preparation and characterization of novel negatively charged hybrid membranes

Research Article

554

Received: 25 May 2009, Revised: 23 July 2009, Accepted: 12 August 2009, Published online in Wiley Online Library: 3 September 2009

(wileyonlinelibrary.com) DOI: 10.1002/pat.1544

Preparation and characterization of novelnegatively charged hybrid membranes

Fengqin Xuana,c, Junsheng Liub* and Tongwen Xua

Charged hybrid membranes with anionic- or cationic

Polym. Adv

-exchange groups have attracted increasing interest due to theirhigher thermal stabilities and structural flexibilities which are considered suitable for use in some harsh conditions,such as higher temperature and strongly oxidizing circumstances, for industrial applications. To develop new routesto synthesize the negatively charged hybrid membranes, a series of hybrid membranes were prepared via free radicalpolymerization of glycidylmethacrylate (GMA) and g-methacryloxypropyl trimethoxy silane (MPTMS) monomers, andring-opening of epoxide to create negatively charged –SO3H groups in the polymer chains. The fundamentalproperties of these prepared membranes were characterized through TGA, ion-change capacity (IEC), and MALDI–TOFmass spectra. TGA showed that the thermal degradation temperature of these membranes could reach up to 300-C and the temperature of the first endothermic peak decreased with an increase in the content of –SO3H groups. IECmeasurements showed that their IECs were within the range of 0.22–0.35mmol gS1. MALDI–TOF spectrometryindicated that the incorporation of GMA into the hybrid matrix could improve the structural stability of themembranes. These findings demonstrated that the ion-exchange properties and structural stability of negativelycharged hybrid membranes can be conveniently controlled by adjusting the GMA moiety in the hybrid matrix.Copyright � 2009 John Wiley & Sons, Ltd.

Keywords: negatively charged hybrid membranes; charged hybrid membranes; ring-opening of epoxide; glycidylmetha-crylate (GMA); MALDI–TOF mass spectra

* Correspondence to: J. Liu, Key Laboratory of Membrane Materials & Processes,Department of Chemical and Materials Engineering, Hefei University, 373Huangshan Road, Hefei, Anhui 230022, China.E-mail: [email protected]

a F. Xuan, T. Xu

Laboratory of Functional Membranes, School of Chemistry and Materials

Science, University of Science and Technology of China (USTC), 96 Jinzhai

Road, Hefei, Anhui 230026, China

b J. Liu

Key Laboratory of Membrane Materials & Processes, Department of Chemical

and Materials Engineering, Hefei University, 373 Huangshan Road, Hefei,

Anhui 230022, China

c F. Xuan

Department of Chemical Engineering, Anhui Vocational and Technical

College, 268 Baohe Road, Hefei, Anhui 230051, China

Introduction

Inorganic–organic hybrid membranes, especially the positivelyand negatively charged ones, have attracted increasing interestin recent years due to their potential applications in industrialprocesses.[1–3] These charged hybrid membranes not onlycombine the advantages of pure organic and inorganic moieties,but also exhibit some excellent properties such as structuralflexibility, large mechanical strength, and higher thermal stability.Especially, they can be used to separate and recover valuablemetals from industrial wastes and contaminated water byelectrostatic interactions.[4,5]

Currently, various innovative approaches are being developedto fabricate charged hybrid membranes.[6,7] Among these, thesol–gel process provides a convenient, versatile, and lowtemperature-demanding route and is, thus, considered as oneof the most effective methods.[8] To prepare such hybrids,inorganic ingredients, such as silane coupling agents, are usuallydirectly used as hybrid precursors for the sol–gel reaction.However, the silica can also be incorporated into the organicpolymers by polymerization of alkoxysilanes with the activefunctional groups of these organic polymers.[9–12] Subsequently,the resulting products will contain the desired ion-exchangegroups. As one type of excellent active functional groups, theepoxy group can be easily converted to cation- and anion-exchange groups by ring-opening of the modified epoxide.[13,14]

