WO 2006/0114839 PCT/US2005/023117
CORROSION-INHIBITING COMPOSITIONS AND USE THEREOF
FIELD OF THE INVENTION
This invention relates to novel multifunctional organosilane structures and their use conosion-inhibiting metal finishing treatments In particular, the invention relates to precursor silane structures as conosion-protective finishes of aluminum alloys
BACKGROUND OF THE INVENTION
Conversion coalings for metals are electrolytic or chemical films that promote adhesion between metal (in particular, aluminum) and an organic adhesive resin Anodizing is a conventional process for making these films by immersing the metal into chromic acids in order to produce a porous surface onto which a coating can penetrate For many decades, chromate has been used in aluminum and aluminum alloy finishing. The toxicity of chromate is widely recognized and its environmental and hazaidous properties have created vast research efforts to identify health/environment-benign alternatives to chromates with comparable corrosion protection performance
Organosilane based coatings have emerged as a commercial alternative to chromates to superior paint adhesion Initial efforts provided monofunctional silane coupling agents, i.e , silane with one hydrolysable alkoxysilyl group. Unfortunately, the properties of monofunctional silanes lacked commercial utility and further research has lead to bifunctional and multi-functional organosilanes
The key to a successful silane-based metal pretreatment process lies in identifying a multifunctional silane with an ideal combination of water solubility (a practical issue), hydrophobicity (for best corrosion protection), high crosslinking capabilities (banier to diffusion of conosive species), slow rate of condensation (long solution life), and reactivity (for paint adhesion). However, currently available organosilanes meet the needs of the industry The identification of compositions that meet the unlelt needs of the industry is desirable

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SUMMARY OF THE INVENTION
Multi-functional organosilane compositions derived from aliphatic diamines and epoxysilanes are provided as depicted in the Formula below.

wherein A is C4-C20 branched or unbranched, saturated or unsaturated modified or unmodified carbon atoms,
X and Y are independently
H or CONH-B-S1 (OR1)3
wherein B is an alkyl linker, and R1 is C3 to C10 carbon atoms, and salts
thereof
Specific examples of these organosilanes include but are not limited to: A tri-functional organosilane having the structure below (hereinafter "TG 13-R")

where R is H or C1 - C6 alkyl and salts thereof;

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3 a tetra functional organosilane (hereinafter "TG 14-R")-

where R is II or C1 - C6 alkyl and salts thereof.
Additional structures are described in the examples Methods for preparing these structures and their use as corrosion-protective coatings on metals are also described
DETAILED DESCRIPTION OK THE INVENTION Definitions The following terms are defined as.
"About" means within 50%, preferably within 25%, and more preferably within 10% of a given value or range Alternatively, the term "about" means within an acceptable standard error of the mean, when considered by one of ordinary skill in the art
"Alkyl" means a linear or branched, saturated or unsaturated carbon atoms of a specified length,
The synthesis of multifunctional silanes useful for metal pretreatment starts from a "core" molecule with multiple reactive organic functional groups A, and a monofunctional silane "arm" with an alkoxysilyl group and an organic reactive B, with

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the raquitement that A and B are capable of covalently linking to each other For example, A is an ammo group and the "core" is a multi-amine, and B is a epoxide group and the "arm" molecule is be an epoxytrialkoxylsilane (such as 3-glycidoxypropyltromethoxy silane) The amino groups are highly reactive to the cpoxy groups, forming convalent C-N bonds Construction of the "core-arm" structure by varying the reaction ratio of A/B leads to multifunctional silanes of "tunable" structures and properties - hydrophobicity, degree of crosslinking, water stability, and optimized conosion protection properties. The synthetic strategy instantly presented is flexible and is capable of extending to other functional group pairs such as anhydride-amine, isocyanate-amine, etc
A "core-arm"-structurcd multiifunctional silane derived from C, C, C-tnmelhylhexancdiamme (TMH) and 3-gIycidoxypropyltrimethoxy (GPS) at TMH/GPS ratio of 1 4 provides commercially desirable corrosion protection properties on various metals, including but not limited to, aluminum alloys when applied as a submicron coating The TG14 molecule is characterized by GC-LC-MS, NMR, and the derived coating by than film techniques - FTIR, prism coupling, AFM, and electrochemical impedance spectroscopy (EIS) The synthetic loute identified herein discloses the importance of a high degree of branching - crosshnking of the multifunctional aminosilane to its corrosion protection of aluminum alloys
Experimental Conditions Chemicals and Materials
3-glycidoxypropyltrimethoxy silane (GPS) and C, C, C-trimethylhexanediamine (TMH) were purchased from Gelest and Aldrich respectively and used as received. Isopropylalcohol, tert-butylalcohol, ethylalcohol and methanol was purchased from VWR with certified water content less than 0.1%. Aluminum panels (unpolished) were purchased from ACT laboratory with a dimension 4" x 6 " Nalco alkaline eleaner Globrite 45 IL, a non-etching silicate containing cleaner was used to clean the panels Sherwin-Williams Permaclad white polyester paint (applied through a draw-

