Schiff base oligomer

Abstract

Embodiments of the present disclosure relate to Schiff base oligomers and uses thereof. In at least one embodiment, the oligomer is represented by formula (I): 4 , R 5 , R 6 , R 7 , R 8 , R 10 , R 11 , R 12 , R 13 and R 14 Each instance of R in formula (I) is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, alkoxyl, aryloxyl, ether, and heterocyclyl. 9 Each instance of R in formula (I) is independently selected from the group consisting of alkyl, cycloalkyl, aryl, heterocyclyl, and ether. 28 and R 29 Each instance of R in formula (I) is independently selected from the group consisting of hydrogen, alkyl, and aryl. 33 Each instance of R in formula (I) is independently selected from the group consisting of alkyl, cycloalkyl, aryl, heterocyclyl, and a bond. 41 Each instance of is independently -NH- or a bond; 40 Each instance of is independently -NH- or -NH-NH-.

Description

[Technical field]

[0001] Aspects of the present disclosure relate to Schiff base oligomers and uses thereof. [Background technology]

[0002] Metals such as steel, aluminum, aluminum alloys, and galvanized metals used in the manufacture of aircraft, spacecraft, and other machines can be susceptible to corrosion. Chromates, such as the zinc salts of hexavalent chromium, have been used as corrosion inhibitors in corrosion-preventive coatings such as paints, sealants, and wash primers. It would be desirable to reduce the amount of chromate used in coatings and other applications.

[0003] Several non-chromate corrosion inhibitors have been proposed. For example, Gupta et al., "Green Schiff's bases as corrosion inhibitors for mild steel in 1 M HCl solution: experimental and theoretical approach," RSC Adv., 2016, 6, 102076-102087, discloses cysteine Schiff bases with molecular weights of 255.05 or less as corrosion inhibitors. Rasool et al., "Coordination Polymers: Preparation, Physicochemical Characterization, Thermal and Biological Evaluation of Thiosemicarbazide Polychelates," J Inorg Organomet Polym 25, 763-771 (2015), discloses Schiff base polymers complexed with Co, Ni, Cu, or Zn transition metals that have antibacterial and antifouling properties.

[0004] Overall, hexavalent chromium replacement corrosion inhibitors may have limitations compared to those containing hexavalent chromium, and their adhesion may be insufficient for the underlying substrate and the coating disposed thereon. Further, alternative corrosion inhibitors often do not meet aerospace performance requirements.

[0005] There is a need for new corrosion inhibitors that provide improved coatings for protecting metal surfaces from corrosion with little or no use of hexavalent chromium.

PRIOR ART DOCUMENTS

NON-PATENT DOCUMENTS

[0006]

Non-Patent Document 1

Non-Patent Document 2

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] Aspects of the present disclosure relate to Schiff base oligomers and their use.

MEANS FOR SOLVING THE PROBLEMS

[0008] In at least one aspect, the oligomer has the formula (I): [Chem.] represented by, wherein R 4 、R 5 、R 6 、R 7 、R 8 、R 10 、R 11 、R 12 、R 13 and R 14 each instance of is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, alkoxyl, aryloxyl, ether and heterocyclyl, R 9 each instance of is independently selected from the group consisting of alkyl, cycloalkyl, aryl, heterocyclyl and ether, R 28 and R 29 each instance of is independently selected from the group consisting of hydrogen, alkyl and aryl, R 33 each instance of is independently selected from the group consisting of alkyl, cycloalkyl, aryl, heterocyclyl and bond, R 41 each instance of is independently -NH- or a bond, and each instance of R 40 is independently -NH- or -NH-NH-, R 42 each instance of is independently -NH- or a bond, and each instance of R 43 is independently -NH- or -NH-NH-, each instance of Q is independently -CH2- or oxygen, each instance of n, m, z and t is an integer from 1 to 50, R 44 is hydroxyl, hydroxy-substituted alkyl, or has the structure: [Chem.] represented by, wherein R 1 is hydrogen or silyl, R 2 and R 3 each independently is selected from the group consisting of hydrogen, alkyl, and aryl, R 31 is selected from the group consisting of alkyl, cycloalkyl, aryl, heterocyclyl, and a bond, R 50 is -NH- or a bond, and R 32 is -NH- or -NH-NH-, R 34 is -NH- or a bond, and R 35 is -NH- or -NH-NH-, x is an integer from 1 to 50, R 30 is hydrogen, silyl, or has the structure:

Chemical formula

Mode for Carrying Out the Invention

[0009] Aspects of the present disclosure relate to Schiff base oligomers and their use. The Schiff base oligomer may have one or more silyl groups to provide bonding to a metal to prevent corrosion and enhance adhesion to the metal and metal oxides. Generally, a Schiff base is a compound having the general structure R1R2C=NR' (wherein R'≠H).

[0010] In some aspects, the Schiff base oligomer includes two or more repeating units of Schiff base monomer units, and each Schiff base monomer unit has at least one thiocarbonyl group. The Schiff base oligomer may have a linking unit that links two or more repeating units of the Schiff base monomer units. For example, the linking unit may have a hydroxyl group. Alternatively, the linking unit may be a urea-containing unit.

[0011] The Schiff base oligomer may be dispersible in a solvent. The Schiff base oligomer may be a composition containing one or more metals (e.g., dispersed or ionically bonded). For example, the metal may be a cationic species of a transition metal.

[0012] In some aspects, the Schiff base oligomer functions as a film-forming coating in which the Schiff base monomer unit prevents metal corrosion. The Schiff base oligomer provides improved adhesion of the Schiff base oligomer to the surface of the metal and an increase in the concentration of the inhibitor on the surface compared to conventional corrosion inhibitors. The Schiff base oligomer can provide a sustained release or controlled release system that can provide long-term corrosion prevention by slow dissolution or slow hydrolysis of the polymer or oligomer compared to small molecule Schiff bases such as small molecule Schiff bases having a molecular weight of less than 300 Daltons.

[0013] In certain aspects, the Schiff base oligomer has a molecular weight of 300 Daltons or more, such as 500 Daltons or more, such as 1,000 Daltons or more, such as 10,000 Daltons or more, such as 15,000 Daltons or more.

[0014] The Schiff base oligomers can interact with a metal (e.g., a composition and / or a metal substrate) via a tertiary nitrogen atom and a thiocarbonyl sulfur atom. By having multiple groups on the same molecule that can interact (e.g., chelate) with the metal, when the first group interacts with, for example, the metal surface, each subsequent group can interact with a lower enthalpy loss, reducing the barrier to formation, enhancing stability, and ultimately improving the adhesion of the Schiff base oligomers compared to conventional corrosion inhibitors. Further, in examples where the Schiff base oligomers have silyl end-capping, the silyl groups can provide additional adhesion of the Schiff base oligomers to the substrate via one or more atoms of the silyl group.

[0015] In certain embodiments, the Schiff base oligomers have good adhesion to the surface of a metal (e.g., a pure metal, a metal alloy, and / or a metal oxide) and provide corrosion protection by coordination to the surface via imine, thiocarbonyl, secondary hydroxyl groups, and / or urea-containing units. Further, the secondary hydroxyl groups can react with epoxy and urethane primers to provide a bonding layer morphology. For example, the hydroxyl groups of the Schiff base oligomers can react with the isocyanate groups of the urethane primer. The oligomers serve to provide durability and provide a plurality of functional binding sites with a glass transition temperature (Tg) low enough (e.g., about -25 °C or lower) to avoid crystallization.

[0016] Adhesion can be determined as described in Rasool et al., J. Inorg. Organomet Polym 2015, Vol. 15, pp 763 - 771, which provides detailed IR (Table 2), 1H NMR (Section 5.3), and electronic spectra (Sections 5.4 and Table 3) of the free Schiff base complexes and the related metal complexes. The data confirm the formation of metal bonds to the nitrogen and oxygen atoms in the complexes. The IR stretching frequencies shift by 8 to 25 cm -1 upon formation of the metal - nitrogen or metal - oxygen bonds. The Schiff base is a polymeric species that forms complexes with individual metal atoms.

[0017] In certain embodiments, the Schiff base oligomer comprises polymer thiosemicarbazone monomer units having imine and thiocarbonyl groups and one or more optional secondary hydroxyl groups and / or one or more urea-containing units for providing adhesion to the metal substrate.

