Bio-based carboxylated itaconate elastomer, rubber glove material and preparation

Abstract

The invention provides a bio-based carboxylated itaconate elastomer, a rubber glove material and preparation methods of the bio-based carboxylated itaconate elastomer and the rubber glove material. According to the invention, the itaconate monomer, the diene compound and the acrylic monomer are subjected to ternary polymerization to obtain the carboxylated bio-based itaconate elastomer, and the third monomer acrylic monomer is introduced to modify the itaconate copolymer, so that the obtained carboxylated itaconate elastomer has better mechanical properties; and the rubber glove material is more environment-friendly, can be used as a novel bio-based rubber glove material, and has a relatively wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of rubber materials, and in particular relates to a bio-based carboxylated itaconate elastomer, a rubber glove material and a preparation method thereof. Background Art

[0002] Bio-based itaconate elastomer is a new type of bio-based elastomer, which is obtained by polymerization of itaconate and conjugated diene. Among them, the bio-based itaconate monomer is obtained by esterification of itaconic acid and monohydric alcohol, and the introduction of diene can not only increase the flexibility of the molecular chain, but also provide double bonds for subsequent cross-linking of the elastomer.

[0003] Zhou Xinxin et al. (ZHOU X., et al. A solvent-less green synthetic route toward asustainable bio-based elastomer: design, synthesis, and characterization of poly (dibutyl itaconate-co-butadiene) [J]. Polymer Chemistry, 2019, 10 (45): 6131-6144) used dibutyl itaconate and butadiene as raw materials and synthesized a high molecular weight, low glass transition temperature bio-based cross-linkable poly (dibutyl itaconate-co-butadiene elastomer) by redox-initiated emulsion polymerization. The tensile strength and elongation at break of the unfilled elastomer reached 2 MPa and 600%. The functionalization of the elastomer by adding a third functionalized monomer during the polymerization process is also a simple and easy-to-control modification method. Qiao He et al. (QIAO H., et al. Preparation and Performance of Silica / Epoxy Group-Functionalized Biobased Elastomer Nanocomposite [J]. Industrial & Engineering Chemistry Research, 2017, 56 (4): 881-889) successfully synthesized epoxy-functionalized poly(dibutyl itaconate)-isoprene-glycidyl methacrylate elastomer by low-temperature emulsion polymerization using glycidyl methacrylate as a modified monomer. The tensile strength and elongation at break of poly(dibutyl itaconate)-isoprene elastomer were 1.1 MPa and 235%, respectively, while the mechanical properties of the epoxidized itaconate elastomer were improved to 1.5 MPa and 250%. However, its performance still does not meet the requirements for use, mainly because the polymer contains only double bonds and is cross-linked by sulfur or peroxide, with a low cross-linking density, so the mechanical properties of the polymer are poor. Summary of the invention

[0004] The invention adopts itaconate, diene compound and methacrylic acid for terpolymerization to obtain carboxylated bio-based itaconate elastomer. The invention introduces methacrylic acid as a third monomer to modify the itaconate copolymer, so that the obtained carboxylated itaconate elastomer has better mechanical properties.

[0005] One of the purposes of the present invention is to provide a bio-based carboxylated itaconate elastomer, comprising: a copolymer of itaconate monomers, diene compounds, and acrylic monomers.

[0006] Wherein, the itaconate ester monomer is selected from at least one of monomethyl itaconate, dimethyl itaconate, monoethyl itaconate, diethyl itaconate, monopropyl itaconate, dipropyl itaconate, monobutyl itaconate, dibutyl itaconate, monopentyl itaconate, dipentyl itaconate, monohexyl itaconate, dihexyl itaconate, monoheptyl itaconate, diheptyl itaconate, monooctyl itaconate, dioctyl itaconate, monononyl itaconate, dinonyl itaconate, monodecyl itaconate and didecyl itaconate, preferably at least one of dimethyl itaconate, diethyl itaconate and dibutyl itaconate;

[0007] The diene compound is selected from at least one of butadiene and isoprene, preferably butadiene;

[0008] The acrylic acid monomer is selected from at least one of acrylic acid, methacrylic acid and itaconic acid, preferably methacrylic acid.

