Research Article Synthesis of Highly Sulfonated Poly(arylene …downloads.hindawi.com/journals/ijps/2016/6545362.pdf · 2019-07-30 · Research Article Synthesis of Highly Sulfonated

Research ArticleSynthesis of Highly Sulfonated Poly(arylene ether) ContainingMultiphenyl for Proton Exchange Membrane Materials

Yi-Chiang Huang Ruei-Hong Tai Hsu-Feng Lee Po-Hsun Wang Ram GopalChun-Che Lee Mei-Ying Chang and Wen-Yao Huang

Department of Photonics National Sun Yat-Sen University No 70 Lienhai Road Kaohsiung 80424 Taiwan

Correspondence should be addressed to Wen-Yao Huang wyhuangfacultynsysuedutw

Received 8 January 2016 Accepted 18 May 2016

Academic Editor Eliane Espuche

Copyright copy 2016 Yi-Chiang Huang et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

A series of sterically hindered sulfonated poly(arylene ether) polymers were synthesized by nucleophilic polycondensationreaction using 441015840101584010158401015840-difluoro-331015840101584010158401015840-bistrifluoromethyl-210158401015840310158401015840510158401015840610158401015840-tetraphenyl-[111015840410158401101584010158404101584010158401101584010158401015840410158401015840101584011015840101584010158401015840]-pentaphenyl and 441015840-biphenol and were prepared through postpolymerization sulfonation The chemical structures were confirmed by 1H NMRSubsequent to sulfonation solvent-casting membranes were provided ion exchange capacity (IEC) values ranging from 039 to290mmolg Proton conductivities of membranes ranged from 143 to 228mScm at 80∘C under fully humidified conditionswhich were higher than that of Nafion 117 The membrane also exhibited considerably dimension stability oxidative stabilityand hydrolytic stability The microphase structure was investigated by transmission electron microscopy (TEM) and the ionicaggregation of sulfonic acid groups exhibited spherical ionic clusters with well-developed phase separated morphology Theresults indicated that the membranes are promising candidates for application as proton exchange membranes This investigationdemonstrates introducing multiphenylated moieties to create a high free volume polymer that provides dimensionally stable andhigh proton conductivity membranes

1 Introduction

In the past few decades proton exchange membrane fuelcells (PEMFC) as an alternative energy have been widelyinvestigated The critical component of PEMFC is the pro-ton exchange membrane (PEM) The PEM required highproton conductivity chemical and thermal stability andhigh dimensional stability when operating at high humidityenvironments and low permeability to separate the reactantgases [1] The most widely used PEM Nafion was kind ofperfluorinated sulfonic acid (PFSA) ionomer membrane andthat was first developed by Dupont Inc Nafion has servedas a benchmark of PEM because of its good chemical andelectrochemical stability as well as excellent proton conduc-tivity However Nafion still has some drawbacks such as highmethanol crossover poor mechanical chemical stability andlow conductivity at elevated temperatures (gt80∘C)Moreoverthe worst of all disadvantages of Nafion is high cost [2]Therefore seeking for alternatives to Nafion is a major topic

In recent years sulfonated aromatic hydrocarbon polymerelectrolytes are widely studied such as poly(arylene etherketone)s poly(arylene ether ketone)s poly(arylene ether)sand polyimides [3ndash5] which are promising candidates toNafion because of their relatively low cost easy tuningof polymer structure processability and good mechanicalthermal and chemical stability [6ndash9]

In general sulfonated aromatic hydrocarbon polymersreach comparable proton conductivity with PFSAs usuallyunder high ion exchange capacity (IEC) and water uptakebecause of their lower acidity and degree of phase separationwith smaller isolated hydrophilic domains [10] Howeverhigher IEC values of hydrocarbon PEMs consequently lead toexcessive swelling and deterioratemechanical propertiesThestrategy for designing PEMs able to maintain water stabilitywithout excessive swelling is to induce phase separation ofthe hydrophilic and hydrophobic regions so as to increasehydrophobic interactions of the polymer chains by locallyand densely sulfonated segments on the main chain and to

Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2016 Article ID 6545362 8 pageshttpdxdoiorg10115520166545362

2 International Journal of Polymer Science

introduce free volume into the polymer for water to occupy[11 12]

To overcome the problems of sulfonated aromatic hydro-carbon polymers many studies have been reported Forexample Chen et al developed amultiphenylated hydrophilicdomain and linear hydrophobic chain copolymer Thesedesigned ionomers gave distinct phase separation and facili-tate forming proton conductive channels and also exhibitedhighly thermal and oxidative stability [13] Wang et alreported new poly(ether sulfone) based on fluorene with twopendant phenyl substituents that provided clustered pendantsulfonic acid groups The sulfonated polymers demonstratedhigh oxidative stability good mechanical properties anda clear phase separation of ionic domains size of 3 to7 nm [14] Nakabayashi et al synthesized highly sulfonatedmultiblock poly(ether sulfone)s followed by postsulfonationwith concentrated sulfuric acid The membranes with higherIEC values of 275ndash279mmolg exhibited similar protonconductivity with Nafion 117 in a range of 50ndash95 RH AFMimage also supported the formation of well-connected protonconductive channels to implement high proton conductivity[15] Pang et al reported novel poly(arylene ether)s attachedhigh density sulfonated hexaphenyl pendent group in orderto control positions and the degree of sulfonation Theseresulting polymers exhibited lower water uptake and gooddimensional stability The membranes showed high protonconductivities and low methanol permeability Pang et alalso presented novel fluorinated poly(arylene ether ketone)scontaining hexa sulfophenyl as a hydrophilic pendent groupwhich enhanced the difference in polarity of hydrophilic andhydrophobic segments The membranes demonstrated lowerdimensional change value and high proton conductivityattributed to well-defined phase separation [16 17] RecentlyJo et al synthesized poly(p-phenylene) block copolymersintroducing trifluoromethyl and multiphenylated pendantgroups to improve the hydrophobicity and enhance denselyand locally sulfonated domains The membranes exhibitedcomparable or superior performance toNafion 212 in fuel celltesting [18]