[0018] The Schiff base oligomer can be reacted with an ether such as polyethylene glycol diglycidyl ether, diglycidyl ether, or other suitable ether to enhance the dispersibility of the Schiff base oligomer. Dispersible Schiff base polymers (e.g., water-soluble, water-dispersible, water-soluble in an aqueous organic solvent blend, dispersible in an aqueous organic solvent blend, soluble in an organic solvent, dispersible in an organic solvent) have good adhesion to metal and metal oxide surfaces and provide corrosion protection by coordination to the surface via imine, thiocarbonyl / carbonyl, and / or hydroxyl groups. Further, hydroxyl groups such as secondary hydroxyl groups can react with epoxy and urethane primers to provide a bond layer form. For example, available secondary hydroxyl groups can react with the isocyanate of a polyurethane coating formulation. The formation of covalent bonds may be desirable for bonding to the primer. The polymer provides multiple functional binding sites, which helps to provide the required durability and has a Tg (e.g., about -25 °C or lower) low enough to avoid crystallization during use in cold environments. The Schiff substrate of the present disclosure can provide a corrosion protection coating suitable for metals that experience the temperature range encountered in civilian and defense aircraft where the outside air temperature can be -40 °F or lower at 40,000 feet.

[0019] Method for producing Schiff base oligomer A method for producing a Schiff base oligomer includes reacting a Schiff base monomer having at least one thiocarbonyl group and at least two terminal -NH2 groups with a dicarbonyl to form a first reaction product. For example, the Schiff base monomer can be thiocarbazide or thiosemicarbazide. The first reaction product has two terminal -NH2 groups. In some embodiments, the Schiff base monomer can be heated, followed by the addition of a dicarbonyl and an acid (e.g., a strong acid such as HCl) to form a reaction mixture. The reaction mixture can be cooled (and optionally cooled below ambient temperature) to form the first reaction product.

[0020] The first reaction product can be reacted with one or more epoxy - containing compounds to form a second reaction product having one or more hydroxyl groups. Alternatively, the first reaction product can be reacted with one or more isocyanate - containing compounds to form a second reaction product having one or more monomer units having one or more urea - containing linkages and thiocarbonyl groups. The reaction of the first reaction product with the epoxy - containing compound (or isocyanate - containing compound) can be carried out in the presence of a base (such as NaOH) and / or an acid (such as barbituric acid).

[0021] A Schiff base oligomer can contain two or more Schiff base monomer units. The Schiff base monomer used can be thiosemicarbazide, thiocarbazide, or any suitable thiocarbonyl-containing compound having two or more terminal (-NH2) groups. For example, a Schiff base oligomer can be prepared by reacting thiocarbazide or thiosemicarbazide with a dicarbonyl containing two or more carbonyl groups. The carbonyl containing two or more carbonyl groups is referred to herein as a "dicarbonyl". The carbonyl groups can be aldehydes, ketones, and combinations thereof. The carbonyl groups of the dicarbonyl can react with the terminal nitrogen atom of either thiocarbazide or thiosemicarbazide. The dicarbonyl can link two or more thiocarbazides or thiosemicarbazides together to form a first reaction product.

[0022] Alternatively, a Schiff base oligomer can be prepared by reacting thiocarbazide or thiosemicarbazide with a diisocyanate containing two or more isocyanate groups. The carbonyl containing two or more isocyanate groups is referred to herein as a "diisocyanate". The carbonyl groups of the diisocyanate can react with the terminal nitrogen atom of either thiocarbazide or thiosemicarbazide. The diisocyanate can link two or more thiocarbazides or thiosemicarbazides together to form a first reaction product.

[0023] The terminal amine groups of the first reaction product can react with a diepoxide to form a Schiff base oligomer. The diepoxide can enhance the dispersibility. For example, a diepoxide having a hydrophilic group can enhance the dispersibility of the Schiff base oligomer in an aqueous solvent or an aqueous organic blend solvent. For example, an epoxy having a hydrophobic group (e.g., an organic group such as alkyl, aryl, etc.) can enhance the dispersibility of the Schiff base oligomer in an organic solvent. Examples of the epoxy that can enhance the water dispersibility include, for example, phenol glycidyl ether, lauryl alcohol glycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether. In a specific embodiment, the epoxy is a low molecular weight epoxy (e.g., about 600 daltons or less) such as low molecular weight polyethylene glycol diglycidyl ether.

[0024] Alternatively, the terminal amine groups of the first reaction product can react with a diisocyanate to form a Schiff base oligomer. The diisocyanate can enhance the dispersibility. For example, a diisocyanate having a hydrophilic group can enhance the dispersibility of the Schiff base oligomer in an aqueous solvent or an aqueous organic blend solvent. For example, a diisocyanate having a hydrophobic group (e.g., an organic group such as alkyl, aryl, etc.) can enhance the dispersibility of the Schiff base oligomer in an organic solvent. Examples of the diisocyanate that can enhance the water dispersibility include, for example, methylene-bis(phenyl isocyanate) (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), naphthalene diisocyanate (NDI), methylene bis-cyclohexyl isocyanate (HMDI) (hydrogenated MDI), and isophorone diisocyanate (IPDI), etc.

[0025] In some embodiments, the Schiff base oligomer is a silyl-terminated Schiff base oligomer. The Schiff base oligomer can have one or more terminal amine groups. The one or more terminal amine groups can be reacted with a silyl-containing end-capping compound to obtain a silyl-terminated Schiff base oligomer. For example, the silyl-containing end-capping can have a reactive moiety (e.g., a leaving group such as an epoxy group or a halogen). In some examples, the silyl-containing end-capping is an epoxy-containing silyl-containing end-capping. The silyl-terminated Schiff base oligomer can provide additional adhesion ability to the substrate.

[0026] Method for disposing a Schiff base oligomer on a substrate In some embodiments, the method includes applying a Schiff base oligomer (e.g., dispersed in a solvent) to a substrate such as a metal substrate. The Schiff base oligomer can be applied onto the metal by spraying, brushing, roller coating, or dipping, for example, for a complete coating of the surface. Materials that can be applied by various methods enable scaling up the use of this technology. The aircraft industry may use spraying, while automotive companies may use dipping tanks for automotive frames, and railway vehicle manufacturers may use roller or brush methods. The Schiff base oligomer can be dispersible in an aqueous solvent, an organic solvent, or an aqueous organic solvent blend. The functional groups of the Schiff base oligomer can be reacted with other components, for example, to enhance its dispersibility. In comparison, small molecule Schiff bases are often solids and can often only be applied as particles.

[0027] In certain embodiments, the Schiff base oligomers provide corrosion protection over long periods of time, as determined by passing or failing the ASTM B117 salt spray exposure test for 3000 hours. The Schiff base oligomers can form a continuous film that provides corrosion prevention of the metal surface over long periods of time. The Schiff base oligomers can form a coating for preventing corrosion of the metal surfaces of aerospace vehicles, automobiles, trucks, trains, boats, ships, buildings, bridges, and other metal parts.

[0028] Schiff base oligomers In some embodiments, the Schiff base oligomers have the formula (I):

Chemical formula

Chemical formula

Chemical formula

[0029] In some embodiments, R 4 , R 5 , R 6 , R 7 , R 8 , R 10 , R 11 , R 12 , R 13 and R 14 (or R 4 ’, R 5 ’, R 6 ’, R 7 ’, R 8 ’, R 10 ’, R 11’ , R 12’ , R 13’ and R 14’ ) each instance is independently selected from the group consisting of hydrogen and C1-C5 alkyl. In some embodiments, R 4 , R 5 , R 6 , R 7 , R 8 , R 10 , R 11 , R 12 , R 13 and R 14 (or R 4 ’, R 5 ’, R 6 ’, R 7 ’, R 8 ’, R 10 ’)11’ , R 12’ , R 13’ and R 14’ ) each instance is hydrogen. In some embodiments, R 28 or R 29 (or R 2 and R 3 ) each instance is independently selected from the group consisting of hydrogen and C1-C5 alkyl. In some embodiments, R 28 or R 29 (or R 2 and R 3 ) each instance is hydrogen. In some embodiments, each instance of Q is oxygen.

