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The Effect of Presence of Glycopolymer Grafts in PolyN-Isopropylacrylamide/Clay Nanocomposite HydrogelsAmal Amin a , Heba Kandil a & Mohamed Nader Ismail aa Polymers & Pigments Department , National Research Center , Dokki , Giza , EgyptAccepted author version posted online: 26 Mar 2013.Published online: 29 Jul 2013.

To cite this article: Amal Amin , Heba Kandil & Mohamed Nader Ismail (2013) The Effect of Presence of GlycopolymerGrafts in Poly N-Isopropylacrylamide/Clay Nanocomposite Hydrogels, Polymer-Plastics Technology and Engineering, 52:10,1034-1042, DOI: 10.1080/03602559.2013.769579

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The Effect of Presence of Glycopolymer Grafts in PolyN-Isopropylacrylamide/Clay Nanocomposite Hydrogels

Amal Amin, Heba Kandil, and Mohamed Nader IsmailPolymers & Pigments Department, National Research Center, Dokki, Giza, Egypt

Two types of poly-N-isopropylacrylamide (p-NIPAM)/Cloisite30B clay nanocomposite (NC) hydrogels were synthesized wherethe first one contained Cloisite 30B without modification. However,the second one contained Cloisite 30B with glycopolymer unitsattached onto its surface by surface-initiated atom transfer radicalpolymerization. The main purpose of this article was to study theeffect of surface grafting of glycopolymer onto Cloisite 30B claysurface on the physical properties of the resulting NC hydrogelssuch as swelling ratio, deswelling behavior and thermal behavior.It was found that NC hydrogels containing glyco-units had betterproperties than the first one.

Keywords Cloisite 30B; Glycopolymer; Hydrogel; Nanocompo-sites; Poly-N-isopropylacrylamide

INTRODUCTION

In the last two decades, polymeric hydrogels such as polyN-isopropylacrylamide (p-NIPAM) gels, have attractedmuch scientific interest and have been used in many poten-tial applications such as drug delivery, solute separation,development of sensors and actuators[1–3]. The importanceof these gels was attributed to their ability to display a sen-sitivity to the external stimuli such as temperature, solventcomposition, pH, light, pressure, magnetic, and electricfields[4]. However, these gels have several significant limita-tions that made their use restricted. Generally, they exhib-ited very slow response and poor mechanical properties[5].The disadvantages of these gels usually arose from theinherent problems of chemically cross-linked polymernetworks.

In the last few years, the researchers succeeded in over-coming some of these disadvantages by synthesizing a newtype of (p-NIPAM) hydrogel with almost ideal proper-ties[6,7]. The novel hydrogel was a nanocomposite-typehydrogel (NC gels)[4]. These gels were obtained by in-situfree radical polymerization of (p-NIPAM) in the presenceof water-swellable inorganic clay. The resulting hydrogelsshowed improvement in their mechanical and swelling=

deswelling properties[8]. All of these characteristics wereattributed to the organic=inorganic networks formed inthe NC gels where the neighboring clay sheets are linkedby large numbers of long and flexible polymer chains. Eachclay sheet acts as a super-multifunctional cross-linkingagent[9]. Several kinds of inorganic clay particles suchas pristine Na-montmorillonite, Cloisite 30B, LaponiteRDS, synthetic hectorite and modified one such as poly(ethylene glycol) (PEG)-modified Laponite platelets wereintroduced into p-NIPAM gel systems with or withoutadditional use of chemical cross-linkers[10–18].

However, to the best of our knowledge, no report hasbeen published on the preparation and properties of NCgels using surface modified Cloisite 30B with inclusion ofglycopolymers. Generally, glycopolymer is a syntheticpolymer carrying carbohydrate (sugar) moieties as pendantor terminal groups[19]. The aim of choosing it for modifyingthe clay surface was attributed to its hydrophilic naturewhich shows very important pharmacological and biologi-cal properties[20].

