Thermal oxidative degradation reactions of linear perfluoroalkylethers

Project Manager, William R. JonesNASA Lewis Research CenterCLeveland, Otf 44L3516 Absn4clThe objective of this contract was to Investigate the mechanisms operative tn thermal and thermaloxidative degradation c)[ Fomblln Z and he×afluoropropene oxide derived fluids and the e{[ect of alloysand additives upon thest+ pr,_cess+;s.'I'h+. nature r_[ arranq(:ments rttsponslbJe for the tnherez_t thermal oxidative instability of the Fon)blJn Zt'luLds has not been establh;hed. Lt was determined that this behavior was not associated withhydruqen end-groups or peroxy linkages. The degradation rate of these fluids at elevated temperaturesLn oxidizing atmospheres was [ound to be dependent on the surface/volume ratio. Once a limitingratio was reached, a steady rate appeared to be attained. Based on elemental analysis and oxygenconsumption data, -CF 2 OCF 2 CF 2 O- ' not -CF 2 CF 2 O- ' Is one o[ the major arrangements present. Theaction ot" the M-50 and TI(4A.I. 4Mn) alloys was [ound to be much more drastic In the case of PombllnZ fluids than that observed for the hexafluoropropene oxide derived materials. The e[fecttveness ofantloxldation/anticorroston additives; P-3 and phospha-s-trlazine, In the presence of metal alloys'was very Limited at 316°C: at 28B°C the additives arrested almost completely the fluid degradation.The phospha-s-triazlne appeared to be at Least twice as effective as the P-3 compound; It alsoprotected the coupon better. The TI{4AI, 4,Mn) alloy degraded the fluid mainly by chain scJsslonprocesses: this took place to a much lesser degree with M-S0.The presence of a certain proportion of hydrogen-terminated chains In Krytox MLO-YL-6 fluid wasverified by NMR spectroscopy. These were eliminated on exposure of the fluid to oxygen at 343°C.]'n oxygen at 316°C, aluminum metal did not seem to promote chain scissJons: a steady but low rateof degradation was observed for pure titanium metal.