Title of Invention	A PROCESS FOR PRODUCING SILOXANE POLYMERS HAVING ATOMIC OXYGEN RESISTANCE AND A METHOD OF PRODUCING ARTICLES COATED THEREWITH
Abstract	This invention relates to a process for producing siloxane polymers from endfunctionalized siloxane oligomers. Siloxane oligomers having different end functional groups are polymerized in a known manner to obtain a polymer having a crosslinked network of siloxane linkage ranging from at least I to 20 units separated by organic moieties in the range of 1 to 10. These polymers exhibit very high atomic oxygen resistance and are useful in coating components for satellites and space stations to protect them against atomic oxygen attack. This invention also includes a method of producing a coated article having atomic oxygen resistance.

Title of Invention

A PROCESS FOR PRODUCING SILOXANE POLYMERS HAVING ATOMIC OXYGEN RESISTANCE AND A METHOD OF PRODUCING ARTICLES COATED THEREWITH

Abstract

This invention relates to a process for producing siloxane polymers from endfunctionalized siloxane oligomers. Siloxane oligomers having different end functional groups are polymerized in a known manner to obtain a polymer having a crosslinked network of siloxane linkage ranging from at least I to 20 units separated by organic moieties in the range of 1 to 10. These polymers exhibit very high atomic oxygen resistance and are useful in coating components for satellites and space stations to protect them against atomic oxygen attack. This invention also includes a method of producing a coated article having atomic oxygen resistance.

