Method for producing hydroxyl-modified diene-based rubber

Abstract

To provide a novel method for producing a hydroxyl-modified diene-based rubber.SOLUTION: A method for producing a hydroxyl-modified diene-based rubber comprises bringing a diene-based rubber into contact with a fluid containing supercritical carbon dioxide and water, wherein the amount of the water is 5 mass% or more relative to the carbon dioxide, to obtain a diene-based rubber modified with hydroxyl groups.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing a hydroxyl group-modified diene rubber.

Background Art

[0002] Conventionally, a method for producing natural rubber having a hydroxyl group introduced into the main chain is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the method described in Patent Document 1 requires epoxidation of natural rubber, and the process is complicated. Further, as another method for introducing a hydroxyl group into the main chain of a diene rubber, for example, a method of putting a diene rubber and sulfuric acid into a mixer and mixing them at a high temperature can be considered. In this case, there are problems such as corrosion of the apparatus by sulfuric acid, the need to remove the acid remaining after the reaction by neutralization or the like, and molecular cleavage due to shear stress.

[0005] Therefore, in view of the above circumstances, an object of the present invention is to provide a novel method for obtaining a hydroxyl group-modified diene rubber.

Means for Solving the Problems

[0006] As a result of intensive studies on the above problems, the present inventors have found that a hydroxyl group-modified diene rubber can be obtained by using a fluid containing supercritical carbon dioxide and water, and have thus arrived at the present invention. That is, the present inventors have found that the above problems can be solved by the following configuration.

[0007] (1) A diene rubber, supercritical carbon dioxide, and water, and the amount of water relative to the carbon dioxide is 5% by mass or more, a fluid, By bringing them into contact, a diene rubber modified with a hydroxyl group is obtained, a method for producing a hydroxyl group-modified diene rubber. (2) The method for producing a hydroxyl group-modified diene rubber according to (1) above, wherein the diene rubber contains isoprene units. (3) The method for producing a hydroxyl group-modified diene rubber according to (1) or (2) above, wherein the pressure in the supercritical state is 10 MPa or more. (4) The method for producing a hydroxyl group-modified diene rubber according to any one of (1) to (3) above, wherein the pH of the fluid is 2 or less. [Advantages of the Invention]

[0008] As shown below, according to the present invention, a novel method for obtaining a hydroxyl group-modified diene rubber can be provided. [Embodiments for Carrying Out the Invention]

[0009] Hereinafter, the method for producing a hydroxyl group-modified diene rubber of the present invention will be described. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. Also, each component may be used alone or in combination of two or more. Here, when two or more of each component are used in combination, the content of that component refers to the total content unless otherwise specified. Increasing the molecular weight of the diene rubber and having a high modification rate described later are also referred to as "excellent effects of the present invention".

[0010] [1] Method for Producing Hydroxyl Group-Modified Diene Rubber The method for producing a hydroxyl group-modified diene rubber of the present invention (hereinafter, also referred to as "the production method of the present invention") is a diene rubber, A fluid containing carbon dioxide in a supercritical state and water, wherein the amount of the water relative to the carbon dioxide is 5% by mass or more, and a method for producing a hydroxyl group-modified diene rubber, which comprises obtaining a hydroxyl group-modified diene rubber by bringing into contact with the fluid.

[0011] In the production method of the present invention, as described above, a fluid (hereinafter also referred to as "specific fluid") containing carbon dioxide in a supercritical state and water, wherein the amount of the water relative to the carbon dioxide is 5% by mass or more, is used. In the specific fluid, it is considered that carbon dioxide and water react to form carbonic acid. Here, since the carbon dioxide is in a supercritical state, the acidity of the generated carbonic acid is higher than normal (pH: about 3). Therefore, when the diene rubber comes into contact with the specific fluid, it is considered that oxonium ions react with the double bond of the diene rubber and hydroxyl groups are introduced into the main chain of the diene rubber. For example, when the diene rubber is polyisoprene, it is considered that hydroxyl groups are introduced as follows.

[0012]

Chemical formula

[0013] Since the above-described reaction occurs simply by bringing the diene rubber into contact with the specific fluid, molecular cleavage as in the case of using a mixer is less likely to occur. When a bulk (mass) of the diene rubber is used, it is considered that the introduction of the above-described hydroxyl groups initially proceeds on the surface of the bulk. Thereafter, as the hydrophilicity is improved by the introduction of the hydroxyl groups, it is considered that the introduction of the above-described hydroxyl groups gradually proceeds also inside the bulk.