For example, Bondar et al.[13] synthesized the cation-exchangeadsorbent by radiation-induced graft polymerization of glycidylmethacrylate (GMA) and subsequent chemical modification ofthe epoxy groups of poly-GMA graft chains with sodiumhydrogensulfite. Wu et al.[14] prepared some anion exchanger

. Technol. 2011, 22 554–559 Copyright � 200

organic–inorganic hybrid materials and membranes by ring-opening of the GMA moiety with trimethylamine hydrochloric.With the increasing demand for ion-exchange hybrid membranesto treat environmentally harmful pollutants, the investigation ofcharged hybrid membranes is, thus, of great significance.Recently, an attempt was made to develop novel charged

hybrid membranes and materials,[15–18] and extend theirapplications in the environmental field.[17,18] In these earlierarticles, negatively charged hybrid membranes were primarilysynthesized via sol–gel process, in which the silicone was directlyused as hybrid precursors. To develop an innovative approach tocharged hybrid membranes, herein, a new route to the negativelycharged hybrid membranes based on the free radical polymeri-zation and a subsequent ring-opening of epoxide is reported.

9 John Wiley & Sons, Ltd.

PREPARATION AND CHARACTERIZATION OF CHARGED HYBRID MEMBRANES

Compared with the previous articles,[15–18] special attention ispaid to this novel route to the negatively charged hybridmembranes and the fabrication of anionic groups in the polymerchains, which are clearly different from those derived from thesol–gel process. Particularly, the inorganic silica is incorporatedinto the organic polymer matrix via free radical polymerization ofalkoxysilane with reactive functional groups. Meanwhile, thenegatively charged –SO3H groups are generated via the ring-opening of epoxy groups in GMA moiety with sodium hydrogensulfite.

Scheme 1. Novel route for the preparation of negatively charged hybrid

membranes. Step 1, copolymerization between GMA and MPTMS mono-mers; Step 2, epoxide ring-opening of hybrid copolymer precursor to

produce the –SO3H groups in the hybrid copolymer chains.

EXPERIMENTAL

Materials

Glycidylmethacrylate (GMA) and g-methacryloxypropyl tri-methoxy silane (MPTMS) monomers were purchased fromShanghai Chemical Reagent Co. Ltd. (Shanghai, China); theywere purified by vacuum distillation (around 2mmHg) overhydroquinone at 958C and 1308C, respectively, prior to use.Initiator azobisisobutyronitrile (AIBN) was dissolved in warmmethanol (358C), recrystallized in an ice bath, and then dried in avacuum oven at room temperature prior to use. Toluene wascommercially obtained and dried via 5 A molecular sieve. Sodiumhydrogensulfite (NaHSO3) and other reagents were used asreceived.

Preparation of negatively charged hybrid membranes

The negatively charged hybrid membranes was synthesized viafree radical polymerization of GMA and MPTMS monomers and asubsequent epoxide ring-opening reaction of GMA with aNaHSO3 aqueous solution. The preparation procedure is similar tothat in the literature.[14] As a typical example, the procedure toprepare sample B is presented as follows:Firstly, 13.2ml (around 0.1mol) GMA and 23.8ml (near 0.1mol)

MPTMS monomers (the molar ratio of monomers in the preparedsamples A–D is listed in Table 1) were dissolved in toluene(145ml). The mixture was heated to 708C to initiate the freeradical polymerization in the presence of the initiator AIBN (near0.3 g) and stirred vigorously for an additional 24 h. After theabove reaction was completed, the product was washed withethanol and vacuum-dried at about 608C. The hybrid copolymerprecursor was thus obtained.To prepare the negatively charged hybrid membrane, the

above-prepared hybrid copolymer precursor was dissolved intoluene to produce the coating solution. The coating solution wascast on a teflon plate and dried at 808C to remove the solvent.Then, the membrane precursor was immersed in an aqueoussodium hydrogensulfite (NaHSO3) solution to perform the ring-