In our previous work we introduced multiphenylatedstructure into the polymer main chain which provides goodmechanically and dimensionally stable PEMs The multi-phenylated structure on the backbone can increase the freevolume As a result multiphenylated structure allowed forsignificant water sorption while maintaining good mechan-ical strength [19] Herein we synthesized a novel alternat-ing poly(arylene ether) comprising commercialized 441015840-biphenol monomer and sterically hindered multiphenylatedmonomer The sulfonated poly(arylene ether)s were easilyprepared by treatment with chlorosulfonic acidThermal sta-bility water uptake mechanical strength dimensional stabil-ity proton conductivity and morphology were investigated

2 Experimental

21 Materials All reactions were performed under prepuri-fied nitrogen All reagents and solvents were purchased fromAldrich Chemical Co Acros Organics Merck Lancaster

Fluoko or Fisher Toluene was dried over Na with benzophe-none as an indicator and freshly distilled under nitrogenatmosphere and deoxygenated by purging with nitrogenfor 20min prior to use 441015840-Biphenol and Pd(PPh

3)4were

purchased from Aldrich Chemical Co and used without fur-ther purification The polymerization was conducted usingstandard vacuum-line techniques

22 441015840101584010158401015840-Difluoro-331015840101584010158401015840-bistrifluoromethyl-210158401015840310158401015840510158401015840610158401015840-tetraphenyl-[111015840410158401101584010158404101584010158401101584010158401015840410158401015840101584011015840101584010158401015840]-pentaphenyl (M1) 441015840101584010158401015840-Dibromo-2101584031015840-51015840-61015840-tetraphenyl-[11101584041015840110158401015840]-terphenyl(5 g 722mmol) 4-fluoro-3-trifluoromethyl phenylboronicacid (45 g 21mmol) Pd(PPh

3)4

(005 g 0432mmol)K2CO3(4 g 289mmol) H

2O (13mL) and toluene (100mL)

were placed in a flame-dried two-neck flask and refluxed for48 h under N

2atmosphere After cooling the mixture was

poured into water and extracted twice with toluene and NaCl(aq) The organic layer was washed dried over MgSO

4 and

concentrated to give a yellow solid The crude monomer waspurified by recrystallization to obtain pure M1 in 92 yield(1H NMR (500MHz CDCl

3 120575 = ppm) 679ndash770 (m 34H

ArH))

23 General Procedure for Polycondensation The condensa-tion reaction was carried out in a 50mL three-neck round-bottom flask equipped with a stir bar and a Dean-Stark appa-ratus fitted with a condenser and under nitrogen atmosphereTheflaskwas chargedwithM1 (2 g 233mmol) 441015840-biphenolmonomer (0433 g 233mmol) potassium carbonate (08 g578mmol) DMAc (20mL) and toluene (15mL) The solu-tion mixture was stirred at 130ndash150∘C for several hours andduring the course of the reaction a slow flow of nitrogen waspassed through the reaction vessel to remove water steamproduced by the reaction The reaction solution was stirredunder reflux for 24 h after complete removal of the waterThecrude mixture was poured into stirred methanol (250mL)with stirring to precipitate a fibrous polymer P1 which wascollected by filtration washed and vacuum-dried for 24 h at120∘C

24 Sulfonation To a solution of P1 (04 g) in dichlorometh-ane (30mL) at room temperature 0125M chlorosulfonicacid solution in dichloromethane was added dropwiseThe reaction mixture was stirred for 24 h and then pouredinto water The sulfonated polymer precipitate was filteredwashed thoroughly with deionized water several times untilpH neutral and dried in vacuum at room temperatureovernight to provide the sulfonated polymer SP1 P1 wassulfonated to different extents according to the above proce-dure by adding 03mL 05mL and 07mL of chlorosulfonicacid respectively SP1 polymers were readily soluble in polaraprotic solvents such as DMF DMAc DMSO and NMP

25 Membrane Preparation The salt form of membraneswas dissolved in DMSO (5ndash7wt) Then the solution wasfiltered and cast onto a glass plate and then the membraneswere obtained after the solvent evaporation process The drymembranes were soaked in 10M HCl solution for 24 h to

International Journal of Polymer Science 3

protonate the sulfonic acid groups andwashedwith deionizedwater to a neutral pH The membranes were dried at 80∘Cfor 12 h and then under reduced pressure at 80∘C for anadditional 12 h

26 Measurements 1H NMR spectroscopic measurementswere carried out on a 500MHz Varian UNITY INOVA-500spectrometer using CDCl

3or DMSO-d

6as the solvent The

gel permeation chromatographic (GPC) analysis was carriedout with Viscotek 270 max with a refractive index detector(Viscotek model 270 THF used as the eluent flow rate of1mLmin) For calibration polystyrene standard (molecularweight between 6770 and 281000Da) was used Thermalstability of the polymers was evaluated by thermogravimetricanalysis (TGA) carried out on a Perkin Elmer Pyris 1instrument with a heating rate of 10∘Cmin from 100∘C to600∘C under N

2atmosphere Before the analysis membranes

were dried in the TGA furnace at 150∘C under N2for 20min

to remove waterThe ion exchange capacity (IEC) of the membranes was

determined using titration method The membranes wereweighed and soaked in 10M NaCl for 24 h and the solutionstitrated using 001M NaOH to a phenolphthalein end pointIEC (mmolg) was calculated as in the following equationIEC (mmolg) = (119881NaOH times 119872NaOH)119882dry where 119881NaOH and119872NaOH are the volume and concentration of the NaOHsolution respectively and 119882dry is the weight of the drymembrane

