Use of a composition for improving adhesive bonding of surfaces, process for bonding surfaces

Abstract

The instant invention concerns the use of a composition comprising a polymer P obtained by radical copolymerization of a mixture of (i) acrylic acid; (ii) optionally methacrylic acid; and (iii) at least one compound being an ethylenically unsaturated polycarboxylic acid, for improving the bonding between a metallic surface (S1) and another surface (S2) through an adhesive layer, in particular, in order to impart a resistance to the adhesive failure to the resulting bonding.

Description

[0001] USE OF A COMPOSITION FOR IMPROVING ADHESIVE BONDING OF SURFACES, PROCESS FOR BONDING SURFACES

[0002] This application claims priority to the application filed on October 3 2023 in Europe with Nr 23306691 .9, the whole content of this application being incorporated herein by reference for all purposes.

[0003] The instant invention relates to the field of adhesive bonding of metallic surfaces / parts. The invention is more especially directed to the use of a composition comprising a specific polymer for improving the bonding between a metallic surface (S1 ) and another surface (S2) through an adhesive layer, in particular, in order to impart the resulting bonding with a resistance to the adhesive failure.

[0004] TECHNICAL BACKGROUND

[0005] In order to provide an enhancement of the adherence of adhesives on metal surfaces, especially on aluminum or steel, several methods have been proposed, including the deposition of inorganic coatings on the surface of the metal, especially the so-called "conversion coating".

[0006] The term "conversion coating" is well known in the art and refers to a layer formed on the surface of a metal, that is an advantageous replacement of native oxide on said surface (especially on aluminum), and which is obtained by the controlled chemical formation of a film or layer on the metallic surface by reaction with chemical elements of the metallic surface, so that at least some of the cations dissolved from the metallic material are deposited in the conversion coating.

[0007] Conversion coatings technologies have evolved a lot in the past decades: hexavalent chromium (Cr-VI such as CrO3), widely used in the past especially on aluminum, has seen its uses more and more limited due to its toxicity. Technologies such as Zinc phosphates (Zn-P), which became predominant for mild steel, galvanized steel and multi-metal lines containing less than 30% of aluminum, are more and more challenged these days: in addition to water and energy consumption significantly higher than with other conversion coating technologies, Zn-P conversion generates toxic wastes / sludges which contain toxic metals (Ni, Mn, Co, ... ) and whose disposal is getting more and more expensive. Issues raised by both Cr-VI and Zn-P allowed new technologies to develop: trivalent chromium (Cr-lll such as Chromium nitrate Cr(NO3)3) and transition metals hexafluorides. While Cr-lll is not classified as of today, it suffers from the bad image of Chromium and its usage is becoming increasingly challenged. Hexafluorides are thus Cr-free and Zinc phosphate-free alternative technologies.

[0008] However, hexafluorides are known to yield relatively smooth surfaces which can negatively affect paint adhesion while other surface treatment technologies create an entanglement of crystals protruding at the metal surface, thus increasing surface area improving coating adhesion through mechanical interlocking.

[0009] For enhancing the adhesion on a coating, such as a conversion coating, it is known to include additives, especially organic polymers. In this connection, it has been for example described the use of copolymers made from acrylic acid and vinyl phosphonic acid. For more details in this connection, it may be especially be referred to GB 2331942 and US 6,020,030. A typical additive is Addibond™ 021 available from SOLVAY that has been widely described for this kind of application.

[0010] However, P-based ingredients are more and more under scrutinity.

[0011] In the last decades, several cities in China and western countries passed bills limiting the concentration in phosphorous of aqueous effluents released into the environment.

[0012] In that context, there’s a need for a P-free polymer showing performances similar to P-based polymers.

[0013] SUMMARY OF THE INVENTION

[0014] One aim of the present invention is to provide a new performing solution for improving the bonding between a metallic surface and another surface, preferably metallic as well, through an adhesive layer, such that this new solution does not contain phosphorous but provides performances similar to well established P-based solutions.

[0015] To this end, the instant invention proposes to make use of a specific polymer, optionally, but not necessarily, together with, namely before, during, or after, the formation of a conversion coating, to treat a metal surface before bonding it with another surface via an adhesive composition or layer (so-called “adhesive bonding”), both surfaces preferably being part of the surfaces of two solid parts (especially metallic ones) to be bonded together through adhesive bonding. It has been discovered that using a composition comprising the specific polymer as coating pretreatment on the metallic surface or as additive in the adhesive composition to be applied between a metallic surface and another surface, provides a particularly good adherence between the two surfaces / parts. The composition comprising the specific polymer used according to the invention allows a resistance to the adhesive failure. In the scope of the invention, the inventors have now observed that the strength of the adherence between the adhesive and the metal surface reveals especially high, to such an extent that cohesive failure appears instead of (or at least more preferably than) adhesive failure when a sufficiently high mechanical stress is applied for separating the adhesive-bonded surfaces / parts.

[0016] The improvement of the bonding between two surfaces treated by a composition comprising the polymer of the invention and then assembled by an adhesive is thus reflected by a resistance to the adhesive failure, which means that a cohesive failure will occur instead, in particular after ageing, compared to other existing treatments. Although compositions based on polymers P as described below have been proposed in prior art for treating metallic surfaces, their use in adhesive bonding of solid parts, especially metallic ones, has never been disclosed.

[0017] DEFINITIONS

[0018] Before the issues of the invention are described in detail, the following should be considered:

[0019] As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compound" means one compound or more than one compound.

[0020] The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of", "consists" and "consists of".

[0021] Throughout this application, the term "about" is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

[0022] As used herein, the term "average" refers to number average unless indicated otherwise.

[0023] As used herein, the terms "% by weight", "wt.- %", "weight percentage", or "percentage by weight", and the terms "% by volume", "vol.- %", "volume percentage", or "percentage by volume", are used interchangeably.

[0024] The recitation of numerical ranges by end points includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1 , 2, 3, 4 when referring to, for example, a number of elements, and can also include 1 .5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1 .0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0025] “Adhesive failure” is understood to mean that failure between two surfaces bonded by an adhesive layer occurs at the surface, the adhesive being retained on one surface.

[0026] “Cohesive failure” is understood to mean that failure between two surfaces bonded by an adhesive layer occurs within the adhesive, which is thus retained on both surfaces.

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] More precisely, the instant invention is directed to the use of a composition C comprising at least one polymer P obtained by radical copolymerization of a mixture comprising:

[0029] (i) acrylic acid;

[0030] (ii) optionally methacrylic acid; and (iii) at least one compound of formula I below: wherein:

[0031] - R and R' are selected from H or a methyl group, provided at least one of R or R' is H, preferably both are H;

[0032] - R1and R2are, independently from one another, H or the compound of formula (I) is in the form of a salt, with R1and / or R2being selected from the group consisting of alkali metals, alkaline earth metals, and quaternary ammonium+NR34, wherein R3are independently from one another H or methyl or ethyl;

[0033] - n is an integer ranging from 1 to 4;

[0034] - m is an integer ranging from 0 to 4;

[0035] - Ra, Rb and Rc are, independently from one another, selected from H, a - COOR4 group, an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR4group, with R4having the same definition as the one of R1and R2, preferably H; provided when Ra, Rb and / or Rc is an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR4group, then at least one of Ra, Rb or Rc is H, preferably at least two of Ra, Rb or Rc are H. for improving the bonding between a metallic surface (S1 ) and another surface (S2) through an adhesive layer.

[0036] Preferably, metallic surface (S1 ) is part of the surface of a solid part (1 ) to be bonded to another solid part (2) of which (S2) is part of the surface. In this case, generally, it is intended to bond surfaces (S1 ) and (S2) together in order to make an adhesive bonding between both said solid parts (1 ) and (2) generally with the aim of making a structure extending beyond surfaces (S1 ) and (S2).

[0037] One specific object of the instant invention is the use of a composition C comprising at least one polymer P as defined above for treating a first metallic surface (S1 ) intended to be bonded to a second surface (S2) by adhesive bonding and for imparting to the bonding a resistance to adhesive failure.

[0038] An additional advantage of the use of a composition C comprising the polymer P according to the invention is that the bonding obtained according to the invention is highly resistant to corrosive atmospheres and to wet atmospheres, which leads to a long lasting adhesive bonding. In most cases, composition C comprising the polymer P is also used for obtaining this additional effect (namely for further imparting to the bonding a resistance to corrosive atmospheres and to wet atmospheres, in other words for obtaining both a very effective, but also long lasting adhesion).

[0039] In other words, the use of a composition C comprising at least one polymer P as defined above for treating a first metallic surface (S1 ) intended to be bonded to a second surface (S2) by adhesive bonding and for imparting a resistance to the adhesive failure to the bonding is also providing a very good resistance to ageing of the adhesive bonding.

[0040] Such a property can be measured according to tensile tests on so-called “Single Lap Shear” (SLS) assemblies, such as defined in ASTM D-1002 10, performed on freshly bonded SLS assemblies and performed on SLS assemblies after ageing in corrosive atmospheres, wet atmospheres, or repeated cycles of corrosive atmospheres followed by wet atmospheres, such as ASTM G85 A3.

[0041] In single lap shear tests, the adhesive is applied on a first solid part, and a second solid part is placed on top to form, after the adhesive is cured, an adhesive joint between the two solid parts. The two ends of the resulting assembly are then placed into their respective grips in the shear tester. The tensile shear tester is then used to apply a load to the joint until it is ruptured. The composition of the invention is particularly suitable for providing a cohesive nature to ruptures in shear testing of solid parts / pieces (especially metallic ones) bonded through adhesive bonding. Adhesive bonding is a process in which joining between two or more solid parts is accomplished by the solidification or hardening of a non-metallic adhesive material, placed between the faying surfaces of the parts. It is widely used in industry, notably in the automotive industry.