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down bat at 20 micron thick) was selected to study paint adhesion of the silane-pretredled panels.
Synthesis of TMH-GPS adducts
The following example represents the general condition for synthesis of polyamine-GPS adducts. A round bottom flask was charged, in the sequential order, with 110 grams of alcohol, 15.8 grams of TMH (0.1 mole), and 94.4 grams of GPS (0.4 mole) The mixture was stirred and at 70 °C in an oil bath for 3 hours or, alternatively, sitting at room temperature for three days In either condition, the reaction reaches a yield of above 90% The resultant adduct is named "TGI4", with the two letters denoting the rcactants and "14" meaning the reactant molar ratio of 1 to 4 (polyamine to epoxysilane)
LC--MS
TG14 was characterized using Flow Injection Electrospray Mass Spectrometry (Flow lnject-ESl MS) Sample was introduced into the mass spectrometer via flow injection using a Waters 2690 LC System (Milford, MA) A Waters 2487 UV detector was also placed on-line in front of the mass spectrometer. The carrier liquid is either methanol or water or isopropanol similar to the solvents that were used in the samples to prevent any alcohol exchange reaction and/or condensation reaction that may occur during the analysis The mass spectrometer was a Thermo Finnigan LCQ Deca System (San Jose, CA) equipped with a standard Finnigan electrospray interface The mass spectra were aequried in the positive ion and centroid mode. Other experimental parameters are listed in Table 1 The samples were diluted with the appropriate solvent 1/1000 Aliquots (5-10 ul) of this solution were then injected onto the ESI-MS system for analysis
Flow Injection -ESI MS Experimental Parameters
Acquisition Mode Positive ESI-MS Ion Range 100 - 2000 AMU

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Applied ESI Spiay Potential -4 0 kV
Interface Capillary Temperature 226 C
Sheath Gas Pressue: 70 psi
Injection mode/ Volume. Flow Injection/10 ul
Carrier Liquid Methanol or Water or Isopropanol
Carner Flow Rale 0 4 tnl/min
Run Time 5 minutes
UV Detector 210 nm wavelength
0 04 AUFS sensitivity
GC-MS
Residual GPS and amine in the reaction products was determined by a GC-MS technique using the starting materials as reference standards The system was an Agilent Technologies (H/P) (Wilmington, DE) 5890 Scries II Gas Chromatograph and 5970 MSD The residual GPS concentration was semi-quantitated using experimental conditions listed in Table II. The samples were diluted with the appropriate solvent 1/100 Ahquots (1 ul) of this solution were then injected onto the GC-MS system for analysis
GC-MS Experimental Conditions for Residual GPS Determination
Column Phenomenex ZB-5 30M x 0.25mm i d x 0 25 urn film (Torrance, CA)
Injection Port Temperature 240C
Oven Temperature 60 °C 3 minutes ramp to 320 °C @ 10°C/min, hold for 5 minutes
Injection Size lul
Mass Range 29 - 550 AMU
Mode +E1
Thermal Giavimetric Analysis
'1G14 and TGI3 samples for the TGA study were prepared by solution casting from
their respective solution onto a 12" x 12" glass plate and cured at 120 °C for 1 hour