The water uptake the hydration number 120582 and theswelling ratiosΔ119871 andΔ119879 were calculated as in the followingequations respectively

water uptake () [(119882dry minus119882wet)119882dry] times 100hydration number 120582 = [1000times (119882dry minus119882wet)](IECtimes119882dry times 18)in-plane swelling ratio () Δ119871 = (119871wet minus119871dry)119871dry times100through-plane swelling ratio () Δ119879 = (119879wet minus119879dry)119879dry times 100

where 119882wet and 119882dry are the weights of the wet and drymembranes 119871wet and 119871dry are the lengths of the wet and drymembranes and119879wet and119879dry are the thickness of thewet anddry membranes respectively

Hydrolytic stability of the membranes was evaluatedby immersing the membranes in water at 140∘C for 24 hOxidative stability was evaluated by immersion into Fentonrsquosreagent (3 H

2O2aq containing 2 ppm FeSO

4) at 80∘C for

1 hIn-plane proton conductivity was performed by AC

impedance spectroscopy with an Agilent 4294A PrecisionImpedance Analyzer according to a procedure described ina previously published paper [17] Proton conductivity (120590)was calculated as the following equation 120590 = 119871(119877119860)where 119871 (cm) is the distance between electrodes 119877 (Ω) isthe membrane resistance which was measured over the fre-quency from 1Hz to 1MHz and119860 (cm2) is the cross-sectionalarea of the membrane The membranes (10mm times 5mm)

were placed between two of platinum electrodes whichwere set in a Teflon cell Conductivity measurements underfully hydrated conditions were carried out in a FIRSTEKBTH8020 environmental chamber with the cell immersed inwater

TEM images were performed with a JEOL JEM-2100(HR) TEM using an accelerating voltage of 200 kV For studythe membranes were stained with Ag3+ ion by immersionovernight in 1M AgNO

3 After that the membranes were

washed thoroughly with deionized water and dried at roomtemperature for 24 hThe stained membranes were enclosureof epoxy resin and ultramicrotomed under cryogenic condi-tion with a thickness of 70 nm

3 Results and Discussion

31 Synthesis and Characterization of Polymers Syntheticroute of poly(arylene ether) (P1) is shown in Scheme 1 Thesynthesis of M1 has been reported in previously publishedIt was synthesized by Suzuki coupling reaction of dibromomonomer with boronic acid and verified structure by 1HNMR spectroscopy The polycondensation was synthesizedby following previously published procedures [20]The poly-mer was prepared by a one-pot nucleophilic polymerizationofM1with 441015840-biphenol compoundwhichwas commerciallyavailable and obtained in 92 yield Obtained polymerwas readily soluble in the common solvent such as DMAcDMSO NMP THF and chloroform Gel permeation chro-matography (GPC) was used to measure the weight-averagemolecular weights (119872

119908) of the polymer119872

119908of P1 was found

to be 193 kDa with a polydispersity index (PDI) of 31 Theintroduction of trifluoromethyl substitution in phenyl groupsenables easier synthesis of high molar mass poly(aryleneether)s by activating the leaving group towards nucleophilicdisplacement reaction during polymerization [21 22]

The 1H NMR spectrum of P1 is shown in Figure 1(a)which consists of multiplet peaks at 68 to 77 ppm assignedto aromatic protons The multiplet peaks between 68 to69 ppm are assigned to the proton of pendant benzene ringand labeled f g and h The doublet peaks between 69 and75 ppm are assigned to the protons of p-pentaphenyl (labeledb c d e i and j) The singlet peak at 77 ppm is assignedto the proton next to the trifluoromethyl group and labeleda P1 was sulfonated using chlorosulfonic acid to variousextents to yield SP1-119883 where 119883 indicates the value of IECand the structure was confirmed by 1H NMR as shown inFigure 1(b) Generally the substituent of sulfonic acid groupsby chlorosulfonic acid preferentially occurs on electron-richaromatic rings The signals at 67ndash72 ppm broadened aftersulfonation (labeled 2 4 5 and 7) showing similar values ashas been presented in previous work [23] According to theliterature new peaks that appear at 805 and 816 are assignedto sulfonated bisphenol [20]

Thermogravimetric analysis is shown in Figure 2 whichdemonstrated that P1 exhibited excellent thermal stabilitywith a 5 weight loss occurring after 538∘C Sulfonatedpolymers are less thermally stable exhibiting several distinctdegradation steps An initial weight loss before 200∘Cconsists


F F

M1

HO OH

DMAcO O

n

P1

O On

SP1R

R

R R

R R

F3C

F3C

F3C

K2CO3

160∘C

+

CF3

CF3

CF3

HSO3ClCH2Cl2

R = H or SO3H

Scheme 1 Synthesis of SP1-119883

Solvent

b f g h and i

d ec j

a

O On

a

b c d e

f gh

i j

P1

80 78 76 74 72 70 6882(ppm)

F3C

CF3

(a)

1 3 6 and 89

10

2 4 5 and 7

O On

1

2 3 4 5

67

8 9

SP1

10R

R

R R

R R80 78 76 74 72 70 6882

(ppm)

F3C

CF3

R = H or SO3H

(b)

Figure 1 1H NMR spectrum of polymer P1 (a) and after sulfonation SP1-119883 (b)


P1SP1-039SP1-222

SP1-280SP1-290

200 300 400 500 600100Temperature (∘C)

0

10

20

30

40

50

60

70

80

90

100

Wei

ght (

)

Figure 2 Thermogravimetric graph of P1 and SP1-119883

SP1-039SP1-222SP1-280

SP1-290Nafion 117

0

100

200

300

400

500

600

700

Wat

er u

ptak

e (

)

40 50 60 70 8030Temperature (∘C)

Figure 3 Water uptake as a function of temperature for SP1-119883membranes

of loss of hydrated water which relate to sulfonic acid groupsnumber (IEC value) SP1-039 with the lowest IEC showsa small amount of weight loss In contrast SP1-290 showsover 5 weight loss of hydrated water because of the highestIEC The degradation step observed at around 220ndash320∘C isattributed to the loss of sulfonic acid groups The final stepsstarting at about 500∘C correspond to the remainder of thepolymer main chain

