3048
J. Zhu et al. / Polymer 51 (2010) 3047e3053
been reported that inter- and intramolecular hydrogen-bonding
interactions between sulfonic acid and hydroxyl groups have been
used to improve the properties of PEMs [20e23]. In our previous
116.33, 123.34, 127.41, 127.70, 132.77, 134.74, 153.17, 167.59, 196.23)
confirmed the formation of monomer DMNF. Anal. Calcd for
26 18 2 4
C H F O : C, 72.22; H, 4.20. Found: C, 72.25; H, 4.28. Mp (DSC):
ꢀ
262 C.
report,
a
series of SPEEK/PHR (phenoxy resin) composite
membranes, the SPEEK with hydroxyl group, was prepared. These
composite membranes displayed an improvement of the mechan-
ical and methanol resistant properties resulting from the interac-
tion of hydrogen bonded [24].
In this study, we reported a novel sulfonated hydroxynaph-
thalene poly(aryl ether ketone)s (SHNPAEKs) containing both
sulfonic acid on the side chain and hydroxyl groups in the structure.
Dimethoxylnaphthalene poly(aryl ether ketone) (MNPAEKs) were
first prepared via the nucleophilic aromatic substitution reactions,
and then the dihydroxynaphthalene poly(aryl ether ketone)s
2.3. Polymer synthesis
2.3.1. Polymerization of dimethoxylnaphthalene poly(aryl ether
ketone) (MNPAEKs)
A 250 mL three-neck flask equipped with a mechanical stirrer,
a Dean-Stark trap and a nitrogen inlet was charged with DMNF
2 3
(8.65 g, 0.02 mol), Bisphenol A (4.56 g, 0.02 mol), K CO (3.036 g,
0.022 mol), NMP (52 mL) and toluene (20 mL). The mixture was
ꢀ
heated at 140 C for about 3 h to remove water by azeotropic
ꢀ
(
HNPAEKs) were obtained from the demethylation reactions. The
distillation with toluene, then slowly heated to 180 C and main-
different sulfonated degree (Ds) of SHNPAEKs was obtained by
changing the ratio of 1,4-butane sultone which reacted with
hydroxyl groups of HNPAEKs by the nucleophilic ring-opening
reactions. Then, the properties of the side-chain-type sulfonated
polymers were investigated as PEMs in detail, such as water uptake,
proton conductivity, methanol permeability and mechanical
properties. All the results demonstrated that SHNPAEKs is a prom-
ising candidate material for PEMFCs.
tained at that temperature for 6 h. When the increase of solution
viscosity became obvious, the mixture was coagulated into a large
excess of deionized water with vigorous stirring. The resulting
fibrous polymer was washed thoroughly with water several times
ꢀ
and dried under vacuum at 100 C for 24 h.
2.3.2. Demethylation of MNPAEKs to dihydroxynaphthalene poly
(aryl ether ketone)s (HNPAEKs)
MNPAEKs (1 g, 3.23 mmol methoxy groups) was dissolved in dry
ꢀ
1
0 mL CH
A threefold excess (0.87 mL, 9.69 mmol) BBr
CH Cl was added dropwise. The reaction mixture was stirred at
2
Cl
2
, and the solution was maintained at 0 C (ice bath).
2
. Experimental
3
dissolved in 5 mL
2.1. Materials
2
2
room temperature under nitrogen for 12 h. When the temperature
increased to reflux, the reaction proceeded for another 6 h. The
mixture was poured into ice-water to hydrolyze the BBr and the
3
2
,6-dimethoxylnaphthalene was obtained from Dalian Jinzhou
Chemical. 4-fluorobenzoyl Chloride and 1,4-butane sultone were
purchased from SigmaeAldrich Ltd. Boron tribromide (BBr
) and
boron complexes, and then washed with methanol and deionized
water thoroughly. The resulting polymers (HNPAEKs) dried under
3
Bisphenol A were obtained from Beijing Chemical Reagents. N,
N-dimethylformamide (DMF), Dimethyl sulfoxide (DMSO), Dime-
thylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP) were
vacuum-distilled prior to use. Other reagents were commercially
available grade and used without further purification.
ꢀ
vacuum at 100 C for 24 h.
2.3.3. Sulfobutylation of HNPAEKs to sulfonated
hydroxynaphthalene Poly(aryl ether ketone) (SHNPAEK-xx)
The sulfobutylation experiment was illustrated by preparation of
SHNPAEK-80. And herein, the sulfonation degree was defined as the
molar ratio (%) of sulfonic acid converted from hydroxyl groups. In
a three-neck flask, HNPAEK (1 g, 3.38 mmol hydroxy groups) was
dissolved in 20 mL DMSO and NaOH (0.2 g, 5 mmol) was used to
convert eOH groups into eONa groups. The reaction mixture was
stirred at room temperature for 6 h. 1,4-butane sultone (0.37 g,
2
2
.2. Monomer synthesis
.2.1. Synthesis of 1,5-bis(4-fluorobenzoyl)-2,6-
dimethoxynaphthalene (DMNF)
As shown in Scheme 1, the monomer DMNF was prepared
following the procedure in our previously report [25]. A mixture of
2
.704 mmol) was added dropwise and the reaction mixture was
2
,6-dimethoxylnaphthalene (9.4 g, 0.05 mol) and 4-fluorobenzoyl
ꢀ
heated to 160 C, stirred at this temperature for 12 h. The resulting
sulfonated polymers were precipitated in acetone and washed by
boiling water several times. The obtained polymer was immersed in
a large excess of HCl (5 wt.%) solution over 24 h to make the salt form
converted into the acid form. The product (SHNPAEK-80) was finally
chloride (17.4 g, 0.11 mol) in chloroform (300 mL) was stirred at
0
ꢀ
e5 C. Then 1.65 g anhydrous ferric chloride (0.01 mol) was added
in small portions to the cold solution. The reaction was conducted
at this temperature for 24 h. The resulting mixture was poured into
cold hydrochloric acid and stirred for another 1 h. The product was
removed by decantation and the brown solid was precipitated
in methanol. The result precipitate was recrystallized twice from
N,N-dimethylformamide (DMF)/water mixture (10:1 v/v).
ꢀ
dried in a vacuum at 80 C. For comparison, we also synthesized the
3
SNPAEK-100 which converted all the eOH into eSO H.
1
13
1
2.4. Membrane preparation
Yield: 82%. H NMR and C NMR analyses ( H NMR (500 MHz,
DMSO-d ):
(ppm): 3.79 (m, 6H), 7.12 (t, J ¼ 8.56, 8.56 Hz, 4H), 7.27
6
d
Membranes were prepared by dissolving 1.0 g SHNPAEK-xx in
(
8
d, J ¼ 8.77 Hz, 2H), 7.63 (d, J ¼ 9.27 Hz, 2H), 7.89 (dd, J ¼ 5.51,
.66 Hz, 4H); 1 C NMR (125 MHz, CDCl
3
DMAc (10 wt.%) casting the solution on glass plate and drying at
3
) d (ppm): 57.04, 115.39,
ꢀ
6
0 C for 24 h. The membranes were then peeled off the substrates.
To remove any excess of the solvent, the membranes were dried
ꢀ
under vacuum at 80 C for 48 h.
2
2
.5. Polymer characterization
.5.1. Measurements
1H NMR spectra were conducted with a 500 MHz Bruker Avance
Scheme 1. Synthesis of the DMNF.
510 spectrometer at 298 K with deuterated dimethyl sulfoxide