JP2010092846A - Natural rubber-based electrolyte, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a natural rubber-based electrolyte, along with a manufacturing method thereof, which is characterized in that a graft polymer phase containing sulfonated phenyl group coexisting with cyclized natural rubber phase has a continuous structure. <P>SOLUTION: The manufacturing method for the natural rubber-based electrolyte includes a step in which, after a radical active point is introduced into natural rubber particle surfaces using a water-soluble radical initiator, a phenyl group containing vinyl monomer is added for graft copolymerization, a step of allowing the principal chain originated from natural rubber of the obtained graft copolymer to be a cyclized rubber structure, and a step of causing the obtained phenyl group of the graft copolymer to be sulfonated. The obtained natural rubber based electrolyte is a polymer electrolyte which is available by sulfonating a phenyl group of the graft natural rubber which is a natural rubber having been graft-copolymerized with a phenyl group containing vinyl monomer. Here, the principal chain originated from natural rubber has a cyclized rubber structure, and the graft polymer phase containing sulfonated phenyl group coexisting with cyclized rubber phase has a continuous structure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte derived from natural rubber and a method for producing the same. Specifically, the graft polymer phase having a sulfonated phenyl group coexisting with the cyclized natural rubber phase has a continuous structure, and preferably the cyclized natural rubber phase and the graft polymer phase having a sulfonated phenyl group have a co-continuous structure. The present invention relates to a natural rubber electrolyte and a method for producing the same.

  Natural rubber latex (colloid) is a form in which natural rubber particles are dispersed in an aqueous system, and a dry polymer obtained by graft copolymerization of styrene or the like with natural rubber particles is natural depending on the amount of polystyrene grafted. Rubber particles show various structures such as nano-matrix or co-continuous covered with polystyrene, and dramatic improvement in properties (such as elastic modulus) is expected.

  The technology to fix and hold the obtained nanomatrix structure or co-continuous structure has not been established, and the structure is irreversibly destroyed when the plastic deformation limit of natural rubber is exceeded, and the nano-order structure is controlled. There is a problem that the function obtained in is impaired.

  As described above, it is known to add styrene and methyl methacrylate to natural rubber latex and to perform graft copolymerization. However, a non-rubber component present in the raw natural rubber latex and a non-rubber component present on the surface of the natural rubber particles floating as a dispersoid cause a side reaction to mainly produce a homopolymer, and the graft polymer. It was difficult to get.

  On the other hand, it has also been proposed to recover a rubber solid content from natural rubber latex and introduce a graft polymer prepared in advance by anionic polymerization in a solid phase and a toluene solution. However, the graft polymer introduction rate was low and the grafting efficiency remained low.

  Attempts have also been made to remove non-rubber components from natural rubber latex and graft copolymerize styrene, and to graft copolymerize monomers to deproteinized natural rubber. However, in the conventional graft copolymerization, the graft efficiency is still low, the graft polymer properties are imparted while retaining the excellent properties of natural rubber, and the fine matrix formed by the graft polymer as a minor component. It was not possible to obtain a nanomatrix-dispersed natural rubber having a unique phase separation structure in which natural rubber particles as the main component were dispersed.

  Therefore, the following Patent Document 1 has the characteristics of a graft polymer as well as the excellent properties of natural rubber, and is used in a wide range of medical fields such as condoms, surgical gloves and catheters, and household products. A nanomatrix-dispersed natural rubber having a specific phase separation structure in which natural rubber particles as a main component are dispersed in a fine matrix formed by a graft polymer as a component is disclosed. Specifically, after deproteinization of natural rubber latex, radical active sites are introduced to the surface of rubber particles with a water-soluble radical initiator, and then graft copolymerization is performed on the surface of natural rubber particles by adding monomers. The desired surface-grafted natural rubber latex is formed into a film to obtain the desired nanomatrix-dispersed natural rubber.

  By the way, the development of fuel cells as fossil fuel alternative energy has been actively conducted. In particular, various proton-conducting polymer electrolytes have been developed for the safe use of fuel cells, but all of them are made from fossil fuels and are used for product development in harmony with the environment such as zero emissions. Has not reached. Therefore, it has been a big problem to synthesize proton-conducting polymer electrolytes using polymers derived from natural products as raw materials.

  In order to synthesize proton-conducting polyelectrolytes using polymers derived from natural products as raw materials, in addition to having polar groups of proton donors, the water that is generated at the time of use and the water at the time of high-temperature use It is required to suppress drying due to evaporation and to secure a path for proton conduction. However, to date, no polymer electrolyte that satisfies the above-mentioned conditions has been synthesized.

Currently, organic materials derived from natural products that are being actively studied include cellulose, chitin / chitosan, sugar chains, polylactic acid, and PHB. When a proton conductive polymer electrolyte is produced using these as raw materials, it is necessary to introduce a functional group that easily releases H ⁺ . Furthermore, it is desired to ensure stability by reducing damage caused by H ⁺ and making it difficult to swell in H ₂ O generated during battery reaction. As the functional group that easily releases H ⁺ , —SO ₃ H seems to be the best, but it is necessary to devise measures to stabilize —SO ₃ ^— . At present, Nafion, which is widely used, is such that —SO ₃ H easily releases H ⁺ due to —CF ₂ — (perfluorocarbon material). As a comparable structure, resonance stabilization of the phenyl group can be considered. However, it is difficult to sulfonate after introducing a phenyl group into cellulose, chitin / chitosan, sugar chain, polylactic acid and PHB. Furthermore, since cellulose, chitin / chitosan, sugar chain, polylactic acid, and PHB contain an ester bond or an ether bond, they have a drawback that they easily swell in H ₂ O and are easily hydrolyzed in the presence of H ⁺ .

JP 2004-155484 A JP-A-6-56902 JP 2004-99696 A Japanese Patent Laid-Open No. 2005-281681

  The nano-matrix structure or co-continuous structure of grafted natural rubber in the present invention is a structure of a very new concept, and by immobilizing this characteristic nano-order structure, excellent functional expression derived from the nano-order structure is stabilized. The second object is to prepare a proton-conducting polymer electrolyte having both high proton conductivity and stability from an organic material derived from a natural product.

  In addition, the graft-copolymerized natural rubber obtained in Patent Document 1 is not strictly a nanomatrix-dispersed natural rubber, and the graft polymer phase is separated into fine particles and does not form a matrix. Therefore, it was insufficient to impart the properties of the graft polymer while maintaining the excellent properties of the natural rubber. Therefore, the present invention forms a continuous structure of the graft polymer phase, preferably by making the graft polymer phase and the natural rubber phase a co-continuous structure, so that the graft polymer can be obtained while maintaining the excellent properties of the natural rubber. A third object is to provide a desired function.

  The present inventors have found that the above-mentioned problems can be solved by subjecting the surface-grafted natural rubber to a specific treatment while advancing the research for enhancing the functionality of natural rubber, and have reached the present invention.

  That is, first, an invention of a polymer electrolyte obtained by sulfonating a phenyl group of a grafted natural rubber obtained by graft-copolymerizing a phenyl group-containing vinyl monomer to a natural rubber, wherein the main chain derived from the natural rubber has a cyclized rubber structure. And a graft polymer phase having a sulfonated phenyl group that coexists with a cyclized natural rubber phase has a continuous structure.

  The second aspect of the invention is a polyelectrolyte in which a phenyl group of a grafted natural rubber obtained by graft copolymerizing a vinyl group-containing vinyl monomer with a natural rubber is sulfonated, and the main chain derived from the natural rubber has a cyclized rubber structure. And a cyclized natural rubber phase and a graft polymer phase having a sulfonated phenyl group have a co-continuous structure.

  In the natural rubber electrolyte of the present invention, untreated natural rubber latex can be used as a raw material, but deproteinized natural rubber is preferred.

  In the present invention, the ratio of the phenyl group-containing vinyl monomer such as styrene to the natural rubber can be selected from a wide range. However, 50 to 300 parts by weight of the phenyl group-containing vinyl monomer is grafted on 100 parts by weight of the natural rubber. A polymerized product is preferable for exhibiting both physical properties.

  Third, the present invention is an invention of the above-mentioned method for producing a natural rubber-based electrolyte. After introducing radical active sites on the surface of natural rubber particles using a water-soluble radical initiator, a phenyl group-containing vinyl monomer is added. A step of performing graft copolymerization, a step of forming a main chain derived from natural rubber of the obtained graft copolymer into a cyclized rubber structure, and a step of sulfonating the phenyl group of the obtained graft copolymer; It is characterized by including.

  The natural rubber-based electrolyte produced by the present invention has a main chain derived from natural rubber having a cyclized rubber structure, and a graft polymer phase having a sulfonated phenyl group coexisting with the cyclized natural rubber phase has a continuous structure, The cyclized natural rubber phase and the graft polymer phase having a sulfonated phenyl group have a co-continuous structure.

  As described above, the deproteinized natural rubber is preferable as the natural rubber to be used. In this case, a step of deproteinizing the natural rubber latex is added to the production method of the present invention.

  In the method for producing a natural rubber electrolyte of the present invention, it is preferable to perform the step of forming a main chain derived from natural rubber into a cyclized rubber structure using a Lewis acid as a catalyst. The Lewis acid is not particularly limited, and preferred examples include sulfuric acid, stannic chloride, boron trifluoride, titanium tetrachloride, and ferric chloride.

  In the method for producing a natural rubber-based electrolyte of the present invention, a step of forming a main chain derived from natural rubber into a cyclized rubber structure and a step of sulfonating the phenyl group of the obtained graft copolymer are performed separately. However, it is preferable to perform both steps simultaneously using chlorosulfonic acid. In this case, chlorosulfonic acid serves as a catalyst for the reaction in which the main chain derived from natural rubber has a cyclized rubber structure, and also serves as a sulfonating agent for the reaction of sulfonating the phenyl group of the graft copolymer.

  In the present invention, a deproteinized natural rubber produced by a known method is used. Of these, natural rubber deproteinized to a deproteinized natural rubber particle having a nitrogen content of 0.1% by weight or less is preferred.

  As a method for producing a deproteinized natural rubber latex, a method using an enzyme and a method using a urea-based protein denaturant and a surfactant are known, and both can be adopted. Among these, from the viewpoint of the level of deproteinization and reaction time, a method using a urea-based protein denaturant and a surfactant is more preferable. Specifically, urea protein modifier and surfactant are added to natural rubber latex, and the protein in raw natural rubber latex is denatured by stirring and mixing, and the protein modified by the above steps is separated and removed. Including the step of.

  It has long been known that cyclized rubber can be obtained by reacting a natural rubber with a Lewis acid such as sulfuric acid, stannic chloride, boron trifluoride, titanium tetrachloride, or ferric chloride. However, the nanomatrix or co-continuous structure of grafted natural rubber is a very new concept structure, and applying the above cyclization technique to immobilize this characteristic nano-ordered structure is a completely new idea. is there. This makes it possible to stabilize the excellent function expression derived from the nano-ordered structure.

  In addition, by graft-copolymerizing a monomer having a phenyl group to natural rubber and then sulfonating, a means for coexisting a part responsible for proton conduction and a part responsible for shape stability is devised. When graft copolymerizing a monomer having a phenyl group with natural rubber, a portion responsible for proton conduction and a portion responsible for shape stability can coexist in a nanometer scale depending on the composition. If this graft copolymer is sulfonated, not only can sulfonic acid groups be introduced into the phenyl group, but also the carbocation of the isoprene unit generated under strong acidity will bridge the rubber by inducing cyclization of the isoprene unit. It seems possible to reduce the degree of unsaturation.

  According to the present invention, by preparing a proton conductive polymer electrolyte having both high proton conductivity and stability from an organic material derived from a natural product, the conventional problems could be overcome.

The production process of the natural rubber electrolyte of the present invention in which the main chain derived from natural rubber has a cyclized rubber structure and the cyclized natural rubber phase and the graft polymer phase having a sulfonated phenyl group have a co-continuous structure. The procedure of graft copolymerization of Example 1 is shown. The procedure of sulfonation of Example 1 is shown. Optical of natural rubber electrolyte obtained in Example 1 in which the main chain derived from natural rubber has a cyclized rubber structure, and the cyclized natural rubber phase and the graft polymer phase having a sulfonated phenyl group have a co-continuous structure. A micrograph is shown. The TEM photograph of the natural rubber type electrolyte before and after sulfonation is shown. It is a figure which shows typically the structure of the natural rubber-type electrolyte of this invention. ¹³ shows ¹³ C CP / MAS NMR spectra of DPNR-graft-PS and sulfonated DPNR-graft-PS. The procedure of graft copolymerization of Example 2 is shown. The sulfonation procedure of Example 2 is shown. The 1H-NMR spectrum of DPNR-graft-PS is shown. (A) Natural rubber deproteinized with urea (U-DPNR), (b) Polystyrene grafted natural rubber (PS-graft-NR), (c) Polystyrene grafted natural rubber sulfonated with 0.006 mol of acetyl sulfate (PS-graft-NR), (d) Polystyrene graft sulfonated with 0.012 mol acetyl sulfate, natural rubber (PS-graft-NR), (e) Polystyrene graft sulfonated with 0.018 mol acetyl sulfate The FT-IR spectrum of natural rubber (PS-graft-NR), (f) polystyrene grafted natural rubber sulfonated with 0.024 mol of acetyl sulfate (PS-graft-NR) is shown.

  The co-continuous structure as referred to in the present invention is not a layered structure having a specific orientation or direction, which is found in the vicinity of the surface of an injection molded product or a part of a stretched film, but a sulfonated natural rubber phase and a sulfonated structure. A structure in which a graft polymer phase having a phenyl group forms a continuous phase together and exists in an intricate manner. The continuous structure as used in the present invention refers to a structure in which only a graft polymer phase having a sulfonated phenyl group coexisting with a cyclized natural rubber phase forms a continuous phase and functions as a nanomatrix.

  In general, in a polymer blend system composed of two types of polymer components A and B that are not compatible, the phase structure changes according to the structure of A and B and the blend ratio, and is roughly divided into three types of phase structures (A is a continuous phase). And B is a sea-island structure in which a dispersed phase is formed, conversely, A is a dispersed phase, B is an inverted sea-island structure in which a continuous phase is formed, and A and B are both co-continuous structures in which a continuous phase is formed). It has been known. Among these, the co-continuous structure has different physical properties from the structure in which only one component becomes a continuous phase, such as the sea-island structure or the reverse sea-island structure, because A and B having different properties form a continuous phase. It is expected.

Hereinafter, the natural rubber electrolyte of the present invention and the production method thereof will be described in more detail.
(Raw material latex)
The natural rubber latex (colloid) used as a starting material for obtaining the nanomatrix-dispersed natural rubber of the present invention means a latex obtained from a natural rubber tree. The latex includes a fresh field latex or a commercially available latex. Any of ammonia-treated latex and the like can be used. As in the present invention, the colloidal material for forming the nanomatrix channel structure described later is not limited to the above natural rubber latex as the graft polymer phase having a sulfonated phenyl group has a continuous structure, and other types of materials are used. Various polymer colloids are also applicable.

(Deproteinization)
These natural rubber latexes are deproteinized by a known method. For example, it may be carried out by a known method such as 1) a method of degrading protein by adding a protease or bacteria to latex (Patent Document 2), and 2) a method of repeatedly washing with a surfactant such as soap. it can.

3) A protein denaturant selected from the group consisting of a urea compound represented by the following general formula (1) and NaClO in natural rubber latex previously proposed as Patent Document 3 by the present inventors. It can also be performed by a method of adding and denaturing and removing proteins in the latex.
RNHCONH ₂ (1)
(Wherein R represents H, an alkyl group having 1 to 5 carbon atoms)

  4) The step of adding a urea-based protein modifier and a surfactant to the raw material natural rubber latex proposed as Patent Document 4 above, and mixing this while moving the flow path to mix the protein in the raw material natural rubber latex It is possible to use a deproteinized natural rubber latex that is substantially free of allergic proteins and peptides, which is produced by the step of denatured and then the step of separating and removing the denatured protein. In the deproteinization of the natural rubber latex, the nitrogen content of the natural rubber particles can be 0.1% by weight or less, preferably 0.05% by weight or less.

(Grafting: Production of surface-grafted natural rubber)
To graft copolymerize phenyl group-containing vinyl monomers such as styrene monomer on the surface of deproteinized natural rubber particles, add phenyl group-containing vinyl monomer to deproteinized natural rubber latex and add an appropriate polymerization initiator to react. Is done.

  When the graft-copolymerized phenyl group-containing vinyl monomer is added to the latex, an emulsifier is added to the latex in advance, or an organic compound having an unsaturated bond is emulsified and then added to the latex. The emulsifier is not particularly limited, but an anionic or nonionic surfactant is preferably used. The addition amount of the phenyl group-containing vinyl monomer is preferably 50 to 300 parts by weight with respect to 100 parts by weight of the deproteinized natural rubber. When the addition amount of the phenyl group-containing vinyl monomer exceeds this range, the formation of homopolymer increases and the grafting efficiency decreases. Conversely, when the addition amount falls below this range, the graft amount of the phenyl group-containing vinyl monomer decreases and the modification is improved. The quality effect becomes small, and it becomes difficult to obtain a natural rubber having a desired continuous structure of the graft polymer phase, preferably a co-continuous structure.

A wide variety of known polymerization initiators can be used. For example, peroxides such as benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, 2,2-azobisisobutyronitrile, potassium persulfate, etc. In particular, it is preferable to use a redox polymerization initiator in order to reduce the polymerization temperature. In the redox polymerization initiator, examples of the reducing agent combined with the peroxide include tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing metal ions, ascorbic acid and the like. Preferable examples of combinations in the redox type polymerization initiator include tert-butyl hydroperoxide and tetraethylenepentamine, hydrogen peroxide and Fe ²⁺ salt, K ₂ SO ₂ O ₈ and NaHSO ₃ and the like.

  The addition amount of a polymerization initiator is 0.3-10 mol% with respect to 100 mol of phenyl group containing vinyl monomers, Preferably it is 0.5-1 mol%. By charging these components into a reaction vessel and reacting at 30 to 80 ° C. for 2 to 10 hours, a grafted natural rubber obtained by graft copolymerizing a phenyl group-containing vinyl monomer on the surface of a deproteinized natural rubber particle is obtained. .

  FIG. 1 shows that the main chain derived from natural rubber of the present invention has a cyclized rubber structure and the graft polymer phase having a sulfonated phenyl group coexisting with the cyclized natural rubber phase has a continuous structure, or cyclized natural. A process for producing a natural rubber electrolyte in which a rubber phase and a graft polymer phase having a sulfonated phenyl group have a co-continuous structure is shown.

  As shown in FIG. 1, in the surface graft copolymerization, an initiator is added to latex in which only natural rubber particles are dispersed, and radicals are preferentially generated on the surface of the rubber particles. Then, a phenyl group-containing vinyl monomer such as a styrene monomer is dropped to cause a polymerization reaction on the particle surface. From this, in surface graft copolymerization, it is considered that radical copolymerization is efficiently occurring on the surface of natural rubber particles.

  Next, a cyclization reaction in which the main chain derived from the natural rubber of the obtained graft copolymer has a cyclized rubber structure and a sulfonation reaction in which the phenyl group of the obtained graft copolymer is sulfonated are performed.

  In the obtained natural rubber-based electrolyte, the main chain derived from natural rubber has a cyclized rubber structure, and the graft polymer phase having a sulfonated phenyl group coexisting with the cyclized natural rubber phase has a continuous structure or cyclized. The natural rubber phase and the graft polymer phase having a sulfonated phenyl group have a co-continuous structure.

  In the present invention, a sulfonated polymer continuous structure, preferably a sulfonated polymer and a cyclized natural rubber nano cocontinuous structure is formed by graft copolymerization of a monomer having a phenyl group to natural rubber and then sulfonation. The proton conductive polymer electrolyte has high proton conductivity while suppressing water swelling and water evaporation during high temperature use.

  Next, the nanomatrix-dispersed natural rubber of the present invention and the method for producing the same will be further described with reference to examples, but the following specific examples do not limit the present invention.

[Deproteinization of natural rubber]
As the natural rubber latex, a commercially available high ammonia natural rubber latex (HA-NR) (DRC: 60 wt / wt%) was used. Deproteinization was performed by diluting HA-NR latex to DRC 30 wt / wt%, adding 1 wt / wt% surfactant (SDS) and 0.1 wt / wt% urea, and incubating at room temperature. This latex was washed by centrifuging at 10,000 g, and adjusted to DRC 30 wt / wt% and surfactant concentration 0.1 wt / wt%, thereby reducing urea deproteinized natural rubber (hereinafter referred to as DPNR) latex. Obtained.

[Purification of styrene]
Styrene was removed by washing the polymerization inhibitor catechol with a 10% aqueous sodium hydroxide solution, and dried over anhydrous magnesium sulfate for 24 hours.

[Example 1]
FIG. 2 shows the procedure of graft copolymerization.
The sample used was deproteinized natural rubber (DPNR) latex that was deproteinized with urea. After adjusting the dry rubber weight (DRC) of DPNR latex to 30%, nitrogen substitution was performed for 1 hour, and 0.2 mol / kg-rubber of tert-butyl hydroperoxide (TBHPO) and 0.2 mol / kg-rubber Of tetraethylenepentamine (TEPA) was added sequentially, and 5.5 mol / kg-rubber of styrene was added as a monomer having a phenyl group. The graft copolymerization of styrene was performed at 30 ° C. for 2 hours.

  After completion of the reaction, unreacted styrene was removed under reduced pressure using an evaporator, and then a film (DPNR-graft-PS) was formed.

FIG. 3 shows the sulfonation procedure.
The product DPNR-graft-PS was dissolved in acetone or chloroform and then sulfonation was performed using 0.2 to 0.8 N chlorosulfonic acid.

  FIG. 4 shows a TEM of the obtained natural rubber electrolyte in which a main chain derived from natural rubber has a cyclized rubber structure and a graft polymer phase having a sulfonated phenyl group coexisting with the cyclized natural rubber phase has a continuous structure. Show photos.

  FIG. 5 shows TEM photographs of DPNR-graft-PS (A) and DPNR-graft-PS (B) sulfonated with 0.8 N chlorosulfonic acid. The bright part is natural rubber and the dark part is polystyrene. As shown in FIG. 5, in the state (A) before sulfonation, the polystyrene particles are not bonded to each other and separated, whereas in the sulfonated state (B), the polystyrene particles are bonded to each other and uniform. A matrix is formed. FIG. 5C is a three-dimensional TEM image of DPNR-graft-PS sulfonated with 0.8 N chlorosulfonic acid, and the size of the box in the image is X: Y: Z = 600 nm: 500 nm. : 100 nm. In FIG. 5C, the dark part is natural rubber and the bright part is polystyrene.

  Based on the above results, the three-dimensional structure of the natural rubber electrolyte of the present invention is schematically shown in FIG. As shown in FIG. 6, the natural rubber electrolyte of the present invention has a continuous structure in which a graft polymer phase (hydrophilic domain) having a sulfonated phenyl group coexisting with a cyclized natural rubber phase (hydrophobic domain) has a continuous structure. A large number of “nanomatrix channels” made of a graft polymer phase are formed vertically and horizontally so that ionic molecules can conduct inside. The width of the nanomatrix channel is about 1 to 100 nm.

  FIG. 7 shows the NMR spectra of DPNR-graft-PS (A) and DPNR-graft-PS (B) sulfonated with 0.8 N chlorosulfonic acid. The 139.1 ppm signal (3) appearing after sulfonation was identified as an aromatic carbon substituted with a sulfonic acid group. The low magnetic field shift from 127.3 ppm and 145.7 ppm signals to 130.1 (2) ppm and 148.0 ppm (4), respectively, is due to the electron withdrawing effect of the sulfonic acid group bonded to the phenyl group. Conceivable.

[Measurement of proton conductivity]
The sample was boiled in 1N sulfuric acid aqueous solution for 1 hour, then boiled in pure water for 1 hour, and further, the pure water was exchanged and boiled for 1 hour to obtain a solid polymer electrolyte membrane activation treatment. The activated sample was sandwiched between gold electrodes, the gold electrode and an impedance analyzer (Solartron SI1260) were wired, and the frequency scan was performed from the high frequency side to the low frequency side at room temperature and atmospheric pressure, and then the impedance in the film thickness direction was obtained. . Based on this impedance, the conductivity was determined by the following formula.
σ (conductivity) = (film thickness) ÷ (film resistance)

  Table 1 below shows the glass transition point Tg, gel content, sulfur content, ion exchange capacity (IEC), proton conductivity, and water swell amount of the natural rubber electrolyte membrane obtained in the present invention. In addition, as Reference Examples 1 and 2, characteristic values measured for sulfonated polystyrene and Nafion (registered trademark) 117 (proton conductive perfluorosulfonic acid membrane) are also shown.

  As is clear from Table 1, the ion exchange capacity (IEC) and the amount of water swelling of the sulfonated DPNR-graft-PS depend on the amount of sulfonic acid groups, and the ion exchange capacity and The amount of water swelling also increased. The IEC value of sulfonated DPNR-graft-PS at 75 wt% was 2.4 meq / g, which was higher than the IEC value of sulfonated polystyrene and Nafion® 117.

Proton conductivity correlates with IEC. The proton conductivity of sulfonated DPNR-graft-PS improved as the amount of sulfonic acid groups increased. The proton conductivity of sulfonated DPNR-graft-PS (75 wt% PS / PS) is 9.5 × 10 ⁻² S / cm, which is three times that of sulfonated polystyrene, and Nafion® It was higher than 117 proton conductivity.

  Despite the high proton conductivity and IEC, sulfonated DPNR-graft-PS at 75 wt% sulfur has a small amount of water swelling, specifically about 1/150 of sulfonated polystyrene. This is advantageous. This low amount of water swelling is considered to be due to the influence of the cyclized natural rubber phase of sulfonated DPNR-graft-PS.

[Example 2]
FIG. 8 shows the procedure of graft copolymerization. FIG. 9 shows the sulfonation procedure.
Using DPNR-graft-PS prepared by the method shown in Example 1 as a raw material, sulfonation was performed using acetyl sulfate.

  In the synthesis of acetyl sulfate, chloroform was sufficiently cooled in an ice bath, and acetic anhydride was added, followed by stirring. After stirring for 10 minutes, sulfuric acid was added dropwise to obtain acetyl sulfate.

  FIG. 10 shows a 1H-NMR spectrum of DPNR-graft-PS. In FIG. 11, (a) natural rubber deproteinized with urea (U-DPNR), (b) polystyrene grafted natural rubber (PS-graft-NR), (c) sulfonated with 0.006 mol of acetyl sulfate. Polystyrene grafted natural rubber (PS-graft-NR), (d) Polystyrene grafted natural rubber sulfonated with 0.012 mol acetylsulfuric acid (PS-graft-NR), (e) Sulfonated with 0.018 mol acetylsulfuric acid The FT-IR spectrum of polystyrene grafted natural rubber (PS-graft-NR), (f) polystyrene grafted natural rubber sulfonated with 0.024 mol of acetyl sulfate (PS-graft-NR) is shown.

  The natural rubber electrolyte of the present invention is obtained by graft-copolymerizing a monomer having a phenyl group to natural rubber and then sulfonating to form a continuous structure of the sulfonated polymer, preferably a nano-cocontinuous of the sulfonated polymer and the cyclized natural rubber. It is a proton conductive polymer electrolyte that forms a structure, suppresses swelling with respect to water and evaporation of water during high temperature use, and also has high proton conductivity.

  The natural rubber electrolyte of the present invention is suitably used for solid polymer fuel cells and the like.

Claims (8)

  A polyelectrolyte in which phenyl group-containing vinyl monomer is graft-copolymerized with natural rubber and the phenyl group of the grafted natural rubber is sulfonated. The main chain derived from natural rubber has a cyclized rubber structure, and the cyclized natural rubber phase A natural rubber-based electrolyte characterized in that a graft polymer phase having a sulfonated phenyl group coexisting with has a continuous structure.   A polyelectrolyte in which a phenyl group-containing vinyl monomer is graft copolymerized with natural rubber, and the phenyl group of the grafted natural rubber is sulfonated. The main chain derived from natural rubber has a cyclized rubber structure, and the cyclized natural rubber phase And a graft polymer phase having a sulfonated phenyl group has a co-continuous structure.   The natural rubber electrolyte according to claim 1 or 2, wherein the natural rubber is a deproteinized natural rubber.   After introducing radical active sites on the surface of natural rubber particles using a water-soluble radical initiator, adding a phenyl group-containing vinyl monomer to perform graft copolymerization, and the resulting graft copolymer derived from natural rubber The method for producing a natural rubber electrolyte according to claim 1 or 2, comprising a step of making the main chain a cyclized rubber structure and a step of sulfonating the phenyl group of the obtained graft copolymer. .   The method for producing a natural rubber electrolyte according to claim 4, wherein the natural rubber is a deproteinized natural rubber and has a step of deproteinizing a natural rubber latex.   6. The method for producing a natural rubber electrolyte according to claim 4, wherein the step of converting the natural rubber-derived main chain into a cyclized rubber structure is performed using a Lewis acid.   The step of converting the natural rubber-derived main chain into a cyclized rubber structure and the step of sulfonating the phenyl group of the obtained graft copolymer are simultaneously performed using chlorosulfonic acid. A method for producing a natural rubber electrolyte according to any one of 4 to 6.   The deproteinization of the natural rubber latex was performed by adding a urea-based protein modifier and a surfactant to the natural rubber latex, and agitating and mixing to denature the protein in the raw natural rubber latex; The method for producing a natural rubber electrolyte according to any one of claims 5 to 7, wherein the method comprises a method comprising a step of separating and removing proteins.

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