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The baked film was removed from the glass plate using a razor blade Thermal gravimetric analysis was done using TGA 2950 (TA instrument). About 10 mg of sample was heated at a rate of 10°C /mm from room temperature to 800 °C in a nitrogen atmosphere.
Silane Film Thickness Measurement by Prism Coupling Thickness measurements were carried out using a combined ellipsometer and reflectometer- SENTECH SE 500 comprised of a He-Ne-laser ellipsometer SE 400 and a Film Thickness Probe FTF advanced The measurement was done in reflectometer mode because the ellipsometer could not be performed due to a strong depolarization due to a highly inhomogerieous surface
Chromating of Aluminum Alloys
Chromate conversion coating was applied from a solution comprising 5% H2CrO4,
0 6% K3Fe(CN) 6 and 1.05% NH4HF onto aluminum panels by dip-coating. The Al
3003 and Al 3105 alloys were immersed in the chromating solution for 1 minute before
being thoroughly unsed with tap water Drying at 150 0F for 5 minutes completes the
process
Preparation of Silane Coating Solution
An aqueous coating solution of TG14 (5% silane on weight basis) was prepared in the following way A glass bottle containing 144 grams of DI water was charged with 1 1 grams of glacial acetic acid under stiring (20% excess of storehiometry to ammo groups), which is followed by 16 grams of TGI 4 concentrate (50% in alcohol, weight basis) The silane was slowly added in 3-5 minutes to the acidified water under vigorous stirring Finally, a surfactant Igepal CO-660 (an ethoxylated nonylphenol) was added at 0 5% (weight basis) to the silane The protonated aminosilane is soluble in water and is allowed to further hydrolyze for at least 8 hrs before coating the metal panels For unpainted bare aluminum protection, 5% concentration is recommended, however, if the parts are to be painted, a more diluted solution of 1-2% can be used

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Coating of Aluminum Alloys with Multifunctional Silanes
Aluminum panels were first cleaned with silicate containing, non-etching cleaner-Nalco Globrite 45 IL at 150 °F for 1 -2 minutes and then rinsed with tap water The panels should be water-break-free after cleaning The panels were then immersed into the silane coating bath for 10-30 seconds and taken out to dry-in-place at 250 °F for 15-60 minutes or 350 °F for 5-20 minutes
Corrosion Tests on Painted and Unpainted Al Alloys Pretreated with TG14 ASTM B117 (neutralsalt spray test) According to the specification, the pretreated but unpainted panels are placed at a till angle of 45 ° in a chamber of atomized 5% sodium chloride salt fog for certain durations
ASTM 1654-92 This test condition is similar to that of Bl 17 except the panels are painted after pretreatment and scribed to expose bare metals prior to the testing. At the end of the test, adhesion of paint to the pretreated metal along the scribed line is
evaluated
ASTM D 610-01 Tins is a standard for evaluating degree of rusting on painted steel suifaces Mere, we borrowed the rating systems described in this test protocol for our study of silane-treated aluminum panels without a paint topcoat The rating system assigns a number from 0-10, each corresponding to various degrees of losting/conosion. 10 is the highest rating, meaning < 0 01% of the total area are couoded, 9 meaning 0 01%-0 03% of the total area is corroded, 8 corresponding to 0 03%-0.1%, 7 to 0 3% -1%, 6 to 0 3-1%, 5 to 1-3%, 4 to 3-10%, 3 to 10-16%, 2 to 16-33%, and 1 to 33-50%, and 0 to great than 50%
AAMA 2603-02 Tins is an American Architectural Manufactures Association (AAMA) voluntary specification Closely related to the paint adhesion affected by underlying conversion coating layer (chromate of silanes) are wet adhesion, dry adhesion and

