Synthesis and characterization of interpenetrating polymer network of Fullerene based poly (α-methyl styrene) and polyurethane

Progress in Organic Coatings 105 (2017) 92–98

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Synthesis and characterization of interpenetrating polymer network of Fullerene based poly (␣-methyl styrene) and polyurethane Mohd. Meraj Jafri a,∗ , Meet Kamal a , D.K. Singh b , T.C. Shami c , H.B. Baskey c a b c

Department of Chemistry, Christ Church Degree College, Kanpur, India Department of Chemistry, Retd. Prof. H.B.T.I., Kanpur, India Strategic Material Group, D.M.S.R.D.E, D.R.D.O, Kanpur, India

a r t i c l e

i n f o

Article history: Received 8 May 2016 Received in revised form 29 September 2016 Accepted 21 November 2016 Keywords: Fullerene Poly (␣-methyl styrene) Polyurethane Conducting polymers Interpenetrating polymer network

a b s t r a c t A Novel flexible fullerene based interpenetrating polymer network (IPN) of poly (␣-methyl styrene) and polyurethane is synthesized. The polymer network is characterized using infrared, 13 C NMR spectroscopy, differential scanning calorimetric analysis, thermo gravimetric analysis, conductivity analysis, transmission electron microscopic techniques, complex permeability and permittivity characteristics. Infrared spectral analysis of polymeric sample show characteristic peaks for fullerene at 1445, 549 and 1600 cm−1 , for poly (␣-methyl styrene)(PAMS) at 3055, 1495, 2981 and 698 cm−1 and for polyurethane it reveals peaks at 3200, 1742, and 2798 cm−1 . The peaks recorded for 13 C NMR spectra shows the signal for fullerene at 136 ppm, for poly (␣-methyl styrene) at 128, 62, 40 and 25 ppm and for polyurethane at 180.0, 63.2, 37.3 and 25.1 ppm respectively. The glass transition temperature value obtained from differential scanning calorimetric analysis is found to be 160 ◦ C. The initial thermal decomposition of polymer network was studied by thermo gravimetric analysis which is found to 392 ◦ C. The conductivity record reveals the semiconductor character of polymer network. The XRD pattern of IPN indicates semi crystalline nature. Transmission electron microscopic examination reveals clear dual phase morphology in the synthesized polymer network. Besides of these characterizations IPN is also analyzed for permeability and pemittivity, which reveals more or less semiconductor nature of synthesized IPN. © 2017 Elsevier B.V. All rights reserved.

1. Introduction To overcome the poor performance of conventional polymer, a new class of polymers “Interpenetrating polymer network (IPN)” came into existence. An IPN is a blend of two or more polymers in a network with one of the systems is being synthesized during immediate presence of another [1]. These networks are entangled such that cannot be pulled apart. IPN is different from polymer blends in a way that it is insoluble in solvents [2]. IPNs combine the characteristics of the cross-linked polymers. Researchers concluded their consideration of stepwise enhancement of IPN and their properties. Analysis of different sequential IPNs was performed by Sperling et al. [3], Zahao X et al. [4] reported synthesis of elastomer and gel from IPN, Buist and Gudgeon [5] synthesize IPN of polyurethane containing isocyanate group, thereafter Gangopadhyay[6] synthe-

∗ Corresponding author. E-mail addresses: [email protected] (Mohd.M. Jafri), meetk [email protected] (M. Kamal), [email protected] (D.K. Singh), [email protected] (T.C. Shami), [email protected] (H.B. Baskey). http://dx.doi.org/10.1016/j.porgcoat.2016.11.021 0300-9440/© 2017 Elsevier B.V. All rights reserved.