It is well known that polymer=clay nanocomposites canbe prepared by melt and solution blending and in-situ poly-merization[21]. In-situ polymerization technique is the mostcommon preparative method for polymers=clay nanocom-posites because the types of the nanofillers and the polymerprecursors can be varied in a wide range to achieve thedesired properties[22]. However, surface-initiated polymeri-zation (SIP) provides an easy way to prepare densely packedand chemically tethered polymer brushes through in-situgrafting polymer chains from substrate surfaces[23]. Severaltechniques for controlled=living SIP are known such as anio-nic, cationic, ring-opening metathesis (ROMP), nitroxidemediated (NMP), reversible addition-fragmentation chain-transfer (RAFT) and atom transfer radical (ATRP)polymerization methods[22,24,25].

Herein, SI-ATRP was particularly chosen to obtainglycopolymers=clay nanocomposites because of its tolerancefor impurities andmild polymerization conditions comparedwith the conditions required for other techniques[26]. Inthis communication, ATRP initiating surface modifiedCloisite 30B was used to polymerize 1,2:5,6-di-O-isopropyli-dene-a-D-glucofuranose (MAIpGlc) as the concerned

Address correspondence to Amal Amin, Polymers & PigmentsDepartment, National Research Center, Dokki, Giza, Egypt.E-mail: aamin_07@yahoo.com

Polymer-Plastics Technology and Engineering, 52: 1034–1042, 2013

Copyright # Taylor & Francis Group, LLC

ISSN: 0360-2559 print=1525-6111 online

DOI: 10.1080/03602559.2013.769579

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glycomonomer to obtain (p-MAIpGlc)=Cloisite 30B nano-composite that was deprotected, then used for synthesisof p-NIPAM=Cloisite nanocomposite hydrogel by in-situfree radical polymerization.

Materials

Cloisite 30B was kindly supplied from Southern ClayProducts, Inc. (Gonzales, TX) with cation-exchange capa-city (CEC) of 90meq=100 g clay. N-isopropylacrylamide(NIPAM), 1,2:5,6-di-O-isopropylidene-a-D-glucofuranoside,methacrylic anhydride, ethyl-2-bromoisobutyrate (2-EiBBr)and 2-bromoisobutyryl bromide (BIBB) were provided fromAldrich. Dodecyl sulfate sodium salt (DSS), which was usedas a surfactant was obtained from Merck. N,N0-methylenebisacrylamide (NMBA), which acted as a cross-linkingagent was purchased from Acros Organics (USA).Potassium persulfate (KPS) initiator was purchasedfrom Sisco Research Laboratories (India). N,N,N0,N0-tetra-methylethylenediamine (TEMED), p-Toluenesulfonic acidmonohydrate, Cu (I) Br, pyridine and triethyl amine wereobtained from Sigma-Aldrich (Germany). All other solventsand chemicals were of analytical grade and used as received.

Characterization and Instrumentation

Analytical measurements such as TGA, FTIR, XRD,TEM, SEM and DSC were performed on samples of gelsin order to identify their compositions and structures. Beforethe characterization, the hydrogels were dried at 70�C ina vacuum oven for 24h. Thermal gravimetric analyses(TGA) were carried out on TGA-50 SHIMADZU thermo-gravimetric analyzer under nitrogen atmosphere with heat-ing rate 10�C=minutes. Fourier transform infrared (FTIR)spectra were obtained using a Jascow FTIR-430 series infra-red spectrophotometer (Jascow, USA). The dried samplewas ground with dried potassium bromide (KBr) powder,compressed into a disc, and then the resulting sample wassubjected to analysis. Transmission electron microscopy(TEM) was operated using a TEM manufactured by JEOLat 120kV for M1and Mg dried gels.

Ultrathin films (ca. 50 nm thick) were prepared for TEManalysis by cutting dried gels embedded in epoxy resin,using an ultra-microtome (EM VC6, produced by LEICAInc.). The morphology of dried NC hydrogel was observedby scanning electron microscopy (SEM, JSM 5410, JEOL,Japan) after sputter coating with gold. Differential scan-ning calorimetry (DSC) analyses were performed on TAInstruments Q600 SDT system with heating rate 10�C=min under nitrogen flow. Glass transition temperatureswere detected from DSC. X-ray diffraction (XRD) patternswere obtained using milled, dried samples with SiemensD5000 diffractometer equipped with an intrinsic ger-manium detector system. Molecular weights ( �MMnGPC) andthe polydispersities (PDI) of the prepared polymers weredetermined by gel permeation chromatography (GPC) by

using GPC-1100 Agilent technologies with refractive indexdetector and 100-104–105 A ultrastyragel columns. Tetra-hydrofurane (THF) was mainly used as the eluent, withflow rate 1mlmin�1 by using polystyrene standards. Pro-ton nuclear magnetic resonance (1HNMR) spectra wereobtained from a JEOL-ECA 500MHz NMR at roomtemperature using CDCl3 or DMSO-d6.

