Characterization of polymer grafts chemically attached on thermally stable polymer films; Detachment of hydrophilic grafts from hydrophobic polymer substrates in aqueous media

Enomoto, Kazuyuki; Takahashi, Shuichi*; Iwase, Takanori*; Yamashita, Takashi*; Iwase, Hiroki*; Koizumi, Satoshi; Maekawa, Yasunari

The degradation behavior of graft-type polymer electrolyte membranes consisting of hydrophilic sulfo-containing graft polymers (grafts) in hydrophobic polymer substrates are examined; We employed poly(styrenesulfonic acid) (PSSA) as a hydrophilic grafts and crosslinked poly(tetrafluoroethylene) (cPTFE), poly(ethylene-co-tetrafluoroethylene) (ETFE), and poly(vinylidene fluoride) (PVDF) as a hydrophobic plastic substrate. PSSA-grafted cPTFE, ETFE, and PVDF films are degraded with more than 30 % weight loss in 85 C for 500 hours. The good agreement between losses of sulfo groups and film weights indicated that only PSSA grafts degraded from cPTFE, ETFE, and PVDF substrates. Using UV, NMR, and GPC, the decomposed extracts in water are confirmed to be PSSA with the same molecular weights. Furthermore, since the elemental analysis of the extracts did not have fluorine atoms, the grafts in all the PSSA-grafted films detach from the fluorinated substrates without decomposition. This is quite new degradation mode of graft-type polymer electrolyte membranes. By taking advantages of the interface abruption of swelled grafts, the chemically and thermally stable grafts attached onto the plastic films can be isolated and analyzed without special treatments.