[0042] Other tests simultaneously combine a corrosion stress and a mechanical stress (eg compression load), such as the Bv 101 -07, known as Ford Durability Stress Test or Arizona Proven Ground Exposure (APGE). Notably an adhesive bonding with the composition C comprising the polymer P according to the invention between two surfaces S1 and S2 has been demonstrated to provide failure facies, after ageing, which remains more cohesive.

[0043] The composition C comprising at least one polymer P can be used as surface treatment of all or parts of the metallic surface (S1 ) and optionally all or parts of the surface (S2) and / or as additive in the adhesive layer.

[0044] Polymer P

[0045] In a preferred embodiment, the polymer P is obtained by radical copolymerization of a mixture consisting essentially of:

[0046] (i) acrylic acid;

[0047] (ii) optionally methacrylic acid; and

[0048] (iii) at least one compound of formula I.

[0049] By “consisting essentially of”, it is understood to mean that the polymer P is produced by using the two or three components above (i), optionally (ii) and (iii) as sole monomers.

[0050] Notably, the polymer P is obtained by radical copolymerization of a mixture consisting essentially of:

[0051] (i) acrylic acid; and

[0052] (iii) at least one compound of formula I.

[0053] Preferably, the polymer P is obtained by radical copolymerization of a mixture having the following molar ratio, based on the total quantity of acrylic acid, methacrylic acid and compound of formula I: acrylic acid: from 5 to 95%, notably from 10 to 90%, preferably from

[0054] 30 to 85% methacrylic acid: from 0 to 50%, preferably from 0 to 40%, more preferably from 0 to 20% compound of formula I: from 1 to 90%, for example from 5 to 50%, notably from 8 to 45%.

[0055] The above molar ratios of each monomer in the polymer P are showing particularly good results in terms of resistance to the adhesive failure to the bonding when compared to polymers that are out of the above ranges. For example, due to the difference between the first pKa of itaconic acid and the pKa of (meth)acrylic acid, the polymer P is more soluble in the acidic treatment aqueous bath when the quantity of compound of formula I in the polymer P is increasing. When the quantity of compound of formula I is increasing, molecular weights become more difficult to control, especially the synthesis of molecular weights above 10 000 g / mole becomes very difficult, and itaconic acid conversion becomes more difficult.

[0056] The presence of methacrylic acid is not mandatory but confers advantageously a higher hydrophobicity to the polymer P and thus to the bonding, improving the resistance to wet atmospheres.

[0057] Besides, the polymer P used according to the invention preferably has a molecular weight, typically a weight average molecular weight, of at least 5,5 kDa, e.g. 6 kDa to 1 ,500 kDa, for example 7 kDa to 500 kDa, notably between 8 and 150 kDa.

[0058] Average molecular weights (typically weight average molecular weight) are measured by Size Exclusion Chromatography (SEC). Notably the SEC is equipped with a MultiAngle Laser Light Scattering (MALLS) Mini Dawn TREOS detector and an Agilent concentration detector (Rl detector). The SEC-MALLS system is running on three columns Varian Aquagel OH mixed H, 8 pm, 3*30 cm at a flow rate of 1 mL I min and with the following mobile phase: 100% water, 100mM NaCI, 25mM NaH2PO4, 25Mm Na2HPO4. Polymer samples were diluted down to 0.5 active wt% in the mobile phase for at least 4 hours then filtrated in a Millipore filter 0.45 pm and 100 microliters were injected in the mobile phase flow. Absolute molar masses were obtained with the dn / dC of the poly(acrylic acid) equal to 0.1875 mL / g. Composition C

[0059] In a particular embodiment of the invention, the composition C used to impart resistance to the bonding is further comprising from 30 to 90% by weight, preferably from 60 to 80% by weight, based on the total weight of the composition, of compound of formula I. Advantageously, the polymer P is mixed with unreacted compound of formula I and this mixture (which does not further react) is applied on all or parts of the metallic surface (S1 ) and optionally all or parts of surface (S2) and / or as additive in the adhesive layer.

[0060] In a preferred embodiment, the composition C used according to the present invention, consists essentially of the polymer P and optionally the compound of formula I. It may be useful according to another preferred embodiment to add to the composition comprising the polymer P and optionally the compound of formula I, solutions containing fluorides or so-called complex fluorides like H2TiFe, H2ZrFe, FhHfFe, H2AIF6, FhSiFe, FhGeFe, H2SNF4, or HBF4 and other transition metal derivatives such as Zr(OH)2CO3*ZrO2.

[0061] Compound of formula I

[0062] In the compound of formula I, R and R' are selected from H or a methyl group, provided at least one of R or R' is H, preferably both are H.

[0063] Also, R1and R2are, independently from one another, H or the compound of formula (I) is in the form of a salt, with R1and / or R2being selected from the group consisting of alkali metals, alkaline earth metals, and quaternary ammonium+NR34, wherein R3are independently from one another H or Me or Ethyl. Preferably R1and R2are H or the compound of formula I is a salt, with R1and R2being sodium.

[0064] In the compound of formula I, n is an integer ranging from 1 to 4, preferably 1 or 2 and m is an integer ranging from 0 to 4, preferably 0 or 1 .

[0065] Regarding Ra, Rb and Rc, they are, independently from one another, selected from H, an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR4group, with R4having the same definition as the one of R1and R2, preferably H; provided when Ra, Rb and / or Rc is an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR4group, then at least one of Ra, Rb or Rc is H, preferably at least two of Ra, Rb or Rc are H. In particularly preferred embodiment Rb and Rc are H and Ra is either H or CH2-COOH.

[0066] The particularly preferred embodiment corresponds to the use described above wherein the compound of formula I is selected from the group consisting of itaconic acid, alpha-methylene glutaric acid, but-3-ene-1 ,2,3-tricarboxylic acid, hex-5-ene- 1 ,3,5-tricarboxylic acid, their salts and mixtures thereof.

[0067] According to a first preferred embodiment, the compound of formula I is itaconic acid (IA) or sodium salt thereof.

[0068] According to a second preferred embodiment, the compound of formula I is alphamethylene glutaric acid (MGA) or sodium salt thereof.

[0069] According to a third preferred embodiment, the compound of Formula I is but-3-ene- 1 ,2,3-tricarboxylic acid (BTA) or sodium salt thereof.

[0070] According to a fourth preferred embodiment, the compound of Formula I is hex-5- ene-1 ,3,5-tricarboxylic acid (HTA) or sodium salt thereof.

[0071] Surfaces

[0072] Regarding the nature of the metallic surface (S1 ) it can be a surface comprising a metal selected from aluminum, steel, zinc, magnesium, titanium, copper and their alloys, or cobalt-nickel alloys, preferably a surface of aluminum or aluminum alloy. The invention is especially suitable for treating metal surfaces of:

[0073] - Aluminum or an aluminum-based alloy ; or

[0074] - Steel, for example galvanized steel (electrogalvanized, EG, hot dip galvanized, HDG, containing up to about 0.2wt% of aluminum, and steel coated with both Zinc and Al containing about 55% of aluminum such as Galvalume™ or Steel coated with both Zinc, 3.5% of aluminum and 3% of Magnesium such as Magnelis™); or cold rolled steel (CRS) ; or stainless steel

[0075] - Magnesium or magnesium-based alloys ; or

[0076] - Zinc or zinc-based alloys ; or

[0077] - Titanium or titanium-based alloys.

[0078] The invention is especially interesting for metal surface of aluminum and aluminum alloys, such as aluminum Alloy AA 5754 tested in the appended examples, or other alloys such as those of Series 1xxx, 2xxx, 3xxx, 4xxx, 5xxxx, 6xxx, 7xxx, such as AA1050, 2024, 3003, 5005, 5182, 6111 , 6113, 6014, 6016, 6060, 6063, 6182, 7075. As for the other surface (S2) it may be a metallic surface as well, identical or different from the metallic surface (S1 ), preferably identical.

[0079] According to another embodiment, the other surface (S2) is a non-metallic surface, for example a plastic surface e.g. based on polyamide, PEEK or ABS, or a composite surface based e.g. on CFRP or Glass Fiber Reinforced Plastics.

[0080] According to an advantageous embodiment, the second surface (S2) is a metallic surface also treated with a composition C comprising a polymer P as described above, generally but not necessarily identical to the composition comprising a polymer P used on the first surface (S1 ).

[0081] According to an interesting variant, both surfaces (S1 ) and (S2) are metallic surfaces of aluminum or aluminum alloys.

[0082] More generally, the composition C comprising the polymer P used according to the invention is preferably used for treating both surfaces (S1 ) and (S2) before the adhesive bonding of the two surfaces through an adhesive layer, especially when (S2) is a metallic surface. Alternatively or additionally, the composition comprising the polymer P according to the invention is used as additive incorporated to an adhesive composition used to form the adhesive layer between the two surfaces.

[0083] Processes / uses

[0084] The present invention is also directed to a process for bonding a metallic surface (S1 ) with another surface (S2), including: treating all or parts of said metallic surface (S1 ) with the composition C as defined previously; and optionally treating all or parts of said second surface (S2) with the composition C as defined previously ; and bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces.

