Preparation method and application of an impact-resistant waterproof and heat-insulating material

Abstract

The present invention discloses a preparation method and application of an impact-resistant waterproof thermal insulation material. Vinyl polyurethane, styrene, and azobisisobutyronitrile are subjected to a polymerization reaction to obtain the impact-resistant waterproof thermal insulation material. Vinyl polyurethane, as a cross-linking agent, undergoes a graft cross-linking polymerization reaction with styrene monomers. The cross-linked polystyrene contains a three-dimensional porous cross-linked network, forming more pore structures in the matrix, which is beneficial to the thermal conductivity and enhances the thermal insulation performance. Moreover, the water absorption rate of the thermal insulation material is low, and the waterproof performance is good. At the same time, spirophosphate and piperazine are grafted into the matrix of the impact-resistant waterproof thermal insulation material to form an intumescent flame retardant system, which promotes the dehydration on the surface of the thermal insulation material to form an intumescent carbon layer, thereby inhibiting the combustion process, increasing the limiting oxygen index of the thermal insulation material, and showing excellent flame retardant performance and impact strength.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal insulation materials, and specifically to a preparation method and application of an impact-resistant and waterproof thermal insulation material. Background Art

[0002] Polystyrene has low water absorption, good insulation performance, and excellent corrosion resistance. It can be made into materials such as foams, plastics, and films, and is widely used in the fields of thermal insulation, building materials, packaging, etc. However, polystyrene foam has problems such as poor mechanical properties and poor impact resistance, and does not have flame retardant properties, which greatly limits its practical applications. Usually, adding a reactive flame retardant to polystyrene can improve the flame retardant properties of the polystyrene material, and at the same time, the reactive flame retardant has little impact on the use performance of the material.

[0003] As a high-elasticity, high-toughness, and excellent mechanical property polymer, polyurethane can be used as a toughening agent to improve the mechanical properties such as toughness and impact resistance of materials. The patent with the publication number CN108948554B discloses that using styrene, initiator, polyolefin polyol, diisocyanate, and diamine chain extender as raw materials, the prepared polyolefin-based polyurethane elastomer toughened polystyrene blend material has excellent physical and mechanical properties and good processing performance. However, the polystyrene material of this patent does not have good flame retardant properties and does not show thermal insulation performance. Summary of the Invention

[0004] Technical problems to be solved: The present invention provides a polystyrene composite material with strong impact resistance, good waterproof performance, excellent heat preservation effect, and at the same time having a flame retardant effect.

[0005] Technical solution: A preparation method of an impact-resistant and waterproof thermal insulation material, comprising the following steps:

[0006] Step (1): Add dry polyol and diisocyanate monomer into a flask, introduce nitrogen, stir and react, then add acetone, vinyl flame retardant chain extender, and dibutyltin dilaurate, continue to stir and react, and subject the solution to vacuum distillation and drying to obtain vinyl polyurethane.

[0007] Step (2): Add N,N-dimethylformamide, vinyl polyurethane, and styrene into a flask, stir and mix evenly, introduce nitrogen, add the initiator azobisisobutyronitrile, stir and react, filter the solvent, place it in a Soxhlet extractor, extract successively with methanol and tetrahydrofuran, and then dry to obtain the impact-resistant and waterproof thermal insulation material.

[0008] Among them, in step (1), the ratio of polyol, diisocyanate monomer, and vinyl flame retardant chain extender is 1 mol:(2.4 - 2.6) mol:(1.2 - 1.3) mol.

[0009] Among them, the polyol includes polyethylene glycol and polytetrahydrofuran ether diol; the diisocyanate monomer includes toluene-2,4-diisocyanate and 4,4'-methylenebis(phenyl isocyanate).

[0010] Among them, in step (2), the ratio of vinyl polyurethane to styrene is (5 - 60) g:100 g.

[0011] Among them, in step (2), the reaction temperature is 65 - 80 °C and the reaction time is 24 - 36 h.

