A polyamide-modified waterborne epoxy curing agent and its preparation method

Abstract

This invention discloses a polyamide-modified waterborne epoxy curing agent and its preparation method. The polyamide-modified waterborne epoxy curing agent contains nonionic polyether hydrophilic segments grafted onto the side chains, and polyamide structural segments introduced into the main chain via linear block copolymerization. The polyamide-modified waterborne epoxy curing agent is synthesized from the following raw materials in weight percentages: 20-40% polyamide resin, 2-6% polyamine, 3-8% polyether amine, 10-15% liquid epoxy resin, 8-12% monoepoxy compound, and the balance being deionized water. The curing agent of this invention has a simple and environmentally friendly synthesis process, low viscosity, and can be cured and crosslinked with waterborne epoxy resin, meeting room temperature curing requirements, and producing coatings with excellent flexibility, corrosion resistance, chemical resistance, and water resistance.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and in particular to a polyamide-modified waterborne epoxy curing agent and its preparation method. Background Technology

[0002] With the national "carbon peaking and carbon neutrality" implementation plan and goals, and the active implementation of the green and low-carbon transformation strategy, green and low-carbon technologies for epoxy resin coatings have emerged. Among these, waterborne epoxy resin coatings are widely used due to their excellent chemical resistance and physical and mechanical properties, as well as their low pollution and ease of application, characteristic of solvent-based epoxy coatings. In the application of waterborne epoxy coatings, the requirements for the matching curing agent vary depending on the epoxy components. Common waterborne epoxy curing agents include three types: amidated polyamines obtained by reacting polyamines with monofatty acids; polyamides formed by the condensation of dimer acids and polyamines; and epoxy-amine adducts obtained by the addition reaction of polyamines with epoxy resins.

[0003] Room temperature curing waterborne coating systems typically use aliphatic polyamine curing agents. These react with epoxy resins to produce a large number of oligomers, resulting in poor adhesion and whitening of the cured film, as well as lower toughness and strength. Due to the influence of molecular structure design, conventional amidated polyamines and polyamide curing agents have certain defects that are difficult to significantly improve. Currently, epoxy-amine adducts are widely used as waterborne epoxy curing agents, accounting for over 80% of the domestic and international market. Currently, most patents such as CN113004495A, CN103183810A, and CN105482079A involve waterborne epoxy curing agents that are epoxy-amine adducts. This involves introducing epoxy resin segments into the molecular structure of a polyamine, improving the compatibility between the curing agent and the epoxy resin. The cured film is dense and has high hardness. Adding an appropriate amount of epoxy reactive diluent to the resin component can increase the toughness of the film and solve the problem of brittleness in films prepared with this type of curing agent. However, this molecular structure itself still has problems such as poor room temperature curing performance, poor initial water resistance, and incomplete curing. Furthermore, in the preparation process of epoxy-amine adduct type waterborne epoxy curing agents, most raw materials are still petrochemical raw materials. With the decreasing availability of energy sources such as petroleum and the increasing environmental awareness, the waterborne epoxy resin coating industry is also seeking new development paths. Summary of the Invention

[0004] To address the shortcomings of existing technologies, such as poor coating performance and the prevalence of petrochemical raw materials, the primary objective of this invention is to provide a branched nonionic polyamide-modified waterborne epoxy curing agent with good room temperature curing performance and water resistance, as well as its preparation method.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A polyamide-modified waterborne epoxy curing agent contains nonionic polyether hydrophilic segments grafted onto the side chains, and polyamide structural segments introduced into the main chain via linear block copolymerization. The polyamide-modified waterborne epoxy curing agent is synthesized from the following raw materials in weight percentages: 20-40% polyamide resin, 2-6% polyamine, 3-8% polyether amine, 10-15% liquid epoxy resin, 8-12% monoepoxy compound, and the balance being deionized water.

