Imidosilane compositions

Abstract: Unsaturated imidosilanes which are essentially free of siloxanes are taught herein for use surface treatments for inorganic solid materials. Novel methods to make such silanes, which do not yield water or siloxanes as a by-product are also taught. Compositions consisting essentially of imidosilane treated inorganic solid materials, resinuous materials and optionally a free radical generator, especially glass fiber reinforced composites, are taught.

Description: BACKGROUND OF THE INVENTION Organofunctional silane compounds have been employed in the treatment of a variety of surfaces, such as metal oxides, silicates, particulate siliceous fibers and pigments, and fibers such as glass fibers, steel fibers and aluminum fibers. (Metal surfaces are regarded as oxide surfaces because they are oxidized even though their subsurfaces are not.) Some organofunctional silane treatments involve coating such a surface with an organic, an aqueous-organic or aqueous solution of the silane either alone or in conjunction with other chemicals. These treatments enhance bonding between the inorganic oxide and resinous media. Consequently, the silanes have utility as components in primers in the application of coatings, adhesives and sealants to inorganic oxide surfaces and as a filler pretreatment to improve the strength and structural integrity of filled resin composites such as those incorporating glass fibers. Such organofunctional hydrolyzable silanes are termed "Coupling Agents" or "Adhesion Promoters". The efficacy of the organofunctional silane is dependent in large part on its ability to react chemically or bond with the resinous media. During the curing reactions of thermosetting resins, the reactivity of the organofunctional group needs to match the reactivity of the thermosetting resin or the curing agent. It must become part of the organic polymer that makes up the resinous media. In fabricating thermoplastic articles, the organofunctional silane also needs to become part of the resinous media, either by reacting with organofunctional groups on the polymers or grafting onto the polymer backbone. The organofunctional silane need not react with all of the resinous media to achieve the enhancement in structural integrity of the article incorporating it. Often, the enhancements can be achieved if the silane reacts with only a part of the resinous media or with additives that are compatible with the resinous media. For example, virgin polypropylene destined for glass fiber reinforcement typically is compounded with maleated polypropylene (a.k.a. coupled polypropylene) as taught in US Patent No. 5,300,547. Maleated polypropylene refers to a graft or co-polymer of propylene and unsaturated organic acids or their anhydrides. For example, maleic anhydride commonly is reacted with propylene to make maleic anhydride-propylene co-polymers. The two polypropylenes, virgin and maleated, along with glass fibers are co-fed into a compounding extruder and pelleted. Glass fibers for this process are manufactured with surface treatments (sizing) to include silanes chemically compatible with the maleic anhydride. An amino silane, such as SILQUEST® A-1100™ 3-aminopropyltriethoxysilane, would be an example of a maleic anhydride compatible silane. The silane on the glass fibers and the maleated polypropylene form chemical bonds during compounding (extrusion). The silane does not react with the virgin polypropylene. This chemical bonding of the glass fiber to the maleated polypropylene is responsible for the performance advantages of the glass fiber reinforced polypropylene. One disadvantage of using maleated polypropylene is its cost relative to that of uncoupled or virgin polypropylene. Another disadvantage of using maleated polypropylene is that the maximum enhancements in structural integrity and strength are not achieved. The maleated polypropylene mixing or dispersion into the virgin polypropylene may not be uniform. Its ability to react chemically with the organofunctional group of the silane on the inorganic surface is inhibited by the presence of the virgin polyproplyene. The maleic functional groups of the polypropylene that do not react with the silane can contribute undesirable properties to the composite, such as making the resinous media more hydrophilic and, therefore, less resistant to degradation due to moisture. Achieving increased performance with glass fiber reinforced virgin polypropylene, by providing a glass fiber reactive toward the uncoupled (virgin) polypropylene, would be useful. Moreover, other organic resins (e.g., nylon) used in conjunction with inorganic materials often have insufficient or non-reactive functional groups. New silanes that are effective at bonding with these materials are