Table 1. The molar ratio of monomers in the preparedsamples A–D

Sample GMA (mol) MPTMS (mol)

A 0.05 0. 1B 0.1 0.1C 0.2 0.1D 0.4 0.1

Polym. Adv. Technol. 2011, 22 554–559 Copyright � 2009 John Wiley

opening reaction of epoxide. The negatively charged –SO3Hgroups are produced in this step. After washing and drying, thefinal charged hybrid membrane containing –SO3H groups (i.e.sample B) was thus obtained. Scheme 1 illustrates the designedreaction steps for membrane preparation.

Sample characterizations

FT–IR spectra of the products at all steps were recorded with aBruker Equinox–55 FT–IR spectrometer in the region of 400–4000 cm�1.The degradation process and the thermal stability of the hybrid

polymers were investigated via TGA and DrTGA thermal analysesusing a Shimadzu TGA–50H thermogravimetric analyzer, under anitrogen flow at a heating rate of 108C/min from 30 to 7008C.The ion-exchange capacity (IEC) of the product at each step

was determined by titration and expressed as mmol/g, which isdescribed in detail in a previous article.[16]

MALDI-TOF mass spectra was collected using a MicromassGCT–MS MALDI-TOF mass spectrometer at resolutions of 7000FWHM (EI) by direct introduction at a nominal electron energy of45 eV, a source temperature of 2008C, and a trap current of300mA.

5

RESULTS AND DISCUSSION

Membrane preparation

As mentioned in the experimental section, the negativelycharged hybrid membranes were primarily synthesized via freeradical polymerization of GMA and MPTMS monomers and asubsequent ring-opening reaction of epoxy groups in GMAmoiety. As both GMA and MPTMS monomers have unsaturateddouble bonds, free radical polymerization between them is, thus,easily conducted.[14] As presented in Scheme 1, step 1 is thecopolymerization between GMA and MPTMS monomers, and

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step 2 is the ring-opening reaction of epoxy groups in the hybridcopolymer precursor, in which the epoxy groups are convertedinto the negatively charged –SO3H groups in the hybrid polymerchains. Meanwhile, the hydrolysis and polycondensation by sol–gel reaction also occur in this step due to the presence of water inthe NaHSO3 aqueous solution. As a result, Si–O–Si bonds arecreated in the membrane matrix during membrane preparation.It should be noted that after the copolymerization, the resulting

hybrid copolymer contains epoxy groups in the polymer chains.Theepoxygroup is amulti-functional activegroupandcanperformthe ring-opening reaction with different reagents; it can beconverted to not only the positively charged –N(CH3)3H

þ

groups,[12,14] but also the negatively charged –SO3H groups inthepresenceof sulfonating reagent.[13,17] Consequently, negativelycharged hybrid membranes can be obtained via the ring-openingof epoxide in GMAmoiety, whichwill be confirmed by FTIR spectra(Fig. 1).

FT-IR spectra

To confirm the products at all steps in Scheme 1, FT-IRspectroscopy was performed and the results are illustrated asFig. 1. Since the FTIR spectra indicate similar changing trends,only the spectra of the products from samples A and C are givenhere as typical examples.

Figure 1. FTIR spectra of the products at steps 1 (a) and 2 (b) from

sample C. For comparison, the FTIR spectrum of the product at step 2 from

sample A was also given and marked as (c).

