POLYSILOXANES
Introduction and synthesis
Mr. Himanshu dubey
M.Sc. Polymer science
2 nd sem (2014-2016)
Enroll. NO.-2014023...
CONTENT
 Introduction
 Preparation of monomer
 Synthesis of polysiloxanes
 Ring opening polymerizations
 Ring-opening...
 Polysiloxanes, also called silicones, are characterized by
combinations of chemical, mechanical, and electrical properti...
These have the general formula (R2SiO)n .
These may be linear ,cyclic or cross linked polymers .They
have high thermal s...
The elemental silicon on which the entire technology is based
is typically obtained by reduction of the mineral silica wit...
This relatively complicated reaction has been replaced by the so-called
“Direct Process” or “Rochow Process, which starts ...
 The polysiloxanes were also prepared by condensation reactions. In
fact, Friedel and Crafts reported the condensation of...
Silphenylene-siloxane polymers can be prepared by a low
temperature step condensation polymerization of a
bis(ureido)silan...
Example-
The condensation of trichlorophenylsilane with water is thought to
produce the ladder-type sesquisiloxane polymer...
The Cyclotrisiloxane [{Si(CH=CH2)2{SiMe2}O3] Can Be Prepared
ByThe Condensation Of Divinyldichlorosilane With
Tetramethyld...
The compound [{SiPh2}{SiMe2}2O3] can be prepared by
the condensation of Me2SiCl2 with tetraphenyldisiloxane-
1,3-diol .
Ex...
Cyclic siloxanes can undergo a ring-opening polymerization that is A chain-
growth process. Free radicals are not useful a...
Cyclosiloxanes, [R2SiO]n, (n = 3,4) can be polymerized by ROP
methods to the corresponding linear polymer [R2SiO]n (R = al...
Several cationic initiators such as Lewis acids or protic acids can be
employed to effect the polymerization of cyclosilox...
In the acidolysis/condensation mechanism the initiation of
the polymerization is believed to generate the linear chain
whi...
The second route of propagation involves condensation of a
molecule containing one hydroxyl end-group with another
molecul...
This type of polymerization reaction can also be used to generate short
chain linear siloxanes.Thus, carrying out the acid...
In the case of the short chain generation, the reactions involved are
summarized.Thus, the initiation is envisaged as the ...
Simultaneously, the disiloxane Me3SiOSiMe3 is also opened up by
the protic acid.
Subsequent combination of either Me3Si0H ...
Linear short-chain polysiloxanes Me3Si(OSiMe2)nOSiMe3 are
used as silicone oils. Such oils are characterized by their high...
The second mechanism of cationic polymerization involves the
generation of an active propagation center.This could be an o...
Another example of an oxonium ion generation involves the reaction
of Me3SiH with [Me2Si0]3 with [Ph3C]+[B(C6F5)4]~ to gen...
Anionic polymerization is more effective than the cationic
polymerization in generating high-molecular-weight polysiloxane...
The anionic polymerization is initiated by the reaction of the base
with a cyclosiloxane such as [Me2Si0]4 to generate the...
The propagation reaction is similar to that encountered in many
conventional anionic polymerizations using organic monomer...
The termination of the reaction can be accomplished by the use of
Me3Si end-capping reactions.
Termination reactions of th...
Copolymers of the type [(SiR2O)n(SiR'2O)m] can be prepared by the
polymerization of mixtures of cyclosiloxanes.Thus, for e...
Crosslinking or curing of polysiloxanes is the most important procedure
that allows these polymers to be used as advanced ...
The siloxane polymers can be tailored to contain a few percent of vinyl
groups and these can be crosslinked with polymers ...
Polymers containing polysiloxane segments and other types of backbones
are of interest in generating new hybrid polymers.T...
Preparation of the monomer OHSiMe2-C6H4-/7-SiMe2OH
Condensation of OHSiMe2-C6H4-p-SiMe2OH with RR'Si(ureido)2 to afford ex...
Another example for the synthesis of hybrid polymers…
Block copolymers containing polysiloxane segments and
polyphosphazen...
[Ronald_D._Archer]_Inorganic_and_Organo
metallic
Mark J., Allcock H.,West R. Inorganic
Polymers
[Vadapalli_Chandrasekha...
Polysiloxanes 1
of 34

Polysiloxanes 1

SYNTHESIS OF POLYSILOXANE
Published on: Mar 4, 2016
Published in: Science      
Source: www.slideshare.net


