• Silicone functional units R3SiO1/2 : Monofunctional, M Chapter 4. Silicones 4.1 Structure and properties • Poly (organosiloxanes) - only industrially important polymers • Silicone functional units R3SiO1/2 : Monofunctional, M R2SiO2/2 : Difunctional, D RSiO3/2 : Trifunctional, T SiO4/2 : Tetrafunctional, Q where R-methyl or phenyl

• Linear poly(organosiloxanes) - a combination of M terminal units and D units • Poly(organosiloxanes) with D units only. Either cyclic or linear with hydroxy or alkoxy end groups • Incorporation of T and Q units => Branched poly(siloxanes)

• Silicone Properties • High temperature stability • Resistance against oxidation and weathering • Hydrophobicity • Antifoaming or foam-stabilizing properties depending on structure • Adhesive • Electrically non-conducting • High Gas and vapor permeability • High stability in physical properties with T • Physiologically Harmless

4.3. Silicone Manufacture 4.3.1. Synthesis of starting materials - Most important starting materials (chloro) Methyl silane (chloro) phenyl silane 4.3.1.1. Chloromethyl silane - Direct Synthesis process by Rochow and Müller Si + 2CH3Cl Cu (CH3)2SiCl2 300℃ in fluidized reactor (99% purity powder) 2-6% Cu as a catalyst(mostly CuO) 0.05-0.5% Zn(ZnO) as an activator

• Byproduct CH3SiCl3, (CH3)3SiCl, CH3SiHCl2 4. 3. 1. 2 • Byproduct CH3SiCl3, (CH3)3SiCl, CH3SiHCl2 4.3.1.2.(Chloro-)Phenyl- and (Chloro)methylphenylsilane • (Chloro-)phenyl silane Direct synthesis from silicon and chlorobenzene at 500℃ Si + 2C6H5Cl Cu(HCl) (C6H5)2SiCl2 500℃ Si + 2C6H5Cl + HCl C6H5SiCl3 + C6H6 CVD

HSiCl3 + C6H5Cl 550~650℃ C6H5SiCl3 + HCl • (Dichloro-)methyl phenyl silane CH3HSiCl2 + C6H5Cl 550~650℃ C6H5(CH3)SiCl2 + HCl 4.3.1.3. Other industrially important silanes 1) (Chloro)Vinyl- and (Chloro)methyl Vinyl Silanes CH2=CH2(CH3)nSiCl3-n - cross-linking silicone Rubbers

2) (Dichloro) methyl (3.3.3-trifluoropropyl) Silanes CF3CH2CH2(CH3)SiCl2 - manufacture of modified poly(organosiloxanes) 3) Organo-functional siloxanes • Trialkoxy(3-aminopropyl)silanes : H2N(CH2)3Si(OR)3 • Trialkoxy(3-mercaptopropyl)silanes : HS(CH2)3Si(OR)3 • Trialkoxy(3-methacryloxypropyl) silanes - mainly as adhesion promoters for glass fiber-reinforced plastics and the surface treatment of fillers

• Manufacture Addition of the appropriate alkene or alkyne to hydrogen-containing silanes w/t. Pt compound • Hydrosilation : 수소화 규소 첨가반응 -Si-H + H2C=CH-R Pt -Si-CH2-CH2-R -Si-H + HC≡C-R Pt -Si-CH=CH-R

4. 3. 2. Linear Poly(organosiloxanes) 4. 3. 2. 1 4.3.2. Linear Poly(organosiloxanes) 4.3.2.1. Synthesis of oligomeric precursors • Most important silicone products - Based on (Chloromethyl)silanes with the derivatives of (dichloro) dimethylsilanes i.e. Silicone elastomer & silicone oils • High molecular weight poly(dimethylsiloxanes) <= linear and cyclic dimethylsiloxanes <= Hydrolysis or methanolysis of(dichloro) dimethylsilane

⊙ Hydrolysis of (Dichloro) dimethylsilane • Cyclic CH3 CH3 nCl-Si-Cl + nH2O Si-O + 2nHCl CH3 CH3 n • Linear CH3 CH3 nCl-Si-Cl + (n+1)H2O HO-Si-O-H + 2nHCl CH3 CH3 n

Continuous reaction In liquid phase w/t * Continuous reaction In liquid phase w/t. 25% HCl solution or In gas phase at > 100℃ • Liquid phase reaction Linear/cyclic siloxanes formed w/t. 28~35% 1:1 ~ 1:2 HCl acid(aq) • Vapor phase reaction CH3Cl by CH3OH technically more complicate due to corrosion problems