Full Text	This invention relates to a process for producing atomic oxygen resistant coatings from end-functionalised siloxane oligomers. These coatings are useful in protecting satellite and space station components as well as other materials from atomic oxygen attack. Atomic oxygen hereinafter referenced as AO is formed by photo dissociation of molecular oxygen in the upper atmosphere and is a severe threat to satellites and space stations placed in low earth orbit The collision energy impacts between AO and the ram surfaces of space craft is about 5 eV. As this energy is above the threshold energy for gas-surface interactions, atmosphere interacts with the space craft materials in a number of ways, affecting their properties. Polyimide films, advanced composites and engineering thermoplastic materials are extensively used in the construction of satellites and space stations to be placed in the low earth orbit As all carbon based materials degrade rapidly on exposure to AO, they need to be protected from AO attack by using a protective coating resistant to AO. Metal oxides have been evaluated as AO resistant since they have negligible erosion rates. However, these coatings lack flexibitity and are susceptible to pin hole defects. In addition, these coatings easily crack on thermal cycling due to thermal expansion mismatch of the coatings and the substrate. Considerable interest has been shown in the use of inorganic and organometallic polymers as AO resistant coating agents. These polymers on reaction with AO form a protective layer on the surface of the coating which prevents further reaction of the coating with AO. Ease and flexibility of application of these polymeric materials by spin coating, dip coating and spraying allow coating of flexible surfaces and complex shapes. These coatings undergo self healing thereby prevents the penetration of AO to the substrate. Siloxanes, poly-{carborane-8(loxane)8, decarborane-based polymers and phosphorous containing polyarylene ethers have been evaluated as AO resistant coatings. UV curable siloxane containing cycloaliphatic-epoxy resins have also been considered as AO resistant coatings and matrix resins for fibre reinforced composites. The potymeric materials described hereinabove are either very expensive or are produced by elaborate synthetic procedures. Further, linear sitoxane polymer coatings exhibit a tendency to unzip and degrade by forming cyclic siloxanes. The main object of this invention is to produce a sitoxane polymer which is AO resistant, which does not unzip and degrade. Siloxane polymers obtained by reacting two siloxane oligomers having two different end function at groups are found to have a cross linked net work of short chains containing siloxane linkage separated by organic moieties. A wide variety of such polymers may be produced by selecting oligomers of different end functions. For example an epoxy end functionalized siloxane oligomer may be reacted with siloxane oligomers containing amine, thiol, hydroxy!, cart>oxylk; acid, anhydride or (socyanate as end terminating groups. A vinyt or allyl terminated siloxane oligomer may be reacted with a hydride (SIH) terminated siloxane oligomer. Hydroxy or carboxylic acid terminated siloxane oligomer may be reacted with an Isocyanate terminated oligomer. The following reaction scheme Illustrates the reaction between an epoxy end functionalized siloxane oligomer with an amine terminated siloxane oligomer. in which a and b vary from 1 to 20 and V and "y" may vary from 1 to 10 and"n may vary from 5 to 100. The reaction may be carried out either in the presence or absence of organic solvents. The molar ratio of the components may vary from 2:1 to 1:1. Preferably, an epoxy end functionalized siloxane oligomer and an amirne end functionalized siloxane oligomer may be reacted in 10 to 30% solution in an organic solvent selected from toluene, xylene, hexane, tatrahydrofurar) and diglyme either atone or incombination with one another. These reactions may be carried out at room temperatures for a period of 3 to 5 days or at 50 to 120°Cf6r 10 to 12 hours. Reaction between one or more allyl terminated oligodiorganosiloxane and one or more hydride terminated oligodiorganosiloxane may the carried out in the presence of a transition metal catalyst at room temperature or at a temperature ranging from 60°C to 150^0. One or more epoxy end functionalized siloxane oligomer with one or more carboxylic add end terminated oligo di-organosoxanes may be reacted at a temperature ranging from 100°C to 200°C. One or more epoxy end functionalized siloxane oligomer may be reacted with one or more thiol terminated oligo di-organosiloxane at a temperature ranging from 60°C to 150°C. Similarly, reaction between one or more isocyanate terminated oligo di-organosiloxane with hydroxy alkyl terminated oligo di-organoeiloxane may be carried out in the presence of any known polymerisation catalyst either at room temperature or at temperatures ranging from 60°C to 150°C. Reaction between one or more epoxy end functionalized sHoxane oligomer with one or more isocyanate terminated oligo di-organosiloxane may be carried out in the presence of a known catalyst at a tennperature ranging from 100°C to 180°C or at room temperature. Reaction between one or more isocyanate terminated oligo di-organosiloxane with carboxylk; acid terminated oligo di-organosiloxane may be earned out in the presence of a known polymerisation catalyst at room temperature or at a temperature ranging from 60°C to 150°C. Isocyanate terrminated oligo di-organosiloxane may be reacted with amine terminated oligo di-organosiloxane at room temperature or at a temperature ranging from 60°C to 150°C. This invention also includes a method of producing a coated article having atomic oxygen resistance. Articles may be components for maidng satellites and space stations. Articles