required (needed) to enhance the organic resin's properties when used with inorganic materials. Imidosilanes, when used alone or in combination with free radical generators are unique in their ability to couple with or bond to various resinous media. Imidosilanes are known, see e.g., US Patent Nos 3,755,354 and 3,249,461 and EP Patent No.0 50861, but these imidosilanes are problematic in that the presence of water is inherent in the method of manufacture of said silanes. Water causes hydrolysis of the silane to form siloxanes and turns the silanes from a liquid to a paste, which is unsuitable for uses in coating or sizing formulations that require the silane to be soluble and flowable over the surface of the inorganic surface. See, e.g., Example 1 of US Patent No. 3,755,354. Other synthetic methods result in the presence of chloride, which degrades the composite matrix. US-A-3,755,354 discloses imido-substituted organosilanes that can be employed to impart improved surface characteristics to cellulosic substrates. EP-A-0 508 610 relates to laminates containing addition-curable silicone adhesive compositions. Such composition may comprise an adhesion promoter such as N-(3-(trimethoxysilyl) alkyl)maleimides. US-A-4,301,075 disclose N-substituted imides which can be used as intermediates for the preparation of silicon-modified adhesion promoters. JP-A-01029385 discloses certain N-maleimidosilane compounds as coupling agents to improve the mechanical properties of rubber compositions reinforced or modified with an inorganic filler. SUMMARY OF THE INVENTION The present invention teaches novel unsaturated imidosilanes and compositions incorporating these silanes. Moreover, novel methods of manufacture of these imidosilanes are disclosed which results in silanes essentially free of siloxanes and chloride. Specifically the subject matter of the present invention is set forth in the attached claims. DETAILED DESCRIPTION OF THE INVENTION The present invention describes the improvement in wet and dry mechanical strengths of inorganic filler reinforced organic resin and in adhesion of organic resin to inorganic surfaces obtained by surface treating the inorganic surface or filler with an unsaturated imidosilane and optionally a free radical generator. The incorporation of fillers treated with ethylenically functionalized silanes, and optionally, free radical induced-grafting, offers even increased performance. Specifically, thermoplastic and thermoset resins that are reinforced with fillers, especially glass fibers, treated with an unsaturated imidosilane and optionally a free radical generator offer composites with dramatically enhanced wet and dry flex strengths. Silane Structure The unsaturated imido silanes of the present invention are of the formula (I) ((R 1 ) b Y) a R 2 3-a SiR 3 N(C=O) 2 X wherein R 1 and R 2 are monovalent radicals, R 3 is a divalent radical, X is a divalent radical selected from the following groups (which incorporate the imido(-C(=O)NC(=O)- functionality): isobutenylmaleimido, 2-octen-1-ylmaleimido and 2-dodecen-1-ylmaleimido; Y is oxygen, nitrogen or sulfur, a = 1 to 3, and b = 1 or 2 depending on the valence of Y. In formula I above, each R 1 is a monovalent radical, e.g., hydrogen, an imino group, a dialkyl amine, or, preferably a hydrocarbon functionality, including, but not limited to, aryl, allyl, cycloalkyl, alkyl (linear or branched) or aralkyl that may contain heteroatoms, e.g., oxygen, nitrogen or sulfur. R 1 could also be an acyl functionality (e.g., acetyl). Examples of R 1 are -N=C(CH 3 ) 2 , and -CH=CHCH 3 . Most preferably R 1 is an alkyl of 1 to 10 carbon atoms, e.g., methyl, ethyl, isopropyl, cyclohexyl, or i-butyl. The value of b depends on the valency of Y, i.e., b=1 for Y = oxygen or sulfur, and b=2 for Y = nitrogen. Preferably Y is oxygen. Preferably a is 3, but if a<3, each R 2 is a monovalent radical, including, but not limited to, a hydrocarbon radical, a saturated hydrocarbon, an unsaturated hydrocarbon or cyano. Preferably R 2 is a cycloalkyl, alkyl (linear or branched) or aralkyl, that may include heteroatoms, e.g., oxygen, nitrogen, or sulfur and 1 to 10 carbon atoms. Exemplary R 2 include, phenyl, phenylethyl or 2-methoxypropyl. Most preferably R 2 is methyl or ethyl. R 3 is a divalent bridging group, including, but not limited to, an alkylene, alkenylene, alkarylene, arylene, or polyalkylene oxide, but preferably is a C 1 -C 12 alkylene, e.g., propylene or n-butylene, and may be branched, e.g., neopentylene, cyclic, e.g., dimethylene cyclohexane, or unsaturated, e.g., dimethylene cyclohexene or phenylene. In novel silanes, R 3 may include a heteroatom substituents, e.g., R 3 may include an amino group either in the backbone or pendant to the backbone. Specific examples of