Thermal analysis characterization of PAAm-co-MC hydrogels

Taıs Vanessa Gabbay Alves • Eraldo Jose Madureira Tavares •

Fauze Ahmad Aouada • Charles Alberto Brito Negrao •

Marcos Ene Chaves Oliveira • Anivaldo Pereira Duarte Junior •

Carlos Emmerson Ferreira da Costa • Jose Otavio Carrera Silva Junior •

Roseane Maria Ribeiro Costa

CBRATEC7 Conference Special Issue

� Akademiai Kiado, Budapest, Hungary 2011

Abstract This paper reports the thermal characterization

of polyacrylamide-co-methylcellulose hydrogels and the

constituent monomers (acrylamide and methylcellulose).

Polymeric materials can be used to produce hydrogels,

which can be natural, synthetic, or a mixture. The hydro-

gels described here were obtained by free radical poly-

merization, in the presence of N,N0-methylene-bis-

acrylamide as a cross-linker agent. Four acrylamide con-

centrations were used for the synthesis of hydrogels: 3.6,

7.2, 14.7, and 21.7% (w/v). The materials so obtained were

analyzed by TG, DTG, DSC, and FT-IR. The TG curves of

acrylamide and methylcellulose showed three mass loss

events. In DSC curves, the acrylamide exhibited one

melting peak at 84.5 �C, and methylcellulose indicated one

exothermic event. Nevertheless, acrylamide was consid-

ered more stable than methylcellulose. The TG curves of

the hydrogels exhibited three mass loss events, and on the

DSC curves, three endothermic events were observed. It

was verified that the different acrylamide proportions

influenced the thermic behavior of hydrogels, and that the

authors considered the 7.2% hydrogel a promising drug

carrier system. The absorption bands were well defined,

confirming the presence of the functional groups in the

samples.

Keywords Hydrogels � Polymers � Thermal analysis �PAAm-co-MC

Introduction

Hydrogels are gels that can absorb large quantities of water.

They are not deformed and are constituted by polymeric

material networks that form three-dimensional structures

which are rich in polar groups. Because of these character-

istics, the hydrogels show high hydrophilicity and insolu-

bility. These polymers can be natural or synthetic and

cross-linked through electrostatic forces or covalent bonds [1,

2]. Hydrogels are being widely used for various purposes,

such as in delivery systems for pesticides [3], anti-inflam-

matories [4], antimicrobials [5], hypoglycemics [6], and

antihypertensives. A more specific example can be seen in

Silva, 2006, who developed a system from the hydrogel of

N-isopolyacrilamide for the carrying of atenolol and insulin

[7]. Another example of carrier is Norplant�, which is a

contraceptive constituted by polydimethylsiloxane and that

carries a steroid dispersion [8].

Several polymers can be used to compose a type of

hydrogel. Examples of hydrogels derived from natural

polymers are: methylcellulose (MC) [2] and hydroxyl

propyl methylcellulose (HPMC) [9], which are hydrophilic

and biodegradable white powders. They are derived from

T. V. G. Alves � A. P. Duarte Junior � J. O. C. Silva Junior �R. M. Ribeiro Costa (&)

Federal University of Para, Augusto Correa Street, 01-Guama,

Belem, PA 66075-110, Brazil

e-mail: rmrc@ufpa.br

E. J. M. Tavares

Embrapa Eastern Amazon, Laboratory of Agrobusiness, Belem,

PA 660095-100, Brazil

F. A. Aouada � M. E. C. Oliveira

Chemistry Institute, Sao Paulo State University, Araraquara, SP

14801-907, Brazil

C. A. B. Negrao

Faculty of Chemical Engineering, Federal University of Para,

Belem, PA 66075-110, Brazil

C. E. Ferreira da Costa

Federal University of Para, Belem, PA 66075-110, Brazil

123

J Therm Anal Calorim (2011) 106:717–724

DOI 10.1007/s10973-011-1572-z

cellulose, which is among the most abundant materials in

nature [3]. Biodegradable polymers suffer the action of

biological processes in which they dissolve gradually until

they are eliminated. Examples of synthetic polymers are

polyacrylamide (PAAm) [10], poly(methacrylic acid) [11],

and poly(latic-co-glycolic acid) (PLGA) [12]. PAAm is a

hydrophilic polymer. Its hydrogel has a good mechanical

strength, swells about 90% its initial weight, and is a

powerful candidate in drug delivery systems [2, 3]. Drug

release will occur in a parallel direction with the polymer

degradation due to the fact that the material is sensitive to

pH changes [13].