sized polypyrrole following the electrochemical polymerization, development of an IPN based on micro spherical formulation using emulsion crosslinking method was examined by Banerjee et al. [7], Isiklan [8] have extensively used carbohydrates and biodegradable polymers for controlled release formulation of drug having short plasma life. Rokhade et al. [9] worked on novel controlled release drug release system, Patel et al. [10] reported the synthesis of dielectric elastomer, Kulkarni et al. synthesized IPN hydrogel membranes consisting of sodium alginate and polyvinyl alcohol [11], Vlad et al., synthesized IPN with an immiscible components [12], some study on the use of castor oil as a component in PU with IPN’s have been published by Zang et al. [13], Al-Kahtani Ahmed et al. [14] reported the synthesis of Chitosan based pH sensitive semi IPN microsphere for controlled release of diclofenac sodium, An et al. [15] reported a themodyanamic model of physical gels. Patel et al. [16] suggested review on hydrogel nanoparticles in drug delivery, A Singh et al. [17] reported synthesis and characterization of interpenetrating polymer network of polyglycidyl methacrylate and acrylamide. Through these polymer networks chemically compatible desired phase morphology can be achieved [18]. IPN have found important applications in various fields such as organic solar

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cells [19], Drug delivery [20], tissue engineering [21], polymer actuators [22] and energy harvesters [23]. Recently in order to overcome the problem of sensitive electronic machines, researchers are focusing on dielectric characteristics, microwave absorption and EMI shielding properties [24,25]. Nowadays polymer based composites are in demand as a microwave absorber and instead of conventional metal based one [26,27]. IPN offers the possibility of combining in network from which otherwise it is not possible to synthesize polymer with opposite properties [24] etc. Literature discussed above reveals that enormous work has been carried on IPN but fullerene based IPN using novel vinyl monomers is still scarce. Thus the present study reveals data on fullerene based poly (␣-methyl styrene) and polyurethane with interpenetrating polymer systems. Present work aims for developing a network system based on these novel vinyl monomers explaining various physiochemical, thermal and electronic phenomena of IPN (Scheme 1).

2. Experimental procedure Monomers [Urethane (Kemphasol, Art. No. K14848, C3 H7 NO2 ) washed ␣-methyl styrene], Solvents, fullerene and divinyl Benzene (DVB) are taken for the experiment. Benzoyl peroxide (BPO) is recrystallized from chloroform.

93

3.3. Thermo gravimetric analysis (TGA) TGA is carried on TGA V% V5 1A 2100, under nitrogen atmosphere at a heating rate of 10 ◦ C/min. 3.4. Permeability and permittivity analysis An Agilent Vector Network Analyzer (VNA) E 8364 B is employed to measure the reflection/transmission coefficients of the composite specimen in the X band (8.2–12.4 GHz) frequency region. Based on the measured scattering coefficients the complex permittivity and permeability is calculated using Nicholson-Ross-Weir (NRW) algorithm. 3.5. Transmission electron microscopy morphology (TEM) The IPN is studied by TEM with a resolution of 100 nm. Samples are prepared by dissolving the powder in ethanol from which an aliquot is taken and deposited on a copper-graphite mesh grid. The sintered products are surface polished and electro polished at 230 K electrolyte of 25% HNO3 and 75% CH3 OH. The magnification and electron diffraction patterns are calibrated in the TEM. The samples are then scanned in a 200 kV JEOL JEM 2000 EX transmission electron microscope. 3.6. Calculation of percentage extractable materials

2.1. Synthesis of polymer of fullerene based poly (˛-methyl styrene) (F-PAMS) The polymer samples are prepared by refluxing a suspension of ␣-methyl styrene (Sigma Aldrich) and fullerene in toluene. The system is kept on water bath for 2.5 h at 70 ◦ C. Synthesized polymer are precipitated in methanol and dried.

2.2. Synthesis of IPN IPNs are synthesized by systematic variations of concentration of fullerene based poly (␣ methyl styrene), urethane (Kemphasol, Art. No. K14848, C3 H7 NO2 ), divinyl benzene and Benzoyl peroxide in toluene for 3 h at 60 ◦ C under an inert atmosphere. The IPN obtained are vacuum dried to constant weight.

3. Characterization of ipn The synthesized IPN is characterized using the spectroscopic techniques, thermal analysis techniques and transmission electron microscopic techniques, conductivity analysis and permeability and permittivity analysis.

3.1. Spectroscopic technique analysis 1. Infrared (IR) spectroscopic studies: The IR peaks of IPN are analysed on vertex 70 (Bruker) instrument. 2. 13 C NMR Spectroscopy: 13 C NMR spectral analysis of fullerene based IPN of poly (␣-methyl styrene) and polyurethane sample is carried out in an ECX 500-JEOL NMR spectrometer. 3.2. Thermal analysis Differential scanning calorimetry (DSC) is performed on a V2.2 Dupont calorimeter, under nitrogen atmosphere at a heating rate of 10 ◦ C/min. The sample weight is 3–5 mg.