Synthetic Procedures

Synthesis of ATRP Surface Initiator (I)[27]

A dry round flask with a magnetic stir bar was chargedwith Cloisite 30B (2 g), triethyl amine (13.93ml, 100mmol),and anhydrous THF (120ml). Then, 2-bromoisobutyrylbromide (BIBB) (18.5ml, 150mmol) was added dropwiseto the former mixture at 0�C. The reaction was progress-ively stirred for 2 h more in an ice bath, then for 24 h moreat room temperature to complete the reaction. Finally, thereaction mixture was diluted with additional THF and thencentrifuged to separate the unreacted 2-bromoisobutyrylbromide in the decanted liquid. The modified clay waswashed with water with further centrifugation to get ridof excess amine. The resulting modified clay (I) was dried,collected and characterized by IR, XRD and TEM.

Synthesis of 3-O-Methacryloyl-1,2:5,6-di-O-isopropylidene-a-D-Glucofuranose Monomer (MAIpGlc)

The synthesis of (MAIpGlc) was achieved accordingto the previously reported method[28] where 10 g of 1, 2:5,6-di-O-isopropylidene-a-D-glucofuranose (38.4mmol)were dissolved in 50ml of absolute pyridine at roomtemperature and then, methacrylic anhydride (10ml,67.1mmol) was added dropwise. The reaction mixturewas heated at 65�C for 4 h and for another 1 h after addingmore 35ml of water. Afterward, the mixture was stirred for24 h at room temperature and then extracted 3 times with50ml of petroleum ether. The extracts were first washedtwice with 100ml of 5% aqueous sodium hydroxide sol-ution and then, three times with 60ml of water and driedover anhydrous sodium sulfate. The solvent was removedin vacuo and the crude product was purified by flash silicagel chromatography with 7:2:1, ethyl acetate: toluene:methanol mixture as eluent to yield the sugar-carryingmonomer (MAIpGlc) as colorless oil, which was character-ized by 1HNMR.

Formation of Grafted Glycopolymers on Clay Surfacevia SI-ATRP: (Synthesis of p-MAIpGlc=CloisiteNanocomposite)[29]

The clay-functionalizedATRP initiator (I, 0.2 g), 2, 20-bpy(0.0389 g, 9.8� 10�4mol), MAIpGlc (4 g, 4.9� 10�2mol)and Cu (I) Br (0.0179 g, 4.9� 10�4mol) were added to50mL Schlenk flask, then the flask was sealed under argon.Xylene (50%v=v) was added via syringe and the flask was

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evacuated and back-filled with Ar three times. Sacrificialinitiator such as ethyl-2-bromoisobutyrate (2-EiBBr;0.0238 g, 4.9� 10�4mol) was injected into the flask viasyringe at ambient temperature with continuous stirringunder argon atmosphere. The reaction mixture was placedat thermostated oil bath at 90�C. After a certain time, thepolymerization was terminated and THF was added to thereaction mixture.

Centrifugation was applied to the previous mixture forseveral times until complete separation of the free polymerin solution was attained. After the catalyst was filtered outthe solution with alumina column, the filtrate was used tomeasure the molecular weight of the free polymer by GPC.The grafted p-MAIpGlc=clay nanocomposite was washedwith aqueous solution of disodiumsalt-ethylenediaminetetraacetic acid (EDTA-disodium salt) to remove theremaining catalyst, then with water and dried in vacuum at40�C. p-MAIpGlc=Cloisite nanocomposite was charac-terized by XRD and TEM.

