2 Silicone Family Tree Si Elastomers Fluids & Emulsions Silicone Resins DimethylCompoundsSilanesOrgano-SiliconesSilicone PolyethersVolatile MethylSiloxanesAmino SiliconesSi
3 Flexibility of Siloxane Chemistry Non-volatileAntifoamSlipperyWater InsolubleExcellent Depth of GlossIncompatible in OrganicsDurableVolatileProfoamStickyWater SolubleShinyCompatibleTransient
4 SILICONES APPLICATIONS Dow Corning’s products and specialty materials are used by customers in virtually every major industry.AerospaceAutomotiveChemicals/ PetrochemicalsConstructionConsumer ProductsElectrical/ElectronicsFood ProcessingIndustrial Maintenance ProductionMedical ProductsPaints & CoatingsPersonal, Household & Automotive CarePharmaceuticalsPlasticsPressure-Sensitive AdhesivesTextiles & Leather
5 Silicone Nomenclature SILICAO Si OOXSILANESXSiXXRSILOXANESOSiOR
6 Silicone Nomenclature Shorthand Precursor Silanol Siloxane Structure Short handMe MeCl-Si-Cl HO-Si-OH Linear Structures D unitMe-Si-Cl Me-Si-OH End-cap group M unitCl-Si-Cl HO-Si-OH Branched Structures T unitCl OHCl-Si-Cl HO-Si-OH Silica Core Q unitMe Me Me Me Me Me Me MeMe-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 crustReduce to Si metal with carbon at 2500FDow Corning purchases silicon metal & methanolMethanol is converted to MeCl with recycled HCl
9 Process Chemistry of Methyl Train Me2SiCl2MeHSiCl2Me3SiClH2OMe2 HydroSiH fluidEBBChlorosilaneMixWaste &RecoverySiMeClCopper Catalysts
11 Volatile Polydimethylsiloxane (PDMS) Fluids R = CH INCI: DimethiconeR = OH INCI: DimethiconolCH CH CH3R - Si - O - Si - O - Si - RCH CH m CH3When 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 differentUnique flexibility of Si-O bondSi-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 )PolyethylenePolytetrafluoroethylenePolydimethylsiloxane < 0.2Key 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 solidAbility to spread out on a wide variety of substratessilky, smooth, non-tacky, aesthetic enhancingflowability and film formingLowest surface shear viscosity and low surface tensionlubricating, antifoaming, waterproofing, release propertiesHigh gas permeabilityExcellent dielectric propertiesVery good thermo-oxidative stabilitygood chemical inertness and temperature resistanceThe 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 notparticularily solvent resistent; however, elastomers made from siloxnes substituted with fluoro groups show good resistance to hydrocarbons ans such.
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