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As shown in curve (a), the distinct absorption peak near 1080–1180 cm�1 is in the region of C–O–C, Si–O–C, Si–O–Si stretchingvibration.[14] The band of C––O can be observed at 1728 cm�1.Three bands at around 1260, 990, and 820 cm�1 can be ascribedto the stretching vibration of epoxy groups in GMA moiety.Comparing curve (b) with curve (a) in Fig. 1, it is interesting to

find that the adsorption peaks at 992 and 820 cm�1 disappearand three new adsorption peaks at 1155, 1030, and 750 cm�1

clearly come into view, which are the characteristic absorptionbands of the sulfonate group.[13] Meanwhile, a stronger bandappears at 3500 cm�1, and this can be ascribed to the stretchingvibration of –OH groups due to the formation of –SO3H groups.These changes in adsorption peaks confirm that the ring-openingreaction of epoxy groups has occurred and the –SO3H groupshave been produced in the hybrid membranes. Furthermore, itcan be seen in curve (b) that the two adsorption bands at 1264and 907 cm�1 become sharp, and this can be ascribed to thestretching vibrations of C–O bond from ester structure and thestrained siloxane bridge.[14,19] The bands at 1260, 950–815, and760 cm�1, which are associated with the epoxy groups in theGMA moiety,[13,14] are not detected in curve (b), suggesting thecompletion of ring-opening reaction of epoxy groups.When comparing curve (c) with curve (b), the shape of

adsorption peaks was very similar, suggesting that the ring-opening reaction of epoxy groups has occurred in sample A.Based on these results, the conversion of epoxy groups in GMAoccurred in all prepared samples.

Thermal analysis

To have insight into the thermal degradation behavior of thenegatively charged membranes produced, TGA and DrTGAthermal analyses were conducted. The TGA and DrTGA curves ofthe products from samples B and C, as typical examples, arepresented in Figs 2 and 3. For comparison, the temperatures ofthermal degradation (i.e. the temperature of endothermic peak,Tep) of all products are summarized in Table 2.As shown in Fig. 2, the changing trends in weight loss are

similar for curves (a) and (c) from step 1, and curves (b) and (d)from step 2. Three or four main thermal degradation stages canbe clearly observed in these curves. Corresponding to thesethermal degradation processes, different endothermic peaks canbe found in the DrTGA curves as presented in Fig. 3.

Figure 2. TGA curves of the products of steps 1 (a) and 2 (b) from sample

B, and the products at steps 1 (c) and 2 (d) from sample C.

009 John Wiley & Sons, Ltd. Polym. Adv. Technol. 2011, 22 554–559

Figure 3. DrTGA curves of the products of steps 1 (a) and 2 (b) from

sample B, and the products at steps 1 (c) and 2 (d) from sample C.


Considering curves (a) and (c), the sharp weight loss at lowerthan 3008C is primarily caused by the bond cleavage of epoxygroups in the prepared hybrid copolymer precursors. A gradualdecline of weight loss from 300 to 3708C is ascribed to thedecomposition of organic ingredients, mainly the cleavage ofether linkages. The small weight loss above 5008C is assigned tothe further degradation of the copolymer residues into thecrystallized silica. With regard to curves (b) and (d), the sharpweight loss at lower than 3108C is chiefly caused by the removalof physically absorbed water and bonded water in thesecopolymer precursors. The weight loss from 310 to 4208C and420 to 7008C can be ascribed to the decomposition of organicingredients, mainly the breaking of ether linkages. The slightweight loss beyond 7008C is assigned to further degradation ofthe copolymer residues into the crystallized silica.Note that the thermal degradation temperature of 10% weight

loss (Td10) increases in samples B and C from step 1 to step 2, whichappeared at 239.5 and 305.28C, 242.18C, and 278.88C, respectively(cf. Table 2), demonstrating an increase in the thermal stability ofthe negatively charged hybrid membranes when compared withthe un-charged ones. Meanwhile, for different samples, the valuesof residualweight at 7008C (R700) are6.6 and13.4% for sample B, 3.4and9.5%forsampleC, respectively,whichexhibitanopposite trendwith that of Td10, implying a decrease of inorganic ingredients insamples B and C (cf. Table 1). However, for the sample derived fromdifferent steps, the R700 value increases from step 1 to step 2 insamples B and C, demonstrating the effect of charged groups onthe thermal stability of these samples. The explanation of suchtrends should be the introduction of –SO3H groups into the

