|Title of Invention||
A PROCESS FOR THE SYNTHESIS OF CROSSLINKED POLYSILAHYDROCARBON
|Abstract||This invention relates trJ a process for the synthesis of crosslinked polysilahydrocarbon which comprises reacting atleast one organodichlorosilane with styrene in the pesence of an alkali metal. One of the organodichlorosilanes in the mixture must. be alkyl vinyldichlorosilane. The crosslinked po1.ysilahydrocarbon is recovered from the reaction mixture by precipitate washirlg and drying.|
This invention relates to a process for the synthesis of cross linked polysilahydrocarbons.
Polysilahydrooarbons are polymers that oontaln sllyl linkages which are separated by two oor more hydrocarbon units.
Major drawback associated with polsilahydrocarbons is thier poor
thermal stability. Lack of branching or cross linking and the presence of disilyl linkage are found to be responsible for the poor thernal stability of these compounds. Thermal stability of polysilahydrocarbons has been improved by subjecting the polymers to heat treating in an inert atmosphere. However, the yield of thermally stable polymer obtained by this method is poor and is only in the range of 20-30%. Highly branched/crosslinked and thermally stable polysilahydrocarbons find use In the preparation of funotionalized polymers and non-oxide ceramic powders.
The object of this invention is to develop a simple synthetic method for producing cross linked thermaly stable polysilahydrocarbons. Alkylvinyldichlorosilane or a mixture of alkylvinyldiohlorosllane and organic substituted dich1orosilanes is treated with styrene in the presence of an alkali metal or an alloy of alkali metals. Dechlorination of the substituted silanes take place initially to result in the formation of disilyl Intermediates which react with styrene to form a copolymer or a terpolymer. During the above dechlorination unsaturated substituted groups such as vinyl groups attached to
Bilicon open up and take part in the cross linking step of the reaction. In otherwords, simultaneous polymerization and cross linking takes place resulting in the production of cross linked polysilahydrocarbons.
This method not only eleminates several process steps but also results in high yield of 75% to 95%. The raw materials used are also easily and cheaply available.
The crosslinked polysilahydrocarbons were synthesized
by the Wurtz type reaction of alkylvinyldichlorosilane with
styrene or a mixture of alkylvinyldichlorosilane and
dialtlkyldichlorosilane/alkylaryldichlorosilane and styrene in
presence of alkali metal in an inert solvent. The
alkylvinyldichlorosilane monomer can be
methylvlnyldiohlorosilane, ethylvlnyldichlorosilane or a combination of these monomers in any proportion. the dialkyldlohlorosilane can be dimethyldlchlorosilane, dlethyldichloresilane, ethylmethyldiohlorosilane or a combintion
of two or more of these monomers in any proportion and the
alkylaryldichlorosilane can be methylphenyldlchlorosllane |or
methyltolyldichlorosilane or a combination of these monomers ;in
any proportion. The alkali metal used for the synthesis can be
sodium, potassium or an alloy of these two metals. the
polymerization is preferably done in a hydrocarbon solvent
selected among benzene, toluene or xylene or a mixture of two for
more of these solvents taken in any proportion. The monomer to
solvent ratio (by weight) can vary from 1:4 to 1:6. The diortfanodlohlorosilane to styrene ratio can vary from 4:1 to 1:7. The polymerization is performed in the temperature range 100 to 135oC. The reaction time can vary from 1 to 5 hr.
The polymerization occurs primarily through, the reaction of disilyl intermediates with the double bonas of styrene resulting in the formation of Si-C bonds. The 'above polymerization reaction is followed by crosslinking involving the
disilyl intermediates or growing polymeric chains and the groups attached to silicon.
This invention relates to a process for the synthesis of crosslinked polysilahydrocarbons which comprises reacting at least one organodichlorosilane with styrene, one of said organodichlorosilane in the reaction mixture being alkylvinyl dichlorosilane, said organo group being an alkyl, alkenyl and aryl, the alkyl and alkenyl group having 1 to 8 carbon atoms and the aryl group being benzyl or alkyl substituted benzyl groups under known dechlorination conditions in the presence of atleast one alkali metal and recovering the resultant crosslinked polysilahydrocarbon therefrom by known methods.
The reaction scheme shown herein below explains the simultaneous polymerization and crosslinking reaction.
