Degradation manner of polymer grafts chemically attached on thermally stable polymer films: swelling-induced detachment of hydrophilic grafts from hydrophobic polymer substrates in aqueous media

Abstract

The degradation manner of graft-type polymer electrolyte membranes consisting of hydrophilic poly(styrenesulfonic acid) (PSSA) graft polymers (grafts) and thermally and mechanically stable hydrophobic polymer substrates such as crosslinked poly(tetrafluoroethylene) (cPTFE), poly(ethylene-co-tetrafluoroethylene) (ETFE), and poly(ether ether ketone) (PEEK) was examined in water at 85 and 95 °C. Severe weight loss was observed in PSSA-grafted cPTFE and ETFE films but not in a PSSA-grafted PEEK film. The decomposed extracts in water were characterized as PSSA during the whole course of degradation, clearly showing that the PSSA grafts detached from the fluorinated substrates without decomposition or scission of graft polymer chains. This is quite a new degradation manner for graft-type polymer electrolyte membranes. PSSA-grafted PEEK films showed severe weight loss in aqueous propanol solutions making PSSA grafts swell; clear correlation was observed between the degree of swelling in PSSA grafts and the film weight loss. The solubility parameters between grafts and the polymer substrates and small angle neutron scattering (SANS) data implied that the grafted films possessing a clear boundary at the interface resulted in significant weight loss. From the above observation, it should be concluded that hydrophilic PSSA grafts detach from hydrophobic polymer substrates due to swelling-induced stress at the interfacial boundary in the grafted films.