32 Water Uptake Swelling Ratio Oxidative Stability andHydrolytic Stability Water uptake is an important factorthat promotes proton conduction and determines lots ofthe mechanical durability especially during dry-wet cyclesas a PEM The resulting water uptake and 120582 are shown in

SP1-039SP1-222SP1-280

SP1-290Nafion 117

40 50 60 70 8030Temperature (∘C)

Hyd

ratio

n nu

mbe

r (H

2OH

O3H

)

0

20

40

60

80

100

120

140

Figure 4 Hydration number as a function of temperature for SP1-119883membranes

Figures 3 and 4 respectively As expected the water uptakeof the membranes increased with an increase in temperatureand higher IEC membranes absorbed more water due to theincreased hydrophilicity All membranes in the measuredtemperature range from 30 to 80∘C SP1-039 showed lowestwater uptake and without an obvious increase trend eventemperatures rising SP1-222 demonstrated gentle risingtrends from 43 to 120 and SP1-280 displayed a largevalue of water uptake at 30∘C and increased dramaticallyup to 372 at 80∘C SP1-290 showed the highest IEC valuebut excessive substitution of sulfonic acid groups causesmembrane soluble in water when the temperature is higherthan 50∘C The above water uptake data were very similar toour previous report the multiphenylated backbone resultsin a high polymer free volume which allowed for watersorption and was able to maintain acceptable mechanicalproperty of the membranes [5 19]

According to previous literature 120582 (hydration numberH2OSO

3H) value can estimate the membrane whether

applied to the fuel cell Larger values of hydration numbermean that each sulfonate is surrounded by a greater numberofwatermoleculesThedifferent structurewould lead to a dif-ferent molecular chain stacked circumstance Therefore thestructure conformation would determine how many watermolecules distributed into the membrane The hydrationnumber of SP1 exhibited similar tendency to water uptakethat increased with elevated temperature with the exceptionthat SP1-039 remained nearly constant In comparison withNafion 117 all of SP1 membranes showed a higher hydrationnumber at 80∘C as listed in Table 1

The swelling of SP1 membranes was listed in Table 1Due to a lower degree of sulfonation the length changingof SP1-039 was less than 5 at high temperature SP1-222exhibited good dimensional stability increasing in lengthchange by only 275 at 80∘C which is similar to that ofNafion 117 [15] or other sulfonated copoly(ether sulfone)s


Table 1 IEC water sorption and dimensional stability of SP1 membranes

Sample IECa (mmolg) Degree of sulfonation ()b Water uptakec 120582c

Δ119871 ()d Δ119879 ()d

SP1-039 039 10 14 20 5 1SP1-222 222 56 120 30 275 8SP1-280 280 70 372 74 105 28SP1-290 290 73 mdashe mdash mdash mdashNafion 117 091 mdash 29 18 18 20aIEC determined by acid-base titrationbCalculated assuming six sulfonic acid groups per monomer unit The theoretical highest IEC value of SP1-119883 is 438mmolg (degree of sulfonation 100)c80∘C in waterdChange in film length (Δ119871) and thickness (Δ119879) 80∘C in watereDissolved in water

Table 2 Proton conductivity and stability of SP1 membranes

SampleProton conductivity (30∘C)

(mScm)Proton conductivity (95 RH)

(mScm) Oxidative stabilityaresidual weight ()

Hydrolytic stabilitybresidual weight ()

40 RH 95 RH 50∘C 80∘CSP1-039 mdashc mdashc mdashc mdashc 100 99SP1-222 191 477 848 143 91 82SP1-280 641 832 151 222 85 73SP1-290 705 71 135 228 mdashd mdashd

Nafion 117 5 64 60 106 mdash mdashaAfter heating in Fenton reagent at 80∘C for 1 hbAfter heating in water at 140∘C for 24 hcNo datadDissolved in reagent

[16] SP1-280 showedmuch larger dimensional length change(105 at 80∘C) caused by its larger water sorption abilityDespite the larger water sorption the change in thickness ofSP1 is relatively low (lt28) which is attributed to the highfree volume and rigidity of tetraphenylated structure

The oxidative stability of the SP1 membranes was eval-uated in Fentonrsquos reagent at 80∘C for 1 h SP1-039 showedgood oxidative and hydrolytic stability (gt99) because of itsvery low IEC value which reduced the positions where thefree radical can be attacked directly SP1-222 is immersedinto reagent after 1 hr it exhibited acceptable oxidative andhydrolytic stability which still maintain 91 and 82 resid-ual weight respectively However oxidative and hydrolyticresidual weight of higher IECmembrane SP1-280 decreasedto 85 and 73 respectively SP1-290 completely dissolvedin Fentonrsquos reagent and water The oxidative stability of themembranes decreased with increasing degree of sulfonation

33 Proton Conductivity The proton conductivity of Nafion117 was also measured under the same conditions as areference The degree of sulfonated P1-039 was too lowto be measurement of proton conductivity The protonconductivity of SP1-119883 membranes showed relative humiditydependence at 30∘C ranging from 40 to 80mScm as shownin Figure 5 Compared to Nafion 117 SP1-280 exhibited acomparable conductivity from 40 to 80 RH and is able toexceed when relative humidity over 80 (83mScm at 30∘C95 RH) The proton conductivity of SP1-119883 membranesincreased with increasing temperature from 30∘C to 80∘C

Nafion 117SP1-222

SP1-280 SP1-290

50 60 70 80 90 10040Relative humidity ()

000001002003004005006007008009010011

Prot

on co

nduc

tivity

(Sc

m)

