Basic Silicone Chemistry (I)
Silicone Family Tree
Elastomers
Fluids & Emulsions
Silanes
Silicone
Resins
Dimethyl
Compounds
Silicone Polyethers
Organo-Silicones
Volatile Methyl
Siloxanes
Amino Silicones
Si
Flexibility of Siloxane Chemistry
•
•
•
•
•
•
•
Non-volatile
Antifoam
Slippery
Water Insoluble
Excellent Depth of Gloss
Incompatible in Organics
Durable
•
•
•
•
•
•
•
Volatile
Profoam
Sticky
Water Soluble
Shiny
Compatible
Transient
SILICONES APPLICATIONS
Dow Corning’s products and specialty materials are used by
customers in virtually every major industry.
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Aerospace
Automotive
Chemicals/ Petrochemicals
Construction
Consumer Products
Electrical/Electronics
Food Processing
Industrial Maintenance Production
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Medical Products
Paints & Coatings
Personal, Household & Automotive
Care
Pharmaceuticals
Plastics
Pressure-Sensitive Adhesives
Textiles & Leather
Silicone Nomenclature
Si
SILICON
O
SILICA
O Si O
O
SILANES
X
X Si
X
X
R
SILOXANES
O Si
R
O
Silicone Nomenclature Shorthand
Precursor
Silanol
Siloxane Structure
Short hand
Me
Cl-Si-Cl
Me
Me
HO-Si-OH
Me
Linear Structures
D unit
End-cap group
M unit
Me
Me-Si-Cl
Me
Me
Me-Si-OH
Me
Me
Cl-Si-Cl
Cl
Me
HO-Si-OH
OH
Branched Structures
T unit
Cl
Cl-Si-Cl
Cl
OH
HO-Si-OH
OH
Silica Core
Q unit
Me Me Me Me Me
Me-Si-O-Si-O-Si-O-Si-O-Si-Me
Me Me Me Me Me
=
Me Me Me
Me-Si-(O-Si)3-O-Si-Me
Me Me Me
=
MD3M
Silicone Classifications by Physical Form
(1) Fluids (hydraulic, release agents, cosmetics, heat transfer
media, polishes, lubricants, damping, dry cleaning)
Polymer chains of difunctional units (D) terminated with monofunctional (M)
units OR cyclics (Dx)
(2) Gums (high temperature heat transfer fluids, lubricants,
greases, cosmetic and health care additives)
Same structure as PDMS fluids, but much higher molecular weight (viscosities
>1,000,000 cSt).
(3) Resins (varnishes, protective coatings, release coatings,
molding compounds, electronic insulation)
Rigid solids based on trifunctional (T) and tetrafunctional (Q) units. Surface
modification with (M) units
(4) Elastomers (Heat cured and RTVs: tubing and hoses,
medical implants, sealants, adhesives, surgical aids,
electrical insulation, fuel resistant rubber parts, rollers, etc)
Soft solids based on crosslinked SiH Fluids
Raw Materials
• Initial material is quartz
– SiO4/2
– 26% of the Earth’s crust
• Reduce to Si metal with carbon at 2500F
• Dow Corning purchases silicon metal & methanol
• Methanol is converted to MeCl with recycled HCl
Process Chemistry of Methyl Train
Me2SiCl2
MeHSiCl2
Me3SiCl
Chlorosilane
Mix
Si
MeCl
Copper Catalysts
H2O
Me2 Hydro
SiH fluid
EBB
Waste &
Recovery
Volatile Polydimethylsiloxane Fluids
INCI NAME: Cyclomethicone
CH3
Si - O
CH3
CH3
CH3
Si
n
CH3
CH3
n = 3 Trimer
n = 4 Tetramer
n = 5 Pentamer
n = 6 Hexamer
CH3
O
O
CH3
Si
Si
O
O
Si
CH3
O
Si
CH3
CH3
CH3
PENTAMER (D5)
Volatile Polydimethylsiloxane (PDMS) Fluids
R = CH3
INCI: Dimethicone
R = OH
INCI: Dimethiconol
CH3 CH3
CH3
R - Si - O - Si - O - Si - R
CH3 CH3 m CH3
When m = 0, R= CH3 called Hexamethyldisiloxane or 200 Fluid,0.65 cS
(.65,1, 1.5 and 2.0 cS are volatile)
Properties of Siloxanes
• Despite the Fact that Silicon and Carbon are both Group IV
elements their chemistry is very different
• Unique flexibility of Si-O bond
•
bond length
bond angle
bond energy
bond barrier
Si-O-Si
1.63
130
106
0.2
C-C-C
1.54
112
83
3.6
C-O-C
1.42
111
86
2.7
units
angstroms
degree
Kcal/mol
Kcal/mol
Siloxane Polymers vs Carbon Polymers
•Barrier to Rotation ( kcal/mole )
–Polyethylene
3.3
–Polytetrafluoroethylene
4.7
–Polydimethylsiloxane
< 0.2
Key Point: Siloxane (Si-O-Si) polymers are
stronger than carbon polymers, yet the polymer
chains are more open and flexible
Siloxane Physical Properties
• Very low glass transition temperature (Tg = -120 °C)
– high molecular weights but not a solid
• Ability to spread out on a wide variety of substrates
– silky, smooth, non-tacky, aesthetic enhancing
– flowability and film forming
• Lowest surface shear viscosity and low surface tension
– lubricating, antifoaming, waterproofing, release properties
• High gas permeability
• Excellent dielectric properties
• Very good thermo-oxidative stability
– good chemical inertness and temperature resistance
Anionic Ring Opening Equilibrations
Me
Me
D4
Si
O
Me
Me
O
KOH
Si
HO
Me
Me
Si
Si
O
Si
Me
Me
Si
K
O
3
O
O
Me
Me
Me
Me
Me
Me
Me
K
O
Si
O
Si
O
K
D4
K
n
O
Si
Me
O
Me
Me
R
R
R
Si
O
R
Ring
10-15%
:
:
Chain Equilibrium
85 – 90%
Si
O
Si
Me
R
R
O
Si
n
R
Si
R
Me
R
R
PDI = 2.0
K
O
7
Me
Me
Si
R
R
Anionic Ring Opening Equilibrations
R
End Blockers
R
Si
R
CH3
H3C
Si
R
O
Si
R
R
CH3
O
Si
CH3
CH3
CH3
H2NCH2CH2CH2
CH3
CH3
Si
O
Si
CH3
CH2CH2CH2NH2
CH3
O
CH3
O
H2N
Si
O
CH3
O
Si
CH3
CH3
O
NH2
Si
CH3
CH3
O
O
Si
O
CH3
CH3
Anionic Ring Opening Equilibrations
CH3
End Blockers
H3C
Si
CH3
Viscosity
CH3
O
Si
CH3
CH3
Maximum in viscosity involves incorporation
of end blocker (which is less reactive than cyclic)
time
Living Anionic Ring Opening Polymerization
H3C
CH3
Si
O
O
cyclohexane
sec-Butyl – Li +
H3C
Si
Si
O
H3C
CH3
H3C
CH3
CH2 CH
Me
CH3
Si
O
2
CH3
CH3
Si
O
Li
Me
D3
10% THF
D3
R
CH3
H3C
CH2 CH
Me
CH3
Si
CH3
O
Si
n
Cl
R
O
Si
R
Si
R
CH3
Me
CH3
R
H3C
CH2 CH
Si
O
Si
R
Me
CH3
LiCl
Living anionic polymerization
n
Me
O
Li