[0012] Among them, the preparation method of the vinyl flame retardant chain extender is as follows:

[0013] Step S1: Under ice bath, add acetonitrile, tetrahydrofuran or N,N-dimethylformamide solvent to the flask, and add 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide, 3-chloro-2-hydroxypropyl methacrylate, and pyridine in a ratio of 1 mol:(2.4 - 3) mol:(2.4 - 3) mol. Then stir and react at room temperature for 18 - 24 h. After filtration, distill the filtrate under reduced pressure, and recrystallize and purify the product in ethanol to obtain the flame retardant chain extender precursor.

[0014] Step S2: Add acetonitrile or N,N-dimethylformamide solvent to the flask, and add the flame retardant chain extender precursor, 1-(2-hydroxyethyl)piperazine, and potassium carbonate in a ratio of 1 mol:(2 - 2.2) mol:(2.5 - 3.2) mol. Heat to 50 - 65 °C, stir and react for 3 - 8 h, distill the solution under reduced pressure, wash with water, and recrystallize and purify the product in ethanol to obtain the vinyl flame retardant chain extender.

[0015] Beneficial technical effects: The present invention uses 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide and 3-chloro-2-hydroxypropyl methacrylate to carry out an esterification reaction, and then carries out a substitution reaction with 1-(2-hydroxyethyl)piperazine to obtain a novel vinyl flame retardant chain extender containing two alkenyl groups and two hydroxyl groups. Using it as the diol chain extender of polyurethane, it reacts with polyol and diisocyanate monomer to obtain vinyl polyurethane.

[0016] The vinyl flame retardant chain extender component in the vinyl polyurethane prepared by the present invention contains two alkenyl groups and can be used as a crosslinking agent to carry out a graft crosslinking polymerization reaction with styrene monomer. The crosslinked polystyrene contains a three-dimensional porous crosslinking network, forming more pore structures in the matrix, which is beneficial to reducing the thermal conductivity of the impact-resistant waterproof and heat-insulating material and enhancing the heat-insulating performance. And the water absorption rate of the heat-insulating material is low and the waterproof performance is good.

[0017] In the present invention, a flame retardant chain extender precursor is used as a chain extender to graft a spirophosphate and a piperazine structure onto a polyurethane matrix. After further polymerization with styrene, the spirophosphate and piperazine are grafted onto the matrix of the impact-resistant waterproof thermal insulation material. The spirophosphate and piperazine form an intumescent flame retardant system, which can generate incombustible gases such as nitrogen during combustion, promote dehydration on the surface of the thermal insulation material to form an intumescent carbon layer, thereby inhibiting the combustion process, increasing the limiting oxygen index of the thermal insulation material, and having excellent flame retardant properties. Moreover, polyurethane has high elasticity, good toughness, and excellent mechanical properties. Grafting polyurethane molecular chains onto polystyrene enhances the interfacial bonding force between polyurethane and polystyrene, improves their compatibility, enables polyurethane to have a better toughening effect on polystyrene, and significantly increases the impact strength of the polystyrene thermal insulation material. Description of the Drawings

[0018] Figure 1 is the preparation reaction formula of the vinyl flame retardant chain extender. Detailed Embodiments

[0019] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments and drawings, but the present invention is not limited to the following embodiments only.

[0020] The CAS number of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide of the present invention is 714-87-4. The CAS number of 3-chloro-2-hydroxypropyl methacrylate is 13159-52-9. The CAS number of 1-(2-hydroxyethyl)piperazine is 103-76-4.

[0021] Example 1

[0022] (1) Under an ice bath, add 20 mL of acetonitrile solvent, 3 mmol of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide, 7.8 mmol of 3-chloro-2-hydroxypropyl methacrylate, and 9 mmol of pyridine to a flask, and then stir the reaction at room temperature for 18 h. After filtration, the filtrate is distilled under reduced pressure, and the product is recrystallized and purified in ethanol to obtain the flame retardant chain extender precursor.

[0023] (2) Add 40 mL of acetonitrile, 3 mmol of the flame retardant chain extender precursor, 6 mmol of 1-(2-hydroxyethyl)piperazine, and 7.5 mmol of potassium carbonate to a flask, heat to 65 °C, stir the reaction for 5 h, distill the solution under reduced pressure, wash with water, and the product is recrystallized and purified in ethanol to obtain the vinyl flame retardant chain extender.