Transcripts - Polysiloxanes 1

  • 1. POLYSILOXANES Introduction and synthesis Mr. Himanshu dubey M.Sc. Polymer science 2 nd sem (2014-2016) Enroll. NO.-201402301157
  • 2. CONTENT  Introduction  Preparation of monomer  Synthesis of polysiloxanes  Ring opening polymerizations  Ring-opening Polymerization of Cyclosiloxanes by Ionic Initiators  Cationic Polymerization  Anionic Polymerization  Preparation of Copolymers by Ring-Opening Polymerization  Crosslinking of Polysiloxanes  Hybrid polymer  Bibliography
  • 3.  Polysiloxanes, also called silicones, are characterized by combinations of chemical, mechanical, and electrical properties which taken together are not common to any other commercially available class of polymers.  Polysiloxanes are unique among inorganic and semi-inorganic polymers.  The most important organometalloid polymers are the polysiloxanes based on the siloxane Si–O linkage found in glass and quartz.
  • 4. These have the general formula (R2SiO)n . These may be linear ,cyclic or cross linked polymers .They have high thermal stability and are also called high Temperature polymers.
  • 5. The elemental silicon on which the entire technology is based is typically obtained by reduction of the mineral silica with carbon at high temperatures. (1) The silicon is then converted directly to tetrachlorosilane by the reaction (2) As already mentioned, this can be used to form an organosilane by the Grignard reaction (3)
  • 6. This relatively complicated reaction has been replaced by the so-called “Direct Process” or “Rochow Process, which starts from elemental silicon. It is illustrated by the reaction (4) But the process also yields RSiCl3 and R3SiCl, which can be removed by distillation. Compounds of formula R2SiCl2 are extremely important, because they provide access to the preparation of a wide variety of substances having both organic and inorganic character.Their hydrolysis gives dihydroxy structures which condense to give the basic [-SiR2O-] repeat unit.
  • 7.  The polysiloxanes were also prepared by condensation reactions. In fact, Friedel and Crafts reported the condensation of Si(C2H5)2(OR)2, where R=alkyl, with water producing [(C2H5)2SiO]n and the alcohol in 1866:  At present, polysiloxane polymers are usually prepared by ring-opening polymerizations of small cyclic oligomers that have been prepared by hydrolysis (a condensation reaction) of the appropriate dihalodialkylsilane. But even today some special siloxanes use condensation reactions for the polymerization step.
  • 8. Silphenylene-siloxane polymers can be prepared by a low temperature step condensation polymerization of a bis(ureido)silane with 1,4bis(hydroxydimethylsilyl)benzene at 20 c. Example- The synthesis of silphenylene-siloxane polymers
  • 9. Example- The condensation of trichlorophenylsilane with water is thought to produce the ladder-type sesquisiloxane polymer. Reaction for producing a sesquisiloxane polymer.
  • 10. The Cyclotrisiloxane [{Si(CH=CH2)2{SiMe2}O3] Can Be Prepared ByThe Condensation Of Divinyldichlorosilane With Tetramethyldisiloxane-1,3-diol . Example-
  • 11. The compound [{SiPh2}{SiMe2}2O3] can be prepared by the condensation of Me2SiCl2 with tetraphenyldisiloxane- 1,3-diol . Example-
  • 12. Cyclic siloxanes can undergo a ring-opening polymerization that is A chain- growth process. Free radicals are not useful as initiator species, because of the nature of the siloxane bond, but anionic and cationic initiators are very effective.The reaction is illustrated using the most common cyclic oligomers, the trimer hexamethylcyclotrisiloxaneor the tetramer octamethylcyclotetrasiloxane where R can be alkyl or aryl x is the degree of polymerization
  • 13. Cyclosiloxanes, [R2SiO]n, (n = 3,4) can be polymerized by ROP methods to the corresponding linear polymer [R2SiO]n (R = alkyl, aryl).Two different types of initiators are used for this reaction- (1) Cationic initiators (2) Anionic initiators.
  • 14. Several cationic initiators such as Lewis acids or protic acids can be employed to effect the polymerization of cyclosiloxanes.Among protic acids, H2SO4, HClO4, CF3SO3H etc. have been widely used. Many Lewis acids have been used including AlCl3 and SnCl4.The mechanism of polymerization initiated by CF3SO3H. Two broad types of mechanisms are envisaged – 1- Acidolysis/condensation 2- Generation of an active propagating center.
  • 15. In the acidolysis/condensation mechanism the initiation of the polymerization is believed to generate the linear chain which contains a hydroxyl terminal group as well as a CF3SO2 end-group. The propagation reaction proceeds in two ways.The first of these involves condensation of two molecules involving their hydroxyl end groups.This leaves terminal triflate groups .
  • 16. The second route of propagation involves condensation of a molecule containing one hydroxyl end-group with another molecule containing a CF3SO2 end-group . Further reactions lead to the formation of the high polymer.