[0007] Preferably, the polyamine is selected from at least one of aromatic amines, aliphatic amines, and alicyclic amines; the aromatic amine is selected from at least one of m-phenylenediamine and m-phenylenediamine; the alicyclic amine is isophorone diamine; and the aliphatic amine is at least one of ethylenediamine, propylenediamine, butanediamine, pentanediamine, hexanediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0008] Preferably, the monoepoxide compound is selected from at least one of butyl glycidyl ether, phenyl glycidyl ether, o-tolyl glycidyl ether, octyl glycidyl ether, and benzyl glycidyl ether.

[0009] Preferably, the liquid epoxy resin is selected from at least one of DER331 produced by DOW Chemical Company and EPON828 produced by Hexion Company.

[0010] Preferably, the polyamide resin is selected from the reaction of fatty diacid and fatty diamine.

[0011] Preferably, the polyamide resin is selected from at least one of polyamide resin 250, polyamide resin 300, polyamide resin 650, and polyamide resin 651.

[0012] Preferably, the solid content of the polyamide-modified waterborne epoxy curing agent is 60% to 70%.

[0013] The preparation method of any of the above-mentioned polyamide-modified waterborne epoxy curing agents includes the following steps:

[0014] ⑤ Preparation of prepolymer:

[0015] Polyamine was added to a reaction vessel, the temperature was raised to 40–60°C, and a monoepoxide compound was added dropwise at this temperature over a period of 2–4 hours. After the addition was complete, the reaction was maintained at 70–90°C for 2 hours to prepare compound A containing a terminal primary amine group. Aminated polyether was added to a reaction vessel, the temperature was raised to 60–80°C, and liquid epoxy resin was added dropwise at this temperature over a period of 2–4 hours. After the addition was complete, the reaction was maintained at 120–140°C for 2 hours to prepare compound B containing a hydrophilic segment. All the above operations were carried out under stirring.

[0016] ⑥ Preparation of nonionic waterborne epoxy curing agent

[0017] Compound A containing terminal primary amine groups, obtained in step ①, and polyamide resin were added to a reaction vessel and mixed evenly. Then, compound B containing hydrophilic segments, obtained in step ①, was slowly added dropwise at 50±5℃ for 2–4 hours. After the addition was complete, the temperature was gradually increased between 60 and 80℃ and maintained for 4–6 hours. Then, a monoepoxy compound was slowly added dropwise and reacted at 70±5℃ for 2–3 hours to obtain a product with terminal primary amine hydrogens blocked. Deionized water was added to obtain a nonionic waterborne epoxy curing agent. All the above operations were carried out under stirring.

[0018] Preferably, the terminal amino polyether is at least one of JEFFAMINE M-1000, M-2070, M-600, ED-600, ED-900 and ED-2003 produced by HUNTSMAN.

[0019] Preferably, the polyamide resin is prepared by reacting fatty diacid with fatty diamine.

[0020] Preferably, deionized water is added in step ② so that the solid content of the final polyamide-modified waterborne epoxy curing agent is 60% to 70%.

[0021] The preparation method and the product obtained by the present invention have the following advantages and beneficial effects:

[0022] (1) The present invention adopts the epoxy-polyamine addition method, which introduces hydrophobic epoxy resin and hydrophilic nonionic chain segments into the polyamine to adjust the hydrophilicity and lipophilicity of the waterborne epoxy curing agent, enhances the compatibility with the waterborne epoxy resin components, and avoids the step of adding organic acid to neutralize and form salt.

[0023] (2) The present invention introduces hydrophilic segments by using side chain blocks, which can reduce the amount of hydrophilic substances used and reduce viscosity while ensuring water-based properties, thus achieving a higher solid content. Therefore, the coatings formulated with the curing agent of the present invention have improved water resistance and corrosion resistance.

[0024] (3) This invention introduces polyamide resin segments into the main chain of an aqueous epoxy curing agent, which contains alkyl chains with ether bonds, resulting in high flexibility. Simultaneously, the six-membered aliphatic ring in the molecule imparts high temperature resistance. When used as a curing agent, this compound exhibits high curing activity and can achieve room temperature curing. Furthermore, the high molecular weight of the main chain molecule leads to significant steric hindrance, extending the system's pot life and facilitating construction.

