Silicone rubber is produced through a multi-step process beginning with reducing silica to silicon, which is then reacted with methyl chloride to form chlorosilanes. These chlorosilanes undergo hydrolysis or methanolysis to form siloxane oligomers, which are then cured using a peroxide or platinum catalyst to form cross-linked silicone rubber. Silicone rubber has advantages over organic rubbers including greater heat resistance, flexibility over a wide temperature range, chemical stability, and physiological inertness. It is used widely in applications such as electronics, seals and gaskets, medical devices, construction, office equipment, and leisure products.

1. Presented by : Muhammad Waleed & Shakir jamal

2. Structure of Silicon Rubber

3. How silicon is produced?
o Silicon does not exist on its own in nature. Most of it is bound with
oxygen in materials like sand and quartz.
o The silicon oxygen bond in quartz is so stable it can only be broken
by white heat.
First step ( reduction ):
o The first step in the production of the silicone involves the reduction
of silica (SiO2) to silicon (Si) in an electric arc furnace at 1900°C in
the presence of charcoal.
SiO2 + 2C 1900 oC Si + 2CO
o The silicon obtained is solid hard material, so ground to 100 to 350
nm

4. Second step( formation of chlorosilanes)
o In the second step we form chlorosilanes from silicon and the
process is known as “Rochow process”.
o Methyl chloride is reacted with solid silicon metal in the presence of
copper as catalyst at 300 oC.
o The reaction of silicon with methyl chloride has a high activation
energy, but the reaction itself is highly exothermic and if uncontrolled,
it leads to impurities.
2 CH3-Cl + Si 300oC (CH3)2SiCl2 80 %
copper
Other compounds:
CH3-Si-Cl3 12 % B.P = 65.7 oC
(CH3)3-Si-Cl 4 % B.P = 57.3 oC
CH3HSiCl2 3 % B.P = 40.7 oC
Si-Cl4 B.P = 56.7 oC

5. o The various components of the reaction are isolated by fractionation.
o Cu is used around 10% of the weight of the silicon metal.
Third Step ( synthesis of oligomeric siloxane)
o This is done either by “Hydrolysis “ or by “Methanolysis”
1) Hydrolysis:
o Chlorosilanes react with excess water in order to convert them into a
mixture of linear and cyclic compounds.
(CH3)2SiCl2 + 2H2O OH-(CH3)2Si-OH + 2HCl
OH-(CH3)2Si-OH + OH-(CH3)2Si-OH HO-Si(CH3)2-[O-Si(CH3)2]n-OH + nH2O
o Polymerization continues until a chain terminator is added like
trimethyl silanol.
(CH3)3SiOH + HO-Si(CH3)2-[O-Si(CH3)2]n-OH + HO-Si(CH3)3
(CH3)3Si-O-Si(CH3)2-[O-Si(CH3)2]n-O-Si(CH3)3

6. o Complete hydrolysis with excess water is carried out continuously in
the liquid phase with 25% HCl or in the gas phase at 100ºC.
o The ratio of cyclic to linear dimethyl siloxanes and the chain length of
the linear oligomers can be varied over a wide range by means of
hydrolysis conditions.
o For example rapid removal of HCl from the reaction mixture by
neutralization leads almost exclusively to short chain siloxane diols.
o Cyclic siloxanes represent up to two thirds of the reaction product if
prolonged contact with HCl occurs.
2) Methanolysis:
o The methanolysis process for the production of siloxanes from
dimethyldichlorosilane allows direct recovery of the chlorine from
methylchlorosilanes as chloromethane.
o Chlorosilanes react with methanol to produce linear and cyclic
compound.

7. m(CH3)2SiCl2 + 2nCH3OH HO[(CH3)2SiO]nH + 2nCH3Cl +(n-1)H2O
n(CH3)2SiCl2 + 2nCH3OH [(CH3)2SiO]n + 2nCH3Cl + nH2O
Curing :
 Silicone elastomers are cured (or “vulcanized”) to turn from thick
liquids or semi-solid pastes into solids. The two most common curing
processes are peroxide initiated curing and platinum catalyzed
curing.
1)Peroxide curing:
 Initially, all silicone elastomers were cured with peroxide-based
chemicals. This curing system is also called free radical cure

8. system or a high-temperature vulcanizing system because the
peroxides generate free radicals that decompose at high
temperatures and initiate the cross-linking reaction.

