Title of Invention

A PROCESS FOR THE SYNTHESIS OF SILOXANE-IMIDE-EPOXY RESINS

Abstract

This invention relates to a process for the synthesis of siloxane-imide- epoxy resins. An imide diacid is reacted with epoxy resins under koown polymerization conditions. Either the imide-diacid, the epoxy resin or both the imide-diacid and the epoxy resin may contain siloxane linkages. The invention also includes a process for the synthesis of siloxane-imide-epoxy resin through epoxidation of siloxane containing diimide-diacid followed by curing with epoxy resin curatives. The resins obtained by the above processes show excellent resistant to atomic oxygen and may be used in coating composites and films used in low earth orbit satellites and space stations.

Full Text

This invention relates to processes for synthesizing siloxane-imide-epoxy resins. The siloxane-imide-epoxy resins are obtained through the reaction of siloxane linkage containing diimide-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-dtacids 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 reains. Siloxane containing epoxy resins are synthesised either by reacting silands or linear siloxanes with spichlorohydrin in the presence of alkali or by the hydrosilylation reaction of allyl gtycidyl ether with silanes in the presence of Pt csftalyst Siloxane epoxy resins are widefy used as coatings, matrix resins for composites and as modifiers for conventional epoxy resins for imparling flexibility and thermal stability thereto. Siloxane-imides are synthesised by the reaction of siloxane linkage contaoing anhydrides with aromaticteliphatic diamines or by the reaction of siloxane linkage containing diamines with dianhydrides follwed by chemical or thermal inrtidization. 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 att the three units, namely, siloxane units, imide units and epoxy functional groups or structural units derived from epoxy functk)nal groups has not been reported. This type of resins are hereinafter referred to as siloxane-imide-epoxy resins. The main object of this invention is directed to a process for the preparation of a siloxane-imide-epoxy polymer or resin. Siloxane-imide-epoxy resin according to the invention may be prepared by reacting an .imide-diacid with an epoxy reein wherein either or both the imide diacid and the epoxy resin contains siloxane linkage. For instance thei resin of the subject invention may be prepared by reacting siloxane epoxy resin with a diimkie-diacid or imide-diacid. It is also possible to achieve the same result by reacting an epoxy resin with a diimide-diacid containing siloxane linkage. Alternately, both the epoxy resin and the diimide-diacid may contain siloxane linkage) 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 erf siloxane containing diepoxy resm and cured at 140o for 30 mte, 170°C for 1 hour and 730oC fx 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 reading 1 mole of siloxane linkage containing diamine with two moles of trimellitic anhydride in an organic solvent such as acetone, dimethyl acetamide. dimethyl fromamide 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 135oC for 30 mts. 170oC for 1 hr and finally at 230oC 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 210o C for 30 mts., 245oC for 1 h and finally at270°Cfor30mts, 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 diamine, and amine terminated polydimethyl siloxane in an organic solvent such as tatrahydrofuran, diglyme, dioxane, ethyl ketone and tsobuty) methyl ketone to get a 10% to 30% resin. This may the applied directly on substrates such as polyimide film, C-polyimide and glass polyimide composites. Coatings may be cured at 100oC to 160oC for 8 to 10 hours. Coated and uncoated samples of Kapton® polyimide film, C-plyimide, and glass polyimkie compositee are exposed to atomb oxygen. It is noticed that uncoated Kapton® film sample of thickness 25 μm (one side aluminized) tost 3 mg/Cm2 whereas the coated sample lost only 0.12 mg/Cm2 when exposed to atomk; oxygen fluence of 4.4 x 1020 atoms/Cm2. The mass loss of the coated sample gradually increases and reaches a value of 0.41 mg/Cm2 when exposed to atomic oxygen fluence of 2 x 1021 atoms/Cm2. Uncoated Kapton® film of thickness 125 μm (one side aluminized) lost 10.2 mg/Cm2 whereas the coated film tost only 0.49 mg/Cm2 on exposure to atomic oxygen fluence of 2 x 1021 atoms/Cm2. Similarly uncoated C-polyimkle composite tost 90.18 mg/cm2 on exposure to atomto oxygen fluence of 9.6 x 1020 atoms/Cm2 whereas the coated composito lost only 0.52 mg/Cm2 even after exposure to atomic oxygen fuence of 2.3 x 1021 atoms/Cm2. An uncoated glass polyimkle composite lost 11.68 mg/Cm2 on exposure to atomic oxygen fluence of 9.6 x 1020 atoms/Cm2 while the coated subsetrarte loat only 0.4 mgfom2 even after exposure to atomic oxygen fluence of 2.3 x 1021 otomatem2. This dearly indicates that siloxane imide-epoxy baaed coating offers excellent protection to substrates which ars susceptible to atomic oxygen attack. Scanning electron microscopic studies of coated and uncoated sutbstrates furthsr confirmed that siloxane imide epoxy reain coating protects substrates susceptible to atomic oxygen attack. This invention will now be