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impact adhesion tests For dry adhesion test, 11x11 cross-hatch cuts (to expose bare metal) with 1 mm apart were made through polyester topcoated, silane treated aluminum panels Then, a tape (Permacel 99 or equivalent) was applied over an area of cuts by pressing down firmly against the coating to eliminate voids and air pockets The next step is to sharply pull the tape off at a tight angle to the plane of the panel The panel is then evaluated for paint loss For wet adhesion test, cuts were made as described above and the panels were immersed in distilled water at 100 °F for 24 hrs. Remove and wipe the sample dry. Repeat the tape pull-off test within five minutes. For impact adhesion test, the following procedure is followed: Using a 16 mm diameter round-nosed impact tester, 18 N-m (160 in-Ib) range, such as a Gardner impact tester, apply a load directly to the coated aluminum of sufficient force to deform the test sample a minimum of 3 mm Do the tape pull-off test to examine the degree of paint delammation
Electrochemical Impedance Spcctioscopy (EIS) Study of Silane-Coated Aluminum
EIS study of aluminum alloy 3003 coated with silane films was carried out in sodium sulfate solution at neutral pH. The EIS instrument is a Gamry CMS300 potentiostat using a frequency range of 1.5kHz-0 00lHz and AC perturbation voltage of 10 mV. A Ag/AgCl reference electrode and a carbon counter electrode together with the coated panel constitute a 3 -electrode system A total area of 20 cm2 in the center of the panels was exposed to the electrolyte for study Before each EIS run, the system was allowed to equilibrate for 300 - 600 seconds until the open curcuit voltage fluctuation was less than 5 mV/second
Synthesis of multifunctional aminosilanes from polyamines and epoxysilane
Epoxy resins constitute an important category of engineering plastics that find wide application, as adhesives, paints coatings, structural and waterproofing materials Most commercially sold bisphenol type epoxy resins are cured by multi-amines (di-

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,tri,tetra amines etc) of either straight chain aliphatic, cycloaliphatic, or aromatic. The straight chain aliphatic being the most reactive among the three, and curing of bisphenol diglyetdyl ether by straight chain aliphatic amines completes in 24 hrs at room temperature On the other hand, it takes elevated temperatures and longer durations to fully cure using aromatic amines, although the latter affords enhanced physical chemical properties For the metal finishing industry, it is important that the conversion coating be applied as water-soluble or water-borne form for VOC emission compliance and for compatibility with existing equipment - both practical concerns. For this reason, straight chain aliphatic amines are preferred over aromatic ones because of high solubility of the neutralized aliphatic ammonium salt
Outcome of temperature on GPS - polyamine reaction yield - Gas Chromatography, Liquid Chromatography (LC)-Mass Spectroscopy (MS) study The reaction yield was confirmed to be ~70% based on the amount of residual GPS (calibrated using 0 1% GPS methanol solution) Note that no TMH is detectable after 24 hours because a large amount of GPS quickly reacts with it to forms mono, bi-, tri-or tetra-adducts The yield rises to -95% after sitting for an additional three days. On the other hand, the same reaction at 70 °C for 3 hrs in ethanol solvent also gives -95% yield. It is well known that primary amines are far more reactive at epoxy ring opening, therefore TMH-GPS mono- and di-adducts form much faster than tri- and tetra-adducts However, it is the 1G14, the tetra-adduct that is target because of its high degree of branching and hence potentially better crosslinking properly.
Painted vs Unpainted Tests
There are two categories of tests involved in evaluation of corrosion protection of a conversion coating that must be differentiated here The first one is the unpainted conosion test that examines the corrosion protection of a conversion coating without a paint topcoat The second type of test is for painted metal parts with an underlying conversion coating This type of test examines the paint adhesion properties of the

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convulsion coating Strictly speaking, these are two distinctly different requirements. The former place demands on barrier protection properties of the conversion coating, while the latter emphasizes surface chemistry compatibility. For example, a Teflon film may very well be an excellent conversion coating/pretreatment layer for unpainted corrosion protection, but it cannot provide paint adhesion due to its low surface energy. Although in actuality most metal parts will be painted (such as automobile body panels or appliance panels), there are occasions where the metal parts need to be unpainted, which is the case for many aluminum alloys (such as aluminum wheels) due to the attractive metallic luster of aluminum Military specification MIL-C-5541E-a mandatory specification for conversion coatings to be applied on military equipments-lequires that both unpamted and painted corrosion tests be passed The target of developing silane-based conversion coating is to meet both requirements so as to justify Us chrome replacement potential-Applicants provide a synthetic approach to multifunctional silanes for corrosion protection of AI alloys as a replacement for carcinogenic chromate-based conventional Al pretreatment The multi-functional organosilane genus is presented and exemplified by specific structures Multi-amine - epoxy silane adducts-TGI4 and TG13 are synthesized and characterized and their utility as corrosion resistant coatings on aluminum are demonstrated
EXAMPLES
Example la
Synthesis of TG1 3
A 3 1 molar ratio of 3-glycidoxypropyltrimethoxysilane(GPS) and C,C,C-trimethyl-1,6-hexanediamine(TMH) is added to an equal weight of ethyl alcohol. The mixture is allowed to react at 70 °C for 3 hours The reaction products are subsequently neutralized with a 20% excess (based on storchrometry) of acetic acid Example lb Testing of TG 13