[0024] (3) Add 1000 of 20 mmol of dry polytetrahydrofuran ether diol and 47 mmol of 4,4'-methylenebis(phenyl isocyanate) to the flask, introduce nitrogen, stir and react, then add 10 mL of acetone, 25 mmol of vinyl flame retardant chain extender, and 0.04 mmol of dibutyltin dilaurate. Continue to stir and react, and distill the solution under reduced pressure and dry to obtain vinyl polyurethane.

[0025] (4) Add 80 mL of N,N-dimethylformamide, 2 g of vinyl polyurethane, and 40 g of styrene to the flask, stir and mix evenly, introduce nitrogen, add 3 g of initiator azobisisobutyronitrile, heat to 65 °C, stir and react for 24 h, filter the solvent, place it in a Soxhlet extractor, extract successively with methanol and tetrahydrofuran, and then dry to obtain an impact-resistant waterproof and heat-insulating material.

[0026] Example 2

[0027] (1) Under an ice bath, add 30 mL of tetrahydrofuran, 3 mmol of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide, 9 mmol of 3-chloro-2-hydroxypropyl methacrylate, and 9 mmol of pyridine to the flask, and then stir and react at room temperature for 18 h. After filtration, distill the filtrate under reduced pressure, and purify the product by recrystallization in ethanol to obtain a flame retardant chain extender precursor.

[0028] (2) Add 40 mL of N,N-dimethylformamide, 3 mmol of flame retardant chain extender precursor, 6.6 mmol of 1-(2-hydroxyethyl)piperazine, and 9.6 mmol of potassium carbonate to the flask, heat to 50 °C, stir and react for 8 h, distill the solution under reduced pressure, wash with water, and purify the product by recrystallization in ethanol to obtain a vinyl flame retardant chain extender.

[0029] (3) Add 1000 of 20 mmol of dry polytetrahydrofuran ether diol and 44 mmol of toluene-2,4-diisocyanate to the flask, introduce nitrogen, stir and react, then add 10 mL of acetone, 24 mmol of vinyl flame retardant chain extender, and 0.03 mmol of dibutyltin dilaurate. Continue to stir and react, and distill the solution under reduced pressure and dry to obtain vinyl polyurethane.

[0030] (4) Add 80 mL of N,N-dimethylformamide, 12 g of vinyl polyurethane, and 40 g of styrene to the flask, stir and mix evenly, introduce nitrogen, add 3.2 g of initiator azobisisobutyronitrile, heat to 80 °C, stir and react for 24 h, filter the solvent, place it in a Soxhlet extractor, extract successively with methanol and tetrahydrofuran, and then dry to obtain an impact-resistant waterproof and heat-insulating material.

[0031] Example 3

[0032] (1) Under an ice bath, add 20 mL of N,N-dimethylformamide solvent, 3 mmol of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide, 7.2 mmol of 3-chloro-2-hydroxypropyl methacrylate, and 7.2 mmol of pyridine to a flask. Then stir the reaction at room temperature for 24 h. After filtration, distill the filtrate under reduced pressure. The product is recrystallized and purified in ethanol to obtain the flame retardant chain extender precursor.

[0033] (2) Add 40 mL of N,N-dimethylformamide solvent, 3 mmol of the flame retardant chain extender precursor, 6 mmol of 1-(2-hydroxyethyl)piperazine, and 7.5 mmol of potassium carbonate to a flask. Heat to 50 °C and stir the reaction for 8 h. Distill the solution under reduced pressure. After washing with water, the product is recrystallized and purified in ethanol to obtain the vinyl flame retardant chain extender.

[0034] (3) Add 20 mmol of dry polyethylene glycol 1000 and 52 mmol of toluene-2,4-diisocyanate to a flask. Pass in nitrogen. After stirring the reaction, add 10 mL of acetone, 26 mmol of the vinyl flame retardant chain extender, and 0.04 mmol of dibutyltin dilaurate. Continue stirring the reaction. Distill the solution under reduced pressure and dry to obtain vinyl polyurethane.

