The document discusses the history and properties of silicones. It notes that during World War II, James Wright added boric acid to silicone oil to create a product that could stretch farther and bounce higher than rubber. Silicones are polymers made of repeating siloxane units consisting of alternating silicon and oxygen atoms. They can occur as fluids, gels, elastomers or resins. Silicones have applications in areas such as medical implants, sealants, and bouncy toys due to their thermal stability, flexibility and biocompatibility. Common processing methods include injection molding and extrusion. Leading manufacturers include Dow Corning and Wacker Silicones.

1. SILICONES
Aoun Hussnain
14-MME-S1-328
Metallurgy & Materials Engineering
Punjab University

2. A Little History
During World War II, James Wright added boric acid to silicone oil (PDMS) and formed a
product that could be stretched farther than rubber and bounced 25% higher than rubber.
Although Dr. Earl Warrick of Dow Corning synthesized the same polymer at about the same
time, Wright gets most of the credit for inventing the polymer
Silicones
• They are polymers that actually are inert and synthetic compounds made up of
repeating units of siloxane, which is a chain of alternating silicon atoms and
oxygen atoms. So Silicones are also named as polysiloxanes.
• Silicones are constructed from inorganic-organic monomers. They consist of an
inorganic silicon-oxygen backbone chain with organic side groups attached to the
silicon atoms.

3. • Silicones have in general the chemical formula [R2SiO]n, where R is an
organic group such as alkyl group.
• By varying Si-O chain lengths, side groups, and crosslinking, silicones of
varied properties are obtained
• They can occur in various forms from fluid to gel to elastomers to resin form.
• Molecules containing silicon-oxygen double bonds do exist and are called
silanones but they are very reactive. Silanones are unstable and favor
oligomerization.
• Silicones are viscoelastic materials. They behave like viscous liquids at high
temperature and behave like elastomers at low temperature.
• The reason behind elastic behavior is flexible silicon-oxygen bonds whose
angle can easily open and close in a scissor-like fashion.
• When the molecular weight is high, these flexible chains become loosely
entangled which imparts a high level of viscoelasticity.

4. Synthesis
Most common silicone is PDMS and it can be synthesized by hydrolyzing
dichlorodimethylsilane as silicon-chlorine bonds are very susceptible to
cleavage by water.
The reaction occurs in this manner
n [Si(CH3)2Cl2] + n H2O ->[Si(CH3)2O]n + 2n HCl
The initial hydrolysis reaction exothermically generates a silanol
Si(CH3)2(OH)2 which readily condenses through loss of water to form the
siloxane polymer.
Cross linking can be achieved by using Siloxanes with vinyl groups and other
Si-H groups with Pt(Platinum) catalyst.

5. Processing techniques
1. Injection molding
2. Extrusion
3. Compression molding
4. Calendaring
5. Emulsion polymerization ( to make premium quality silicone emulsion resin emulsion
paints)
Limitations
• Poor resistance to acids and alkalis.
• Poor abrasion, tear and cut growth resistance.
Leading Manufacturers
• Dow Corning
• JNC corporation
• Bluestar silicones
• Wacker SIlicones

6. Properties
• Thermal Stability
• Chemical Stability
• Electrical Insulation
• High gas permeability
• Water repellant surface
• Bio-compatibility
• Resistance to oxidation
• Low toxicity
Applications
• Blood coagulation prevention
• Needle lubrication
• Catheters and drains
• Cardiac valves & Pace makers
• Orthopedic & Aesthetic implants
• Electrical Insulations
• Sealant for aquariums, automobiles,
aero planes
• Silicone foams as fire extinguishers
• Silicone grease for chains and air
guns
• Making toys specially bouncing balls
• Mobile devices’ back cases

7. AN ANTIFUNGAL COATING FOR DENTAL SILICONES
COMPOSED OF CHLORHEXIDINE NANOPARTICLES
JOURNAL OF DENTISTRY
VOLUME 43, ISSUE 3, MARCH 2015, PAGES 362–372
Procedure:
CHX-NPs were precipitated in aqueous reaction by
mixing CHX with solutions of sodium triphosphate
(TP), trimetaphosphate (TMP) or
hexametaphosphate (HMP). CHX-NPs were coated
on commercial dental silicones, and these were
characterized for hydrophilicity (contact angle) and
water uptake (mass change). Antifungal efficacy
against Candida albicans was investigated.
Results:
Candida albicans metabolic activity was inhibited
by presence of CHX-HMP-NPs in suspension. The
study suggests that CHX-NPs may be a useful
strategy in design of antifungal coatings for these
materials.

8. Purpose:
To investigate the effect of a lubricating drop on optical quality & tear film
stability in individuals wearing silicone hydrogel contact lens.
Method:
In this clinical study, Pre-lens Tear Deformation Time, Root-Mean-Square of
Low and High Order Aberrations were assessed in 43 volunteers at 6 h after
inserting the contact lens and then at 60 min after instilling a lubricating drop.
Result & Conclusion:
PL-TDT, LOA-RMS, and HOA-RMS values measured before drop instillation
were not significantly different with those measured after drop. Severity values
in blurry vision, dryness, discomfort, burning, itching and excessive blinking
were seen after drop instillation.
Our results showed that although the lubricating drop did not improve the tear
film stability and optical quality in the silicone hydrogel contact lens wearers
but subjects experienced a slight improvement.
Objective and subjective assessing efficacy of a lubricating drop in
eyes wearing silicone hydrogel contact lenses

9. Conclusion
• Silicones have great uses particularly in medical field, its importance can’t be
denied.
• Silicone has medical applications ranging from nose, cheeks and breast implants to
orthopedic implants ,cardinal devices ,pace makers and catheters.
• They are considered world’s most adapted materials.
• They are cheap and readily available.
• They are not degradable as they are inert and don’t react with atmosphere but can
be recycled.
• The annual production is boosting year after year because of broader applications and
increasing awareness of using more environment friendly materials.

10. THANKS
for tolerating me for so long 
You are grown enough to google your questions :P
But still I’m here, if you have any questions?