Precise Controllable Post-sulfonation for Preparation of Sulfonated Poly(arylene ether sulfone)s and Their Properties for Proton Exchange Membrane†

doi:10.7503/cjcu20170842

Abstract

Abstract:

A series of poly(arylene ether sulfone)s with high molecular weight was prepared from 4-fluorophenyl sulfone, 4,4'-biphenol and bis(4-hydroxyphenyl) sulfone with different mole ratio. Due to the large difference between the electronic effects of biphenyl fragment and phenyl sulfone fragment on the polymer, the sulfonation reaction is easily carried out on biphenyl fragments with higher electron cloud density. The sulfonic acid groups were introduced to ortho-position of the oxy ether group on the biphenyl and sulfonation degree were successfully predicted after post-sulfonation process. Sulfonated polylarylene ether sulfone(SPAES)-based proton exchange membranes(PEM) were prepared by solution casting method, of which relative viscosity, ion exchange capacity(IEC), water uptake and swell ratio, proton conductivity, oxidative stability, mechanical properties and cell performance were investigated. Relative viscosity of sulfonated copolymers was higher than 1.2 dL/g. The sulfonated copolymers showed that titration and ¹H nuclear magnetic resonance calculated value of IEC were accordingly to that of theoretical. Water uptake and swell ratio obviously increased with increasing of IEC and temperature, and the size change ratio of the thickness direction was larger than that of plane direction in the membranes. The thermal gravimetric analyse(TGA) results indicated that the PEMs have the decompose temperature at about 280 ℃. All the PEMs showed maximum tensile strength above 50 MPa, and the elongation at break over 15% at 20 ℃ and 20% RH. Free radical oxidative stability test showed the PEMs with low IEC become brittle in Fenton’s reagent over 200 h at 20 ℃. The proton conductivity of PEMs were increased rapidly with the increase of the IEC and temperature, for example, the conductivity of M2-SPAES(1.34 mmol/g) and M4-SPAES(1.60 mmol/g) were 68 and 89 mS/cm at 60 ℃ in water, and 99 and 129 mS/cm at 80 ℃ in water, respectively. H₂/O₂ Fuel cell performance showed that the open circuit voltage and maximum power output were higher than 1.0 V and 0.54 W/cm² under 60 ℃, 80% RH and 0.1 MPa back pressure, respectively.

Key words: Sulfonated poly(arylene ether sulfone), Proton exchange membrane, Post-sulfonation, Controlled sulfonated degree

CLC Number:

O631

TrendMD:

XIAO Lei, ZHANG Chen, HE Meiyu, CHEN Kangcheng. Precise Controllable Post-sulfonation for Preparation of Sulfonated Poly(arylene ether sulfone)s and Their Properties for Proton Exchange Membrane^†[J]. Chem. J. Chinese Universities, 2018, 39(6): 1281.

Figures/Tables 10

Scheme 1 Synthetic routes of M-SPAES polymer

Fig.1 1H NMR spectra of DB, SDB before(A) and after sulfonation(B) in DMSO-d6

Fig.2 1H NMR spectra of copolymers in DMSO-d6a. M3-SAPES; b. M5-SAPES; c. M7-SAPES; d. M7-PAES.

Table 1 Physical properties of polymers and membranes

Polymer	IEC/(mmol·g^-1)			Water uptake(%)			Swell ratio(%)				η_r ^f	λ^g
	Theo.^a	Titr.^b	NMR^c	30 ℃	60 ℃	80 ℃	30 ℃		60 ℃
	Theo.^a	Titr.^b	NMR^c	30 ℃	60 ℃	80 ℃	Δ $l d c$	Δ $l e c$	Δ $l d c$	Δ $l e c$
M1-SPAES	1.09	1.03	1.05	32	39	42	4	20	7	25	1.16	17
M2-SPAES	1.34	1.26	1.31	44	57	67	5	25	11	28	1.49	18
M3-SPAES	1.50	1.44	1.49	60	81	128	9	26	11	29	1.52	22
M4-SPAES	1.60	1.54	1.57	65	84	133	10	28	15	35	1.70	23
M5-SPAES	1.70	1.63	1.65	70	121	163	15	31	23	39	1.85	23
M6-SPAES	1.83	1.80	1.89	78	133	188	16	34	28	44	1.95	24
M7-SPAES	1.95	1.94	1.95	106	249	467	25	36	29	45	2.10	30
M8-SPAES	2.30	2.23	2.28	170	—	—	31	40	—	—	2.67	41
R1-SPAES	1.56	1.41	—	27	37	42	11	10	—	—	1.51	17
R2-SPAES	1.80	1.63	—	37	50	61	13	14	—	—	1.55	21