[0025] (4) The synthesis process of this invention is simple and environmentally friendly. It is a reaction system without organic solvents, and no small molecule byproducts are generated during the reaction process. The synthesized product meets high environmental protection requirements. In addition, the use of bio-based raw materials can reduce excessive dependence on petroleum resources in the face of the increasingly depleted petroleum resources.

[0026] (5) Although the reaction principle of this invention is an amine-epoxy ring-opening reaction, it differs from the traditional amine-epoxy ring-opening reaction in the following ways: a. This invention uses stepwise feeding, which can ensure the regularity of the structure. Specifically, the diamine is first subjected to single-end capping treatment to obtain a long-chain terminal primary amino compound, which can reduce the activity of the amino group and ensure that the subsequent reaction reacts with the single primary amine as much as possible, which can avoid the gel phenomenon in the addition reaction to a certain extent; b. In this case, the terminal amino compound is mixed with a polyamide resin with a larger molecular weight, and then reacted with a hydrophilic segment compound to introduce polyamide segments (long carbon flexible segments) into the molecular backbone. The high molecular weight of the backbone molecule leads to large steric hindrance, which prolongs the pot life of the system; in addition, forming the terminal primary amino compound first and then carrying out the addition reaction can reduce the presence of small molecular weight compounds, improve the purity of the reactants, and enhance the crosslinking density of the coating film; the introduced side chain hydrophilic segments and the long carbon chain hydrophobic segments of the backbone can both improve the water resistance of the coating film. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0028] Example 1

[0029] ① Preparation of prepolymer:

[0030] 10.32 g of diethylenetriamine was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 50 °C, and 15.02 g of phenyl glycidyl ether was slowly added dropwise with stirring. After the addition was completed in 3 hours, the mixture was kept at 80 °C for 2 hours to prepare compound A containing a primary amino group. 14.18 g of amino-terminated polyether JEFFAMINEM2070 (HUNSTMAN) was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 70 °C, and 33.10 g of liquid epoxy resin EPON828 (HEXION) was slowly added dropwise with stirring. After the addition was completed in 2 hours, the temperature was raised to 130 °C and the mixture was kept at 80 °C for 2 hours to prepare compound B containing a hydrophilic segment.

[0031] ②Preparation of nonionic waterborne epoxy curing agent

[0032] 25.34 g of compound A containing terminal primary amine groups, prepared in step ①, and 74.00 g of polyamide resin 560, were added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. After mixing thoroughly, the mixture was heated to 50 °C. While stirring, 47.28 g of compound B containing hydrophilic segments, prepared in step ①, was slowly added dropwise over a period of 2 hours. After the addition was complete, the mixture was kept at 50 ± 2 °C for 2 hours, then heated to 70 ± 2 °C for 2 hours, and then heated to 80 ± 2 °C for 2 hours. 12.01 g of phenyl glycidyl ether was then slowly added dropwise. The mixture was reacted at 70 °C for 2 hours to obtain a product with terminal primary amine hydrogens blocked. 85.40 g of deionized water was added to obtain a nonionic waterborne epoxy curing agent.

[0033] The curing agent has a solid content of 65.0 wt% and an amine hydrogen equivalent of 208.6 ± 10 (in solid form).

[0034] Example 2

[0035] ① Preparation of prepolymer:

[0036] 10.32 g of diethylenetriamine was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 40 °C, and 13.02 g of butyl glycidyl ether was slowly added dropwise with stirring. After the addition was completed in 4 hours, the mixture was kept at 70 °C for 2 hours to prepare compound A containing a primary amino group. 14.18 g of amino-terminated polyether JEFFAMINEM2070 (HUNSTMAN) was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 70 °C, and 33.10 g of liquid epoxy resin EPON828 (HEXION) was slowly added dropwise with stirring. After the addition was completed in 4 hours, the temperature was raised to 120 °C and the mixture was kept at 70 °C for 2 hours to prepare compound B containing a hydrophilic segment.

