Silicone polymers structure, prepartion, properties, uses

Silicone polymers structure, prepartion, properties, uses
INORGANIC POLYMERS
Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are hybridpolymers. One of the best known examples is polydimethylsiloxane, otherwise known commonly as silicone rubber.
 Of synthetic polymers whose backbone is made of repeating silicone to oxygen bonds (siloxane bonds) with organic side groups, such as methyl, phenyl or vinyl.The basic repeating unit became known as siloxane and the most common available silicone is polydimethylsiloxane
Organo-silicone polymers contain chains or network of alternating silicone and oxygen atoms in their structures ,that is exhibited in some natural silicone minerals
Polymeric molecules in silicones held together by weak van der waals force results, they are liquids of varying viscosity or gums or solids containing polymeric molecules which generally soluble in organic mediaHydrolysis of dichloro dimethyl silane (CH3)2SiCl2 gives long chain polymers.As there is active OH group at each end .The length of the chain increasing.so it is called chain building unit

properties
1.The si-o-si bond in silanes is shorter than the expected si-o-si bond as calculated from the their radii.This indicates that there is some ionic character in si-o bond due to which it becomes quite stable.
2.This the the reason for why polysiloxanes are thermally stable and do not decompose even upto 350-400`C.
1. Highly polar character of si-o bond and the ability of si to expand its valency shell by utilizing its d-orbitals renders polysiloxanes susceptible to attack by several reagents.
2.The siloxanes may undergo hydrolysis and alcoholysis at elevated temperature in the presence of strong acids and bases
to give silanols and alkaxysilanes .In general, the greater the extent of substitution on Si atom, the greater is the case of hydrolysis in the presence of acids and greater is the difficulty of hydrolysis in the presence of bases.

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ESWARAN .M [email protected]

1. SILICONE POLYMERS 01 1 BY ESWARAN.M (17PCH003 ) i nboxeswaran @gmail.com

2. Out line STRUCTURE OF SILICONES POLYMERS PREPARATOIN OF SILICONE POLYMERS PROPERTIES OF SILICONE POLYMERS USES OF SILICONE POLYMERS 02 2 INTRODUCTION

3. INORGANIC POLYMERS Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are hybridpolymers . One of the best known examples is polydimethylsiloxane , otherwise known commonly as silicone rubber. 03

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5. Silicone polymers   O f synthetic polymers whose backbone is made of repeating silicone to oxygen bonds ( siloxane bonds) with organic side groups, such as methyl, phenyl or vinyl.The basic repeating unit became known as siloxane and the most common available silicone is polydimethylsiloxane 05 5

6. X=0 , Inorganic polymer X=4 , Organometallic polymers X=0 to 4, Polymeric silicones Structure of silicone polymers 06 6

7. Organo -silicone polymers contain chains or network of alternating silicone and oxygen atoms in their structures ,that is exhibited in some natural silicone minerals 07 7

8. Polymeric molecules in silicones held together by weak van der waals force results, they are liquids of varying viscosity or gums or solids containing polymeric molecules which generally soluble in organic media 07 8

9. Silicones are organo -silicon polymers 08 9 It may be oil or rubber or grease according to the kind and number of organic group

10. Preparation – By hydrolysis of alkyl substituted chlorosilane 09 10 tetrachlorosilianes dialkyl dichlorosilanes Chain iniciation

11. Hydrolysis of dichloro dimethyl silane (CH3) 2 SiCl 2 gives long chain polymers.As there is active OH group at each end .The length of the chain increasing.so it is called chain building unit 10 11 Chain Propagation

12. Chain goes on increasing 11 12 In hydrolysis under carefully controlled conditions yield cyclic structure with 3,4,5,6 Si atoms Tris cyclo dimethyl siloxane Tetrakis cyclo dimethyl siloxane

13. When hydrolysis of Trimethyl mono chloro silane gives (CH3) 3 SiOH 13 13

14. When on Trichloro silane 14 14 3D polymer

15. PROPERTIES OF SILICONE POLYMERS Some charcteristics properties of silicones are discussed below, 1.Thermal Stability. 2. Chemical stability. 3.Chemical reactivity 4.Other properties 15 15

16. Thermal stability 1.The si -o- si bond in silanes is shorter than the expected si -o- si bond as calculated from the their radii.This indicates that there is some ionic character in si -o bond due to which it becomes quite stable. 2.This the the reason for why polysiloxanes are thermally stable and do not decompose even upto 350-400`C. 16 16

17. Chemical stability 1. Highly polar character of si -o bond and the ability of si to expand its valency shell by utilizing its d-orbitals renders polysiloxanes susceptible to attack by several reagents. 2. Strong bases and acids may cause depolymerisation.similarliy , some electron deficient salts may cause the cleavage of Si-O as well as the Si-C bonds. 3.Dry chlorine attacks silicones resulting in chlorination of alkyl groups. 4. Except for the above reactions, polysiloxanes are chemically inert.Common chemical reagents such as dil.acids and bases,metal salts ,water at room temperature,hydrogenperoxide , ammoniumhydroxide, etc .,have little effect of polysiloxanes . 17 17

18. Chemical reactivity. Siloxanes bond can be cleaved by Grignard reagents,alkyl Li as also by lithium aluminium hydride. 18 18

19. 2.The siloxanes may undergo hydrolysis and alcoholysis at elevated temperature in the presence of strong acids and bases to give silanols and alkaxysilanes .In general, the greater the extent of substitution on Si atom, the greater is the case of hydrolysis in the presence of acids and greater is the difficulty of hydrolysis in the presence of bases. Other properties. 1.Polysiloxanes are water repellent. When glass is coated with polysiloxanes,the oxygen atoms of polysiloxanes adhere to the glass surface while the R groups on Si are directed outwards, i.e , towards the air. 2.Polysiloxanes are electrical insulators. They are transparent to visible light but absorb considerable amount of ultraviolet light, especially of shorter wave lengths. 19 19

20. Uses of silicone polymers 20 20 Silicon Rubber Insulator Silicone oil Silicone grease Lubricant fot making water proof cloths and papers for making panit and Enamel

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22. QUESTIONS SESSION 22

23. THANKYOU 23