Swelling effects in cross-linked polymers by thermogravimetry

Abstract

The present study focuses on the mechanism of swelling and evaluates interactions between solvents of different chemical characters (polar—ethanol, nonpolar—n-heptane) and commercially available porous Amberlite polymers (XAD4, XAD16, XAD7HP) by temperature-programmed desorption (TPD). The first two polymers are the product of copolymerization of styrene and divinylbenzene. Despite having the same chemical composition, they differ in pore size and volume. The Amberlite XAD7HP is composed of an acrylic matrix and has lower pore volume and specific surface area than XAD16 and XAD4. All three resins have the ability to swell, though the per cent of polymeric network expansion during this process varies depending on the solvent used (e.g. in tetraethyl orthosilicate, XAD4 and XAD16 spherical particles increase in volume by 20–30%, while XAD7HP particles can expand by more than 120%). The TPD experiment was performed in dynamic linear and quasistatic heating mode. Based on thermogravimetric data, the desorption energy of selected liquids and pore size distribution in the swollen state were estimated. The obtained results are discussed in terms of both mathematical modelling and low-temperature nitrogen adsorption–desorption experiment.