Hi YouYou,
Apparently, Styrene was developed in the early 1950s in America, and was seen as a cheaper material for pressing records. The main producers of styrene at this time were labels under the Columbia group (Okeh, Columbia, Epic etc). During the late '50s, some UK budget labels like Gala used it, and called it "Lustrex", for reasons I don't know. It is these UK budget LPs (from between 1958 - 1960) that are the only example of Styrene LPs I know of - as far as I am aware, no other LPs have been made from styrene.
The way to tell a styrene record is that it is always lighter in weight compared to solid vinyl. If you hold a styrene record by its edge and centre hole, then tap on the edge, you should hear a brittle, hollow sound. Not a good idea to try and flex or bend a styrene record though, as they will crack easily.
Providing you play styrene records on a lightweight cartridge, they should last forever. If DJing, it's probably a good idea to avoid cueing them up, as back-tracking with a crap stylus will cause serious needle burn which is also permanent.
Hope this helps.
Gene