[0085] In other words, the use of the invention may involve the steps of treating all or parts of said metallic surface (S1 ) with the composition C as defined previously; and optionally treating all or parts of said second surface (S2) with the composition C as defined previously ; and bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces.

[0086] The surface (S1 ) and / or (S2) are preferably cleaned and / or activated before the treatment with the composition C.

[0087] In this process and use according to the invention, the composition C may be: a conversion composition; and / or a solution or a dispersion applied on the surface after having applied a conversion coating on the surface to be treated.

[0088] According to a possible embodiment, a conversion coating may be applied on the metallic surface (S1 ), by reaction of said surface with a conversion composition (in other words, a conversion composition is applied on the metallic surface for forming a conversion coating thereon). The use of a conversion coating is however not compulsory according to the invention, and, according to a specific embodiment, no conversion coating is applied on the surface (S1 ). When a conversion composition is used, typically:

[0089] - the conversion composition includes all or part of the composition C comprising the polymer P as an additive ; and / or

[0090] - the conversion coating is applied on the surface (S1 ) and then all or part of the composition C comprising the polymer P is applied on the conversion coating.

[0091] The second surface (S2) may also receive a similar conversion coating, in the same conditions, especially when this second surface (S2) is a metallic surface. But again, the use of a conversion coating is not compulsory according to the invention, and, according to a specific embodiment, no conversion coating may be applied on the surface (S2).

[0092] The present invention is also directed to a process for bonding a metallic surface (S1 ) with another surface (S2), including: bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces, said adhesive layer comprising the composition C comprising the polymer P as defined above. Hence, in the use according to this embodiment of the invention, composition C is comprised in the adhesive layer.

[0093] According to this possible embodiment, the composition C comprising the polymer P may typically be introduced in the adhesive composition for example as a solid powder, said powder comprising the composition C alone or the composition C comprising the polymer P at the surface of a filler (said powder may typically be obtained by spray drying a solution or suspension of the composition C comprising the polymer P, typically in presence of a filler).

[0094] According to a preferred embodiment, said process and use further includes, before the step of bonding the surfaces S1 and S2, a step consisting in: treating all or parts of said metallic surface (S1 ) with the composition C as defined previously; and optionally treating all or parts of said second surface (S2) with the composition C as defined previously.

[0095] In other words, the composition C comprising the polymer P may typically be:

[0096] - a conversion composition or a part of it; and / or

[0097] - a solution or a dispersion or a part of it, applied on the surface(s) after having applied a conversion coating on the surface to be treated ; and / or

[0098] - an adhesive composition or a part of it.

[0099] Typically, the composition C is present in the conversion composition and / or in a solution or dispersion applied on a conversion coating. In that case, the adhesive is applied on a surface previously treated by the composition C.

[0100] According to some specific embodiments, an additional layer is applied between the treated surface (S1 ) (and / or (S2)) and the adhesive. This is for example the case for the treatment of metal coil or part on a first site, that has then to be bonded on a second site: in that case, a lubricant and / or an oil may be applied on the treated coil or part, in order to protect it during transportation and storage and to facilitate downstream operations (coil cutting into sheets, blanking, stamping, forming, ... ).

[0101] According to yet another aspect, a specific object of the instant invention is the material comprising two adhesive-bonded surfaces comprising a metal surface (S1 ) which is in all or part (i) treated with a composition C comprising at least a polymer P as defined above and (ii) bonded to a second surface (S2) preferably as defined above via an adhesive layer.

[0102] Specific features and possible embodiments will now be described in more details.

[0103] The optional conversion coating

[0104] When a conversion coating is applied on one or both of the surfaces (S1 ) and / or (S2), it may be obtained by contacting the surface with any conversion composition known from the prior art.

[0105] Contacting the metal surface with the conversion composition may be made by any means known per se, such as roll coating, immersion (coil coating, parts coating) or spray (coil coating, parts coating), as illustrative examples. The bath, when polluted by multi-valent cations leaching from the substrate, such as AI3+ in the case of aluminum strips or parts, may be rejuvenated by off-line or preferable on-line methods such as those known by people familiar with the art (ion exchange resin). When the conversion step is followed by a rinse step, this rinse water may contain some polymer ; the polymer may be recovered from the rinse water by reverse osmosis membrane and returned to the conversion bath.

[0106] The conversion composition used according to the invention may typically contain fluorides or so-called complex fluorides like H2TiFe, H2ZrFe, FhHfFe, H2AIF6, FhSiFe, FhGeFe, H2SNF4, or HBF4 and other transition metal derivatives such as Zr(OH)2CO3-ZrO2.

[0107] The conversion composition may also include other compounds, such as silane precursors for example, and / or cerium salts, and / or terbium molybdate.

[0108] The use as additive in coating and adhesion compositions

[0109] The invention also concerns coating and adhesive compositions comprising the polymers described above, including but not limited to inks and paints, such as water-borne and powder paints, as well as the use of the above described polymers as adhesion promoters in coatings, inks and paints (e.g., water-borne paints and powder paints) or as adhesion promoters imparting corrosion resistance in (post-)conversion coatings i.e. in any step performed prior to painting.. This means that these polymers can be incorporated into inks and paints, including for example water-borne paints and powder paints as additives that promote the adhesion of the ink / paint to a substrate and / or the adhesion of another coating on the ink / paint. Or they can be incorporated as additives in conversion coatings as defined above in order to promote adhesion of a painting thereon.

[0110] Water-borne paints are aqueous compositions that typically provide coatings through the action of a voltage, or physical and / or chemical phenomena e.g. water evaporation, UV crosslinking etc.

[0111] Powder paints / coatings are typically applied electrostatically as a free-flowing, dry powder and then cured under heat or with ultraviolet light.

[0112] In a preferred embodiment, the present invention concerns a process for bonding a paint or varnish to a metallic surface (S1 ), including : treating all or parts of said metallic surface (S1 ) with a composition comprising a polymer P as described above ; and applying a paint or varnish to the surface (S1 ).

[0113] In the embodiments set forth above, during the treatment step with the composition comprising the polymer P, the concentration of polymer P in the treatment medium is preferably from 1 to 10,000 ppm, more preferably from 10 to 8,000 ppm, typically from 20 to 5,000 ppm.

[0114] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0115] The following examples illustrate the invention.

[0116] EXPERIMENTAL PART

[0117] FIRST TEST CAMPAIGN

[0118] Polymers 1-4 synthesis and characterization:

[0119] Polymers 1 -4: the copolymers poly(acrylic acid-co-methacrylic acid-co-ltaconic acid), Poly(AA-co-MAA-co-IA), and the copolymers poly(acrylic acid-co-itaconic acid), Poly(AA-co-IA), were prepared by conventional radical polymerization in water using recipes known by those familiar with the state of the art. The polymerization is performed at 70°C, the monomers are fed over 4h (feed 1 ), the oxidizer is fed over 5h (feed 2), 80% of the reducing agent is fed over 5h and 20% of it over 30mn (feed 3).

[0120] The quantities of each reagent used are listed in Table 1 a below.

[0121] Table 1a

[0122] NaPS is sodium persulfate; and MBS is sodium metabisulfite

[0123] A Polymer 3b was also prepared in the same conditions as Polymer 3 but with higher concentrations in red-ox in order to get lower molecular weights.

[0124] A sample is taken and analyzed by1H NMR in D2O. The final conversion in AA, MAA and IA is near quantitative. The molecular weight is determined by size exclusion chromatography (SEC) coupled with a Rl and a multi-angle light scattering diffusion (MALLS) detector. Results are reported Table 1 b below.

[0125] Polymers 5-7 synthesis and characterization:

[0126] Polymers 5-7: the copolymers poly(acrylic acid-co-methacrylic acid-co-methylene glutaric acid), Poly(AA-co-MAA-co-MGA) are prepared by conventional radical polymerization in water using recipes known by those familiar with the state of the art, involving a red-ox, te / t-butyl hydroxyperoxyde (f-BHP) I erythorbic acid. Details are provided Table 1 c below for Polymer 5, poly(AA-co-MAA-co-MGA) with a molar ratio 80 / 12 / 8. A first fraction of monomers are introduced up-front, while the rest is added as a 44% water solution over 5h. When the reaction medium has cooled to 25°C, a sample was taken and analyzed by1H NMR in D2O. The final conversion in AA, MAA and AMG was near quantitative. The molecular weight was determined by size exclusion chromatography (SEC) coupled with a Rl and a multi-angle light scattering diffusion (MALLS) detector. Results are reported Table 1 b below.

[0127] Table 1c

[0128] Polymers 8-11 synthesis and characterization:

[0129] Polymers 8-12 are Poly(AA-co-IA); they were prepared using a recipe similar to the recipe used for Polymers 1 -4.

[0130] NMR was used to check the conversion is quantitative. The molecular weight was determined by size exclusion chromatography (SEC) coupled with a Rl and a multiangle light scattering diffusion (MALLS) detector. Results are reported Table 1 b.

[0131] Polymer 12 synthesis and characterization

[0132] Polymer 12 results from the polymerization of acrylic acid, methacrylic acid and a monomer blend (i.e. MGA-BTA) which contains both MGA and a triacid (BTA) ,2,3-tricarboxylic acid (BTA)

[0133] This monomer blend MGA-BTA was prepared in a 2-step process:

[0134] Step 1 : Phosphine catalyzed cross-coupling between methyl acrylate and dimethyl maleate. CO2Me - * MeO2C J CO2Me cat. fBuOH11

[0135] In a 1 L double jacketed reactor equipped with a mechanical stirrer, a condenser and a temperature probe are added at room temperature:

[0136] - 200g of methyl acrylate (208.4mL, 2.3mol).