Thermal analysis is a tool that is widely used in the

characterization of polymeric materials. In Brazel and

Peppas, 1995, hydrogels of poly(N-isopropylacrylamide-

co-methacrylic acid) are analyzed by swelling experiments,

differential scanning calorimetry (DSC) and thermal

mechanical analysis (TMA) [13, 14]. Thermogravimetry

(TG) and DSC are important techniques because of their

ability of clarifying properties and characteristics such as

stability, glass transition, and polymorphism, among oth-

ers. Accordingly, the pharmaceutical industry has targeted

these techniques to be relatively quick and simple, being

employed in the products quality control both in production

phase, and at the end [15–20]. The aim of this work is to

characterize the PAAm-co-MC hydrogels and its constit-

uent monomers (AAm and MC) by TG, DTG, DSC, and

FT-IR, in order to explore the stability of the whole system.

Experimental

Material and reagents

Acrylamide (AAm) was purchased from Vetec (Brazil),

methylcellulose (viscosity 2%) from Aldrich (Germany),

N,N0-methylene-bis-acrylamide (MBAAm) from Sigma-

Aldrich (Germany); N,N,N0,N0-tetramethylethylenediamine

(TEMED) from Merck (Germany); and sodium persulfate

(PS) from Dinamica Reagentes Analıticos (Brazil), all

analytical degree.

Synthesis of PAAm-co-MC hydrogels

The PAAm-co-MC hydrogels were synthesized by free

radical polymerization. They were prepared in the

following sequence: aqueous solutions are prepared,

consisting of AAm and MC 1.0% (w/v); MBAAm

(8.55 lmol mL-1) was added as a cross-linker agent; TE-

MED (3.21 lmol mL-1) was added as a reaction catalyst;

and PS (3.38 lmol mL-1) was added as a reaction initia-

tor. After homogenization, the solution was purged by N2

bubbling for 25 min, and the material was dried in an oven

at 35 �C. The AAm concentrations are fluctuated in the

formulations of hydrogels in 3.6, 7.2, 14.7, and 21.7%

(w/v) [3, 21].

Thermal analysis study

The hydrogels and monomers were analyzed by TG using

the thermo balance Shimadzu DTG-60H model, and by

DSC using the Shimadzu model DSC60. The samples

weighed 5 ± 0.5 mg, ranging in temperature from ambient

to 500 �C, in dynamic nitrogen atmosphere, flow rate

10 mL min-1, heating rate 10 �C min-1, alumina crucible

for TG, and alumina crucible for the DSC [22]. The curves

are analyzed using the software Origin Pro 8.0.

FT-IR spectroscopy

The spectroscopy characterization of PAAm-co-MC

hydrogels and their monomer components was performed

by Infrared Spectroscopy and Fourier Transform (FT-IR).

Dried hydrogels were analyzed through the Thermo Elec-

tron Corporation IR 100 spectrometer with 128 scans in the

range of 4000 to 400 cm-1, with a 2 cm-1 resolution [2,

23]. All the bands were analyzed by software Origin Pro

8.0.

Results and discussion

Thermal analysis characterization

According to Fig. 1, AAm presents three events of degra-

dation. The first one occurs in the interval of 95–185 �C

corresponding to 66.3% of mass loss; the second occurs in

the range of 185–362 �C, with 12% of mass loss; and the

third event occurs between 380 and 500 �C, with 11% of

mass loss. The DSC curves show a narrow endothermic

peak which is characteristic of melting at about 84.5 �C,

and then two successive exothermic events related to the

release of energy caused by mass loss.