The solute or uncross linked component of IPN is removed by soxhlet extractor using dimethyl sulphoxide (DMSO) as a solvent for better results. The percentage extractable material was calculated using the following equation. % Extractable material =

W − W  a b Wa

× 100

(1)

where Wb = Weight of IPN before extraction and Wa = Weight of IPN after extraction. 3.7. Swelling measurements Cross-linked density of polymer network is calculated by measurements of solvent absorbency. The swelling data is calculated by soaking sample in different polar and nonpolar solvents such as dimethyl formamide (DMF), dimethyl sulphoxide (DMSO), dioxane, benzene or toluene until an equilibrium weight is achieved (∼ 24 h). Weight measurements are made by blotting the samples and immediately weighing them. The percentage swelling is calculated according to the following relationship [28]. % Swelling =

W − W  s d Wd

× 100

(2)

Where, Ws = weight of swollen IPN and Wd = Weight of dry IPN. 3.8. Crosslink density IPN sample is taken and its cross-link density is determined by swelling data of IPN in DMF by using Flory-Rehner equation [29]. 1 = Mc



In(1 − Vp ) + Vp + X12 Vp 2



pV1 (Vp 1/3 − Vp /2)

where, Mc = average molecular weight of IPN, p = density of IPN, V1 = molar volume of solvent, and Vp = volume fraction of polymer in swollen gel, X12 = polymer solvent interaction parameter [30].



X12 = B +

V1 ıp − ␦s RT

2

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Scheme 1. Synthesis of IPN based on fullerene (Containing ␣-methyl styrene and urethane as polymerizing units).

where ␦p and ␦s = solubility parameters of polymer and swelling solvent, respectively, and B = lattice constant (0.34).

70

68

The samples are taken in sample holder which is placed in vacuum (10−5 torr). A calibrated copper constant thermocouple was mounted very near to the sample. The resistance is measured by Kiethely electrometer.

Transmittance [%]

3.9. Electrical conductivity 64

60

56

4. Results and discussions 52

4.1. FTIR spectroscopy The structural IR analysis of polymer network is studied by IR spectroscopic technique. We have determined the detailed vibrational analysis of IPN. FTIR study for pure fullerene shows peaks at 1430, 527 (for C C vibration mode) and 1600 cm−1 (for C C mode). For poly(␣-methyl styrene), it reveals peaks at 3000 (stretching vibrations), 1490 ( C C vibrations), (C H stretching vibrations), 699(benzene ring C C bending) and 1444 cm−1 for bending vibrations of C H bond of CH3 group and for polyurethane linkage it assign a signal at 3300(NH units), 1710(C O stretching of urethane linkage), 2913(CH symmetric stretching of CH2 ), 2843(CH asymmetric stretching of CH2 groups), 2249(remaining isocyanate ( NCO) group) 1489 and 1441 cm−1 (CH2 and CH bending). While the IR analysis for polymer network (Fig. 1) reveals the presence of fullerene at 549 for caged vibrations), 1600 cm−1 (for C C mode), for poly (␣-methyl styrene) it shows the peaks at 3055(stretching), 1495( C C vibrations), 2981(C H) and 698 cm−1 (benzene ring C C out of plane bending) and for polyurethane it reveals peaks at 3200(NH units), 1742(C O stretching of urethane linkage), 2798(CH symmetric stretching of CH2 ) and 2000 cm−1 (remaining isocyanate ( NCO) group). 4.2.

