Basic Silicone Chemistry (I)

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Basic Silicone Chemistry (I)
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Silicone Family Tree
Elastomers
Silicone Resins
Fluids Emulsions
Dimethyl Compounds
Silanes
Organo-Silicones
Silicone Polyethers
Volatile Methyl Siloxanes
Amino Silicones
Si
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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

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SILICONES APPLICATIONS
Dow Cornings products and specialty materials
are used by customers in virtually every major
industry.

• Aerospace
• Automotive
• Chemicals/ Petrochemicals
• Construction
• Consumer Products
• Electrical/Electronics
• Food Processing
• Industrial Maintenance Production

• Medical Products
• Paints Coatings
• Personal, Household Automotive Care
• Pharmaceuticals
• Plastics
• Pressure-Sensitive Adhesives
• Textiles Leather

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Silicone Nomenclature
O
O Si O
SILICA
O
X
SILANES
Si
X
X
X
R
SILOXANES
Si
O
O
R
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Silicone Nomenclature Shorthand
Precursor Silanol
Siloxane Structure Short hand
Me Me Cl-Si-Cl
HO-Si-OH Linear
Structures D unit Me
Me Me
Me Me-Si-Cl Me-Si-OH
End-cap group
M unit Me Me
Me Me Cl-Si-Cl
HO-Si-OH Branched
Structures T unit Cl
OH Cl
OH Cl-Si-Cl HO-Si-OH
Silica Core
Q unit Cl OH
Me Me Me Me Me
Me Me Me Me-Si-O-Si-O-Si-O-Si-O-Si-Me
Me-Si-(O-Si)3-O-Si-Me Me Me
Me Me Me Me Me
Me
MD3M
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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 gt1,000,000 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

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Raw Materials

• Initial material is quartz
• SiO4/2
• 26 of the Earths crust
• Reduce to Si metal with carbon at 2500F
• Dow Corning purchases silicon metal
  methanol
• Methanol is converted to MeCl with recycled HCl

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Process Chemistry of Methyl Train
Me2SiCl2 MeHSiCl2 Me3SiCl
H2O
Me2 Hydro SiH fluid EBB
Chlorosilane Mix
Waste Recovery
MeCl
Copper Catalysts
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Volatile Polydimethylsiloxane FluidsINCI NAME
Cyclomethicone

• CH3
• Si - O
• CH3
• n 3 Trimer
• n 4 Tetramer
• n 5 Pentamer
• n 6 Hexamer

n
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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)
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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
• Si-O-Si C-C-C C-O-C
  units bond length 1.63 1.54
  1.42 angstroms bond angle 130
  112 111 degree
  bond energy 106 83
  86 Kcal/mol bond barrier 0.2
  3.6 2.7
  Kcal/mol

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Siloxane Polymers vs Carbon Polymers

• Barrier to Rotation ( kcal/mole )
• Polyethylene 3.3
• Polytetrafluoroethylene 4.7
• Polydimethylsiloxane lt 0.2

Key Point Siloxane (Si-O-Si) polymers are
stronger than carbon polymers, yet the polymer
chains are more open and flexible
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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

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Anionic Ring Opening Equilibrations
D4
Ring Chain Equilibrium 10-15
85 90 PDI 2.0
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Anionic Ring Opening Equilibrations
End Blockers
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Anionic Ring Opening Equilibrations
End Blockers
Maximum in viscosity involves incorporationof
end blocker (which is less reactive than cyclic)
Viscosity
time
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Living Anionic Ring Opening Polymerization
sec-Butyl Li
D3
Living anionic polymerization
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