![Introduction
• Polymers in which the main chain consists of repeating -Si-O- units
with organic side groups are referred to as polyorganosiloxanes or
as silicones.
• The silicones are a group of organosilicon polymers.
• The most common example is poly-dimethylsiloxane or PDMS.
• This synthetic polymer has a repeating [(CH3)2SiO] unit.
• This is the basic building block of silicones
• They have unique properties due to the presence of organic groups
attached to a chain.
• They have a wide variety of commercial uses. 2](https://image.slidesharecdn.com/silicones-180213020000/85/Silicones-and-silicones-in-technology-2-320.jpg)
Silicones and silicones in technology
- 1. Silicones and Silicones in Technology 1
- 2. Introduction • Polymers in which the main chain consists of repeating -Si-O- units with organic side groups are referred to as polyorganosiloxanes or as silicones. • The silicones are a group of organosilicon polymers. • The most common example is poly-dimethylsiloxane or PDMS. • This synthetic polymer has a repeating [(CH3)2SiO] unit. • This is the basic building block of silicones • They have unique properties due to the presence of organic groups attached to a chain. • They have a wide variety of commercial uses. 2
- 3. History • 1904 - Frederic Stanley Kipping was the first to achieve extensive synthesis of silicone compounds and coined the name ‘silicones’. He is considered to be the ‘founder’ of silicone science. • 1931- James Franklin Hyde carries out the first successful research leading to commercial production of silicones. 3https://www.onthisday.com/people/j-franklin-hydehttp://charlesduval.org/frederic_stanley_kipping
- 4. Synthesizing silicones • 1940 - Richard Gustav Müller and Eugene George Rochow develop, a direct method for synthesizing silicones on an industrial scale. https://www.ua.tu-dresdef_CD.asp?Code=Chemie&ID=656n.de/Detail_pro http://www.chemheritage.org/discover/collections/oral-histories/details/rochow-eugene-g.aspx 4 R.G.Muller E.G.Rochow
- 5. Moon Landing • 1969 - The first imprint that Neil Armstrong left on lunar soil was made with a silicone rubber boot sole. In addition, new silicone materials used in the lunar for the crew’s safety and support systems. 5
- 6. Computer technology • 1980's - Silicones played an integral role in advancements in computer technology, telecommunications and all other related fields that rely on the microchip. • Without silicone to protect products from extreme temperatures and contamination, we would not have many of the technological and electronic innovations we take for granted today. 6
- 7. Preparation and Properties Of Silicones 7
- 9. Synthesis of Silicones • The production of silicones from silicon takes place in three stages: Synthesis of chlorosilanes Hydrolysis of chlorosilanes Condensation of silanols 9 General formula:RnSiX4-n Keith Purcell ,Koltz,Inorganic chemistry
- 10. Preparation of Silicones 10 250-280°C Cu •Silicones are commercially produced from silicon and methyl chloride in a process known as the "direct reaction" or the "Rochow- Muller direct process."
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- 14. Important differences between silicon and carbon Silicon Carbon Size Larger than C Comparatively smaller than Si electronegativity Lesser than C (1.8) Comparatively higher than Si(2.5) Bond distance and angle (X-O) (X=Si,C) Larger than C Comparatively smaller than Si Forms of bond (X-O) (X=Si,C) (stability consideration) Single bond(stable) All forms of bond 14
- 15. The Siloxane Bond - Structural Considerations • The siloxane bond have a great impact on the chemistry of polysiloxanes. • The Si-O bond distance, shorter than the sum of covalent radii, 1.64 Å compared to 1.76 Å implies a partial double bond character of Si-O. • The basicity of siloxanes is lower than that of ethers. • The barrier of rotation around the Si-O axis, ca. 2.5 kJ /mol in (as well as the barrier of linearisation of the SiOSi angle, ca. 1.3 kJ /mol , are very low.Thus, the polysiloxane chain is unusually flexible. • The Si-O-Si angle, 140-180°, is much wider than the tetrahedral angle, the silicon atom has a relatively large size and the substituents appear only at every second atom in the chain. • These features account for the relatively low steric hindrance to the attack of a nucleophile on silicon. 15R.O. Jones et al. (eds.), Silicon-Containing Polymers, 3-41
- 16. • The propensity of silicon toward the nucleophilic attack is connected with its electronic character • The siloxane bond are used to be attributed to the p(O) d(Si)π interaction. • The contribution of the d orbitals at Si to the total electron distribution is small. • Many authors prefer to approach these features as a consequence of the strongly ionic character of the Si-O bond and of the negative hyperconjugation p(O) σ*(Si-X)π where X is any atom bound to silicon • The interaction is particularly strong when X is an electronegative atom, e.g., O, F, Cl. • But (p-d)π concept not provide unequivocal information about the character of the Si- O bond. 16R.O. Jones et al. (eds.), Silicon-Containing Polymers, 3-41