Figure 2 shows the thermal events of MC, which pre-

sented at first an amount of mass lost on the water surface

of the material. Subsequently, there are two events of

degradation, the first being from 264 to 359 �C with 73.5%

of mass loss, and the second from 462 to 484 �C with 5.1%

of mass loss. Thus, we can say that AAm is much more

stable than MC, because the AAm mass remains steady

within a large scale of temperature compared to MC. The

DSC curve of MC indicates an exothermic event in the

interval between 264 and 359 �C related to high energy

degradation caused by its greater weight loss, which is the

same temperature range than that of AAm but with the

biggest sample mass loss, evidenced by the same DTG [9].

718 T. V. G. Alves et al.

123

The Figs. 3, 4, 5, and 6 exhibited the curves of the

hydrogels. In Fig. 3, the TG curve shows three degradation

events. The first was caused by water or volatile substances

evaporation, the second event originated from successive

degradation reactions, and the last happened due to the MC

degradation, where, according to the DTG data, the greater

mass loss was observed. Figure 4 exhibits two mass loss

events. The first is about the water loss, and the second has

an extent range of temperature, since it is related to the

AAm and MC degradation, as showed by the DTG. The

interaction in this proportion of AAm is much evidenced.

In Fig. 5, the TG curve shows three degradation events in

which the first happens due to water loss, the second is

related to AAm degradation, and finally, the third evi-

dences the MC degradation; however, the second event

appears a little discrete due to the interaction with MC.

The Fig. 6 presents events which are similar to those

observed in Fig. 5. Nevertheless, Fig. 6 shows a great

definition of AAm degradation event directly related to the

fact that this hydrogel has a larger proportion (21.7%) of

AAm. In the comparative study of themogravimetric

analysis of four hydrogels, it was observed that when AAm

is used in lesser proportion (3.6%), its degradation is not

visualized very well in the TG curve because it does not

outline events as they occur in other proportions studied.

The 7.2% hydrogel presented a greater interaction between

AAm and MC, showing that it is possible to visualize

monomers degradation-peaks junction. In the 14.7%

hydrogel, a discrete separation of peaks between monomers

AAm and MC was verified. This characteristic was verified

by the fact that AAm proportion was greater in the system

than in the preceding hydrogels. Events observed in the

Fig. 1 TG, DSC, and DTG

curves of AAm

Fig. 2 TG, DSC, and DTG

curves of MC

Thermal analysis characterization of PAAm-co-MC hydrogels 719

123

21.7% hydrogel showed a distinct separation of those

monomers peaks because the AAm peaks were pronounced

due to the higher proportion in the polymeric system.

It is seen in DTG curves the relocation of AAm degra-

dation range to the right, a phenomenon caused by inter-

action of AAm and MC. It was observed in all hydrogels in

different proportions. The hydrogels mass losses generally

happen in the range from 25 to 250 �C. The hydrogel loses

about 7–11% of its mass successively from cleaving

reactions of the polymer chain. The differences in degra-

dation and mass loss between the hydrogels are due to the

connection with water, which is more difficult to be

removed from the polymer because of its intrinsic linkages.

The degradation of polymers takes place through

mechanical distortion, cracking, fissures, and so forth [8].

The hydrogels events of mass loss generally result from

the water loss and/or solvents and posteriorly from their

thermic or oxidative degradation. The percentage of water

loss is differentiated in each polymer, since this charac-

teristic is related to the cross-linking degree of each

material. Therefore, in comparative analysis of the same

polymer, the tendency is the occurrence of similar mass

loss percentage. Besides, the more the cross-linking degree,

the more the polymeric stability. This phenomenon is

governed by the breaking of polar groups, such as

hydroxyls. When it is observed the breaking of chemical

links before 100 �C, water molecules are usually linked to

amine groups [24].