[0014] In addition, in the production method of the present invention, since carbon dioxide in a supercritical state is used, carbonic acid can be volatilized as carbon dioxide simply by returning the system to normal pressure after the introduction of the hydroxyl groups. That is, the acid remaining after the reaction can be easily removed.

[0015] Hereinafter, each component and the like used in the production method of the present invention will be described in detail.

[0016] [Diene rubber] The diene rubber used in the production method of the present invention is not particularly limited. The above diene rubber may be used alone or in combination of two or more.

[0017] 〔Specific examples〕 Specific examples of the above diene rubber include natural rubber (NR), butadiene rubber (polybutadiene) (BR), aromatic vinyl-conjugated diene copolymer rubber, isoprene rubber (polyisoprene) (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), etc. Examples of the above aromatic vinyl-conjugated diene copolymer rubber include styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, etc.

[0018] 〔Molecular weight〕 The weight average molecular weight (Mw) of the above diene rubber is not particularly limited, but for the reason that the effect of the present invention is more excellent, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000.

[0019] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are standard polystyrene conversion values obtained by gel permeation chromatography (GPC) measurement.

[0020] 〔Preferred embodiment〕 The above diene rubber preferably contains isoprene units, more preferably natural rubber or polyisoprene, and even more preferably polyisoprene, for the reason that the effect of the present invention is more excellent.

[0021] [Specific fluid] The specific fluid used in the production method of the present invention is a fluid containing supercritical carbon dioxide and water, and the amount of the water relative to the carbon dioxide is 5% by mass or more.

[0022] Supercritical carbon dioxide Supercritical carbon dioxide refers to carbon dioxide placed under a temperature of 31.1 °C or higher and a pressure of 7.38 MPa or higher, which is the critical temperature and critical pressure of carbon dioxide, respectively.

[0023] <Temperature> For reasons that the effects of the present invention are more excellent, the temperature of the supercritical state is preferably 40 °C or higher, more preferably 50 °C or higher. Although the upper limit of the temperature of the supercritical state is not particularly limited, for reasons that the effects of the present invention are more excellent, it is preferably 100 °C or lower, more preferably 90 °C or lower, still more preferably 80 °C or lower, and particularly preferably 70 °C or lower.

[0024] <Pressure> For reasons that the effects of the present invention are more excellent, the pressure of the supercritical state is preferably 10 MPa or higher, more preferably 15 MPa or higher, still more preferably 20 MPa or higher. Although the upper limit of the pressure of the supercritical state is not particularly limited, for reasons that the effects of the present invention are more excellent, it is preferably 50 MPa or lower, more preferably 40 MPa or lower, still more preferably 30 MPa or lower.

[0025] <Content> Although the content of the carbon dioxide in the specific fluid is not particularly limited, for reasons that the effects of the present invention are more excellent, it is preferably 60 to 99% by mass, more preferably 70 to 95% by mass, still more preferably 80 to 90% by mass.

[0026] <Amount relative to diene rubber> The amount of the above carbon dioxide with respect to the above diene rubber is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 100 to 2000% by mass, more preferably 300 to 1500% by mass, still more preferably 500 to 1000% by mass, and particularly preferably 700 to 800% by mass.

[0027] 〔Water〕

[0028] <Water / Carbon Dioxide> In a specific fluid, the amount of the above water with respect to the above carbon dioxide (hereinafter, also referred to as "water / carbon dioxide") is 5% by mass or more. For the reason that the effects of the present invention are more excellent, water / carbon dioxide is preferably 10% by mass or more, and more preferably 12% by mass or more. The upper limit of water / carbon dioxide is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 100% by mass or less, more preferably 50% by mass or less, still more preferably 30% by mass or less, particularly preferably 20% by mass or less, and most preferably 115% by mass or less.

[0029] <Content> The content of the above water in the specific fluid is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 1 to 40% by mass, more preferably 5 to 30% by mass, and still more preferably 10 to 20% by mass.

[0030] <Amount with Respect to Diene Rubber> The amount of the above water with respect to the above diene rubber described above is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 10 to 500% by mass, more preferably 30 to 300% by mass, still more preferably 50 to 150% by mass, and particularly preferably 80 to 120% by mass.

