Polyphenylenes are a family of resins that exhibit good flame resistance. The main classes are PolyPhenylene Sufide (PPS), PolyPhenyleneSulfone (PPSU) [though this is typically classified as a polysufone] and PolyPhenylene Ether (PPO) [the "O" is for Olefin which covers a broader array of chemicals]. They are used in high performance and high tolerance applications. Wikipedia Links: Poly(P-Phenylene) and Polyphenylene Sulfide