[0035] (4) Add 100 mL of N,N-dimethylformamide, 20 g of vinyl polyurethane, and 40 g of styrene to a flask. Stir and mix well. Pass in nitrogen. Add 3.5 g of the initiator azobisisobutyronitrile. Heat to 70 °C and stir the reaction for 36 h. Filter the solvent and place it in a Soxhlet extractor. Extract successively with methanol and tetrahydrofuran, and then dry to obtain the impact-resistant waterproof thermal insulation material.

[0036] Example 4

[0037] (1) Under an ice bath, add 30 mL of acetonitrile solvent, 3 mmol of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide, 7.8 mmol of 3-chloro-2-hydroxypropyl methacrylate, and 7.8 mmol of pyridine to a flask. Then stir the reaction at room temperature for 24 h. After filtration, distill the filtrate under reduced pressure. The product is recrystallized and purified in ethanol to obtain the flame retardant chain extender precursor.

[0038] (2) Add 40 mL of N,N-dimethylformamide solvent, 3 mmol of the flame retardant chain extender precursor, 6.3 mmol of 1-(2-hydroxyethyl)piperazine, and 8.4 mmol of potassium carbonate to a flask. Heat to 65 °C and stir the reaction for 3 h. Distill the solution under reduced pressure. After washing with water, the product is recrystallized and purified in ethanol to obtain the vinyl flame retardant chain extender.

[0039] (3) Add 20 mmol of dry polyethylene glycol 1000 and 44 mmol of 4,4'-methylenebis(phenyl isocyanate) to the flask, introduce nitrogen, stir and react, then add 10 mL of acetone, 24 mmol of vinyl flame retardant chain extender, and 0.03 mmol of dibutyltin dilaurate. Continue to stir and react, distill the solution under reduced pressure, and dry to obtain vinyl polyurethane.

[0040] (4) Add 120 mL of N,N-dimethylformamide, 30 g of vinyl polyurethane, and 40 g of styrene to the flask, stir and mix evenly, introduce nitrogen, add 3.6 g of initiator azobisisobutyronitrile, heat to 80 °C, stir and react for 30 h, filter the solvent, place it in a Soxhlet extractor, extract successively with methanol and tetrahydrofuran, and then dry to obtain an impact-resistant waterproof and heat-insulating material.

[0041] Comparative Example 1

[0042] (1) Add 80 mL of N,N-dimethylformamide and 40 g of styrene to the flask, stir and mix evenly, introduce nitrogen, add 3 g of initiator azobisisobutyronitrile, heat to 65 °C, stir and react for 24 h, filter the solvent, place it in a Soxhlet extractor, extract successively with methanol and tetrahydrofuran, and then dry to obtain an impact-resistant waterproof and heat-insulating material.

[0043] Comparative Example 2

[0044] (1) Add 20 mmol of dry polytetrahydrofuran ether glycol 1000 and 47 mmol of 4,4'-methylenebis(phenyl isocyanate) to the flask, introduce nitrogen, stir and react, then add 10 mL of acetone, 25 mmol of 1,4-butanediol, and 0.04 mmol of dibutyltin dilaurate. Continue to stir and react, distill the solution under reduced pressure, and dry to obtain polyurethane.

[0045] (2) Add 80 mL of N,N-dimethylformamide, 2 g of polyurethane, and 40 g of styrene to the flask, stir and mix evenly, introduce nitrogen, add 3 g of initiator azobisisobutyronitrile, heat to 65 °C, stir and react for 24 h, filter the solvent, place it in a Soxhlet extractor, extract successively with methanol and tetrahydrofuran, and then dry to obtain an impact-resistant waterproof and heat-insulating material.

[0046] Use a fully automatic specific surface area and porosity analyzer to measure the pore volume of the impact-resistant waterproof and heat-insulating material. Before measurement, vacuum degas the heat-insulating material in a nitrogen atmosphere at 100 °C for 3 h.

