Poly (PPO) or poly(p-phenylene ether) (PPE) is a high-temperature thermoplastic

Thermoplastic

Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...

. It is rarely used in its pure form due to difficulties in processing. It is mainly used as blend with polystyrene, high impact styrene-butadiene copolymer or polyamide.
Polyphenylene ether was discovered in 1956 by A. S. Hay, and was commercialized by General Electric in 1960. The common name "polyphenylene oxide (PPO)" is incorrect because it is not an oxide but an ether.

While it was one of the cheapest high-temperature resistant plastics, processing was difficult and the impact and heat resistance decreased with time.