R 3 are ethylene propylene amine, diphenylene amine, di(ethylene) ethyl amine. Such silanes, including specifically those with an amine in R 3 , are advantageous because they allow for further chemistry to be performed during the composite fabrication process. X is a divalent species wherein each valence is attached to a carbonyl group and each carbonyl group is attached to the nitrogen, thus forming one ring. X (which incorporate the imido (-C(=O)NC(=O)-) functionality) is (I) isobutenylmaleimido, (II) -2-octen-1-ylmaleimido, or (III) 2-dodecen-1-ylmaleimido. Preferably, the unsaturated imidosilanes are substantially free of siloxanes. Water generated during synthesis causes premature hydrolysis of the alkoxy silane to form siloxanes. Preferably, there is less than 5 percent siloxane by weight of silane, more preferably, less than 2 weight percent and most preferably less than 0.5 weight percent and even more preferably no siloxanes. Being essentially free of siloxanes is a result of the process of the novel methods of manufacture recited below. Such freedom from water provides benefits in not interfering with silane reactions. Moreover, the presence of water causes the alkoxy silane to hydrolyze and condense to a siloxane, said siloxane would be a solid or a paste and could not be used as such in the processing of glass fibers. The silanes preferably should also be free of halogens, specifically, chlorine, since these halogens may be detrimental to the composite. Halogen levels should be below 1 weight percent, more preferably 0.01 weight percent, and most preferably at zero weight percent of halogen. Compositions Containing the Silane The silane may by encompassed within compositions that contain inorganic surfaces, such as fillers or flat surfaces, resinous media and optionally a free radical generator. The modes of incorporating the silane into these compositions included treatment of the inorganic surfaces with an organic, an aqueous-organic or an aqueous solution of the silane either alone or in conjunction with other chemicals, or coating the surface with the silane without the aid of a solvent. These silane treated surfaces then can be combined with the resinous media and optionally, a free radical generator. In some instances, the silane can be added directly to the resinous media in a process called "integral blending". The resinous media in conjunction with the inorganic surfaces treated with the silane can be employed, for example, for molding including extrusion, injection, calendering, casting, compression, lamination, and transfer molding, for coatings including lacquers, film bonding, paints, primers, inks, dyes, binders and glass fiber sizes. The inorganic surfaces that can benefically treated with the silane are inorganic solid materials which possesses either oxide or hydroxyl groups at its exposed surface, and includes any material that can be treated by coupling agents known in the prior art. The inorganic solid material can be in any form, including particles or irregular or regular, e.g., spherical, shape, individual fibers, woven fiber mats or fabric, or continuous surfaces such as sheets, films, slabs and formed shapes. Specific illustrations of suitably employed inorganic solids materials are, for example brass with surface oxidation, copper metal oxidized at its surface, iron, steel, alumina, aluminum trihydrate, siliceous materials such as fumed silica, hydrated silica, silica aerogels, aluminum silicates, calcium magnesium silicate, clays, mica, molecular sieves, wollastonite, E-glass, S-glass, A-glass and the like. The amount of silane used is that amount which alters the surface characteristics of the inorganic solid material so that it is more compatible with and/or adherent to the resinous medium within which they are incorporated. When the silane is supplied to the resin by the integral blending method, the effective amount of the silane can vary from about 0.05 weight percent to about 15 weight percent and is preferably from 0.1 weight percent to 2.0 weight percent, based upon with weight of the solid inorganic material that is incorporated into the resin. When the silane is supplied directly to the surface of the inorganic solid material in the form of a fibrous or particluate filler, pigment or the like, the effective amount can vary from about 0.01 weight percent to about 10 weight percent, and is preferably from 0.1 weight percent to about 0.5 wieght percent based upon the weight of the inorganic solid material. When applying the silane as a primer to a surface of inorganic solid material, the effective amount of silane applied to the surface can vary from about 0.005 grams/m 2 to about 1.5 grams/m 2 , and is preferably from about 0.01 grams/m 2 to 0.1 grams/m 2 , calculated as