In studies carried out with co-polymers, smaller varia-

tions, like the difference between the concentration of one

Fig. 3 TG, DSC, and DTG

curves of PAAm-co-MC

hydrogels 3.6% (w/v)

Fig. 4 TG, DSC, and DTG

curves of PAAm-co-MC

hydrogels 7.2% (w/v)

720 T. V. G. Alves et al.

123

of the components, can result in sudden changes within

their proprieties, such as the difference in the melting

enthalpy, and again in the glass transition temperature, but

this study there were no changes in the properties men-

tioned [25]. The literature reports that thermogravimetric

studies of monomer in isolation tend to have defined events

of degradation which can characterize it. However, if the

material is proceeded from more than one monomer, the

number of thermic events tends to be enhanced. Relocation

may happen and often these events are occasioned by

hydrolysis and cracking of the polymeric chain [26].

According to the literature, water molecules in cross-liked

PAAm evaporated before 300 �C was reached [27]. In

hydrogels with polymers derived from cellulose, water

volatilization happens rapidly and before reaching 70 �C,

and stability is generally maintained till 200 �C. Events

found in different proportions of hydrogels under this study

corroborated the results found out by others authors.

According to Silva 2006, in acrylic-derived hydrogels, an

important mass loss of the system is visualized at about

400 �C. In this process, the breaking of water molecules

occurs gradually, followed by polymers breaking, which is

the reason why there is degradation in higher temperature.

In addition, the fact that the hydrogel has a three-dimen-

sional structure and hydrogen bonds contributes to this

characteristic [7].

The results found in this work corroborated those

reported in literature because water had the same behavior

too, besides the fact that the greater degradation band

persisted at the same temperature. Hydrogels thermic

profile description is showed in Table 1.

For stability evaluation between hydrogels, their deg-

radation percentages are analyzed at the end of the first

thermic event to compare and see what hydrogel variations

Fig. 5 TG, DSC, and DTG

curves of PAAm-co-MC

hydrogels 14.7% (w/v)

Fig. 6 TG, DSC, and DTG

curves of PAAm-co-MC

hydrogels 21.7% (w/v)

Thermal analysis characterization of PAAm-co-MC hydrogels 721

123

remain with their percentage near 100%. It was noticed that

the most stable was the one with the smaller mass loss. It

was observed that the difference between mass losses of

the 3.6 and 7.2% is smaller (1%), and it can be concluded

that there is no significant difference between these two

hydrogels. However, considering the fact that interaction

between AAm and MC is better visualized in 7.2% pro-

portion, this can be considered as a promising drug carrier.

The DSC curves of the four hydrogels have similar

events, because they present three endothermic reactions,

but only the 3.6% hydrogel differed from others, since it

shows two endothermic and one exothermic events, due to

the same material differing only in the intensity of the

events because of the difference in ratios of AAm present

in each of them. Table 2 shows reactions and enthalpies of

the hydrogels.

Besides, the glass transition temperature (Tg) of pure

polyacrylamide is around 97 �C and the Tg of the hydrogel

is between 90 and 117 �C. This change is due to the

addition of another polymer, forming a co-polymer,

increasing then the Tg because the connections of hydrogen

bonds between the polymers are stronger [1, 28]. The Tg of

polymers has different values, for example: L-poly(lactic

acid) * 55 �C and of poly(glycolic acid) * 35 �C, and in

Tg of copolymers is usually greater than 37 �C [8].

FT-IR spectroscopy

The spectra of AAm and MC showed well-defined bands

(Fig. 7). In the case of AAm, the bands are 3333 cm-1,

referring to the group –NH; from 1280 to 1050 cm-1,

referring to –CO; 1680 cm-1, referring to –CO of primary

amide [29]. However, in the spectrum of MC, the bands

visualized were 3790–2990 cm-1, referring to the group –

OH; 1614 cm-1, that are related to water molecules

Table 1 Events of lost mass of hydrogels

Hydrogels/% Events Mass loss/% What was lost

3.6 1 12 3 mol of water

2 37.8 0.5 mol of MC

3 13 0.8 mol of AAm

7.2 1 13 3 mol of water

2 43 0.5 mol of MC

14.7 1 18 4.66 mol of water

2 19 1.2 mol of AAm

3 46 0.5 mol of MC

21.7 1 13 3 mol of water

2 17 1 mol of AAm

3 43 0.5 mol of MC

Table 2 Events of hydrogels energy variation

Hydrogels/% Events/reaction Enthalpy (DH/J g-1)

