Hi Gene & 427,
"Alpha" olefins are linear hydrocarbons with a double bond in the "alpha" position, that is, between the first and second carbons. "Internal" olefins would haven the double bond "internal", that is, further down the hydrocarbon chain as opposed to between the first and second carbons. When you oligomerize the internal olefins the resulting "polyinternalolefin" should have more and shorter branching compared to PAOs which would reduce the VI and raise volatility to some degree. Otherwise I would expect them to perform similar to PAOs.
Sales of PIOs were hurt badly by stiff competition from PAOs and Grp IIIs, and the Sasol plant in Italy where they were made was running below 50% capacity. It may have been shut down based on comments in a 2004 Sasol report.
Tom