made from polyimide films and carbon-polyimide, glass polyimide. carbon epoxy and glass epoxy composites may be coated to produce atomic oxygen resistant articles. Coating may the applied to these articles either as neat resin or as a solution in an organic solvent selected from toluerie, xylene, tetrahydrofuran hexane, diglyme, methylethylketone and isomethyl ketone. A solution containing 30 to 50% of resin may be used for coating. As already stated resins obtained by polymerizing at least a first and a secound siloxane oligomer each having a different end functional group are used to provided resistant coating. After coating the articles with such resins, the components may be left at room temperatures for curing. Alternately the coated components may be heated to 80° to 100°C for 8 to 10 hrs. Coated and uncoated subatrates and a Kapton® film (polylmide film) of known dimensions are kept in a plaama barrel system which produces AO. The instrument is operated at a radio frequency of 13.56 MHz and power supply of 50 to 100 watts under 0.3 to 1 torr. The coated and uncoated samples are removed at regular intervals. Mass loss or mass gain is measured for each sample. From the mass kiss of Kapton® film which is used as a standard, the atomic oxygen fluence in atoms/Cm2 is calculated using the following equatnn: sample - mass at the time of measurement in gms; A is the area in Cm2, p is density in g/Cm2 and E is the eroeion yield. Erosion yield of Kapton® (polyimkle) obtained from AO exposure study in space environment is 3 x 1024 cm3/atom. Thus, the mass loss of the coated and uncoated samples at different fluence levels may be obtained. This invention relates to a process for producing siloxane polymers having atomic oxygen resistance which compnses reacting under known polymerizatk)n condttiorw at least one first and one second siloxane oligomers, each of said first and second oligomers having different end functional groups selected from epoxy, amine, thiol, hydroxyl, carboxylic acid, anhydride, isocyanate, vinyl and ally! to produce a polymer having a cross-linked net work of siloxane linkage ranging from at least 1 to 20 units separated by organic moities ranging from1 to 10. This invention also includes a method of producing a coated article such as components for satellites and space stations having resistance to atomic oxygen, which comprises the steps of applying at least one layer of a siloxane polymer obtained by polymerising at least one first and one second siloxane oligomers, each said first and second oligomer having diffierent end functional groups, on the surface of said articles and allowing said coatings to dry. This invention also includes a coated article such as components for satellites and space stations having an atomk; oxygen resistant coating produced by reacting at least one first and one second oligomer having different end functional groups. The following examples illustrate specific embodiments relating to the process of preparing atomic oxygen resistant siloxane polymers from end-functionalized siloxane oligomers and method of coating articles therewith. Stress is given to establish the atomic oxygen resistant property of the coated article. EXAMPLE 1: Siloxane - epoxy based AO resistant coating for polyimide film. Igm of epoxy end functionalized siloxane oligomer is mixed with 0.7g of amine end functionatized siloxane oligomer, each end functionalized siloxane oligomer having atleast 1 to 20 units and the mixture is applied on 2.5 x 2.5 cm Kapton® film of 25 μm thickness which is aiuminized on one side. This coafing process is repeated to get the required thickness of 4 to 5 μm. The coating is then cured at room temperature for one day and is then heated to about SOT. This coated Kapton® film, an ucoated Kapton® film of the same dimension aiuminized on one side and a plain Kapton® film are exposed to AO in a plasma barrel system described herein above. The mass loss of the films was measured. It is observed that uncoated film lost 1.8 mg/Cm2 on exposure to AO fluence of 0.6 x 1020 atoms/Cm2 whereas the coated film lost only 0.0022 mg/Cm2 even after exposure to AO fiuence of 30 x 1O20 atoms/Cm2. EXAMPLE 2: Siloxane epoxy based AO resistant coating on C-polyimide composite. The procedure described in Example i is repeated. C-pdy-imide composite of dimension 33.5 mm x 5.5 mm x 6 mm is coated with polymer olatained in Example I. The coated and uncoated composites of the same dimension are exposed to AO in a similar manner. The uncoated sannple has to be removed after exposure to AO fluence of 10.6 x 1020 atoms/cm as it is found to contaminate the equipment It is observed that the uncoated composite lost 71 mg/cm2 on exposure to AO fluence of 30 x 1020 atom/Cm2 where as the coated sample loses only 0.324 mg/Cm2 even after exposure to AO fluence of 30 x 1020 atoms/Cm2. EXAMPLE 3; A glass-polyimide composite of the dimension 33.7 mm x 6.1 mm X 3.5 mm is coated with a siloxane polymer prepared by the process according to this invention. Coated and uncoated composites having the same dimensions are exposed to AO as described in the previous examples. It is observed that the coated composite did not lose weight even after exposure to AO fluence of 30 x 1020 atom/Cm2 proving that the glass-polyimide composite sample provided with the coating offers excellent resistance to AO attack. Advantages of using siloxane potynter of subject invention to provide AO resistant coatings are numerous. The polymers are easily fomiulated with or without the addition of solvent medium. The end-functionalized siloxane oligomers required for producing the polymer can be selected in such a way that the coating undergoes curuig at ambient or at elevated temperature thereby adding flexibility to the processing conditions. Curing by UV radiation is not at all necessary. The coatings are flexible and transparent in nature. These coatings do not undergoe unzipping at elevated temperatures resulting in the formation of cyclic siloxanes. Though this invention has been described herein above with specific embodiments, obvious equivalents and alterations known to persons skilled in the art are not excluded from the scope and ambit of the appended claims. WE CLAIM: 1. A process for producing siloxane polymers, having atomic oxygen resistance characterized by reacting at least one first and one second siloxane oligomers, each of said first and second oligomers having different end functional groups selected from epoxy, amine, thiol, hydroxyl, carboxylic acid, anhydride, isocyanate, vinyl and allyl to produce a polymer having a cross-linked net work of siloxane linkage ranging from at least 1 to 20 units separated by organic moieties ranging from 1 to 10. 