3.6 1/Endothermic -316.15

2/Endothermic -410.37

3/Exothermic ?149.42

7.2 1/Endothermic -88.46

2/Endothermic -163.41

3/Endothermic -125.76

14.7 1/Endothermic -68.67

2/Endothermic -188.19

3/Endothermic -123.39

21.7 1/Endothermic -226.07

2/Endothermic -378.74

3/Endothermic -205.78

Fig. 7 FT-IR of monomers AAm and MC

Fig. 8 FT-IR of PAAm-co-MC hydrogels 3.6, 7.2, 14.7, and 21.7%

(w/v)

722 T. V. G. Alves et al.

123

absorbed; 1230 to 900 cm-1, referring to b-glycosidic

linkages between MC monomers; and 620 cm-1, referring

to the pyranosidic ring [30, 31].

In the spectra of hydrogels (Fig. 8), bands are observed

in 1640–1680 cm-1, referring to stretching lead of –NH of

PAAm; in 1117 and 1070 cm-1, assigned to linkage of

MC; and in 3455 cm-1, due to the vibration of the group

–OH of MC [27, 32–36].

Conclusions

The thermic characterization of the monomers showed that

the TG curves of AAm have three events of mass loss,

66.3, 12, and 11% sequentially. On the other hand, the DSC

curve shows a narrow melting peak of the material at about

84.5 �C. The TG curve of MC shows two events of mass

loss: 73.5, and 5.1%. As a result, the MC is more stable

than AAm, resisting longer without loss of mass. In the TG

curves of the hydrogels there were three events of mass

loss, the first due to release of water and the following due

to breakage of the polymer chain, releasing all or part of

the monomers. The monomer AAm influenced the hydro-

gels thermic behavior, in which the hydrogel variation that

presented the stronger interaction between AAm and MC

was the 7.2%, showing, therefore, greater stability, indi-

cating that this variation is a possible system for thera-

peutic applications. The infrared absorption bands of the

monomers and hydrogels made it possible to identify the

functional groups present in the material.

Acknowledgements All the authors thank the National Council for

Scientific and Technological Development (CNPq), Sao Paulo

Research Foundation (FAPESP), Brazilian Federal Agency for Sup-

port and Evaluation of Graduate Education (CAPES), Brazilian

Agricultural Research Corporation (Embrapa) for financial support,

FAPESPA by the approved project.

References

1. Aouada FA. Sıntese e caracterizacao de hidrogeis de poliacrila-

mida e metilcelulose para liberacao controlada de pesticidas. Sao

Carlos, Brasil: Universidade Federal de Sao Carlos; 2009.

2. Aouada FA, Menezes EA, Nogueira ARA, Mattoso LHC. Sıntese

de hidrogeis e cinetica de liberacao de amonio e potassio. R Bras

Ci Solo. 2008;32(4):7. doi:10.1590/S0100-06832008000400029.

3. Aouada FA, Chiou B, Orts WJ, Mattoso LHC. Physicochemical

and morphological properties of poly(acrylamide) and methyl-

cellulose hydrogels: effects of monomer, crosslinker and poly-

saccharide compositions. Polym Eng Sci. 2009;49(12):2467–74.

doi:10.1002/pen.21505.

4. Kulkarni RV, Sa B. Electroresponsive polyacrylamide-grafted-

xanthan hydrogels for drug delivery. J Bioact Compat Polym.

2009;24(4):368–84. doi:10.1177/0883911509104475.

5. Sutar P, Mishra R, Pal K, Banthia A. Development of pH sen-

sitive polyacrylamide grafted pectin hydrogel for controlled drug

delivery system. J Mater Sci: Mater Med. 2008;19(6):2247–53.

doi:10.1007/s10856-007-3162-y.

6. Nakamura K, Murray RJ, Joseph JI, Peppas NA, Morishita M,

Lowman AM. Oral insulin delivery using P(MAA-g-EG)

hydrogels: effects of network morphology on insulin delivery

characteristics. J Control Release. 2004;95(3):589–99.