• Advantage production of gas phase HCl Easier to form CH3Cl ⊙ Methanolysis of (Dichloro) dimethyl silane • Products : CH3Cl and α,β -dihydroxy dimethyl siloxane(yield:>98%) cyclic poly(dimethyl loxane) n(CH3)2SiCl2 + 2nCH3OH [(CH3)2SiO]n + 2nCH3Cl + nH2O

⊙ Purification - only highly pure dichlorodimethyl silane ( > 99 ⊙ Purification - only highly pure dichlorodimethyl silane ( > 99.99%) => linear and cyclic dimethylsiloxane oligomers => Manufacture of high molecular weight linear poly(dimethyl siloxanes) Trace of ( trichloro) methyl silane => Troublesome

Otherwise, CH3 CH3 Si-O and HO-Si-O-H CH3 n CH3 n KOH Cyclic dimethyl siloxanes + >160℃ Trifuctional impurities D3: Hexamethyl trisiloxane D4: Octamethyl tetrasiloxanes or Larger

D3 : (CH3)2Si O Si(CH3)2 O O Si (CH3)2 D4 : (CH3)2Si O Si(CH3)2 O O (CH3)2Si O Si(CH3)2

Then, D3, D4 or larger Distillation and D3, D4 & larger Trifunctional impurities 4.3.2.2. Synthesis of high molecular weight Linear poly(dimethyl siloxanes) - Silicone oil and silicone rubber • Manufactured either from 1) Cyclic methylsiloxanes by alkaline or Acidic ring opening polymerization 2) Poly condensation of linear α,β-dihydroxy methyl siloxane oligomers

• Control of chain length( or viscosity) Addition of chain termination agents i.e. Trimethyl Siloxy-containing siloxanes (Hexamethyl disiloxane) or water ⊙ Alkaline Ring Opening Polymerization • Cyclic Poly(dimethyl siloxanes) (i.e. Octamethyl cyclotetrasiloxane) in the presence of KOH(10ppm) => Linear poly(dimethylsiloxane) with a broad molecular weight distribution and cyclic siloxanes of different ring sizes

⊙ Acidic Ring opening polymerization • Ring opening polymerization of octamethyl cyclotetrasiloxane • equilibrium catalysts - Sulfuric Acid - Perfluoro alkyl Sulfonic acid - Acid-activated clay particles • Advantageous for the manufacture of the low-viscosity and Si-H containing Poly(dimethylsiloxanes) * Removal of cyclic siloxanes - possible by distillation after neutralizing the reaction product

⊙ Non-equilibrating polycondensation • Polycondensation of α,β-dihydroxy methyl siloxane oligomers with OH-end groups at room temperature • Catalyst : Phosphonitrile dichloride (PNCl2)x, where x=3 • This reaction can be terminated by neutralization with amines

4.3.3. Manufacture of Branched Poly(organosilioxane)-silicone Resins • Two step manufacturing process 1) Hydrolysis of a (chloro) organosilane mixture (methyl and phenyl groups) with the branching (trichloro) organosilanes - proceeds in the presence of solvents (i.e. Xylene) and higher alcohols. 2) The Resulting hydrolysate with silanol or alkoxysilyl groups => Resins by thermal polymerization

4. 4. Industrial Silicone products 4. 4. 1 4.4. Industrial Silicone products 4.4.1. Silicone oils • Industrially most important silicone oil α,w-trimethylsilyl poly(dimethylsiloxanes) R (CH3)3Si-O-Si-O-Si(CH3)3 R n R/R : CH3/CH3, CH3/C6H5, C6H5/C6H5 or CH3/H

• Properties • pour point : -60~-35℃ • High stabilities to high temperature stress and oxidative degradation i.e. Silicon oil with phenyl groups - Highest thermal stability - Lifetime : months at 250℃ in air and 350℃ in closed system • Good electric insulating properties • Low surface tension • Odorless, tasteless and physiologically inert

• Applications • Heat transfer media • Lubricant • Hydraulic oil • Brake fluid • Transformer oil • Flow and Glow improvers in paint industry • Foam stabilizers in poly(urethane) foams • Defoaming agents in the crude oil industry • Hydrophobicity - Cosmetics, Cars and furniture polishing