[0009] In the above-mentioned bio-based carboxylated itaconate elastomer, based on 100 parts by weight of the itaconate monomer, the diene compound is 10 to 900 parts, and the acrylic monomer is 1 to 50 parts. Preferably, based on 100 parts by weight of the itaconate monomer, the diene compound is 25 to 100 parts, and the acrylic monomer is 3 to 20 parts.

[0010] The second object of the present invention is to provide a method for preparing the above-mentioned bio-based carboxylated itaconate elastomer, comprising: subjecting the components including the itaconate monomer, the diene compound, and the acrylic monomer to a polymerization reaction under the action of an initiator to obtain the bio-based carboxylated itaconate elastomer. The preparation method specifically comprises the following steps:

[0011] Step 1. Add deionized water, emulsifier, dispersant, electrolyte, activator, antioxidant, itaconate monomer, and acrylic monomer into a reaction container and mix well;

[0012] Step 2. Add the diene compound to the mixture obtained in step 1, stir and pre-emulsify, then add the initiator to carry out polymerization reaction;

[0013] Step 3. After the reaction is completed, a terminator is added into the reaction container, and the bio-based carboxylated itaconate elastomer is obtained after stirring.

[0014] In the preparation method of the above-mentioned bio-based carboxylated itaconate elastomer:

[0015] The emulsifier is selected from at least one of sodium dodecylbenzene sulfonate and sodium dodecyl sulfate, preferably sodium dodecylbenzene sulfonate;

[0016] The diffusing agent is selected from sodium methylene dinaphthalene sulfonate;

[0017] The electrolyte is selected from disodium ethylenediaminetetraacetate;

[0018] The activator is selected from ferrous sulfate;

[0019] The antioxidant is selected from sodium dithionite;

[0020] The terminator is selected from hydroxylamine;

[0021] The initiator is selected from persulfate initiators, preferably at least one of potassium persulfate and ammonium persulfate;

[0022] Based on 100 parts by weight of the itaconate monomer, the emulsifier is 1 to 100 parts, the dispersant is 0.1 to 10 parts, the electrolyte is 0.05 to 2 parts, the activator is 0.1 to 4 parts, the terminator is 0.1 to 6 parts, the antioxidant is 0.01 to 0.6 parts, and the initiator is 0.1 to 5 parts; preferably, based on 100 parts by weight of the itaconate monomer, the emulsifier is 1.25 to 20 parts, the dispersant is 0.38 to 3 parts, the electrolyte is 0.1 to 1.5 parts, the activator is 0.1 to 0.8 parts, the terminator is 0.1 to 1.2 parts, the antioxidant is 0.01 to 0.12 parts, and the initiator is 0.1 to 1.5 parts.

[0023] In the preparation method of the above-mentioned bio-based carboxylated itaconate elastomer:

[0024] The pre-emulsification conditions are: temperature of 20-70°C and time of 1-4h;

[0025] The polymerization reaction conditions are: temperature of 20-70°C and time of 4-8h;

[0026] The polymerization reaction is carried out under a protective gas atmosphere, for example, under nitrogen protection;

[0027] The bio-based carboxylated itaconate elastomer obtained in step 3 may be optionally subjected to demulsification, washing and drying.

[0028] The third object of the present invention is to provide a bio-based rubber glove material, comprising: the above-mentioned bio-based carboxylated itaconate elastomer or the bio-based carboxylated itaconate elastomer obtained by the above-mentioned preparation method, sulfur, zinc oxide, and an accelerator.

[0029] The accelerator is selected from at least one of dithiocarbamates and thiazoles, preferably at least one of 2-mercaptobenzothiazole, zinc di-n-butyl dithiocarbamate, and zinc diethyl dithiocarbamate;

[0030] Based on 100 parts by weight of the bio-based itaconate rubber, the amount of sulfur is 0.3 to 3 parts, the amount of zinc oxide is 1 to 10 parts, and the amount of accelerator is 0.1 to 2 parts; preferably, the amount of vulcanizing agent is 0.5 to 1.5 parts, the amount of zinc oxide is 2 to 5 parts, and the amount of accelerator is 0.5 to 1 part.