[0030] In some embodiments, when R 41 is -NH-, R 40 is -NH-, and / or when R 41 is a bond, R 40 is -NH-NH-. In some embodiments, when R 42 is -NH-, R 43 is -NH-, and / or when R 42 is a bond, R 43 is -NH-NH-.

[0031] In some embodiments, when R 50 is -NH-, R 32 is -NH-, and when R 50 is a bond, R 32 is -NH-NH-. In some embodiments, when R 34 is -NH-, R 35 is -NH-, and when R 34 is a bond, R 35 is -NH-NH-.

[0032] In some embodiments, each instance of R 9 (or R 9’ ) is independently C1-C 10 alkyl or polyether. For example, R 9 (or R 9’It may be a polyether selected from polyethylene glycol and polypropylene glycol. Polyethylene glycol or polypropylene glycol can have a molecular weight of about 100 g / mol to about 1,000 g / mol, for example, about 400 g / mol to about 700 g / mol.

[0033] In some embodiments, R 33 (or R 31 ) each instance is a bond. In some embodiments, R 33 (or R 31 ) each instance is independently selected from C1-C 10 alkyl. In some embodiments, R 33 (or R 31 ) each instance is independently selected from phenyl. For example, phenyl is represented by the formula:

Chemical formula

Chemical formula

[0034] In some embodiments, R 30 and R 1 are hydrogen. In some embodiments, one or both of R 30 and R 1 is silyl. For example, silyl can be glycidyl ether silyl. In some embodiments, silyl is represented by the formula:

Chemical formula

Chemical formula

Chemical formula

[0035] In some embodiments, the Schiff base oligomer has the formula (II):

Chemical formula

[0036] In some embodiments, each of x, y, and z of formula (II) is the integer 1.

[0037] In some embodiments, R of formula (II) 4 、R 5 、R 6 、R 7 、R8 , R 10 , R 11 , R 12 , R 13 , R 14 , R 17 , R 18 , R 19 , R 20 , R 21 , R 23 , R 24 , R 25 , R 26 and R 27 Each instance of, R is independently selected from the group consisting of hydrogen and C1-C5 alkyl. In some embodiments, R 4 , R 5 , R 6 , R 7 , R 8 , R 10 , R 11 , R 12 , R 13 , R 14 , R 17 , R 18 , R 19 , R 20 , R 21 , R 23 , R 24 , R 25 , R 26 and R 27 Each instance of, R is hydrogen. In some embodiments, R 2 , R 3 , R 15 , R 16 , R 28 and R 29 Each instance of, R is independently selected from the group consisting of hydrogen and C1-C5 alkyl. In some embodiments, R 2 , R 3 , R 15 , R 16 , R 28 and R 29 Each instance of, R is hydrogen. In some embodiments, each instance of Q is oxygen.

[0038] In some embodiments, R of formula (II) 34 , R 37 , R 38 , R 41 , R 42and R 50 When each of them is -NH-, R 32 , R 35 , R 36 , R 39 , R 40 and R 43 are each -NH-. In some embodiments, R 34 , R 37 , R 38 , R 41 , R 42 and R 50 are bonds, R 32 , R 35 , R 36 , R 39 , R 40 and R 43 are each -NH-NH-.

[0039] In some embodiments, each instance of R 9 and R 22 in formula (II) is, independently, C1-C 10 alkyl or polyether. For example, R 9 or R 22 may be a polyether selected from polyethylene glycol and polypropylene glycol. Polyethylene glycol or polypropylene glycol can have a molecular weight of about 100 g / mol to about 1,000 g / mol, such as about 400 g / mol to about 700 g / mol.

[0040] In some embodiments, each instance of R 31 , R 33 and R 51 in formula (II) is a bond. In some embodiments, each instance of R 31 , R 33 and R 51 is independently selected from C1-C 10 alkyl. In some embodiments, each instance of each instance of R 31 , R 33 and R 51 is independently selected from phenyl. For example, phenyl has the formula:

Chemical formula

[0041] In some embodiments, R 1 and R 30 of formula (II) are hydrogen. In some embodiments, one or both of R 1 and R 30 are silyl. For example, the silyl can be glycidyl ether silyl. In some embodiments, the silyl is of the formula: [Chem.] represented by, wherein R 45 , R 46 and R 47 are independently selected from the group consisting of hydrogen and C1-C 20 alkyl, such as C1-C5 alkyl, and R 48 is selected from the group consisting of (divalent) alkyl, cycloalkyl, ether and aryl. In some embodiments, R 48 is alkyl or ether. In some embodiments, the silyl is [Chem.] or [Chem.] is.

[0042] In some embodiments, the Schiff base oligomer is of formula (III) [Chemical formula] represented by, wherein The wavy line is a line that breaks a single bond shown to indicate the connection point in the second wavy line of the oligomer represented by formula (III) (in other words, the NH group adjacent to the wavy line is attached to the carbon located at the alpha of R 14 ), R 4 R 5 R 6 R 7 R 8 R 10 R 11 R 12 R 13 R 14 R 17 R 18 R 19 R 20 R 21 R 23 R 24 R 25 R 26 and R 27 each is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, alkoxyl, aryloxyl, heterocyclyl and ether, R 9 and R 22 each is independently selected from the group consisting of alkyl, cycloalkyl, aryl, heteroaryl and ether, R 2 R 3 R 15 R 16 R 28 and R 29 each instance is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl and aryl, R 31 R 32 and R 33 each instance is independently selected from the group consisting of alkyl, cycloalkyl, aryl, heterocyclyl and bond, Each instance of n, m, p, and q is an integer independently selected from the group consisting of integers from 1 to 50, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. R 1 and R 30 each is independently selected from the group consisting of hydrogen and silyl.

[0043] In some embodiments, R of formula (III) 4 R 5 R 6 R 7 R 8 R 10 R 11 R 12 R 13 R 14 R 17 R 18 R 19 R 20 R 21 R 23 R 24 R 25 R 26 and R 27 each instance is independently selected from the group consisting of hydrogen and C1-C5 alkyl. In some embodiments, R 4 R 5 R 6 R 7 R 8 R 10 R 11 R 12 R 13 R 14 R 17 R 18 R 19 R 20 R 21 R 23 R 24 R 25 R 26 and R 27 each instance is hydrogen. In some embodiments, R 2 R 3 R 15 R 16 R 28 and R 29Each instance of is independently selected from the group consisting of hydrogen and C1-C5 alkyl. In some embodiments, R 2 , R 3 , R 15 , R 16 , R 28 and R 29 is hydrogen in each instance.

[0044] In some embodiments, each instance of R 9 and R 22 in formula (III) is independently C1-C 10 alkyl or polyether. For example, R 9 or R 22 may be a polyether selected from polyethylene glycol and polypropylene glycol. The polyethylene glycol or polypropylene glycol can have a molecular weight of about 100 g / mol to about 1,000 g / mol, such as about 400 g / mol to about 700 g / mol.

[0045] In some embodiments, each instance of R 31 , R 32 and R 33 in formula (III) is a bond. In some embodiments, each instance of R 31 , R 32 and R 33 is independently selected from C1-C 10 alkyl. In some embodiments, each instance of R 31 , R 32 and R 33 is independently selected from phenyl. For example, phenyl is of the formula:

Chemical formula

Chemical formula

[0046] In some embodiments, R 1 and R 30 of formula (III) are hydrogen. In some embodiments, one or both of R 1 and R 30 are silyl. For example, the silyl can be glycidyl ether silyl. In some embodiments, the silyl is of the formula:

Chemical formula

Chemical formula

Chemical formula

[0047] In some embodiments, the Schiff base oligomer is of formula (IV):

Chemical formula

Chemical formula

Chem.

[0048] In some embodiments of formula (IV), each instance of R 28 or R 29 (or R 2 and R 3 ) is independently selected from the group consisting of hydrogen and C1-C5 alkyl. In some embodiments, each instance of R 28 or R 29 (or R 2 and R 3 ) is hydrogen.

[0049] In some embodiments of formula (IV), when R 41 is -NH-, R 40 is -NH-, and / or when R 41 is a bond, R 40 is -NH-NH-. In some embodiments, when R 42 is -NH-, R 43 is -NH-, and / or when R 42 is a bond, R 43 is -NH-NH-.

