Morphological and Spatial Aspects in Polymer Degradation: From Heterophasic Polymers to Proton Exchange Membranes Used in Fuel Cells Shulamith Schlick, University of Detroit Mercy, DMR 0412582 1. Danilczuk, M.; Schlick, S. Coms, F.D. Macromolecules 2009, 42, 8907-8913. 2. Danilczuk, M.; Perkowski, A.J.; Schlick, S. Macromolecules 2010, 43, 3352-3358. 3. Spulber, M.; Schlick, S. J. Phys. Chem. A 2010, 114, 6217-6225. (A)The stabilization of perfluorinated membranes by addition of Ce(III) has been studied in an In Situ fuel cell (FC) inserted in the resonator of an ESR spectrometer . 1 Scheme 1 shows the deduced stabilization mechanism : Scavenging of the most aggressive oxygen radical, HO•, and generation of Ce(IV); and formation of Ce(III) and of the less reactive HOO• radical. SCHEME 1 HO • + Ce(III) + H + → H 2 O + Ce(IV) Ce(IV) + H 2 O 2 ↔ Ce(III) + HOO • + H + Ce(IV) + HOO • → Ce(III) + O + H + (B) We have developed a kinetics approach that allowed ranking of membrane stability to attack of hydroxyl radicals, by monitoring the competition between the spin trap (DMPO) and the membrane for these radicals. 2 Results indicated that the membranes’ stability depends on the structure of the side chain. Most stable: membrane without the ether bond in the side chain , for example the 3M and Aquivion membranes shown below. (C) Inclusion in cyclodextrins (CDs) leads to the increase of the lifetime of short-lived spin adducts, for example DMPO/OH. 3 The Figure shows the generation of the adduct and its decay at 300 K in the absence (line 1) and in the presence of increasing CD concentrations (lines 2 to 6). The red arrow in the inset indicates the signal whose intensity was monitored in the time scan. (CF 2 CF 2 ) n CF 2 CF OCF 2 CF 2 CF 2 CF 2 SO 3 H (CF 2 CF 2 )pC F 2 CF OCF 2 CF 2 SO 3 H 0 500 1000 1500 2000 2500 0 10 20 30 40 3300 3320 3340 3360 3380 3400 M agnetic Field /G In ten s ity /a .u . Tim e S can /s 1 2 3 4 5 6 U V off