[0137] - 331 ,5g of dimethyl maleate (288.3mL, 2.3mol).

[0138] - 97.95g of f-BuOH (124.2mL, 1.32mol).

[0139] The solution is then allowed to stir at 600 rpm and 8.34g of bis(diethylamino)phenylphosphine (8.79mL, 0.033mol, 0.7mol% wrt. reactants) is added at room temperature.

[0140] The solution is then allowed to stir at 40°C and the reaction progress is followed up thanks to1H NMR analysis.

[0141] After 7h00 reaction time at 40°C, NMR analysis on the crude indicates the following conversion levels for the reactants:

[0142] - Methyl acrylate: 67%

[0143] - Dimethyl maleate: 29%

[0144] The molar ratio between methyl acrylate dimer and methyl acrylate + dimethyl maleate cross-coupling adduct is 0.65 : 1 (triester : diester).

[0145] An additional amount of bis(diethylamino)phenylphosphine catalyst is added into the reaction mixture at 40°C (162.2g of the solution, 0.039mol of catalyst, additional 0.8mol% wrt. total amount of reactants). After 24h00 at 40°C (overall reaction time) NMR analysis of the crude indicates the following conversion levels for the reactants:

[0146] - Methyl acrylate: 100%

[0147] - Dimethyl maleate: 64%

[0148] The molar ration between methyl acrylate dimer and methyl acrylate + dimethyl maleate cross-coupling adduct is 1 : 1 (triester : diester).

[0149] The solvents as well as the unconverted dimethyl maleate / fumarate reactant are then removed through vacuum distillation. Overall 158.4g of material has been collected in the distillate containing mainly f-BuOH, dimethyl maleate / fumarate and anisole with some traces of dimer product.

[0150] In order to complete dimethyl fumarate removal from the crude mixture, the residue in the boiler is cooled down at 4°C to allow crystallization. The precipitated solid is then separated through filtration allowing to recover 27.6g of dimethyl fumarate.

[0151] Finally the filtrate is again distilled under vacuum (160°C, 3mbar) in order to distillate out the desired dimer and trimer products allowing to recover 172.5g of a mixture composed of 47mol% of trimer and 53mol% of dimer.

[0152] Step 2: Diester and trimester hydrolysis to afford diacid+triacid mixture.

[0153] H+cat.

[0154] In a 2L double-jacketed reactor equipped with a mechanical stirrer, a short path distillation bridge connected to a 500mL round bottom flask and a temperature probe are added:

[0155] - 172.45g of the mixture obtained in example 1 above.

[0156] - 182m L of water

[0157] - 0.086g of hydroquinone. The mixture is then allowed to stir at 450 rpm and 2.8mL of H2SO4 (96.1 %, 5.15g, 6mol% with respect to the reactants) is progressively added into the mixture while monitoring for the exotherm.

[0158] The reaction mixture is then allowed to stir at 130°C in order to carry out the hydrolysis and to distillate out the formed methanol by-product (with distillates along with H2O). Over the course of the distillation, additional amount of water is progressively added into the reactor in order to compensate water loss through the distillation. After 17h00 stirring at 110°C,1H NMR analysis shows complete conversion of the ester to the acid. In total 635g of water has been added into the reactor and 807g of distillate has been collected. The temperature of the reaction mixture is then cooled down at 80°C and 11 ,55g of NaOHaq (35 wt%) (2 eq. wrt. H2SO4) is added into the mixture for catalyst neutralization (pH~2.5).

[0159] The solution is then allowed to cool down at room temperature allowing recrystallization of the polyacid products to occur. The solid is then filtered out. The filtrate is allowed to cool down at 4°C to allow additional amount of polyacid to recrystallize and the solid is filtered out and washed several times with diethyl ether. Finally the newly obtained filtrate is concentrated under vacuum and is allowed to recrystallize at 4°C a second time. The obtained solid is then filtered out and washed several times with diisopropyl ether. All the solids are finally combined, dried under vacuum at 65°C (1 Ombar) to obtain 90.5g of a white solid containing 39wt% of triacid (But-3-ene-1 ,2,3-tricarboxylic acid) and 61wt% of diacid (MGA).

[0160]

[0161] Table 1b: copolymers and terpolymers used for the tests TESTING

[0162] Testing, Part 1 :

[0163] The use of polymers to treat metal substrates prior to bonding them with adhesives is described below. Performances were assessed through Single Lap Shear (SLS) tests, before and after ageing in corrosive conditions. Coupons were prepared according to the protocol below and assembled to form SLS assemblies as described in D1002-10.

[0164] Step 1 is performed according to Step 1 a or Step 1 b or Step 1 c:

[0165] Step 1a: 20 coupons (aluminum alloy coupons: AA5754, from FBCG; 100mm long, 25mm wide, 3mm thick) go through each of the following steps:

[0166] - degreasing by immersion for 1 mn in a 4L stainless steel bath containing NP Kleen 160 from Quaker (1wt%) heated to 50°C under light stirring,

[0167] - rinsing with tap water (at about 50°C),

[0168] - etching by immersion for 30 seconds in a 4L stainless steel containing sulfuric acid (10%) heated to 50°C under light stirring,

[0169] - rinsing with tap water (at about 50°C),

[0170] - rinsing with deionized water.

[0171] Step 1b: 20 coupons (aluminum alloy coupons: AA5754, from FBCG; 100mm long, 25mm wide, 3mm thick) go through each of the following steps:

[0172] - degreasing by immersion for 3mn in a 4L stainless steel bath containing NP kleen 160 from Quaker (1wt%) heated to 50°C under light stirring,

[0173] - rinsing with tap water (at about 50°C),

[0174] - etching by immersion for 3mn in a 4L stainless steel containing NP Kleen 190 (1wt%) and Additivo 200 (0.075wt%) heated to 50°C under light stirring,

[0175] - rinsing with tap water (at about 50°C),

[0176] - rinsing with deionized water. Step 1c: 20 coupons (aluminum alloy coupons: AA5754, from FBCG; 100mm long, 25mm wide, 3mm thick) go through each of the following steps:

[0177] - degreasing by immersion for 3mn in a 4L stainless steel bath containing NP kleen 160 from Quaker (1wt%) heated to 50°C under light stirring,

[0178] - rinsing with tap water (at about 50°C),

[0179] - etching by immersion for 1 mn in a 4L stainless steel containing NP Kleen 190 (1wt%) and Additivo 200 (0.075wt%) heated to 50°C under light stirring,

[0180] - rinsing with tap water (at about 50°C),

[0181] - rinsing with deionized water.

[0182] Step 2- the coupons are then treated by dipping for 2mn in a 4L stainless steel treatment bath, containing the polymer at 50°C and at several concentrations indicated in the Table 1 below. They are then rinsed altogether with a flow of deionized water for 1 mn and dried for 30mn at 60°C.

[0183] Step 3- the coupons are then assembled in pairs, each pair forming a so-called single lap shear “assembly”: two coupons are placed horizontally, parallel, one above the other forming an overlap of 12.5mm length and 25mm width (“overlap zone”, including one of terminal zone of each of the two coupons, namely the last 12.5mm of the 100mm length of the coupon). A structural high T curing epoxy adhesive bead (Betamate™ 1496, from DuPont and Sikapower® 494 G from Sika) is applied with a 7-bar compressed air gun on the overlap zone of the lower coupon and glass beads are sprinkled over the adhesive bead to guarantee a 0.2-0.25pm bond line. The upper coupon is then positioned on the overlap zone, thus forming a bonding zone of 12.5mm length, and 25mm width. Paper clips are used to maintain the assembly integrity before and during curing. The adhesive is then cured according to adhesive producer guidelines, typically for 40mn at 180°C. Finally, paper clips are removed.

[0184] Step 4- tensile strength test on assemblies as obtained in step 3 eventually after ageing in a cyclic test as described below. Tensile strength test

[0185] Used material: Zwick / Roell - Z50, with jaws grasping assembly tips over 2.50cm.

[0186] The upper jaw is then moved upwards at 10mm / mn till the joint breaks.

[0187] Ageing cyclic test

[0188] A cyclic ageing test is performed according to ASTM G85 - Annex 3 (SWAAT, 2011 ) in a corrosion chamber Q-FOG CRH 600L, from Q-FOG in the following conditions:

[0189] • a 30-m inute acidified salt fog spray followed by

[0190] • a 90-m inute soak at >98% relative humidity under the following conditions:

[0191] • Chamber temperature - constant 49°C

[0192] • Air saturator temperature - constant 57°C

[0193] • Relative humidity - >98%

[0194] • pH of fall out solution - 2.8 - 3.0

[0195] • Volume of fall out solution - 1 .0 - 2.0 ml / 80cm2 / hour

[0196] • Exposure period - 1000 hours

[0197] After the exposure period is completed, the assemblies are washed down with lukewarm water to remove and neutralize excess acid and any remaining salt residues. All assemblies are then air dried using forced ambient temperature before being for submitted to lap-shear tensile testing.

[0198] In a first series, performances of terpolymers containing 8, 20, 30 and 40mol% of IA were compared at 3 distinct concentrations (50, 500, 1 ,000ppm) with Sikapower® 494G. They were tested versus blanks (no cleaning nor conversion, cleaning but no conversion).

[0199] The conditions used in steps 1 and 2 are summarized Table 2 below.