[0050] In some embodiments of formula (IV), when R 50 is -NH-, R 32 is -NH-, and when R 50 is a bond, R 32 is -NH-NH-. In some embodiments, when R 34 is -NH-, R 35 is -NH-, and when R 34 is a bond, R 35is -NH-NH-.

[0051] In some embodiments of formula (IV), R 9 (or R 9’ ) each instance is independently C1 - C 10 alkyl or aryl. R 9 (or R 9’ ) can be C1 - C 10 cycloalkyl which is cyclohexyl. R 9 (or R 9’ ) can be aryl which is phenyl. For example, phenyl is represented by the formula:

Chemical formula

Chemical formula

[0052] In some embodiments of formula (IV), each instance of R 33 (or R 31 ) is a bond. In some embodiments, each instance of R 33 (or R 31 ) is independently selected from C1 - C 10 alkyl. In some embodiments, each instance of R 33 (or R 31 ) is independently selected from phenyl. For example, phenyl is represented by the formula:

Chemical formula

Chemical formula

[0053] In some embodiments of formula (IV), R 30 and R 1 are hydrogen. In some embodiments, one or both of R 30 and R 1 is silyl. For example, the silyl can be glycidyl ether silyl. In some embodiments, the silyl is of the formula:

Chemical formula

Chemical formula

Chemical formula

[0054] In some embodiments, the Schiff base oligomer is of formula (V):

Chemical formula

[0055] In some embodiments, each of x, y, and z of formula (V) is the integer 1.

[0056] In some embodiments of formula (V), R 2 , R 3 , R 15 , R 16 , R 28 and R 29 each instance is independently selected from the group consisting of hydrogen and C1-C5 alkyl. In some embodiments, R 2 , R 3 , R 15 , R 16 , R 28 and R 29 each instance is hydrogen.

[0057] In some embodiments, when R 34 , R 37 , R 38 , R 41 , R 42 and R 50 of formula (V) are each -NH-, then R 32 , R 35 , R 36 , R 39 , R 40 and R 43 are each -NH-. In some embodiments, when R 34 , R 37 , R 38 , R 41 , R 42 and R 50 are a bond, then R 32 , R 35 , R 36 , R 39 , R 40 and R 43 are each -NH-NH-.

[0058] In some embodiments, each instance of R 9 and R 22 of formula (V) is independently C1-C 10 alkyl or aryl. R 9 and R 22 can be C1-C 10 cycloalkyl which is cyclohexyl. R 9 and R 22 can be aryl which is phenyl. For example, phenyl has the formula: [Chemistry] or [Chemistry] is represented by, where R 60 , R 61 , R 62 and R 63 are independently selected from hydrogen and C1-C 10 alkyl. In some examples, each of R 60 , R 61 , R 62 and R 63 is hydrogen.

[0059] In some embodiments, each instance of R 31 , R 33 and R 51 in formula (II) is a bond. In some embodiments, each instance of R 31 , R 33 and R 51 is independently selected from C1-C 10 alkyl. In some embodiments, each instance of each instance of R 31 , R 33 and R 51 is independently selected from phenyl. For example, phenyl is of the formula: [Chemistry] or [Chemistry] is represented by, where R 60 , R 61 , R 62 and R 63 are independently selected from the group consisting of hydrogen and C1-C 10 alkyl. In some examples, each of R 60 , R 61 , R 62 and R 63 is hydrogen.

[0060] In some embodiments, R of formula (V) 1 and R 30 are hydrogen. In some embodiments, R 1 and R 30 are each or both silyl. For example, the silyl can be glycidyl ether silyl. In some embodiments, the silyl has the formula:

Chemical formula

Chemical formula

Chemical formula

[0061] In some embodiments, the Schiff base oligomer has the formula (VI):

Chemical formula

[0062] In some embodiments of formula (VI), R 2 , R 3 , R 15 , R 16 , R 28 and R 29 Each of which is independently selected from the group consisting of hydrogen and C1-C5 alkyl. In some embodiments, R 2 , R 3 , R 15 , R 16 , R 28 and R 29 Each of which is hydrogen.

[0063] In some embodiments, each instance of R in formula (VI) 9 and R 22 is independently C1-C 10 alkyl or aryl. R 9 and R 22 can be C1-C 10 cycloalkyl which is cyclohexyl. R 9 and R 22 can be aryl which is phenyl. For example, phenyl has the formula:

Chemical formula

Chemical formula

[0064] In some embodiments, each instance of R 31 and R 32 and R 33 in formula (VI) is a bond. In some embodiments, each instance of R 31 and R 32 and R 33 is independently selected from C1-C 10 alkyl. In some embodiments, each instance of each instance of R 31 and R 32 and R 33 is independently selected from phenyl. For example, phenyl is represented by the formula:

Chemical formula

Chemical formula

[0065] In some embodiments, R 1 and R 30 in formula (VI) are hydrogen. In some embodiments, R 1 and R 30One or both of them are silyl. For example, silyl can be glycidyl ether silyl. In some embodiments, silyl has the formula:

Chemical formula

Chemical formula

Chemical formula

[0066] Metal Schiff base oligomers may be dispersible in a solvent. The Schiff base oligomer may be a composition containing one or more metals (e.g., dispersed or ionically bonded). For example, the metal can be a cationic species of a transition metal.

[0067] The metal can be in the form of a cation or a metal salt. For example, the metal may be selected from the group consisting of alkaline earth metals, transition metals, and rare earth metal salts such as Zn, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ce, Co, Y, Bi, Cd, Pb, Ag, Sb, Sn, Cu, Fe, Ni, Li, Ca, Sr, Mg, Zr, Nd, Ba, Sc, and any combination thereof. For example, the metal may be selected from the group consisting of Zn, La, Pr, Ce, Co, Y, Ca, Sr, Ba, Sc, and Zr. The metal may be selected from at least one of Zn, Pr, and Ce. The metal may be Zn. The metal may be Ce. The metal may be Pr. Some examples of salts that can be used are nitrates, chloride salts, acetates, or any combination thereof.

[0068] It will be understood that the metal can have any suitable oxidation state. For example, the typical oxidation state of Zn is +2. The typical oxidation states of Pr are +2, +3, and / or +4. The typical oxidation states of Ce are +2, +3, and +4. It will be understood that the various combinations and groups of the above metal salts can be used in the compositions of the present disclosure.

[0069] Substrate for corrosion prevention A substrate that can be protected from corrosion by a Schiff base oligomer or a composition thereof can be any suitable substrate such as a metal substrate or a plastic substrate. A metal substrate can include any substrate material in which at least a part of its surface is metal, for example, a part of its outer surface is metal. The metal substrate may include any metal that requires protection from corrosion. The metal substrate can include a metal or alloy selected from aluminum, for example, an aluminum alloy. The metal substrate may be an alloy of aluminum and one or more metals selected from the group consisting of copper, magnesium, manganese, silicon, tin, zinc, and combinations thereof, such as an aluminum alloy. The aluminum alloy may be an alloy containing copper. The metal substrate may be a copper-containing alloy such as a copper-containing aluminum alloy. The amount of copper in the alloy may be about 1 wt% to about 20 wt%, about 1 wt% to about 18 wt%, about 1 wt% to about 10 wt%, or about 1 wt% to about 6 wt%. The aluminum alloy may be an aerospace alloy, such as AA2XXX and AA7XXX series. For example, the aluminum alloy may be AA2024 and AA7075 series. The aluminum alloy may be an automotive alloy, such as AA6XXX series. The aluminum alloy may be a marine alloy, such as AA5XXX series.

[0070] Composition The present disclosure also relates to a composition (e.g., for suppressing corrosion) comprising (a) a Schiff base oligomer and (b) a metal (e.g., a metal salt) selected from a rare earth metal, an alkaline earth metal, a transition metal, or a combination thereof. The Schiff base oligomer can interact (e.g., chelate) with the metal. When a solvent (such as water) is included in the composition of the present disclosure, the Schiff base oligomer can dissociate (e.g., reversibly coordinate) from the metal. In embodiments where the composition is substantially free of a solvent, the Schiff base oligomer and the metal (e.g., a metal salt) can be in the form of a coordination oligomer (e.g., a compound having an ionic bond between the Schiff base oligomer and the metal), but such a coordination oligomer is still considered a composition for the purposes of the present disclosure.

