Apical long-chain

Thermosetting polyimides are commercially available as uncured resins, thin sheets, and laminates. Thermoplastic polyimides are very often called pseudothermoplastic. There are two general types of polyimides. One type is linear polyimides which are made by combining imides into long chains. Aromatic heterocyclic polyimides are the other usual kind, where R and R" are two carbon atoms of an aromatic ring. Examples of polyimide films include Apical, Kapton, and Kaptrex. Polyimide parts and shapes include Meldin, Vespel, and Plavis. Polyimides have been in mass production since 1955. 

In this structure two apical oxygens of each Si04 tetrahedron are shared in a way to form a long single chain of linked tetrahedra. (Fig. 3.3C). The basic structural imit of single chain inosilicates is Si206" or SiOg" with an Si 0 ratio of 1 3. In some cases AE can replace Si " in the tetrahedral site. 

---