3. INORGANIC POLYMERS
Inorganic polymers are macromolecules composed of repeating structural units that contain
elements other than carbon as part of their principal backbone structure.
They are having inorganic repeating units in their main polymeric backbone.
It forms giant 3D or 2D network structure through covalent bonding.
Examples: Mica, clays, silicones, zeolites, polyphosphazenes etc.
Heterocatenation :
It is a common phenomenon related to inorganic polymers in which chains or rings are built up from
alternating atoms of different elements.
e.g. silicones contain -Si-O-Si-O- heterocatenation and polyphosphazenes contain
-P-N=P-N=P- heterocatenation.
Zeolite Mica
4. Why inorganic polymers ?
ORGANIC POLYMERS INORGANIC POLYMERS
• React with oxygen or ozone over a long period of time
and lose their properties.
• Inorganic elements have different valencies than carbon.
• Burn with the release of toxic smoke. • Different side groups can be attached to the backbone.
• Degrade when exposed to UV or gamma radiation. • Fine tune of flexibility of the macromolecule.
• Less thermal stability. • High thermal stability and chemical resistance.
• Swell or dissolve in organic solvents, oils. • Bonds formed are stronger and more resistant to
degradation.
Inorganic polymers are stronger, harder and more brittle than the organic polymers.
5. Glass transition temperature (Tg) of polymers
Glass transition temperature( Tg), is a temperature at which the polymer experiences the
transition from the hard and rigid glassy state to more flexible rubbery state.
Tg
Glassy state, Hard
and Brittle
Rubbery state, soft
and flexible
Factors affecting Tg
o Chain flexibility and rigidity.
o Degree of crosslinking.
o Chain length.
o Steric effect.
o Crystallinity etc.
For example, poly(dimethyl siloxane), extremely flexible
polymer due to the large separation between the methyl
substituted silicon atoms. Tg= -123.15˚C.
n
6. Silicones
Silicones are synthetic organosilicon polymers with repeated R2SiO units held together by Si-O-Si
linkage. The repeating unit is known as siloxane.
R1 and R2 = alkyl or aryl group
Technically they are known as “polyorganosiloxanes”.
There are three structural types of silicones : (1) Linear or straight chain silicones, (2) cyclic
silicones, and (3) crosslinked or three dimensional silicones.
n
n
siloxane
Polydialkylsiloxane Tris-cyclodialkylsiloxane Tetrakis-cyclodialkylsiloxane
Linear silicone Cyclic silicones
es
7. Preparation of silicones
Preparation of R2SiCl2
2RCl + Si R2SiCl2
Cu powder
573 K
Alkyl chloride Dialkylchlorosilane
Hydrolysis of dialkylchlorosilane
+ 2HCl
+ H2O
Dialkylchlorosilane Silanol
Formation of polysiloxane
-(n-1) H2O
n
n
Silanol Silicone
Intermolecular polycondensation with
elimination of H2O molecules to form
silicone.
8. Hydrolysis under carefully controlled conditions can produce cyclic structures, with rings
containing three, four, five, or six Si atoms.
The straight chain growth can be regulated by adding (CH3 )3SiCl to R2SiCl2 during hydrolysis.
The ratio of the (CH3)3SiCl and R2SiCl2 will determine the average chain size.
+
- H2O
9. Types of silicones
Depending on the number of repeating units/ molecular weight polysiloxanes are classified into
three : Silicone fluids, Silicone elastomers or rubbers and Silicone resins.
SILICONE FLUID SILICONE ELASTOMERS/ RUBBERS SILICONE RESIN
Mixture of straight chain polymers
and cyclic tetramers.
High molecular weight linear
polymers-6000 to 6 lakhs Si units.
Highly crosslinked polymer.
Varying molecular mass polymers. Used for making heat-resistant
containers due to its high thermal
stability.
It contains maximum one organic
substituents.
Varying viscosities and boiling
points.Both increases with
increase in chain length.
Used for cable and wire insulation. Harder and stiffer.
So watery liquids to viscous oils
and grease.
Used for making water repellant
coatings.
Used in water proofing paper,
textiles, polishes and waxes.
It has insulating properties.
Added in ppm quantities to
prevent frothing of cooking oil
while making chips.
10. SILICONE FLUID SILICONE ELASTOMERS/
RUBBERS
SILICONE RESIN
Silicates are also an example for silicon based inorganic polymers.
Zeolites coming under three dimensional silicates are widely used in ion-exchange
method, Shape selective catalysis and as molecular sieves.