13 CNMR

spectroscopy

The 13 CNMR spectra for pure fullerene (C60 ) is recorded at 138 ppm, for poly(␣-methyl styrene) it shows peaks at 128 ppm (aromatic carbon), 63 ppm ( CH2 -), 44 ppm (>C<) and 25 ppm ( CH3 ) and for polyurethane it is recorded at 173.3 ppm (carbonyl carbon) and 64.3, 40.6, 25.3 ppm (CH2 respectively. While

47 4000

3500

3000

2500

2000

1500

1000

500

Wavenumber (cm )

Fig. 1. IR spectrum of IPN 9.

the 13 CNMR spectra for IPN (Fig. 2) reveals spectra of fullerene (C60 ) at 136 ppm, for poly(␣-methyl styrene) at 128 ppm (aromatic carbon), 62 ppm ( CH2 −), 40 ppm (>C<) and 25 ppm ( CH3 )and for polyurethane at 180.0 ppm (carbonyl carbon) and 63.2, 37.3, 25.1 ppm (CH2 ) respectively. Observed data reveals shift in peak values of fullerene, poly (␣-methyl styrene) and polyurethane, there by showing incorporation of polymer on fullerene surface, which increases the solubility and processability of polymer network. 4.3. Electrical conductivity Conductivity analysis of IPN is performed which is found to be 1.3882 × 10−6 −1 m−1 at frequency range 20–50 Hz, which reveals the semiconductor character of IPN. 4.4. Thermal properties The DSC thermogram of IPN contains crystallization peaks (Fig. 3) at (Tg ) at 160 ◦ C, which is higher than Tg of polyurethane (120 ◦ C) and lower than Tg of poly(␣-methyl styrene) (173 ◦ C). It can be caused by high crosslinking density in the sample. The crosslinking usually strongly depresses the chain mobility. In

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0.12

90

0.1

80 70

0.04

50 40 30 200

180

160

140

Fig. 2.

120 13

100

80

60

40

20

0

391.50 C

60

0.02

0.06

Weight (%)

0.14

100

0.08

0.16

110

0

abundance

95

ppm

20

C NMR spectra of IPN 9.

Heat Flow Endo up (m/W)

10

0 44.25 100

0

300

400

500

600

700

800

Temperature ( C) Fig. 4. TGA curve of IPN 7.

-5

4.6. Measurement of the complex permittivity and permeability of the IPN

-10 Peak = 160oC -15 100

200

120

140

180

160

200

o

Temperature ( C) Fig. 3. DSC curve of IPN 7.

the composition of fullerene and poly (␣-methyl styrene) with polyurethane an increase of Tg by about 10–20 ◦ C is observed. It is an evidence of restricted chain mobility. As suggested above, polyurethane macromolecules are entangled or even covalently bonded to crosslink poly (␣-methyl styrene) (result of interpenetration). Poly (␣-methyl styrene) has stiff backbone length which provides stiffness to polymer network and polyurethane has flexible backbone and no side group which provide flexibility and strength to polymer network. Owing to the presence of nitrogen in urethane group, polyurethane chains can participate in hydrogen bonding and act as ‘flexible crosslinks’. Fig. 4 shows the TGA graph of IPN with initial thermal decomposition at 392 ◦ C. The thermal decomposition pattern of IPN ranges between the Poly (␣-methyl styrene) and polyurethane. This result indicates the incorporation of urethane units in the polymer network.

4.5. XRD analysis The XRD patterns of native poly (␣-methyl styrene) shows sharp and intense peak of 2␪ = 28.45◦ and interplanar distance is 4.45 Å. On the other hand XRD pattern of polyurethane is quite broad which suggest for relatively small sized crystals of the polymer. Fig. 6 reveals XRD pattern of IPN is in between poly (␣-methyl styrene) and polyurethane which indicate the semi crystalline nature.

The polymer network is analyzed for its complex per  mittivity (ε* = ε’-jε") and permeability (* = r −r ) values in X band (8.2–12.4 GHz) frequency region. Measurement of the reflection/transmission coefficient of the polymer network (size 22.86 mm × 10.16 mm) is carried out using Agilent Vector Network Analyzer E8364 B (10 MHz–50 GHz) in the waveguide environment. Further the complex permittivity and permeability is calculated using Nicholson-Ross-Weir (NRW) algorithm in the frequency   band. Fig. 7(a), (b) and (c) depicts the graph of εr Vs frequency εr Vs frequency and tan␦␧ Vs frequency of the IPN specimen. The maxi  mum value of εr , εr and tan␦␧ for the synthesized IPN reached 2.47, 0.15 and 0.08 respectively.  Similarly Fig. 8(a), (b) and (c) depicts the graph of r Vs   frequency, r Vs frequency and tanr Vs frequency of the IPN respectively. It reveals that the values ranging from 0.92 to 1.20,    0.01–0.103 and 0.01–0.08 forr ,r and tanr respectively. 4.7. Morphology The microstructure of fullerene based interpenetrating polymer network of poly (␣-methyl styrene) and polyurethane is observed by means of transmission electron microscopy (TEM) which reveals dual phase morphology of the synthesized IPN (Fig. 5). The network structure is diversified, which indicate sample heterogeneity of solution used for film preparation. It means phase separation has occurred just after solvent evaporation which is clearly distinguished in the microscopic images. The surface of sample composed of fullerene, poly (␣-methyl styrene) and polyurethane is not smooth, some protrusions of different sizes are observed. It indicates that under top layer heterogeneous domains (connected to crystallization and phase separation) are formed and clear dual phase morphology of different regions is observed in IPN films which is due to both the components.

