SILICONES AND SILICONES AND PHOSPHAZENESPHOSPHAZENES

Silicones and phosphazenes are examples of inorganicPolymers. Inorganic elements can have different valenciesThan carbon and therefore different numbers of side groups may be attached to a skeletal atom. This will affect the flexibility of polymers, their ability to react with chemical reagents and interactions with other polymers. Among inorganic polymers, silicones and phosphazenesare two important class of polymers with high commercial potential.

SILICONESSILICONES

Silicones are polymeric organosilicone derivative Silicones are polymeric organosilicone derivative containing containing Si-O-Si linkages. These containing containing Si-O-Si linkages. These contain alternate silicon and oxygen atoms in contain alternate silicon and oxygen atoms in which the silicone atoms are joined to organic which the silicone atoms are joined to organic

groups.these are also called groups.these are also called Polysiloxanes.Polysiloxanes.These These have the general formula (Rhave the general formula (R22SiO)SiO)nn

These may be linear ,cyclic or cross linked polymers .TheyHave high thermal stability and are also called high Temperature polymers.

FACTORS AFFECTING THE FACTORS AFFECTING THE NATURE OF SILICONE POLYMERSNATURE OF SILICONE POLYMERS

1)1) The nature of alkyl and aryl groups.The nature of alkyl and aryl groups.

2)2) The distribution of organic groups.The distribution of organic groups.

3)3) The type and proportions of structural units.The type and proportions of structural units.

4)4) The extent of cross linking.The extent of cross linking.

5)5) The length of the chainThe length of the chain

PROPERTIES OF SILICONESPROPERTIES OF SILICONES

Thermal stability-Thermal stability-

The silicones polymers areThe silicones polymers are

Highly stable towards heat. They exhibit thermal Highly stable towards heat. They exhibit thermal stability up to 200 to 300stability up to 200 to 300°C and have low glass °C and have low glass transition temperature.transition temperature.

Chemical Stability-Chemical Stability-

The silicones are stable towards the chemical reagents Some The silicones are stable towards the chemical reagents Some electron deficient salts may result into cleavage of Si-O as electron deficient salts may result into cleavage of Si-O as well asSi-C bonds. These are quite stable to attack by well asSi-C bonds. These are quite stable to attack by oxygenoxygen

Chemical properties-

The siloxanes bond in silicones may be The siloxanes bond in silicones may be cleaved by grignard reagent, alkyl lithium cleaved by grignard reagent, alkyl lithium and lithium aluminium hydrides.and lithium aluminium hydrides.

SOME OTHER PROPERTIES SOME OTHER PROPERTIES OF SILICONESOF SILICONES

They are water repellants.They are water repellants. They are good insulators.They are good insulators. They have non stick and anti foaming They have non stick and anti foaming

properties.properties. They have high strength of the Si-C bond.They have high strength of the Si-C bond. They are resistant to oxidation.They are resistant to oxidation.

USES OF SILICONE USES OF SILICONE POLYMERSPOLYMERS

They are used for high temperature oil baths They are used for high temperature oil baths high vacuum pumps.high vacuum pumps.

They are used as grease, varnishes and these They are used as grease, varnishes and these can be used even at very low temperatures.can be used even at very low temperatures.

They are used as lubricants in both high and They are used as lubricants in both high and low temperatures.low temperatures.

Their toxicity is low and therefore ,these are Their toxicity is low and therefore ,these are used in medicinal and cosmetic implants. used in medicinal and cosmetic implants.

SILICON FLUIDS OR SILICON FLUIDS OR OILSOILS

The silicon fluids are usually linear The silicon fluids are usually linear polysiloxanes of 50 to 200 units having low polysiloxanes of 50 to 200 units having low

molecular weight. They make up about 60% the molecular weight. They make up about 60% the silicones used. If they are prepared by the silicones used. If they are prepared by the hydrolysis of a mixture of (CHhydrolysis of a mixture of (CH33))22SiClSiCl22 and and

(CH(CH33))33SiCl, then the chain lengths may vary SiCl, then the chain lengths may vary

considerably. considerably.