Deprotection of the Isopropylidenyl Group in p-MAIpGlc=Cloisite 30B Nanocomposite

The deprotection process was carried out under acidicconditions[30], where about 50mg of p-MAIpGlc=claynanocomposite were added to 20ml of 80% formic acidand stirred for 48 h at room temperature. Then, 10ml ofwater were added and the mixture was stirred for further12 h. The resulting solid product was then collected afterseveral cycles of centrifugation and water washing. Thefinal product (p-AIpGlc=cloisite 30B nanocomposite, (A))was characterized by FTIR and the chemical structure ofp-AIpGIc polymer was identified by 1HNMR after itscleavage from clay surface via the method reportedelsewhere in the literature and as the following.

Cleavage of the Grafted Polymers from the Clay Surface[31]

The cleavage process was performed on the resultingpolymer=clay nanocomposite such as p-MAIpGlc. Inthis procedure, about 0.1 g of the polymer=clay nanocom-posite was dispersed into a mixture of 150ml toluene and10ml methanol in 200ml round flask, then 20mg ofp-toluenesulphonic acid was sequentially added. The reac-tion mixture was heated under reflux for 72 h. Afterwards,the centrifugation process was applied to the previous mix-ture for several times until complete separation of the solidmaterial. Polymer in supernatant was precipitated by meth-anol and its average molecular weight was characterized byGPC and its chemical structure was identified by 1HNMR.

Preparation of Hydrogels

Hydrogel Containing Cloisite 30B Only (blank, M1)

First, 99% of NIPAM (1.1203 g) and 1% of Cloisite 30B(0.0113 g) were added to 10mL deionized water. To this

solution, 5mol % NMBA (0.077 g) and DSS (0.025 g) werewell mixed overnight at room temperature in vials. Finally,1mol % KPS and 1mol % TEMED were added to the for-mer solution with stirring at 0�C. Then, free-radical poly-merization was allowed to proceed in a water bath at20�C for 20 h. After completion of gelation, the gel rodwas immersed in an excess amount of deionized water for4 days to remove the residual unreactive components.Swollen gel was dried at 25�C for 1 day and then dried ina vacuum oven for 2 days.

Hydrogel Containing p-AIpGlc=Cloisite Nanocomposite (Mg)

The same procedure with the same ratios of reactantsthat used for preparation of hydrogel containing Cloisite30B (blank) was used here but by using p-AIpGlc=Cloisitenanocomposite (A) instead of using Cloisite 30B only. Dif-ferent ratios from (NIPAM: A) were used such as NIPAM(99%, 1.1202 g, Mg1) with A (1%, 0.0118 g) and NIPAM(85%, 0.9618 g, Mg2) with A (15%, 0.1764 g). The aim ofthis experiment was to study the effect of increasing theamount of (A) on the swelling of the prepared hydrogel.

Preparation of NIPAM Hydrogel without Inclusion ofClay (N)

The same procedure that was used for preparing thehydrogel containing Cloisite 30B (blank, M1) was followedhere with the same ratios of reactants but by using 100%(1.1316 g) of NIPAM without clay.

Measurements Done on Hydrogels

The following measurements were done:

a. Swelling Ratio. Swelling experiments were performed byimmersing purified gels in a large excess of water at25�C until the swelling equilibrium was attained, andthen the swollen gels were dried. Swelling ratios are repre-sented in Eq. (1) by the ratio of weights of the swollenhydrogel (Wg) to the corresponding dried gel (Wd).

Q ¼ ðWg �Wd=WdÞ � 100 ð1Þ

b. Swelling and Deswelling Kinetics. To measure the deswel-ling kinetics ofM1 andMg gels, the dried hydrogels of thesame size were immersed in an excess amount of deio-nized water at 50�C. The gels were taken out of water atcertain time intervals and weighed after excess waterwas removed from the surface[32]. The deswelling ratios(DSR) were calculated with the following equation:

DSR ¼ Wt=W0 ð2Þ

WhereWt is the weight of the de-swollen hydrogel at timet, and W0 is the weight of the corresponding initial gels.