Table 2. Thermal analysis data of samples B and C in TGA and D

Sample Curves Td10 (8C)a R700

B (a) 239.5(b) 305.2 1

C (c) 242.1(d) 278.8

a The thermal degradation temperature of 10% weight loss.b The residual weight at 7008C.


copolymer chains because it leads to an increase in thehydrophilicity of the hybrid membranes due to their larger waterabsorption than epoxy groups.[2,7]

Figure 3 presents the DrTGA curves. There exist differentendothermic peaks (i.e. weight loss peak) as listed in Table 2, andthey correspond to different weight loss stages as demonstrated inthe TGA curves (cf. Fig. 2). In the cases of samples B and C, theseendothermicpeaks rise asGMAcontent increases if thepeakbelow1008C is ignored. Meanwhile, the amount of these endothermicpeaks decreases slightly when comparing curve (a) with curve (c),and curve (b) with curve (d). These findings indicate that thethermal stability of the product increases with both the GMAcontent and –SO3H groups in the explored samples, and theincorporation of negatively charged groups into the hybridmembranes enhances their thermal stabilities. However, when itcomes to the endothermic peaks below 1008C, the temperaturedecreases significantly from93 to798Cwith increase in the contentof GMA (cf. the curves (b) and (d) in Fig. 3).Several factorsmight be responsible for the above trends. One is

the copolymerization of GMA and MPTMS monomers and theformation of crosslinked hybrid network between the organic andinorganic moieties, which leads to the improvement on thermalstability as GMA content increases. As shown in Table 2, fromsamples B to C, the trend in Td10 seems to be inconsistent with thetheoretical one (i.e. the thermal degradation temperaturedecreases with an increase in the organic ingredient of a polymer).However, if the crosslinking of epoxide andmethoxysilane to formhybrid network is considered,[20] this is reasonable and easilyunderstood. Such crosslinkingwill lead to the formation of intimatemolecular structure and elevation of thermal degradationtemperature, which is confirmed by Tep values in Table 2.Another can be ascribed to the grafting of –SO3H groups in the

copolymer chains, which will result in a compact molecularstructure and prevent the further degradation of the negativelycharged groups. As a result, the R700 value increases from step 1to step 2 in samples B and C as discussed above.Considering the decrease in the temperature of endothermic

peaks below 1008C, the main reason is the increasing amount of–SO3H groups in the polymer chains as GMA content increasesand thus leads to an increase in the hydrophilicity of the preparedcharged hybrid membranes.

Ion-exchange capacity (IEC)

IEC is a useful tool to characterize the ion-exchange property ofcharged hybrid membranes.[14,15] To determine the chargecontent of the –SO3H groups in the synthesized hybrid

rTGA curves

(wt%)b

Tep value (8C)

First Second Third

6.6 301 3703.4 93 315 4193.4 3039.5 79 416


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membranes, IEC values were determined and shown in Table 3.For comparison, the theoretical IEC values are also listed inTable 3.The measured IEC data increase from sample A to D, indicating

an increase with an increase in GMA content in the chargedhybrid membranes, and this is consistent with the trend oftheoretical IEC values. The amount of ionic groups in the hybridmembranes might be responsible for such increase. As presentedin Scheme 1, the –SO3H groups are primarily produced from thering-opening of epoxide in GMA moiety; hence, the higher theepoxy groups in the polymer chains, the higher amount of –SO3Hgroups in the hybrid membranes will be generated when thering-opening reaction of epoxide occurs. Accordingly, the IECincreases with an increase in the amount of –SO3H groups.Consequently, the IEC values increase from sample A to D.Although the measured IEC values exhibit the same trend as

that of the theoretical ones, they are much lower than thetheoretical ones, which can be explained as follows. Firstly, thering-opening reaction of epoxide is incomplete and thus a part ofepoxy groups in the polymer chains will remain intact, but totalconversion of the epoxy groups is assumed when calculating thetheoretical values.[14] Secondly, the –OH groups in GMA moietyhave a certain impact. As illustrated in Scheme 1, the –OH groupsare situated adjacent to –SO3H groups, and thus the negativecharge of –OH groups will give rise to electrostatic repulsion onthe –SO3H groups due to the deprotonation effect of –OH groups,which can be expressed in Equations (1) and (2). As a result, theion-exchange ability of –SO3H groups is reduced, resulting inlower IEC values than the theoretical ones.