[0031] The fourth object of the present invention is to provide a method for preparing the above-mentioned bio-based rubber glove material, comprising: vulcanizing and molding the components including the bio-based carboxylated itaconate elastomer, sulfur, zinc oxide, and accelerator to obtain the bio-based rubber glove material. The vulcanization conditions are: the vulcanization temperature is 100-150°C, and the vulcanization time is 0.15-1h; after the molding, the bio-based rubber glove material with a thickness of 0.5-1 mm is obtained.

[0032] The present invention modifies the itaconate copolymer by introducing a third monomer, an acrylic monomer. After the acrylic monomer is introduced into the main chain of the copolymer, the elastomer can not only be cross-linked using sulfur or peroxide, but also can be cross-linked using metal oxides such as zinc oxide by means of carboxyl groups. The large number of salt bonds in the unsaturated carboxylate molecules formed by carboxyl groups and zinc ions have a strong electrostatic effect, which can limit the fluidity of the surrounding rubber chains. At the same time, the ion clusters formed by carboxyl groups and zinc ions have a high modulus and can be used as an effective reinforcement. The carboxylated itaconate latex has excellent film-forming properties, and the film has good mechanical properties after vulcanization molding, the tensile strength can reach 10MPa, and the elongation at break exceeds 300%, and can be used for new bio-based itaconate rubber gloves.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. The present invention adopts acrylic monomers to modify itaconate elastomers. Only a small amount of acrylic monomers needs to be added to make the carboxylated itaconate elastomer have excellent mechanical properties;

[0035] 2. Itaconate raw materials are obtained through biological fermentation, which can reduce the dependence on Hevea brasiliensis and petrochemical energy;

[0036] 3. Itaconate rubber does not contain protein. Applying it to rubber gloves can avoid the risk of allergies and shock during the wearing of gloves. DETAILED DESCRIPTION

[0037] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0038] The test instruments and test conditions used in the examples are as follows:

[0039] The carboxy itaconate rubber film sample was cut into dumbbell-shaped specimens using a cutter, and the tensile strength, elongation at break, and elongation at set point of the material were obtained by performing a tensile test on the sample using a CMT4104 electronic tensile testing machine according to ASTM D412. The test tensile rate was 500 mm / min.

[0040] The raw materials used in the examples and comparative examples, unless otherwise specified, are disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0041] Example 1

[0042] Preparation of dibutyl itaconate latex with low methacrylic acid content:

[0043] (1) adding an emulsifier, deionized water, an electrolyte, an activator, an antioxidant, dibutyl itaconate monomer, and methacrylic acid monomer into a reaction kettle, and then sealing the reaction apparatus and replacing it with a nitrogen atmosphere;

[0044] (2) Butadiene was added to the reactor and pre-emulsified at 50°C for one hour. During this process, the temperature began to rise. Then, an initiator was added and the polymerization reaction was carried out at 50°C for 8 hours.

[0045] (3) After the reaction is completed, a terminator is injected into the reactor, and after stirring, itaconate latex (the molar ratio of dibutyl itaconate monomer, butadiene, and methacrylic acid is 1:3:0.3) is obtained. The raw materials, amounts, and sources used are listed in Table 1.

[0046] Table 1. Raw materials, amounts and sources used in Example 1

[0047]

[0048] Preparation of dibutyl itaconate rubber film with low methacrylic acid content:

[0049] The synthesized latex was poured into anhydrous ethanol, and the latex was demulsified to obtain a carboxyitaconate elastomer solid, which was washed three times with deionized water and then dried in an oven at 60°C. The carboxyitaconate dibutyl rubber was mixed with sulfur, zinc oxide, and zinc di-n-butyl dithiocarbamate using a double-roll mill, and the mixing formula is shown in Table 2. The mold was vulcanized and molded at 150°C in a flat vulcanizer to finally obtain a film with a thickness of 1 mm. The performance tests are listed in Table 9.

[0050] Table 2. Mixing formula

[0051] raw material Dosage(g) Carboxy itaconate rubber 100 sulfur 1 Zinc Oxide 5 Zinc di-n-butyldithiocarbamate 0.5

[0052] Example 2

[0053] Preparation of dibutyl itaconate latex with high methacrylic acid content:

[0054] (1) adding an emulsifier, deionized water, an electrolyte, an activator, an antioxidant, dibutyl itaconate monomer, and methacrylic acid monomer into a reaction kettle, and then sealing the reaction apparatus and replacing it with a nitrogen atmosphere;

[0055] (2) Butadiene was added to the reactor and pre-emulsified at 50°C for one hour. During this process, the temperature began to rise. Then, an initiator was added and the polymerization reaction was carried out at 50°C for 8 hours.

