What is the different for polyester & Polyamide ?

唔同的polymer(chemistry)
polyetser = any of a class of organic substances composed of large linear (chainlike) or cross-linked (network) molecules, or polymers, formed from a large number of smaller molecules, or monomers, by establishment of ester linkages between them. Polyesters most commonly are prepared from equivalent amounts of glycols (organic compounds containing two hydroxyl groups) and dibasic acids (containing two carboxyl groups).

The long-chain polyester made from ethylene glycol and terephthalic acid is the basis of the fibre called Dacron, Fortrel, or Terylene and the film Mylar. The polycarbonate resin Lexan is also a long-chain polyester.

polyamide = A polyamide is a polymer that contains recurring amide groups (R−CO−NH−R′) as integral parts of the main polymer chain. Synthetic polyamides are produced by a condensaton reaction between monomers, in which the linkage of the molecules occurs through the formation of the amide groups. They may be produced by the interaction of a diamine (a compound containing two amino [NH2] groups—e.g., hexamethylenediamine) and a dicarboxylic acid (containing two carboxyl [CO−OH] groups—e.g., adipic acid), or they may be formed by the self-condensation of an amino acid or an amino-acid derivative. The most important amide polymers are the nylons, an extremely versatile class of material that is an indispensable fibre and plastic. In this section the aramids, “aromatic polyamides” that contain benzene rings in their carboxylic-acid portions, are also described.