2. The process as claimed in claim 1, wherein one or more epoxy end functionalized siloxane oligomer having the structure given below is reacted with one or more amine end functionalized siloxane oligomer of the formula to produce siloxane polymers having following formula wherein a and b vary from 1 to 20, x and y vary from 1 to 10 and n can vary from 5 to 100. 3. The process as claimed in claims 1 or 2, wherein said polymerisation reaction is carried out in the absence of any solvents. 4. The process as claimed in claims 1 or 2, wherein said polymerization reaction is carried out in the presence of a solvent such as toluene, xylene, hexane, tetrahydrofuran, diglyme either alone or in combination. 5. The process as claimed in any one of the claims 1 to 4, wherein the ratio of the first siloxane oligomer to the second siloxane oligomer vary form 2:1 to 1:1. 6. The process as claimed in any one of the claims 1 to 5, wherein one or more vinyl tenninated oligo di-organosiloxane is reacted with one or more hydride terminated otigo di-organosiloxane in the presence of a transition metal catalyst at room temperature or at a temperature ranging from 60°C to 100°C. 7. The process as claimed in any one of the claims 1 to 5, wherein one or more allyl terminated oligo di-organosiloxane is reacted with one or more hydride terminated oligo di-organosiloxane in the presence of a known transition metal catalyst at room temperature or at a temperature ranging from 60°C to 150°C. 8. The process as claimed in claims 1 to 5, wherein one or more epoxy end functionalized siloxane oligomer is reacted with one or more carboxylic acid terminated oligo di-organosiloxane at a temperature ranging from 100°C to 200°C. 9. The process as claimed in any one of the claims 1 to 5 wherein one or more epoxy end functionalized siloxane oligomer is reacted with one or more anhydride terminated oHgo di-organosiloxane in the presence of a known catalyst at room temperature or at 100°C to 200°C. 10. The process as claimed in any one of the claims 1 to 5, wherein one or more epoxy end functionalized siloxane oligomer is reacted with one or more thiol terminated oligo dl-organosiloxane at a temperature ranging from 60°C to 150°C. 11. The process as claimed in any one of claims 1 to 5. wherein one or more isocyanate terminated oligo di-oranosiloxane is reacted with hydroxy aikyl terminated oligo di-organosiloxane in the presence of a known polymerization catalyst at room temperature or at a temperature ranging from 60°C to 150°C. 12. The process as claimed in any one of the claims 1 to 5, wherein one or more epoxy end functionalized sitoxane oligomer is reacted with one or more isocyanate terminated oligo di-organosiloxane in the presence of a known polymerization catalyst at a temperature ranging from 100°C to 180°C. 13. The process as claimed in any one of the claims 1 to 5, wherein one or more isocyanate terminated oligo di-organosiloxane is reacted with carboxylic acid terminated ohgo di-organosiloxane in the presence of a known catalyst at temperature ranging from 60°C to 150°C. 14. The process as claimed in any one of the claims 1 to 5, wherein one or more isocyanate terminated oligo di-organosiloxane is reacted with one or more amine-terminated oligo di-organosiloxane at room temperature or at a temperature ranging from 60°"C to 100°C. 15. A method for producing coated articles such as components for satellites and space stations with a coating having resistance to atomic oxygen comprising the steps of applying at least one layer of siloxane polymer on the surface thereof and allowing said coating to dry, wherein said siloxane polymer is obtained by the process claimed in any one of the claims 1 to 14. 16. The method as claimed in claim 15, wherein said coating is applied in the form of neat polymer or as a solution in a known organic solvent. 17. The method as claimed in claims 15 or 16 wherein a 30 to 50% solution of ihe polymer in an organic solvent selected from toluene, xylene, tetrahydrofliran hexane, diglyme, methyl ethyl ketone and isomethyl ketone either alone or in combination with each other is used for coating the components. 18. The method as claimed in any one of the claims 15 to 17, wherein the components are allowed to dry at room temperature after coating. 19. The method as claimed in any one of the claims 15 to 17, wherein the components are heated to a temperature ranging from 80°C to l00°C for 8 to 10 hours after coating. 20. A coated article such as components for satellites and space stations produced by the method claimed in claims 15 to 19. 21. A process for producing siloxane polymers having atomic oxygen resistance substantiany as herein described. 22. A method for producing a coated article such as components for satellites and space stations having resistance to atomic oxygen substantially as herein described. 23. An article such as components for satellites and space stations provided with a coating having resistance to atomic oxygen substantially as herein described.