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RESULTS AND DISCUSSION

Synthesis of ATRP Surface Initiator (I)

The clay-functionalized ATRP initiator was obtained bytreating Cloisite 30B with BIBB (Scheme 1). The immobi-lized initiator onto clay surface was characterized by FTIRand XRD. In FTIR (Fig. 1), the broad absorption band ofsurface OH at 3400 cm�1 disappeared and another bandappeared at 1750 cm�1, which was referred to n CO ofbutyrate group. XRD (Fig. 2) recorded significant increasein the d-spacing from 1.85 nm for neat Cloisite 30B tod¼ 2.35 nm for ATRP- surface initiator (I).

Preparation of Glycomonomer

The glycomonomer (MAIpGlc) was prepared by thereaction of methacrylic anhydride with 1,2:5,6-di-O-isopropylidene-a-D-glucofuranose in absolute pyridine[28].Its chemical structure was identified by 1HNMR. 1HNMRof MAIpGlc (CDCl3), chemical shift (d, ppm): 1.25–1.55(4 CH3), 1.95 (CH3-C=CH2), 5.60 (1 H, CH2¼C), 6.10 (1H, CH2¼C), 4.05, 4.25, 4.51, 5.29, 5.87 (7 H, sugar moiety).

Synthesis of Homo-Glycopolymer (P-MAIpGlc)/CloisiteNanocomposite

SI-ATRP was carried out on the prepared glycomono-mer (MAIpGlc) to form its homoglycopolymer=cloisitenanocomposite (Scheme 1) by using the prepared ATRPfunctionalized clay surface initiator (I) with ethyl-2-bromoisobutyrate (2-EiBBr) as sacrificial initiator, 2,20-bipyridine (bpy) as ligand and CuBr at 90�C[29]. Theattached polymers to the clay surface were cleaved by theaction of p-toluenesulphonic acid and methanol mix-ture[31]. The free and bound polymers were characterizedby GPC as indicated in Table 1, where low polydispersity

values were observed. Relative higher molecular weights( �MMnGPC) than the calculated ones were determined viaGPC and that was ascribed to slower initiation than

SCH. 1. Synthesis M1, Mg1 and Mg2 nanocomposite hydrogels.

FIG. 1. FTIR of (a) neat Cloisite and (b) ATRP macroinitiator (I).

FIG. 2. XRD of neat cloisite, ATRP macroinitiator (I), p-MAIpGlc=

clay nanocomposite, Mg1 and M1 nanocomposite hydrogels.

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propagation might be a result of the bulkiness of thesurface initiating moiety including the clay. p-MAIpGlc=cloisite nanocomposite was characterized by XRD. InXRD spectrum (Fig. 2), no distinct band was observedand this indicated that there was a complete inclusion ofthe polymer inside the clay platelets causing completedestruction of the platelets ordering, which led to exfo-liated nanocomposite.

Deprotection of Isopropylidene Group inp-MAIpGlc/Cloisite Nanocomposite

The isopropylidene group in (p-MAIPGIc)=cloisitenanocomposite was deprotected by formic acid and thisled to produce OH ended polymer (p-AIpGlc)=clay nano-composite (A) which was confirmed by FTIR[29,30]. InFTIR spectrum, the absorption peaks at 2800–3100 cm�1

became weaker and the peak of hydroxyl group at3450 cm�1 became stronger due to the cleavage of CH3-groups and the formation of hydroxyl groups. The chemi-cal structure of p-AIpGIc was also confirmed by 1HNMRby cleavage of the grafted polymer (p-AIpGlc) from theclay substrate as previously described[31]. 1HNMR forp-AIpGlc (DMSO-d6), the chemical shifts (d, ppm):1(CCH3), 1.9–2.1 (CH2), 3.6 (OCH3), 4–6 (H of sugar moi-ety), 6.5–7 (OH bands appeared). H2O molecules appearedat 3.2–3.3 ppm.

Preparation and Characterization of theNanocomposite Hydrogels

The importance of using anionic surfactant DSS in pre-paring p-NIPAM nanocomposite hydrogels was mainly toprevent phase separation or precipitation of the Cloisite30B clay. That was attributed to the ability of DSS to uni-formly disperse the clay layers in aqueous medium[33].Uniform p-NIPAM nanocomposite hydrogels (M1, Mg1and Mg2) were successfully prepared by in-situ free radicalpolymerization in aqueous medium at low temperature.