[0200] Table 2: Conditions used for steps 1 and 2

[0201] Below are performances before ageing, after ageing, and the ratio between values after ageing and values before ageing, called “retention” (Tables 3-6):

[0202]

[0203]

[0204] Table 4: Maximum LOAD

[0205]

[0206] Table 5: ENERGY measured at the maximum load

[0207]

[0208] Table 6: FACIES after tensile test

[0209] (c): cohesive fracture

[0210] (~c): rather cohesive fracture

[0211] (a): adhesive fracture

[0212] Compared to the controls, polymers containing 8mol% of IA, and especially polymers containing 20mol% of IA, make the adhesive bond resist better to ageing (the maximum load at break is increased as well as the strain and energy) and improve the cohesivity of the fracture. In a second series of tests, coupons were treated as above (steps 1 and 2) and then bonded with Betamate™ 1496.

[0213] The conditions used in steps 1 and 2 are summarized Table 7 below and the performances are reported in Tables 8-11 below.

[0214] Table 7: conditions used for Step 1 and Step 2

[0215] Table 8: STRAIN measured at the maximum load

[0216] Table 9: Maximum LOAD

[0217] Tab e 10: ENERGY measured at the maximum load

[0218] Table 11 : FACIES after tensile test

[0219] (c): cohesive fracture

[0220] (~c): rather cohesive fracture

[0221] (c / a): significantly adhesive fracture

[0222] (a): adhesive fracture

[0223] Compared to the controls, polymers containing MGA units, including the polymers containing 8mol% of IA, make the adhesive bond resist better to ageing (the maximum load at break is increased as well as the strain and energy) and improve the cohesivity of the fracture.

[0224] In a third series of tests, coupons were treated as above (steps 1 and 2) and then bonded with Betamate™ 1496.

[0225] The conditions used in steps 1 and 2 are summarized in Tables 12a and 12b below and the performances are reported in Tables 13-16 below.

[0226] Table 12a: conditions used for Step 1 and Step 2

[0227] Table 12b : conditions used for Step 1 and Step 2

[0228] Table 13: Maximum STRAIN measured at the maximum load

[0229] Table 16: FACIES after tensile test

[0230] (c): cohesive fracture

[0231] (~c): rather cohesive fracture

[0232] (a): adhesive fracture

[0233] Conclusion:

[0234] Whatever the process used to degrease and etch the substrates, P-free poly(AA- co-IA) provide performances similar to the reference, poly(acrylic acid-co-vinyl phosphonic acid) in terms of strain, maximum load and energy at break and similar facies after ageing. The polymer containing the triacid, poly(AA-co-MAA-co-MGA- BTA) performs at least as well as the reference in spite of its lower dosage in the bath (1 ,000ppm versus 1 ,530ppm for the reference polymer).

[0235] In a fourth series of tests, the use of polymers in conversion coatings to treat metal substrates prior to coating them with paints was evaluated as described below.

[0236] Preparation of panels: Tests have been performed on aluminum alloy panels (AA3003, from Q-Panel), with usual lab equipment (heater, stirring, beakers, oven, ... ), a powder coating installation (GEMA) , a corrosion chamber (Q-FOG CCT 600, from QFOG), a automatic cupping tester (SP4500, from TQC), a impact tester (from TQC).

[0237] Step 1- Cleaning

[0238] It was made by dipping each panel to be tested in a mild alkaline cleaning bath, which was typically a 2L bath made by diluting a commercially available formulation, Bonderite C-AK 414, available from Henkel (60g of Bonderite C- AK 414 into 1 ,940g of water). The panel was dipped in the cleaning bath for 5 min under stirring (500rpm) at 50°C. The panel was then rinsed with over-flowing de-ionized water for 30s.

[0239] Step 2- Etching

[0240] The cleaned panel was further processed in an acid pickling bath, which typically was a 2L bath made by diluting a commercially available formulation, Bonderite M-NT 2040, available from Henkel (40g of Bonderite M-NT 2040 into 1 ,960g of water). The panel was dipped in the acid pickling bath for 3 min under stirring (500rpm) at 30°C. The panel was then further rinsed with over-flowing deionized water for 30s.

[0241] Step 3- Treatment

[0242] Surface treatment was performed at 2L-scale: tests were done without any polymer in the conversion bath (blank), with polymers according to the invention and with a well established P-based polymeric additive, AddibondTM021 , in conditions detailed Table 17.

[0243] Table 17: conditions used for Step 3

[0244] The surface treatment was performed by dipping the panels obtained after steps 1 and 2 in the conversion baths for 2.5min at 25°C. The panels were then rinsed with over-flowing de-ionized water for 30s and dried for 15m in in a oven at 120°C.

[0245] Step 4- Painting:

[0246] Each panel was then painted with a polyarylate powder paint from AKZO Nobel (Interpon A4740), which is widely used in wheel market and spec-in by OEMs. The painted panels were cured at 180°C for 25min with 80-120pm film thickness.

[0247] Performances evaluation:

[0248] Corrosion resistance and paint adhesion performances were assessed as follows:

[0249] Corrosion Tests:

[0250] Corrosion Test 1 : Copper Accelerated Salt Spray (CASS) Test An “X” scribe was made on each Panel as described in ISO 17872 (First Edition, 2007-03-01 ); the panels were then placed in a CASS chamber for 240h: T=50(+ / - 2)°C, [NaCI] = 50(+ / - 5)g / L, [Cucl2]=0.2g / L and pH = 3.1 -3.3, adjusted with glacial acetic acid (ISO 9227). The maximum size of blisters on each side of the “X” scribe was measured and the average of the maximum on the left and the maximum on the right of each scribing line was calculated.

[0251] Corrosion Test 2 : Filiform Test

[0252] Each panel was tested according to protocols described in PSA B15 5260:

[0253] • Scribing protocol: as described in ISO 17872 (First Edition, 2007-03-01 )

[0254] • Initial exposure: 72h in a CASS chamber as described in ISO 9227 (Fourth Edition, 2017-03)

[0255] • Panel rinsing: with de-ionized water for 5min

[0256] • Final exposure: 1000 hours in a climatic chamber in the following conditions: atmosphere: air; relative humidity: 60%; temperature: 25°C.

[0257] Quotations were carried out at the end of the 1 ,000h exposure by drawing on each side of the score mark lines which fix the maximum detachment observed. The representative value of the corrosion I detachment at the score mark is the maximum perpendicular length between the quotation line and score mark line.

[0258] Corrosion tests results are gathered Table 18.

[0259] Paint Adhesion Tests:

[0260] All tests described below are wet adhesion tests: the painted samples were aged in boiling water under pressure for 4 hours in a pressure cooker, before being submitted to the tests listed below.

[0261] 1. Cupping Test This test was performed with an automatic cupping test to characterize deep- drawing capability of paint film as described in ISO 1520 (Third Edition, 2006- 11 -15). A steel ball was pressed into the panel which was held in fixed position, and slowly deformed the paint film at a steady rate of 0.2mm / s until reaching the maximum depth of 6.2cm. The surface damage degree is done based on an evaluation grid presented in Appendix A.

[0262] 2. Impact Test

[0263] Following ISO 6272-2 (Second edition, 2011 -08-15) standard process, a weight puncher was dropped from 1 ,0m to strike the painted panel from front to deform both coatings and substrates. The surface damage degree from front and back side is done based on an evaluation grid presented in Appendix B.

[0264] 3. Cross-hatch Test:

[0265] 2 types of crosshatch tests were employed according to ISO 2409 (Third edition 2007-05-15):

[0266] Type 1 : cuts, across the paint film, down to the substrate, were formed to get 10*10 lattice patterns using a cross-hatch cutter. The test area was then brushed to remove any loose film particles and a 3MTMadhesion test tape was firmly pressed across the crosshatched area. The tape was then quickly peeled away to reveal the amount of coating lifted off by the test tape. The crosshatched test area was then visually compared to ASTM D33359.

[0267] Type 2: A 15*15 parallel lattice pattern was first cut to form a checkerboard pattern and another 15*15 lattice patterns were cut into the checkerboard diagonally.

[0268] Paint adhesion tests results are reported Table 19.

[0269] Appendix A Damage scale for evaluation after cupping test

[0270] Appendix B

[0271] Damage scale for evaluation after impact (front) test

[0272] Table 18: Corrosion test results 5

[0273] Table 19: Wet paint adhesion test results (painted panels aged for 4h in a pressure cooker) These results show that, when the P-free polymers according to the invention are added during the conversion step, they improve both corrosion resistance and wet paint adhesion performances (comparison test 1 and test 2). In addition, the performances of these polymers are approaching corrosion resistance performances of well established P-based polymers while completely matching their performances in wet paint adhesion.

[0274] In a fifth series of test, Polymer 5 was put in a latex formulation as detailed in Table 20 below.

[0275] Table 20

[0276] This latex was applied on a Gardobond® OE HDG galvanized steel substrate, precleaned with a Addikleen™ T2 KD cleaning bath, as follows:

[0277] Bath preparation: Cleaning procedure:

[0278] Two metallic panels were immersed in the bath at 30°C, one after the other, under stirring during 5min then rinsed with distilled water and dried in a oven at 50°C for 5min. Before application the panels were kept in absolute ethanol. Application procedure in a controlled environment (23°C + / - 2°C and 50%RH + / - 5%): The panels were removed from absolute ethanol and dried. After ethanol evaporation, a manual applicator was used to apply the paint on the metallic panels. The paint film was dried for 24h before adhesion testing. The thickness of the dried film was about 50pm

[0279] It was then tested according to standard ISO 2409 (cross-cut test) in order to assess its resistance to separation from the substrate. According to this standard, a pressure sensitive adhesive (Elcomoter® 99 adhesive tape) is used to remove the pieces of paint which are loose (the case being); a value of 0 stands for outstanding performances and a value of 5 for poor performances.

