Title of Invention	A PROCESS FOR THE SYNTHESIS OF SILOXANE-IMIDE-EPOXY RESINS
Abstract	ABSTRACT 1002/CHE/2005 A process for the synthesis of siloxane imide-epoxy resins The present invention relates to a process for the synthesis of siloxane imide-epoxy resin comprising of reacting a siloxane containing diimide-diacid with epichiorohydrin under epoxidation conditions in the presence of a quaternary ammonium halide catalyst and thereafter recovering the resin.

Full Text

This invention relates to processes for synthesizing siloxane-imide-epoxy resins. The siioxane-imide-epoxy resins are obtained through the reaction of siloxane linkage containing diimlde-diacids with siloxane epoxy resin or through the reaction of imide-diacids/diimide-diacids with siloxane epoxy resins or by epoxidation of siloxane linkage containing diimide-diacids followed by curing with epoxy resin curatives. Presence of imide unit in the resins imparts toughness to the coating while siloxane group provides flexibility and atomic resistance. Epoxy groups or structural units derived therefrom make the system versatile as in the case of other epoxy resins. Sijoxane containing epoxy resins are synthesised either by reacting silanols or linear siloxanes with epichlorohydrin in the presence of alkali or by the hydrosilylation reaction of allyl glycidyl ether with silanes in the presence of Pt catalyst. Siloxane epoxy resins are widely used as coatings, matrix resins for composites and as modifiers for conventional epoxy resins for imparting flexibility and thermal stability thereto. Siloxane-imides are synthesised by the reaction of siloxane linkage containing anhydrides with aromatic/aliphatic diamines or by the reaction of siloxane linkage containing diamines with dianhydrides followed by chemical or thermal imidlzation. These compounds find wide use in membrane production, atomic oxygen resistant coatings, structural adhesives and matrix resins for composites. Though considerable amount of literature is available on the synthesis of siloxane-epoxy resins and siloxane imides, synthesis of resins having a polymer backbone containing all the three units, namely, siloxane units, imide units and epoxy functional groups or structural units derived from epoxy functional groups has not been reported. This type of resins are hereinafter referred to as siloxane-imide-epoxy resins. In yet another modification process, the siloxane-imide-epoxy resin may be prepared by the epoxidation of siloxane linkage containing diimide-diacid. Epoxidation of -COOH groups present in siloxane linkage containing diimide-diacid is carried out in a known manner and the resultant resin is cured subsequently. This invention relates to a process for the synthesis of siloxane-imide-epoxy resin which comprises reacting imide-diacid with epoxy resins, wherein the imide-diacid and/or the epoxy resin contain siloxane linkages, under known polymerization conditions and thereafter recovering the resin produced in a known manner. The imide-diacid used in the reaction may be a diimide-diacid which may be synthesised by the reaction of aliphatic or aromatic aminocarboxylic acid with trimellitic anhydride in an organic solvent such as acetone, dimethyl acetamide, dimethyl formamide or N-methyl pyrrollidone followed by imidization in a known manner. Preferably, 1 mole of imide-diacid or diimide-diacid is mixed with 1 mole of siloxane containing diepoxy resin and cured at 1 AO^C for 30 mts, 17Q°C for 1 hour and 230°C for 30 mts to obtain siloxane-imide-epoxy resin. In another altemative, siloxane containing diimide diacid is reacted with diglycidyl ether of bisphenol A. Siloxane containing diimide-diacid may be prepared by reacting 1 mole of siloxane linkage containing diamine with two moles of trimellltic anhydride in an organic solvent such as acetone, dimethyl acetamide, dimethyl formamide and the like followed by known imidization reaction. One mole of diimide-diacid obtained by this method is mixed with 1 mole of diglycidyl ether of bisphenol resin and cured at 135°C for 30 mts. 170*^0 for 1 hr and finally at 230°C for 30 mts. In another altemative siloxane containing diimide-diacid is reacted with siloxane containing epoxy resin. 