Full Text

This invention relates to a process for producing atomic oxygen resistant coatings from end-functionalised siloxane oligomers. These coatings are useful in protecting satellite and space station components as well as other materials from atomic oxygen attack.
Atomic oxygen hereinafter referenced as AO is formed by photo dissociation of molecular oxygen in the upper atmosphere and is a severe threat to satellites and space stations placed in low earth orbit The collision energy impacts between AO and the ram surfaces of space craft is about 5 eV. As this energy is above the threshold energy for gas-surface interactions, atmosphere interacts with the space craft materials in a number of ways, affecting their properties.
Polyimide films, advanced composites and engineering thermoplastic materials are extensively used in the construction of satellites and space stations to be placed in the low earth orbit As all carbon based materials degrade rapidly on exposure to AO, they need to be protected from AO attack by using a protective coating resistant to AO. Metal oxides have been evaluated as AO resistant since they have negligible erosion rates. However, these coatings lack flexibitity and are susceptible to pin hole defects. In addition, these coatings easily crack on thermal cycling due to thermal expansion mismatch of the coatings and the substrate.

Considerable interest has been shown in the use of inorganic and organometallic polymers as AO resistant coating agents. These polymers on reaction with AO form a protective layer on the surface of the coating which prevents further reaction of the coating with AO. Ease and flexibility of application of these polymeric materials by spin coating, dip coating and spraying allow coating of flexible surfaces and complex shapes. These coatings undergo self healing thereby prevents the penetration of AO to the substrate. Siloxanes, poly-{carborane-8(loxane)8, decarborane-based polymers and phosphorous containing polyarylene ethers have been evaluated as AO resistant coatings. UV curable siloxane containing cycloaliphatic-epoxy resins have also been considered as AO resistant coatings and matrix resins for fibre reinforced composites. The potymeric materials described hereinabove are either very expensive or are produced by elaborate synthetic procedures. Further, linear sitoxane polymer coatings exhibit a tendency to unzip and degrade by forming cyclic siloxanes.
The main object of this invention is to produce a sitoxane polymer which is AO resistant, which does not unzip and degrade.

Siloxane polymers obtained by reacting two siloxane oligomers having two different end function at groups are found to have a cross linked
net work of short chains containing siloxane linkage separated by organic moieties. A wide variety of such polymers may be produced by selecting oligomers of different end functions. For example an epoxy end functionalized siloxane oligomer may be reacted with siloxane oligomers containing amine, thiol, hydroxy!, cart>oxylk; acid, anhydride or (socyanate as end terminating groups. A vinyt or allyl terminated siloxane oligomer may be reacted with a hydride (SIH) terminated siloxane oligomer. Hydroxy or carboxylic acid terminated siloxane oligomer may be reacted with an Isocyanate terminated oligomer.
The following reaction scheme Illustrates the reaction between an epoxy end functionalized siloxane oligomer with an amine terminated siloxane oligomer.

in which a and b vary from 1 to 20 and V and "y" may vary from 1 to 10 and"n may vary from 5 to 100.
The reaction may be carried out either in the presence or absence of organic solvents. The molar ratio of the components may vary from 2:1 to 1:1.
Preferably, an epoxy end functionalized siloxane oligomer and an amirne end functionalized siloxane oligomer may be reacted in 10 to 30% solution in an organic solvent selected from toluene, xylene, hexane, tatrahydrofurar) and diglyme either atone or incombination with one another. These reactions may be carried out at room temperatures for a period of 3 to 5 days or at 50 to 120°Cf6r 10 to 12 hours.
Reaction between one or more allyl terminated oligodiorganosiloxane and one or more hydride terminated oligodiorganosiloxane may the carried out in the presence of a transition metal catalyst at room temperature or at a temperature ranging from 60°C to 150^0.
One or more epoxy end functionalized siloxane oligomer with one or more carboxylic add end terminated oligo di-organosoxanes may be reacted at a temperature ranging from 100°C to 200°C.

One or more epoxy end functionalized siloxane oligomer may be reacted with one or more thiol terminated oligo di-organosiloxane at a temperature ranging from 60°C to 150°C.
Similarly, reaction between one or more isocyanate terminated oligo di-organosiloxane with hydroxy alkyl terminated oligo di-organoeiloxane may be carried out in the presence of any known polymerisation catalyst either at room temperature or at temperatures ranging from 60°C to 150°C.
Reaction between one or more epoxy end functionalized sHoxane oligomer with one or more isocyanate terminated oligo di-organosiloxane may be carried out in the presence of a known catalyst at a tennperature ranging from 100°C to 180°C or at room temperature.
Reaction between one or more isocyanate terminated oligo di-organosiloxane with carboxylk; acid terminated oligo di-organosiloxane may be earned out in the presence of a known polymerisation catalyst at room temperature or at a temperature ranging from 60°C to 150°C.