Mg1 and Mg2 gave analogous results with respect toFTIR and XRD where they possess similar structural fea-tures with exfoliated morphology as two p-NIPAM con-taining nanocomposite hydrogels; however, the results ofMg1 were particularly mentioned here with respect to thesetwo analyses because we were much interested in compar-ing the nanocomposite gels containing the lower percentof clay (Mg1) with that of the blank (M1).

The molecular structures of the nanocompositeshydrogels were investigated using FTIR. (Fig. 3) showsFTIR spectra of M1and Mg1 with respect to that of theneat p-NIPAM (N) gel. The peaks of p-NIPAM (N) gener-ally appeared in the three nanocomposites where the peakappeared at 1651 cm�1 was attributed to the stretchingvibration of the C=O group of p-NIPAM, yet the one thatappeared at 1542 cm�1 was referred to the in-plane bendingvibration of NH groups of p-NIPAM. Absorption bands at1454 cm�1 and 1416 cm�1 were ascribed to the scissor andbending vibrations of CH2 and CH-CO groups, respect-ively. Moreover, the absorption band at 2935 cm�1 wasdue to stretching of CH2 groups and the absorption bandat 2973 cm�1 was corresponding to stretching of CH3

groups.Finally, the wide-strong absorption band between 3200

to 3600 cm�1 was due to the NH stretching absorptionband, whereas the absorption band between 950 to1300 cm�1 was due to the overlapping of the stretchingC-N, and C=O. However, in FTIR spectra of M1 andMg1 there was additional peak appeared at 1005 cm�1,

TABLE 1GPC data for free and bound p-MAIpGlc in p-MAIpGlc=Cloisite nanocomposite

Entry

Free polymer Bound polymer

Time h Conversion % �MMnth�MMnGPC g=mol PDI �MMnGPC g=mol PDI

MAIpGlc 2 60 19680 23200 1.39 9800 1.32

FIG. 3. FTIR of (a) neat PNIPAM gel, (b) Mg1 and (c) M1 nanocompo-

site hydrogels.

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which was attributed to Si-O stretching of clay. The spectraof M1 and Mg1 as in [Figs. 3(b, c)] were almost the sameexcept for the additional peak appeared at 1730 cm�1 incase of Mg1, which was attributed to carbonyl groups inglycopolymer that was firstly grafted onto clay.

The thermal stabilities of the nanocomposite hydrogelswere studied by thermal gravimetric analysis (TGA). It isclear from (Fig. 4) in comparison with neat p-NIPAMgel (N), that the onset temperature of degradationincreased by almost 40�C by adding cloisite 30B orp-AIpGlc=cloisite nanocomposite (A). The thermal stab-ility of the nanocomposite hydrogels increased in the orderof Mg2>Mg1>M1>N. This might be attributed to exten-sive interaction between the p-AIpGlc=Cloisite and thepolymer matrix as well as the formation of sub-networksin Mg1 and Mg2 leading to restricted molecular mobilityof the polymer chains and resulting in inhibition of the dif-fusion of the decomposed product in the polymer matrix.

Glass transition temperature (Tg) for M1 and Mg1 driedNC gels with low clay content appeared at the sametemperature as that for linear polymer of PNIPAM

(i.e., 142�C) as shown in (Figs. 5a, 5b, 5c). Although fordried (Mg2) gels with higher clay content, the glass tran-sition was unobservable as seen in (Figure 5d). That obser-vation was referred to the direct interaction of the polymermolecules with the hydrophilic surface of the clay platelets.The direct coupling of the polymer molecules and silicatesurfaces might have negative effect on the motional free-dom of the polymer chains[34]. Therefore, the thermalresponse from such nanocomposites was reduced or com-pletely quenched where sufficient hydrophilic surfaces wereavailable (as in high loading).

To reveal the level of dispersion of clay platelets in NCgels, XRD measurements were made on dried NC gels.The XRD patterns of various NC gels were plotted in(Fig. 2). The XRD of the various nanocomposite hydrogelsshowed the disappearance of the diffraction peaks in all sam-ples and hence exfoliated structure was attained in case ofp-MAIpGlc=cloisite nanocomposite and the other NC gels.

