Thermal oxidative studies of poly(hexafluoropropene oxide) fluids

Abstract

SynopsisElucidation of mechanisms operative in thermal oxidative degradation of hexafluoropropene oxide derived polyethers and the effect of metals on these processes are reported. Thermal oxidative instability of a commercial fluid, at moderate temperatures (550'F), was found to be due to the presence of -3% of thermooxidatively unstable chains believed to be hydrogen terminakk treatment at 6 5 0 ' F in oxygen volatilized these chains by unzipping. The resultant fluid was unaffected by oxygen at 650'F and by M-50 and Ti(4A44Mn) alloys at 600'F in oxidizing atmospheres. M-50 alloy catalyzed the degradation of the hydrogen-terminated chains below and at 600'F, but after completion of this process did not affect the remainder of the fluid at these temperatures. A t 650'F a chain scission process promoted by the metals constituting the alloy, or their oxides or fluorides, came into play. Ti(4Al,4Mn) alloy in the presence of CF3COF and COFz species, formed via decomposition of the hydrogen-terminated chains, degraded poly(hexafluoropropene oxide) fluids at 550'F by chain scissions.

Thermal oxidative degradation reactions of linear perfluoroalkylethers

“…The degradation studies were performed using the procedures and the apparatus described previously (Paciorek et al, 1979). Unless specifically stated, the tests were carried out on 3-4 g of fluid over a period of 24 h in the denoted atmosphere at the specified temperature.…”

“…Fluorine-terminated poly(hexafluoropropene oxides) possess extremely high thermal and oxidative stabilities with incipient decomposition temperatures in the vicinity of 410 °C (Gumprecht, 1966(Gumprecht, , 1967. The lower oxidative f Ultrasystems, Inc., 2400 Michelson Drive, Irvine, CA 92715. stability of the commercial materials has been found to be due to some unstable chains which could be removed by oxidation at elevated temperatures (Paciorek et al, 1979). The linear perfluoroalkyi ethers, devoid of side chains or pendant groups, have better viscosity-temperature properties than poly(hexafluoropropene oxides); however, their thermal oxidative stabilities are significantly lower (Snyder et al, 1981), which is unexpected.…”

A review of the effect of metals on the thermo-oxidative stability of perfluoropolyalkylether lubricants

“…They include end chain reactions [8] and chain scissions [7,19] [8,32], FeF 3 [31], Fe alloys [10,19,33], pure Fe (powder and slab) [20], and Ti alloys [10,19,33].…”

Behavior of High Temperature Lubricants in a Pressure Differential Scanning Calorimeter

“…It has been well documented (16)- (19) that PFAEs degrade by an unzipping or scissioning mechanism that produces lower molecular weight material rather than the higher molecular weight degradation products that are typical of the other high temperature candidate fluids. PFAE-Z had been shown by thermogravimetric analysis to undergo sudden weight losses under isothermal conditions at 200°C (16) and 250°C (20) in the presence of a wide variety of inorganic oxides. Thus, catalytic effects, particularly from metal and metal oxides, dominate the degradation of the lubricant rather than the peroxide mediated autoxidation reactions that characterize the degradation of hydrocarbon lubricants.…”