[0037] ②Preparation of nonionic waterborne epoxy curing agent

[0038] 23.34 g of compound A containing terminal primary amine groups, prepared in step ①, and 74.00 g of polyamide resin 560, were added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. After mixing thoroughly, the mixture was heated to 50 °C. While stirring, 47.28 g of compound B containing hydrophilic segments, prepared in step ①, was slowly added dropwise over 3 hours. After the addition was complete, the mixture was kept at 50 ± 2 °C for 2 hours, then heated to 70 ± 2 °C for 2 hours, and then heated to 80 ± 2 °C for 2 hours. 10.41 g of butyl glycidyl ether was then slowly added dropwise. The mixture was reacted at 70 °C for 2 hours to obtain a product with terminal primary amine hydrogens blocked. 83.47 g of deionized water was added to obtain a nonionic waterborne epoxy curing agent.

[0039] The curing agent has a solid content of 65.0 wt% and an amine hydrogen equivalent of 204.0 ± 10 (in solid form).

[0040] Example 3

[0041] ① Preparation of prepolymer:

[0042] 10.32 g of diethylenetriamine was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 60 °C, and 15.02 g of phenyl glycidyl ether was slowly added dropwise with stirring. After the addition was completed in 2 hours, the reaction was maintained at 80 °C for 2 hours to prepare compound A containing a primary amino group. 15.59 g of amino-terminated polyether JEFFAMINE M1000 (HUNSTMAN) was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 60 °C, and 36.36 g of liquid epoxy resin EPON828 (HEXION) was slowly added dropwise with stirring. After the addition was completed in 2 hours, the temperature was raised to 140 °C and the reaction was maintained at 80 °C for 2 hours to prepare compound B containing a hydrophilic segment.

[0043] ②Preparation of nonionic waterborne epoxy curing agent

[0044] 25.34 g of compound A containing terminal primary amine groups, prepared in step ①, and 74.00 g of polyamide resin 560, were added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. After mixing thoroughly, the mixture was heated to 50 °C. While stirring, 51.95 g of compound B containing hydrophilic segments, prepared in step ①, was slowly added dropwise over a period of 4 hours. After the addition was complete, the mixture was kept at 50 ± 2 °C for 2 hours, then heated to 70 ± 2 °C for 2 hours, and then heated to 80 ± 2 °C for 2 hours. 12.01 g of phenyl glycidyl ether was then slowly added dropwise. The mixture was reacted at 70 °C for 2 hours to obtain a product with terminal primary amine hydrogens blocked. 87.91 g of deionized water was added to obtain a nonionic waterborne epoxy curing agent.

[0045] The curing agent has a solid content of 65.0 wt% and an amine hydrogen equivalent of 214.8 ± 10 (in solid form).

[0046] Example 4

[0047] ① Preparation of prepolymer:

[0048] 14.62 g of triethylenetetramine was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 50 °C, and 15.02 g of phenyl glycidyl ether was slowly added dropwise with stirring. After the addition was completed in 3 hours, the mixture was kept at 70 °C for 2 hours to prepare compound A containing a primary amino group. 14.18 g of amino-terminated polyether JEFFAMINEM2070 (HUNSTMAN) was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 70 °C, and 33.10 g of liquid epoxy resin EPON828 (HEXION) was slowly added dropwise with stirring. After the addition was completed in 3 hours, the temperature was raised to 120 °C and the mixture was kept at 70 °C for 2 hours to prepare compound B containing a hydrophilic segment.