[0031] 〔Temperature〕 The temperature of the specific fluid is equal to or higher than the critical temperature of carbon dioxide (31.1 °C). A preferred embodiment of the temperature of the specific fluid is the same as the temperature of the supercritical state described above.

[0032] 〔Pressure〕 The pressure of the specific fluid is 7.38 MPa or more, which is the critical pressure of carbon dioxide. A preferred embodiment of the pressure of the specific fluid is the same as the pressure of the supercritical state described above.

[0033] 〔pH〕 The pH of the specific fluid is not particularly limited, but for better effects of the present invention, it is preferably 6 or less, more preferably 5 or less, even more preferably 4 or less, particularly preferably 3 or less, and most preferably 2 or less. The lower limit of the pH of the specific fluid is not particularly limited, but for better effects of the present invention, it is preferably 1 or more. The pH of the specific fluid can be adjusted, for example, by adding an acid.

[0034] 〔Acid〕 The specific fluid may contain an acid other than carbonic acid (for example, phosphoric acid).

[0035] <Content> When the specific fluid contains the above acid, the content of the above acid in the specific fluid is not particularly limited, but for better effects of the present invention, it is preferably 0.001 to 1% by mass, and more preferably 0.01 to 0.1% by mass.

[0036] <Amount relative to diene rubber> When the specific fluid contains the above acid, the amount of the above acid relative to the above diene rubber described above is not particularly limited, but for better effects of the present invention, it is preferably 0.01 to 10% by mass, and more preferably 0.1 to 1% by mass.

[0037] [Contact method] The method of bringing the above-mentioned diene rubber into contact with the above-mentioned specific fluid is not particularly limited. For example, a method can be mentioned in which the diene rubber is placed in a pressure-resistant container, and further, water and carbon dioxide are added and left standing. Note that the temperature inside the container is set to be equal to or higher than the critical temperature of carbon dioxide, and the pressure is set to be equal to or higher than the critical pressure of carbon dioxide. The standing time is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 1 to 600 minutes, more preferably 10 to 300 minutes, and even more preferably 60 to 120 minutes.

[0038] [2] Hydroxyl group-modified diene rubber The hydroxyl group-modified diene rubber of the present invention is a diene rubber modified with a hydroxyl group obtained by the above-mentioned production method of the present invention.

[0039] [Method for confirming hydroxyl group modification] The introduction of a hydroxyl group into the diene rubber can be confirmed, for example, by measuring an IR (infrared spectroscopy) spectrum.

[0040] Hereinafter, specific examples of the method for confirming hydroxyl group modification will be shown by taking the examples described later as examples. First, measure the IR spectrum of 2-methyl-2-butanol (a model compound of hydroxyl group-modified polyisoprene). In the measured IR spectrum, a broad peak derived from a hydroxyl group (O-H stretching vibration) is observed around 3370 cm -1 Next, measure the IR spectra of polyisoprene (raw material rubber), polyisoprene obtained in Example 1 (hereinafter also referred to as "polyisoprene 1"), and polyisoprene obtained in Example 2 (hereinafter also referred to as "polyisoprene 2"). Since peaks are observed around 3370 cm in the IR spectra of polyisoprene 1 to 2, it can be said that hydroxyl groups are introduced into polyisoprene 1 to 2. -1

[0041] [Modification rate] ​Regarding the hydroxyl group-modified diene rubber of the present invention, the ratio (%) of the repeating unit into which the hydroxyl group is introduced among all the repeating units (hereinafter, also referred to as "modification rate") is not particularly limited, but it is preferably 0.1% or more, more preferably 0.5% or more, even more preferably 1% or more, and particularly preferably 2% or more. The upper limit of the above modification rate is not particularly limited, but it is preferably 90% or less, more preferably 50% or less, even more preferably 10% or less, and particularly preferably 5% or less.

[0042] Hereinafter, taking the examples described later as an example, a specific example of the method for obtaining the modification rate will be shown. In the above-mentioned IR spectrum, the peak observed around 2940 cm -1 is a peak derived from C-H stretching vibration. The modification rate is obtained from the ratio of the peak intensity around 3370 cm -1 described above to this peak intensity (hereinafter, also referred to as "peak intensity ratio"). That is, the peak intensity ratio is obtained for 2-methyl-2-butanol, and this peak intensity ratio is set as the modification rate of 100%, and the respective modification rates are obtained from the peak intensity ratios of polyisoprene 1 to 2.