[0280] A value of 0.4 (average of the 3 crosses on each panel) was obtained both in wet & dry conditions. “Dry conditions” means the adhesion test was performed after 24h of drying in a controlled environment (see application procedure). For the wet conditions, a wet tissue was put in contact with the crosses during 30m in and then removed. The removal of the loose paint with the adhesive is made 30m in later (this procedure is following ISO 2812-3). By comparison, a reference paint (same paint without adhesion promoter) tested in the same conditions gave an average value of about 3.5 also both in wet & dry conditions.

[0281] SECOND TEST CAMPAIGN

[0282] Polymers 13 and 14 synthesis and characterization:

[0283] The HTA monomer was synthesized through a 2-step process as described below:

[0284] Hex-5-ene-1 ,3,5-tricarboxylic acid (HTA) hyl acrylate and

[0285] The triester was obtained following the process described for the preparation of alkyl acrylate dimer (Ref. WO 2023 / 066829). After this catalytic first step, a distillation under vaccum has been performed to obtain in good purity the dimer product. The remaining distillation residue was mainly composed of methyl acrylate oligomers.

[0286] In order to obtain the desired triester, two successive distillations were performed using a wiped film evaporator apparatus.

[0287] First, 900g of distillate residue was introduced at 5g / min rate, 190°C and under 2mbar pressure. This first feeding allowed to remove all the heavy oligomers and salts residue, thus obtaining a mixture (605g) of remaining dimer, trimer and quadrimer. This fraction was then distillated at 5g / min rate, 150°C and under 25mbar pressure, allowing us to obtain 285g of a purified fraction in trimer (>90% by1H NMR).

[0288] Step 2: Triester hydrolysis to afford diacid+triacid mixture.

[0289] H+cat.

[0290] In a 1 L double-jacketed reactor equipped with a mechanical stirrer, a short path distillation bridge connected to a 500mL round bottom flask and a temperature probe were added:

[0291] - 275g of the mixture obtained in step 1 above.

[0292] - 259m L of water

[0293] - 0.138g of hydroquinone. The mixture was then allowed to stir at 450 rpm and 5.8mL of H2SO4 (98%, 10.7g, 10mol% with respect to the reactants) was progressively added into the mixture while monitoring for the exotherm.

[0294] The reaction mixture was then allowed to stir at 130°C in order to carry out the hydrolysis and to distillate out the formed methanol by-product (which distillates along with H2O). Over the course of the distillation, an additional amount of water was progressively added into the reactor in order to compensate water loss through the distillation. After 16h00 stirring at 130°C,1H NMR analysis showed complete conversion of the ester to the acid. In total 304g of water has been added into the reactor and 573g of distillate has been collected. The temperature of the reaction mixture was then cooled down at 80°C and 28.4g of NaOHaq (35 wt%) (2 eq. wrt. H2SO4) were added into the mixture for catalyst neutralization (pH~2.5).

[0295] The solution was then allowed to cool down at room temperature. Diisopropylether (200m L) was then added allowing recrystallization of the triacid product to occur. The solid was then filtered out and washed with diisopropyl ether (3*100mL). The solid was then dried at 50°C to obtain a white solid, Hex-5-ene-1 ,3,5-tricarboxylic acid (HTA).

[0296] The BTA monomer synthesis protocol described above was improved to produce a higher BTA / MGA ratio than in the monomer described in the FIRST TEST CAMPAIGN:

[0297] This monomer (mixture) was prepared in a 2-step process:

[0298] Step 1 : Phosphine catalyzed cross-coupling between methyl acrylate and dimethyl maleate.

[0299] CO2Me CO2Me

[0300] Me02C\^+<2^COoMe - *■ MeO2C J CO2Me cat. If fBuOH11

[0301] In a 1 L double jacketed reactor equipped with a mechanical stirrer, a condenser and a temperature probe were added at room temperature:

[0302] - 217.4g of methyl acrylate (227.4mL, 2.5mol). - 375.3g of dimethyl maleate (326.4mL, 2.5mol).

[0303] - 108.1 g of f-BuOH (138.5mL, 1.46mol).

[0304] The solution was then allowed to stir at 400 rpm and heated at 60°C.

[0305] Then, 189g of bis(diethylamino)phenylphosphine (10% in solution in anisole, 200mL, 0.075mol, 1.5mol% wrt. reactants) were added over 6h20.

[0306] The solution was then allowed to stir at 60°C and the reaction progress was followed up thanks to1H NMR analysis.

[0307] After 7h00 reaction time at 60°C, NMR analysis on the crude indicated the following conversion levels for the reactants:

[0308] - Methyl acrylate: 90%

[0309] - Dimethyl maleate: 53%

[0310] The molar ratio between methyl acrylate dimer and methyl acrylate + dimethyl maleate cross-coupling adduct was 1 :2 (diestertriester).

[0311] The solvents as well as the unconverted methyl acrylate and dimethyl maleate / fumarate reactants were then removed through vacuum distillation. In order to distillate the desired trimester product, final distillation parameters were set at 175°C / 3mbar. This allowed to recover 232.4g of a mixture composed of 88mol% of trimer and 12mol% of dimer. is to afford diacid+triacid mixture.

[0312] In a 1 L double-jacketed reactor equipped with a mechanical stirrer, a short path distillation bridge connected to a 500mL round bottom flask and a temperature probe were added:

[0313] 146.2g of the mixture obtained step 1 above.

[0314] 155mL of water

[0315] 0.073g of hydroquinone. The mixture was then allowed to stir at 450 rpm and 3.5mL of H2SO4 (98%, 6.8g, 10mol% with respect to the reactants) were progressively added into the mixture while monitoring for the exotherm.

[0316] The reaction mixture wa then allowed to stir at 130°C in order to carry out the hydrolysis and to distillate out the formed methanol by-product (which distillates along with H2O). Over the course of the distillation, an additional amount of water was progressively added into the reactor in order to compensate water loss through the distillation. After 19h00 stirring at 130°C,1H NMR analysis showed complete conversion of the ester to the acid. In total 316g of water has been added into the reactor and 454g of distillate has been collected. The temperature of the reaction mixture was then cooled down at 80°C and 17g of NaOHaq (35 wt%) (2 eq. wrt. H2SO4) were added into the mixture for catalyst neutralization (pH~2.5).

[0317] The solution was then allowed to cool down at room temperature. Diisopropylether (200mL) was then added allowing recrystallization of the polyacid products to occur. The solid was then filtered out and washed with diisopropyl ether (2*100mL). The solid was then dried under vacuum at 60°C (1 Ombar) to obtain 54.4g of a white solid containing 90wt% of triacid (But-3-ene-1 ,2,3-tricarboxylic acid) and 10wt% of diacid, respectively 87 mol% of BTA and 13% mol% of MGA.

[0318] Polymer 13 was prepared by polymerization in water solution, initiated with an azoic initiator at 75°C. In a reactor, 6.11 grams of AA (99% purity), 14.58 grams of HTA (83% purity), and 1.585 grams of V501 (4,4'-Azobis(4-cyanovaleric acid), CAS N° 2638-94-0, 99% purity) were added in the presence of 14.14 grams of water. The mixture was then neutralized with 27.617 grams of a 30% caustic soda solution, keeping the temperature below 30°C. The polymerization was then carried out at 75°C for 5 hours. A conversion of 98% for HTA and 99% for AA was determined by1H NMR. Molecular weights were determined by size exclusion chromatography (SEC) coupled with a Rl and a multi-angle light scattering diffusion (MALLS) detector. Results are reported Table 21 . Polymer 14 was prepared by polymerization in water solution, initiated with an azoic initiator at 75°C. In a reactor, 9.214 grams of AA (99% purity), 20.099 grams of BTA (79% purity), and 2.389 grams of V501 (99% purity) were introduced. The mixture was then neutralized with 41 .63 grams of a 30% caustic soda solution, keeping the temperature below 30°C. The polymerization was then carried out at 75°C for 10 hours. A conversion of 79% for BTA and 91 % for AA was determined by1H NMR. Molecular weights were determined by size exclusion chromatography (SEC) coupled with a Rl and a multi-angle light scattering diffusion (MALLS) detector. Results are reported Table 21 .

[0319] Table 21 : polymers used for the tests

[0320] In a first series of experiments, the polymers according to the invention were used to treat Aluminum substrates prior to bonding with adhesives. They are introduced into the conversion bath.

[0321] Coupons are treated like described in the FIRST TEST CAMPAIGN; more details figure in Table 22 below.

[0322]

[0323] Table 22: conditions used to treat substrates

[0324] Coupons are then assembled with Betamate™ 1496 and tested like described in the FIRST TEST CAMPAIGN. Performances are reported Tables 23-26 below.

[0325] Table 23 : Maximum LOAD

[0326] Table 25: FACIES after tensile test

[0327] (c): cohesive fracture

[0328] (~c): rather cohesive fracture (a): adhesive fracture

[0329] Conclusion:

[0330] The polymers according to the invention perform as well as well-known P-based polymers such as Addibond™ 021 , but without containing Phosphorous. It is also noteworthy that for each polymer tested, the variation in concentration, from 100 and 1500 ppm active matter, has no influence on performances. Such a tolerance means the bath management would be lighter.