Figure 5 Proton conductivity of SP1-119883membranes as a function ofRH at 30∘C

under fully hydrated states (95 RH) as shown in Figure 6and listed in Table 2 SP1-222 SP1-280 and P1-290 exhibitedthe proton conductivities of 143 222 and 228mScm at80∘C under fully hydrated states respectively higher thanthat of Nafion 117 Compared to other hydrocarbon-basedmembranes the proton conductivity of SP1-119883 demonstratedbeneficial results for example a poly(aryl ether) comprising


Nafion 117SP1-222

SP1-280 SP1-290

40 50 60 70 8030Temperature (∘C)

00

01

02

03

04

05

Prot

on co

nduc

tivity

(Sc

m)

Figure 6 Proton conductivity of SP1-119883membranes as a function oftemperature under 95 RH

of fluorine and bisphenol A units showed a conductivityof 100mScm at 80∘C [24] As mentioned above protonconductivities of SP1-119883 satisfy the requirement of protonexchange membrane for fuel cell

34 Morphology of the Membranes The morphology of thesulfonated polymers SP1-222 SP1-280 and SP1-290 wasinvestigated by transmission electron microscopy (TEM)the images are shown in Figure 7 The dark regions repre-sent localized hydrophilic (sulfonate groups) ionic domainsand the brighter regions refer to the domains formed byhydrophobic polymer backbones All of the membranesexhibited spherical ionic clusters with relatively uniformsize But the polymer at lower sulfonation degree as SP1-222 only formed small part of particle aggregation andionic clusters In contrast the polymers with higher sulfona-tion degree as SP1-280 and SP1-290 show well-developedhydrophilichydrophobic phase separation SP1-222 SP1-280 and SP1-290 relative diameter of ionic cluster sizes is3ndash7 6ndash9 and 10ndash15 nm respectively Compared to poly(p-phenylene) containing multiphenylated pendant (IEC =258mmolg) (5sim10 nm diameter) [18] and Nafion 117 (4sim5 nm diameter) [25] these sulfonated membranes exhibitsimilar or larger ionic cluster sizes

4 Conclusions

In summary we introduced a new series of sulfonatedpoly(arylene ether)s as proton conducting polymer elec-trolyte membranes The polymer (P1) was synthesizedby nucleophilic polycondensation and sulfonated polymers(SP1-119883) were obtained through postsulfonation by usingchlorosulfonic acid 1H NMR spectroscopy confirmed thestructures of monomer and polymer SP1-119883 exhibited gooddimensional stability under high water uptake SP1-222 andSP1-280 showed acceptable oxidative and hydrolytic stability

10nm 100nm

10nm 100nm

10nm 100nm

Figure 7 TEM image of SP1-222 SP-280 and SP1-290 mem-branes

The proton conductivity of membranes (SP1-222 SP1-280and SP1-290) reached 143 222 and 228mScm at 80∘C underfully hydrated conditions which was much higher than thatof Nafion 117 TEM images analysis of sulfonated membranesrevealed spherical ionic cluster and a well-dispersed phaseseparation with slightly interconnected ionic clusters (3ndash15 nm) The combination of good thermal stability highproton conductivity and well-dispersed phase separationmakes SP1-119883 conspicuous as PEMs for fuel cell applications

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors are grateful to the National Science Councilof Taiwan (NSC 104-2623-E-110-005-ET and 104-2221-E-110-074-) for financial support of this work The authors alsogratefully acknowledge Y Y Chuang at Fuel Cell Center ofYuan Ze University for the TEMmeasurements


References

[1] H Zhang and P K Shen ldquoRecent development of polymerelectrolyte membranes for fuel cellsrdquoChemical Reviews vol 112no 5 pp 2780ndash2832 2012

[2] L Wu Z Zhang J Ran D Zhou C Li and T Xu ldquoAdvancesin proton-exchange membranes for fuel cells an overviewon proton conductive channels (PCCs)rdquo Physical ChemistryChemical Physics vol 15 no 14 pp 4870ndash4887 2013

[3] R P Pandey A K Thakur and V K Shahi ldquoSulfonatedpolyimideacid-functionalized graphene oxide composite poly-mer electrolyte membranes with improved proton conductivityand water-retention propertiesrdquoACS AppliedMaterials amp Inter-faces vol 6 no 19 pp 16993ndash17002 2014

[4] B Smitha S Sridhar andAA Khan ldquoSolid polymer electrolytemembranes for fuel cell applicationsmdasha reviewrdquo Journal ofMembrane Science vol 259 no 1-2 pp 10ndash26 2005

[5] S Lee J Ann H Lee et al ldquoSynthesis and characterizationof crosslink-free highly sulfonated multi-block poly(aryleneether sulfone) multi-block membranes for fuel cellsrdquo Journal ofMaterials Chemistry A vol 3 no 5 pp 1833ndash1836 2015

[6] T Higashihara K Matsumoto and M Ueda ldquoSulfonated aro-matic hydrocarbon polymers as proton exchange membranesfor fuel cellsrdquo Polymer vol 50 no 23 pp 5341ndash5357 2009

[7] A KMohanty E AMistri A Ghosh and S Banerjee ldquoSynthe-sis and characterization of novel fluorinated poly(arylene ethersulfone)s containing pendant sulfonic acid groups for protonexchange membrane materialsrdquo Journal of Membrane Sciencevol 409-410 pp 145ndash155 2012

[8] R Devanathan ldquoRecent developments in proton exchangemembranes for fuel cellsrdquo Energy and Environmental Sciencevol 1 no 1 pp 101ndash119 2008

[9] S J Peighambardoust S Rowshanzamir and M AmjadildquoReview of the proton exchange membranes for fuel cellapplicationsrdquo International Journal of Hydrogen Energy vol 35no 17 pp 9349ndash9384 2010

[10] Y ChangG F Brunello J Fuller et al ldquoAromatic ionomerswithhighly acidic sulfonate groups acidity hydration and protonconductivityrdquo Macromolecules vol 44 no 21 pp 8458ndash84692011

