Polyphenylene Sulfide (PPS) or Poly (p-Phenylene sulfide) (PPS) is a polymer made up of alternating sulfur atoms and phenylene rings in a para-substitution pattern. The highly stable chemical bonds of its molecular structure provide a remarkable degree of molecular stability toward both thermal degradation and chemical resistance. The molecular structure also readily packs into a very thermally stable crystalline lattice, hence PPS is a semi-crystalline polymer with a high crystalline melting point of about 285°C (545°F). Because of its molecular structure, PPS also tends to char during combustion, making the material inherently flame retardant. There are no known-solvents that would attack or dissolve PPS at temperatures below 200°C (392°F).