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Basic Silicone Chemistry (I)

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Presentation on theme: "Basic Silicone Chemistry (I)"— Presentation transcript:

1 Basic Silicone Chemistry (I)

2 Silicone Family Tree Si Elastomers Fluids & Emulsions Silicone Resins
Dimethyl Compounds Silanes Organo-Silicones Silicone Polyethers Volatile Methyl Siloxanes Amino Silicones Si

3 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

Dow Corning’s 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

5 Silicone Nomenclature

6 Silicone Nomenclature Shorthand
Precursor Silanol Siloxane Structure Short hand Me Me Cl-Si-Cl HO-Si-OH Linear Structures D unit Me-Si-Cl Me-Si-OH End-cap group M unit Cl-Si-Cl HO-Si-OH Branched Structures T unit Cl OH Cl-Si-Cl HO-Si-OH Silica Core Q unit 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 = MD3M

7 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

8 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

9 Process Chemistry of Methyl Train
Me2SiCl2 MeHSiCl2 Me3SiCl H2O Me2 Hydro SiH fluid EBB Chlorosilane Mix Waste & Recovery Si MeCl Copper Catalysts

10 Volatile Polydimethylsiloxane Fluids INCI NAME: Cyclomethicone
CH3 Si - O n = 3 Trimer n = 4 Tetramer n = 5 Pentamer n = 6 Hexamer PENTAMER (D5) Si CH3 O n

11 Volatile Polydimethylsiloxane (PDMS) Fluids
R = CH INCI: Dimethicone R = OH INCI: Dimethiconol CH CH CH3 R - Si - O - Si - O - Si - R CH CH 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)

12 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 angstroms bond angle degree bond energy Kcal/mol bond barrier Kcal/mol

13 Siloxane Polymers vs Carbon Polymers
Barrier to Rotation ( kcal/mole ) Polyethylene Polytetrafluoroethylene Polydimethylsiloxane < 0.2 Key Point: Siloxane (Si-O-Si) polymers are stronger than carbon polymers, yet the polymer chains are more open and flexible

14 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 The flexibility of the backbone provides one very unique distinguishing point compared to organics: very low glass transition temperature that allows high molecular weights (as high as 500,000) to still be fluid. At the same time, the chemistry kit will allows for water-like volatiles, to rubber-like, tacky or solid resins. Further, since the molecule can easily rotate, the surface tension becomes low from the methyl groups and allows for easy spread for silky, smooth, non-tacky aesthetic non-greasy or oily feel. Compared with conventional organic polymers, many silicones show superior thermal properties. Some silicone elastomers, for example, remain flexible at - 100C and retain their properties for long periods at 200 C. Most of the common silicone polymers are quite hydrophobic but are permeable to water vapor and to other gases. Their resistance to unltraviolet and other radiation means that they weather well. They are good electrical insulators. The low surface tensioin of polydimethylsiloxanes (~20 dynes/cm) permit them to spread easily over irregular surfaces. They are often used as additives to promote easier application and to give additional water repellency to the surface. Some silicones are excellent release agents; even the most aggressive organic adhesives do not adhere to them. Most silicones are not particularily solvent resistent; however, elastomers made from siloxnes substituted with fluoro groups show good resistance to hydrocarbons ans such.

15 Anionic Ring Opening Equilibrations
D4 Ring : Chain Equilibrium 10-15% : – 90% PDI = 2.0

16 Anionic Ring Opening Equilibrations
End Blockers

17 Anionic Ring Opening Equilibrations
End Blockers Maximum in viscosity involves incorporation of end blocker (which is less reactive than cyclic) Viscosity time

18 Living Anionic Ring Opening Polymerization
sec-Butyl – Li + D3 Living anionic polymerization




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