9. 2) Platinum catalyzed curing:
Platinum-based curing systems are sometimes called addition cure
systems, because there is a silicone hydride (Si – H) polymer that
adds across the double bond of a vinyl functional siloxane polymer in
the presence of a platinum-based catalyst to create a cross-linking
reaction.
Curing
agent
Oligomer
chain
pt

10. General properties of silicon rubber:
1) High binding energy:
The siloxane bonds (-Si-O-Si-) that form the backbone of silicone
rubber highly stable. At 433 kJ/mol, their binding energy is higher
than that of carbon bonds (C-C), at 355 kJ/mol. Thus compared to
common organic polymers , silicon rubber have higher:
 Heat resistance
 Flame retardancy
 Chemical stability
2) Low intermolecular force with spiral structure:
With its coil shaped spiral structure and low intermolecular force,
silicone (dimethylpolysiloxane) is highly elastic and compressible.
Furthermore as methyl groups are located in the outside of coil
structure, they are free to rotate on its own.

11. As a result silicone rubber has outstanding,
 water repellency and
 contact resistance
3) Heat and Cold resistance:
Silicon rubber withstands high and low temprature far better than
organic rubbers, Because it has broad operating-temperature range
from - 50 °C to +250 °C,(specialty grades: -110 °C to +300 °C).
4) Flexibility:
In general silicon rubber is flexible at low temperatures due to its low
glass transition temperature (Tg). However, they also tend to stiffen up
at higher temperatures.
5) Gas permeability:
Compare to organic rubber or plastic films, thin films of silicon rubber
have better gas and vapor permeability.

12. 6) Physiologically inert:
Living tissues are affected by contact with silicone rubber to a lesser
degree than by exposure to other organic polymers. Silicone rubber
is physiologically inert, and is thus used for baby bottle nipples and
stoppers in medical applications.
7) High purity:
High Purity Compared to other elastomers, silicone rubber is
exceptionally pure and is therefore also suitable for use in the food
and medical sectors.
8) Transparency and coloring properties:
Most organic rubbers are black due to their carbon content. In
contrast, it is possible to make highly transparent silicone rubber by
using fine silica.
Its high transparency makes silicon rubber easy to color with
pigments.

13. Uses of silicon rubber:
1) Electronics:
There is no end to the number of silicone rubber applications in the
field of electronics today. It is often used to seal the inner circuits
and processors of most electronic gadgets, protecting them from
heat, corrosion, moisture and other conditions that can cause wear
and tear.
2) Gaskets and seals:
Gaskets and seals are used in between mechanical parts and to
prevent leaks Rubber is generally a good gasket and seal material
because of its compressibility, flexibility, and its resistance to many
liquids. Silicone is particularly an effective material due to its ability
to withstand a wide range of temperatures and its resilience to
chemicals.

14. 3) Medical devices:
The low toxicity of the rubber and its chemical inertness allow the
rubber to be used in medical applications. The elastomer is easy to
mold, very flexible and is available in translucent forms for monitoring
purposes. Tubing for dialysis equipment, catheters and baby bottle
nipples are all made of silicone.
4) Construction and Restoration:
Due to its adhesive properties, it can be used to bind together
building material. Such as concrete , plastic ,glass etc. This enhance
the strength and durability of a structure and protect it against
moisture pollution, heat and other element that cause wear and tear.
5) Office automation Equipment:
Silicon rubber also used in office automation equipment such as
keypads of calculator & keyboard of computer, photocopier rollers
and printer rollers.

15. THANK YOU 
6) Leisure:
Due to high transparency, and physiological inertness silicon rubber
is used in swimming goggles , snorkels, Mouthpiece and goggles
band.