A branched organosilicon defoamer, its preparation method and application

Abstract

The present invention relates to a branched organosilicon defoamer and its preparation method and application. The branched organosilicon defoamer is prepared by an addition reaction of a (meth)acrylate having a branched structure and a hydrosilyl siloxane having a symmetric Si-O-Si structure centered on a silicon-hydrogen bond. The defoamer is a small molecule organosilicon compound, and the synthesis process is simple, but the defoaming and foam inhibition effects are excellent.

Description

Technical Field

[0001] The present invention specifically relates to a branched silicone defoamer and its preparation method and application. Background Art

[0002] As a functional additive, defoamers are widely used in fields such as chemical industry, medicine, coatings, and construction to eliminate or inhibit foams. The foams that are inevitably generated during industrial production may have an adverse impact on production equipment or product quality. Defoamers can inhibit the formation or generation of foams and have important application value in the industry.

[0003] In the prior art, there are various types of defoamers. For example, small molecule alcohols, and high molecular weight polysiloxane silicones. However, the defoaming effect of small molecule alcohols such as n-butanol is limited and it is difficult to be used in fields with high defoaming requirements. The widely used high molecular weight polysiloxane defoamers usually have a linear structure, and the modified or decorated structures are relatively complex, the synthesis process is cumbersome, and the molecular weight is relatively high. Summary of the Invention

[0004] The object of the present invention is to provide a branched silicone defoamer, which is a small molecule silicone compound with a simple synthesis process but excellent defoaming and foam inhibition effects.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A branched silicone defoamer having a structure represented by Formula I, Formula II or Formula III:

[0007]

[0008]

[0009] Wherein,

[0010] R1 is independently H or methyl;

[0011] R2 is independently a C1-C6 alkyl group;

[0012] And in Formula I, each R1 is the same, and each R2 is the same;

[0013] In Formula II, each R1 is the same, and each R2 is the same;

[0014] In Formula III, each R1 is the same, and each R2 is the same.

[0015] In some embodiments, R1 is H or methyl, and R2 is methyl or ethyl.

[0016] In some embodiments, R1 is H and R2 is methyl.

[0017] In some embodiments, the branched silicone defoamer is selected from the following structural formulas:

[0018]

[0019]

[0020] In the prior art, the defoaming effect of small molecule alcohol defoamers such as n-butanol is limited and it is difficult to be used in fields with high defoaming requirements. The widely used high molecular weight polysiloxane defoamers usually have a linear structure, and the modified or modified structures are relatively complex, the synthesis process is relatively cumbersome, and the molecular weight is relatively high. The inventors of the present application have found through research that by using the branched silicone small molecules with the above specific structures, excellent defoaming performance can be achieved, and compared with the traditional high molecular weight linear polysiloxane defoamers, its defoaming performance is improved. The reason is that the defoamer of the present application has a branched structure. Compared with linear molecules, after the branched molecules enter the surface of the liquid film to be defoamed, due to their more complex and disordered structure, they cannot be arranged in an orderly manner on the foam surface of the liquid film, and thus can quickly replace the original foaming system molecules at the gas-liquid interface, resulting in a rapid decrease in the surface tension of the liquid film, a pressure difference is formed between the liquid films, and finally the foam quickly breaks, achieving the defoaming effect. The traditional high molecular weight linear polysiloxane defoamers mainly have defoaming performance because they have a siloxane hydrophobic chain segment structure. However, its hydrophobic chain segment is short and it is easy to be densely arranged on the liquid film surface, which is instead not conducive to the improvement of its defoaming effect.

[0021] The structures of each branched chain segment of the above-mentioned branched silicone defoamer are the same, and in each branched chain segment, the siloxane structure is also symmetric. By adopting this specific symmetric structure, the branched silicone defoamer has high symmetry and isotropy. Furthermore, when the branched silicone defoamer is fully mixed with the system to be defoamed, the intermolecular forces between the two are isotropic at the hydrophobic end of the branched silicone defoamer, and there will be no situation where the defoamer cannot uniformly destroy the foam due to the too strong hydrophobicity at one end of the branched silicone defoamer. Therefore, this specific symmetric structure is beneficial to further improving its defoaming effect.