[0331] In a second series of experiments, the polymers according to the invention were used to treat Aluminum substrates prior to bonding with adhesives. They were not introduced into the conversion bath but in the rinse that follows the conversion step, also called the post-conversion rinse, or “passivation”.

[0332] In the examples below, the conversion step is performed with a commercially available concentrate, containing hexafluorides and especially Titanium hexafluoride (namely Bonderite® M-NT 400).

[0333] The conditions used to treat the aluminum coupons are summarized in Table 26 below and the performances are reported in Tables 27 - 30 below. Table 26: conditions used to treat substrates Conversion Process CP1: Bonderite® M-NT 400, 2% dilution rate, 30s immersion, 40°C

[0334] Conversion Process CP2: Bonderite® M-NT 400, 0.5% dilution rate, 90s immersion, 40°C

[0335] Conversion Process CP3: Bonderite® M-NT 400, 0.5% dilution rate, 30s immersion, 40°C

[0336] Passivation Process PP1: Polymer 3b WOOppm, 90s, 40°C Passivation Process PP2: Polymer 3b WOOppm, 3s, 40°C

[0337]

[0338] Table 27: Maximum STRAIN measured at the maximum load

[0339] Table 28: Maximum LOAD

[0340] Table 29: ENERGY measured at the maximum load

[0341] Table 30: FACIES after tensile test

[0342] (c): cohesive fracture (~c): rather cohesive fracture

[0343] (a): adhesive fracture

[0344] Conclusion: The addition of polymers according to the invention in the passivation that follows a conversion step with hexafluorides results into performances which are more robust: the average strain, force and energy at break are higher while the standard deviations are lower than compared to the conversion step alone. In addition, the facies after ageing are also improved (tests 6-11 ) compared with conversions alone with no passivation (tests 3-5).

[0345] The addition of the polymers in post-conversion rinse allows to compensate for variations in performances coming from variations in conversion coating conditions, and especially losses of performances due to lower concentrations, shorter contact times...

[0346] In a third series of experiments, the polymers according to the invention have been added into conversion baths to treat aluminum substrates prior to coating them with powder coats.

[0347] Preparation of panels:

[0348] Tests have been performed on aluminum alloy panels (AA3003, from Q-Panel), with usual lab equipment (heater, stirring, beakers, oven, ... ), a powder coating installation (GEMA) , a corrosion chamber (Q-FOG CCT 600, from QFOG), a automatic cupping tester (SP4500, from TQC), a impact tester (from TQC).

[0349] Step 1- Cleaning

[0350] Same as above (FIRST TEST CAMPAIGN, Fourth series of tests).

[0351] Step 2- Etching

[0352] Same as above (FIRST TEST CAMPAIGN, Fourth series of tests).

[0353] Step 3- Treatment

[0354] Surface treatment was performed at 2L-scale by dipping the panels obtained after steps 1 and 2 in the conversion baths for 2.5min at 25°C. The panels were then rinsed with over-flowing de-ionized water for 30s and dried for 15min in a oven at 120°C.

[0355] Blank tests were done without any polymer in the conversion bath (Test 1 ). Copolymers according to the invention were tested in conditions detailed Table 31 (Tests 2-5) and compared to a widely used P-based polymeric additive tested as reference (Addibond™ 021 , Test 6). Terpolymers according to the invention were tested in the same conditions (Tests 7-10).

[0356] Table 31: conditions used for Step 3

[0357] Step 4- Painting:

[0358] Each panel was then painted with a polyacrylate powder paint from AKZO Nobel (Interpon A4740, clear coat), which is widely used in the Aluminum wheels market. The painted panels were cured at 180°C for 25 min, yielding 80-120pm film thickness.

[0359] Performances evaluation:

[0360] Corrosion resistance and paint adhesion performances were assessed as follows:

[0361] Corrosion Tests: Corrosion Test 1 : Copper Accelerated Salt Spray (CASS) Test

[0362] An “X” scribe was made on each Panel as described in ISO 17872 (First Edition, 2007-03-01 ); the panels were then placed in a CASS chamber for 480h: T=50(+ / - 2)°C, [NaCI] = 50(+ / - 5)g / L, [Cucl2]=0.2g / L and pH = 3.1-3.3, adjusted with glacial acetic acid (ISO 9227). The maximum size of blisters on each side of the “X” scribe (i.e. on the 4 branches) was measured and the average of the maximum on the left and the maximum on the right of each scribing line (branch) was calculated.

[0363] Corrosion Test 2 : Filiform Test

[0364] Each panel was tested according to protocols described:

[0365] • Scribing protocol: as described in ISO 17872 (First Edition, 2007-03-01 )

[0366] • Initial exposure: 96h in a CASS chamber as described in ISO 9227 (Fourth Edition, 2017-03)

[0367] • Panel rinsing: with de-ionized water for 5 min

[0368] • Final exposure: 720 hours in a climatic chamber in the following conditions: atmosphere: air; relative humidity: 60%; temperature: 80°C.

[0369] Quotations were carried out at the end of the 720 hours exposure by drawing on each side of the score mark lines (branches of the “X” scribe) which fix the maximum detachment observed. The representative value of the corrosion I detachment at the score mark is the maximum perpendicular length between the quotation line and score mark line.

[0370] Corrosion tests results are gathered Table 32.

[0371] Paint Adhesion Tests:

[0372] All tests described below are wet adhesion tests: the painted samples were aged in boiling water under pressure for 4 hours in a pressure cooker, before being submitted to the tests listed below. 1. Cupping Test

[0373] Before cupping test application, the painted samples were formed to get 10*10 lattice patterns using a cross-hatch cutter. Then the cupping test was performed at a crosshatched area with an automatic cupping test to characterize deep-drawing capability of paint film as described in ISO 1520. A steel ball was pressed into the panel which was held in fixed position, and slowly deformed the paint film at a steady rate of 0.2mm / s until reaching the maximum depth of 6.2cm. The surface damage degree is done based on an evaluation grid presented in Appendix A bis.

[0374] 2. Impact Test

[0375] Same as above (FIRST TEST CAMPAIGN, Fourth series of tests).

[0376] 3. Cross-hatch Test:

[0377] Same as above (FIRST TEST CAMPAIGN, Fourth series of tests).

[0378] Paint adhesion after cupping were assessed using the grid provided Appendix A bis. The other paint adhesion performances were assessed using the same protocols as before (FIRST TEST CAMPAIGN, Fourth series of tests).

[0379] All paint adhesion results are gathered Table 33.

[0380] Appendix A bis

[0381] Damage scale for evaluation after cupping test

[0382] Table 32: Corrosion test results

[0383] Table 33: Wet paint adhesion test results (painted panels aged for 4h in a pressure cooker)

[0384] Conclusion:

[0385] These results show that, when the P-free polymers according to the invention are added during the conversion step, they improve both corrosion resistance and wet paint adhesion performances (comparison test 1 and test 2). In addition, the performances of these polymers are approaching and sometimes matching performances of well established P-based polymers.

[0386] In a fourth series of experiments, copolymers according to the invention have been added into conversion baths to treat Cold Rolled Steel substrates prior to coating them with powder coats.

[0387] • Substrate: Standard cold roll steel panels

[0388] Q-PANEL R46 CRS

[0389] • Alkaline degreasing: With an alkaline degreaser, immersion for 5 min at55 °C.

[0390] Addikleen™ T4 KD (from Syensqo) 0.3 wt.% as is

[0391] KOH 0.25 wt.% as active

[0392] Na2P2O? 0.13 wt. % as active

[0393] K3PO4 0.25 wt.% as active • Rinse after degreasing: With deionized water for about 1 min.

[0394] • Conversion: Dip the degreased metal surface in a circulating conversion bath at RT for 3 min.

[0395] H2ZrFe « 250 ppm as is (in which Zr element « 110 ppm)

[0396] Polymers added into the bath, at 120 ppm as active matter

[0397] Bath pH adjusted to about 4.5 by Na2COs

[0398] • Rinse after conversion: With deionized water for about 30 s.

[0399] • Drying: In an oven under 105 °C for 5 - 10 min.

[0400] • Powder coating: Apply powder coat with automatic powder spray equipment according to the requirements in the powder coat TDS.

[0401] AkzoNobel Interpon 700, thickness 60 - 70 pm, cured under 190 °C for 10 min.

[0402] • Corrosion test: Neutral salt spray (NSS) according to ISO 9227 (Fourth Edition, 2017-03) with the following procedure: o Scribing: One single scribe (6 - 7 cm) deep down to the metal surface was made at the center of the painted metal substrate by the ‘vanlaar’ tool (Erichsen scratching tool Model 426, tip diameter 0.5 mm) o Corrosion: Place the panels in neutral salt spray (Q-FOG cyclic corrosion testers) for 504 hrs or 1008 hrs. o Remove the salt and rust on the test panels afterwards, and condition the test panel under room temperature for at least 24 hrs. o Remove the loose paint along the scribe, measure and calculate the average one-side delamination. o 3 repeated samples are made for each of the variations. Evaluate the corrosion resistance with the average one-side delamination results of the 3 samples.

[0403] • Dry paint adhesion: Cross-hatch according to ISO 2409 o A cross-hatch area is made by 6 vertical and 6 horizontal scribes with 1 mm spacing with a sharp knife on the powder coat down to the metal substrate. o 3 cross-hatch areas are made in 3 different places on one test panel o Remove the loose paint with adhesive tape (Tesa 4124 high tack PVC tape) as much as possible. o Grade the residue pattern in comparison to the standard patterns listed in ISO 2409. o 3 repeated panels are made for each of the variations. Evaluate the dry paint adhesion with the average results of 9 dry cross-hatch results.