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Fig. 6. XRD graph of IPN 9.

Fig. 5. TEM photograph of IPN 9.

4.8. Effect of composition Effect of composition of fullerene, polyurethane and poly(␣methyl styrene) shows a trend, since an increase in polyurethane base for poly(␣-methyl styrene) results in increased swelling and Mc . It shows that polyurethane restricts crosslinking of poly (␣-methyl styrene). Furthermore, in solution interpenetrating polymerization, it is believed that polyurethane becomes cross-linked to poly (␣-methyl styrene). As the concentration of polyurethane increases the probability of interpenetration of poly (␣-methyl styrene) also increases. The crystallinity of polymer network is directly proportional to the concentration increase of poly(␣-methyl styrene). Thus higher amount of poly(␣-methyl





Fig. 7. εr εr and tan␦␧ Vs frequency graph of 8.0–12.50 Ghz of IPN 9.

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97

Table 1 Percentage swelling of IPN in different solvent and extractable material (%). Sample % Swelling in DMF In solvents

Toluene % Extractable material

Benzene DMSO IPN 1 IPN 2 IPN 3 IPN 4 IPN 5 IPN 6 IPN 7 IPN 8 IPN 9 IPN 10 IPN 11 IPN 12

58 46 51 80 73 79 61 75 79 38 53 43

21 20 29 65 32 38 25 40 37 22 28 20

50 38 40 80 73 68 50 62 60 24 35 31

23 22 42 63 54 47 33 43 50 32 30 30

12.2 11.9 36.1 28.1 20.1 11.5 7.9 18.1 20.3 12.3 29.2 7.2

Table 2 Effect of variation in concentration of BPO on IPN properties. Sample

BPO mol/100 ml

Swelling (%) in DMF

Mc in DMF

IPN 1 IPN 2 IPN 3 IPN 4

2.0 × 10−2 4.1 × 10−2 6.2 × 10−2 8.2 × 10−2

58 46 51 80

165 134 153 164

Table 3 Effect of variation in concentration of Fullerene- PAMS on IPN properties. Sample Fullerene- PAMS (mol/100 ml) Yield Swelling (%) in DMF Mc in DMF IPN 5 IPN 6 IPN 1 IPN 7

1 × 10−3 2 × 10−3 3 × 10−3 4 × 10−3

6.53 5.68 7.34 11.55

73 79 58 61

160 180 165 173

Table 4 Effect of variation in concentration of urethane on IPN properties.







Fig. 8. r ,r and tan␦␮ r Vs frequency spectra in the range of 8.0–12.50 Ghz of IPN 9.

styrene) usually enhances polymer crystallinity and hence the higher glass transition value of IPN is obtained. On other hand according to the data obtained from Table 4, the increase in concentration of urethane favors the flexibility of the IPN, but this also causes some decrease of glass transition temperature of IPN. It leads to a higher degree of crosslinking between polyurethane phases. Similarly explanation can be given for the fact that the percentage swelling and Mc vary inversely to the concentration of poly(␣-methyl styrene) (Table 3). 4.9. Effect of cross-linker (DVB) Variation of DVB concentration has direct impact on percentage of extractable material (Table 5). The reason is that an increase of concentration of DVB increases the crosslinking between the two polymeric networks, which results in decreased swelling and decreased Mc . It is interesting to note that concentration increase in divinyl benzene enhances the crosslinking in the polymer network, and hence depress the chain mobility. This ultimately increases the glass transition temperature. 4.10. Effect of initiator (BPO) The variation and effect of BPO concentration over swelling and Mc of IPN is shown in Table 2. It is clear that both swelling and Mc increases with increasing molar concentration of BPO. Table 1