7. Silva FP. Sıntese e caracterizacao de hidrogeis de poli[(N-iso-

propilacrilamida)-co-(acido acrılico)] e sua aplicacao como sist-

emas de liberacao de medicamentos. Belo Horinzonte, Brasil:

Universidade Federal de Minas Gerais; 2006.

8. Griffith LG. Polymeric biomaterials. Acta Mater. 2000;48:

263–77.

9. Aouada FA, de Moura MR, Rubira AF, Muniz EC, Fernandes

PRG, Mukai H, et al. Birefringent hydrogels based on PAAm and

lyotropic liquid crystal: optical, morphological and hydrophilic

characterization. Eur Polym J. 2006;42(10):2781–90.

10. Lopes CM, Lobo JMS, Costa P. Formas farmaceuticas de liber-

acao modificada: polımeros hidrifılicos. Braz J Pharm Sci.

2005;41:143–54.

11. He H, Guan J, Lee JL. An oral delivery device based on self-

folding hydrogels. J Control Release. 2006;110(2):339–46.

12. Jain RA. The manufacturing techniques of various drug loaded

biodegradable poly(lactide-co-glycolide) (PLGA) devices. Bio-

materials. 2000;21(23):2475–90.

13. Peppas NA, Huang Y, Torres-Lugo M, Ward JH, Zhang J.

Physicochemical foundations and structural design of hydrogels

in medicine and biology. Annu Rev Biomed Eng. 2000;2(1):

9–29. doi:10.1146/annurev.bioeng.2.1.9.

14. Brazel CS, Peppas NA. Synthesis and characterization of thermo-

and chemomechanically responsive poly(N-isopropylacrylamide-

co-methacrylic acid) hydrogels. Macromolecules. 1995;28(24):

8016–20. doi:10.1021/ma00128a007.

15. Matos JR, Machado LDB. Analise termica—termogravimetria.

In: Canevarolo Junior SV, editor. Tecnicas de caracterizacao de

polımeros. Sao Paulo: Artliber; 2004. p. 209–28.

16. Gabbott P. Principles and applications of thermal analysis. 1st ed.

Oxford: Blackwell Publishing; 2008.

17. Neto H, Novak C, Matos J. Thermal analysis and compatibility

studies of prednicarbate with excipients used in semi solid

pharmaceutical form. J Therm Anal Calorim. 2009;97(1):367–74.

doi:10.1007/s10973-009-0234-x.

18. Bernardi L, Oliveira P, Murakami F, Silva M, Borgmann S,

Cardoso S. Characterization of venlafaxine hydrochloride and

compatibility studies with pharmaceutical excipients. J Therm

Anal Calorim. 2009;97(2):729–33. doi:10.1007/s10973-009-

0282-2.

19. Oliveira P, Bernardi L, Murakami F, Mendes C, Silva M. Ther-

mal characterization and compatibility studies of norfloxacin for

development of extended release tablets. J Therm Anal Calorim.

2009;97(2):741–5. doi:10.1007/s10973-009-0347-2.

20. Bruni G, Berbenni V, Milanese C, Girella A, Marini A. Drug-

excipient compatibility studies in binary and ternary mixtures by

physico-chemical techniques. J Therm Anal Calorim. 2010;

102(1):193–201. doi:10.1007/s10973-009-0382-z.

21. Aouada FA, Muniz EC, Vaz CMP, Mattoso LHC. Correlacao

entre parametros da cinetica de intumescimento com cara-

cterısticas estruturais e hidrofılicas de hidrogeis de poliacrilamida

e metilcelulose. Quım Nova. 2009;32:1482–90.

22. Vimala K, Samba Sivudu K, Murali Mohan Y, Sreedhar B,

Mohana Raju K. Controlled silver nanoparticles synthesis in

semi-hydrogel networks of poly(acrylamide) and carbohydrates:

a rational methodology for antibacterial application. Carbohydr

Polym. 2009;75(3):463–71.