Commerciallly,these are prepared by treating a mixture Commerciallly,these are prepared by treating a mixture of tetrakis cyclodimethyl siloxane and hexamethyl of tetrakis cyclodimethyl siloxane and hexamethyl

disiloxane with a small quantity of100% Hdisiloxane with a small quantity of100% H22SOSO4 4 ..

USES OF SILICON FLUIDS OR USES OF SILICON FLUIDS OR OILSOILS

Silicon oils/fluids are used as water repellents Silicon oils/fluids are used as water repellents for treating building and fabrics.for treating building and fabrics.

silicones oils are used as heat transfer media silicones oils are used as heat transfer media in heating belts.in heating belts.

B’cos of low surface tensions ,silicon oils can B’cos of low surface tensions ,silicon oils can be used as antifoaming agents.be used as antifoaming agents.

Their complete inertness and non toxicity Their complete inertness and non toxicity allow them to be used in cooking oils.allow them to be used in cooking oils.

SILICONE ELASTOMERS(RUBBERS)SILICONE ELASTOMERS(RUBBERS)

The silicone rubbers make up about 30% of The silicone rubbers make up about 30% of silicones produced. These are highly useful silicones produced. These are highly useful b’cos they retain their elasticity from -100 to b’cos they retain their elasticity from -100 to +250°C which is wider range than for natural +250°C which is wider range than for natural rubber. These elastomers, may be rubber. These elastomers, may be vulcanizedvulcanized to get rubber.to get rubber.

Vulcanization is a process in which bonds Vulcanization is a process in which bonds are formed between different chains by are formed between different chains by cross linking reactionscross linking reactions

TYPES OF ELASTOMERSTYPES OF ELASTOMERS

Room temperature vulcanized elastomers Room temperature vulcanized elastomers (RTV).(RTV).

Liquid rubbers (LR).Liquid rubbers (LR). High temperature vulcanizing elastomers High temperature vulcanizing elastomers

(HTV) also called heat curing elastomers(HC). (HTV) also called heat curing elastomers(HC).

USES OF SILICONE USES OF SILICONE ELASTOMERSELASTOMERS

The room temperature silicones have good The room temperature silicones have good adhesive propertiesadhesive properties

These are also used as sealants for sealing.These are also used as sealants for sealing. Liquid rubbers were developed particularly for Liquid rubbers were developed particularly for

quick, automated and cheap production of small quick, automated and cheap production of small objects in a high no. of pieces by injecting objects in a high no. of pieces by injecting molding.molding.

HTV silicone rubbers are finding wide HTV silicone rubbers are finding wide applications as transparent tubing in food industry applications as transparent tubing in food industry medicines,gaskets and rollers etc.medicines,gaskets and rollers etc.

SILICONE RESINSSILICONE RESINS

Silicone resins are solvent solutions of Silicone resins are solvent solutions of branched chain siloxanes containing residual branched chain siloxanes containing residual hydroxyl groups. Silicone resins are made by hydroxyl groups. Silicone resins are made by dissolving a mixture of phenyl substituted dissolving a mixture of phenyl substituted trichlorosilane, PhSiCltrichlorosilane, PhSiCl33 and dichlorosilane n and dichlorosilane n

toluene and hydrolysis with water.toluene and hydrolysis with water.

USES OF SILICONE RESINSUSES OF SILICONE RESINS

Used as insulating material.Used as insulating material. Mixed with glass fibers for additional strength.Mixed with glass fibers for additional strength. Used as laminates for printed circuit boards.Used as laminates for printed circuit boards. Used for encapsulation of components such as Used for encapsulation of components such as

resistors.resistors. Used for non stick coating for domestic Used for non stick coating for domestic

cooking ware.cooking ware.