[0049] ②Preparation of nonionic waterborne epoxy curing agent

[0050] 29.64 g of compound A containing terminal primary amine groups, prepared in step ①, and 74.00 g of polyamide resin 560, were added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. After mixing thoroughly, the mixture was heated to 50 °C. While stirring, 47.28 g of compound B containing hydrophilic segments, prepared in step ①, was slowly added dropwise over 3 hours. After the addition was complete, the mixture was kept at 50 ± 2 °C for 2 hours, then heated to 70 ± 2 °C for 2 hours, and then heated to 80 ± 2 °C for 2 hours. 10.41 g of butyl glycidyl ether was then slowly added dropwise. The mixture was reacted at 70 °C for 2 hours to obtain a product with terminal primary amine hydrogens blocked. 86.87 g of deionized water was added to obtain a nonionic waterborne epoxy curing agent.

[0051] The curing agent has a solid content of 65.0 wt% and an amine hydrogen equivalent of 187.6 ± 10 (in solid form).

[0052] Example 5

[0053] ① Preparation of prepolymer:

[0054] 14.62 g of triethylenetetramine was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 60 °C, and 13.02 g of butyl glycidyl ether was slowly added dropwise with stirring. After the addition was completed in 2 hours, the mixture was kept at 80 °C for 2 hours to prepare compound A containing a primary amino group. 15.59 g of amino-terminated polyether JEFFAMINE M1000 (HUNSTMAN) was first added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. The temperature was raised to 80 °C, and 36.36 g of liquid epoxy resin EPON828 (HEXION) was slowly added dropwise with stirring. After the addition was completed in 4 hours, the temperature was raised to 120 °C and the mixture was kept at 120 °C for 2 hours to prepare compound B containing a hydrophilic segment.

[0055] ②Preparation of nonionic waterborne epoxy curing agent

[0056] 27.64 g of compound A containing terminal primary amine groups, prepared in step ①, and 74.00 g of polyamide resin 560, were added to a 500 mL four-necked flask equipped with a dropping funnel, stirrer, and thermometer. After mixing thoroughly, the mixture was heated to 50 °C. While stirring, 51.95 g of compound B containing hydrophilic segments, prepared in step ①, was slowly added dropwise over a period of 4 hours. After the addition was complete, the mixture was kept at 50 ± 2 °C for 2 hours, then heated to 70 ± 2 °C for 2 hours, and then heated to 80 ± 2 °C for 2 hours. 12.01 g of phenyl glycidyl ether was then slowly added dropwise. The mixture was reacted at 70 °C for 2 hours to obtain a product with terminal primary amine hydrogens blocked. 89.16 g of deionized water was added to obtain a nonionic waterborne epoxy curing agent.

[0057] The curing agent has a solid content of 65.0 wt% and an amine hydrogen equivalent of 192.6 ± 10 (in solid form).

[0058] Example 6: Preparation of a two-component waterborne epoxy coating

[0059] According to the formula in Table 1, the waterborne epoxy curing agent, various additives, pigments, fillers, and deionized water were mixed evenly at high speed. The mixture was then poured into a small laboratory sand mill, and an appropriate amount of zirconium beads were added. The mixture was ground and dispersed until the scraper fineness was <30μm, then allowed to stand to defoam. Finally, the mixture was filtered out as component A of the two-component waterborne epoxy coating. Component A was mixed evenly with commercially available epoxy emulsion component B according to the specified ratio. The mixture was then sprayed onto a substrate using a spray gun and cured at room temperature. As a control, a substrate was prepared using a commercially available epoxy curing agent. The dry film thickness was controlled between 40 and 50μm.

[0060] Table 1 Formulations of Two-Component Waterborne Epoxy Coatings

[0061]

[0062] Example 7: Preparation of two-component waterborne epoxy coatings of Example 1, Comparative Example 1, and Comparative Example 2 and testing of coating performance.

[0063] Table 2 Performance Tests of Coatings

[0064]

[0065] The coating formulations of Comparative Examples 1 and 2 are basically the same as those of Example 1, except that the curing agent of Comparative Example 1 is a commercially available pure polyamide curing agent with a solid content of 65±2wt%; the curing agent of Comparative Example 2 is a commercially available block nonionic waterborne epoxy curing agent with a solid content of 60±2wt%.

