: magnesium icosanoate, magnesium α,ω‐dicarboxylatopoly(ethylene adipate), ‐poly(1‐hexylethylene adipate), ‐poly(propylene succinate), and ‐poly(propylene maleate‐co‐fumarate), swollen by various solvents or in the dry state. The results were compared with those obtained for commercial unsaturated polyester resins after neutralization with MgO, leading to the conclusion that the formation of aggregates is the key phenomenon of the so‐called thickening reaction of polyester resins. The existence of high amounts of branched units in the polyester chain does not appear to hinder ion aggregation. The aggregates are small (Guinier radius RG = 4 to 9 Å) and their average distance increases with chain length and swelling.

Telechelic Ionomers: Molecular Structure and Kinetics of Physical Gelation of Unsaturated Polyester as Studied by Solid State NMR and X-ray

“…Despite numerous studies, the thickening mechanism of UP is not well understood. − Three basic mechanisms have been proposed: (1) polymerization mechanism, (2) coordination complex mechanism, , and (3) ionomeric mechanism. ,,− According to all these mechanisms, the thickening starts with an acid−base reaction between a metal oxide (usually MgO) and carboxylic end groups which results in the formation of basic and/or neutral salts. The reaction is accomplished within 2−45 h after addition of MgO to UP.…”