4.4.2. Products from silicone oils ⊙ Silicone oil emulsions - produced from poly(dimethylsiloxane) or poly(hydrogen methylsiloxane) oils with trimethyl siloxy groups • Applications • Mold releasing and deaeration agents in the manufacture of tires • Hydrophobizing and bulking of fabrics in the textile industry • Antifoaming agents(silica containing emulsion)

⊙ Silicone paste and Greases • Silicone paste - manufactured by incorporating large quantities of highly dispersed silicas or calcium or lithium soaps • Sealants and specialty Greases 4.4.3. Silicone Rubbers • product types ∽ crosslinking mechanism and application areas 4.4.3.1. Room temperature vulcanizable single component silicone rubber

• Steps of Cross linking of single component Silicone rubbers 1) Reaction of a hydroxy group-terminating poly(dimethyl siloxane) with a hydrolyzable group-containing silane or siloxane crosslinking agent in the presence of fillers and a condensation catalyst

The above mixtures are stable in the absence of moisture But In the presence of moisture, the reactive groups are hydrolyzed

• Highly dispersed silicas as reinforcing filler 1~30 wt% incorporation to improve the mechanical properties. • Maximum 30% of trimethoxy-terminated Poly(dimethyl siloxane)silicone oil -> Pliant silicone Rubber • Sn-organic compound: Hardening process (condensation) • Room temperature vulcanizable single component silicone rubber used as -sealing compounds in the construction industry, sanitory sector, glass sector and automobile industry

- Adhesives for heat-resistant bonds and seals 4. 4. 3. 2 - Adhesives for heat-resistant bonds and seals 4.4.3.2. Room Temperature vulcanizable two component silicone rubbers - Mixture of the polymer and the crosslinking component • Two different crosslinking systems i) Based on polycondensation ii) Polyaddition i) Polycondensation systems poly(dimethylsiloxane) with hydroxy end groups and a viscosity of 103 to 105 mPas is crosslinked with a crosslinking component containing tetraalkoxysilanes and a condensation catalyst

Tetra alkoxy silanes, i. e Tetra alkoxy silanes, i.e. TEOS(crosslinking agent) Condensation Catalyst : Dibutyl tin dilaurate Therfore, a poly(dimethyl Siloxane) with hydroxy groups is corss-linked with TEOS an condensation catalyst ii) Poly addition system Methyl vinyl Siloxy-Containing poly(dimethyl Siloxane) with trimethyl siloxy or dimethyl vinyl siloxy end groups with a similar viscosity

• Hydrosilation These polymer components react with hydrogen methyl siloxy-containing poly(dimethyl siloxane) having either trimethyl siloxy or hydrogen dimethyl siloxy end groups -> Crosslinking • Catalyst : Pt (H2Pt2Cl6)

4.4.3.3. 4.4.3.4. - Read Text. 4.4.3.5. 4.4.3.6. Silicone Rubber Properties • Excellent thermal stability i.e. Elastomeric properties, very stable in hot air at 180℃ Mechanical properties at 180℃, as good as those at 25℃ ∴ Much better tensile strength at 180~200℃ than organic rubbers while 2~3 times the tensile strength of silicone rubber at room temperature

• Constant and high hardness down to -50℃ • Good chemical stabilities except for strong acids and bases and chlorine • Good insulators both at Room T. and higher T. • Electrically conducting with the incorporation of carbon black • Flame resistant and self-extinguishing by adding Pt.compound * Upon firing, No toxic products formed except for CO

4.4.4. Silicone Resins - Poly(organosiloxanes) w/t a high proportion of branched tri- or tetra-functional siloxy groups D3 D4 RSi-O3/2 Si-O4/2 • Hardening process of silicone resins subjecting liquid silicone resins or silicone resin solutions to several hours heating at 180~250℃ • Thermally stable coatings maintain their transparancy, gloss or elasticity even at 200~ 250℃(phenyl group) • Hydrophobic and extremely weather resistant

Applications of methyl- or methylphenyl resins • Raw materials for paints, binders and building preservation • Electrically insulating lacquer (wire enamel) • Bonding of glass filaments or mica(운모) insulating materials •Corrosion-protection stoving enamel, pigmented w/t. Zinc dust • Enameling of metal chimney • Applications of silicone-polyester compound resins • Heat resistant stoving enamels for cooking and roasting utensils

• Heating apparatus and cookers • Coil coating of metallic plates for façade • Rendering plastics scratch resistant