Sample

Urethane (mol/100 ml)

Yield

Swelling (%) in DMF

Mc in DMF

IPN 9 IPN 10 IPN 4 IPN 11

6 × 10−3 1.1 × 10−2 1.7 × 10−2 2.2 × 10−2

4.7 6.3 7.9 10.4

38 53 58 43

170 168 165 162

Table 5 Effect of variation in concentration of DVB on IPN properties. Sample

DVB (mol/100 ml)

Yield

Swelling (%) in DMF

Mc in DMF

IPN 10 IPN 4 IPN 11 IPN 12

7.0 13.8 21.0 28.0

6.5 7.2 8.3 8.4

34 58 56 43

171 156 173 142

represents effect of various solvent on swelling of IPN. The variation in percentage of extractable material is shown in Table 2–5. A detailed study is performed over the effect of composition of different chemicals on the different physical and chemical properties of IPN. The relative study is discussed below. 5. Conclusions Spectral analysis of IPN of fullerene containing poly(␣-methyl styrene) and polyurethane shows ideal polymer network formation between ␣-methyl styrene and urethane monomers and complete intermingling of polymer over fullerene surface. The DSC thermogram shows higher Tg for IPN as compared to the homo-polymer polyurethane, which is a result of higher crosslink density and restricted chain mobility. IPN microstructure calculations indicate higher urethane content along with ␣-methyl styrene monomer

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units. It results into more dense and compact polymer network structure. The synthesized IPN shows moderate values of complex permeability and permittivity which reveals more or less semi conducting nature of IPN. Acknowledgemen We are grateful to the Principal, Christ Church, degree college, Kanpur for maximum support of laboratory facilities to the department of chemistry, Joint director, D.M.S.R.D., Kanpur, A.M.U., Aligarh for providing microscopic facilities and also to the department of chemistry, I.I.T., Kanpur for spectroscopic facilities, H.B.T.I. for providing conductivity testing facility and at last but not least to the department of chemistry, Central institute of plastic and engineering and technology, Lucknow for providing the thermal analysis facilities. References [1] L.H. Sperling, R. Hu, in: L.A. Utracki (Ed.), Interpenetrating Polymer Networks, in Polymer Blends Handbook, Springer, Dordecht, The Netherlands, 2003, pp. 417–447. [2] V. Kudela, I. Kroschwitz, Hydrogels, Encyclopedia of Polymer Science and Engineering. J. Ed., pp. 783–807, (1987). [3] H. Sperling, in: H. Sperling (Ed.), IPN and Related Materials, Plenum, New York, NY, USA, 1981. [4] X. Zhao, A theory for large deformation and damage of interpenetrating polymer networks, J. Mech. Phys. Solids 60 (2012) 319–332. [5] J.M. Buist, H. Gudgeon, Advances in Polyurethane Technology, Elsevier, London, 1970. [6] R. Gangopadhyay, A. De, An electrochemically synthesized conducting Semi-IPN from polypyrrole and poly (N-vinyl alcohol), J. Mater. Chem. 12 (2002) 3591–3598. [7] S. Banerjee, S. Ray, S. Maiti, Interpenetrating polymer network (IPN) a novel biomaterial, Int. J. Appl. Pharmacol. 2 (2010) 28–34. [8] N. Isiklan, Controlled release of insecticide carbaryl from sodium alginate, sodium alginate/gelatin and sodium alginate/sodium carboxymethyl cellulose blends beads crosslinked with glutaraldehyde, J. Appl. Polym. Sci. 99 (2006) 1310–1319. [9] A.P. Rokhade, S.A. Patil, T.M. Aminabhavib, Synthesis and charachterization of semi-interpenetrating microsphere of acylamide grafted dextran and chitosan for controlled release of acyclovir, Carbohydr. Polym. 67 (2007) 605–613. [10] B. Patel, L. Patel, H. Shah, K. Modasiya, Review on hydrogel nanoparticles in drug delivery, J. Pharm. 1 (2011) 19–38.

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