[0056] (3) After the reaction is completed, a terminator is injected into the reactor and stirred to obtain itaconate latex (the molar ratio of dibutyl itaconate monomer, butadiene, and methacrylic acid is 1:3:0.7). The raw materials, amounts, and sources used are listed in Table 3.

[0057] Table 3. Raw materials, amounts and sources used in Example 2

[0058]

[0059] Preparation of dibutyl itaconate film with high methacrylic acid content:

[0060] The preparation method is the same as that of Example 1, and the performance tests are listed in Table 9.

[0061] Example 3

[0062] Preparation of diethyl carboxyitaconate latex:

[0063] (1) adding an emulsifier, deionized water, an electrolyte, an activator, an antioxidant, diethyl itaconate monomer, and methacrylic acid monomer into a reaction kettle, and then sealing the reaction apparatus and replacing it with a nitrogen atmosphere;

[0064] (2) Butadiene was added to the reactor and pre-emulsified at 50°C for one hour. During this process, the temperature began to rise. Then, an initiator was added and the polymerization reaction was carried out at 50°C for 6 hours.

[0065] (3) After the reaction is completed, a terminator is injected into the reactor and stirred to obtain itaconate latex (the molar ratio of diethyl itaconate monomer, butadiene, and methacrylic acid is 1:3:0.3). The raw materials, amounts, and sources used are listed in Table 4.

[0066] Table 4. Raw materials, amounts and sources used in Example 3

[0067]

[0068] Preparation of diethyl carboxyitaconate rubber film:

[0069] The preparation method is the same as in Example 1, and the performance test is listed in 9.

[0070] Example 4

[0071] Preparation of dimethyl carboxyitaconate latex:

[0072] (1) adding an emulsifier, deionized water, an electrolyte, an activator, an antioxidant, dimethyl itaconate monomer, and methacrylic acid monomer into a reaction kettle, and then closing the reaction apparatus and replacing it with a nitrogen atmosphere;

[0073] (2) Butadiene was added to the reactor and pre-emulsified at 60°C for one hour. During this process, the temperature began to rise. Then, an initiator was added and the polymerization reaction was carried out at 60°C for 5 hours.

[0074] (3) After the reaction is completed, a terminator is injected into the reactor and stirred to obtain itaconate latex (the molar ratio of dimethyl itaconate monomer, butadiene, and methacrylic acid is 1:3:0.3). The raw materials, amounts, and sources used are listed in Table 5.

[0075] Table 5. Raw materials, amounts and sources used in Example 4

[0076]

[0077] Preparation of dimethyl carboxyitaconate rubber film:

[0078] The preparation method is the same as that of Example 1, and the performance tests are listed in Table 9.

[0079] Example 5

[0080] Preparation of diethyl carboxyitaconate latex:

[0081] (1) adding an emulsifier, deionized water, an electrolyte, an activator, an antioxidant, diethyl itaconate monomer, and methacrylic acid monomer into a reaction kettle, and then sealing the reaction apparatus and replacing it with a nitrogen atmosphere;

[0082] (2) Butadiene was added to the reactor and pre-emulsified at 50°C for one hour. During this process, the temperature began to rise. Then, an initiator was added and the polymerization reaction was carried out at 50°C for 6 hours.

[0083] (3) After the reaction is completed, a terminator is injected into the reactor and stirred to obtain itaconate latex (the molar ratio of diethyl itaconate monomer, butadiene, and methacrylic acid is 1:3:0.3). The raw materials, amounts, and sources used are listed in Table 6.

[0084] Table 6. Raw materials, amounts and sources used in Example 5

[0085]

[0086] Preparation of dimethyl carboxyitaconate rubber film:

[0087] The preparation method is the same as that of Example 1, and the performance tests are listed in Table 9.