[11] Y Zhang J Li L Ma W Cai and H Cheng ldquoRecent develop-ments on alternative proton exchangemembranes strategies forsystematic performance improvementrdquo Energy Technology vol3 no 7 pp 675ndash691 2015

[12] K Matsumoto T Nakagawa T Higashihara and M UedaldquoSulfonated poly(ether sulfone)s with binaphthyl units as pro-ton exchange membranes for fuel cell applicationrdquo Journal ofPolymer Science Part A Polymer Chemistry vol 47 no 21 pp5827ndash5834 2009

[13] D Chen S Wang M Xiao Y Meng and A S Hay ldquoNovelpolyaromatic ionomers with large hydrophilic domain and longhydrophobic chain targeting at highly proton conductive andstable membranesrdquo Journal of Materials Chemistry vol 21 no32 pp 12068ndash12077 2011

[14] C Wang D W Shin S Y Lee et al ldquoA clustered sulfonatedpoly(ether sulfone) based on a new fluorene-based bisphenolmonomerrdquo Journal of Materials Chemistry vol 22 no 48 pp25093ndash25101 2012

[15] K Nakabayashi T Higashihara and M Ueda ldquoHighly sul-fonated multiblock copoly(ether sulfone)s for fuel cell mem-branesrdquo Journal of Polymer Science Part A Polymer Chemistryvol 48 no 13 pp 2757ndash2764 2010

[16] J Pang K Shen D Ren S Feng Y Wang and Z JiangldquoPolymer electrolyte membranes based on poly(arylene ether)swith penta-sulfonated pendent groupsrdquo Journal of MaterialsChemistry A vol 1 no 4 pp 1465ndash1474 2013

[17] J Pang X Jin Y Wang S Feng K Shen and G WangldquoFluorinated poly(arylene ether ketone) containing pendenthexasulfophenyl for proton exchange membranerdquo Journal ofMembrane Science vol 492 pp 67ndash76 2015

[18] S G Jo T Kim S J Yoon et al ldquoSynthesis and investigationof random-structured ionomers with highly sulfonated multi-phenyl pendants for electrochemical applicationsrdquo Journal ofMembrane Science vol 510 pp 326ndash337 2016

[19] H-F Lee P-H Wang Y-C Huang et al ldquoSynthesis and pro-ton conductivity of sulfonated multi-phenylated poly(aryleneether)srdquo Journal of Polymer Science Part A Polymer Chemistryvol 52 no 18 pp 2579ndash2587 2014

[20] W Y Huang M Y Chang Y K Han and P T Huang ldquoSyn-thesis and proton conductivity of sulfonated multi-phenylatedpoly(arylene ether)srdquo Journal of Polymer Science Part A Poly-mer Chemistry vol 48 no 24 pp 5872ndash5884 2011

[21] M G Dhara and S Banerjee ldquoFluorinated high-performancepolymers poly(arylene ether)s and aromatic polyimides con-taining trifluoromethyl groupsrdquoProgress in Polymer Science vol35 no 8 pp 1022ndash1077 2010

[22] S Banerjee GMaier A Salunke andMMadhra ldquoNovel high-Tg high-strength poly(aryl ether) containing quadrephenylunitrdquo Journal of Applied Polymer Science vol 82 no 13 pp3149ndash3156 2001

[23] H F Lee Y C Huang P H Wang et al ldquoSynthesis of highlysulfonated polyarylene ethers containing alternating aromaticunitsrdquo Materials Today Communications vol 3 pp 114ndash1212015

[24] I Hajdok V Atanasov and J Kerres ldquoPerfluoro-p-xylene asa new unique monomer for highly stable arylene main-chainionomers applicable to low-T and high-T fuel cell membranesrdquoPolymers vol 7 no 6 pp 1066ndash1087 2015

[25] K A Mauritz and R B Moore ldquoState of understanding ofNafionrdquoChemical Reviews vol 104 no 10 pp 4535ndash4585 2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

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Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


introduce free volume into the polymer for water to occupy[11 12]

To overcome the problems of sulfonated aromatic hydro-carbon polymers many studies have been reported Forexample Chen et al developed amultiphenylated hydrophilicdomain and linear hydrophobic chain copolymer Thesedesigned ionomers gave distinct phase separation and facili-tate forming proton conductive channels and also exhibitedhighly thermal and oxidative stability [13] Wang et alreported new poly(ether sulfone) based on fluorene with twopendant phenyl substituents that provided clustered pendantsulfonic acid groups The sulfonated polymers demonstratedhigh oxidative stability good mechanical properties anda clear phase separation of ionic domains size of 3 to7 nm [14] Nakabayashi et al synthesized highly sulfonatedmultiblock poly(ether sulfone)s followed by postsulfonationwith concentrated sulfuric acid The membranes with higherIEC values of 275ndash279mmolg exhibited similar protonconductivity with Nafion 117 in a range of 50ndash95 RH AFMimage also supported the formation of well-connected protonconductive channels to implement high proton conductivity[15] Pang et al reported novel poly(arylene ether)s attachedhigh density sulfonated hexaphenyl pendent group in orderto control positions and the degree of sulfonation Theseresulting polymers exhibited lower water uptake and gooddimensional stability The membranes showed high protonconductivities and low methanol permeability Pang et alalso presented novel fluorinated poly(arylene ether ketone)scontaining hexa sulfophenyl as a hydrophilic pendent groupwhich enhanced the difference in polarity of hydrophilic andhydrophobic segments The membranes demonstrated lowerdimensional change value and high proton conductivityattributed to well-defined phase separation [16 17] RecentlyJo et al synthesized poly(p-phenylene) block copolymersintroducing trifluoromethyl and multiphenylated pendantgroups to improve the hydrophobicity and enhance denselyand locally sulfonated domains The membranes exhibitedcomparable or superior performance toNafion 212 in fuel celltesting [18]

