We have previously shown that poly(ethylene glycol) (PEG) assumes a helical conformation in isobutyric acid. We now show that the formation of helices by PEG in isobutyric acid requires the presence of a trace amount of water:  We can make the helices coil and uncoil by adding or removing trace water to/from the solvent. We also show that the similar polymer poly(ethylene imine) (PEI) forms helices in isobutyric acid and that PEG forms helices in isopentanoic and n-propanoic acids but not in isobutanol or n-butanol. PEI (M n = 21.8 kg/mol) forms only helices in isobutyric acid, whereas PEG (M n = 21.0 kg/mol) forms a mixture of helices and coils. Helical PEI (M n = 21.8 kg/mol) shows a helix-to-coil transition when the temperature is increased to about 50 °C, while PEG (M n = 21.0 kg/mol) shows a helix-to-coil transition at 40−45 °C. When the trace water in the solution is D2O, the PEG (M n = 21.0 kg/mol) helix-to-coil transition moves to a higher temperature of about 56 °C, perhaps due to stronger hydrogen bonding.

No abstract

The thermal oxidation and viscosity degradation for poly-α-olefins (PAO) and di-esters (DOS) was studied under the GC/MS investigation. Through the oxidative pyrolysis conditions, these two synthetic base fluids were characterized to get their simulated “areo-engine” conditions’ for thermal stability, such as oxidative and kinematic viscosity variation. The experimental results suggests that the oxidation products generated from oxidation reactions of DOS is mainly single esters, di-esters, ketone, ether, organic acids and alcohol, which results much bigger total acid values than that of PAO treated in similar conditions. The substantial increment of the kinematic viscosity of DOS reveals its limited thermal oxidation stability compared to PAO.

The deterioration of aero lubricating oil at high temperatures was accelerated by using a specific device simulating the operating conditions of engines, where the deterioration mechanism was obtained. Structures of the deteriorated lubricating oils were analyzed by gas chromatograph/mass spectrometer. From the results, it can be concluded that deterioration of aero lubricating oil at high temperatures was composed of thermal pyrolysis, oxidation, and polymerization, with the generation of a variety of products, such as alcohols, aldehydes, acids, and esters, which caused the deterioration of physicochemical properties of the aero lubricating oil.