Table 1 Physical properties of polymers and membranes

Polymer	IEC/(mmol·g^-1)			Water uptake(%)			Swell ratio(%)				η_r ^f	λ^g
	Theo.^a	Titr.^b	NMR^c	30 ℃	60 ℃	80 ℃	30 ℃		60 ℃
	Theo.^a	Titr.^b	NMR^c	30 ℃	60 ℃	80 ℃	Δ $l d c$	Δ $l e c$	Δ $l d c$	Δ $l e c$
M1-SPAES	1.09	1.03	1.05	32	39	42	4	20	7	25	1.16	17
M2-SPAES	1.34	1.26	1.31	44	57	67	5	25	11	28	1.49	18
M3-SPAES	1.50	1.44	1.49	60	81	128	9	26	11	29	1.52	22
M4-SPAES	1.60	1.54	1.57	65	84	133	10	28	15	35	1.70	23
M5-SPAES	1.70	1.63	1.65	70	121	163	15	31	23	39	1.85	23
M6-SPAES	1.83	1.80	1.89	78	133	188	16	34	28	44	1.95	24
M7-SPAES	1.95	1.94	1.95	106	249	467	25	36	29	45	2.10	30
M8-SPAES	2.30	2.23	2.28	170	—	—	31	40	—	—	2.67	41
R1-SPAES	1.56	1.41	—	27	37	42	11	10	—	—	1.51	17
R2-SPAES	1.80	1.63	—	37	50	61	13	14	—	—	1.55	21

Fig.3 FTIR spectra of un-sulfonated and sulfonated copolymersa. M3-SAPES; b. M5-SAPES; c. M7-SAPES; d. M7-PAES.

Fig.4 TGA curves of the membranesa. M1-SPAES; b. M3-SPAES; c. M5-SPAES; d. M7-SPAES.

Table 2 TGA and proton conductivity of PEMs

Polymer	IEC/(mmol·g^-1)	TGA		σ/(mS·cm^-1)			E_a/(kJ·mol^-1)
Polymer	IEC/(mmol·g^-1)	T_d1/℃	T_d2/℃	40 ℃	60 ℃	80 ℃	E_a/(kJ·mol^-1)
M1-SPAES	1.09	298	494	31	57	94	26.7
M2-SPAES	1.34	290	463	44	68	99	19.1
M3-SPAES	1.50	293	506	48	74	110	18.9
M4-SPAES	1.60	287	488	57	89	129	19.5
M5-SPAES	1.70	286	499	87	129	175	17.2
M6-SPAES	1.83	283	491	102	142	184	14.5
M7-SPAES	1.95	306	483	108	161	188	17.5
M8-SPAES	2.30	311	496	126	178	211	15.1
R1-SPAES	1.56	—	—	68	85	117	14.0
R2-SPAES	1.80	—	—	107	133	158	9.6
SPAES40^[10]	1.51	—	—	71	83	127	6.8
SPES-20^[28]	1.61	—	—	100	111	142	4.6
Nafion	0.91	—	—	104	142	179	12.6

Table 3 Mechanical properties and oxidative stability of PEMs

Polymer	IEC/(mmol·g^-1)	Y^a/GPa	S^b/MPa	E^c(%)	Oxidative stability^d
Polymer	IEC/(mmol·g^-1)	Y^a/GPa	S^b/MPa	E^c(%)	t/h(20 ℃)	t/min(80 ℃)
M1-SPAES	1.09	1.19	56	15	216	84
M2-SPAES	1.34	1.32	61	28	209	65
M3-SPAES	1.50	1.26	60	15	198	57
M4-SPAES	1.60	1.25	57	26	183	43
M5-SPAES	1.70	1.36	52	18	175	24
M6-SPAES	1.83	1.23	58	28	167	17
M7-SPAES	1.95	1.29	54	24	167	9
M8-SPAES	2.23	1.34	51	16	112	5
R1-SPAES	1.56	0.91	50	15	—	—
R2-SPAES	1.80	0.96	54	11	—	—

Fig.5 Temperature dependence of proton conductivity of membranesa. M2-SPAES; b. M3-SPAES; c. M4-SPAES; d. M6-SPAES; e. R1-SPAES; f. R2-SPAES; g. Nafion.

Fig.6 PEMFC performances for M2-SPAES(●, ○) and M4-SPAES(▲, △) membranes at 60 ℃, 80% RH and 0.1 MPa back pressure

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