[0022] The present invention also provides a preparation method of the aforementioned branched silicone defoamer. The preparation method uses the (meth)acrylate shown in Formula I-1, Formula II-1 or Formula III-1 and the siloxane shown in Formula I-2 as raw materials and performs an addition reaction in the presence of a catalyst;

[0023]

[0024] Among them, in Formula I-1, R1 is H or methyl; in Formula II-1, R1 is H or methyl;

[0025] In formula III-1, R1 is H or methyl;

[0026] In formula I-2, R2 is a C1-C6 alkyl group.

[0027] The carbon-carbon double bond on the aforementioned (meth)acrylate reacts with the silicon-hydrogen bond in the siloxane shown in formula I-2 to form the target branched silicone defoamer. The siloxane shown in formula I-2 has a symmetric Si-O-Si structure centered on the silicon-hydrogen bond. Using the siloxane with this structure as the raw material can make the target product of the branched silicone defoamer have a symmetric structure, which is beneficial to its effective use as a defoamer.

[0028] In some embodiments, R1 is H or methyl; R2 is methyl or ethyl.

[0029] In some embodiments, R1 is H and R2 is methyl.

[0030] In some embodiments, the (meth)acrylate is selected from one or a combination of more than one of dipentaerythritol hexa(meth)acrylate, bis-trimethylolpropane tetra(meth)acrylate, and trimethylolpropane tri(meth)acrylate. Among them, dipentaerythritol hexa(meth)acrylate corresponds to formula I-1, where R1 is H or methyl; bis-trimethylolpropane tetra(meth)acrylate corresponds to formula II-1, where R1 is H or methyl; trimethylolpropane tri(meth)acrylate corresponds to formula III-1, where R1 is H or methyl.

[0031] In some embodiments, the catalyst is a platinum-based catalyst, preferably chloroplatinic acid.

[0032] In some embodiments, the molar ratio of the (meth)acrylate to the siloxane is 1:3.3 to 6.6.

[0033] In some embodiments, the total molar amount of the (meth)acrylate and the siloxane is in a molar ratio of 1:0.02 to 0.06 to the molar amount of the catalyst.

[0034] In some embodiments, the addition reaction is carried out under the protection of an inert gas.

[0035] In some embodiments, the temperature of the addition reaction is 100 to 105 °C.

[0036] In some embodiments, the time of the addition reaction is 6 to 8 h.

[0037] In some embodiments, the preparation method includes the following steps:

[0038] (1)Disperse the (meth)acrylate shown in Formula I-1, Formula II-1 or Formula III-1 in the siloxane shown in Formula I-2 to obtain a dispersion;

[0039] (2)Heat the dispersion to 45-55 °C and mix it evenly under stirring;

[0040] (3)Pass an inert gas into the dispersion, and then add the catalyst;

[0041] (4)Heat the dispersion to 100-105 °C to carry out the addition reaction.

[0042] The (meth)acrylate shown in Formula I-1, Formula II-1 or Formula III-1 contains an unsaturated carbon-carbon double bond. Before the reaction starts, the catalyst such as chloroplatinic acid first coordinates with the siloxane such as bis(trimethylsilyloxy)methylsilane shown in Formula I-2 to generate an active metal-silicon compound complex. The π-electrons of the olefin form an electrophilic addition reaction with the silicon-hydrogen bond in the metal-silicon compound complex, generating a new carbon-silicon bond and a new carbon-carbon bond. The mechanism of the addition of the unsaturated carbon-carbon double bond and the silicon-hydrogen bond is a metal-catalyzed electrophilic addition process.

[0043] In some embodiments, the preparation method further includes separating the reaction system after the addition reaction to obtain the target product.

[0044] In some embodiments, the separation is rotary evaporation under reduced pressure.

[0045] The present invention also provides the use of the aforementioned branched organosilicon defoamer for defoaming in the fields of chemical industry, medicine, coatings or construction.

[0046] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0047] (1)The present invention adopts a branched organosiloxane small molecule with a specific structure, which can achieve excellent defoaming performance, and compared with the traditional high-molecular linear polysiloxane defoamer, its defoaming performance is improved.