1 mole of siloxane containing diimide-diacid is mixed with 1 mole of siloxane containing epoxy resin and cured at 210° C for 30 mts., 245°C for 1 h and finally at 270°C for 30 mts. In yet another alternative siloxane containing diimide-diacid is epoxidised directly with epichlorohydrin in the presence of a quaternary, ammonium halide. The molar ratio of siloxane containing diimide-diacid to epichlorohydrin may vary from 1: 50 to 1:250. This synthesis may be carried out in the absence of any solvent as epichlorohydrin itself acts as a medium of the reaction. This reaction is carried out at 50**C to 120°C for 45 mts to 5 hrs. Hydrochloric acid liberated during this reaction is absorbed by excess epichlorohydrin to form glycerol dichlorohydrin which may be removed by washing with water. Epoxy value of this siloxane-imide-epoxy resin is in the range of 0.4 to 2.8 eqv/kg. This resin may be cured by reacting with known epoxy curatives. Siloxane-imide-epoxy resins disclosed hereinabove, are « advantageous over siloxane imides, epoxy imides and siloxane epoxy resins as siloxane-imide-epoxy resins combine the features of all the three units namely, siloxane, epoxy and imide in one resin. Further, the siloxane, imide and epoxy content may be varied as desired. This invention also includes a process for synthesising atomic oxygen resistant coating. Siloxane containing epoxy imide resin is made to react with a siloxane containing diepoxy resin, a siloxane containing oligomeric dfamine, and amine terminated polydimethyl siloxane in an organic solvent such as tetrahydrofuran, diglyme, dioxane, ethyl ketone and isobutyl methyl ketone to get a 10% to 30% resin. This may be applied directly on substrates such as polyimide film, C-polyimlde and glass polyimide composites. Coatings may be cured at 100°C to 180*^0 for 8 to 10 hours. Coated and uncoated samples of Kapton® polyimide film, C-polyimide, and glass polyimide composites are exposed to atomic oxygen. It is noticed that uncoated Kapton® film sample of thickness 25 \xm (one side aluminized) lost 3 mg/cm^ whereas the coated sample lost only 0.12 mg/cm^ when exposed to atomic oxygen fiuence of 4.4 x 10^° atoms/cm^. The mass loss of the coated sample gradually increases and reaches a value of 0.41 mg/cm^ when exposed to atomic oxygen fiuence of 2 x 10^^ atoms/cm^. Uncoated Kapton® film of thickness 125 ^im (one side aluminized) lost 10.2 mg/cm^ whereas the coated film lost only 0.49 mg/cm^ on exposure to atomic oxygen fiuence of 2 x 10^^ atoms/cm^. Similarly uncoated C-polyimide composite lost 90.18 mg/cm^ on exposure to atomic oxygen fiuence of 9.6 x 10^ atoms/cm^ whereas the coated composite lost only 0.52 mg/cm^ even after exposure to atomic oxygen fiuence of 2.3 x 10^^ atoms/cm^. An uncoated glass polyimide composite lost 11.68 mg/cm^ on exposure to atomic oxygen fluence of 9.6 x 10^ atoms/cm^ while the coated substrate lost only 0.4 mg/cm^ even after exposure to atomic oxygen fluence of 2.3 x 10^*' atoms/cm^. This clearly indicates that siloxane imide-epoxy based coating offers excellent protection to substrates which are susceptible to atomic oxygen attack. Scanning electron microscopic studies of coated and uncoated substrates further confirmed that siloxane imide epoxy resin coating protects substrates susceptible to atomic oxygen attack. This invention will now be described with reference to specific examples. EXAMPLE 1: Synthesis of siloxane containing diimide-diacid:- 24.85g of siloxane linkage containing diamine is reacted with 40.32 g of trimellitic anhydride in 175 ml of an organic solvent such as acetone, dimethyl acetamide, dimethyl formamide, methyl ethyl ketone, methyl isobutyl ketone, or N-methyl pyrrollidone. After completion of the reaction, a mixture of acetic anhydride and anhydrous sodium acetate is added to imidize the product. This imidization may also be effected by heating the product to 120°C to 220®C. This reaction is shown below in scheme 1. EXAMPLE 2 Synthesis of siioxane-imide-epoxy resin from diimide-diacid and siloxane epoxy resin:- 75.8g of diimide-diacid viz. 2,2-bis[4-(4-trimellitimidophenoxy) phenyl] propane is mixed with 36.2 g of siloxane epoxy resin and cured. This reaction is shown in scheme 2 as follows: The cure reaction is initially carried out at 140°C for 30 mts. This temperature is further raised to 170°C for 1 hr and then to 230°C for 30 mts. The sample was removed thereafter. EXAMPLE 3: Synthesis of siloxane-imide-epoxy resin from siloxane containing diimide diacid and epoxy resin:- 59.6 g of siloxane containing diimide-diacid prepared according to example 1 is mixed with 19.05 g of diglycidyl ether of bisphenol -A herein after referred as DGEBA and cured. The reaction proceeds as shown in scheme 3 shown below: Reaction may be carried out at 135°C for 30 mts, 172°C for 1 hour and finally at 230*0 for 30 mts to complete curing. EXAMPLE 4: Synthesis of siloxane-imide-epoxy resin from siloxane containing dlimlde-diacid and siloxane epoxy resin:- 59.6 g of siloxane containing diamide-diacid prepared according to example 1 is admixed with 36.2 g of siloxane epoxy resin. The reaction proceeds as shown in scheme 4 below: This resin is initially cured at a temperature of about 21 O^'C for 30 mts. This temperature is further raised to 245°C for 1 hour and then to 275°C for 30 mts. The sample was removed thereafter. EXAMPLE 5: This example relates to the synthesis of siloxane-imlde-epoxy resin by epoxidation. 