the weight of the silane per square meter of inorganic solid material's surface treated. The resinous medium can be a thermoplastic or thermosetting material, and the use of the term "resinous media" does not exclude the possibility that the material is formed in situ and therefore is derived from a monomeric material while in contact with an inorganic solid material. Preferably thermoplastic resins are used for the present invention. The resinous medium with which the silane can be employed suitably includes a large number of resins which are reactive with the unsaturated imido functional group of the silane either alone or optionally with a free radical generator. For illustration purposes, the resinous media may be alkyd resins, unsaturated polyesters, vinyl esters, nylons, thermoplastic polyesters, polyethylenes, polypropylenes, polybutylenes, polystyrenes, styrene and butadiene copolymers, ethylene and propylene copolymers, SBR, natural rubbers, and the like. Most preferably polypropylene is used herein. The size may include a free-radical generator, selected from the group of water soluble or oil soluble peroxides, such as hydrogen peroxide, ammonium persulfate, potassium persulfate, various organic peroxide, such as dialkyl peroxides, e.g., diisopropyl peroxide, dilauryl peroxide, di-t-butyl peroxide, di-(2-t-butylperoxyisopropyl)benzene; dicumyl peroxide, alkyl hydrogen peroxides such as t-butyl hydrogen peroxide, t-amyl hydrogen peroxide, cumyl hydrogen peroxide, diacyl peroxides, for instance acetyl peroxide, lauroyl peroxide, benzoyl peroxide, peroxy ester such as ethyl peroxybenzoate, and the azo compounds such as 2-azobis(isobutyronitrile). It is also invisioned that the free radical generator can be the resinous material, especially the thermoplastic resins, in conjunction with high shear processes. The high shear degrades the thermoplastic resins to generate radicals on the polymer backbone or at chain terminus. The coatings that are used to treat the inorganic surfaces can be organic, aqueous-organic or aqueous solution of the silane either alone or in conjunction with other chemicals. The other chemicals are used as wetting agents, antistatic agents, leveling agents, binders, lubricants, fiber protectants, film formers and the like. When the solutions of the silanes are used to treat glass fibers, they are called "sizings". Such compositions may include film-forming polymers usually in the form of emulsions, e.g, polyurethane, epoxy, unsaturated polyester, epoxyester, bisphenol-A epoxy, bisphenolic polyester, polyvinyl acetate, vinyl acetate and acrylic copolymers, polyethylene, ethylene vinyl acetate copolymers, melamine formaldehyde, and the like. The size may also include plasticisers, e.g., phthalates, phosphates, polyesters and the like. The size may also include a lubricant, e.g., cationic acid solubilized fatty acid amides, polyalkylene oxides, alkyl imidazoline derivatives, amide substituted polyethylene amines, microcrystalline waxes, aliphatic polyamines and the like. The size may include acids, (e.g., acetic acid or cis-butenedioc acid), water, surfactants, anti-foaming agents, emulsifying agents, or other silanes (e.g., ethylenically unsaturated silanes). Water is necessary within the size to activate the silane toward the glass fiber. The other chemicals used in the size are referenced in K.L. Loewenstein, The Manufacturing Technology of Continuous Glass Fibres , 3rd revised ed. (Elsevier, Amsterdam, 1993). Adding the silane and water together within the context of the size allows for dispersion of the silane within the size; however, pre-combination of water and silane and allowing the size to age for > 72 hours would result in a siloxane gel, which would not be useful. Preferably the size is applied to glass fibers which are intended for incorporation into polymer composities. The manufacture of such compositions are known in the art. Resulting composites have enhanced wet and dry strength, enhanced wet out, and improved strand integrity. Method of Manufacture The imidosilanes are made from an amino alkyl dialkoxy silane or an amino trialkoxysilane (e.g., aminopropyltrialkoxysilane, or N-aminoethyl-3-aminopropylmethyldialkoxy silane) and an unsaturated acid anhydride. It is preferred not to use halogen containing silanes since they will result in the presence of undesirable halides. Such reaction results in a ring opened silane. This first step may be conducted in the presence or absence of a solvent, with or without heating, though it is preferred not to heat, which may cause the formation of water. Suitable solvents include, methylene chloride, chloroform, alcohols, aliphatic and aromatic hydrocarbons, and ethers. The ring opened silane (i.e., amicacid silane) is treated with a capping