Isocyanate terrminated oligo di-organosiloxane may be reacted with amine terminated oligo di-organosiloxane at room temperature or at a temperature ranging from 60°C to 150°C.
This invention also includes a method of producing a coated article having atomic oxygen resistance. Articles may be components for maidng satellites and space stations. Articles made from polyimide films and carbon-polyimide, glass polyimide. carbon epoxy and glass epoxy composites may be coated to produce atomic oxygen resistant articles.
Coating may the applied to these articles either as neat resin or as a solution in an organic solvent selected from toluerie, xylene, tetrahydrofuran hexane, diglyme, methylethylketone and isomethyl ketone. A solution containing 30 to 50% of resin may be used for coating. As already stated resins obtained by polymerizing at least a first and a secound siloxane oligomer each having a different end
functional group are used to provided resistant coating.
After coating the articles with such resins, the components may be left at room temperatures for curing. Alternately the coated components may be heated to 80° to 100°C for 8 to 10 hrs.

Coated and uncoated subatrates and a Kapton® film (polylmide film) of known dimensions are kept in a plaama barrel system which produces AO. The instrument is operated at a radio frequency of 13.56 MHz and power supply of 50 to 100 watts under 0.3 to 1 torr. The coated and uncoated samples are removed at regular intervals. Mass loss or mass gain is measured for each sample. From the mass kiss of Kapton® film which is used as a standard, the atomic oxygen fluence in atoms/Cm2 is calculated using the following equatnn:

sample - mass at the time of measurement in gms; A is the area in Cm2, p is density in g/Cm2 and E is the eroeion yield. Erosion yield of Kapton® (polyimkle) obtained from AO exposure study in space environment is 3 x 1024 cm3/atom. Thus, the mass loss of the coated and uncoated samples at different fluence levels may be obtained.
This invention relates to a process for producing siloxane polymers having atomic oxygen resistance which compnses reacting under known polymerizatk)n condttiorw at least one first and one second siloxane oligomers, each of said first and second oligomers having different end functional groups selected from epoxy, amine,

thiol, hydroxyl, carboxylic acid, anhydride, isocyanate, vinyl and ally! to produce a polymer having a cross-linked net work of siloxane linkage ranging from at least 1 to 20 units separated by organic moities ranging from1 to 10.
This invention also includes a method of producing a coated article such as components for satellites and space stations having resistance to atomic oxygen, which comprises the steps of applying at least one layer of a siloxane polymer obtained by polymerising at least one first and one second siloxane oligomers, each said first and second oligomer having diffierent end functional groups, on the surface of said articles and allowing said coatings to dry.
This invention also includes a coated article such as components for satellites and space stations having an atomk; oxygen resistant coating produced by reacting at least one first and one second oligomer having different end functional groups.
The following examples illustrate specific embodiments relating to the process of preparing atomic oxygen resistant siloxane polymers from end-functionalized siloxane oligomers and method of coating articles therewith. Stress is given to establish the atomic oxygen resistant property of the coated article.

EXAMPLE 1:
Siloxane - epoxy based AO resistant coating for polyimide film. Igm of epoxy end functionalized siloxane oligomer is mixed with 0.7g of amine end functionatized siloxane oligomer, each end functionalized siloxane oligomer having atleast 1 to 20 units and the mixture is applied on 2.5 x 2.5 cm Kapton® film of 25 μm thickness which is aiuminized on one side. This coafing process is repeated to get the required thickness of 4 to 5 μm. The coating is then cured at room temperature for one day and is then heated to about SOT. This coated Kapton® film, an ucoated Kapton® film of the same dimension aiuminized on one side and a plain Kapton® film are exposed to AO in a plasma barrel system described herein above. The mass loss of the films was measured. It is observed that uncoated film lost 1.8 mg/Cm2 on exposure to AO fluence of 0.6 x 1020 atoms/Cm2 whereas the coated film lost only 0.0022 mg/Cm2 even after exposure to AO fiuence of 30 x 1O20 atoms/Cm2.
EXAMPLE 2:
Siloxane epoxy based AO resistant coating on C-polyimide composite.