POLYSILOXANE POLYSILOXANE COPOLYMERSCOPOLYMERS

Polysiloxane copolymers are obtain by Polysiloxane copolymers are obtain by combining polysiloxane structure with organic combining polysiloxane structure with organic polymer structure. These are basically of two polymer structure. These are basically of two types types

1)1) Block copolymerBlock copolymer

2)2) Craft copolymer Craft copolymer

Block copolymersBlock copolymers

In which shorter or longer siloxanes are In which shorter or longer siloxanes are connected by blocks of organic polymersconnected by blocks of organic polymers

Craft copolymersCraft copolymers

In which there are continuous polysiloxane In which there are continuous polysiloxane chains which are either connected or chains which are either connected or substituted by organic polymers blocks. substituted by organic polymers blocks.

POLY PHOSPHAZENESPOLY PHOSPHAZENES

Inorganic polymers containing alternate Inorganic polymers containing alternate phosphorous and nitrogen atoms with two phosphorous and nitrogen atoms with two substituent on each phosphorous atom.substituent on each phosphorous atom.

PREPARATIONS OF PREPARATIONS OF PHOSPHAZENESPHOSPHAZENES

(A) Methods for polyphosphazene

2. (P3N5)n +nCl2 ( PNCl2)n+ Other product

1. nPCl5 +nNH4Cl ( PNCl2)n + 4nHCl phosphonitrilic chloride

3. S4N4 + 6SOCl2 +12 PCl3 4(PNCl2)3+side product

4. 5PCl5 + 3NH3 (PNCI2)3 + 9HCl

5. (PNCl2)3 + 6KSO2F (PNF2)3 +6KCl +5SO2

6. (PNCL2)3 + PbF2 (PNFCl)4+PbCl2+ other pdt

(B) Methods of other polyphosphazene(B) Methods of other polyphosphazene

The other type was obtained from trimer (hexachlorocyclotriphosphazene)by general scheme summerized in figure. The trimer is obtained by rection of PCl5 and NH4Cl in an organic solvent (chlorobenzene).

(C) Polymerisation of organo or (C) Polymerisation of organo or organometallic substituted cyclic organometallic substituted cyclic

phosphazenephosphazene

In this method organic substituents are introduced at the Cyclic trimerphosphazene followed by ring opening polymerisation of the substituted cyclic trimer to a high Polymer.

PROPERTIES AND PROPERTIES AND STRUCTURESSTRUCTURES

Cyclic phosphonitrilic halides,( NPCl2)3 and (NPCl2)4 have been studied1. PHYSICAL PROPERTIES : on heating (NPCl2)3 and (NPCl2)4 polymerise to elastic product of high molecular weight and on heating the product gets depolymerised.

2. SUBSTITUTION REACTIONS : The chlorine atom in phosphonitrilic chloride is very reactive and it can be easily replaced by monovalent groups like F, Br,

OH, OR, SH, SR, SCN, NH2 , NR2 et c

3. HYDROLYSIS : The trimer can be hydrolysed to trimetaphosphamic acid which undergoes isomeric change totrimetaimido phosphoric acid.

4. REACTION WITH AMMONIA : (NOCl2)3 reacts with ammonia to give various

substituted products by replacing chlorine .however in presence of excess ammonia P3N5 formed.

USES OF PHOSPHAZENESUSES OF PHOSPHAZENES

1. The phosphonitrilic halides are used as rigid 1. The phosphonitrilic halides are used as rigid plastics, fibers b’cos they are water proof and plastics, fibers b’cos they are water proof and fire proof and are unaffected by oil and fire proof and are unaffected by oil and petrol.petrol.

2. They are used as catalysts in manufacture of 2. They are used as catalysts in manufacture of silicones.silicones.

3. Thin films of poly( aminophosphazene) are 3. Thin films of poly( aminophosphazene) are used to cover severe burns b’cos they prevent used to cover severe burns b’cos they prevent the loss of body fluids and keep germs out.the loss of body fluids and keep germs out.