[0071] For example, the composition can include (a) at least one Schiff base oligomer and (b) at least one metal (e.g., a metal salt), and the metal is selected from the group consisting of Zn, La, Pr, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Co, Y, Ca, Sr, Ba, Sc, and Zr. For example, at least one metal can be any one of Zn, Ce, Pr, or a combination thereof.

[0072] The composition can include (a) at least one Schiff base oligomer and (b) at least one metal (e.g., a metal salt), and the metal is selected from the group consisting of Zn, Pr, Ce, and combinations thereof.

[0073] The compositions of the present disclosure may further include a solvent to provide solubility / dispersibility of the Schiff base oligomer. The solvent can be water, a glycol, or a ketone. The glycol can include glycol acetates such as glycol ether acetate. The ketone can include acetone or pentanone. In some embodiments, the solvent is 1-methoxy-2-propanol acetate, 4-methyl-2-pentanone, or a combination thereof.

[0074] The concentration of the Schiff base oligomer can be from about 0.001 wt% to about 20 wt%, such as from about 0.1 wt% to about 10 wt%, such as from about 1 wt% to about 5 wt%, or from about 5 wt% to about 10 wt%, which can provide solubility / dispersibility of the Schiff base oligomer.

[0075] In some embodiments, the molar ratio of the metal in the composition (e.g., metal salt: Schiff base oligomer) is provided with an excess of metal (e.g., metal salt) compared to the Schiff base oligomer due to the presence of multiple moieties of the Schiff base oligomer that can interact with the metal. For example, the molar ratio of metal salt: Schiff base oligomer in the composition can be greater than about 1:1, greater than about 1.1:1, greater than about 1.2:1, greater than about 1.3:1, greater than about 1.4:1, greater than about 1.5:1, greater than about 1.6:1, greater than about 1.7:1, greater than about 1.8:1, greater than about 1.9:1, greater than about 2:1, greater than about 3:1, greater than about 4:1, greater than about 5:1, greater than about 6:1, greater than about 7:1, greater than about 8:1, greater than about 9:1, or greater than about 10:1. The ratio of metal salt: Schiff base oligomer in the composition can be less than about 45:1, less than about 40:1, less than about 35:1, less than about 30:1, less than about 25:1, less than about 20:1, less than about 15:1, or less than about 10:1. The ratio of metal: corrosion inhibitor in the composition can be from about 1:1 to about 45:1, from about 1.5:1 to about 40:1, from about 2:1 to about 35:1, from about 2.5:1 to about 30:1, from about 3:1 to about 25:1, from about 3.5:1 to about 20:1, from about 4:1 to about 15:1, or from about 5:1 to about 10:1. For example, the ratio of metal: corrosion inhibitor in the composition can be from about 1.1:1 to about 45:1, from about 1.2:1 to about 40:1, from about 1.3:1 to about 35:1, from about 1.4:1 to about 30:1, from about 1.5:1 to about 25:1, from about 1.6:1 to about 20:1, from about 1.7:1 to about 15:1, from about 1.8:1 to about 10:1, from about 1.9:1 to about 9:1, or from about 2:1 to about 8:1.

[0076] The corrosion inhibitor composition is suitable for use and application to various substrates such as metal substrates and can be provided, for example, as a coating composition. The composition can include one or more other additives or corrosion inhibitors suitable for use with the intended substrate.

[0077] After depositing the composition on a substrate, the solvent (if used) can be partially, substantially, or completely removed by any suitable curing process. For example, the coating composition can be applied to the substrate in either a wet state or in a "not fully cured" state that dries or cures over time, i.e., the solvent evaporates. The coating can be dried or cured at ambient temperature or by means of acceleration, such as an ultraviolet curing system, to form a film or a "cured" paint. The coating can also be applied in a semi-cured or fully cured state, such as an adhesive.

[0078] The composition can be a coating composition containing a film-forming organic polymer. The coating composition can also be a paint composition. The coating composition may contain one or more resins, such as epoxy resins. The coating composition can be a paint composition, such as an epoxy resin-based paint composition.

[0079] The coating composition can be a powder coating composition, for example, a powder coating composition suitable for use in powder coating various metal substrates including the aluminum alloys or steels described herein.

[0080] The compositions of the present disclosure can include one or more additives such as pigments, fillers, and extenders. Examples of suitable additives that can be combined with the corrosion inhibitors described herein include, for example, binders, solvents, pigments (including soluble or insoluble extenders, fillers, corrosion-inhibiting pigments, etc.), additives (such as curing agents, surfactants, dyes, amino acids, etc.), and the like. It should be noted that some additives can also be appropriately considered as pigments and vice versa (for example, matting agents). More specifically, these "additives" include glycine, arginine, methionine, and derivatives of amino acids such as methionine sulfoxide, methyl sulfoxide, and iodide / iodate, gelatin and gelatin derivatives such as animal and fish gelatin derivatives, linear and cyclic dextrins such as α and β cyclodextrins, trifluoro acid, triflate, acetate, talc, kaolin, organic ion exchange resins such as organic cation and anion exchange resins, salts, oxides, and / or mixed oxides of rare earth materials pre-exchanged or reacted with organic ion exchange resins, and / or metal sulfates such as sulfates of rare earth materials, magnesium sulfate, calcium sulfate (anhydrous and hydrated forms), strontium sulfate, barium sulfate, etc., and combinations thereof, but are not limited thereto.

[0081] The composition may also include other additives such as rheology modifiers, fillers, reinforcing agents, heat or UV stabilizers, flame retardants, lubricants, surfactants, etc. The additives are usually present in an amount of less than about 10% based on the total weight of the cured composition. Examples include the following. (a) Rheology modifiers such as hydroxypropyl methylcellulose (for example, Methocell 311, Dow), modified urea (for example, Byk 411, 410), and polyhydroxycarboxylic acid amide (for example, Byk 405), (b) Film-forming agents such as esters of dicarboxylic acids (for example, Lusolvan FBH, BASF), glycol ethers (for example, Dowanol, Dow), (c) Wetting agents such as fluorosurfactants (e.g., 3M Fluorad), polyether-modified polydimethylsiloxanes (e.g., Byk 307, 333), (d) Surfactants such as fatty acid derivatives (e.g., Bermadol SPS 2543, Akzo) and quaternary ammonium salts, (e) Dispersants such as nonionic surfactants based on primary alcohols (e.g., Merpol 4481, Dupont) and alkylphenol-formaldehyde-polysulfide condensates (e.g., Clariants 1494), (f) Antifoaming agents (g) Corrosion inhibitors such as phosphate esters (e.g., ADDAPT, Anticor C6), alkylammonium salts of (2-benzothiazolylthio)succinic acid (e.g., Irgacor 153 CIBA), triazinedithiol, (h) Stabilizers such as benzimidazole derivatives (e.g., Bayer, Preventol BCM, biocidal film protection), (i) Levelling agents such as fluorocarbon-modified polymers (e.g., EFKA 3777), (j) Pigments or dyes such as fluorescent agents (Royale Pigment and chemicals), (k) Organic and inorganic dyes such as fluorescein, and (l) Lewis acids such as lithium chloride, zinc chloride, strontium chloride, calcium chloride and aluminum chloride, (m) Appropriate flame retardants that can optionally contain any of the following (or combinations thereof) to delay flame propagation, heat release and / or smoke generation: · Phosphorus derivatives such as molecules containing phosphate, polyphosphate, phosphite, phosphazene and phosphine functional groups, e.g., melamine phosphate, dimelamine phosphate, melamine polyphosphate, ammonium phosphate, ammonium polyphosphate, pentaerythritol phosphate, melamine phosphite and triphenylphosphine. · Nitrogen-containing derivatives such as melamine, melamine cyanurate, melamine phthalate, melamine phthalimide, melem cyanurate, melam cyanurate, melon cyanurate, hexamethylenetetraamine, imidazole, adenine, guanine, cytosine and thymine. · Molecules containing a borate functional group such as ammonium borate and zinc borate. · Molecules containing two or more alcohol groups such as pentaerythritol, polyethylene glycol, polyglycol and carbohydrates such as glucose, sucrose and starch. · Molecules that endothermically release a non-combustible decomposition gas such as a metal hydroxide such as magnesium hydroxide and aluminum hydroxide. · Expandable graphite.