� OHþ H2O !Hþ �O� þ H3O

þ (1)

� OHþ OH� !OH��O� þ H2O (2)

Lastly, although many efforts were made to preciselydetermine the IEC values, experimental errors via titrimetricanalysis cannot be entirely excluded, and thus will bring aboutsome differences between the measured IEC values and thetheoretical ones (as observed in Table 3). Consequently, it isreasonable to consider impact of –OH groups on the measuredIEC values in this case.

MALDI-TOF spectrometry

Matrix-assisted laser desorption/ionization time-of-flight massspectrometry (MALDI-TOF MS) is a useful analytical technique to

Table 3. Ion-exchange capacities (IECs) of the investigatedsamples

SampleThe measuredIECs (mmol g�1)

The theoreticalIECs (mmol g�1)a

A 0.217 1.58B 0.27326 2.34C 0.31136 3.07D 0.3491 3.64

a Assuming a total conversion of the epoxy groups in thepolymer chains.

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study polymer synthesis.[3,21] To investigate the molecularstructural stability of the four prepared samples A–D, MALDI–TOF mass spectra were collected and shown in Fig. 4a–d.For samples A–D, their base peaks (100% abundance) had

similar positions in m/z-axis, i.e., the base peaks located at m/z

Figure 4. MALDI –TOF mass spectra of samples A, B, C, and D. Residence

time16 s.

009 John Wiley & Sons, Ltd. Polym. Adv. Technol. 2011, 22 554–559


43.9900, 43.9902, 43.9901, and 43.9897 for A, B, C, and D,respectively. This indicates that the molecular structure of theproduced copolymers has not been destroyed and thedegradation and cleavage of the backbone have not occurredduring membrane preparation.[3,21] However, the abundances offragment ion peaks exhibit different trends. For example, forsample A, more than ten primary fragment ion peaks(abundances larger than 30%) can be observed (Fig. 4a). Butfor samples B, C, and D, seven, six, and three main fragment ionpeaks (abundances larger than 30%) are detected (Fig. 4 b, c, andd), suggesting an increase in the stability of molecular structure ofthese negatively charged hybrid membranes with increase in theGMA content. In general, the incorporation of GMA moiety intothe hybrid matrix will stabilize the molecular structure of thesenegatively charged hybrid membranes.Two major reasons are responsible for such trend. One is

related to the formation of hybrid network due to theintroduction of GMA moiety in the polymer chains. The otheris the polymerization of organic and inorganic moieties because itprovides more compact molecular backbones[22] and thus leadsto an increase in the stability of molecular structure as confirmedby the thermal degradation temperature of the products (cf.Table 2).

Conclusion

A novel route to prepare negatively charged hybrid membranesis proposed and four types of negatively charged hybridmembranes are prepared via free radical polymerization ofGMA and MPTMS monomers. The negatively charged –SO3Hgroups are produced via the ring-opening of epoxy groups in theGMA moiety. These charged hybrid membranes have a thermalstability as high as 3008C, and the IECs of 0.22–0.35 mmol g�1.MALDI–TOF measurements demonstrate that the incorporationof GMA into the copolymer matrix improves the molecularstructure stability of these negatively charged hybrid mem-branes, suggesting the effect of hybrid network on the stabilitiesof negatively charged hybrid membranes.Note that this study mainly focuses on the preparation of

negatively charged hybrid membranes and examines theirfundamental properties, and little work is done on theirapplications due to the relatively lower IECs of these negativelycharged hybrid membranes. However, this does not imply thatthis is less important. For their industrial applications, especially inenvironmental field, further work is required to optimize themembrane preparation process so as to highly elevate the IECvalues of these hybrid membranes. We believe this problem will


be solved with further improvement of the membrane propertiesand optimization of operational parameters. When the mem-brane properties are improved and ideal IECs are obtained, theiradsorption behaviors for removal of heavy metal ions fromaqueous solutions will be further investigated, which will be ourfuture job.

