Department of Chemical Engineering, IIT Delhi
Dr. Sreedevi Upadhyayula
Gurdeep Singh Somal 2010CH10078
Gurvineet Singh Dhillon 2010CH10079 Gaurav Singh Sinsinwar 2010Ch10077
Polyimide is a polymer of imide monomers. The structure of imide is as shown. Polyimides have been in mass production since 1955. Typical monomers include pyromellitic dianhydride and 4,4'-oxydianiline. Polyimides are a very interesting group of incredibly strong and astoundingly heat and chemical resistant polymers. Their strength and heat and chemical resistance are so great that these materials often replace glass and metals, such as steel, in many demanding industrial applications. Polyimides are even used in many everyday applications CLASSIFICATION According to the composition of their main chain, polyimides can be:
Aliphatic (linear polyimides), Semi-aromatic, Aromatic: R' and R" are two carbon atoms of an aromatic ring. 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
PROPERTIES Exceptional mechanical strength Low dielectric constant Flexible Polishable to Angstrom level surface finishes Excellent dimensional stability Low water absorption High temperature stability Excellent machinability Non-contaminating Low coefficient of thermal expansion
REASON FOR ITS MECHANICAL STRENGTH The charge transfer complex between various imide monomers works between adjacent units in the polymer chain and between chains. The chains will stack together like strips of paper, with donors and acceptors paired up.
This charge transfer complex holds the chains together very tightly, not allowing them to move around very much. When things can't move around on the molecular level, they can't move around in the whole material. This is why polyimides are so strong. APPLICATIONS Electronics industry- Flexible cables, as an insulating film on magnet wire and for medical tubing. For example, in a laptop computer, the cable that connects the main logic board to the display (which must flex every time the laptop is opened or closed) is often a polyimide base with copper conductors Semiconductor industry - As a ◦ ◦ High-temperature adhesive Mechanical stress buffer.
◦ Photoresist-both "positive" and "negative" types of photoresist-like polyimide exist in the market. ◦ Because of high mechanical and tensile strength, this combined with gold film act as a good insulator under various environmental stresses.
Manufacture of digital-semiconductor and MEMS Chips
Manufacturing Industry◦ ◦ ◦ ◦ Polyimide powder used to produce parts and shapes by sintering technologies. Used as bushings, bearings, sockets Microwave cookware and food packaging because of their thermal stability, resistance to oils, greases and fats and transperancy to microwave radiation. Can also be used in circuit boards, insulation, fibres for protactive clothing, composites and adhesives.
In coal-fired power plants, waste incinerators or cement plants, polyimide fibres are used in hot gas filtration. A polyimide needle felt separates dust and particulate matter from the exhaust gas. The IKAROS solar sailing spacecraft uses polyimide resin sails to operate without rocket engines. Polyimide film in the form of Kapton can be used as a diaphragm in loudspeaker tweeters. POLYIMIDE SYNTHESIS Several methods are possible to prepare polyimides, among them: 1. Method 1:The reaction between a dianhydride and a diamine (the most used method) 2. Method 2:The reaction between a dianhydride and a diisocyanate (rarely used) METHOD 1 This method involves reacting a dianhydride and a diamine at ambient conditions in...
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