[0048] (2)The defoamer of the present application has a branched structure. Compared with the linear molecule, after the branched molecule enters the surface of the liquid film to be defoamed, due to its more complex and disordered structure, it cannot be oriented on the foam surface of the liquid film, and thus can quickly replace the molecules of the original foaming system at the gas-liquid interface, resulting in a rapid decrease in the surface tension of the liquid film, forming a pressure difference between the liquid films, and finally causing the foam to quickly break, achieving the defoaming effect.

[0049] (3) The structure of each branched chain segment of the branched organosilicon defoamer of the present invention is the same, and in each branched chain segment, the siloxane structure is also symmetric. By adopting this specific symmetric structure, the branched organosilicon defoamer has high symmetry and isotropy. Furthermore, when the branched organosilicon defoamer is fully mixed with the system to be defoamed, the intermolecular force between the two is isotropic at the hydrophobic end of the branched organosilicon defoamer, and it will not occur that the defoamer cannot uniformly destroy the foam due to the overly strong hydrophobicity at one end of the branched organosilicon defoamer.

[0050] (4) The defoamer of the present invention is a small molecule, and the preparation process is simple. Description of the Drawings

[0051] Figure 1 : Infrared spectrum of the branched organosilicon defoamer prepared in Example 1, where TSO refers to bis(trimethylsiloxy)methylsilane, T1 refers to dipentaerythritol hexaacrylate, and T1-TSO refers to the reaction product branched organosilicon defoamer.

[0052] Figure 2 : NMR spectrum of the branched organosilicon defoamer prepared in Example 1.

[0053] Figure 3 : Effect diagram of the branched organosilicon defoamer prepared in Examples 1-3 for defoaming AEO-9.

[0054] Figure 4 : Effect diagram of the branched organosilicon defoamer prepared in Examples 1-3 for foam inhibition of AEO-9.

[0055] Figure 5 : Effect diagram of the branched organosilicon defoamer prepared in Examples 1-3 for defoaming SDBS.

[0056] Figure 6 : Effect diagram of the branched organosilicon defoamer prepared in Examples 1-3 for foam inhibition of SDBS.

[0057] Figure 7 : Effect diagram of the branched organosilicon defoamer prepared in Examples 1-3 for defoaming TDAB.

[0058] Figure 8 : Effect diagram of the branched organosilicon defoamer prepared in Examples 1-3 for foam inhibition of TDAB.

[0059] Figure 9 : Effect diagram of the branched organosilicon defoamer prepared in Examples 1-3 for defoaming DP.

[0060] Figure 10:Effect diagram of the branched silicone defoamer prepared in Examples 1-3 for DP defoaming. Detailed implementation mode

[0061] The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention, but the present invention is not limited to the scope of the examples described herein.

[0062] Example 1

[0063] This example provides a branched silicone defoamer prepared based on dipentaerythritol hexaacrylate and bis(trimethylsiloxy)methylsilane, and its preparation method is as follows:

[0064] The whole reaction is carried out under the condition of normal pressure and 105 °C. An oil bath is used for heating. Nitrogen is introduced at the right end of the three-necked flask to exhaust the air in the system and protect the reaction system. Condensed water is connected at the upper end, and a thermometer is inserted at the left end.

[0065] (1) Accurately weigh 2 g of dipentaerythritol hexaacrylate and place it in a round-bottom flask, then add 12 g of bis(trimethylsiloxy)methylsilane, and put in a magnetic rotor.

[0066] (2) Set up the device according to the above structure, then immediately introduce nitrogen, turn on the magnetic stirring and heat to 105 °C in 40 minutes.

[0067] (3) After introducing nitrogen for 10 minutes, use a pipette to add 110 μL of chloroplatinic acid catalyst to the round-bottom flask. Under the action of the catalyst, the reaction process can be stopped after 6 hours.

[0068] (4) Collect the product by rotary evaporation under reduced pressure: Rotary evaporate the mixture after the reaction for 2 hours under reduced pressure. The water bath temperature during rotary evaporation is 80 °C, and the branched silicone defoamer of formula I can be obtained, marked as T1-TSO.