[0066] As can be seen from Table 2, compared with the curing agents used in Comparative Examples 1 and 2, the two-component waterborne epoxy coating film prepared with the polyamide-modified waterborne epoxy curing agent obtained by the technical solution of this invention has reached or exceeded the single-type curing agent products in terms of flexibility, pencil hardness, water resistance, acid and alkali resistance, and salt spray resistance. It has obvious technical effects and broad market prospects.

[0067] The above description is only the best specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A polyamide-modified waterborne epoxy curing agent, characterized in that, The polyamide-modified waterborne epoxy curing agent contains nonionic polyether hydrophilic segments grafted onto the side chains, and polyamide structural segments introduced into the main chain via linear block copolymerization. This polyamide-modified waterborne epoxy curing agent is synthesized from the following raw materials in weight percentages: 20-40% polyamide resin, 2-6% polyamine, 3-8% polyether amine, 10-15% liquid epoxy resin, 8-12% monoepoxy compound, and the balance being deionized water. The polyamide resin is selected from the reaction of fatty diacid and fatty diamine. The polyetheramine is an amino-terminated polyether, and the amino-terminated polyether is at least one of JEFFAMINE M-1000, M-2070, M-600, ED-600, ED-900 and ED-2003 produced by HUNTSMAN. The liquid epoxy resin is selected from at least one of DER331 produced by DOW Chemical Company and EPON828 produced by Hexion Company. The polyamide-modified waterborne epoxy curing agent is prepared by the following method, including the following steps: ① Preparation of prepolymer: Polyamine was added to a reaction vessel, the temperature was raised to 40–60°C, and a monoepoxide compound was added dropwise at this temperature over a period of 2–4 hours. After the addition was complete, the reaction was maintained at 70–90°C for 2 hours to prepare compound A containing a terminal primary amine group. Aminated polyether was added to a reaction vessel, the temperature was raised to 60–80°C, and liquid epoxy resin was added dropwise at this temperature over a period of 2–4 hours. After the addition was complete, the reaction was maintained at 120–140°C for 2 hours to prepare compound B containing a hydrophilic segment. All the above operations were carried out under stirring. ②Preparation of nonionic waterborne epoxy curing agent Compound A containing terminal primary amine groups, obtained in step ①, and polyamide resin are added to a reaction vessel and mixed evenly. Then, compound B containing hydrophilic segments, obtained in step ①, is slowly added dropwise at 50±5℃ for 2–4 hours. After the addition is complete, the temperature is gradually increased between 60 and 80℃ and maintained for 4–6 hours. Then, a monoepoxide compound is slowly added dropwise, and the reaction is carried out at 70±5℃ for 2–3 hours to obtain a product with terminal primary amine hydrogens blocked. Deionized water is added to obtain a nonionic waterborne epoxy curing agent. All the above operations are carried out under stirring. The polyamine is selected from at least one of aromatic amines, aliphatic amines, and cycloaliphatic amines. The aromatic amine is selected from at least one of m-phenylenediamine and m-phenylenediamine dimethyldiamine. The cycloaliphatic amine is isophorone diamine. The aliphatic amine is at least one of ethylenediamine, propylenediamine, butanediamine, pentanediamine, hexanediamine, diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

2. The polyamide-modified waterborne epoxy curing agent according to claim 1, characterized in that, The monoepoxide compound is selected from at least one of butyl glycidyl ether, phenyl glycidyl ether, o-tolyl glycidyl ether, octyl glycidyl ether, and benzyl glycidyl ether.

3. The polyamide-modified waterborne epoxy curing agent according to claim 1, characterized in that, The polyamide resin is selected from at least one of polyamide resin 250, polyamide resin 300, polyamide resin 650, and polyamide resin 651.

4. The polyamide-modified waterborne epoxy curing agent according to claim 1, characterized in that, The solid content of the polyamide-modified waterborne epoxy curing agent is 60% to 70%.

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