described with reference to apecifk; examples. EXAMPLE 1: Synthesis of siloxane containing diimide-diacid: 24.85g of siloxane linkage containing diamine is reacted with 40-32 g of trimeflitic anhydnde in 175 ml of an organic solvent such as acetone, dimethyl acetamide. dimethyl fdrmamide. methytl ethyl ketone, methyl isobutyl, ketone, or N-methyl pyrrollidone. After completion of the reacton, a mixture of acetic anhydrkle and anhydrous sodium acetate is added to Imidize the product This imkiization may also be effected by heating the product to 120oC to 220oC. This reaction is shown below in scheme 1. EXAMPLE 2 Synthesis of siloxane-imide-epoxy resin from dtimide-diacid and siloxane epoxy resin: 75.8g of dijmide-diacid viz. 2,2-bis[4-(4-trimellitimdophenoxy) phenyl] propane is mixed with 36.2 g of siloxane epoxy renin and cured. This reaction is shown in scheme 2 as follows; The cure reaction is initially carried out at 140oC for 30 mts. This temperature is further raised to 170oC for 1 hr and then to 230oC 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 diglyctdyl ether of biaphenoi -A herein after referred as DGEBA and cured. The reaction proceeds as shown in scheme 3 shown t3elow: Reaction may be carried out at 135°C for 30 mts, 172°C for 1 hour and finally at 230oC for 30 mts to complete owing. EXAMPLE 4: Synthesis of siloxane-imide-epoxy resin from siloxane containing diimide-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 betow: This resin is initially cured at a temperaturs of about 210oC fbr 30 mts. This temperature is further raised to 245oC for 1 hour and than to 275oC for 30 mts. The sample was removed thereafter. EXAMPLE S: This example relates to the synthesis of siloxane-imide-epoxy resin by epoxidation. 59.6 g of siloxane containing diimide-diacid is reacted with 1380 g of epichlorohydrin in the preeence of 5.24 g benzyl trialkyl ammonium halide catalyst at 120oC 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 epichlorohy drin is removed by cfistillation 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 1H- and 13C-NMR spectra. The absorption peak due to oxtrane ring is observed at 910 cm-1 Absorption peaks at 1777 and 1717 cm"o we ckje to the presertce of imide groups. In the 13C-NMR spectrum of the resin, peaks corresponding to 13COOH is absent The sitoxane imkle 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 resjstant properties. A mixture of sfloxane-epoxy imide resin described hereinabove, a sjloxane containing diepoxy, a sitoxane containing oligomeric diamine and amine terminated poly dHnethylsiloxane 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 sdieme (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 100oC 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 μm k)st 3 mg/cm2 while the coated sample lost only 0.12 mg/cm2 when exposed to atomic oxygen ftuance of 4.4 x 1020 atoms/cm2. The mass loss of the coated sample increases gradually till a value of 0.41 mg/cm2 is reached when the sample is exposed to atomic oxygen fluence of 2 x 1021 atoms/cm2. Uncoated Kapton® polyimide film of thicknes8 125 μm lost 10.2 mg/cm2 whereas the coated film lost only 0.49 mg/Cm2 on exposure to atomic oxygen fluence of 9.6 x 1020 atoms/Cm2, whereas the coated sample k)st only 0.52 mg/Cm2 even after exposure to atomic oxygen fluence of 2.3 x 1021 atoms/Cm2. Similarly, uncoated glass polyimide composite lost 11.68 mg/Cm2 on exposure to atomic oxygen fluence of 9.6 x 1020 atoms/Cm2 while the coated sample lost only 0.4 mg/Cm2 after exposure to atomic fluence of 2.3 x 1021 atoms/Cm2. This clearly indicates that the fomulation containing siloxane-fimide-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 descrribed 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 resins comprising reacting imide-diacid with epoxy resins, wherein the imide-diacid and/or, the epoxy resin contains siloxane linkages under polymerisation conditions and thereafter recovering the resin produced. 2. The process as claimed in claim 1, wherein said imide is a diimide. 3. The process as claimed in claims ! or 2, wherein said imide-diacid has siloxane linkage, 4. The process as claimed in claims 1 or 2, wherein said epoxy resin is a siloxane epoxy resin. 5. The process as claimed in claim 1 or 2, wherein said imide-diacid and said epoxy resin contain siloxane linkages. 6. The process as claimed in claim I, wherein 1 mole of imide-diacid or diimide-diacid is mixed with 1 mole of siloxane containing diepoxy resin, and reacted at a temperature ranging from 140°C to 230°C. 7. The process as claimed in claim 1, wherein, one mole of diimide diacid is mixed with one mole of diglycidyl ether of bisphenol A and reacted at a temperature ranging from 135°C to 230°C. 8. 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 7.

Documents:

278-mas-2002 abstract-duplicate.pdf

278-mas-2002 abstract-duplicate.tif

278-mas-2002 abstract.pdf

278-mas-2002 claims-duplicate.pdf

278-mas-2002 claims.pdf

278-mas-2002 correspondence-others.pdf

278-mas-2002 correspondence-po.pdf

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

278-mas-2002 description (complete).pdf

278-mas-2002 form-1.pdf

278-mas-2002 form-19.pdf

278-mas-2002 form-26.pdf

278-mas-2002 form-3.pdf