[0069] The reaction formula is as follows:

[0070]

[0071] The infrared spectrum of the above-prepared branched silicone defoamer is as Figure 1 shown, where TSO refers to the raw material bis(trimethylsiloxy)methylsilane, T1 refers to the raw material dipentaerythritol hexaacrylate, and T1-TSO refers to the reaction product branched silicone defoamer. It can be seen that for the branched silicone defoamer product T1-TSO relative to the T1 raw material, the stretching vibration peak of the carbon-carbon double bond at 1650 cm -1 completely disappears, indicating that the double bond reaction is complete, while for T1-TSO relative to the TSO raw material, at 2160 cm -1The peak of the Si-H bond at [location] disappeared, indicating that the raw material of bis(trimethylsilyloxy)methylsilane with an excessive stoichiometric ratio had been completely removed by rotary evaporation.

[0072] The NMR spectrum of the branched organosilicon defoamer prepared as described above is as Figure 2 shown. Among them, for the hydrogen on the Si-methyl, the chemical shift is generally around 0, corresponding to Figure 2 the two peaks a and b in [reference]. For the hydrogen on the Si-methylene, the chemical shift is generally a little larger than that of the Si-methyl, around 1. Figure 2 The methylene in the d peak in [reference] (usually around 2.0) is affected by the electron-withdrawing effect of the carbonyl group and is located around 2.25. The e peak is the hydrogen on the methylene connected to the ester group (usually around 4.0). Affected by the electron-withdrawing effect of the ester group and directly connected to oxygen, its chemical shift is relatively large and is located around 4.2. The f peak is the hydrogen on the methylene directly connected to oxygen.

[0073] Example 2

[0074] This example provides a branched organosilicon defoamer material prepared based on ditrimethylolpropane tetraacrylate and bis(trimethylsilyloxy)methylsilane. The preparation method is as follows:

[0075] The whole reaction is carried out under the condition of normal pressure at 105 °C. An oil bath is used for heating. Nitrogen is introduced at the right end of the three-necked flask to exhaust the air in the system and protect the reaction system. Condensed water is connected at the upper end, and a thermometer is inserted at the left end.

[0076] (1) Accurately weigh 2 g of ditrimethylolpropane tetraacrylate and place it in a round-bottom flask. Then add 8 g of bis(trimethylsilyloxy)methylsilane and put in a magnetic rotor.

[0077] (2) Set up the device according to the aforementioned structure. Then immediately introduce nitrogen, turn on the magnetic stirring and heat to 105 °C in 40 minutes.

[0078] (3) After introducing nitrogen for 10 minutes, use a pipette to add 110 μL of chloroplatinic acid catalyst to the round-bottom flask. Under the action of the catalyst, this reaction process can be stopped after 6 hours.

[0079] (4) Collect the product by rotary evaporation under reduced pressure: Rotate the mixture after the reaction under reduced pressure for 2 hours. The water bath temperature during rotary evaporation is 80 °C, and the branched organosilicon defoamer of formula II can be obtained, marked as T2-TSO.

[0080] The reaction formula is as follows:

[0081]

[0082] Example 3

[0083] This embodiment provides a branched organic silicon defoamer material prepared based on trimethylolpropane triacrylate and bistrimethylsiloxymethylsilane, and the preparation method thereof is as follows:

[0084] The entire reaction was carried out at normal pressure and 105°C, heated in an oil bath, and nitrogen was introduced into the right end of the three-necked flask to exhaust the air in the system and protect the reaction system. Condensed water was connected to the upper end and a thermometer was inserted into the left end.

[0085] (1) Accurately weigh 2 g of trimethylolpropane triacrylate and place it in a round-bottom flask. Then add 6 g of bistrimethylsiloxymethylsilane and place it in a magnetic rotor.

[0086] (2) The apparatus was assembled according to the above structure, and then nitrogen was immediately introduced, magnetic stirring was turned on, and the mixture was heated to 105°C for 40 min.

[0087] (3) After nitrogen was introduced for 10 min, 110 μL of chloroplatinic acid catalyst was added to the round-bottom flask using a pipette. Under the action of the catalyst, the reaction process continued for 6 h and then stopped.

[0088] (4) Collecting the product by vacuum rotary evaporation: The mixed solution after the reaction was completed was subjected to vacuum rotary evaporation for 2 h at a water bath temperature of 80° C., thereby obtaining a branched organosilicon defoaming agent of formula II, which was labeled as T3-TSO.