[0082] Aspect The present disclosure provides, among other things, the following aspects, each of which can optionally include any alternative aspect. Clause 1. Formula (I):

Chemical formula

Chemical formula

Chemical formula

Chemical formula

[0083] Examples Example 1 After synthesizing bis-thiosemicarbazone and a dicarbonyl compound, an oligomer was formed using polyethylene glycol diglycidyl ether or a similar diglycidyl ether. The water-soluble diglycidyl ether of polyethylene glycol is commercially available in 20 kg amounts from Nagase America LLC (Nagase, 2020a, 2020b) and has an average of 4, 9, 13, or 22 EO (ethylene oxide) repeating units, corresponding to molecular weights of approximately 300, 480, 640, and 1000, respectively.

[0084] Example 2 A simple dialdehyde such as methylglyoxal or isophthalaldehyde is reacted with two molecules of thiosemicarbazide to obtain bis-thiosemicarbazone by refluxing in ethanol. This has both the ability to bind to the metal surface via the thiocarbonyl and the tertiary nitrogen atom of the Schiff base, and the ability to form a polymer via the thiocarbamide group by reacting with another carbonyl group or a reactive chain extender such as a diglycidyl ether. The use of low-cost diketones such as 2,4-pentanedione (acetylacetone) or 2,5-hexanedione (acetonylacetone) was also carried out in the same way to obtain bis-thiosemicarbazone with a greater distance between the binding sites.

[0085] Synthesis of monomer Schiff base Thiosemicarbazide (0.01 mol, 0.91 g) was added to ethanol (50 cm 3 in a three-necked round-bottom flask 3) was dissolved and attached to an ice-cooled reflux condenser attached to a magnetic stirrer. To this solution, salicylaldehyde (0.02 mol, 2.44 cm 3 ) in ethanol (20 cm 3 ) was added dropwise. The reaction mixture was acidified with concentrated HCl and refluxed with continuous stirring at room temperature for 2 hours. The reaction mixture was left standing for 40 minutes. A pale yellow precipitate was obtained, which was filtered and purified by repeated washing with distilled water and diethyl ether. This was dried at 40 °C for 8 hours to obtain the monomer Schiff base, N,N'-bis(salicylidene)thiosemicarbazide Schiff base, in a yield of 72%.

[0086] Synthesis of Schiff base oligomer (STFB) A monomer Schiff base (0.01 mol, 2.99 gm) in 50 cm 3 of DMF in a 250 cm 3 three-necked round-bottomed flask equipped with a thermometer, condenser and magnetic stirrer was added with formaldehyde (0.02 mol, 1.5 cm 3 ) in a molar ratio of (2:1) to synthesize a Schiff base oligomer. 0.5 cm 3 of 40% aqueous NaOH solution was added to this reaction mixture. The temperature was maintained at 70 ± 5 °C for 1 hour with continuous stirring. The progress of the reaction was monitored by TLC (thin layer chromatography). To this mixture, barbituric acid (0.01 mol, 1.28 gm) in 20 cm 3 of DMF was added and stirred again to 100 °C for about 2.5 hours until a red-yellow sticky compound was obtained. Then, this was precipitated in distilled water and washed several times with acetone and diethyl ether. After drying this in an oven at 40 °C for 5 - 7 hours, Schiff base oligomer STFB was obtained in a yield of 70%.

[0087] Synthesis of coordination oligomer By using Schiff base ligands and metal(II) acetates in equimolar ratios (1:1), coordination oligomers of [Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)] were prepared. A typical preparation procedure for the metal polychelates of manganese(II) was as follows. A Schiff base oligomer (0.01 mol) was dissolved in (20 cm 3 ) DMF and heated at 60 °C in a three-necked round-bottom flask equipped with an ice condenser. A solution of manganese(II) acetate tetrahydrate Mn(CH3COO)2·4H2O (0.01 mol, 2.45 gm) was added to the clear solution of the Schiff base in 15 cm 3 DMF at high temperature with continuous stirring and refluxed for 7 hours. Stirring was continued until complete dissolution and a distinct color change were achieved. Finally, a brown viscous solution was obtained. This was then precipitated, filtered, and washed several times with distilled water and diethyl ether, thereby obtaining a brown precipitate. This was then oven-dried at 45 °C for 5 - 6 hours to obtain the polychelate of manganese [STFB-Mn(II)] in 81% yield.

[0088] Proof-of-concept of Reaction 1 - Schiff base reaction Using ethanol as the solvent and concentrated HCl as the reaction catalyst, both ends of thiosemicarbazide react with aldehydes such as salicylaldehyde as shown below in 72% isolated yield. Scheme 1

Chemical formula

[0089] Reaction 2 As shown below, oligomeric species are prepared using approximately 1.8 equivalents of dialdehyde (or other dicarbonyls such as keto-aldehyde or diketone) and 1 equivalent of thiosemicarbazide. Scheme 2

Chemical formula

Chemical formula

Chem.

[0090] Formation of bis - thiosemicarbazone of terephthalaldehyde (1) A 250 mL three - necked round - bottom flask was charged with a solution of thiosemicarbazide (9.11 g, 0.100 mol) dissolved in 100 mL of ethanol. A PTFE stir bar was added and the flask was placed in a soft heating mantle on a magnetic stirrer plate. A reflux condenser was attached to the central neck. A dropping funnel charged with a solution of terephthalaldehyde (6.57 g, 0.049 mol) in 50 mL of ethanol was attached to one of the side necks. A second dropping funnel charged with a solution of 1 mL of 12 N HCl (concentrated HCl) in 20 mL of ethanol was attached to the other side neck. Scheme 5

Chem.

[0091] The solution of terephthalaldehyde was slowly added to the flask with stirring at room temperature over 30 minutes, followed by the addition of the HCl solution. After the addition of the acid, the heating mantle was turned on and the mixture was refluxed for 2 - 3 hours. The heating was stopped and the mixture was slowly allowed to return to room temperature. The product precipitated as a yellow solid and was recovered by filtration through a Buchner funnel. The product was washed with pure water (3×50 mL) and ethyl ether (1×50 mL) and dried overnight in a 100 °C oven. C 10 H 12 N6S2: Product with a molecular weight of 280.41. Yield = 13.74. The by - products are 0.18 g of excess thiosemicarbazide and 1.76 g of water.

[0092] (1) Reaction with diglycidyl ether or diisocyanate A solution of 5 grams of the polymer prepared in the previous section and 0.05 grams of the appropriate catalyst was dissolved in 25 mL of solvent. This solution was charged into a 100 mL three-neck round bottom flask containing a PTFE stir bar and equipped with a reflux condenser, a dropping funnel, and a thermocouple. The flask was placed in a water bath and on a magnetic heating stir plate. The dropping funnel was charged with a solution of 0.9 equivalents of the desired chain extender (described below) dissolved in 25 mL of the same solvent. This was added dropwise to the flask with stirring for 30 minutes while monitoring the temperature. When the two components combine, the temperature should rise. The temperature should be maintained below 100 °C by appropriate means such as adding ice to the water bath.

[0093] After 1 hour, all of the reactive chain extender should have been consumed. The residual epoxy content can be determined by titration (ASTM D1652), and the residual isocyanate can be determined by titration (Dow, 2000).

[0094]

Table 1

[0095] Formation of bis-thiosemicarbazone of pyruvaldehyde (2) A 250 mL three-neck round bottom flask was charged with a solution of thiosemicarbazide (10.02 g, 0.110 mol) dissolved in 100 mL of ethanol. A PTFE stir bar was added and the flask was placed in a soft heating mantle on a magnetic stirring plate. A reflux condenser was attached to the central neck. A dropping funnel was attached to one of the side necks and charged with a solution of pyruvaldehyde dimethyl acetal (5.78 g, 0.049 mol) in 50 mL of ethanol. This compound was also called methylglyoxal dimethyl acetal. A second dropping funnel was attached to the other side neck and charged with a solution of 1 mL of 12N HCl (concentrated HCl) in 20 mL of ethanol. Scheme 6

Chemical formula

[0096]

Table 2

[0097] The solution of thiosemicarbazide was heated to 50 - 60 °C (under direct reflux). To this, a solution of pyruvaldehyde dimethyl acetal was added while stirring at room temperature for 30 - 40 minutes, and then a solution of HCl was added. After adding the acid, the heating mantle and stirrer were stopped, and the mixture was slowly cooled to room temperature for about 2 hours. If possible, the reaction mixture was placed in the refrigerator for 2 or 3 days to increase the crude yield. The product should precipitate as a yellow solid. The solid was collected with a Buchner funnel.

