Ionomeric interpretation of thickening of polyesters by alkaline earth metal oxides

Abstract

Four resins of poly(propylene glycol adipate) were mixed with different amounts of MgO and their viscosities were measured after a month. The viscosities increased by several thousand but the increase was less for resins containing more water. The existing explanations of the thickening behavior, namely the polymerization and the coordinate complex formation theories, were found to be inadequate in accounting for the observations. Small‐angle x‐ray scattering (SAXS) and transmission electron microscopy (TEM) of the thickened resins revealed formation of aggregates of magnesium ions, much like those observed in other ionomers. It is postulated that domain formation is the cause of observed thickening. A correlation between the viscosity of thickened resins and the amount of metal oxide reacted, the water content, and other properties of resin was obtained.

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

“…Adamantane was used to optimize the Hartmann-Hahn condition. 13 C chemical shifts were referenced to the methylene resonance of adamantane (38.3 ppm relative to tetramethylsilane). 13 C CP/MAS spectra were recorded for three different values of the crosspolarization time: 0.08, 0.8, and 8 ms.…”

“…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.…”

“…The ionomeric mechanism suggests that the network is formed by means of aggregation of magnesium carboxylato salts into ionic clusters, similar to the mechanism in ionomers. Numerous studies of SMC suggest that the ionomeric mechanism is the most realistic one. ,,− However, detailed structural information is not available and a possible influence of coordination of other chain portions with Mg 2+ ions on the viscosity cannot be excluded.…”

“…13,14,[17][18][19][20] However, detailed structural information is not available and a possible influence of coordination of other chain portions with Mg 2+ ions on the viscosity cannot be excluded. 1 H and 13 C solid state NMR, WAXD, and SAXS experiments were used in this study to determine (1) the structure development during thickening, (2) the molecular structures which are formed during thickening, and (3) the molecular mechanism which is responsible for the viscosity increase. The results are briefly compared with those obtained from a simultaneous study using dynamic mechanical experiments and dielectric spectroscopy.…”

“…C MAS, CP/MAS and inversion-recovery CP/MAS NMR spectra were recorded on a Varian Inova-400 MHz wide-bore NMR spectrometer operating at a 13 C frequency of 100.58 MHz, using a 7 mm CP/MAS probe. The 1 H and 13 C 90°pulse width was about 5 µs.…”