material thereby avoiding the formation of water during cyclization. Preferably this step should be performed without heating. Suitable capping materials which are silylating agents include trialkylsilyl halides, bis-(trimethylsilyl)trifluoroacetamide, N,O-bis(trimethylsilyl)acetamide, N-methyl-N-trimethylsilyltrifluoroacetamide, 1-(trimethylsilyl)imidazole, N-trimethylsilyldiethylamine, hexamethyldisilazane, and mixtures thereof. Specifically, trimethylchlorosilane is useful. Other capping materials are those which convert carboxylic acids to esters, such as chlorinated hydrocarbons, dialkyl carbonates, dialkyl pyrocarbonates, dialkyl sulfonates, diazomethane and the like. However, alcohols which are commonly used to convert acids into esters are not suitable because they generate water during the capping reaction. Preferably, this reaction step is done in the presence of an acid scavenger (e.g., a base) when the capping material generates hydrogen halides. The base is used to remove the halides. Suitable examples of the base, include triethyl amine, pyridine or dimethylamino pyridine or any tertiary amine. The third step is the heating of the capped amic-acid silane to form an imidosilane. When the capping material is a silylating agent, two equivalents are required. The silylating agent reacts with both the hydroxyl group of the carboxylic acid and the N-H group of the amide. The temperature should be from 40 to 80°C with a vacuum. During this step, the reaction product of the capping material (e.g., hexamethyldisiloxane (MM)) will be released incorporating the oxygen of the original anhydride. Said reacted capper preferably may be distilled or flashed stripped from the imidosilane. If the capping material forms a carboxylic acid ester, then the cyclicization can be promoted by heating the amic-ester silane. The temperature should be from 40 to 220 °C and preferrably from 80 to 120 °C. During this step, an alcohol will be formed. The resulting product avoids the presence of siloxanes and results in low halide levels. Another method to form the imidosilane, which avoids the formation of water (and siloxanes) is to react an unsaturated acid anhydride with an isocyanatosilane in one step, which process releases CO 2 , as well as the imidosilane. A stoichiometric ratio of anhydride and isocyanate in the presence of a catalyst, preferably a phospholene, are heated at reflux, cooled and filtered. Alternatively an unsaturated imide with a vinyl functionality may be hydrosilated with a hydrido alkoxy silane. The hydrosilation may conducted as known in the art. See, e.g., Marciniec, ed., Comprehensive Handbook on Hydrosilylation (1992). A fourth, water free process is to start from a bis(amido silane), heat at about 190 to 240 °C (with or without catalysts), which will yield the imidosilane and an aminosilane.

Claims: An unsaturated imidosilane of the formula ((R 1 ) b Y) a R 2 3-a SiR 3 N(C=O) 2 X wherein R 1 and R 2 are monovalent radicals, R 3 is a divalent radical, X is a divalent radical selected from the following groups (which incorporate the imido(-C(=O)NC(=O)- functionality): isobutenylmaleimido, 2-octen-1-ylmaleimido and 2-dodecen-1-ylmaleimido; Y is oxygen, nitrogen or sulfur, a = 1 to 3, and b = 1 or 2 depending on the valence of Y. The silane according to claim 1, wherein R 1 is hydrogen, an imino group, a dialkyl amine, aryl, acyl, allyl, cycloalkyl, linear or branched alkyl or aralkyl, optionally containing heteroatoms selected from oxygen, nitrogen or sulfur. The silane according to claim 2, wherein R 1 is -N=C(CH 3 ) 2 , -C=CHCH 3 or an alkyl of 1 to 10 carbon atoms. The silane according to any of claims 1 to 3, wherein R 2 is cyano, cycloalkyl, linear or branched alkyl or aralkyl, optionally containing heteroatoms selected from oxygen, nitrogen or sulfur and having 1 to 10 carbon atoms. The silane according to claim 4, wherein R 2 is phenyl, phenylethyl, 2-methoxypropyl, methyl or ethyl. A silane according to any of claims 1 to 5, wherein R 3 is alkylene, alkenylene, alkarylene, arylene or polyalkylene oxide. The silane according to claim 6, wherein R 3 is a linear, branched or cyclic C 1 -C 12 alkylene, dimethylene cydohexane or phenylene. The silane according to claim 1, wherein a = 3, Y = O and R 1 is ethyl or methyl. The silane according to claim 2, wherein a = 2, Y = O and R 2 is an alkyl. A material comprising an unsaturated imidosilane according to any of claims 1 to 9, a thermoplastic resinous material reactive with an imido group, an inorganic filler and a free radical generator.

Inventors: GUNTHER MICHAEL L, PETTY HERBERT E, POHL ERIC R, GUNTHER, MICHAEL L., PETTY, HERBERT E., POHL, ERIC R.
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1999
Main classification: C07F7
IPC codes: C07F7, C08K5