Example

[0043] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0044] [Production of Hydroxyl Group-Modified Diene Rubber] The hydroxyl group-modified diene rubber was produced as follows (Examples 1 to 2).

[0045] 〔Example 1〕 A 200 mL pressure-resistant container (manufactured by Toyo Koatsu Co., Ltd.) was filled with polyisoprene (Nipol IR2200 manufactured by Nippon Zeon Co., Ltd., weight-average molecular weight 650,000 g / mol), and further filled with water and carbon dioxide. The temperature inside the container was 60 °C and the pressure was 25 MPa. The usage amounts (parts by mass) of each component are as shown in Table 1. In this way, polyisoprene was brought into contact with a fluid containing water and supercritical carbon dioxide (water / carbon dioxide: 14% by mass, pH around 3). It was left standing in this state for 90 minutes. Then, the container was opened and the carbon dioxide was volatilized. Next, the polyisoprene was taken out from the container, and when its IR spectrum was measured, it was confirmed that hydroxyl groups were introduced into the polyisoprene. The modification rate of the obtained hydroxyl group-modified polyisoprene was estimated to be 0.6%.

[0046] [Example 2] Polyisoprene was brought into contact with a fluid containing polyisoprene, water, phosphoric acid, and supercritical carbon dioxide (water / carbon dioxide: 14% by mass, pH: 2 or less) according to the same procedure as in Example 1, except that a 0.02 mol / L phosphoric acid aqueous solution was used instead of water. The usage amounts (parts by mass) of each component are as shown in Table 1. It was left standing in this state for 90 minutes. Then, the container was opened and the carbon dioxide was volatilized. Next, the polyisoprene was taken out from the container, and when its IR spectrum was measured, it was confirmed that hydroxyl groups were introduced into the polyisoprene. The modification rate of the obtained hydroxyl group-modified polyisoprene was estimated to be 2.4%.

[0047] [Comparative Example] Polyisoprene and a 0.5 mol / L phosphoric acid aqueous solution were put into a mixer. The usage amounts (parts by mass) of each component are as shown in Table 1. Then, they were mixed at 90 °C for 30 minutes. After that, the polyisoprene was taken out, and when its IR spectrum was measured, it was confirmed that no hydroxyl groups were introduced into the polyisoprene (modification rate: 0%).

[0048] [Summary] Examples and comparative examples are summarized in Table 1 below. Note that the "raw rubber" in Table 1 is the polyisoprene itself used in the examples and comparative examples. In Table 1, the numerical values of each component represent the amount used (parts by mass) of each component. In Table 1, "Mw (index)" represents the Mw of the polyisoprene (hydroxyl group-modified polyisoprene or polyisoprene) obtained in each example. Note that Mw was expressed as an index with the raw rubber being 100. In Table 1, "modification rate" represents the modification rate of the polyisoprene (hydroxyl group-modified polyisoprene or polyisoprene) obtained in each example.

[0049]

Table 1

[0050] As described above, hydroxyl group-modified polyisoprene (hydroxyl group-modified polyisoprene) was obtained by the methods of Examples 1 to 2 using a specific fluid.

[0051] The Mw of the obtained hydroxyl group-modified polyisoprene was larger than the Mw of the raw rubber. In addition to the reaction between the carbocation and water, it is considered that crosslinking of polyisoprene occurred due to the reaction between carbocations. On the other hand, the Mw of the polyisoprene obtained in the comparative example using a mixer was smaller than the Mw of the raw rubber. As described above, it is considered that molecular cleavage occurred due to the shear stress of the mixer.

Claims

**Claim 1** A diene rubber, supercritical carbon dioxide, and water, wherein the amount of water relative to the carbon dioxide is 5% by mass or more, and a fluid, By bringing them into contact, a diene rubber modified with a hydroxyl group is obtained. A method for producing a hydroxyl group-modified diene rubber. **Claim 2** The method for producing a hydroxyl group-modified diene rubber according to claim 1, wherein the diene rubber contains isoprene units. **Claim 3** The method for producing a hydroxyl group-modified diene rubber according to claim 1 or 2, wherein the pressure in the supercritical state is 10 MPa or more. **Claim 4** The method for producing a hydroxyl group-modified diene rubber according to claim 1 or 2, wherein the pH of the fluid is 2 or less.

Images