[0404] • Wet paint adhesion: Cross-hatch according to ISO 2409 according to the following procedure: o A cross-hatch area is made by 6 vertical and 6 horizontal scribes with 1 mm spacing with a sharp knife on the powder coat down to the metal substrate. o 3 cross-hatch areas are made in 3 different places on one test panel o Immerse the panel with 3 cross-hatch areas in boiling deionized water for 2 hrs. o Remove the loose paint with adhesive tape (Tesa 4124 high tack PVC tape) as much as possible. o Grade the residue pattern in comparison to the standard patterns listed in ISO 2409. o 3 repeated panels are made for each of the variations. Evaluate the wet paint adhesion with the average results of 9 dry cross-hatch results.

[0405] Results are gathered Table 34.

[0406]

[0407] Table 34: Corrosion test results and paint adhesion tests results

[0408] Conclusion:

[0409] Considering the entire set of performances (half delamination after exposure to a corrosive environment, dry paint adhesion and wet paint adhesion), the addition of polymers according to the invention into a conversion bath containing hexafluorides proves to be beneficial.

[0410] In a fifth series of experiments, polymers according to the invention have been added into conversion baths to treat CRS prior to coating them with powder coats, according to the same protocol as above (4thseries of experiments). Results are reported in Table 35 below.

[0411] Table 35: Corrosion test results and paint adhesion tests results

[0412] Conclusion:

[0413] The addition of polymers according to the invention into the conversion results in a significant improvement of both corrosion resistance and paint adhesion.

[0414] In a sixth series of experiments, the polymers according to the invention have been added in conversion coatings using a dry-in-place processes, meaning the drying step comes next right after the conversion step. Of particular importance, are processes where the conversion coat is applied to the metal, through roll coating for example in the case of coil processes. These processes involve cleaning steps, rinses, a conversion step, a drying step and coating steps (coating, curing).

[0415] • Substrate: Standard hot-dip galvanized panels GARDOBOND® HDG

[0416] • Alkaline degreasing: Dip in an alkaline degreaser for 5 min under room temperature.

[0417] Henkel C-AK 909, diluted by 50 g / L

[0418] • Rinse after degreasing: With deionized water for about 1 min.

[0419] • Conversion: Use a 10 pm wire rod to apply the conversion coating onto the degreased panels, and cure the conversion coating under PMT 80 °C for 90 s. The polymers according to the invention have been introduced into two types of conversion coats according to the following procedure: o CrHIconversion coat

[0420] H2TiFe 6.8 wt.% as active

[0421] H3PO4 3.5 wt.% as active

[0422] Polymer 0.2 wt% as active

[0423] Diluted by 30% o Cr-free conversion coat

[0424] H2ZrF6 1 .3 wt.% as active

[0425] Cr(NO3)31 .2 wt.% as active

[0426] Polymer 0.2 wt.% as active

[0427] Diluted by 10%

[0428] • Primer: Use a wire rod to apply the primer on the conversion coating and cure it according to the requirements in corresponding TDS.

[0429] Beckers DE-216-98602, dry film thickness ~5 pm, curing under PMT 232 °C for 90 s

[0430] • Top coat: Use a wire rod to apply the top coat on the conversion coating and cure it according to the requirements in corresponding TDS.

[0431] Beckers DJ-228-88071 , dry film thickness ~15 pm, curing under PMT 232 °C for 90 s

[0432] • Corrosion test: Copper accelerated salt spray (CASS) according to ISO 9227 (Fourth Edition, 2017-03) o Scribing: One single scribe (6 - 7 cm) deep down to the metal surface was made at the center of the painted metal substrate by the ‘vanlaar’ tool (Erichsen scratching tool Model 426, tip diameter 0.5 mm) o Corrosion: Place the panels in neutral salt spray (Q-FOG cyclic corrosion testers) for designated duration.. o Remove the salt and rust on the test panels afterwards, and condition the test panel under room temperature for at least 24 hrs. o Remove the loose paint along the scribe, measure and calculate the average one-side delamination. o 3 repeated samples are made for each of the variations. Evaluate the corrosion resistance with the average one-side delamination results of the 3 samples. o Performances are reported in Table 36 and Table 37 below. formulations and a dry-in-place process Conclusion:

[0433] A very significant improvement of corrosion resistance and paint adhesion is achieved when the polymers according to the invention are added to the concentrate, used as such, and added to the concentrate, diluted by 20% and used as such. In addition, current technologies (AA / VPA copolymers) are not stable in this concentrate, while these polymers are, which is another added value of the polymers according to the invention.

[0434]

[0435] Table 37: Corrosion test results and paint adhesion tests results with Cr-free formulations and a dry-in-place process Conclusion:

[0436] A significant improvement of corrosion resistance and paint adhesion is also achieved by polymers according to the invention, especially when the concentrate is applied without dilution. They perform as well as well known AA / VPA polymers (like Addibond ™ 800).

Claims

CLAIMS1 . The use of a composition comprising at least one polymer P obtained by radical copolymerization of a mixture comprising(iv) acrylic acid;(v) optionally methacrylic acid; and(vi) at least one compound of formula I below:wherein:- R and R' are selected from H or a methyl group, provided at least one of R or R' is H, preferably both are H;- R1and R2are, independently from one another, H or the compound of formula (I) is in the form of a salt, with R1and / or R2being selected from the group consisting of alkali metals, alkaline earth metals, and quaternary ammonium+NR34, wherein R3are independently from one another H or methyl or ethyl;- n is an integer ranging from 1 to 4;- m is an integer ranging from 0 to 4;- Ra, Rb and Rc are, independently from one another, selected from H, a - COOR4group, an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR4group, with R4having the same definition as the one of R1and R2, preferably H; provided when Ra, Rb and / or Rc is an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR4group, then at least one of Ra, Rb or Rc is H, preferably at least two of Ra, Rb or Rc are H;for improving the bonding between a metallic surface (S1 ) and another surface (S2) through an adhesive layer.

2. The use according to claim 1, for imparting to the bonding a resistance to adhesive failure and / or for further imparting to the bonding a resistance to corrosive atmospheres and to wet atmospheres.

3. The use according to claim 1 or 2, wherein the composition is used as surface treatment of all or parts of a metallic surface (S1 ) and optionally all or parts of surface (S2) and / or as additive in the adhesive layer.

4. The use according to any one of claims 1 to 3, wherein the polymer P is obtained by radical copolymerization of a mixture consisting essentially of:(i) acrylic acid ;(ii) optionally methacrylic acid ; and(iii) at least one compound of formula I.

5. The use according to any of claims 1 to 4, wherein the polymer P is obtained by radical copolymerization of a mixture having the following molar ratio, based on the total quantity of acrylic acid, methacrylic acid and compound of formula I:- acrylic acid: from 5 to 95%, notably from 10 to 90%, preferably from 30 to 85%- methacrylic acid: from 0 to 50%, preferably from 0 to 40%, more preferably from 0 to 20%- compound of formula I: from 1 to 90%, for example from 5 to 50%, notably from 8 to 45%.

6. The use according to any one of claims 1 to 5, wherein the composition is further comprising from 10 to 75% by weight, preferably from 25 to50% by weight, based on the total weight of the composition, of compound of formula I.

7. The use according to any one of claims 1 to 6, wherein the compound of formula I is selected from the group consisting of itaconic acid, alphamethylene glutaric acid, but-3-ene-1 ,2,3-tricarboxylic acid, hex-5-ene- 1 ,3,5-tricarboxylic acid, their salts and mixtures thereof.

8. The use according to any of claims 1 to 7, wherein the metallic surface(51 ) is a surface comprising a metal selected from aluminum, steel, zinc, magnesium, titanium, copper and their alloys, or cobalt-nickel alloys, preferably a surface of aluminum or aluminum alloy.

9. A process for bonding a metallic surface (S1 ) with another surface(52), including: treating all or parts of said metallic surface (S1 ) with the composition as defined in any one of claims 1 to 7 ; and optionally treating all or parts of said second surface (S2) with the composition as defined in any one of claims 1 to 7 ; and bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces.

10. The process according to claim 9, wherein the composition is: a conversion composition; and / or a solution or a dispersion applied on the surface after having applied a conversion coating on the surface to be treated.

11. A process for bonding a metallic surface (S1 ) with another surface (S2), including: bonding the surfaces (S1 ) and (S2) via an adhesivelayer applied between the two surfaces, said adhesive layer comprising the composition as defined in any one of claims 1 to 7.

12. A process according to claim 11 , further including, before the step of bonding the surfaces S1 and S2, a step consisting in: treating all or parts of said metallic surface (S1 ) with the composition as defined in any one of claims 1 to 7 ; and optionally treating all or parts of said second surface (S2) with the composition as defined in any one of claims 1 to 7.

13. A coating or adhesion composition comprising a polymer P as defined in any one of claims 1 to 7, including but not limited to inks and paints, such as water-borne and powder paints.

14. The use of a polymer P as defined in any one of claims 1 to 7, as adhesion promoters in coatings, inks and paints (e.g., water-borne paints and powder paints), or as adhesion promoters imparting corrosion resistance in (post-)conversion coatings i.e. in any step performed prior to painting.

15. A process for bonding a paint or varnish to a metallic surface (S1 ), including : treating all or parts of said metallic surface (S1 ) with a composition comprising a polymer P as defined in any one of claims 1 to 7; and applying a paint or varnish to the surface (S1 ).

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