In our previous work we introduced multiphenylatedstructure into the polymer main chain which provides goodmechanically and dimensionally stable PEMs The multi-phenylated structure on the backbone can increase the freevolume As a result multiphenylated structure allowed forsignificant water sorption while maintaining good mechan-ical strength [19] Herein we synthesized a novel alternat-ing poly(arylene ether) comprising commercialized 441015840-biphenol monomer and sterically hindered multiphenylatedmonomer The sulfonated poly(arylene ether)s were easilyprepared by treatment with chlorosulfonic acidThermal sta-bility water uptake mechanical strength dimensional stabil-ity proton conductivity and morphology were investigated

2 Experimental

21 Materials All reactions were performed under prepuri-fied nitrogen All reagents and solvents were purchased fromAldrich Chemical Co Acros Organics Merck Lancaster

Fluoko or Fisher Toluene was dried over Na with benzophe-none as an indicator and freshly distilled under nitrogenatmosphere and deoxygenated by purging with nitrogenfor 20min prior to use 441015840-Biphenol and Pd(PPh

3)4were

purchased from Aldrich Chemical Co and used without fur-ther purification The polymerization was conducted usingstandard vacuum-line techniques

22 441015840101584010158401015840-Difluoro-331015840101584010158401015840-bistrifluoromethyl-210158401015840310158401015840510158401015840610158401015840-tetraphenyl-[111015840410158401101584010158404101584010158401101584010158401015840410158401015840101584011015840101584010158401015840]-pentaphenyl (M1) 441015840101584010158401015840-Dibromo-2101584031015840-51015840-61015840-tetraphenyl-[11101584041015840110158401015840]-terphenyl(5 g 722mmol) 4-fluoro-3-trifluoromethyl phenylboronicacid (45 g 21mmol) Pd(PPh

3)4

(005 g 0432mmol)K2CO3(4 g 289mmol) H

2O (13mL) and toluene (100mL)

were placed in a flame-dried two-neck flask and refluxed for48 h under N

2atmosphere After cooling the mixture was

poured into water and extracted twice with toluene and NaCl(aq) The organic layer was washed dried over MgSO

4 and

concentrated to give a yellow solid The crude monomer waspurified by recrystallization to obtain pure M1 in 92 yield(1H NMR (500MHz CDCl

3 120575 = ppm) 679ndash770 (m 34H

ArH))

23 General Procedure for Polycondensation The condensa-tion reaction was carried out in a 50mL three-neck round-bottom flask equipped with a stir bar and a Dean-Stark appa-ratus fitted with a condenser and under nitrogen atmosphereTheflaskwas chargedwithM1 (2 g 233mmol) 441015840-biphenolmonomer (0433 g 233mmol) potassium carbonate (08 g578mmol) DMAc (20mL) and toluene (15mL) The solu-tion mixture was stirred at 130ndash150∘C for several hours andduring the course of the reaction a slow flow of nitrogen waspassed through the reaction vessel to remove water steamproduced by the reaction The reaction solution was stirredunder reflux for 24 h after complete removal of the waterThecrude mixture was poured into stirred methanol (250mL)with stirring to precipitate a fibrous polymer P1 which wascollected by filtration washed and vacuum-dried for 24 h at120∘C

24 Sulfonation To a solution of P1 (04 g) in dichlorometh-ane (30mL) at room temperature 0125M chlorosulfonicacid solution in dichloromethane was added dropwiseThe reaction mixture was stirred for 24 h and then pouredinto water The sulfonated polymer precipitate was filteredwashed thoroughly with deionized water several times untilpH neutral and dried in vacuum at room temperatureovernight to provide the sulfonated polymer SP1 P1 wassulfonated to different extents according to the above proce-dure by adding 03mL 05mL and 07mL of chlorosulfonicacid respectively SP1 polymers were readily soluble in polaraprotic solvents such as DMF DMAc DMSO and NMP

25 Membrane Preparation The salt form of membraneswas dissolved in DMSO (5ndash7wt) Then the solution wasfiltered and cast onto a glass plate and then the membraneswere obtained after the solvent evaporation process The drymembranes were soaked in 10M HCl solution for 24 h to




3or DMSO-d

6as the solvent The











4) at 80∘C for















F F

M1

HO OH

DMAcO O

n

P1

O On

SP1R

R

R R

R R

F3C

F3C

F3C

K2CO3

160∘C

+

CF3

CF3

CF3

HSO3ClCH2Cl2

R = H or SO3H


Solvent

b f g h and i

d ec j

a

O On

a

b c d e

f gh

i j

P1

80 78 76 74 72 70 6882(ppm)

F3C

CF3

(a)

1 3 6 and 89

10

2 4 5 and 7

O On

1

2 3 4 5

67

8 9

SP1

10R

R

R R

R R80 78 76 74 72 70 6882

(ppm)

F3C

CF3

R = H or SO3H

(b)



P1SP1-039SP1-222

SP1-280SP1-290

200 300 400 500 600100Temperature (∘C)

0

10

20

30

40

50

60

70

80

90

100

Wei

ght (

)


SP1-039SP1-222SP1-280

SP1-290Nafion 117

0

100

200

300

400

500

600

700

Wat

er u

ptak

e (

)

40 50 60 70 8030Temperature (∘C)




SP1-039SP1-222SP1-280

SP1-290Nafion 117

40 50 60 70 8030Temperature (∘C)

Hyd

ratio

n nu

mbe

r (H

2OH

O3H

)

0

20

40

60

80

100

120

140










Δ119871 ()d Δ119879 ()d












Nafion 117SP1-222

SP1-280 SP1-290


000001002003004005006007008009010011

Prot

on co

nduc

tivity

(Sc

m)




Nafion 117SP1-222

SP1-280 SP1-290

40 50 60 70 8030Temperature (∘C)

00

01

02

03

04

05

Prot

on co

nduc

tivity

(Sc

m)