The procedure described in Example i is repeated. C-pdy-imide composite of dimension 33.5 mm x 5.5 mm x 6 mm is coated with polymer olatained in Example I. The coated and uncoated composites of the same dimension are exposed to AO in a similar manner. The uncoated sannple has to be removed after exposure to AO fluence of 10.6 x 1020 atoms/cm as it is found to contaminate the equipment It is observed that the uncoated composite lost 71 mg/cm2 on exposure to AO fluence of 30 x 1020 atom/Cm2 where as the coated sample loses only 0.324 mg/Cm2 even after exposure to AO fluence of 30 x 1020 atoms/Cm2.
EXAMPLE 3;
A glass-polyimide composite of the dimension 33.7 mm x 6.1 mm X 3.5 mm is coated with a siloxane polymer prepared by the process according to this invention. Coated and uncoated composites having the same dimensions are exposed to AO as described in the previous examples. It is observed that the coated composite did not lose weight even after exposure to AO fluence of 30 x 1020 atom/Cm2 proving that the glass-polyimide composite sample provided with the coating offers excellent resistance to AO attack.

Advantages of using siloxane potynter of subject invention to provide AO resistant coatings are numerous. The polymers are easily fomiulated with or without the addition of solvent medium. The end-functionalized siloxane oligomers required for producing the polymer can be selected in such a way that the coating undergoes curuig at ambient or at elevated temperature thereby adding flexibility to the processing conditions. Curing by UV radiation is not at all necessary. The coatings are flexible and transparent in nature. These coatings do not undergoe unzipping at elevated temperatures resulting in the formation of cyclic siloxanes.
Though this invention has been described herein above with specific embodiments, obvious equivalents and alterations known to persons skilled in the art are not excluded from the scope and ambit of the appended claims.

WE CLAIM:
1. A process for producing siloxane polymers, having atomic oxygen resistance characterized by reacting at least one first and one second siloxane oligomers, each of said first and second oligomers having different end functional groups selected from epoxy, amine, thiol, hydroxyl, carboxylic acid, anhydride, isocyanate, vinyl and allyl to produce a polymer having a cross-linked net work of siloxane linkage ranging from at least 1 to 20 units separated by organic moieties ranging from 1 to 10.
2. The process as claimed in claim 1, wherein one or more epoxy end functionalized siloxane oligomer having the structure given below

is reacted with one or more amine end functionalized siloxane oligomer of the formula

to produce siloxane polymers having following formula

wherein a and b vary from 1 to 20, x and y vary from 1 to 10 and n can vary from 5 to 100.
3. The process as claimed in claims 1 or 2, wherein said
polymerisation reaction is carried out in the absence of any
solvents.
4. The process as claimed in claims 1 or 2, wherein said
polymerization reaction is carried out in the presence of a
solvent such as toluene, xylene, hexane, tetrahydrofuran,
diglyme either alone or in combination.

5. The process as claimed in any one of the claims 1 to 4, wherein the ratio of the first siloxane oligomer to the second siloxane oligomer vary form 2:1 to 1:1.
6. The process as claimed in any one of the claims 1 to 5, wherein one or more vinyl tenninated oligo di-organosiloxane is reacted with one or more hydride terminated otigo di-organosiloxane in the presence of a transition metal catalyst at room temperature or at a temperature ranging from 60°C to 100°C.
7. The process as claimed in any one of the claims 1 to 5, wherein one or more allyl terminated oligo di-organosiloxane is reacted with one or more hydride terminated oligo di-organosiloxane in the presence of a known transition metal catalyst at room temperature or at a temperature ranging from 60°C to 150°C.
8. The process as claimed in claims 1 to 5, wherein one or more epoxy end functionalized siloxane oligomer is reacted with one or more carboxylic acid terminated oligo di-organosiloxane at a temperature ranging from 100°C to 200°C.

