POLYIMIDES-K.SAI MALLESWAR

What are polyimides? what is the basic structural unit?

INTRODUCTION

Polyimides are polymers formed by the combination of acid dianhydrides and diamines.

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TYPES OF POLY IMIDES :

• Linear polyimides• Aromatic hetero cyclic polyimides

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Density 1430 kg/m3

Young's modulus 3200 MPa

Tensile strength 75-90 MPa

Elongation 4-8%

Glass temperature >400 °C

melting point none

Thermal conductivity 0.52 W/(m·K)

Coefficient of thermal expansion 5.5×10-5 /K

Specific heat capacity 1.15 kJ/(kg·K)

Water absorption Coefficient 0.32

Dielectric constant 3.5

PHYSICAL AND THERMAL PROPERTIES:

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•Characteristic colour – orange/yellow• Very low creep•Inherent resistance to flame combustion• Un effected by commonly used solvents and oils• Un effected by hydro carbons, esters, alcohols and freons• Resistant to weak acids• Not usable in alkaline or highly acidic environment.

Other properties:

Significance of polyimides:

• Polyimides have high tensile strength.

• They are highly heat resistant and chemical resistant.

• They can often replace glass and metals such as steel.

• They are transparent to microwave radiation.

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WHY POLYIMIDES ARE SO STRONG???

CHARGE TRANSFER COMPLEX

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WHY POLYIMIDES ARE SO STRONG???

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SYNTHESIS:

By Step Growth Polymerization in two steps:• 1.Poly addition • 2.Subsequent Dehydration

• They are prepared by the reaction of Acid Anhydrides and Diamines

• Intially, soluble and fusible high molecular weight polyamic Acid is formed in polar aprotic solvent.

• Later, Polyamic acid is processed into final insoluble and infusible polymer product.

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APPLICATIONS:

Polyimides are used as struts and chasis in cars

Polyimides are used as the outerlayer of thermal insulation covering of external surfaces of aircrafts

They are also used in vane brushes,bearings and washers for aircrafts

They are also used as polyimide heaters.

Polyimides are used in the cooking cavity of microwave oven.

Polyimides are also used in food packaging.

•As an insulating layer in the manufacture of IC chips

• Polyimides are used as mechanical stress buffers

•As flexible cables in electronics industry

•As a coating on tubes used in surgeries

•As a photoresist in IC chip fabrication.

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BEARINGS MADE OF POLY IMIDEA POLYIMIDE RESIN

A POLYIMIDE TAPE

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DEGRADATION OF POLYIMIDES:

Photo Degradation:• It is molecular degradation caused by ultraviolet radiation.• Here bond between carbonyl carbon(C=O) and alkyl group breaks.Oxidative Degradation:• It leads to hardening, discolouration and surface changes.• In this R-C=O will be converted into R=C.

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• Structural and Environmental factors lead to thermal degradation of Polyimides• This may be Thermal or thermo oxidative degradation• Cross linked bonds will break during thermal degradation• They will become insoluble in nature after thermal degradation•They retain their weight at elevated temperatures• Incase of aromatic polyimides, delocalization energy of Pi-electrons is released.

THERMAL DEGRADATION OF POLYIMDES:

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BIBLIOGRAPHY:

1.www.wikipedia.org2. Polymer Science and Technology by Joel R.Fried3.www.google.com4. Text Book Of Polymer Science by Fred W. Billmeyer

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THANK YOU