4 Conclusions


10nm 100nm

10nm 100nm

10nm 100nm



Competing Interests


Acknowledgments



References

































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






3or DMSO-d

6as the solvent The











4) at 80∘C for















F F

M1

HO OH

DMAcO O

n

P1

O On

SP1R

R

R R

R R

F3C

F3C

F3C

K2CO3

160∘C

+

CF3

CF3

CF3

HSO3ClCH2Cl2

R = H or SO3H


Solvent

b f g h and i

d ec j

a

O On

a

b c d e

f gh

i j

P1

80 78 76 74 72 70 6882(ppm)

F3C

CF3

(a)

1 3 6 and 89

10

2 4 5 and 7

O On

1

2 3 4 5

67

8 9

SP1

10R

R

R R

R R80 78 76 74 72 70 6882

(ppm)

F3C

CF3

R = H or SO3H

(b)



P1SP1-039SP1-222

SP1-280SP1-290

200 300 400 500 600100Temperature (∘C)

0

10

20

30

40

50

60

70

80

90

100

Wei

ght (

)


SP1-039SP1-222SP1-280

SP1-290Nafion 117

0

100

200

300

400

500

600

700

Wat

er u

ptak

e (

)

40 50 60 70 8030Temperature (∘C)




SP1-039SP1-222SP1-280

SP1-290Nafion 117

40 50 60 70 8030Temperature (∘C)

Hyd

ratio

n nu

mbe

r (H

2OH

O3H

)

0

20

40

60

80

100

120

140










Δ119871 ()d Δ119879 ()d












Nafion 117SP1-222

SP1-280 SP1-290


000001002003004005006007008009010011

Prot

on co

nduc

tivity

(Sc

m)




Nafion 117SP1-222

SP1-280 SP1-290

40 50 60 70 8030Temperature (∘C)

00

01

02

03

04

05

Prot

on co

nduc

tivity

(Sc

m)




4 Conclusions


10nm 100nm

10nm 100nm

10nm 100nm



Competing Interests


Acknowledgments



References

































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




F F

M1

HO OH

DMAcO O

n

P1

O On

SP1R

R

R R

R R

F3C

F3C

F3C

K2CO3

160∘C

+

CF3

CF3

CF3

HSO3ClCH2Cl2

R = H or SO3H


Solvent

b f g h and i

d ec j

a

O On

a

b c d e

f gh

i j

P1

80 78 76 74 72 70 6882(ppm)

F3C

CF3

(a)

1 3 6 and 89

10

2 4 5 and 7

O On

1

2 3 4 5

67

8 9

SP1

10R

R

R R

R R80 78 76 74 72 70 6882

(ppm)

F3C

CF3

R = H or SO3H

(b)



P1SP1-039SP1-222

SP1-280SP1-290

200 300 400 500 600100Temperature (∘C)

0

10

20

30

40

50

60

70

80

90

100

Wei

ght (

)


SP1-039SP1-222SP1-280

SP1-290Nafion 117

0

100

200

300

400

500

600

700

Wat

er u

ptak

e (

)

40 50 60 70 8030Temperature (∘C)




SP1-039SP1-222SP1-280

SP1-290Nafion 117

40 50 60 70 8030Temperature (∘C)

Hyd

ratio

n nu

mbe

r (H

2OH

O3H

)

0

20

40

60

80

100

120

140










Δ119871 ()d Δ119879 ()d












Nafion 117SP1-222

SP1-280 SP1-290


000001002003004005006007008009010011

Prot

on co

nduc

tivity

(Sc

m)




Nafion 117SP1-222

SP1-280 SP1-290

40 50 60 70 8030Temperature (∘C)

00

01

02

03

04

05

Prot

on co

nduc

tivity

(Sc

m)




4 Conclusions


10nm 100nm

10nm 100nm

10nm 100nm



Competing Interests


Acknowledgments



References

































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




P1SP1-039SP1-222

SP1-280SP1-290

200 300 400 500 600100Temperature (∘C)

0

10

20

30

40

50

60

70

80

90

100

Wei

ght (

)


SP1-039SP1-222SP1-280

SP1-290Nafion 117

0

100

200

300

400

500

600

700

Wat

er u

ptak

e (

)

40 50 60 70 8030Temperature (∘C)




SP1-039SP1-222SP1-280

SP1-290Nafion 117

40 50 60 70 8030Temperature (∘C)

Hyd

ratio

n nu

mbe

r (H

2OH

O3H

)

0

20

40

60

80

100

120

140










Δ119871 ()d Δ119879 ()d












Nafion 117SP1-222

SP1-280 SP1-290


000001002003004005006007008009010011

Prot

on co

nduc

tivity

(Sc

m)




Nafion 117SP1-222

SP1-280 SP1-290

40 50 60 70 8030Temperature (∘C)

00

01

02

03

04

05

Prot

on co

nduc

tivity

(Sc

m)




4 Conclusions


10nm 100nm

10nm 100nm

10nm 100nm



Competing Interests


Acknowledgments



References

































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Δ119871 ()d Δ119879 ()d












Nafion 117SP1-222

SP1-280 SP1-290


000001002003004005006007008009010011

Prot

on co

nduc

tivity

(Sc

m)




Nafion 117SP1-222

SP1-280 SP1-290

40 50 60 70 8030Temperature (∘C)

00

01

02

03

04

05

Prot

on co

nduc

tivity

(Sc

m)




4 Conclusions


10nm 100nm

10nm 100nm

10nm 100nm



Competing Interests


Acknowledgments



References

































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Nafion 117SP1-222

SP1-280 SP1-290

40 50 60 70 8030Temperature (∘C)

00

01

02

03

04

05

Prot

on co

nduc

tivity

(Sc

m)




4 Conclusions


10nm 100nm

10nm 100nm

10nm 100nm



Competing Interests


Acknowledgments



References

































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




References

































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

Research Article Synthesis of Highly Sulfonated Poly(arylene …downloads.hindawi.com/journals/ijps/2016/6545362.pdf · 2019-07-30 · Research Article Synthesis of Highly Sulfonated