[0088] Example 6

[0089] Preparation of dimethyl carboxyitaconate latex:

[0090] (1) adding an emulsifier, deionized water, an electrolyte, an activator, an antioxidant, dimethyl itaconate monomer, and methacrylic acid monomer into a reaction kettle, and then closing the reaction apparatus and replacing it with a nitrogen atmosphere;

[0091] (2) Butadiene was added to the reactor and pre-emulsified at 50°C for one hour. During this process, the temperature began to rise. Then, an initiator was added and the polymerization reaction was carried out at 50°C for 6 hours.

[0092] (3) After the reaction is completed, a terminator is injected into the reactor and stirred to obtain itaconate latex (the molar ratio of dimethyl itaconate monomer, butadiene, and methacrylic acid is 1:0.97:0.12). The raw materials, amounts, and sources used are listed in Table 7.

[0093] Table 7. Raw materials, amounts and sources used in Example 6

[0094]

[0095] Preparation of dimethyl carboxyitaconate rubber film:

[0096] The preparation method is the same as that of Example 1, and the performance tests are listed in Table 9.

[0097] Comparative Example 1

[0098] Preparation of dibutyl itaconate latex without methacrylic acid:

[0099] (1) adding an emulsifier, deionized water, an electrolyte, an activator, an antioxidant, dibutyl itaconate monomer, and methacrylic acid monomer into a reaction kettle, and then sealing the reaction apparatus and replacing it with a nitrogen atmosphere;

[0100] (2) Butadiene was added to the reactor and pre-emulsified at 50°C for one hour. During this process, the temperature began to rise. Then, an initiator was added and the polymerization reaction was carried out at 50°C for 8 hours.

[0101] (3) After the reaction is completed, a terminator is injected into the reactor and stirred to obtain itaconate latex (the molar ratio of dibutyl itaconate monomer to butadiene is 1:3). The raw materials, amounts and sources used are listed in Table 8.

[0102] Table 8. Raw materials, dosage and sources used in Comparative Example 1

[0103]

[0104] Preparation of dibutyl itaconate rubber film without methacrylic acid:

[0105] The preparation method is the same as that of Example 1, and the performance tests are listed in Table 9.

[0106] Table 9. Performance test results of Examples 1 to 6 and Comparative Example 1

[0107]

[0108] It can be seen from the performance test results of Examples 1 to 6 and Comparative Example 1 that the tensile strength of the carboxyitaconate rubber gloves provided by the present invention reaches more than 10 MPa, and the elongation at break of dibutyl carboxyitaconate rubber and diethyl carboxyitaconate rubber in Examples 1 to 3 reaches more than 300%. It can be seen that after the introduction of methacrylic acid, the mechanical properties of the carboxyitaconate elastomer have been greatly improved. Therefore, the carboxyitaconate elastomer provided by the present invention has better mechanical properties and is more environmentally friendly, and can be used as a new type of bio-based rubber glove material with a relatively broad application prospect.

Claims

1. A bio-based carboxylated itaconate elastomer, comprising: A copolymer of itaconate monomers, diene compounds and acrylic monomers.

2. The elastic body according to claim 1, characterized in that The itaconate ester monomer is selected from at least one of monomethyl itaconate, dimethyl itaconate, monoethyl itaconate, diethyl itaconate, monopropyl itaconate, dipropyl itaconate, monobutyl itaconate, dibutyl itaconate, monopentyl itaconate, dipentyl itaconate, monohexyl itaconate, dihexyl itaconate, monoheptyl itaconate, diheptyl itaconate, monooctyl itaconate, dioctyl itaconate, monononyl itaconate, dinonyl itaconate, monodecyl itaconate and didecyl itaconate, preferably at least one of dimethyl itaconate, diethyl itaconate and dibutyl itaconate; and / or, The diene compound is selected from at least one of butadiene and isoprene, preferably butadiene; and / or, The acrylic acid monomer is selected from at least one of acrylic acid, methacrylic acid and itaconic acid, preferably methacrylic acid; and / or, Based on 100 parts by weight of the itaconate monomer, the diene compound is 10 to 900 parts, and the acrylic monomer is 1 to 50 parts. Preferably, based on 100 parts by weight of the itaconate monomer, the diene compound is 25 to 100 parts, and the acrylic monomer is 3 to 20 parts.