[0047] Make specimens of the thermal insulation material with dimensions of 50mm×50mm×5mm, place them in distilled water, soak them at 25°C for 72 hours. After soaking, press the specimens to ensure they are completely immersed in water. Take out the specimens, wipe the surface moisture, weigh them, and calculate the water absorption rate. Water absorption rate = (m - m0) / m0×100%. m is the mass of the specimen after water absorption, and m0 is the mass of the specimen before water absorption.

[0048] According to the method of GB / T 42919.1-2023, use a thermal conductivity analyzer to test the thermal conductivity of the thermal insulation material. The size of the thermal insulation material is 20mm×20mm×3mm. The test results are shown in the following table.

[0049] <![CDATA[Total pore volume (m 3 / g)]]> Water absorption rate (%) Thermal conductivity [W / (m·k)] Example 1 0.2472 0.253 0.0629 Example 2 0.3890 0.390 0.0507 Example 3 0.3058 0.328 0.0540 Example 4 0.2187 0.272 0.0742 Comparative Example 1 0.0043 0.024 0.1896 Comparative Example 2 0.0076 0.036 0.1803

[0050] Place the impact-resistant and waterproof thermal insulation material in a flat vulcanizing machine, hot press it at 180°C for 5 minutes under a pressure of 10 MPa, and then cold press it at room temperature for 10 minutes to make standard specimens for performance testing.

[0051] Test the notched impact strength of the thermal insulation material according to the method of GB / T 1043.1-2008.

[0052] Test the oxygen index of the thermal insulation material according to the method of GB / T 2406.1-2008.

[0053]

[0054]

[0055] After testing, in Examples 1-4, vinyl polyurethane containing alkenyl is used as a crosslinking agent to carry out graft crosslinking polymerization reaction with styrene monomer. The crosslinked polystyrene contains a three-dimensional porous crosslinked network, forming more pore structures in the matrix, and the total pore volume reaches 0.2187-0.3890%. Generally, the larger the total pore volume, the more pore structures, the lower the thermal conductivity, the better the thermal insulation performance, and the thermal conductivity is only 0.0507-0.0742 W / (m·k). And the water absorption rate is relatively low, only 0.253-0.390%.

[0056] In Comparative Example 1, vinyl polyurethane was not added, and the styrene monomer could not carry out crosslinking polymerization reaction. The obtained polystyrene does not contain a three-dimensional crosslinked network and porous structure, and the total pore volume of the obtained material is relatively low, the thermal conductivity is large, and the thermal insulation performance is poor.

[0057] In Comparative Example 2, 1,4-butanediol was used as a chain extender, and the obtained polyurethane does not contain alkenyl and cannot carry out crosslinking polymerization reaction with styrene monomer. The total pore volume of the obtained material is relatively low, the thermal conductivity is large, and the thermal insulation performance is poor.

[0058] Meanwhile, in Examples 1-4, a flame retardant chain extender precursor was used as the chain extender to graft the spirophosphate ester and piperazine structure onto the polyurethane matrix. After further polymerization with styrene, the spirophosphate ester and piperazine were grafted onto the matrix of the impact-resistant, waterproof and thermal insulation material. The spirophosphate ester and piperazine formed an intumescent flame retardant system, which could generate incombustible gases such as nitrogen during combustion, promote dehydration on the surface of the thermal insulation material to form an intumescent carbon layer, thus inhibiting the combustion process, increasing the limiting oxygen index of the thermal insulation material, and having excellent flame retardant properties. Moreover, polyurethane has high elasticity, good toughness and excellent mechanical properties. Grafting polyurethane molecular chains onto polystyrene enhanced the interfacial bonding force between polyurethane and polystyrene, making their compatibility better, enabling polyurethane to have a better toughening effect on polystyrene, and significantly improving the impact strength of the polystyrene thermal insulation material.

[0059] In Comparative Example 1, no polyurethane was added, resulting in poor impact strength and low limiting oxygen index of the polystyrene-based thermal insulation material, and poor flame retardancy.

