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Concept
Polyimide
Summary
Polyimide (sometimes abbreviated PI) is a polymer containing imide groups belonging to the class of high-performance plastics. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, e.g. high temperature fuel cells, displays, and various military roles. A classic polyimide is Kapton, which is produced by condensation of pyromellitic dianhydride and 4,4'-oxydianiline.
The first polyimide was discovered in 1908 by Bogart and Renshaw. They found that 4-amino phthalic anhydride does not melt when heated but does release water upon the formation of a high molecular weight polyimide. The first semialiphatic polyimide was prepared by Edward and Robinson by melt fusion of diamines and tetra acids or diamines and diacids / diester.
However, the first polyimide of significant commercial importance - Kapton - was pioneered in the 1950s by workers at Dupont who developed a successful route for synthesis of high molecular weight polyimide involving a soluble polymer precursor. Up to today this route continues being the primary route for the production of most polyimides. Polyimides have been in mass production since 1955. The field of polyimides is covered by various extensive books and review articles.
According to the composition of their main chain, polyimides can be:
Aliphatic,
Semi-aromatic (also referred to as alipharomatic),
Aromatic: these are the most used polyimides because of their thermostability.
According to the type of interactions between the main chains, polyimides can be:
Thermoplastic: very often called pseudothermoplastic.
Thermosetting: commercially available as uncured resins, polyimide solutions, stock shapes, thin sheets, laminates and machined parts.
Several methods are possible to prepare polyimides, among them:
The reaction between a dianhydride and a diamine (the most used method).
The reaction between a dianhydride and a diisocyanate.
The polymerization of a diamine and a dianhydride can be carried out by a two-step method in which a poly(amidocarboxylic acid) is prepared first, or directly by a one-step method.
Official source
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