[0098] The crude product was recrystallized by dissolving it in the minimum amount of refluxing methanol in a beaker on a hot plate in a fume hood. An equal volume of distilled water was added, removed from the heat, and then cooled. The product precipitated as yellowish-white needles. Collect by filtration with a Buchner funnel. Dry overnight in an oven at 100 °F. C5H 10 N6S2: Molecular weight 218.29 Yield = 10.69 of the product The by-products are 1.09 g of excess thiosemicarbazide, 3.13 g of methanol, and 0.88 g of water. References: Petering, 1964.

[0099] (2) Reaction with a general diglycidyl ether The reaction of two Schiff bases (SB) with three diglycidyl ethers is shown below. The starting SB is a crystalline solid, but the product is expected to be a viscous liquid more suitable for coating the metal surface either independently or as a component in a coating formulation. Other difunctional chain extenders can be considered. Scheme 7

Chemical formula

[0100] Schiff Base Oligomer and Epoxy Composition #1 A reaction vessel equipped with a 500 cc stirrer and a water condenser was charged with 179 grams (0.5 mol) of diglycidyl polyether of polypropylene glycol having an epoxy equivalent of 78.5 grams of Schiff base polymer, and 2.6 grams of powdered sodium hydroxide as a catalyst. During the first hour, cooling was used to moderate the reaction to 100 °C to 120 °C. At the end of this time, less than 1% of the diepoxide remained unreacted.

[0101] Schiff Base Oligomer and Epoxy Composition #2 2.47 grams of Schiff base oligomer and epoxy composition or Schiff base oligomer composition was mixed with 0.87 grams (0.01 equivalent) of toluene diisocyanate (TDI) and 1.5 grams of dimethylformamide diluent. These compounds were mixed and finally TDI was added. A film was cast on an adhesive steel panel and baked at 300 °F for several minutes to obtain a thermosetting transparent orange coating with high hardness.

[0102] Materials The following table lists the materials used as disclosed herein, including exemplary difunctional chain extender molecules containing diglycidyl ether and diisocyanate.

[0103]

Table 3

[0104] Schiff Base Oligomer with Silyl End-Capping A solution of 5 grams of bis-thiosemicarbazone and 0.05 grams of the appropriate catalyst prepared in the previous section was dissolved in 25 mL of the desired solvent. This solution was charged into a 100 mL three-necked round-bottom flask containing a PTFE stir bar and equipped with a reflux condenser, a dropping funnel, and a thermocouple. The flask was placed in a water bath and on a magnetic heating stir plate. The dropping funnel was charged with a solution of 1.2 equivalents of the desired chain extender dissolved in 25 mL of the same solvent. This was added dropwise to the flask while stirring for 30 minutes, and the temperature was monitored. When the two components combine, the temperature should rise. The temperature was maintained below 100 °C by appropriate means such as adding ice to the water bath. After 1 hour, all of the reactive chain extender should have been consumed. The residual epoxy content can be determined by titration (ASTM D1652), and the residual isocyanate can be determined by titration (Dow, 2000).

[0105] The use of a small amount of trimethoxysilylpropyl glycidyl ether provided end groups that could react with the metal surface via metal-O-Si bond formation. Scheme 8

Chemical formula

[0106] This type of structure has multiple modes of attachment to the metal surface, including three bis-Schiff base groups, secondary hydroxyl groups, and, for example, cleavage of three ethoxysilyl groups by OH groups on the metal surface.

[0107] This Schiff base oligomer with silyl end-capping can be dissolved in a suitable solution at low solids to prepare a solution for dip coating or spray coating metal parts. Drying can be achieved by heating with an IR heat source, a hot air source, or some combination of the two.

[0108] Chemical terms As used herein, the wavy line of a chemical structure indicates the point of attachment between the portion shown and the remainder of the molecule.

[0109] As used herein, the term "composition" can include the components of the composition (e.g., oligomers and metals and / or metal salts) and / or the reaction product of two or more components of the composition.

[0110] Unless otherwise stated / claimed, the groups / portions of the Schiff base oligomers described in this disclosure are unsubstituted or substituted. The term "substituted" means that the group is substituted at any available position. Substitutions can be, for example, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, heterocyclyl, heteroaryl, formyl, alkanoyl, cycloalkanoyl, aroyl, heteroaroyl, carboxyl, alkoxycarbonyl, cycloalkyloxycarbonyl, aryloxycarbonyl, heterocyclyloxycarbonyl, heteroaryloxycarbonyl, alkylaminocarbonyl, cycloalkylaminocarbonyl, arylaminocarbonyl, heterocyclylaminocarbonyl, heteroarylaminocarbonyl, cyano, alkoxy, cycloalkoxy, aryloxy, heterocyclyloxy, heteroaryloxy, alkanoate, cycloalkanoate, arylate, heterocyclylate, heteroarylate, alkylcarbonylamino, cycloalkylcarbonylamino, arylcarbonylamino, heterocyclylcarbonylamino, heteroarylcarbonylamino, nitro, hydroxyl, halo (-F, -Cl, -Br, -I), haloalkyl, haloaryl, halocycloheterocyclyl, haloheteroaryl, haloalkoxy, silylalkyl, alkenylsilylalkyl, alkynylsilylalkyl or amino. In some embodiments, the substitution can be halo, alkyl, formyl, or amino. Optional substituents can include salts of the group, such as carboxylate salts. It will be understood that "substituted" may include other groups not specifically described.

[0111] "Alkyl", whether used alone or in compound words such as alkoxy, alkylthio, alkylamino, dialkylamino or haloalkyl, represents a straight or branched chain hydrocarbon in the range of 1 to about 10 carbon atoms or more. Thus, the alkyl moiety includes, unless explicitly limited to smaller groups, moieties in the range of 1 to about 6 carbon atoms or more, such as methyl, ethyl, n-propyl, iso-propyl, butyl, pentyl, hexyl, etc., and higher isomers including straight or branched chain hydrocarbons in the range of about 6 to about 10 carbon atoms or more.

[0112] "Cycloalkyl" represents monocyclic or polycyclic ring systems of various sizes, such as from about 3 to about 10 carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or cycloheptyl. The term cycloalkyloxy represents the same group bonded through an oxygen atom, such as cyclopentyloxy and cyclohexyloxy. The term cycloalkylthio represents the same group bonded through a sulfur atom, such as cyclopentylthio and cyclohexylthio.

[0113] As is understood, an aromatic group means a cyclic group having 4m + 2 π electrons, where m is an integer of 1 or more. As used herein, "aromatic" is used interchangeably with "aryl" to refer to an aromatic group, regardless of the valence of the aromatic group. Thus, aryl refers to monovalent aromatic groups, divalent aromatic groups and higher polyvalent aromatic groups.

[0114] "Aryl", whether used alone or in compound words such as arylalkyl, aryloxy or arylthio, represents (i) an optionally substituted monocyclic or polycyclic aromatic carbocyclic moiety having, for example, from about 6 to about 60 carbon atoms, such as phenyl, naphthyl or fluorenyl or (ii) an optionally substituted partially saturated polycyclic carbocyclic aromatic ring system in which an aryl and a cycloalkyl or cycloalkenyl group are fused together to form a cyclic structure such as tetrahydronaphthyl, indenyl, indanyl or fluorene ring.