9. The process as claimed in any one of the claims 1 to 5 wherein one or more epoxy end functionalized siloxane oligomer is reacted with one or more anhydride terminated oHgo di-organosiloxane in the presence of a known catalyst at room temperature or at 100°C to 200°C.
10. The process as claimed in any one of the claims 1 to 5, wherein one or more epoxy end functionalized siloxane oligomer is reacted with one or more thiol terminated oligo dl-organosiloxane at a temperature ranging from 60°C to 150°C.
11. The process as claimed in any one of claims 1 to 5. wherein one or more isocyanate terminated oligo di-oranosiloxane is reacted with hydroxy aikyl terminated oligo di-organosiloxane in the presence of a known polymerization catalyst at room temperature or at a temperature ranging from 60°C to 150°C.
12. The process as claimed in any one of the claims 1 to 5, wherein one or more epoxy end functionalized sitoxane oligomer is reacted with one or more isocyanate terminated oligo di-organosiloxane in the presence of a known polymerization catalyst at a temperature ranging from 100°C to 180°C.

13. The process as claimed in any one of the claims 1 to 5, wherein one or more isocyanate terminated oligo di-organosiloxane is reacted with carboxylic acid terminated ohgo di-organosiloxane in the presence of a known catalyst at temperature ranging from 60°C to 150°C.
14. The process as claimed in any one of the claims 1 to 5, wherein one or more isocyanate terminated oligo di-organosiloxane is reacted with one or more amine-terminated oligo di-organosiloxane at room temperature or at a temperature ranging from 60°"C to 100°C.
15. A method for producing coated articles such as components for satellites and space stations with a coating having resistance to atomic oxygen comprising the steps of applying at least one layer of siloxane polymer on the surface thereof and allowing said coating to dry, wherein said siloxane polymer is obtained by the process claimed in any one of the claims 1 to 14.

16. The method as claimed in claim 15, wherein said coating is applied in the form of neat polymer or as a solution in a known organic solvent.
17. The method as claimed in claims 15 or 16 wherein a 30 to 50% solution of ihe polymer in an organic solvent selected from toluene, xylene, tetrahydrofliran hexane, diglyme, methyl ethyl ketone and isomethyl ketone either alone or in combination with each other is used for coating the components.
18. The method as claimed in any one of the claims 15 to 17, wherein the components are allowed to dry at room temperature after coating.
19. The method as claimed in any one of the claims 15 to 17, wherein the components are heated to a temperature ranging from 80°C to l00°C for 8 to 10 hours after coating.
20. A coated article such as components for satellites and space stations produced by the method claimed in claims 15 to 19.

21. A process for producing siloxane polymers having atomic oxygen resistance substantiany as herein described.
22. A method for producing a coated article such as components for satellites and space stations having resistance to atomic oxygen substantially as herein described.
23. An article such as components for satellites and space stations provided with a coating having resistance to atomic oxygen substantially as herein described.

Documents:

279-mas-2002 abstract-duplicate.pdf

279-mas-2002 abstract.pdf

279-mas-2002 claims-duplicate.pdf

279-mas-2002 claims.pdf

279-mas-2002 correspondence-others.pdf

279-mas-2002 correspondence-po.pdf

279-mas-2002 description (complete)-duplicate.pdf

279-mas-2002 description (complete).pdf

279-mas-2002 form-1.pdf

279-mas-2002 form-19.pdf

279-mas-2002 form-26.pdf

279-mas-2002 form-3.pdf

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Patent Number

216622

Indian Patent Application Number

279/MAS/2002

PG Journal Number

17/2008

Publication Date

25-Apr-2008

Grant Date

17-Mar-2008

Date of Filing

12-Apr-2002

Name of Patentee

INDIAN SPACE RESEARCH ORGANISATION

Applicant Address

ISRO Headquarters Department of space, Antariksh Bhavan, New Bel Road, Bangalore 560 094,

Inventors:

#	Inventor's Name	Inventor's Address
1	SHANMUGAM PACKIRISAMY	C/O Vikram Sarabhai Space Centre, Trivandrum - 695 022,
2	GINU ABRAHAM	C/O Vikram sarabhai space centre, Trivandrum -695 022,
3	RAJAGOPALAN RAMASWAMY	C/O Vikram sarabhai space centre, Trivandrum -695 022,
4	KOVOOR NINAN NINAN	C/O Vikram sarabhai space centre, Trivandrum -695 022,
5	KUCHIBHATLA SITARAMA SASTRI	C/O Vikram sarabhai space centre, Trivandrum -695 022,

PCT International Classification Number

C09D 143/04

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA