Sulfonated polyphosphazene copolymer proton exchange membrane material and method for preparing such membrane

Abstract

A sulfonated polyphosphazene copolymer proton exchange membrane material, and a method for preparing such membrane includes a macromolecule initiator as bromo polyphosphazene is subjected to atom transfer radical polymerization with styrene, yielding a graft copolymer, which is hydrazinolyzed with hydrazine hydrate resulting in a copolymer including a hydroxyl group. The copolymer is reacted with 1,4-butane sultone to yield a sulfonated copolymer finally. The polymer is cross-linked with 2,6-di(hydroxymethyl)-4-methyl phenol (BHMP) as a cross linking agent in the presence of methyl sulfonic acid, yielding cross-linked proton exchange membrane. Such cross-linked graft copolymer membrane has high proton conductivity, low methanol hindrance, and low cost, and has ideal effect when applied in fuel cells as proton exchange membrane material.

Claims

1. A chemical composition for a sulfonated polyphosphazene copolymer proton exchange membrane material, the chemical composition comprising: a polyphosphazene-graft-sulfonated polystyrene copolymer, being comprised of a copolymer of polyphosphazene as a main chain with a polystyrene as a side chain, and a plurality of aliphatic sulfonate group grafted onto said side chain, the polyphosphazene-graft-sulfonated polystyrene copolymer having a structural formula below: ##STR00008## wherein R.sub.1 is OCH.sub.3 or F in para-position; wherein R.sub.2 is Na or H; wherein n is a number of phosphazene residue units corresponding to length of a polyphosphazene chain; wherein x is a number of styrene residue units, ranging from 0 to 100; wherein y is a number of p-(4-sulfonato butoxy)styrene residue units, ranging from 0 to 100; wherein m is a number of combination units of styrene residues and p-(4-sulfonato butoxy)styrene residues, ranging from 0 to 100; and wherein r indicates that the copolymer of styrene residue and p-(4-sulfonato butoxy)styrene residue is a random copolymer.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIGS. 1a and 1b are 1H NMR spectra of poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene] (PMMPP) and poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.10-co-[(4-acetyloxy)styrene].sub.17} (M-PS.sub.10-PAS.sub.17) of the application, respectively.

(2) FIGS. 2a and 2b are .sup.1H NMR spectra of poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.10-co-[(4-hydroxy)styrene].sub.17} and poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.10-co-[(4-(4-sulfonato butoxy)styrene].sub.17} (M-PS.sub.10-PSBOS.sub.17) of the application, respectively.

(3) FIG. 3 is the infrared spectra of cross-linked polyphosphazene-type proton exchange membranes of the application. wherein (a)-(h), respectively, are: M-PS.sub.10-PSBOS.sub.11; M-PS.sub.10-PSBOS.sub.17; M-PS10-PSBOS26; M-PS.sub.8-PSBOS.sub.30; M-PSBOS.sub.40; F-PS.sub.12-PSBOS.sub.11; F-PS.sub.12-PSBOS.sub.17; and F-PSBOS.sub.26.

(4) FIG. 4 shows thermal analysis curves of cross-linked polyphosphazene-type proton exchange membranes of the application.

(5) FIG. 5 shows curves of hydration number (A) of cross-linked polyphosphazene-type proton exchange membranes of the application changing over proton exchange capacity (IEC).

(6) FIG. 6 shows changes of proton conductivity of cross-linked polyphosphazene-type proton exchange membranes of the application over proton exchange capacity (IEC).

(7) FIG. 7 shows changes of proton conductivity of cross-linked polyphosphazene-type proton exchange membranes of the application over temperature.

(8) FIG. 8 is the equilibrium diagram of relative proton conductivity vs. relative methanol permeability of cross-linked polyphosphazene-type proton exchange membranes of the application.

(9) FIGS. 9a and 9b are transmission electron micrographs of polyphosphazene-type proton exchange membranes of poly[(4-fluoro phenoxy)(4-methyl phenoxy)phosphazene-graft-poly[4-(4-sulfonato butoxy)styrene].sub.26} (F-PSBOS.sub.26) and poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.8-co-[(4-(4-sulfonato butoxy)styrene].sub.30} (M-PS.sub.8-PSBOS.sub.30) of the application, respectively.

DETAILED DESCRIPTION OF THE INVENTION

(10) The present invention is further illustrated in combination with Examples hereinafter. The Examples are for illustration purposes only, and are not intended to limit the scope of the present invention in any way. All parameters and descriptions in Examples are based on mass, unless otherwise stated. In Examples, testing methods that are not specifically noted with operating conditions are carried out under conventional conditions known to the skilled ones of the art, or according to manufacturers' recommendations.

(11) All technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skilled in the art, unless defined otherwise. Furthermore, any methods and materials that is similar with or equal to those recited herein can be applied in methods of the present invention.

(12) In order to make the above-mentioned objects and advantages of the present invention more apparent, the following detailed description of the present invention is made by combining accompanying drawings and specifical embodiments.

Example 1

(13) Poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene)10-co-[4-(4-sulfonato butoxy)styrene]17} (M-PS10-PSBOS17).

(14) ##STR00007##

(15) Hexachloro cyclotriphosphazene was ring opening polymerized at 250 C. yielding poly(dichloro phosphazene) (PDCP). Poly(dichloro phosphazene) (5 g, 43 mmol) was dissolved in 80 mL 1,4-dioxane; 4-methoxy phenol (5.33 g, 43 mmol) was dissolved in 60 mL 1,4-dioxane, sodium hydride (1.72 g, 43 mmol) and n-butylammonium bromide (0.33 g, 1 mmol) were added, and the reaction mixture thus obtained was refluxed overnight, yielding a sodium salt. The obtained salt solution was added dropwise into a solution of poly(dichloro phosphazene) with stirring, and the reaction mixture was heated under refluxing under argon protection for 24 hrs. Then 1,4-dioxane solution comprising sodium 4-methyl phenolate was added dropwise. The sodium 4-methyl phenolate was obtained as follows: 4-methyl phenol (9.29 g, 86 mmol) was dissolved in 1,4-dioxane, and sodium hydride (3.44 g, 86 mmol) was added, then heated under refluxing. The reaction mixture was heated under refluxing at 115 C. for 36 hrs. Precipitate was resulted after adding water to the reaction solution, which was then vacuum dried for 24 hrs, the resulting product was dissolved in tetrahydrofuran, into which water was added to form precipitate. Finally, the product was dissolved in tetrahydrofuran, into which n-hexane was added to form precipitate, yielding a white fibrous macromolecular compound, i.e. poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene] (PMMPP). The yield is 50%. The .sup.1H NMR spectrum of the obtained macromolecular compound was shown in FIG. 1a. .sup.1H MNR (400 MHz, CDCl.sub.3; ppm): : 6.6-6.8 (m, OC.sub.6H.sub.4CH.sub.3), 6.28 (m, OC.sub.6H.sub.4OCH.sub.3), 3.48 (s, OCH.sub.3), 2.08 (s, CH.sub.3).

(16) PMMPP (1.0 g, 3.6 mmol), N-bromo succinimidyl (0.128 g, 0.72 mmol), benzoyl peroxide (0.017 g, 0.072 mmol) and carbon tetrachloride (100 mL) were added into a 200 mL round flask under nitrogen protection, and the obtained mixture was refluxed at 80 C. for 3 hrs. Then, the mixture was cooled and filtered. The filtrate was added to n-hexane, and the product was precipitated, which was then dried in vacuum at 50 C. for 24 hrs. The macromolecule initiator, bromo polyphosphazene (PMMPP-Br), was obtained. The yield is 90%. .sup.1H MNR (400 MHz, CDCl.sub.3; ppm): : 6.6-6.8 (m, OC.sub.6H.sub.4CH.sub.3), 6.28 (m, OC.sub.6H.sub.4OCH.sub.3), 4.2 (s, CH.sub.2Br), 3.48 (s, OCH.sub.3), 2.08 (s, CH.sub.3).

(17) The macromolecule initiator PMMPP-Br (0.5 g, 0.26 mmol), styrene (1.083 g, 10.4 mmol), 4-acetyloxy styrene (1.68 g, 10.4 mmol), 2,2-bipyridyl (0.24 g, 1.56 mmol) and copper bromide (0.52 mmol) were added into a dry reaction tube equipped with a piston and a magnetic stirrer. The polymerization was performed at 115 C. for 24 hrs. Then, the resulting mixture was purified through column chromatography and vacuum drying. The graft copolymer of poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.10-co-[(4-acetyloxy)styrene].sub.17} (M-PS.sub.10-PAS.sub.17) was obtained. The 1H NMR spectrum of the obtained compound was shown in FIG. 1b. .sup.1H MNR (400 MHz, CDCl.sub.3; ppm): : 7.08-7.26 (m, OC.sub.6H.sub.4), 6.6-6.8 (m, OC.sub.6H.sub.4CH.sub.3), 6.28 (m, OC.sub.6H.sub.4OCH.sub.3), 3.48 (s, OCH.sub.3), 2.26 (s, OOCCH.sub.3), 2.08 (s, CH.sub.3), 1.2-1.9 (m, CH.sub.2, CH).

(18) Poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.10-co-[(4-acetyloxy)styrene].sub.17} (M-PS.sub.10-PAS.sub.17) (1.0 g, 3.6 mmol) was dissolved in tetrahydrofuran, and 2.0 mL hydrazine hydrate was added. The reaction mixture was stirred under nitrogen at room temperature for 5 hrs. After the reaction completed, the resulting mixture was precipitated from water, then dried at 60 C. for 24 hrs, yielding the product, poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.10-co-[(4-hydroxy)styrene].sub.17} (M-PS.sub.10-PHS.sub.17). Yield: 80%. The .sup.1H NMR spectrum of the obtained compound was shown in FIG. 2a. .sup.1H MNR (400 MHz, DMSO-d6, ppm): : 9.04 (s, OH), 7.08-7.26 (m, OC.sub.6H.sub.4), 6.28-6.8 (m, OC.sub.6H.sub.4CH.sub.3, OC.sub.6H.sub.4OCH.sub.3), 3.60 (s, OCH.sub.3), 2.02 (s, CH.sub.3), 1.2-1.9 (m, CH.sub.2, CH).

(19) Poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.10-co-[(4-hydroxy)styrene].sub.17} (M-PS.sub.10-PHS.sub.17) (0.5 g, 1.8 mmol) was dissolved in a DMSO solution, then NaH (0.052 g, 2.16 mmol) was added. The reaction mixture was stirred at 40 C. for 24 hrs, then 1,4-butane sultone (0.25 g, 0.18 mL) was added into the reaction system. The resulting mixture was stirred at 100 C. for 24 hrs, then added into isopropanol, from which a polymer was precipitated. The isolated polymer was dried in vacuum at 80 C. for 10 hrs, yielding the product poly[(4-methoxy phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.10-co-[4-(4-sulfonato butoxy)styrene].sub.17} (M-PS.sub.10-PSBOS.sub.17). Yield: 90%. The .sup.1H NMR spectrum of the compound obtained was shown in FIG. 2b.

Example 2

(20) Poly[(4-fluoro phenoxy)(4-methyl phenoxy)phosphazene-graft-poly{(styrene).sub.x-co-[4-(4-sulfonato butoxy) styrene].sub.y} (F-PS.sub.x-PSBOS.sub.y).

(21) The preparation was performed as described in Example 1, except that sodium 4-fluoro phenolate was substituted for sodium 4-methoxy phenolate in Example 1.

(22) Table 1 shows the molecular weight of two series of graft copolymer obtained respectively in Example 1 and Example 2, the GPC results (Table 1) indicating that polymers of high molecular weights are obtained.

(23) TABLE-US-00001 Length of Graft Graft Copolymer (P.sub.s/P.sub.4As).sup.a M.sub.n (Da).sup.b M.sub.w (Da).sup.b PDI M-PS.sub.10-PAS.sub.11 10:11 2.20 10.sup.5 4.96 10.sup.5 2.25 M-PS.sub.10-PAS.sub.17 10:17 2.91 10.sup.5 3.60 10.sup.5 1.24 M-PS.sub.10-PAS.sub.26 10:26 2.04 10.sup.5 4.62 10.sup.5 2.26 M-PS.sub.8-PAS.sub.30 8:30 1.74 10.sup.5 3.16 10.sup.5 1.82 M-PAS.sub.40 0:40 1.46 10.sup.5 3.11 10.sup.5 2.14 F-PS.sub.12-PAS.sub.11 12:11 4.06 10.sup.5 8.60 10.sup.5 2.12 F-PS.sub.12-PAS.sub.17 12:17 8.06 10.sup.5 14.64 10.sup.5 1.82 F-PAS.sub.26 0:26 1.13 10.sup.5 1.94 10.sup.5 1.72 .sup.athe average number of styrene units in a graft copolymer, calculated from 1H NMR spectra. .sup.bPolystyrene is used as the standard in gel permeation chromatography (GPC).

Example 3

(24) Sulfonated polyphosphazene graft copolymers obtained in Example 1 and Example 2 were cross-linked, yielding sulfonated polyphosphazene copolymer proton exchange membrane. The preparation process was as followed: polyphosphazene-type graft copolymer having an aliphatic sulfonate branch side chain and cross-linking agents were dissolved in DMSO, resulting a solution with concentration 10 w/v %. The solution was poured in a polytetrafluoroethylene die, and dried at 120 C. for 1 hr, then dried further at 70 C. for 24 hrs. The obtained membrane was immersed into 2 mol/L dilute sulfuric acid solution for 48 hrs, then washed with deionized water, yielding a membrane of H+ form. FIG. 3 shows the FT-IR spectrum of the membrane obtained in Example 3. It can be seen in FIG. 3 that there are two special absorptions at about 1238 cm-1 and 1040 cm-1 indicating the symmetrical and asymmetrical stretching vibrations of sulfonate groups, respectively.

Example 4

(25) The sulfonated polyphosphazene copolymer proton exchange membrane obtained in Example 3 was subjected to a thermal analysis testing.

(26) Thermal weight losses of the polymers were analyzed on TGA-Q500 thermal analyzer, and the measuring conditions were: temperature rising at a rate of 10 C./min from 40 C. to 700 C. under a nitrogen atmosphere. FIG. 4 shows the thermo-weight curves of the membranes. All samples were heated at 100 C. for 20 min to remove residual water in the samples prior to TGA characterization. As shown in FIG. 4, there are three thermal weight loss intervals in each sample. The first thermal weight loss interval at 150-250 C. is the decomposition temperature of sulfonate group, which, in a series of membrane, rises as the styrene content increasing, indicating that the heat stability of a membrane rises gradually as the styrene content increasing. The second and the third thermal weight loss temperatures start at about 250 C. and 350 C., respectively, which are attributed to the decomposition of the polystyrene block and the polyphosphazene backbone, respectively.

Example 5

(27) The sulfonated polyphosphazene copolymer proton exchange membrane obtained in Example 3 was subjected to an oxidation resistance testing.

(28) Oxidation resistance testing: membrane samples were immersed in Fenton reagent (which is 3% H2O2 solution comprising 2 ppm FeSO4) at 80 C. for 1 hr, then the weight changes and physic-chemical characteristics of samples after immersed were measured. The results of oxidation resistance testing are shown in Table 2, the analysis of which indicates that the sulfonated polyphosphazene copolymer proton exchange membranes obtained according to the present invention exhibit better stability in oxidation resistance as compared with the other sulfonated polymers.

Example 6

(29) The proton exchange capacity (IEC), water uptake and swelling degree of the sulfonated polyphosphazene copolymer proton exchange membranes obtained in Example 3 were assayed.

(30) The assay method of proton exchange capacity (IEC): proton exchange capacity (IEC) is assayed through neutralization titration. Proton exchange membranes in the form of proton were immersed in 50 mL 2 mol/L NaCl solution for 24 hrs to sufficiently exchange H+ on sulfonate groups with Na+ from sodium chloride, then the resulting solution was titrated with 0.02 mol/L NaOH solution using phenolphthalein as a pH indicator. IEC was calculated according to the formula:

(31) $IEC=\frac{C_{\mathrm{NaOH}}{V}_{\mathrm{NaOH}}}{W}$

(32) CNaOH is the concentration of NaOH solution, VNaOH is the consumed volume of NaOH solution, and w is the mass of a membrane.

(33) The method for assaying water uptake (WU): a proton exchange membrane was immersed in deionized water at room temperature for over 24 hrs to ensure the membrane had uptaken water sufficiently, the membrane was removed and swabbed with filter paper to clean the water on its surfaces, and then the membrane weight Wwet was measured immediately; after that, the membrane was baked to dry, and the membrane weight at this time Wdry was measured immediately; the water uptake of a membrane was calculated according to the formula:

(34) $\mathrm{Water}\mathrm{uptake}\left(\%\right)=\frac{W_{\mathrm{wet}}-W_{\mathrm{dry}}}{W_{\mathrm{dry}}}100\%$

(35) The assay method for the swelling degree of a membrane is as follows: the membrane was immersed in deionized water at room temperature for 24 hrs to ensure that the membrane swelled sufficiently, and its length Lwet was measured, then the membrane was dried and its length Ldry was measured; swelling degree was determined by the change in length after a membrane uptaking water, which is calculated according to the formula:

(36) $\mathrm{SW}\left(\%\right)=\frac{L_{\mathrm{wet}}-L_{\mathrm{dry}}}{L_{\mathrm{dry}}}100\%$

(37) Hydration number is the average water molecules uptaken corresponding to each proton exchange site ([H2O]/[SO3-]), which is often referred as value and calculated according to the formula:

(38) $=\frac{\left[H_{2}O\right]}{\left[{\mathrm{SO}}_3^{-}\right]}=\frac{WU\left(\%\right)10}{18IEC\left(\mathrm{mmol}\text{/}g\right)}$

(39) The IEC values, water uptakes, swelling degrees and hydration numbers of the sulfonated polyphosphazene copolymer proton exchange membranes are shown in Table 2.

(40) It can be seen in Table 2 that IEC values of all the proton exchange membranes range from 1.04 mequiv/g to 2.30 mequiv/g. The IEC value of a proton exchange membrane is related closely with its swelling degree. A membrane with a higher IEC value typically has a higher water uptake. The hydration numbers ([H.sub.2O]/[SO.sub.3.sup.] or ) of the cross-linked polyphosphazene-type graft copolymer membranes, M-PS.sub.x-PSBOS.sub.y and F-PS.sub.x-PSBOS.sub.y, increase as their IEC values increase. FIG. 5 shows the curves of hydration numbers () of sulfonated polyphosphazene copolymer proton exchange membranes changing over proton exchange capacity (IEC). The cross-linked polyphosphazene graft copolymer membranes have lower water uptakes than Nafion117.

(41) TABLE-US-00002 TABLE 2 The Proton Exchange Capacities (IECs), Water Uptakes (WUs), Swelling degrees (SWs) and Hydration Numbers () of the Cross-linked Polyphosphazene-type Proton Exchange Membranes and Nafion Membrane. IEC.sup.a water swelling hydration polyphosphazene (mequiv/ uptake degree number membrane g) (%) (%) () RW.sup.b (%) M-PS.sub.10-PSBOS.sub.11 1.14 33.2 36.8 16 98 M-PS.sub.10-PSBOS.sub.17 1.32 48.1 41.1 20 96 M-PS.sub.10-PSBOS.sub.26 1.43 74.3 43 29 95 M-PS.sub.8-PSBOS.sub.30 2.14 128.5 55 32 94 M-PSBOS.sub.40 2.30 140.6 57.6 34 93 F-PS.sub.12-PSBOS.sub.11 1.04 36.9 20.3 20 97 F-PS.sub.12-PSBOS.sub.17 1.26 51.2 24 23 96 F-PSBOS.sub.26 1.49 69.5 27 26 94 Nafion 117 0.9 35 17 22 .sup.adetermined through titration. .sup.bthe mass fraction measured after immersing a membrane into Fenton reagent (3% H.sub.2O.sub.2, 2 ppm FeSO.sub.4) for 1 hr.

(42) The preparation was performed as described in Example 1, except that sodium 4-fluoro phenolate was substituted for sodium 4-methoxy phenolate in Example 1.

Example 7

(43) The Proton Conductivity Assay of the Sulfonated Polyphosphazene Copolymer Proton Exchange Membrane Obtained in Example 3.

(44) Proton conductivity was assayed on CHI 660D electrochemistry workstation (100 Hz10.sup.5 Hz). Calculated according to the formula:
=l/RS wherein l is the distance in cm between electrodes; R is the electric resistance in of the membrane determined by AC impedance method; S is the cross-sectional area in cm.sup.2 of the proton exchange membrane; and is the proton conductivity in S/cm.

(45) Proton conductivities of the membranes are shown in Table 3. FIG. 6 shows proton conductivity changes of the sulfonated polyphosphazene copolymer proton exchange membranes over the proton exchange capacities of the membranes obtained at room temperature in Example 6. It can be seen in FIG. 6 that the proton conductivities of sulfonated polyphosphazene copolymer proton exchange membranes, M-PS.sub.x-PSBOS.sub.y and F-PS.sub.x-PSBOS.sub.y, increase as IEC increases at room temperature, and the proton conductivities of the membranes increase substantially when IEC value ranges from 1.2 mequiv/g to 1.5 mequiv/g, indicating that IEC value has a dramatic effect on the proton conductivity of a membrane. When the IEC value is higher, the proton exchange membrane F-PS.sub.x-PSBOS.sub.y has higher proton conductivity than that of M-PS.sub.x-PSBOS.sub.y.

(46) TABLE-US-00003 TABLE 3 Proton Conductivity and Methanol Permeability of Cross-linked Polyphosphazene-type Proton Exchange Membrane. proton methanol conductivity permeability polyphosphazene (S/cm) coefficient selectivity.sup.a membrane 25 C. 80 C. (10.sup.7 cm.sup.2/s) (10.sup.5 Ss/cm.sup.3) M-PS.sub.10-PSBOS.sub.11 0.09 0.184 2.02 4.46 M-PS.sub.10-PSBOS.sub.17 0.11 0.22 3.78 2.91 M-PS.sub.10-PSBOS.sub.26 0.15 0.26 4.49 3.34 M-PS.sub.8-PSBOS.sub.30 0.176 0.266 7.10 2.47 M-PSBOS.sub.40 0.125 0.202 10.4 1.20 F-PS.sub.12-PSBOS.sub.11 0.067 0.147 1.60 4.19 F-PS.sub.12-PSBOS.sub.17 0.09 0.158 2.20 4.09 F-PSBOS.sub.26 0.17 0.284 8.50 2.0 Nafion 117 0.10 0.191 15.80 0.63 .sup.aselectivity = proton conductivity/methanol permeability coefficient

(47) Table 1 shows the molecular weight of two series of graft copolymer obtained respectively in Example 1 and Example 2, the GPC results (Table 1) indicating that polymers of high molecular weights are obtained.

(48) FIG. 7 shows changes of proton conductivity changes of the sulfonated polyphosphazene copolymer proton exchange membranes over temperature. It can be seen in FIG. 7 that proton conductivities of all the membranes increase as temperature increases. When IEC value is greater than 1.32 mequiv/g, the proton conductivities of sulfonated polyphosphazene copolymer proton exchange membranes obtained according to the present invention is greater than Nafion 117.

Example 8

(49) Methanol Hindrance Testing of the Sulfonated Polyphosphazene Copolymer Proton Exchange Membrane Obtained in Example 3.

(50) Methanol permeability testing of a membrane: the cell for measuring methanol permeation of a membrane was a self-designed methanol-diffusing cell, which consisted of sumps A and B; wherein sump A (VA=50 mL) was filled with 1 mol/L solution of methanol in water, sump B (VB=50 mL) was filled with deionized water, the membrane was immobilized perpendicularly between the two sumps to separate the two solutions, the methanol solution in sump A would slowly diffuse into sump B due to the interdiffusion between different kinds of fluids, then the solution in sump B was sampled periodically and the methanol content was measured through gas chromatography, and the methanol permeability coefficient of the proton exchange membrane as calculated by applying the methanol content change rate in solution B into the formula:

(51) $P=\frac{K{V}_{B}h}{A{C}_A}$ wherein P is methanol permeability coefficient in cm.sup.2/s; K is change rate of methanol concentration in solution B over time detected through gas chromatography. V.sub.B is the volume solution B in mL; A is available diffusing area in cm.sup.2; C.sub.A is methanol concentration in mol/L in solution A; and h is the thickness in cm of the membrane.

(52) The proton exchange membranes suitable for a methanol fuel cell need to have not only higher proton conductivity, but also lower methanol permeability coefficient. As shown in Table 3, the methanol permeability coefficients of polyphosphazene copolymer proton exchange membranes obtained according to the present invention range from 1.6010.sup.7 cm.sup.2/s to 10.410.sup.7 cm.sup.2/s. The selectivity, which is the ratio of proton conductivity to methanol permeability coefficient and a common parameter for assessing the performance of a membrane for methanol fuel cells, of all sulfonated polyphosphazene copolymer proton exchange membranes obtained according to the present invention is higher than Nafion membrane. FIG. 8 is an equilibrium diagram of relative proton conductivity vs. relative methanol permeability of proton exchange membranes in the present Example. As shown in FIG. 8, all the membranes are positioned in the top left area, especially M-PS.sub.10-PSBOS.sub.26 and M-PS.sub.8-PSBOS.sub.30, which exhibit the best selectivity, and have potential for application in the proton exchange membrane of methanol fuel cells.

Example 9

(53) Microscopic Morphology Analysis of the Sulfonated Polyphosphazene Copolymer Proton Exchange Membranes Obtained in Example 3.

(54) Transmission electron microscopy (TEM) testing: in order to test the topological structure and the ion cluster size of a membrane, the membrane was immersed into a solution of lead nitrate in water for 3 days, then embedded into epoxy resin, sectioned to 70 nm thickness, and observed using JEOL JEM-2010 transmission electron microscope.

(55) The proton conductivity of a membrane is closely related to membrane morphology. The proton transporting channel formed by a hydrophilic domain facilitates the proton transporting. FIG. 9a and FIG. 9b are the transmission electron micrographs of F-PSBOS.sub.26 and M-PS.sub.8-PSBOS.sub.30, respectively, wherein because the membrane samples were immerse in Pb(NO.sub.3).sub.2 solution prior to the test, hydrogen protons in the polymers were replaced by Pb.sup.2+, therefore, the darker colored areas represent hydrophilic phase, and the lighter colored areas represent a hydrophobic phase. The hydrophilic/hydrophobic phase distribution on the entire membrane can be revealed by the distribution of the two colors. It's indicated in the transmission electron micrographs that ion channels that are narrow and interconnected with each other can provide the migration path for proton, which improves the proton conductivity of the polyphosphazene-type proton exchange membrane according to the present invention.

(56) While the sulfonated polyphosphazene copolymer proton exchange membrane material provided in the present invention as well as and the preparation and the use of such membrane have been discussed in detail above, and the principles and implementations of the present invention have been illustrated through particular examples herein, the Examples above are described to help understanding the method and the core concept of the present invention only. It should be appreciated further that variations and modifications of the present invention would occur to those skilled in the art upon reading the contents above, and these equivalents are deemed to be within the scope defined by the appended claims.