[0089] The reaction formula is as follows:

[0090]

[0091] Example 4

[0092] This embodiment provides an example of using the branched organosilicon defoamer prepared in Examples 1-3 for AEO-9 defoaming and foam suppression: wherein AEO-9 refers to the non-ionic surfactant polyoxyethylene laurate.

[0093] The specific preparation method of the surfactant foaming liquid refers to the national standard GB / T 21885-2008. The foaming liquid uses water as a solvent, and the concentration is set to 0.5wt.%. 5g of the surfactant (accurate to 0.01g) is accurately weighed and dissolved in 1000mL of deionized water, and fully stirred to ensure that the surfactant is evenly dispersed to form a homogeneous foaming liquid.

[0094] When preparing the defoamer of the present invention, water is used as a dispersion medium and petroleum ether is used as a spreading agent. The T1-TSO or T2-TSO or T3-TSO prepared above, petroleum ether and deionized water are uniformly mixed in a mass ratio of 3:1:6 to obtain a defoamer stock solution with a defoamer content of 30 wt.% for standby use.

[0095] When preparing the comparative linear silicone oil defoamer, water is used as the dispersion medium and petroleum ether is used as the spreading agent. Linear dimethyl silicone oil (polydimethylsiloxane), petroleum ether, and deionized water are uniformly mixed according to a mass ratio of 3:1:6 to obtain a 30 wt.% content of the comparative defoamer stock solution for standby.

[0096] The rapid shaking flask method is used to evaluate the foaming ability of the foaming liquid and the defoaming and foam inhibition efficiency of the defoamer. A stoppered graduated cylinder with a calibrated volume of 100 mL is used as the container for foaming, defoaming, and foam inhibition.

[0097] The foaming ability of the foaming liquid is related to its ability to capture air volume. The volume of air it captures is calculated by subtracting the volume of the solution itself from the total volume of the foam system (solution + foam).

[0098] The foaming operation is as follows: Take 15 ml of the prepared foaming liquid and add it to the stoppered graduated cylinder. At a temperature of 25 °C, a water bath is used to seal and preserve the foaming liquid during the test. Cover the graduated cylinder stopper and shake it up and down 100 times. During this process, the solution collides violently with the inner wall of the graduated cylinder and captures air to form foam. After the up-and-down shaking operation is completed, let the graduated cylinder stand still until the foam column is stable. When the height of the foam column in the graduated cylinder does not change with time, record the maximum volume Vmax of the foam column at this time.

[0099] The defoaming operation is as follows: Accurately weigh 0.01, 0.05, and 0.1 grams of the defoamer stock solution into the graduated cylinder respectively, time for 90 s, and record the remaining height of the foam. The results are as Figure 3 shown, where T1 - TSO(0.01) in the abscissa represents the use of the T1 - TSO defoamer with a dosage of 0.01. Among them, XXSY refers to the comparative linear dimethyl silicone oil. The defoaming ability refers to the ability to eliminate the foam after it is generated.

[0100] The foam inhibition operation is as follows: Take 15 ml of the prepared foaming liquid and add it to the stoppered graduated cylinder. Accurately weigh 0.01, 0.05, and 0.1 grams of the defoamer stock solution into the graduated cylinder respectively. At a temperature of 25 °C, a water bath is used to seal and preserve the foaming liquid during the test. Cover the graduated cylinder stopper and shake it up and down 100 times. During this process, the solution collides violently with the inner wall of the graduated cylinder and captures air to form foam. After the up-and-down shaking operation is completed, let the graduated cylinder stand still until the foam column is stable. When the height of the foam column in the graduated cylinder does not change with time, record the height of the foam column at this time. The results are as Figure 4 shown, and the meaning of the abscissa is the same as Figure 3 . The foam inhibition ability refers to the ability to inhibit the generation of foam.

[0101] It can be seen that the defoamers prepared in Examples 1 - 3 have excellent defoaming performance and foam inhibition performance for non-ionic surfactants, and their effects are better than those of traditional linear dimethyl silicone oil.

[0102] Example 5

[0103] This example provides an example of using the branched organosilicon defoamer prepared in Examples 1 - 3 for defoaming and foam suppression of SDBS: Among them, SDBS refers to the anionic surfactant sodium dodecylbenzenesulfonate.