The following non-limitive examples illustrate the invention:
Bxaaple 1: Synthesis of crosslinked polysilahydrocarbons from Bethylvlnyldlohlorosllane and styrene (1:0.25 sole ratio)
A four necked round bottomed flask fitted w1th a stirrer mantle, condenser, inlet and outlet for inert gas and n calcium chloride guard tube is charged with 7.5 g(0.327 mol) of freshly cut sodium in 90 ml of toulene. Sodium is melted under reflux conditions of toluene with stirring. To the finely divided sodium, monomer mixture containing 21.15 g (0.15 mol:) of methylvinyldlchlorosilane and 3.9 g (0.375 mol) of styrenei is
added using a pressure equalizing funnel over a period of 10 min.
The reactuion mixture is allowed to reflux gently for a period of
2 hr. The; unreacted sodium is neutralized with methenol/toluene
mixture and the reaction mixture is poured into excess of
methanol. The precipitate obtained is collected and washed several times with methanol/water mixture to remove Rodium chloride and finally with methanol and then dried in a vacuum oven at 100oC for 10 hr. After drying, the polymer is soaked in 100ml of toluene and kept overnight. It is filtered to remove the soluble fraction. The soluble fraction is obtained in negligible yield. The insoluble polymer obtained is dried in a vacuum oven at 100oC for 1 hr. The yield of the final product is about 79%.
Example 2, Synthesis of crosslinked polysilahydrocarbon from nethylvinyldichlorosilane and styrene (1:0.5 mole ratio)
Following the experimental procedure described above, a orosslinked copolymer is synthesized by reaotinrt a mixture of
21.15g (0.15 mol) methylvinyldichlorosilane and 7.8 g (0.07.H mol)
of styrene in 90 ml of toluene at 110˚C. The soluble polymer is obtained in 2% yield and the insoluble polymer is obtained '\x\ 93% yield.
Bxample 3, SyntheslB of polyBllahydrocarbon from methylvlnyldlnhloroailane, dinethyldlchloroBllane and styrene (1:1:0,9 mole ratio)
Following the procedure,described above, a crosslinked terpolymer is synthesized in 79% yield by reacting a monomer mixture containing 7.26 g (0.0515 mol) methylvinyldichlorosilane, 6.7 g (0,0519 mol) of dimethyldichlorosilane and 5.02 g (0.048 mol) of styrene in 100 ml of toluene with 5.52 g (0.24 mol) of sodium. This polymer is stable up to 400˚C in nitrogen atmosphere and undergoes degradation above this temperature giving a ceramic residue of 40% at 900^0.
Though the invention is described hereinabove with specific embodiments, obvious equivalents known to persons skilled in the art are within its scope and that of the appended claims.
1. A process for the synthesis or crosslinked
polysilahydrooarbons comprising reacting atleast one
organodiohlorosilane with styrene, one of said
organodlohlorosilane in the reaction mixture being alkyl
vinyldichlorosilane, said organo group being alkyl, alkenyl and
aryl, the alkyl and alkenyl group having 1-8 carbon atoms and the
aryl group being benzyl or alkyl substituted benzyl groups, under
known dechlorination condition in the presence of at least one
alkali metal or an alkali metal alloy and recovering the resultant crosslinked polysilahydrocarbon there from by known methods.
2. The process as claimed in claim 1, wherein the reaction is carried out in the presence of an organic solvent.
3. The process as claimed in claim 2, wherein said organic solvent is a hydrocarbon solvent selected from benzene, toluene or xylene or a mixture thereof.
4. The process as claimed in claims 13. wherein ; the
monomer solvent ratio is from 1:4 to 1:6 by weight.
5. The process as claimed in any of the preceding claims
wherein the organodichlorosilane to styrene ratio is from 4 1 to 1:7 by weight.
6. The process as claimed in any of the preoeedinrt claims wherein the reaction is carried out at a temperature range of 100 to 135˚C.
7. The process as claimed in any of the preceding claims. wherein the alkali metal is sodium, potassium or an alley thereof.
8. The process as claimed in any of the preced ing olaims,
wherein the reaction mixture is refluxed for a period of 30hts
hours and the unreacted alkali metal is neutralised
9. The process as claimed in claim 8 wherein the reaction
\ ill mixture is poured into excess alcohol to precipitate said polymer
which is subsequently washed and dried.
10. A process for the synthesis of cross 1 inked
polysllahydrocarbons substantially as herein described with
particular reference to the Examples.
|Indian Patent Application Number||1164/MAS/1999|
|PG Journal Number||26/2007|
|Date of Filing||02-Dec-1999|
|Name of Patentee||INDIAN SPACE RESEARCH ORGANISATION|
|Applicant Address||ANTARIKSH BHAVAN, NEW BEL ROAD, BANGALORE-560 094.|
|PCT International Classification Number||C07F7/02|
|PCT International Application Number||N/A|
|PCT International Filing date|