3. A method for preparing the bio-based carboxylated itaconate elastomer according to claim 1 or 2, comprising: The components including the itaconate monomer, the diene compound and the acrylic monomer are polymerized under the action of an initiator to obtain the bio-based carboxylated itaconate elastomer.

4. The preparation method according to claim 3, characterized in that: The preparation method specifically comprises the following steps: Step 1. Add deionized water, emulsifier, dispersant, electrolyte, activator, antioxidant, itaconate monomer, and acrylic monomer into a reaction container and mix well; Step 2. Add the diene compound to the mixture obtained in step 1, stir and pre-emulsify, then add the initiator to carry out polymerization reaction; Step 3. After the reaction is completed, a terminator is added into the reaction container, and the bio-based carboxylated itaconate elastomer is obtained after stirring.

5. The preparation method according to claim 4, characterized in that: The emulsifier is selected from at least one of sodium dodecylbenzene sulfonate and sodium dodecyl sulfate, preferably sodium dodecylbenzene sulfonate; and / or, The diffusing agent is selected from sodium methylene dinaphthalene sulfonate; and / or, The electrolyte is selected from disodium ethylenediaminetetraacetate; and / or, The activator is selected from ferrous sulfate; and / or, The antioxidant is selected from sodium dithionite; and / or, The terminator is selected from hydroxylamine; and / or, The initiator is selected from persulfate initiators, preferably at least one of potassium persulfate and ammonium persulfate; and / or, Based on 100 parts by weight of the itaconate monomer, the emulsifier is 1 to 100 parts, the dispersant is 0.1 to 10 parts, the electrolyte is 0.05 to 2 parts, the activator is 0.1 to 4 parts, the terminator is 0.1 to 6 parts, the antioxidant is 0.01 to 0.6 parts, and the initiator is 0.1 to 5 parts; preferably, based on 100 parts by weight of the itaconate monomer, the emulsifier is 1.25 to 20 parts, the dispersant is 0.38 to 3 parts, the electrolyte is 0.1 to 1.5 parts, the activator is 0.1 to 0.8 parts, the terminator is 0.1 to 1.2 parts, the antioxidant is 0.01 to 0.12 parts, and the initiator is 0.1 to 1.5 parts.

6. The preparation method according to claim 4, characterized in that: The pre-emulsification conditions are: temperature of 20-70°C and time of 1-4h; and / or, The polymerization reaction conditions are: temperature of 20-70° C., time of 4-8 hours; and / or, The polymerization reaction is carried out under a protective gas atmosphere; and / or, The bio-based carboxylated itaconate elastomer obtained in step 3 may be optionally subjected to demulsification, washing and drying.

7. A bio-based rubber glove material, comprising: The bio-based carboxylated itaconate elastomer according to claim 1 or 2, or the bio-based carboxylated itaconate elastomer obtained by the preparation method according to any one of claims 3 to 6, sulfur, zinc oxide, and an accelerator.

8. The bio-based rubber glove material according to claim 7, characterized in that: The accelerator is selected from at least one of dithiocarbamates and thiazoles, preferably at least one of 2-mercaptobenzothiazole, zinc di-n-butyldithiocarbamate, and zinc diethyldithiocarbamate; and / or, Based on 100 parts by weight of the bio-based itaconate rubber, the amount of sulfur is 0.3 to 3 parts, the amount of zinc oxide is 1 to 10 parts, and the amount of accelerator is 0.1 to 2 parts; preferably, the amount of vulcanizing agent is 0.5 to 1.5 parts, the amount of zinc oxide is 2 to 5 parts, and the amount of accelerator is 0.5 to 1 part.

9. A method for preparing the bio-based rubber glove material according to claim 7 or 8, comprising: The bio-based rubber glove material is obtained by vulcanizing and molding the components including the bio-based carboxylated itaconate elastomer, sulfur, zinc oxide, and accelerator.

10. The preparation method according to claim 9, characterized in that: The vulcanization conditions are: a vulcanization temperature of 100 to 150° C. and a vulcanization time of 0.15 to 1 h; and / or, after the molding, a bio-based rubber glove material with a thickness of 0.5 to 1 mm is obtained.

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