“…16,17 For instance, the thermal stability of phosphonate ester can be signicantly improved by its linking with multiple benzene rings, such as 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10-phosphaphenanthrene-10-oxide (DDP), bis(4-carboxyphenyl)phenyl phosphine oxide (BCPPO), and bis(4-carboxyanilino)phenyl phosphine oxide (BCNPO). [18][19][20][21][22][23][24] However, the bulky structure makes it difficult to copolymerize with PA66 salt, which results in decreased content of retardant in the copolymers. Recently, 2-carboxyethyl phenyl phosphinic acid (CEPPA), having only one benzene ring, was introduced into PA66 to enhance its ame-retardancy.…”