- 17. Properties of silicones • Silicones are highly valued materials because they have a combination of physical properties not found in other polymers. • They have outstanding heat stability and can be used in applications where organic materials would melt or decompose. • Many silicones seem to be impervious to the effects of aging, weather, sunlight, moisture, heat, cold, and some chemical assaults. • Numerous silicones are used to stick, bond, or couple things together. 17
- 18. • The chemical behaviour and physical properties of silanols depend much on their structure. • Generally, their reactivity increases with the number of hydroxyl groups at the silicon atom in order R3SiOH < R2Si(OH)2 < RSi(OH)3 • The enhanced reactivity of the monomeric polyols and the activating influence of the silanol group on the reactivity of other electronegative substituents at silicon are explained by the negative hyperconjugation. 18
- 19. Facts of relevance to the preparation and properties of silicone polymers • Silicon is usually tetravalent but assume hexavalent characteristics. • Silicon is more electropositive than carbon and hence Si-C bonds are polar (12% ionic) • The reactivity also depends on the nature of the attacking molecule. • The siloxane Si-O link has number of interesting properties. 19
- 20. Fundamental Characteristics of PDMS • Low intermolecular forces between methyl groups • Compact size of methyl groups • High siloxane backbone flexibility • High siloxane bond energy • Partial ionic nature of siloxane bond. 20
- 22. The Si-O bond – the key to silicone’s unique properties • The Si-O bond has higher bond energy than the C-O bond. • The Si-O bond is longer and flatter than the C-O bond. • The Si-O bond has a lower barrier to rotation than the C-O bond and higher free volume. 22
- 23. • Depending on the number of repeat units in the polymer chain and the degree of cross-linking (how the polymer chains are tied together) • at least six classes of commercially important families of products can be produced: fluids, emulsions, compounds, lubricants, resins, and elastomers or rubbers. 23
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- 36. • Airbags are able to meet changing design and tougher foldability and cushioning requirements. • Silicones in airbags provide additional strengthening, sealing and uniformity functionality. • Silicone coatings also render the fabric gastight and heat. 36
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- 39. Silicone Hydrogels- a gel composed usually of one or more polymers suspended in water 39 •Silicone hydrogel contact lenses are advanced soft lenses that allow more oxygen to pass through the lens to the cornea than regular soft ("hydrogel") contacts. • In fact, silicone hydrogel lenses enable up to five times more oxygen to reach the cornea than regular hydrogel lenses. •Benefits of silicone hydrogel lenses Extended wear (sometimes for up to six straight nights and days ) Continuous wear (sometimes for up to thirty days before replacement ) Increased comfort and performance
- 40. • Menstrual cups are usually made of medical grade silicone, shaped like a bell and flexible and are also used internally. • One cup is reusable for up to five years or more 40 http://www.dailymail.co.uk/news/article-3553275/Use-sea-sponges-not-tampons-Spanish-politicians-tell-women.html#ixzz55EnFKpPB
- 41. Breast implants 41 •Implant grade silicone is of long linear chain length often exceeding one million molecular weight •These implants were introduced in the late 1980s and gained popularity in the 1990s. X-ray of breast implant
- 42. Complications • The suspected mechanisms of breast implant rupture are: • damage during implantation • damage during (other) surgical procedures • chemical degradation of the breast implant shell 42
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- 44. • Cases of a rare type of cancer that is linked to breast implants appear to be on the rise, according to a new review. • The first case of BIA-ALCL was documented in 1997. • An FDA report published last year revealed 359 reported cases and nine deaths. 44
- 45. References • James E. Mark,Harry R. Allcock,Robert West, Inorganic Polymers, OXFORD UNIVERSITY PRESS,Second edition,2005. • Vadapalli Chandrasekhar,Inorganic and Organometallic Polymers, Springer publications,2005. • Chatwal,G.R, Inorganic Polymers, Himalaya Publishing House, Bombay, First Edition,1996. • Stephen J. Clarson1, John J. Fitzgerald, Science and Technology of Silicones and Silicone- Modified Materials, ACS Symposium Series, Volume 964,August 02, 2007 • http://www.silicones.eu/silicones-uses • https://dash.harvard.edu/bitstream/handle/1/8965609/Abrams.html?sequence=2 • http://www.brainkart.com/article/Silicones---structure-and-uses_2820/ • http://www.essentialchemicalindustry.org/polymers/silicones.html • https://www.dowcorning.com/content/publishedlit/01-3077.pdf • http://www.chemistryexplained.com/Ru-Sp/Silicone.html#ixzz55A0R9t00 • http://wwwcourses.sens.buffalo.edu/ce435/Polysiloxanes/#jones 45
- 46. Thank you 46