Acknowledgements

This project was supported by Significant Foundation of Edu-cational Committee of Anhui Province (No. ZD2008002-1) andAnhui Provincial Natural Science Foundation (No. 090415211).Special thanks was extended to Dr. Chuanhui Huang for proof-reading the manuscript.

REFERENCES

[1] Z. Shi, X. Wang, Polym. Adv. Technol. 2009, DOI: 10.1002/pat.1358.[2] C. M. Wu, T. W. Xu, W. H. Yang, J. Membr. Sci. 2003, 216, 269–278.[3] R. K. Nagarale, G. S. Gohil, V. K. Shahi, R. Rangarajan, Macromolecules

2004, 37, 10023–10030.[4] T. W. Xu, W. H. Yang, J. Membr. Sci. 2001, 183, 193–200.[5] K. Volchek, E. Krentsel, Y. Zhilin, G. Shtereva, Y. Dytnersky, J. Membr.

Sci. 1993, 79, 253–272.[6] V. K. Shahi, Solid State Ionics 2007, 177, 3395–3404.[7] C. M. Wu, T. W. Xu, M. Gong, W. H. Yang, J. Membr. Sci. 2004, 247, 111–

118.[8] C-H. Lin, C-H. Chang, W-C. Jao, M-C. Yang, Polym. Adv. Technol. 2009,

20, 672–679.[9] H. P. Fu, R. Y. Hong, Y. J. Zhang, H. Z. Li, B. Xu, Y. Zheng, D. G. Wei, Polym.

Adv. Technol. 2009, 20, 84–91.[10] T. Takaki, K. Nishiura, Y. Mizuta, Y. Itou, J. Nanosci. Nanotechnol. 2006,

6, 3965–3968.[11] S. K. Medda, D. Kundu, G. I. De, J. Non-Cryst. Solids 2003, 318, 149–156.[12] J. S. Liu, T. W. Xu, M. Gong, Y. X. Fu, J. Membr. Sci. 2005, 264, 87–96.[13] Y. Bondar, H. J. Kim, S. H. Yoon, Y. J. Lim, React. Funct. Polym. 2004, 58,

43–51.[14] Y. H. Wu, C. M. Wu, M. Gong, T. W. Xu, J. Appl. Polym. Sci. 2006, 102,

3580–3589.[15] C. M. Wu, T. W. Xu, W. H. Yang, J. Solid State Chem. 2004, 177, 1660–

1666.[16] C. M. Wu, T. W. Xu, W. H. Yang, J. Membr. Sci. 2003, 224, 117–125.[17] J. S. Liu, T. Li, K. Y. Hu, G. Q. Shao, J. Appl. Polym. Sci. 2009, 112, 2179–

2184.[18] J. S. Liu, X. H. Wang, T. W. Xu, G. Q. Shao, Sep. Purif. Technol. 2009, 66,

135–142.[19] Y. Inaki, H. Yoshida, T. Yoshida, T. Hattori, J. Phys. Chem. B 2002, 106,

9098–9106.[20] S-S. Hou, P-L. Kuo, Macromol. Chem. Phys. 1999, 200, 2501–2507.[21] X. X. Cheng, X. F. Zhang, J. S. Liu, T. W. Xu, Eur. Polym. J. 2008, 44, 18–

931.[22] J. S. Liu, T. W. Xu, X. Z. Han, Y. X. Fu, Eur. Polym. J. 2006, 42, 2755–2764.


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