TEM of neat Cloisite 30B (Fig. 6) showed agglomer-ation from layered silicate, however, this agglomerationbegan to separate from each other by inserting the ATRPinitiator moiety to the Cloisite clay surface. After insertionof the glycopolymer chains, better and perfect dispersion ofclay platelets was observed where a complete destruction ofordering within the clay platelets was mostly recorded forexfoliated morphology. Figure 6 shows transmission elec-tron micrographs of ultrathin films of dried M1 and Mg1gels. It was found that the clay in both gels was substan-tially exfoliated and dispersed homogeneously throughoutthe polymer matrix. It was therefore concluded that fineand homogeneous clay dispersions were achieved in thehydrogels.

FIG. 4. TGA of neat cloisite, ATRP initiator (I), neat PNIPAM gel (N),

Mg1 and Mg2 nanocomposite hydrogels.

FIG. 5. DSC of (a) neat PNIPAM gel (N), (b) M1, (c) Mg1 and (d) Mg2nanocomposite hydrogels.

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SEM images of the air-dried samples of neat p-NIPAMgel (M1) and Mg1 were shown in (Fig. 7). Single clay par-ticles embedded in the polymer matrix were observed inSEM image of Mg1 where the exfoliated structure of Mg1was further confirmed and the single sheets from Cloisite30B clay were well distributed in the polymer matrix.

Effect of Presence of Grafted p-AIpGlc Units inp-NIPAM/Cloisite Nanocomposite Hydrogelson the Hydrogel Properties

Two features were studies here such as swelling ratioand swelling=deswelling kinetics.

Swelling Ratio Equilibrium

The capacity of the swelling was one of the most impor-tant parameters to evaluate the property of the hydrogels.Although all the prepared hydrogels showed rapid swelling,and their equilibrium was attained after 1000min (Fig. 8);however, Mg1 and Mg2 showed faster swelling and respondrates more than that of M1. This indicated that thecross-linking interaction between Cloisite and polymer(p-NIPAM) chains was weaker than that betweenp-AIpGlc=cloisite and polymer (P-NIPAM) chains in

FIG. 6. TEM of (a) neat cloisite, (b) I, (c) p-MAIpGlc=clay nanocompo-

site, (d) Mg1 and (e) M1 nanocomposite hydrogels.

FIG. 7. SEM of (a) Mg1 and Neat PNIPAM gel.

FIG. 8. Swelling ratio as a function of time for M1, Mg1 and Mg2nanocomposite gels in deionized water at 25�C.

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Mg1 and Mg2 and this also indicated that Mg1 and Mg2hydrogels had larger pores than that of M1, i.e., Mg1 andMg2 hydrogels exhibited porous networks.

Deswelling Kinetics

The deswelling rate is one of the most important factorsand, in particular, high rates are needed in many applica-tions[4]. In deswelling kinetics, the gels were moved from20�C to 50�C. Figure 9 shows the deswelling behaviors mea-sured for M1, Mg1 and Mg2 gels under the same experi-mental conditions. Thereby, the shrinking for M1wasalmost complete within 8–10min, while the shrinking forMg1 gel that contained the same amounts of clay i.e., (1%)as in M1 was almost complete within 25–30min. Accord-ingly, the gels that contained the same amounts of clay 1%(Mg1 and M1) exhibited the most rapid deswelling rate ifthey are compared with Mg2. In another word, the deswel-ling rate gradually decreased as clay percent increased.

CONCLUSION

A novel temperature-responsive porous nanocompositehydrogel was prepared by in-situ free-radical polymeriza-tion using inorganic clay as a cross-linker and DSS as a sur-factant. TEM and SEM analyses showed that the clayplatelets were exfoliated and dispersed in the NC hydrogels.XRD data also confirmed that. The produced gels exhibitedextraordinary thermal and swelling=deswelling propertiesin comparison with the hydrogel nanocomposite that con-tained cloisite 30B without further modification where thepresence of glycopolymer units provided their nanocompo-site hydrogels with higher thermal stability and higherswelling ratios than those containing cloisite 30B only.

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