23. Mandal BB, Kapoor S, Kundu SC. Silk fibroin/polyacrylamide

semi-interpenetrating network hydrogels for controlled drug

Thermal analysis characterization of PAAm-co-MC hydrogels 723

123

release. Biomaterials. 2009;30(14):2826–36. doi:10.1016/

j.biomaterials.2009.01.040.

24. Neto CGT, Giacometti JA, Job AE, Ferreira FC, Fonseca JLC,

Pereira MR. Thermal analysis of chitosan based networks. Car-

bohydr Polym. 2005;62(2):97–103. doi:10.1016/j.carbpol.2005.

02.022.

25. Bouwstra JA, Salomons-de Vries MA, van Miltenburg JC. The

thermal behaviour of water in hydrogels. Thermochim Acta.

1995;248:319–27. doi:10.1016/0040-6031(94)01948-g.

26. Khalid MN, Agnely F, Yagoubi N, Grossiord JL, Couarraze G.

Water state characterization, swelling behavior, thermal and

mechanical properties of chitosan based networks. Eur J Pharm

Sci. 2002;15(5):425–32. doi:10.1016/s0928-0987(02)00029-5.

27. Sun J, Lu J, Zhu X, Zhang K, Lu Z, Zhu J. Preparation and

thermal decomposition of polyacrylamide and its derivatives by

plasma initiated polymerization. J Therm Anal Calorim. 1999;

58:301–7.

28. Xia Y-q, Guo T-y, Song M-d, Zhang B-h, Zhang B-l. Hemo-

globin recognition by imprinting in semi-interpenetrating poly-

mer network hydrogel based on polyacrylamide and chitosan.

Biomacromolecules. 2005;6(5):2601–6. doi:10.1021/bm050324l.

29. Ozeroglu C, Sezgin S. Polymerization of acrylamide initiated

with Ce(IV)- and KMnO4-mercaptosuccinic acid redox systems

in acid-aqueous medium. Express Polym Lett. 2007;1:132–41.

doi:10.3144/expresspolymlett.2007.22.

30. Oh SY, Yoo DI, Shin Y, Seo G. FTIR analysis of cellulose treated

with sodium hydroxide and carbon dioxide. Carbohydr Res.

2005;340(3):417–28. doi:10.1016/j.carres.2004.11.027.

31. Valente AJM, Sobral AJFN, Jimenez A, Patachia S, Oliveira

ARCB, Lobo VMM. Effect of different electrolytes on the

swelling properties of calyx[4]pyrrole-containing polyacrylamide

membranes. Eur Polym J. 2006;42(9):2059–68.

32. Koschella A, Heinze T, Klemm D. First synthesis of 3-O-func-

tionalized cellulose ethers via 2,6-di-O-protected silyl cellulose.

Macromol Biosci. 2001;1(1):49–54. doi:10.1002/1616-5195

(200101)1:1\49::AID-MABI49[3.0.CO;2-C.

33. Liu W, Zhang B, Lu WW, Li X, Zhu D, De Yao K, et al. A rapid

temperature-responsive sol-gel reversible poly(N-isopropylac-

rylamide)-g-methylcellulose copolymer hydrogel. Biomaterials.

2004;25(15):3005–12.

34. Sowwan M, Faroun M, Musa I, Ibrahim I, Makharza S, Sultan W,

et al. Study on the morphology of polyacrylamide–silica fumed

nanocomposite thin films. Int J Phys Sci. 2008;3(6):144–7.

35. Caykara T, Bulut M, Demirci S. Preparation of macroporous

poly(acrylamide) hydrogels by radiation induced polymerization

technique. Nucl Instrum Methods Phys Res Sect B. 2007;265(1):

366–9. doi:10.1016/j.nimb.2007.09.006.

36. Yu H, Xu Z, Lei H, Hu M, Yang Q. Photoinduced graft polymer-

ization of acrylamide on polypropylene microporous membranes

for the improvement of antifouling characteristics in a submerged

membrane-reactor. Sep Purif Technol. 2007;53(1):119–25.

724 T. V. G. Alves et al.

123