  • 17. This type of polymerization reaction can also be used to generate short chain linear siloxanes.Thus, carrying out the acid-catalyzed ROP of [Me2SiO]4 in the presence of the disiloxane Me3Si-O-SiMe3 allows the formation of (predominantly) Me3SiO(SiMe2O)4Me3Si.
  • 18. In the case of the short chain generation, the reactions involved are summarized.Thus, the initiation is envisaged as the ring-opening of the eight-membered ring.This generates the difunctional linear siloxane (containing Si-OH and Si-OSO2CF3 end-groups).
  • 19. Simultaneously, the disiloxane Me3SiOSiMe3 is also opened up by the protic acid. Subsequent combination of either Me3Si0H or Me3SiOSO2CF3 with the linear siloxane affords Me3Si0(SiMe20)4Me3Si .
  • 20. Linear short-chain polysiloxanes Me3Si(OSiMe2)nOSiMe3 are used as silicone oils. Such oils are characterized by their high thermal stability and low viscosity temperature coefficient (VTC).
  • 21. The second mechanism of cationic polymerization involves the generation of an active propagation center.This could be an oxonium ion (oxygen centered cation) or a siliconium ion (silicon-centered cation).This type of ion has been detected in small molecule experiments.Thus, the reaction of Me3SiH and Me3Si0SiMe3 with [Ph3C]+[B(C6F5)4]~ leads to the formation of [(Me3Si)3O]+ which has been detected by NMR spectroscopic methods.
  • 22. Another example of an oxonium ion generation involves the reaction of Me3SiH with [Me2Si0]3 with [Ph3C]+[B(C6F5)4]~ to generate the cyclotrisiloxane-centered oxonium ion. Generation of a cyclotrisiloxane-based oxonium ion
  • 23. Anionic polymerization is more effective than the cationic polymerization in generating high-molecular-weight polysiloxanes. Generally, the molecular weights obtained in this method are in the order of 2-5 x 106. The initiators could be metal hydroxides such as KOH or even lithium salts of silanediols such as Ph2SiO2Li2.
  • 24. The anionic polymerization is initiated by the reaction of the base with a cyclosiloxane such as [Me2Si0]4 to generate the open-chain compound with a Si-O"K+end-group .
  • 25. The propagation reaction is similar to that encountered in many conventional anionic polymerizations using organic monomers. Thus, the incoming monomer can insert between the ion-pair.This leads to chain propagation. Propagation reaction in the anionic polymerization of Me2SiO4
  • 26. The termination of the reaction can be accomplished by the use of Me3Si end-capping reactions. Termination reactions of the anionic polymerization
  • 27. Copolymers of the type [(SiR2O)n(SiR'2O)m] can be prepared by the polymerization of mixtures of cyclosiloxanes.Thus, for example, heating a mixture of [Me2SiO]4 and [Ph2SiO]4 in the presence of KOH as the catalyst affords the random copolymer [{Me2SiO}n{Ph2SiO}m] Copolymerization of a mixture of [Me2SiO]4 and [Ph2SiO]4
  • 28. Crosslinking or curing of polysiloxanes is the most important procedure that allows these polymers to be used as advanced elastomers. High-molecular-weight polysiloxanes, along with reinforcing fillers such as fumed high-surface-area silica (as opposed to silica obtained from hydrolysis) are heated together with organic peroxides (along with some amount of cyclosiloxanes and some coloring pigments) to afford crosslinked products via -CH2CH2- links. This crosslinking is different from that applicable in organic rubber materials where sulfur cross-links are quite effective.
  • 29. The siloxane polymers can be tailored to contain a few percent of vinyl groups and these can be crosslinked with polymers that contain Si-H units.
  • 30. Polymers containing polysiloxane segments and other types of backbones are of interest in generating new hybrid polymers.These polymers are expected to possess new properties which could be an increase in glass transition temperatures, increase in the thermal stability etc.These polymers are synthesized by using a step-growth condensation polymerization method. The silarylene unit is introduced by the monomerOH-Si(Me2)-C6H4:p- Si(Me2)-C)H .while the siloxane is introduced by the diueridosilane, Me2Si(Ureido)2. Condensation of these reagents in a solvent such as chlorobenzene leads to the elimination of urea as an insoluble by-product leaving the exactly alternating copolymer in solution .
  • 31. Preparation of the monomer OHSiMe2-C6H4-/7-SiMe2OH Condensation of OHSiMe2-C6H4-p-SiMe2OH with RR'Si(ureido)2 to afford exactly alternating hybrid copolymers R = R' = CH3 R = Me,R' = CH=CH2
  • 32. Another example for the synthesis of hybrid polymers… Block copolymers containing polysiloxane segments and polyphosphazene segments have been synthesized by the reaction of hydride-terminated polysiloxane H-[Si(Me2)-O]n-SiMe2H with the telechelic polyphosphazene containing an amino end-group. Poly(phosphazene-siloxane) block copolymers
  • 33. [Ronald_D._Archer]_Inorganic_and_Organo metallic Mark J., Allcock H.,West R. Inorganic Polymers [Vadapalli_Chandrasekhar]_Inorganic_and_ organometallic

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