I'm copying this here so I don't lose it.
It's info about polyol ester, from Hatco.
After reading this, I'm feeling even more comfortable now to try RLI Bio-Syn in my Camry in September.
In our family of polyol ester, you find high purity dipentaerythritol, pentaerythritol and trimethylolpropane esters for use in applications where thermal stability, high viscosity index and lubricity are essential. Typical usages include raw material for spin finishers and oiling agents, lubricants, lubricating oil, and as jet engine lubricants.
The term "polyol esters" is short for neopentyl polyol esters which are made by reacting monobasic fatty acids with polyhedric alcohols having a "neopentyl" structure. The unique feature of the neopentyl structure of polyol alcohols molecules is the fact that there are no hydrogens on the beta-carbon. As a result, polyol esters usually have added polarity, reduced volatility and enhanced lubricity characteristics. This makes polyol esters ideally suited for the higher temperature applications where the performance of diesters and PAOs may fade.
Hatco uses many different acids and alcohols for manufacturing polyol esters and an even greater number of permutations are possible due to the multiple ester linkages. The difference in ester properties as they relate to the alcohols are primarily those related to molecular weight such as viscosity, pour point, flash point, and volatility. The versatility in designing these fluids is mainly related to the selection and mix of the acids esterified onto the alcohols.
The major application for polyol esters is jet engine lubricants where they have been used exclusively for more than 30 years. In this application, the oil is expected to flow at -54 C, pump readily at -40 C, and withstand sump temperature approaching 200 C with drain intervals measured in years. Only polyol esters have been found to satisfy this demanding application.
Polyol esters are also the ester of choice for blending with PAOs in passenger car motor oils. This application reduces fuel consumption and lowers volatility in modern specifications. They are used in 2-cycle oils for the same reasons plus biodegradability.
Polyol esters are used extensively in synthetic refrigeration lubricants due to their miscibility with non-chlorine refrigerants. They are also widely used in a variety of very high temperature applications such as industrial oven chains, stationary turbine engines, high temperature grease, fire resistant transformer coolants, fire resistant hydraulic fluids, and textile lubricants.
Link:
http://www.hatcocorporation.com/pages/syntheticlubes/polyolesters.htm