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The neutralized silane concentrate of Example la is diluted with water to 5% silane (by weight) and applied to aluminum panels by dip-coating
The panels dip coated with this Coating Mixture are first baked in an oven at 120 "C for about 0 5 hours and then further coated with about 20 microns of white polyester based paint, obtained from Sherwin Williams Coatings Company. The white painted panels are then subjected to an ASTM Bl 17 condition Neutral Salt Spray Corrosion test After 3000 hours of salt spray, no paint loss or blistering is found along the scribe lines
The conclusion reaches is that the Coating Mixture comprising TG13 bonds the paint to aluminum very well even when the aluminum is exposed to humid and corrosive conditions
Example 2
Synthesis of FG14
A 4 1 molar ratio of 3-glycidoxypropyltrimethoxysilane(GPS) and C,C,C-tinnethyl-l^-hcxanediaminetTMH) is added to an equal weight of ethyl alcohol The mixture is allowed to react at 70 °C for 3 hours The reaction products are subsequently ncutialized with a 20% excess (based on storchiometry) of acetic acid.
Example 2b First Testing of TG14
The neutralized silane concentrate of Example 2a is diluted with water to 5% silane (by weight) and applied to aluminum panels by dip-coating.
The coated aluminum panels are found to tolerate over 360 hours of salt spray (tested according to ASTM Bl 17) without showing any signs of corrosion, equivalent in performance to conventional chrome-based conversion coating
In contrast to the results obtained using the Coating Mixture of the instant claimed invention, bare Al panels start to corrode in 6 hours Other commercially available silane based coatings failed at 96 hours (bis-[trimethoxysilyl]amme and vinyltrnacetoxysilane mixture) and 240 hours (structures of 3-

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glycidoxypropyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane)
Example 2c Second Testing of TG14
In a second test, the neutralized silane concentrate of Example 2a is diluted with water to 5% silane (by weight) and applied to aluminum panels by dip-coating The panels dip coated with this TGI4 Coating Mixture are first baked in an oven at 120 °C for about 0 5 hours and then further coated with about 20 microns of white polyester based paint, obtained from Sherwin Williams Coatings Company The white painted panels are then subjected to an ASTM Bl 17 condition Neutral Salt Spray Corrosion test After 3000 hours of salt spray, no paint loss or blistering is found along the scribe lines
Example 3
The following exemplify the preparation of multifunctional silane from aromatic ring-containing multiamines The starting amines compnse the multiamines or a mixture of multiamines comprising the following structures, where Rl, R2, R3 and R are independently H, or C1-C4 alkyl. K, I, m are integers from 1:1000 For polyoxyalkyleneammes, the -(OCH2CHR)n- denotes homo or block-co-, or random-copolymei of ethylene and/or propylene oxide
The multramines or a mixture of multiamines is selected from a list comprising the following structures, where Rl, R2, R3 and R are independently H, or C1-C4 alkyl. K, I, m are integers from 1 1000. For polyoxyalkyleneamines, the -(OCH2CHR)n-denotcs homo or block-co-, or random-copolymer of ethylene and/or propylene oxide Sample starting materials include

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Examples of making multifunctional silane from aromatic ring-containing multrimmnes