59.6 g of siloxane containing diimide-diacid is reacted with 1380 g of epichlorohydrin in the presence of 5.24 g benzyl trialkyi ammonium halide catalyst at 120°C for 1 hour. The reaction proceeds as shown in scheme 5 below: The reaction product is washed with water repeatedly to remove the catalyst and glycerol dichlorohydrin formed during the reaction. Excess of epichlorohydrin is removed by distillation under vacuum. The resultant resin is dried under vacuum for for 6 hours. The resin produced has an epoxy value of 1.7 eqv/kg. The resin is characterized by GPC, IR and ^H- and ^^C-NMR spectra. The absorption peak due to oxirane ring is observed at 910 cm"^ Absorption peaks at 1777 and 1717 cm"^ are due to the presence of imide groups. In the ^^C-NMR spectrum of the resin, peaks corresponding to -COOH is absent. The siloxane imide epoxy resin prepared by this process contains epoxy functional groups which can be cured by treating with any known curatives such as aliphatic or aromatic diamines, diol, dithiol, diacid, or anhydride to obtain a cured resin. EXAMPLE 6: This example relates to a process for the production of a coating composition having atomic oxygen resistant properties. A mixture of siloxane-epoxy imide resin described hereinabove, a siloxane containing diepoxy, a siloxane containing oligomeric diamine and amine terminated poly dimethylsiloxane is made to react in an organic solvent selected from THF, diglyme, dioxane, methyl ethyl ketone and isobutyl methyl ketone to get a 10 to 30% solution of the resin produced according to the following reaction scheme (scheme 6). This formulation is applied on substrates such as polyimide film, and C-polyimide and glass-polyimide composites. This coating is allowed to cure at 100*'C to 150°C for 8 to 10 hrs. Coated and uncoated Kapton® polyimide film, C-polyimide, glass polyimide and the like composites are exposed to atomic oxygen. It is noticed that Kapton® film sample of thickness 25 ^im lost 3 mg/cm^ while the coated sample lost only 0.12 mg/cm^ when exposed to atomic oxygen fluence of 4.4 x 10^ atoms/cm^. The mass loss of the coated sample increases gradually till a value of 0.41 mg/cm^ is reached when the sample is exposed to atomic oxygen fluence of 2 x 10^^ atoms/cm^. Uncoated Kapton® polyimide film of thickness 125 jim lost 10.2 mg/cm^ whereas the coated film lost only 0.49 mg/cm^ on exposure to atomic oxygen fluence of 9.6 x 10^ atoms/cm^, whereas the coated sample lost only 0.52 mg/cm^ even after exposure to atomic oxygen fluence of 2.3 x 10^^ atoms/cm^. Similarly, uncoated glass polyimide composite lost 11.68 mg/cm^ on exposure to atomic oxygen fluence of 9.6 x 10^ atoms/cm^ while the coated sample lost only 0.4 mg/cm^ after exposure to atomic fluence of 2.3 x 10^^ atoms/cm^. This clearly indicates that the fomulation .containing siloxane-imide-epoxy resin coating offers excellent protection to substrates which are susceptible to atomic oxygen attack. Atomic oxygen resistant coating may also be made from siloxane-epoxy imide resins described in examples 2 to 5. Though this invention has been described hereinabove obvious alterations and modifications known to persons skilled in the art are within the scope of this invention and that of the appended claims. WE CLAIM: 1. A process for the synthesis of siloxane imide-epoxy resin comprising of reacting a siloxane containing diimide-diacid with epichiorohydrin under epoxidation conditions in the presence of a quaternary ammonium halide catalyst and thereafter recovering the resin. 2. The process as claimed in claim 1, wherein the molar ratio of siloxane imide diacid to epichiorohydrin varies from 1:50 to 1:250. 3. The process as claimed in claims 1 and 2, wherein said reaction is carried out at 50°C to 120°C, the reaction mixture washed with water and cured by the addition of epoxy curatives. 4. A coating composition having atomic oxygen resistant properties characterised in that it contains 10-30% of at least one siloxane-imide-epoxy resin produced by a process claimed in any of claims 1 to 3.

Documents:

1002-che-2005 abstract.pdf

1002-che-2005 claims-duplicate.pdf

1002-che-2005 claims.pdf

1002-che-2005 correspondence-others.pdf

1002-che-2005 correspondence-po.pdf

1002-che-2005 description (complete)-duplicate.pdf

1002-che-2005 description (complete).pdf

1002-che-2005 form-1.pdf

1002-che-2005 form-18.pdf

1002-che-2005 form-26.pdf

1002-che-2005 form-3.pdf

1002-che-2005 form-8.pdf

1002-che-2005 petition.pdf