[0104] The operations of defoaming and foam suppression are the same as those in Example 4. Among them, the defoaming result is as Figure 5 shown, and the foam suppression result is as Figure 6 shown.

[0105] It can be seen that the defoamer prepared in Examples 1 - 3 has excellent defoaming performance and foam suppression performance for anionic surfactants, and its effect is better than that of traditional linear dimethyl silicone oil.

[0106] Example 6

[0107] This example provides an example of using the branched organosilicon defoamer prepared in Examples 1 - 3 for defoaming and foam suppression of TDAB: Among them, TDAB refers to the cationic surfactant cetyltrimethylammonium bromide.

[0108] The operations of defoaming and foam suppression are the same as those in Example 4. Among them, the defoaming result is as Figure 7 shown, and the foam suppression result is as Figure 8 shown.

[0109] It can be seen that the defoamer prepared in Examples 1 - 3 has excellent defoaming performance and foam suppression performance for cationic surfactants, and its effect is better than that of traditional linear dimethyl silicone oil.

[0110] Example 7

[0111] This example provides an example of using the branched organosilicon defoamer prepared in Examples 1 - 3 for defoaming and foam suppression of DP: Among them, DP refers to the commercially available Diaopai detergent.

[0112] The operations of defoaming and foam suppression are the same as those in Example 4. Among them, the defoaming result is as Figure 9 shown, and the foam suppression result is as Figure 10 shown.

[0113] It can be seen that the defoamer prepared in Examples 1 - 3 has excellent defoaming performance and foam suppression performance for commercially available detergents, and its effect is better than that of traditional linear dimethyl silicone oil.

[0114] The above examples are only for illustrating the technical concept and characteristics of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A branched organosilicon defoamer for defoaming in the chemical, pharmaceutical, coating or construction fields, characterized by: The branched organosilicon defoamer has a structure shown in the following formula I or formula II: in, R1 is independently H or methyl; R2 is independently C1-C6 alkyl; And in Formula I, each R1 is the same, each R2 is the same; In Formula II, each R1 is the same, and each R2 is the same.

2. The use according to claim 1, characterized in that: R1 is H or methyl, and R2 is methyl or ethyl.

3. The use according to claim 1, characterized in that: The branched organosilicon defoamer is selected from the following structural formula:

4. The use according to any one of claims 1 to 3, characterized in that: The branched organosilicon defoamer is prepared by the following preparation method: the preparation method uses the (meth)acrylate represented by formula I-1 and formula II-1 and the siloxane represented by formula I-2 as raw materials, and performs an addition reaction in the presence of a catalyst; Wherein, in formula I-1, R1 is H or methyl; In formula II-1, R1 is H or methyl; in formula I-2, R2 is C1-C6 alkyl.

5. The use according to claim 4, characterized in that: In formula I-1 or II-1, R1 is H or methyl; in formula I-2, R2 is methyl or ethyl; and / or, the (meth)acrylate is selected from dipentaerythritol hexa(meth)acrylate.

6. The use according to claim 4, characterized in that: The catalyst is a platinum catalyst.

7. The use according to claim 4, characterized in that: The catalyst is chloroplatinic acid.

8. The use according to claim 4, characterized in that: The molar ratio of the (meth)acrylate to the siloxane is 1:3.3-6.6; and / or the ratio of the total molar amount of the (meth)acrylate and the siloxane to the molar amount of the catalyst is 1:0.02-0.

06.

9. The use according to claim 4, characterized in that: The addition reaction is carried out under the protection of an inert gas; and / or, the temperature of the addition reaction is 100 to 105° C.; and / or, the time of the addition reaction is 6 to 8 hours.

10. The use according to claim 4, characterized in that: The preparation method comprises the following steps: (1) dispersing the (meth)acrylate represented by formula I-1 or formula II-1 in the siloxane represented by formula I-2 to obtain a dispersion; (2) heating the dispersion to 45-55° C. and mixing uniformly under stirring; (3) introducing an inert gas into the dispersion and then adding the catalyst; (4) The dispersion is heated to 100-105° C. to carry out the addition reaction.

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