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A mixture of 3-glycidoxypropyltrimcthoxysilane(GPS) and 1,3-xylenediamine at 4.1 molar ratio was added to equal weight of methyl alcohol under stir. The mixture was allowed to react at 60 °C for 16 hours
A mixture of 3-glycidoxypropyltrimethoxysilane(GPS) and
methylenedianiline at 4 1 molar ratio was added to equal weight of n-butyl alcohol under stir The mixture was allowed to react at 120 °C for 16 hours
Examples of making multifunctional silanes from cyclic multiammes A mixture of 3-glycidoxypropyltrimcthoxysiIane(GPS) and 1,2-
diaminocyclohexane at 4:1 molar ratio was added to equal weight of methyl alcohol
under stil The mixture was allowed to react at 80 °C for 3 hours
A mixture of 3-glycidoxypropyltrimelhoxysiIane(GPS) and 5-amino-l,3,3-tnmethyleyelohexanemethylamine (isophoron diamine) at 41 molar ratio was added to equal weight of methyl alcohol under stir. The mixture was allowed to react at 60 °C tor 16 hours
Examples of making multifunctional silanes from polyoxyalkyleneamines A mixture of 3-glycidoxypropyltnmelhoxysilane(GPS) and T-403 Jemfamine
(Huntsman) at 6 I molar ratio was added to equal weight of methyl alcohol under stir
The mixture was allowed to react at 60 °C for 5 hours.
Examples of making multifunctional silanes from di(hexamethylene)triamine
A mixture of 3-glycidoxypropyltrimethoxysilane(GPS) and
di(hexamclbylene)tnamine at 5.1 molar ratio was added to equal weight of methyl alcohol under stil The mixture was allowed to react at 60 °C for 5 hours

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A mixture of 3-glycidoxypropyltrimethoxysilane(GPS) and 1,3-xylenediamme at 4 1 molar ratio was added to equal weight of methyl alcohol under stir The mixture was allowed to react at 60 °C for 16 hours
A mixture of 3-glycidoxypropyitrimcthoxysilanc(GPS) and methylenedianihne at 4 1 molar ratio was added to equal weight of n-butyl alcohol under stir The mixture was allowed to react at 120 °C for 16 hours
Corrosion protection of unpainted aluminum alloys is shown in the following Table:
conosion ptotection of unpainted Al alloys by coatings derived from epoxysilane and multiamines NII cpoxidc= 1 I, days of protection from ASTM B117 salt spray without showing visible pitting

Example 4
Examples of applying epoxysilane-multi-amme adducts as prctreatment to aluminum alloys to piomole paint adhesion
C,C,C-trimethylhexancdiamine - glycidoxypropyltrimethoxysilanc 1-3 adduct (TGI 3) was neutralized with storehrometric amount of acetic acid and made into 1.0% water solution Aluminum panels were degreased with Nalco Globrite 451L alkaline

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cleaner and brought to contact with the pretreatment solution. The aluminum panels were subsequently dried and painted with 10 micron waterborne polyurethane paint (Shcrwm-Williams). Painted panels were fully cured at 350 F for 0.5 hour, and scribed in the center to expose bare metal before being put into a salt spray chamber (conforming to ASTM B117) Creepage of the corrosion along the scribe lines were measured after 14 days of salt spray Results are shown in the following Table. Corrosion protection of painted Al alloys pretreated with coatings derived from
epoxysilane and multiarmnes after 14 days of ASTM B117 salt spray
(Shervvin-Williams waterborne polyurethane paint, Al 2024 T3 alloy)

Various changes and modifications to the presently preferred embodiments desonbed herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spint and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims

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1 A multifunctional organosilane of formula

wherein A is C4-C20 branched or unbranched, saturated or unsaturated modified or unmodified carbon atoms;
X and Y are independently
H or CONH-B-Si (OR1)3
wherein 13 is an alkyl linker, and R1 is C3 to C10 carbon atoms, and salts thereof.
A composition of mailer of formula TG 13-R

where R is II or C1 -C6 alkyl

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3 A composition of matter of formula TG 14-R.

where R is H or C1 - C6 alkyl
4 A composition of matter of formula TG13'

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5 A composition of matter of formula TG14-

6 A method of coating a metal comprising
(a) optionally cleaning the surface of the metal with a cleaner,
(b) coating the surface of the metal with a Coating Mixture; and
(c) thermally annealing the Coaling Mixture on the surface of the metal to
form a crosslinked coating,
wherein the Coating Mixture comprises a composition of matter of formula
1G13-11-

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where R is H or C1-C6 alkyl,
or a composition of matter of formula TGI4-R:

where R is, H or C1-C6 alkyl, or a combination thereof; and wherein the metal is aluminum or an aluminum alloy
7 The method of claim 6, wherein the coating mixture is applied to the
metal by acrosol spraying

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8 The method of claim 6, wherein the coating mixture is applied to the
metal by manual wiping