[0115] "Heterocyclyl" or "heterocyclic", whether used alone or in compound words such as heterocyclyloxy, represents (i) an optionally substituted cycloalkyl or cycloalkenyl group having from about 3 to about 60 ring members which may contain one or more heteroatoms such as nitrogen, oxygen, or sulfur (examples include pyrrolidinyl, morpholino, thiomorpholino, or fully or partially hydrogenated thienyl, furyl, pyrrolyl, thiazolyl, oxazolyl, oxadazinyl, thiazinyl, pyridyl and azepinyl), (ii) an optionally substituted partially saturated polycyclic system in which an aryl (or heteroaryl) ring and a heterocyclic group are fused together to form a ring structure (examples include chromanyl, dihydrobenzofuryl and indolinyl), or (iii) an optionally substituted fully or partially saturated polycyclic fused ring system having one or more bridges (examples include quinuclidinyl and dihydro-1,4-epoxynaphthyl).

[0116] A heteroaromatic group is an aromatic group or ring containing one or more heteroatoms such as N, O, S, Se, Si or P. As used herein, "heteroaromatic" is used interchangeably with "heteroaryl", and a heteroaryl group refers to a monovalent, divalent and higher polyvalent aromatic group containing one or more heteroatoms. "Heteroaryl" is considered to be one non-limiting type of "heterocyclyl".

[0117] "Heteroaryl", whether used alone or in compound words such as heteroaryloxy, represents a monocyclic or polycyclic aromatic organic moiety which is optionally substituted and which, for example, has from about 1 to about 10 ring members, one or more of which ring members are elements other than carbon, such as nitrogen, oxygen, sulfur or silicon, and the heteroatoms interrupt the carbocyclic ring structure and have a sufficient number of delocalized π electrons to provide aromaticity, provided that the ring does not contain adjacent oxygen and / or sulfur atoms. Typical 6-membered heteroaryl groups are pyrazinyl, pyridazinyl, pyrazolyl, pyridyl and pyrimidinyl. All positional isomers, such as 2-pyridyl, 3-pyridyl and 4-pyridyl are contemplated. Typical 5-membered heteroaryl rings are furyl, imidazolyl, oxazolyl, isoxazolyl, isothiazolyl, oxadiazolyl, pyrrolyl, 1,3,4-thiadiazolyl, thiazolyl, thienyl, triazolyl and silol. All positional isomers, such as 2-thienyl and 3-thienyl are contemplated. Bicyclic groups are typically benzofused ring systems derived from the above heteroaryl groups, such as benzofuryl, benzimidazolyl, benzothiazolyl, indolyl, indolizinyl, isoquinolyl, quinazolinyl, quinolyl and benzothienyl, or (ii) optionally substituted partially saturated polycyclic heteroaryl ring systems in which a heteroaryl and a cycloalkyl or cycloalkenyl group are fused together to form a cyclic structure such as a tetrahydroquinolyl or pyrindinyl ring.

[0118] "Hydroxyl" and "hydroxy" can be used interchangeably and represent the -OH moiety.

[0119] "Alkoxy" and "alkoxyl" can be used interchangeably and represent an -O-alkyl group where the alkyl group is as defined above. Examples include methoxy, ethoxy, n-propoxy, isopropoxy, as well as the different butoxy, pentoxy, hexyloxy and higher isomers.

[0120] "Aryloxy" and "aryloxyl" can be used interchangeably and represent an -O-aryl group where the aryl group is as defined above. Examples include, but are not limited to, phenoxy and naphthoxy.

[0121] The compounds described herein may include salts, solvates, hydrates, isomers, tautomers, racemates, stereoisomers, enantiomers or diastereoisomers of those compounds. For example, the salts may include sodium, potassium, calcium, nitrates, phosphates, sulfates, chlorides, or combinations thereof.

[0122] The above is directed to aspects of the present disclosure, but other aspects and further aspects of the present disclosure may be devised without departing from the basic scope thereof, which is determined by the following appended claims.

Claims

1. An oligomer represented by formula (I): 【Chemical 1】 wherein each instance of n, m, z, and t is an integer from 1 to 50, R 4 、R 5 、R 6 、R 7 、R 8 、R 10 、R 11 、R 12 、R 13 and R 14 each example of which is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, alkoxyl, aryloxyl, ether and heterocyclyl, R 9 each example of which is independently selected from the group consisting of alkyl, cycloalkyl, aryl, heterocyclyl, and ether R 28 and R 29 each instance of which is independently selected from the group consisting of hydrogen, alkyl, and aryl, R 33 each instance of which is independently selected from the group consisting of alkyl, cycloalkyl, aryl, heterocyclyl and a bond R 41 Each instance of which is independently —NH— or a bond, R 40 Each instance of which is independently —NH— or —NH—NH—, R 42 each instance of which is independently —NH— or a bond, R 43 each instance of which is independently —NH— or —NH—NH— Each instance of Q is, independently, -CH 2 - or oxygen, represented by, wherein R 44 is hydroxyl, hydroxy-substituted alkyl, or has the structure: [Chemical Formula 2] x is an integer from 1 to 50, R 1 is hydrogen or silyl, R 2 and R 3 are independently selected from the group consisting of hydrogen, alkyl and aryl, R 31 is selected from the group consisting of alkyl, cycloalkyl, aryl, heterocyclyl and a bond, R 50 is -NH- or a bond, and R 32 is -NH- or -NH-NH-, R 34 is -NH- or a bond, and R 35 is -NH- or -NH-NH-, represented by, wherein R 30 is hydrogen, silyl, or has the structure: [Chemical 3] each of n' and m' is an integer from 1 to 50. The oligomer. R 4’ 、R 5’ 、R 6’ 、R 7’ 、R 8’ 、R 10’ 、R 11’ 、R 12’ 、R 13’ and R 14’ each is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, alkoxyl, aryloxyl, ether and heterocyclyl; R 9’ is selected from the group consisting of alkyl, cycloalkyl, heterocyclyl, and ether, R 44’ is hydroxyl or hydroxy-substituted alkyl, and Each instance of Q’ is independently, —CH 2 — or oxygen,

2.

3. R 4 、R 5 、R 6 、R 7 、R 8 、R 10 、R 11 、R 12 、R 13 and R 14 each instance of which is independently selected from the group consisting of hydrogen and C 1 -C 5 alkyl, and optionally, each instance of R 4 、R 5 、R 6 、R 7 、R 8 、R 10 、R 11 、R 12 、R 13 and R 14 is hydrogen, the oligomer according to claim 1.

4. R 28 and R 29 each example of 1 -C 5 The oligomer according to claim 1, independently selected from the group consisting of hydrogen and C-C alkyl

5. R 28 and R 29 The oligomer according to claim 1, wherein each example of The oligomer according to claim 1, wherein each instance of Q is oxygen.

6. The oligomer according to claim 1. R 41 When R is -NH-, 40 R is -NH-, and when 41 R is a bond, 40 R is -NH-NH-. R 42 When R is -NH-, 43 R is -NH-, and when 42 R is a bond, 43 R is -NH-NH-.

7.

8. R 9 Each example of 1 -C 10 is alkyl or polyether, and optionally, each example of R 9 is polyether, the oligomer according to claim 1. The oligomer according to claim 7, wherein the polyether has a molecular weight of 400 g / mol to 700 g / mol.

9.

10. R 33 The oligomer according to claim 1, wherein each example of

11. R 33 Each example of 1 -C 10 The oligomer according to claim 1, independently selected from alkyl. or R 33 Each example of 【Chemical Formula 4】

12. 【Chemical Formula 5】 Independently selected from phenyl represented by, wherein R 60 , R 61 , R 62 and R 63 are independently selected from hydrogen and C 1 -C 10 alkyl, the oligomer according to claim 1.

13. R 30 and R 1 The oligomer according to claim 1, wherein each of

14. R 30 The oligomer according to claim 1, wherein R is Cyrillic. wherein the silyl is glycidyl ether silyl and / or the silyl is selected from the group consisting of and [Chemical Formula 6] and / or the silyl is of the formula: 【Chemical Formula 7】

15. [Chemical 8] represented by, wherein R 45 , R 46 and R 47 each independently selected from the group consisting of hydrogen and C 1 -C 20 alkyl, and R 48 is selected from the group consisting of alkyl, cycloalkyl, ether and aryl, the oligomer according to claim 1. ​ R 45 、 R 46 and R 47 each is hydrogen, and / or R 45 、 R 46 and R 47 each is C 1 -C 5 alkyl, the oligomer according to claim 14.

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