[0060] In Comparative Example 2, the added polyurethane did not contain alkenyl groups and could not undergo cross-linking polymerization reaction with styrene monomers. The interfacial bonding force between polyurethane and polystyrene was low, and their compatibility was poor, resulting in poor impact strength of the material. Moreover, the polyurethane did not contain spirophosphate ester and piperazine intumescent flame retardants, and the limiting oxygen index of the material was low, with poor flame retardancy.

[0061] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several improvements and modifications can be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for preparing an impact-resistant, waterproof and heat-insulating material, characterized in that: The preparation method comprises the following steps: Step (1), adding dry polyol and diisocyanate monomer into a flask, introducing nitrogen, stirring for reaction, adding acetone, vinyl flame retardant chain extender, and dibutyltin dilaurate, continuing stirring for reaction, distilling the solution under reduced pressure, and drying to obtain vinyl polyurethane; The structural formula of the vinyl flame retardant chain extender is Step (2), add N,N-dimethylformamide, vinyl polyurethane and styrene into a flask, stir and mix, introduce nitrogen, add initiator azobisisobutyronitrile, stir and react, filter the solvent, place in a Soxhlet extractor, extract with methanol and tetrahydrofuran in sequence, and then dry to obtain an impact-resistant, waterproof and thermal insulation material.

2. The method for preparing the impact-resistant, waterproof and heat-insulating material according to claim 1, characterized in that: In the step (1), the ratio of the polyol, the diisocyanate monomer, and the vinyl flame retardant chain extender is 1 mol: (2.4-2.6) mol: (1.2-1.3) mol.

3. The method for preparing the impact-resistant, waterproof and heat-insulating material according to claim 1, characterized in that: The polyol includes polyethylene glycol and polytetramethylene glycol; the diisocyanate monomer includes toluene-2,4-diisocyanate and 4,4'-methylenebis(phenyl isocyanate).

4. The method for preparing the impact-resistant, waterproof and heat-insulating material according to claim 1, characterized in that: In the step (2), the ratio of vinyl polyurethane to styrene is (5-60) g:100 g.

5. The method for preparing the impact-resistant, waterproof and heat-insulating material according to claim 1, characterized in that: In the step (2), the reaction temperature is 65-80°C and the reaction time is 24-36h.

6. The method for preparing the impact-resistant, waterproof and heat-insulating material according to claim 1, characterized in that: The preparation method of the vinyl flame retardant chain extender is: Step S1, in an ice bath, adding a solvent, 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide, 3-chloro-2-hydroxypropyl methacrylate, and pyridine to a flask, and then stirring the mixture at room temperature for 18-24 hours, filtering the mixture, and distilling the filtrate under reduced pressure, and purifying the mixture by recrystallization to obtain a flame retardant chain extender precursor; Step S2, adding solvent, flame retardant chain extender precursor, 1-(2-hydroxyethyl)piperazine and potassium carbonate into a flask, heating to 50-65° C., stirring and reacting for 3-8 hours, distilling the solution under reduced pressure, washing, and recrystallizing and purifying to obtain a vinyl flame retardant chain extender.

7. The method for preparing the impact-resistant, waterproof and heat-insulating material according to claim 6, characterized in that: The solvent in step S1 is acetonitrile, tetrahydrofuran or N,N-dimethylformamide.

8. The method for preparing the impact-resistant, waterproof and heat-insulating material according to claim 6, characterized in that: In the step S1, the ratio of 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane 3,9-dioxide, 3-chloro-2-hydroxypropyl methacrylate and pyridine is 1 mol:(2.4-3) mol:(2.4-3) mol.

9. The method for preparing the impact-resistant, waterproof and heat-insulating material according to claim 6, characterized in that: The solvent in step S2 is acetonitrile or N,N-dimethylformamide.

10. The method for preparing the impact-resistant, waterproof and heat-insulating material according to claim 6, characterized in that: In the step S2, the ratio of the flame retardant chain extender precursor, 1-(2-hydroxyethyl)piperazine, and potassium carbonate is 1 mol:(2-2.2) mol:(2.5-3.2) mol.

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